Oral History Transcript — Dr. E. P. Wohlfarth
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E. P. Wohlfarth; July 2, 1981
ABSTRACT: Education including time as a student working with E. C. Stoner at Leeds; work on single particle ferromagnetisms and collective electron ferromagnetisms, research at Imperial college on magnetisms.
Keith:Interview with Professor E. P. Wohlfarth, interviewed at Imperial College, 2nd July 1981, by Stephen Keith. Professor Wohlfarth, I don't really have any great details of your childhood. I know you were born in Poland in 1924. Could you elaborate on some of the background.
Wohlfarth:I was born in a town called nowadays Gliwice which is as you say in Polish, but when I was born in 1924 it was German and called Gleiwitz. It was a German town close to the old pre-war, that is to say Second World War, pre-war Polish border.
Keith:It's part of what you would call Silesia?
Wohlfarth:It was called Silesia then, it's still called Silesia now. My father was in the legal profession. In about 1930 he was transferred to Breslau which is now also Polish and called Wroclaw and we lived there for about nine years. The persecution of the Jews started in 1933 and came to a head in 1938 and we emigrated to England.
Keith:Did you have any brothers and sisters?
Wohlfarth:Yes, one brother who is two or three years younger than me. He is now in Israel where he is head of a fish growing institute in the neighborhood of Caesarea. A second brother was born in England. He's fourteen years younger than me, and a Professor of Comparative Literature in Eugene, Oregon. My father died about ten years ago and my mother's still alive—she's about eighty and lives in Israel as well, near to my brother.
Keith:What were the actual circumstances of the move to England? Was it protracted; did it involve a lot of organization over a long period of time or did you just leave very quickly?
Wohlfarth:I just left, but there was a lot of preparation. What had to be done in those days (this was 1938/1939 — I left in early 1939) was that each child and each immigrant had to find a guarantor who would guarantee their immediate financial affairs. Most people found such a guarantor — and we did. My brother and I left about March 1939. You know the crisis for the German Jews came in November 1938 with the —- the so-called Kristalnacht and after that it was clear that one had to get out. My father was sent to a concentration camp at that time but it was still possible to get out. He got out, and it was clear that we had to leave the country. It was going to get worse. So preparations had to be made, visas had to be got and this guarantor to be found. All of which happened because we had friends in England. We got out relatively fast in March 1939. My parents did not get out immediately. There was some problem and they barely got out at all before the war. After the war started it would have been impossible. They got out in July 1939 — the war started on 3rd September as you know.
Keith:Did your father have any job fixed up in England?
Wohlfarth:No. Because he was in the legal profession — the German legal system and the British legal system are different — completely different — so at no time after he left had he any such job in this country — he had to work menial jobs—fire watching, an office job and so on.
Keith:It must have meant quite a good deal of economic restraint.
Wohlfarth:Yes, we were incredibly poor and what kept us going was the desire to make it in this country.
Keith:You think that gave a great deal of motivation to you at school.
Wohlfarth:Yes, it was clear to me that it was up to me—I had to make it myself. Nobody was going to help me. After a time though my qualities became clear to the authorities a little bit and I began to get scholarships and so on.
Keith:It's a real pattern that I have come across on this project. There are a group of people, some older who came over in the early thirties, but a distinct number came over as children. Peter Hirsch is one example. And they all seem to have had this personal motivation. They were isolated within their own communities. Were there many friends of yours who were in a similar position as children or were you very isolated within their own communities?
Wohlfarth:I was isolated, yes. People came over who we used to know who went to other places. Some slightly older had the bad luck to be interned. The British Government interned people rather indiscriminately. This is now known. Some were sent abroad to Australia and Canada. So I lost all contact with my previous friends and I had to make new friends which I found very easy.
Keith:Was the decision of the family made to stay in England or were there ever plans to go further abroad to the United States for instance?
Wohlfarth:Yes, the initial plan was to go to England and then go to America but this was never a serious idea once we got here. We found this country so marvelous in many respects and we wanted to stay here.
Keith:Where about did you actually settle down?
Wohlfarth:Well, after some time in the south of England we had to get out because we lived in a restricted area and my father was still an enemy alien. That was soon put right afterwards. So we moved to Yorkshire. We moved to a town called Bingley and I lived there for about ten years.
Keith:A remarkable cultural transition if I may say so.
Wohlfarth:The cultural transition is extremely interesting. I am glad you mentioned that. What it meant for me is having these two different cultural backgrounds have been an enormous advantage to my whole development since then — it still is. The middle class German Jewish intellectual background and the background in the North of England in Yorkshire, which I took a great interest in — it meant a lot to me in my developing years — has meant that I developed in a very broad sort of way. I am a liberal with a small ‘l’ as a person, partly as a result of this.
Keith:What are the sort of Northern influences then, do you think, that were important to you?
Wohlfarth:Well, almost a dislike of the "la-de-da" as J.B. Priestley puts it of the Southerners. That was a part of it. You're used to a tough life and living in a working class area as we did for all those years gave me an enormous motivation in joining and being active in the Labour Party, which I still am. Those things, the straightforwardness of the Yorkshire people, the working class influence and things like this I think have meant a lot to me.
Keith:And what particular influence do you think you brought from Europe?
Wohlfarth:From Europe? I must have brought — it now seems after all these years that I think I know what it is — it's my Jewish background which has been the most important development, as coming from Central Europe. I am now very much aware of my background from my ancestors in quite detail with the help of my father's papers and so on. So it's my Jewish background which I brought with me from there, — militant Zionism for example and things like that.
Keith:There were quite strong active Jewish communities in that part of Yorkshire.
Wohlfarth:I was never a member of any Jewish community, my Jewishness is within me and not related to a community; very personal.
Keith:What kind of friends did you make when you first arrived?
Wohlfarth:In Yorkshire? At school, at Bingley Grammar, I got quite friendly with people. Never very intimate, but we were friendly, we talked together. They accepted me in a very marvelous sort of way. Never finding it funny that I was there. I found the same afterwards when I came down South after coming to this College, to Imperial College. When I joined the Labour Party I found exactly the same acceptance of myself, as a person and not as somebody with an odd sort of background. This is a very English sort of thing and I appreciated it enormously.
Keith:What kind of a house did you live in in Bingley?
Wohlfarth:We had a working class house, with one sitting room downstairs, a largish kitchen of the old fashioned type, and three bedrooms upstairs and of course there were my parents and three children. There was an inside toilet and a small back garden. So it was a working class house but I found it a comfortable house.
Keith:They're quite small those houses? One always has problems with doing homework and things like that.
Wohlfarth:No, I had no problems. I sat in my own bedroom—I had my own bedroom and that was no problem doing my homework — I could spend hours in there.
Keith:Of course a great majority of your schooling was done before you actually came to England.
Wohlfarth:Well, no. I was fourteen when I came and I didn't learn all that much over there. The upsets were a bit too much I suppose and the teaching one got over there was not all that good. My teaching started for the short time we lived in the South of England and at Bingley Grammar School. I soon caught up.
Keith:Whereabouts were you in the South of England?
Wohlfarth:I was in Slough Grammar for a year.
Keith:When did you really first come into contact with science in terms of school?
Wohlfarth:With the introduction of a course of physics and mathematics in Bingley Grammar. Bingley Grammar isn't outstanding as a grammar school although it had Fred Hoyle as one of its most famous pupils, who's recently become famous again. We had some mathematics teaching because the headmaster, Mr. Smailes, was a mathematician, and we had an applied mathematics teacher, he was a little bit odd. We had a physics teacher who was also a bit odd. But all three managed to transfer something to me and it was in Bingley Grammar that I got keen. I didn't know what I was going to do, but when it was put to me by one or other of these people that I should study physics, I said O.K., that seems to be what I should do.
Keith:Did your parents have any real aspirations as to careers.
Wohlfarth:Yes, my parents, my father especially, had an enormous influence on me, in telling me that an academic career was thing one should have. This is the central European thing, a good Jewish boy becomes an academic.
Keith:And that was for a career and not simply a qualification?
Wohlfarth:For a career. At worse as a qualification but a career as the best. The "Herr Professor" thing is very strong. So when I was found to be adequate to embark on a university career in physics this was accepted with great joy by my parents.
Keith:How big was Bingley Grammar?
Wohlfarth:Bingley Grammar? I've forgotten. It was a medium size Grammar School.
Keith:So about four or five hundred
Wohlfarth:That sort of thing.
Keith:What can you actually remember about the science classes you had at school — is there anything that stands out in your memory — one always has memories of particular experiments.
Wohlfarth:No I don't. I'm a person who doesn't remember things a great deal — except a few flashes which come back now and again. I somehow have a bad memory. I suppose we did some experiments but I don't particularly understand why those schoolteachers who weren't exactly the greatest inspired me so much. They must have had something I don't quite understand now.
Keith:A lot of them were characters and eccentricity comes after being at the same school year after year.
Wohlfarth:That's right and especially the physics teachers was like that but something was transferred obviously.
Keith:I'm sure a lot of those teachers emphasized their own eccentricity.
Wohlfarth:I find that I'm doing this now myself with my students — now and again.
Keith:So you can't remember really what aspects of physics you enjoyed the most?
Wohlfarth:It must have been the analytical aspects, because I had a tendency towards the analytical to some slight extent. I think I'll tell you later that my main trend is towards the empirical but there were some analytical aspects of physics that I got somehow from the applied mathematics teacher that I had that, seemed to appeal to me. It's not the experiments themselves but the analytical aspects of seeing what the experiments mean. That's how I'm still working now forty odd years later.
Keith:Did you do any background reading in your own time at all or were you just concentrating on the schoolwork itself.
Wohlfarth:No I did quite a lot of reading. I read Eddington and Jeans like most people. It was the thing one read in those days. It was natural but I didn't get as much inspiration out of this as some other people must have done.
Keith:There was a real movement to popularize science at that time.
Wohlfarth:Yes. To me it seems that, now you mention it, it seems in order to understand the experiments, analytically and mathematically — that's exactly how I still work now — interesting isn't it?
Keith:Presumably in the economic position of your family then any university career depended on scholarships. When did you start thinking in terms of scholarships?
