Alan Portis

Portis:

Let me say little something about Berkeley. Berkeley had up to, say, 1950 been a department in which nuclear physics and spectroscopy would be done and that was it. And that was probably characteristic to most of the major departments. It was clear that the University of California, the state was developing, and this University, this campus particularly would be developing. The university gave the department something like six positions to fill and various things were done. Francis Jenkins, who was an experimental spectroscopist made the tour of the country looking for bright, young people, and brought Walter Knight to Berkeley, John Reynolds(?).Walter Knight had been working at Brookhaven; John Reynolds was a graduate student at Chicago. Carson Jeffreys who was a graduate student of Bloch at Stanford. Arthur Kip who had been here as a student of Leonard Loeb's and was at M.I.T. as an assistant professor was offered a position to come back. Erwin Hahn had caught Ed MacMillan's attention and came back. I think that Kittel may also have had some connection with MacMillan (he was at Bell Labs). He had done some very fine work on magnetic domains walls, the study of domain wall motion and magnetic processes, and he came to Berkeley. I started graduate work in the fall of '49 and began research in the fall of '51, summer '51. Now, probably this fall of '50 or spring of '51 Kittel was here in winter and gave a course in thermodynamics. I sat in on this course and really was very taken by him and liked very much his physical approach. It was a period when there was a lot of upheaval here, because of the loyalty oath. People were leaving. I talked to him about — I was interested in doing theoretical physics - and talked to him about that and about the prospects of Berkeley. He was himself thinking about coming here and taking a regular position. He kind of encouraged me to stay on and to do experimental work, and so, I made an arrangement with him that I would, during the following summer, I guess summer '51, begin to set up an experimental laboratory. Another graduate student, Tom Griswald, and then Kittel came in the summer and Kip came in the summer. We had already sort of had something of a start before Kip came. Kittel had had some connection, close connection with the group at Bell Telephone Laboratories that was doing ferromagnetic resonance. So, he was certainly familiar with the resonance technique and he in fact had interpreted the resonance behavior of ferro magnets and showed… What he said to us, said to me particularly was that he thought that Blumbergen, who was then a student of Purcell's and had done his thesis on nuclear resonance but was switching to the ESR… good sense of what was a promising field and how to do it and we should try to model what we did after Blumbergen. Kittel was someone who wasn't that involved with the experimental technique but he was very conscientious in the direction of experiments and experimental results and their interpretation. Arthur Kip had been doing ESR at M.I.T., so when Kip came already he brought with him some experience and a lot of equipment. (Tinkham…) So we set about putting together a laboratory — Kip, and Tom Griswald and I. We built most of our equipment, and Kittel almost instantaneously acquired a theoretical group because there were a fair number of graduate students at the department who wanted to do theoretical physics. Wick had left to go to Carnegie Tech; Serber left to go to Columbia, so there was a group of graduate students who were looking… (The circumstances of their decision to leave) Kittel said that he never worked harder. I mean, he really had to find problems for all these people. He suddenly found himself with a very promising group of young people. Kittel came and became the senior theoretician of the department and all these students… to him and he had something like six theoretical thesis going. The experimental activity was to some extent separate. I mean, there was Arthur Kip's program, Kip and Kittel were thought closely associated during that period and Kittel would come by and sort of follow what we were doing and of course, once we had the spectrometer going then he became quite actively interested in what we put into it. And then we saw him very rarely (?). He wanted to follow the results on day to day basis. Everything that we looked up — yes, I think without exception - was because of the ideas we had. He certainly had connections with Bell laboratory people; he watched very closely the kind of things that were going on there and at other places, but I think more than anything he followed literature. He looked at every journal that came in. He scanned and he scanned for ideas. He looked at what experimental people were doing, he looked at the analysis, and if he decided… what was promising and what wasn't; what kind of interpretation would hold water and what wouldn't… (Seitz's book more or less set boundaries of what was considered the solid state physics) Kittel began pretty soon to work on his own undergraduate text in solid state physics. He taught an undergraduate course here and a lot of graduate students were ordered (?) in that course, and a half of the department was probably ordered (?). So, that was the subject.

Szymborski:

Who, in fact, brought Kittel here? Who was the head of the department?

Portis:

Well, the head of the department was Raymond Birge. Now, I don't think it would be good to know that — (after a while of cross-talk) Oh, I know what connection there might have been. He was at the theoretical summer school at Michigan, maybe a year earlier. Nirenberg (?) was also at that summer school. Nierenberg was already on the faculty and I think… Nierenberg had been a student, I guess, of Rabi's and I think MacMillan had certainly had close connection to the Columbia group and I think, Nierenberg may have put the Department onto (?) Kittel. MacMillan was strongly interested in seeing the department develop and strongly felt that just to have nuclear physics and spectroscopy wasn't enough and we had to get into other areas. I mean, I was just an advanced undergraduate student, and really didn't know all that but I think (I learned it from comments later?). So, it may have been Nierenberg having met Kittel in the summer, being impressed and then MacMillan's interest… And, of course, Birge followed all this up, he was very well organized, very directed and certainly did everything that needs to be done to get the University to support this kind of development.

Szymborski:

What about contacts with Seitz?

Portis:

Seitz had been here, he visited, and I think when we started the first support was through the Office of Naval Research; I think Seitz was an adviser to ONR and visited us a number of times. That seemed almost official tours of the laboratory in the groups. So, I think, he was kind of coming in a kind of advisory capacity. He was certainly seen as a senior figure in the field and, I think, we really wanted him to think well of what we were doing and we certainly valued his advice and I am sure the fact that that much attention has been given as it was to color centers in this country was a consequence of Seitz's interests. We happened to get involved in the color centers really because of Clyde Hutchison’s work in Chicago. I know what happened — Hutchison published something in Phys. Rev. Letters (reporting) the observation of the electron spin resonance in color centers. He said that the line was... he attributed the line width to dipole-dipole interaction. Kittel just didn't believe it, he didn't believe that the dipole interaction can be that broad and he thought we got to get into it. (We will return to it later)

Szymborski:

What was the interaction between Kittel and his students?

Portis:

I think they were close. I think these were collaborator kinds (relations). He had started out with a weekly seminar for both experimental and theoretical students; all together, just one seminar. He ran it as a kind of a journal club. What he would do — he would find things that he thought that he'd like to have someone work on and present. We would get two or three weeks of advance notice and we would work on it. So, I can remember the first one I got — I was really putting together equipment and didn't know the field, and was very nervous about it. It was something out of the Oxford Group — that group had been doing really a great deal in magnetic resonance well before we got into it. And I think it would have been the simplest thing in the world to simply follow the direction of that group and to work on the ESR in transition metals ions. It was Bleaney's (?) group. That was really the major program, I think anywhere in the world. A lot of groups just followed what Bleaney was doing. Kittel didn't at all. He did entirely different things. I will come back to this later. Well, he worked very closely with the students. He had an office up on the third floor of LeConte (?), next door to him was a large room where his theoretical students worked, and he would be going in to see them and to talk to them about how they were doing, he would be in in the morning and put notes around for them on the desks about things that he thought about. He was thinking all the time about the problems that they were working on, and would send them notes, and he expected to