Wohlfarth:I didn't have to. At that time it was clear that I was someone who should be pushed. So my headmaster Mr. Smailes pushed me against all sorts of objections by the hardheaded Yorkshire businessmen who had to deal with it — the counselors, and then I didn't have to think about anything — this seemed to come from him.
Keith:Was it a State Scholarship?
Wohlfarth:No, I don't think I was eligible. It was a local scholarship. He worked for me in all sorts of roundabout ways to get this, but he got it.
Keith:Was it competitive, did you have to sit an examination?
Keith:Was it for a particular university?
Wohlfarth:I tried to get into Cambridge but I simply didn't have enough preparation. I was up against boys who had been trained for years for this. So I failed to get into Cambridge. The next thing was to get into Leeds which was the nearest university and that's where I was put.
Keith:So there was the attraction of Leeds presumably because of your family?
Wohlfarth:Yes, I could live at home. I went on the train every morning at 7:30 for ten old pence return from Bingley to Leeds which is fifteen miles. That meant I had enough money, because I didn't eat all that much, to give my mother something like two-thirds of my scholarship for the household.
Keith:In this period before you went to University, did you have any language problems?
Wohlfarth:No, I never had any language problems. I seem to be gifted to some extent in languages.
Keith:But presumably you didn't have any English before you came.
Wohlfarth:We had a bit because it was clear we were going to an Anglo-Saxon country, England or America — so we learnt a bit; but I have no memory of ever having problems with English.
Keith:Did you have any other language skills at that time?
Wohlfarth:I had Latin which I'm extremely glad about because I find Latin a marvelous language. But I had no French — I learnt a bit of French at school — I think I took it up to "subsid." as we called it — between "O" and "A" — one year after "O" levels. I remember my father teaching me a bit of French. French was never a big deal. I picked it up later when I lived in France.
Keith:Your natural language was presumably German?
Wohlfarth:No — then it was English — we didn't speak German at home. We spoke English at home and my German disappeared almost entirely. But I can speak it almost perfectly now.
Keith:This must have been useful going into research at that time being able to read German.
Wohlfarth:Not so much at that time. German science was completely destroyed and only in the last two decades has it come back again. Now it's useful because I can live in Germany, which I have done, live in Austria, which I have done, and converse with no problems at all. Also in French.
Keith:So what year did you go to Leeds University — was it 1942?
Wohlfarth:It must have been 1943. Because in those days it was war-time and you had to get a degree in two years and one term — so I must have gone in September, October 1943 and I graduated at Christmas 1945 or January 1946. So it was two years and a third.
Keith:And you went to take a physics degree?
Wohlfarth:Yes, physics. I went to take an honors physics course, with mathematics and we had to do electronics.
Keith:The department of physics you went into had been very much built up in the period before that by Whiddington. Whiddington presumably wasn't there when you went to university.
Wohlfarth:No he was somewhere else. He was involved in war-work.
Keith:Did he do some work that Stoner was involved in on the magnetron?
Wohlfarth:Stoner was working on the magnetron in the war but Whiddington was working on something else.
Keith:Wasn't he Science Adviser to the Ministry of Supply?
Wohlfarth:That's very possible. Stoner worked on the magnetron, magnetron calculations.
Keith:He was still at Leeds during the war?
Wohlfarth:He was at Leeds, he was acting head of department. But he had to go abroad, he worked for a while with J.C. Slater.
Keith:Who were the principal lecturers at that time?
Wohlfarth:In Leeds? There was MacDougall, Long, Brindley, those are the names of three people I remember — there were some younger ones — but they seemed to have made the biggest impression on me.
Keith:MacDougall was the person who had helped Stoner with the tabulation of the Fermi-Dirac functions before the war. Brindley worked with X-rays?
Wohlfarth:Brindley, he worked on X-rays of materials. Long was no longer doing research. He was involved in a rather interesting paper in the thirties on hematite which is an iron oxide — Chatsworth and Long — he discovered the transition in hematite which wasn't appreciated until many years later but at that time he was no longer doing research.
Keith:Can you remember any of the other members of staff?
Keith:It would have been a small staff.
Wohlfarth:It was a small staff. Those are the three main people I remember. There were some younger ones but they haven't made an impression on me.
Keith:And Stoner of course.
Wohlfarth:Stoner didn't lecture us until the second year. The first year it was mainly those three.
Keith:And which particular courses did they take? Can you remember?
Wohlfarth:Not too well, but Brindley gave a course on acoustics which was really a subject I found so exciting. I was going to devote my life to acoustics, acoustics of buildings in particular, absolutely fascinating; but then I was asked at the end of my third year what research did I want to do. It became clear that I was going to go in for research. I said "the acoustics of building." But I was told "no, there is no point because nobody here really knows anything about it, Dr. Brindley only gave this course, he's not an expert". That's something which has stuck in my mind. We had lectures on atomic physics, later on quantum theory, electricity and magnetism. In fact I've still got my old lecture notes up there — I could look this up but I think you are after impressions and — I don't have so many — as I said acoustics of buildings is something which still stands out in my mind.
Keith:Presumably you worked very hard on this degree course. You were determined to establish yourself.
Wohlfarth:Well I tell you it's rather odd. In the first year I didn't have to work hard because there was a lot of repetition of what I had had at school. So it came too easy to me. It came too easy to me. The second year therefore I went right down. I moved into what you would call, the second class. The first year I came top of the form with a first class mark and then I moved into the second class. The shock was too great from doing something I'd done already to doing something completely new. At one time I'd earned some money. I'd worked part-time in a local mill, a local woollen mill, this was woollen mill country.
Keith:That's in Leeds or Bingley?
Wohlfarth:In Bingley. Then it became clear that I wasn't doing as well as I should do. Of course it was clear I was a first class person — no doubt about it. Stoner was by that time lecturing to us. He said "I'll find you some more money—you have to stop that," so I stopped it.
Keith:Where did Stoner get the money from?
Wohlfarth:There were ways of getting money. There were scholarships around and so on. I was interviewed for something — some thing stands in my mind — I was asked "who's going to win the U.S. election". Things like that. Money was found. There was never any problem in finding money. This was my second year. The real development came in the third year. I'd caught up by then and I moved into the top class again. We were a small class of ten and we were all rather good. As it turns out five of us got first class honors degrees including some people who are well known even now. Geoff Farnell who's at Kodak, and Jim Tait who's a famous hospital physicist.
Keith:Can you remember any of your other fellow students?
Wohlfarth:Geoff Farnell most, there were two girls — one luscious blonde and one not so luscious. There was a boy called Philip Wood, but I don't know what's happened to him.
Keith:It's unusual presumably to have girls doing physics?
Wohlfarth:Yes. I must remember Geoff Farnell best. We were sort of slightly rivals. As it turned out he came top and I came second in the finals exam.
Keith:Did you have many friends outside the subject area?
Wohlfarth:At the university? No, not really, I didn't take part in any student activities — of course I lived at home.
Keith:Did you retain friends from school?
Wohlfarth:Not so much. I didn't socialize too much.
Keith:Did you have any background interests apart from physics itself?
Wohlfarth:Yes, music. I also developed an enormous interest in Labour Party affairs.
Wohlfarth:In politics, yes.
Keith:So when the first time you became involved with the Labour Party?
Wohlfarth:The Labour Party? I can tell you exactly. There was an old lady called Mrs. Hudson, who lived down the road. She was a great heroine of the Labour movement in the early days. She was rather poor and one day she had to buy a bag of coal for which she had to pay a pound and she gave the coal merchant a golden sovereign and said "that's it, that's a pound." This struck me as so horrific. That's the motivation I have in my mind now. There was another old lady Mrs. Walton who was similarly a heroine of the early days who also talked a lot and she introduced me. So I got this from the working class background and mainly from two heroines of the Labour movement.
Keith:And what dates are we talking about — can you remember when you first joined the Party?
Wohlfarth:I didn't join the Party until we moved to the South. Before that I went to meetings, and took an interest, but I didn't actually join the Party then. I had an enormous interest. It was to me a thing I should have. I think my Central European background also helps. I remember there was some election in Germany in 1933, and my father voted Social Democrat. That must have helped me too. So together there was my father voting Social Democrat — and the hostility I got when I said like an idiot to some boy that's what my father was voting, which wasn't very wise of me — and these two old ladies.
Keith:So how often did you go to meetings during your university days?
Wohlfarth:I didn't go to meetings. I had no emotional interest in the matter. I didn't actually become involved in meetings until about 1954 and then lived in London.
Keith:Did you do any political reading?
Wohlfarth:No, I'm an a — theoretical political beast, but very emotional about that and about Zionism. Both of which are political matters. I haven't read too much.
Keith:Changing the subject. When did you first come across magnetism — in your undergraduate course?
Wohlfarth:Stoner in this third year lectured on magnetism, which was most unusual. Hardly any universities in the world had this sort of course. The fact that I was able to speak German got him to give me this book to read. It's a German book from the 1930s on technical magnetism. Afterwards when he died his widow asked me what I wanted and I said I'd like these two books. 
Wohlfarth:There are two sets of the Becker and Doring book. One is the original book. The allies destroyed the plates when they took over Germany. This particular book was reprinted in America — Ann Arbor — some firm in Ann Arbor — and that's out of print too — but this is an original one. When I got this when Stoner died in the late 1960s it was in a mess, it was a paperback—so I had it bound by a local bookbinder.
Keith:So those were the two books he gave you to read?
Wohlfarth:Well he didn't give me Becker and Doring's but he gave me this one. His lecture course was very interesting to me.
Keith:Was it roughly based around his own book?
Wohlfarth:Partly but also round this sort of book — I suppose basically around his own book yes.
Keith:That would be "Magnetism and Matter"?
Wohlfarth:Magnetism and Matter, which he published in 1934, which I also have there.
Keith:There's one thing I noticed about Stoner's writings. More than anybody he always has an historical introduction — he seems to emphasize this as important to see the actual development of the subject as crucial and that presumably came over in his teaching.
Wohlfarth:Yes, to quite an extent, yes. Peter Peregrinus, and Gilbert and so on, it was mentioned. It's funny that nowadays the historical approach is very fashionable — for example Physics Today often has historical articles. Professor Blackman, whom you may have interviewed already, is at present working on the so-called ‘lodestone problem’. When his paper's written it will be incredibly interesting. [Now published in Contemporary Physics, September 1983; S.K. Blackman died in May 1983.]
Keith:How recent did Stoner go in his lecture course in terms of developments in magnetism? — did he cover impacts of quantum mechanics?
Wohlfarth:Oh yes. Quantum Mechanics was brought in, Fermi Statistics was brought in, because that's the basis of his itinerant electron model. He went into all the modern physical concepts, up to before the war. During the war nothing much was done and recent in those days was up to 1939.
Keith:It would have been then, as you say, a very unusual course. Not only were there few magnetism courses but presumably those that did exist certainly wouldn't go up to the time of the war.
Wohlfarth:No, it was a very, very unusual course.
Keith:Did you come across the other main texts in this period — Bates' book presumably?
Wohlfarth:No. Bates' book I came across only when I started my post-graduate work.
Keith:What about Van Vleck's?
Wohlfarth:Also –- that’s later yes.
Keith:So we're basically talking about Stoner's Magnetism and Matter and the Becker book.
Wohlfarth:The Becker — edited book of this German Conference and the lecture notes he gave us which were extremely interesting.
Keith:You said yourself previously that the one thing you wanted to do was acoustics in buildings — so presumably it couldn't have made a really great impression at that time if you still wanted…
Wohlfarth:Ah! That's right, that's right. It made an impression, but not overwhelming, because Stoner wasn't an inspiring lecturer like apparently Brindley must have been.
Keith:What was Stoner's style then of lecturing?
Wohlfarth:Very quiet — he didn't emphasize things too much — he was friendly alright but not too outgoing and so you probably know from what's been written about him he was suffering from diabetes which at that time he had to deal with in the old fashioned way by injections. The pill which he took later didn't come till a bit later when I think one pill a day could be taken. At that time he was injecting himself maybe several times a day — I didn't know this at the time but I knew about it later. Diabetes which he caught rather early as you will have read isn't good. It affects other things. He suffered from things like colds — bad colds in the winter, bronchitis and so on. This didn't show. He was quiet, he wasn't too outgoing, he didn't inspire enormous enthusiasm but you could see that there was something interesting there.
Keith:Did he explain things well?
Wohlfarth:Yes, he explained things well in a quiet sort of way but I'd no overwhelming enthusiasm from him.
Keith:I remember reading his own personal memoirs and he talks about the poor quality of a lot of the teaching he had at Cambridge and how that influenced him as a teacher.
Wohlfarth:Well, he was a good teacher but not a great inspiring teacher, and he must have given me something although to be quite frank, when it came to not doing acoustics of buildings, I could see magnetism was a subject which I should do and I did it. I had enough from him to see there was something in this too. So that's how it started for me.
Keith:What about experimental work, did you do much?
Wohlfarth:In the third year we had to do projects, but I'm not an experimentalist I'm not good with my hands.
Keith:What was the project you did in your third year? Can you remember?
Wohlfarth:No, as I told you before I can easily forget things. The more lousy the memory must be the more resilient you get. I've just forgotten — something about a bridge, some electrical experiment.
Keith:Like a Wheatstone bridge?
Wohlfarth:Yes, that sort of thing.
Keith:When you were coming to the end of your undergraduate career did you have ambitions to stay on at Leeds?
Wohlfarth:Yes, I wanted to stay on and do research. This was the obvious thing to do. There was never any doubt in my mind that was for me the next best thing. That's all I could think of doing.
Keith:And it would be theoretical research?
Wohlfarth:Yes, because it was clear I wasn't fit to be an experimentalist. This wasn't all clear to me but it was clear to Stoner. Stoner was looking for somebody because during the war, he was doing his war-work on the magnetron and so, and he wanted to develop after the war some of the ideas which he had to leave in 1939. I must have impressed him as a likely candidate for it.
Keith:So it was simply a case of inviting you to stay on as a student?
Wohlfarth:That's right. I was highly flattered and that's how it was. These things came to me. All these things came to me very easily. When something was needed I got it.
Keith:A very general point. What was your own image of physics at that time? I mean how did you see physics contributing towards material life or did you see it as a very intellectual thing? How much did you think of the relationships between the theoretical developments and developments in technology? What was physics to you then?
Wohlfarth:Yes, I didn't look at it analytically like this at all. It was something I felt I had to do — an academic career — this was clear to me, because of the background which I mentioned to you earlier. And as this arose, I just did it. I didn't have much of an image of things, no. I didn't think of those things you just mentioned at all really. That came much later, I'm a late developer in many respects, all these things came much later. Now I think about it in a very analytical way. But not in 1945, 1946.
Keith:In many ways it seems you were almost carried along by circumstance.
Wohlfarth:Yes, that's right.
Keith:You were still staying at home then?
Wohlfarth:Yes, I was living at home. In Bingley, the same house I mentioned to you earlier.
Keith:So did you become a post-graduate student after you finished?
Keith:And how were you financed? Was it a DSIR grant?
Wohlfarth:Yes, a DSIR grant.
Keith:Now you didn't become a U.K. citizen until 1948 is that right?
Keith:So were you in fact eligible for that DSIR post-graduate award?
Wohlfarth:Just a minute, so we are now talking about 1946 and 1948. No I wasn't eligible so it couldn't have been a DSIR grant, sorry, so it was something else. It must have been a university grant. It was a grant from the University of Leeds which Stoner got for me, yes. He wanted me so he had to pay for this. The university had to pay for this. That's right, so it was not a DSIR grant, I got one later for my post-doctoral work when I became his academic assistant. Then I was eligible in 1948 just, and that's when I got it.
Keith:And what was the first problem that Stoner set you to do. I mean did he suggest the problem?
Wohlfarth:It was really interesting. The very first problem was the paramagnetic susceptibility of atomic oxygen, yes and this he gave to me before I got my degree. He had something from Sir Edward Appleton and — this is a problem you should read up in Van Vleck's book. Van Vleck came in then in a big way.
Keith:So it was a very old problem?
Wohlfarth:Yes. It came in from something which arises in the upper atmosphere. The upper atmosphere is oxygen.
Keith:That was Appleton's field wasn't it?
Wohlfarth:That's right, Appleton's field. Oxygen dissociated into atoms and suddenly the question arose, "What is the susceptibility of atomic oxygen?", and that's what I worked out. It's never been tested since. There are some very anomalous results which came out and can't be tested. No one's gone in for it.
Keith:How much work did that paper actually involve?
Wohlfarth:About two weeks of computing on a Brunsviga calculating machine. Half-way through it I got it wrong, I got the energy levels the wrong way round so, O.K. it was a big disaster, but then I got it right and it came out.
Keith:How much guidance did Stoner actually give you on this problem?
Wohlfarth:I've forgotten. He must have given me quite a bit. Then the question arose of the magnetic hysteresis of heterogeneous alloys which was around at that time. He said, "Let's work on this together." But I tell you how it was. He said, "Here's the problem, you should work this out numerically like you've just shown you can on this Brunsviga calculating machine." After two days I could see this wasn't necessary, and that I could do the whole thing analytically. So I rushed into his office and I said "You don't have to do this, you can do it analytically."
Keith:He must have been a little sad over that prospect was he?
Wohlfarth:He was sad, yes. He was sad because he was always dead keen on computing. He was extremely keen on computing. He loved to do the computing with MacDougall which you mentioned earlier, and he felt that it was something else you could compute. And I said, "A lot of this can be worked out analytically," and he looked a bit startled. There was enough computing left as a matter of fact in this problem and this paper is now a very long paper, I can see, of 43 pages long with a lot of computing still left.
Keith:Again Stoner presumably very much set up that particular problem. The ideas had been developing from before the war and in fact he had produced a paper about 1944 of the computed tables related to that problem? 
Wohlfarth:I didn't know that. No, no, the tables were worked out by us after the war. The other thing about my involvement in this work as an original physicist was not just what I've just told you about the analytical work, but also the relationship to the real world. I was rapidly developing now into a person who could see the relevance of this to experiment. And I remember when going through the literature, which I did in a big way, I came across one aspect on impure alloys — this is things like copper with a bit of iron in, which seemed to fit in exactly.
Keith:On this particular problem, the hysteresis problem, presumably Stoner pushed you in the direction of all the pre-war literature.
Wohlfarth:Yes. But with the help of these German books and other books.
Keith:Becker and Doring have quite a large section summarizing this area.
Wohlfarth:Yes, but also some of the original papers, for example Bradley and Taylor on Fe-Ni-Al alloys and papers like that. So I got extremely interested in metallurgy at that time. Ternary diagrams — iron, nickel, aluminum—became something of enormous fascination to me.
Keith:That was something that developed from own interests?
Keith:There was quite a lot of Soviet work was there not in the thirties on domains — was it Akulov?
Wohlfarth:Yes, Akulov, and Kondorsky. That's right.
Keith:And were you reading into their work?
Wohlfarth:Yes, very much. Akulov and Kondorsky I was reading. In fact I met those Russians later. Kondorsky's still alive. Akulov, he must be dead by now.
Keith:Where did they work in the 1930s?
Keith:Did you actually read any Russian?
Wohlfarth:No, in English or in German. In English most of the time. A key paper was Landau and Lifshitz which I read very early and that I think was published in German. It must have been in German — I'm not sure.  Lots of these papers were written in German in those days.
Keith:And it was while you were doing this particular problem when the two papers by Neel came out?
Keith:He was working in a very similar area on powders.
Wohlfarth:Yes that's right. It was interesting, I hear about this from the great Dutch physicist called Snoek who worked at Philips in Eindhoven. He told me about this at a conference in Bristol to which I went. The very first conference and I found out that the work we were doing was being paralleled by Neel. So I rushed home and said that we should publish this.
Keith:So Stoner didn't know about this?
Wohlfarth:No, I had to tell him this and finally he published the letter in Nature in 1947.
Keith:How similar was the approach you were taking to what Neel was doing?
Wohlfarth:Neel only worked out the critical size of the single domains and it was only a small part of what we were doing. We worked out the actual hysteresis mechanism in much greater detail than him although he got the final result which we got after a lot of computing, he got out intuitively in a few lines in Comptes Rendus.
Keith:This particular paper was a standard paper for a very long time.
Wohlfarth:It still is, it's the most quoted paper in magnetism since the war.
Wohlfarth:I think so, yes.
Keith:It had tremendous relationships to technological developments.
Keith:Were you aware of that at the time?
Wohlfarth:I rapidly became aware of this, with respect to permanent magnets and later on recording tape materials. I was doing a lot of consultancy in the 1950s and 1960s and also starting in the 1950s this work on permalloy films. I became aware very rapidly and it became clear to me that this had a lot of industrial relevance.
Keith:There had been had there not quite a lot of development in magnetic tapes in Germany during the war?
Wohlfarth:Yes that's right. The Germans did a lot on recording wires and recording tapes which was taken over by the allies when they went in.
Keith:The relationship of a research student to a professor is very different from an undergraduate. You must have been at that time getting to know Stoner a little better as a character. What were the things that occurred to you at that time, the things that came over about his personality?
Wohlfarth:Well, he was always very quiet with a rather wry sense of humor. No great intimacy existed although I have been told by his widow that he was extremely keen on having me around as a research student. I was exactly what he wanted apparently.
Keith:So did he have quite a reserved personality?
Wohlfarth:He was reserved, yes, he was reserved and introverted on the one hand. He wasn't easy to get on with, as was found by many other people. We don't want to go into this in enormous detail but I have some letters here by his widow which throw a different light on him than the general public knows about him.
Keith:The impression I get is that although he obviously had this reserved quality he could feel very strongly about specific issues.
Wohlfarth:That's right. He was very keen on pushing his department and his university and he sometimes met with hostility in both respects.
Keith:Within the department?
Wohlfarth:Within the department and within the university itself.
Keith:How did he see the department going at that time? It expanded very rapidly after the war.
Wohlfarth:Well he wanted to build it up into the number one school of magnetism in the world. This wasn't possible; it didn't happen like that.
Keith:Because of the resources and the problems of attracting students?
Wohlfarth:Oh mainly because of hostility and envy. He was a very great man, he was a Fellow of the Royal Society, he was well known everywhere. People could see that he was a great man and when a great man is around there are others who feel envious and do things to harm him. That is what must have happened in many respects.
Keith:What was his attitude towards administration, did he find it a bind?
Wohlfarth:No, he took it extremely seriously. He took it so seriously that in 1954 he wrote his last paper when he was only in his mid-fifties — roughly my age now, he was slightly younger than me. He stopped research completely because he was so keen to do administration and this was a mistake. That's when he began to spend all his time in these fights.
Keith:His output after the war itself wasn't that great. There were some particularly important papers but not a high number.
Wohlfarth:After the war there are two important papers, this one which he wrote with me on hysteresis and the other he wrote with Philip Rhodes on thermodynamics.
Keith:Who is Philip Rhodes. I know of his work with you.
Wohlfarth:Philip Rhodes was the student who came to work with Stoner the year after me and he was given the job of working on the thermo-dynamics of the hysteresis cycle. This was an extremely interesting and good paper because thermodynamics is something which Stoner was always keen on — he's transferred this love to me actually, but it hasn't had any great influence on future developments unfortunately. Those were the two papers he wrote. He wrote some papers also from the war.
Keith:The very major papers of course are the two review papers he wrote in that period.
Wohlfarth:When I started to work with him on this Phil. Trans. paper on hysteresis, he was already ready to wind up — very, very young. It must have been these tensions he was living under with the people that I mentioned to you earlier. He was ready to finish already at that time, unfortunately. Maybe he felt it was O.K. for me to take this over — maybe I don't know — he never mentioned anything like this — there was never an emotional discussion like this with him — never.
Keith:Did you ever get invited as students to his house?
Wohlfarth:Yes, I went to his house. I met his mother who was as you will have read from his writings, an enormous influence on him, not a strong woman, not too well; I went there once or twice. The only time I was close to him really was when we went for a walk to Barden Tower and the abbey — what's it called, the abbey up there — we walked for several miles and that's when I told him about the dilute alloy, the discovery that I had made.
Keith:What about his relationships with other scientists in the field, particularly British ones, was he close to any?
Wohlfarth:Not really, and he had lots of dislikes.
Wohlfarth:Personal and intellectual dislikes. This has to come out, I don't see why I shouldn't bring it out: he disliked Blackett enormously.
Keith:Was Stoner involved in politics at all?
Wohlfarth:No, I think he voted Labour but not in a very big way.
Keith:There's another thing that comes out of Stoner's writings a lot about the relationship between theory and experimental work; he obviously had extremely strong feelings on this.
Wohlfarth:He hated theoreticians who worked on theory for its own sake — this is clear from his writings. He felt the relationship with experiment was what the theoreticians ought to be reading about.
Keith:It's very Baconian, this view of Stoner's — the Baconian idea that all theory must be related to experiment and that one guides the other.
Wohlfarth:That's right, I think he went too far in this — there's some theory worth doing for its own sake, that's clear. Sitting in this mathematics department, that's clear to me. But one wants some sort of balance and he was unhappy about the balance being too much towards a pure theoretical or philosophical approach without relevance. So he was very, very keen on what you say — the relationship between theory and experiment.
Keith:How much were these feelings brought about with the experience of developing the collective electron theory. What comes out not only in his papers but in your papers is the difficulty of actually relating experimental results to the actual theoretical aspects you were developing because there really was this division.
Wohlfarth:That's right. I'll tell you how it was. He had developed this theory before the war and published the seminal papers in 1938 and 1939 and then had to leave it. He published at the time one more paper in the Transactions of the Leeds Philosophical Society where he looked at iron, cobalt and nickel. That's the sum total of his looking at experimental results — it was left entirely to me just after the war because as you've just seen he was no longer a full-time scientist — he had all these other duties — so it was up to me. He could trust me to do as much as was possible in those days to look into the relationship between the collective electron or itinerant electron model and experiment which I did with great enthusiasm. It seemed to suit me enormously to do this. I was keen to go into the archives with the papers and I could see what it all meant and so on.
Keith:So let's get the dating right. When did you actually finish the work on hysteresis?
Wohlfarth:Well, it all went very quickly. I think we must have finished this in, round about, the autumn of 1946. Then it had to be written up. The trouble was he didn't write it up immediately allowing Neel to get ahead of us to some extent.
Keith:So it was Stoner who wrote it up?
Wohlfarth:Stoner wrote the letter to Nature and afterwards he wrote the Phil. Trans. paper. Yes. Of course his writing — maybe it should be mentioned here was incredibly beautiful — he wrote very beautiful English.
Keith:So when did you actually start on the collective electron model?
Wohlfarth:It must have been in the autumn of 1946. Yes, autumn of 1946.
Keith:So you were only working for less than a year on hysteresis problems?
Wohlfarth:At the time yes.
Keith:How did you begin to approach this problem; Stoner presumably led you towards those three papers he'd written on the subject. Was that your first introduction to it?
Wohlfarth:The collective electron model?
Wohlfarth:Yes, I read his papers. But it wasn't at all long before the problem arose — "What does it mean?" — "Let's look at what it means." So I had iron, cobalt, and nickel from him and I said, "That's not quite enough we should also look at alloys." So I looked at nickel-copper-alloys — that was a paper I published in 1949. I also said we should look at palladium and I wrote a paper in 1948 on palladium and platinum which was an unknown story really although a lot of the basis for this was laid by Mott and Jones in the 1930s.
Keith:Did you go back to the original papers by Mott and Slater?
Wohlfarth:Yes, yes. About that time, or slightly later when it came to looking into the quantum mechanical background of this — the early part of this work was largely formal just based on the use of Fermi statistics with a parameter, the parameter being what we used to call Ξ’ and is now called U or I and that was put in. Later the problem arose — "What does it mean?" — That I didn't start work on until I came to Imperial College, Mathematics Department, where we are now, when it became clear that this had to be explained on quantum mechanical grounds.
Keith:The collective electron model conceptually is very difficult. How difficult did you actually find it?
Wohlfarth:Well, it's extremely difficult and nothing is solved now in 1981. It's still very controversial. This is still going on, and will go on, as I have said somewhere else, for several decades. So at the time I just had the formalism based on Fermi statistics, and that was no problem, because that had to be applied. The problem then arose, "How do the parameters vary in an alloy?" My main contribution was the alloys which Stoner hadn't done. Based on what Stoner had done on nickel I looked at nickel copper alloys. It turns out now that that was a lousy system, but at that time it was a good system. The metallurgy of the system was at the time thought to be easy — it's now known to be extremely difficult — but never mind. So the question I was asking was, "How do the parameters once you put them in vary with alloying?"
Keith:What kind of parameters are we talking about?
Wohlfarth:Magnetization, Curie temperature — those are the observables and how those were to vary in a certain way from experiment. I had a lot of experimental results — mainly from people like Sucksmith.
Keith:How much reading were you actually doing on alternative work at looking at theories of ferromagnetism?
Wohlfarth:I didn't have time — at that time — I didn't start on that until I came to Imperial College in 1949.
Keith:Do you think that was a weakness at the time — that you hadn't looked at other material?
Wohlfarth:Yes, I think so — I think I should have looked into this earlier.
Keith:Presumably the danger of doing this is that you get a very blinkered approach?
Wohlfarth:Yes. But that came to an end. Fairly soon after I got to Imperial College, because the atmosphere was different. The atmosphere in Leeds was that this was the model one should use. Whereas at Imperial College, the (laughs) atmosphere was that maybe other models are much better which began my period in the wilderness as I have described it in another place.
Keith:Were you building up any outside contacts in your period at Leeds — was there any correspondence?
Wohlfarth:Yes, I had lots of correspondence with people on other problems I was working on. For example I was working on thermionic emission constants and I had some correspondence on that.
Keith:How did you actually get into that particular problem? You had two papers on that I believe?
Wohlfarth:It seemed to arise as follows. In applying the collective electron model to real materials you had to look into two energy bands — the d band and the s band. The original work of Stoner's was only for the d band and the problem arose "how important is the s band?" The s band was found to be not all that important but thermal excitations from the d band to the s band could under certain circumstances be important. So the transfer effect came in and that led me to thermionic emission.
Keith:Were these papers particularly stimulated by this earlier 1946 paper you'd read?
Wohlfarth:Which 1946 paper was that?
Keith:It's the one that's mentioned in this paper itself. 
Wohlfarth:That's right, yes.
Keith:So, it was more or less a responsive thing — you saw this and you thought you had something to contribute.
Wohlfarth:Yes, that's right. It's always all like that with me. I see something and I respond to it.
Keith:And what other aspects were you working on in that period before you left Leeds?
Wohlfarth:Other applications to other alloys. I've mentioned nickel-copper, and palladium and platinum and also I applied it to mixed cobalt and related alloys. I see here that in 1949 in Phil. Mag. Volume 40 I did try to go a little bit into the quantum mechanisms already before I left Leeds, but not very effectively. I don't think this paper is very good now. My best paper on this is Reviews of Modern Physics in 1953.
Keith:The Washington Conference one?
Wohlfarth:Yes, the Washington Conference paper, which I wrote soon after I arrived here. So I did try a little bit before but not very effectively. I think my main work on the collective electron model was to apply it to alloys.
Keith:Was there any great support for the collective electron model outside Leeds?
Wohlfarth:No, there was only hostility and this went on till 1960.
Keith:What was the hostility based on?
Wohlfarth:The hostility was based on misunderstanding that the collective electron treatment is a model only for free electrons.
Keith:And that was because of the parabolic band assumption?
Wohlfarth:Yes, it was the parabolic band assumption in it which misled people into thinking it was a free electron model whereas it was clear to Stoner himself that this is not on — that d electrons had to do with it.
Keith:Now the parabolic band assumption was being made for computation ease was it?
Wohlfarth:Only for computation so that he could use the Fermi-Dirac integrals which he had calculated with MacDougall. That is why I wanted at the time to work on the rectangular band. Stoner said "No we shouldn't work on this."
Keith:Why not? Why didn't he want you to work in it?
Wohlfarth:Because he felt this was overdoing the whole thing. Another thing, talking about alloys, was that I was keen on looking at the way the collective electron model changed when the alloys were no longer uniform. In other words when the fluctuations of concentration are important. Again — I have to say this about him — he put me off this — it was only later when I was here that I started seriously searching for, and I am still doing it to this day, the importance of concentration fluctuations. I knew at the time this was important. I had some experimental evidence on this, in nickel-copper alloys; I'm rather pleased that I did say this — it was published in my 1949 paper — but I was never really encouraged to go on with this at the time. Professor Rushbrook was there and he encouraged me, but not Stoner.
Keith:How would Stoner actually discourage you.
Wohlfarth:He'd say, "That is very interesting but maybe we shouldn't look into this just now." He was always a gentleman — he never said, "You are forbidden" — he was always a gentleman, but he said, "Maybe you shouldn't concentrate on this" or words to that effect.
Keith:What did he want you to emphasize?
Wohlfarth:I think he wanted me at the time to go into the quantum mechanics. Then it was time to leave and I took this up fairly soon after I got to Imperial College.
Keith:What were the major objections, then, to the collective electron model at that time.
Keith:We've mentioned that it was misunderstood because of the parabolic hands. For example, in a few of Van Vleck's papers. He simply calls it the free electron model.
Wohlfarth:Yes, that's wrong. That was a misunderstanding even by a great genius like Van Vleck. That was one thing. The second thing is that we didn't at the time have spin-waves in it. Spin-waves were not in it and the third objection is that the localized model is easily understood from a physical point of view whereas the physical meaning of the collective electron model is not easy, it's extremely complicated although as I've said earlier the applications to real materials was fairly straightforward. So there were three things — parabolic hands, we did not at the time have spin-waves in it — as far as I was concerned that came much later — I'm now a great fan of spin-waves, and thirdly the difficulty of seeing what was going on compared to the Heisenberg model.
Keith:This last factor is important as regards how things get into text-books. The Heisenberg model is always in textbooks.
Wohlfarth:Our model isn't in text-books as well as it should be even now. I should write it but I haven't got time — I'm too busy with my own work still.
Keith:What exactly are spin-waves?
Wohlfarth:Spin-waves are collective excitations made up in a metal out of the collective motion through the lattice of electron-hole pairs with a characteristic wave vector and energy related by a well known Q2 dispersion relation, for which the evidence is incontrovertible. They exist and they are very important elementary excitations.
Keith:Were you aware of this at the time?
Wohlfarth:No. I didn't take this seriously enough. In fact I was highly against it. I have a paper which I'm not too fond of which showed that they are not important. We all make mistakes, especially when we are young, that was a mistake, they are incredibly important and the question right now in 1981 is which is more important, those or the single particle or Stoner excitations in metals like say nickel.
Keith:What about the problem that was often brought up about correlations?
Wohlfarth:Yes, that I became fully aware of in 1951 and 1952, especially in 1952. I had this talk at the Washington Conference where correlation was a central feature of the matter. Stoner said to me, "What about correlation?" He seemed to be aware of its importance — but I was not at the time fully trained or prepared to do as well on this as I should have done — on the correlation problem. But this came when I came to Imperial College when I was able to get the benefit of Professor Harry Jones, who was here.
Keith:Do you think that looking back on that period that Stoner maybe could have given you better guidance. It was a fact that he was going more towards administration. It wasn't until later that you look up the quantum mechanical problems.
Wohlfarth:Stoner gave me enormous inspiration into looking at experiments and I said, "OK let's look at these alloys." He did not give me enough inspiration in quantum mechanics which I've missed ever since. He was keen I should go to lectures in pure mathematics, so I went to lecture on complex variable theory in the mathematics department of Leeds University. What I was missing at the time and I had to pick up very fast when I came to this department, at Imperial College was the quantum mechanics. I did not get enough guidance on quantum mechanics. I had a very strong guide from him on statistical mechanics and on thermodynamics but not on quantum mechanics.
Keith:A few points that I'm not too sure exactly what they mean by in the literature. What do we mean by effective interaction?
Wohlfarth:That's exactly the same question you've just asked me. If you work out the interaction on the basis of the so-called Hartree-Fock approximation you get a value which is very much too high and that came out exactly in my paper at the Washington Conference. So this is to be reduced by correlation effects which are not in the Hartree-Fock approximation. This has been a very difficult problem in quantum mechanics whose solution is not too satisfactory but there is now a usable approach to this by Hubbard and Kanamori.
Keith:That came much later, didn't it, in the early 1960s?
Wohlfarth:Yes, that's it. And the effective interaction is the bare value IB which is reduced to its effective value which can be very much smaller, or a little smaller, depending on the circumstances of this correlation effect which we've just been talking about.
Keith:Similarly what do you mean by effective temperature?
Wohlfarth:Effective degeneracy temperature do you mean?
Wohlfarth:There's an effective degeneracy temperature which is one of my special things and is still not understood. This is a concept which is clear and could have been understood in the 1930s after Mott and Jones' book for example. It is a temperature to which the measurement temperature, or observation temperature is to be scaled to find out how important it is in the statistical mechanical development. Now this temperature called Tf — f stands for Fermi — is a lot less than people think because people think of a smooth density of state curve for which these two temperatures are the same. But for the real d band the temperature, which I've called the effective degeneracy temperature can be a lot less than the temperature which is determined only by the filling up of the d band. Those two can be enormously different by a large factor. This is still not understood and I'm still having to put this into papers. When talking to highly intelligent youngsters I'm horrified that even now they don't often understand the whole concept. It's extremely simple and the joke is that I started with a parabolic band and now I am in real d bands and the real d bands have fine structure which determines this effective degeneracy temperature you've asked me about. In fact one of my young colleagues calculated this from first principles much later in the early seventies and it comes out more or less like you want it to for experimental results. This is not understood by the majority of people working in the subject.
Keith:A few general points about Leeds. What other people were working in that department after the war? You've mentioned Philip Rhodes and obviously yourself, and Stoner.
Wohlfarth:There was Elcock, Ted Elcock.
Keith:No. I don't know him.
Wohlfarth:He's somewhere in Scotland. He was very promising but never fulfilled his promise.
Keith:What was he working on at the time?
Wohlfarth:He worked on, was it diamagnetism? He worked on non-ferromagnetic metals, and then there was—I've forgotten his name.  He worked with Stoner on the Neel model. There was the Neel model produced during the war on coercive force, a highly complicated theory, which was typical of Neel — nobody could understand it — and Stoner wanted to understand it so he put this fellow on it. But I've forgotten his name now.
Keith:Who else? Was Tebble there?
Wohlfarth:Tebble was on the experimental side. Are you asking me about the experimental side too?
Keith:As well, because there was the low temperature work wasn't there?
Wohlfarth:Yes. Ok now we come to the experimental side. There was Tebble and his colleagues. Tebble is still around — he's Professor in Salford. Then there was Henry Hoare who worked on the low temperature side. He did some extremely pioneering work of enormous importance and his death very early was a great tragedy. Brindley left.
Keith:At what date?
Wohlfarth:He must have left soon after the war — maybe 1948, that sort of time. He went to America where he did a lot of excellent work on clays. At the time in Leeds there was an enormous group on solid-state physics as it is now called, theoretically and experimentally. We could have conquered the world, but this didn't happen.
Keith:What kind of work were they doing on the experimental side?
Wohlfarth:Barkhausen Effect was done by Tebble, and low temperature physics was done by Hoare et al., basically susceptibilities and specific heats. This covered for example the famous maximum in the susceptibility of palladium.
Keith:Was there much interaction between the department and the departments at Nottingham and Sheffield.
Wohlfarth:Yes we went a lot to Sheffield and to Nottingham. There was a lot of interaction. The thermodynamic work of Rhodes and Stoner was based entirely on the experimental work of Bates et al. in Nottingham. The work on nickel was based on work by Sucksmith before the war — Sucksmith and Pearce, and yes, there was interaction with lots of those groups, we formed the so-called "magnetic belt" as it's called in the history of the subject.
Keith:Where were the other centres in magnetism. What about the Clarendon — particularly in low temperature work?
Wohlfarth:I can't comment on that really. On magnetism, mainstream magnetism is was those same centres. In the Clarendon it was more on non-metals.
Keith:Was there anything at the Cavendish?
Wohlfarth:There was some war work on real materials, about 1944 I remember. Bragg had some war work on this, but this didn't continue after the war.
Keith:What were the circumstances — in your coming to Imperial?
Wohlfarth:Well, I got a Ph.D. in 1948.
Keith:What was your Ph.D. on?
Wohlfarth:It was in two parts, part one on the hysteresis problem and part two on the collective electron treatment. And then they appointed me as a research assistant. I got 350 a year which was an enormous sum and, I was research assistant to him and we carried on with some of the work I was talking about. But then he felt I should leave. He should have allowed me to leave with the understanding I'd come back one day. I think he had this in mind but circumstances were against this because with my experience in London I could have really helped him build us up into the centre of excellence it should have been and never was.
Keith:Why did you want to leave? Why did you think you had to leave?
Wohlfarth:He said I should leave. And it seemed to me that I shouldn't carry on like this and there were several problems. I was bursting with ideas in the direction of quantum mechanics. That's what was missing as I've said before, and this couldn't have been done up there. So I could either have gone to Mott or Jones and I finished up going to Jones here.
Keith:And was there a job advertised?
Wohlfarth:No, in those days. It's horrible to think about it now especially today (laughs) when the government's statement is going to be made on the universities. There were six lecturers appointed in October 1949 in this mathematics department. It was absolutely no problem. Nothing was advertised. Stoner wrote a letter to Harry Jones saying "I've a bright young man here," and Jones said, "Yes, that's exactly what I want here!"
Keith:Who were the other people who came at the same time to this department?
Wohlfarth:Harry Fairbrother, who's still here, we're the oldest serving members of this department. I mean the ones who've been here longest. It's a long time 1949 to 1981. And Stanley Raimes, some statisticians, people like that.
Keith:Were you taken on as a lecturer?
Wohlfarth:As a lecturer, yes.
Keith:And what particular courses were you expected to teach?
Wohlfarth:Well there were so many staff around, and so few courses that I wasn't given a course until later. I was basically teaching ancillary mathematics to other departments.
Keith:How much contact did you have with people like Bryan Coles?
Wohlfarth:Bryan Coles must have arrived here in 1950 to 1951 and we had immediate contact. Almost the day he got here he came to see me and we've been discussing things on and off ever since.
Keith:Presumably you have contact in terms of electron theory of metals, band theory.
Wohlfarth:Yes, he felt that my approach was what he wanted too. Because as soon as I put in the quantum mechanics the things improved enormously.
Keith:One person that did come in in that period was Lidiard.
Wohlfarth:That's right, Lidiard did some excellent work and we talked with each other an enormous amount at that time and he did some of the quantum mechanics, starting before me in fact.
Keith:But where was Lidiard, because he did his Ph.D. on the collective electron model.
Wohlfarth:That's right, now where was Lidiard? King's College. So I saw a lot of him.
Keith:Who else would you have had contact with here?
Wohlfarth:Tredgold who is at the University of Coleraine and Geoff Fletcher was my first research student. He started more or less as soon as I arrived. And I had some correspondence with John Slater who was most impressed by my band calculation with Fletcher.
Keith:That was the 1951.
Wohlfarth:Yes, the 1951 Phil. Mag. paper.
Keith:Did you have any reservations about putting Fletcher onto an area that was very controversial?
Wohlfarth:No. I was absolutely confident that this was right. Of course the band calculation that I did with Fletcher would stand up on its own as a band calculation for nickel. It turns out that this was the first direct band calculation on any transition metal after the war or any time during using this method. There are some by Slater before the war but those were based on the so-called cellular approximations which are now discounted.
Keith:It was the tight binding.
Wohlfarth:Tight binding approximation. So this could have stood up on its own. But I was sure that the collective electron treatment was the right thing to do for nickel. At that time. I'm not so sure now because of developments since then — that was thirty years ago.
Keith:What was your own attitude then to the collective electron model? Was it that you weren't looking at it as a general theory, more that it could be applied to specific metals — was that the case?
Wohlfarth:To metals and alloys, yes. Transition metals and alloys.
Keith:So it was never necessarily in complete conflict with the Heisenberg model; it was an alternative approach that might be better in specific situations.
Wohlfarth:That's right. Heisenberg's approach was obviously right for non-metals where you can talk about exchange integrals and so on. But for transition metals I felt the Heisenberg model was not appropriate and the model you should use is the collective electron model. Then I had to deal with the quantum mechanics of the time so I could talk about things like effective interaction.
Keith:What kind of help did Harry Jones give you when you came here?
Wohlfarth:He gave me unspoken help by just having an atmosphere of quantum mechanics here which is what, as I said earlier, I missed. But he was also uncertain of the merits of the collective electron model, like everybody else. I'm not being neurotic about this or paranoid. The model was not accepted by most people with a few exceptions like Herring. There was enormous hostility by most of the establishment against it which went on until 1960.
Keith:Who were among the most hostile then of the critics?
Wohlfarth:Well, Van Vleck was fairly hostile. Slater was not hostile, he was an exception like Herring.
Wohlfarth:Zener, yes. Zener was hostile. There was this famous controversy with Stoner about the merits of this model. Zener found no merits in it.
Keith:And this would all presumably come out at conferences in a particularly heated manner.
Wohlfarth:At conferences, yes, particularly between Zener and Stoner, that's right.
Keith:And this would be the Grenoble Conferences in 1950.
Wohlfarth:Wasn't it even earlier?
Keith:And there was the 1952 Washington Conference.
Wohlfarth:At the Washington Conference it came out, yes. There was a famous round table discussion at the Washington Conference in 1952, where I should have been, but the late unlamented Senator McCarthy kept me out of the United States. Stoner was at it. He was sitting in for me so to speak. It must have been one of his last conferences. Van Vleck, Slater and Zener were also there. This became a very hostile and quarrelsome occasion which apparently there's a tape of which someone has hidden away (laughter).
Keith:Of course the discussions were never printed, it's simply a summary which describes it as a "lively" discussion.
Wohlfarth:That's right and I wasn't there, I couldn't get into the United States at the time. It was lively, it was bad-tempered and there's one tape of it which exists somewhere in America. Osborn has it I think. Osborn who was at Washington — John Osborn. It would still be worth listening to.
Keith:You said you weren't allowed into the United States — because of your political activities?
Wohlfarth:No, I was hoping to go to Pittsburgh where I was invited to go by Fred Keffet for one year and this would have started by me going to the Washington Conference to give this invited paper. I applied for a visa and a Fullbright Fellowship neither of which turned up in time — one was turned down completely. Fulbright was turned down and the visa arrived too late and the reason is unclear to me but must have been because I was born in a place which was after the war Polish and had nothing to do with me because when I was born, it was German. That's how it must have been. But as you know when it comes to extremists like McCarthy logic doesn't always enter the problem.
Keith:You were a member of the Labour Party by then?
Wohlfarth:I joined the Labour Party in 1954 which was after this.
Keith:It seems from your publications from about 1953 you effectively stopped the work on collective electron ferromagnetism.
Wohlfarth:Yes, I couldn't stand the aggro so I went back into fine particles and applied this to things like recording tapes. At that time I was made a consultant to EMI with the help of Blackett. I also worked with Blackett on rock magnetism, which is still a love I have now. I did some work on further applications of fine-particle ferromagnetism and I finished up with a review article in Advances in Physics in 1959.
Keith:Whereabouts was you consultancy?
Wohlfarth:At EMI, EMI Research Labs, Hayes.
Keith:Was there much interaction between industry and university scientists at this time?
Wohlfarth:Not from mathematics departments naturally but there must have been a lot from mining, engineering, and metallurgical departments. A little bit from physics but it was unusual for a mathematician to do this, but of course I'm not a mathematician. There wasn't enough, but there was a bit.
Keith:What obviously always stands out is if you take some of the major figures in American solid state physics a lot of them had jobs in industry. The obvious reason for that, it seems to me is that the firms in the States were so big that they could actually support people doing very basic research.
Wohlfarth:Bell Labs and G.E. and IBM and so on.
Keith:But that also occurred at Philips in Holland which was a lot smaller.
Wohlfarth:And Siemens in Germany. An obvious example which did happen here was Gabor, Dennis Gabor, but it wasn't so common as in these other countries you mentioned.
Keith:Do you think it gave the American physicists a slightly different attitude to what they were doing?
Wohlfarth:I think so, yes. I think contact with industry is very important, as far as I'm concerned for the healthy attitude you have towards real materials.
Keith:If one looks at the conferences in the 1950s one thing that really stands out is the real expansion in magnetism as a field. If you look for instance at the Grenoble Conference and the Washington one you have got something like six British representatives and the conferences get more common and also the numbers get a lot larger. What was the reason for that. Was it simply the expansion of science per se or the field itself and the relationship to technological development.
Wohlfarth:Everything extended — all the things you say happened. It was felt magnetism was essential to pure physics because basically it's at the meeting point of chemistry, mathematics, metallurgy, electrical engineering, etc. that's from the pure physics side. It is essential, it is a meeting point for all those things. And it was also felt to be highly important for applications, for industrial applications and the intellectual challenge was seen to be more and more attractive. The problems were found to be more and more interesting as intellectual exercises.
Keith:I suppose it was much more established as a research area?
Wohlfarth:Yet, it grew enormously in the 1950s.
Keith:Presumably there were provincial groups beginning to spring up in some of the other universities.
Wohlfarth:In England? Yes in the 1960s and 1970s.
Keith:But not so much in the 1950s?
Wohlfarth:I can't remember great groups.
Keith:So it would still be essentially Leeds, Sheffield and Nottingham during the 1960s.
Wohlfarth:Well, Oxford, where other aspects were looked at. Now in 1981 there are lots of provincial centres of excellence in magnetism but this came really rather later. There was some sort of a gap when this magnetic belt collapsed with the grand old men, they died and so on.
Keith:It was really built round the three figures which left the gap.
Wohlfarth:Yes, which Hoselitz and I tried to fill, but it took a long time for this to happen.
Keith:While we're on that, can you fill me in on the characters of the other two main figures, Bates and Sucksmith?
Wohlfarth:Yes. I can to a point, but I think you should talk to some of their pupils. Sucksmith was a very unusual man and he built up a measurement group in Sheffield which at the time was second to none based around the ring balance. He was keen on measuring precisely magnetic properties of real materials in the great tradition of the Strasbourg School under Pierre Weiss. He was more or less keen to do this in England. Bates was also extremely keen on measurements on real materials and his thermodynamic work was what inspired Rhodes and Stoner. So they were both very keen on real materials which is now of course the in-thing to be but they had very little knowledge of theory but Stoner and his pupils, tended to supply this.
Keith:So there was a continuous movement of students from Leeds to Sheffield and Nottingham?
Wohlfarth:No, no, not really, there was no movement of students. Some people, like Tebble, moved around. But each of these three each had their own students and Stoner had fewer, far fewer students than either of the other two. Bates had many, many students who are all over the world in responsible positions.
Keith:Who would you consider to be Bates' main students?
Wohlfarth:Professor Crangle was at Sheffield.
Keith:That's with Sucksmith, Hoselitz, we've mentioned before.
Wohlfarth:Yes, Hoselitz, a very remarkable man. He's still doing research now —.
Keith:Yes, I'm going to see him in two weeks time.
Wohlfarth:You'll have a marvelous time. The Viennese charm. Let's get this straight — that's a lot you are asking, thirty years ago — Crangle was the student of Sucksmith, Hoselitz was the student of Sucksmith and Lee was the student of Bates, who afterwards went to Sheffield — didn't he? Yes, and is now at Southampton.
Keith:Let's go back to you own work. In the fifties you went back to the fine particle work. The problem you began to look at was the interaction between the particles — which we haven't covered before.
Wohlfarth:A similar development occurred as in the collective electron treatment. I felt that correlation effects had to come into both. It came in, quantum mechanically into the collective electron problem. Then I had to look into the interaction problem with fine particles. It was a paper I had in the Proc. Roy. Soc., 1955, "Effect of Particle Interactions on Coercive Force".
Keith:Did you have any students working with you on that?
Wohlfarth:Not on that. I've never felt it would be fair. I had David Tonge — Tonge and Wohlfarth — yes, otherwise I had no students, only Tonge.
Keith:Why didn't you think it was fair?
Wohlfarth:Because the mainstream of work in this department is quantum mechanical and it wouldn't be fair to have people working on something like this. It now appears from what David Edwards has said that Tonge must have been a bit unhappy and isolated. In fact he never finished his Ph.D. Nevertheless our two papers, in 1957 and 1958 are still being quoted as useful — for applications which is a considerable achievement after all these years.
Keith:Do you think the main benefit of these papers was in applications?
Wohlfarth:Yes, applications to real materials. It was mathematical but with a point of view to real materials.
Keith:It has reminded me of a point that Stoner made I think in 1944 in the Kelvin Lecture. When he was talking about magnetism, practical magnetism, and how it had been very much a craft trade, and he felt the time had come when theoreticians were moving in to enlighten the subject and it would have to be taken up by practical workers.
Wohlfarth:That's what Stoner wanted, yes.
Keith:And it's what you were very much contributing to with this kind of work. Who did you keep in contact with from Leeds?
Wohlfarth:Philip Rhodes, we had personal sympathies. He was Jewish, that must have been part of it. There weren't so many people there.
Keith:Did you stay very much in contact with Stoner after you left?
Wohlfarth:I went to see him every year when we went up to see my parents and I went to see him. He was keen on what I was doing because he could see that I was supplying the quantum mechanics which he had not supplied. So, for example, the paper on "The influence of exchange and correlation forces on the specific heat of metals" of 1950 was something he was keen on especially because this seemed to him to be going beyond what he had supplied. It was written very soon after I had got here. This was one of the papers he was keen on and was pleased I'd be publishing because it was definitely beyond what he was supplying.
Keith:Was he disappointed when you dropped it for a short period?
Wohlfarth:Dropped — the model? You know he was keen on what I was doing, whatever it was.
Keith:Were you both confident it would be taken up again?
Wohlfarth:I was hoping so and it started about 1960 with the fermiology. It was found that the Fermi-surface really exists in these things and you can't get away with the Heisenberg model, and discuss that as well. Heisenberg comes into it to some extent but that discovery was made only very recently.
Keith:What about parallel developments in what is generally called itinerant ferromagnetism, work in the United States?
Wohlfarth:There wasn't any. 1960 was the key date when it all began. The only work which is really seminal is the work of Herring and Kittel on spin waves in the itinerant model.
Keith:And that is early 1950s.
Wohlfarth:Early 1950s and you know, you've seen what Herring had to put up with from referees. So hostility against this model existed not just to me but to a great man like Herring who also contributed.
Keith:So maybe you would like to take up the story from about 1960?
Wohlfarth:That's when the subject exploded you see. Nineteen sixty is exactly the date when it started up again. — What happened from about 1960 onwards to raise the model to its present state of excellence? — independent evidence began from the Fermi surface studies — that's point (1). Point(2) — energy band calculations improved immeasurably and the results showed the assumption of parabolic bands was never justified. But that was alright because David Edwards and I were already thinking about how to put this straight.
Keith:Edwards was one of your students.
Wohlfarth:Yes, the boy who just came in. Boy — he's nearly fifty. Point 3. — the localized model lost most of its appeal when applied to metallic ferromagnets. For nickel-iron alloys neutron studies of the ranges of relevant Heisenberg exchange integrals showed these ranges to be extremely large making nonsense of nearest neighbor Heisenberg models for these metals. The 4th point was that work based on Herring and Kittel and by other people including David Edwards, my second student, made it completely clear that spin-wave excitations and single particle Stoner excitations can co-exist. So it is possible to talk about both excitations being important for metals like nickel. The question is how important are they at different temperatures, that's an unsolved problem. And the fifth point was another misconception about the Stoner model. It was felt that each atom had to have the same magnetic moment, otherwise the model couldn't be applied, otherwise the magnetization had to be completely uniform. That's not the case, the coherent potential approximation for alloys permits as a natural consequence a different magnetic moment considering different atoms and the model is still applicable. And something I've worked on for many years is the so-called Landau-Ginzberg model which is again a treatment of spatially variable magnetic atoms. So the model could be taken into a situation where the magnetization is not constant and the model still applies. The Stoner model is thus in the 1980s on a completely different plane that it was before its renaissance in 1960.
Keith:If you take that period from 1960, presumably there were people that were still reluctant to accept the benefits of the model which were obviously becoming more and more apparent.
Wohlfarth:No, it wasn't quite like that. What happened was the overwhelming evidence in the 1960s was in favor of this model, and round about the end of the 1960s it was fully accepted from many examples. In the 1970s the controversy has begun again, and now, as I describe in some of these papers: "How important are other spin fluctuations? How important are many body effects not included in the model? How important are interactions between elementary excitations like electrons and spinwaves?" So one has to go beyond the Stoner model and the controversy now in the 1980s is: how wrong is it, what connections have to be made to it? That is now the argument in the 1980s. So it was fully accepted, but maybe the resolution went too far and now one has to backtrack slightly to see what errors are still being made in this model. So it is an interesting history the way it has gone up and down.
Keith:In that review paper that Herring wrote in 1964 — he compares the two models together and his emphasis is that they both very much changed and moved towards each other — how much is that true?
Wohlfarth:I think it’s true if you allow for correlation effects on the one hand and maybe allowing the hypothetical exchange integrals to be slightly formal parameters on the other but this movement hasn't gone all that far — there is still a controversy — the controversy is now about the importance of spin waves. There is a Japanese school under Professor Moriya who claims enormous merits for his scheme which he feels is useful to interpolate between the two extremes which is something which has been wanted. So I think the movement of Herring hasn't been all that successful and the matter is still very controversial now even in 1981.
Keith:Didn't Herring produce a school of people working on these problems?
Wohlfarth:No, Herring never did. He worked with Kittel but they were not a school—they're equivalent people. Herring was at Bell Labs. for many years. He never had a real school, not on this subject, no. When I met him several times there was an immediate rapport between us, a very great scientist.
Keith:And what about Slater?
Wohlfarth:Yes, Slater was a great pioneer in the thirties of the Stoner model. He was before Stoner in the 1930s. Stoner developed it in a much more systematic way so it's rightly called the Stoner model. Slater — his contribution cannot be overestimated — it's very important. Slater was a very difficult person — he wanted everything to be worked out numerically, he wanted numerical results for everything and he had problems with — Van Vleck. Slater had schools but not on the itinerant model, more on band calculations. That's why he like my work with Fletcher so much. Because that was pioneering work in his subject. Whereas I regard him as a great man partly because of his 1936 work on nickel, you see.
Keith:So he didn't make any important contributions towards the model after the 1930s.
Wohlfarth:No, he had a paper at the Boston Conference of 1967. He was extremely outspoken on one of these controversies which I mentioned to you earlier.
Keith:Did these ideas seep through to the Soviet Union and Japan?
Wohlfarth:In Japan there was some work of some importance in the late 1940s by Watanabe and other people, of which I was fully aware and we had correspondence. But it wasn't as sophisticated as what we were doing. The Stoner model itself has been pushed enormously in Japan by Shimizu. Some of us feel he's pushed it too far. He is the great advocate of this model in Japan. The controversies also come from Japan from Professor Moriya as I mentioned earlier. Many Japanese have applied the model to magnetovolume effects which I have been working on since the late sixties. Some of the papers I mention in my list of publications. The Japanese who are leading in magnetism — there's no way out that's how it is — have accepted this model and, in a positive way and also in a negative way because I feel the controversy raised by Moriya is going too far in the other direction.
Keith:What about work in the Soviet Union?
Wohlfarth:The Soviet Union. Kondotsky has been keen on it -– Vonsovsky — these are the grand old men. Vonsovsky was not keen on it until the 1960s although he should have been as he had a pioneering paper in the early 1930s. Shubin and Vonsovsky, Dzyaloshinsky had also worked on the itinerant model to some extent and some experimental groups are now working on it using my formalism for magnetovolume effects to a very large extent. There's one group near Moscow, there's one group in Svedlovsk for example.
Keith:We've seen how the work you did on small particles and hysteresis had a very close relationship to technological change. What are the impacts that developments of theories of ferromagnetism have had in general.
Wohlfarth:The domain, fine particle aspect, bubble domains, and so on, that's one thing. Now you're asking "do the electron and quantum mechanical, and statistical mechanical aspects, have implications in industry." The "invar" problem which involves magnetovolume effects should have but it hasn't gone too far. We're very sad about that. We understand the "invar" problem to a very large extent, it's become essential to the entire controversy of the 1980s, but it hasn't had much impact.
Keith:Sorry, what is the "invar" problem?
Wohlfarth:That would take too long — it's a magnetovolume effect — interaction between volume effect and magnetism—and there are many such alloys as a result of these interactions; there are anomalies in pressure dependence, magnetostriction, thermal expansion which occur. "Invar" means invariance, so it’s got anomalies in thermal expansion. So that's where it should have happened. I'm particularly keen to use my work on spatially variable magnetization in helping to characterize real materials, but that is not yet the case, that is one of my dreams — that any work on variable magnetism will help in metallurgy.
Keith:What are the problems? Is it just that it's such a complex problem to describe real materials?
Wohlfarth:On the one hand that's right. On the other hand real materials like the one's of interest to us like nickel/platinum alloys or zirconium zinc too are rather esoteric and not immediately useful in practice.
Keith:I suppose it’s not simply a case that a theoretical approach must be able to explain real metals but that it has a real impact when it makes specific predictions.
Wohlfarth:Now in the area of amorphous magnetism there is a chance that this will go a little bit further than it has done in the past. I can now understand a lot of amorphous magnetism from the point of view of the model but again what you want to know for amorphous magnets for applications are things like their strain sensitivity and what happens when you anneal it there's still an enormous gap between that and the quantum mechanical models.
Keith:That this particular work within the area of the theory of ferromagnetism hasn't had such an immediate impact must relate to the number of people working on it—there must be very few.
Wohlfarth:That's right. I think in semiconductors where the applications are more immediate there are more people working but there are still sufficient people working in magnetism, in metallic magnetism, to fill lecture rooms all over the world and at conferences, seminars and so on. It's not insignificant but it is pure research and pure research can still be carried out. About the importance of spin waves, etc., there is an enormous gap between that and real applications.
Keith:You mentioned earlier that Japan has a lead in magnetism now—since when has that been the case? Obviously Japan has a long tradition in magnetism.
Wohlfarth:It goes back to Ewing in the nineteenth century.
Keith:Ewing went to Japan didn't he?
Wohlfarth:Ewing worked in Japan. The history's interesting. There was Ewing, then Nagaoka and Honda followed him. Honda has his pupils who go right through to the present day.
Keith:When really then is the time when this Japanese ascendancy in magnetism occurred. As we've said it goes right back, the Japanese tradition, but you say now there is a real lead in Japan.
Wohlfarth:I think so. The work of Honda spanned many decades and he discovered an enormous number of new materials, for example permanent magnets. Alnico magnets, that sort of thing. So he was keen on materials. Theoretical work did not come, of course, from Honda, but somehow developed. I've never really thought of the real reason for this. That was also very strong from the 1930s onwards. They're keen on real materials, and are not ashamed of dirtying their hands with real materials.
Keith:But isn't that the case about the United States, there's a lot of work on materials there?
Keith:It must be very much related to the industrial concentration in various areas of electronics?
Wohlfarth:I'm not able to analyze the difference in the development of magnetism in American and Japan, but it is different. There's somehow a more concentrated thing in Japan, there are so many centres where it is done whereas in America there are not so many. They are the best in the world clearly at Bell Labs and G.E. but those are localized whereas in Japan it is more widespread.
Keith:So you'd accept that in Japan it's accepted more as a professional discipline.
Wohlfarth:That's how it must be, yes.
Keith:Because if you take the people we have been talking about, like Kittel and Slater, they're not just thought of in terms of magnetism. What you seem to be suggesting is that in Japan it is much more of a profession itself.
Wohlfarth:That's right, yes. That's how it must be. I hadn't thought of it like that, but that seems very likely as a first approximation to the problem of why the Japanese are so good. Don't get me wrong the Americans have an enormous output in magnetism, but it's very localized. So it's the feeling that it's localized in America and itinerant in Japan (laughs).
Keith:One country we've hardly mentioned at all is France.
Wohlfarth:It's like this. Modern magnetism was born in Strasbourg in the early years of the century and its tradition has been extremely strong from Pierre Weiss, who did all these accurate measurements, Weiss and Forrer, and so on. The breakaway of Neel made Grenoble a major centre which has been going for many years and is still outstanding especially as they now have access to the reactor. Since the 1950s and 1960s this has spread right through France mainly through the influence of some very great men like Friedel and de Gennes. Friedel founded some really new schools and his people are working in several centres including Strasbourg, Orsay, where Friedel himself is, and so on. He used the French genius, and the French background to some extent to build this up. How far that is, I do not know, that is up to him to say. So magnetism is now extremely strong and you see this from conferences where often the French delegation is one of the biggest if not the biggest.
Keith:One person we haven't mentioned in regard to magnetism in this country is the work that Kapitza did in the 1930s. How important is that in your mind?
Wohlfarth:Ah, Kapitza? Built the big magnet in Cambridge and the direct line there is to Shoenberg and the de Haas-Van Alphen effect and Fermiology, so indirectly that has helped enormously because the de Haas-Van Alphen effect is one of the things which set us up in the early 1960s. Kapitza, himself — you know the history — left. But I think the big magnet which he had in Cambridge has done a lot of good for our subject, yes.
Keith:What about the status of magnetism as a subject?
Wohlfarth:We've always had to fight for an image through comparing ourselves with semiconductors. We're talking about materials now, magnetic materials, and semiconductors have always had the edge because of their broader applicability. What we desperately need to improve our image is some outstanding application and we're hoping that amorphous magnetics will provide this, but it's no guarantee. The G.E. Lab is very much working on this, and I've been working there. They're very keen and are going to produce a transformer at a conference in Sendai, Japan very shortly in August or so. We hope this will be a breakthrough in magnetism as a subject where real industrial applications can be made. We've had them — tape recorders, recording tapes is an enormous business. But somehow it hasn't got the same glamorous appeal as semiconductors.
Keith:The applications of magnetism are very diffuse and often as components when it's not so immediately apparent that they have this crucial role. And also if you consider that the thing about the transistor is that it occurred very suddenly whereas magnetism has got a much greater historical tradition which in one sense makes it look less modern. It is an incredibly complicated subject — so it is taught in schools at a very simple level and that must reflect on the overall image of an area.
Wohlfarth:That's all part of it, yes we need a breakthrough like the transistor and we haven't had one: bubble domains, right; and amorphous magnetism, we hope; recording tapes, as you said, goes back right to the war and there has been nothing traumatic or dramatic like the transistor. We are always following behind semiconductors. I'm fighting this in articles.
Keith:Presumably that affects the quality of students you get?
Wohlfarth:No. I think the quality of students is quite good in magnetism. I can't compare the quality of students in magnetism and in semiconductors.
Keith:But the status of the subject must have a role in the abilities of students you get?
Wohlfarth:I can't say. I can't compare it. Sorry.
Keith:Is there anything that you would like to bring out that I haven't mentioned and should have done?
Wohlfarth:I'm obviously an enthusiast but I'm a realist too. I think the subject is a very great subject. And why is it great? It's because it's at the centre of so many other subjects, much more than say semiconductor physics. It's extremely important in the whole realm of the physics of the solid state. I mean we haven't mentioned things like rock magnetism yet or lunar rocks, etc. So it's very broad and is the centre of all these things.
Keith:There is one point I wanted to mention that's come to mind, that I had to think about earlier. The thing that it seems to me about the collective electron theory, that had a real attraction in terms of my understanding of where it fits in, is that it's through the collective electron treatment that you begin to see magnetism as a solid part of solid state physics because then you begin to see the relationships between different properties, transport properties, and things like this. Does that mean that in solid state physics the real centre of modern solid state physics is electron theory of metals and the application of quantum mechanics?
Wohlfarth:For the electronic aspects, yes. For the electronic aspects, yes. But there are other things like dislocations and strength of materials and so on.
Keith:But that's a strange thing because the other area I've looked at is dislocations, dislocations doesn't depend on quantum mechanics.
Wohlfarth:No but it should do because you want to know how the forces go. But I don't know how far this has got, probably not very far. 
Keith:And, yes, dislocations is obviously part of, well, it's seen as part of solid state physics. But if you take things like electron structure, band models, you can see it almost in the Kuhnian sense of the paradigm of solid state physics. But even dislocations doesn't fit in there and it's almost as if it's accepted as part of this area called solid state physics, that it's got it's own linear development.
Wohlfarth:That's right. And within the electronic aspects the energy band concept which is basic to the itinerant electron model is of course central, and the effective interactions and all the things we have talked about.
Keith:So essentially, as I have said, it seems to me that in the collective electron model you are almost attempting to fit magnetism into the mainstream of solid state.
Wohlfarth:Yes, that's right, that's what we are trying to do there, yes. I haven't talked about what we do here now but this is part of the story.
Keith:OK. Well, thanks for talking to me.
That's alright, a pleasure.
R. Becker et al., Probleme der technischen Magnetisierungskurve (Berlin: Springer, 1938); R. Becker and W. Doring, Ferromagnetismus (Berlin: Springer, 1939).
This must have been the demagnetizing factors of ellipsoids, published in Phil. Mag., 36 (1945) 803, after the war.
In English; Phys. Zeits. Sov. Union, 1935, rest of note unclear as was spelling of above.
B.A. Lilley, Phil. Mag. 41, 792 (1950).
In 1983 it has!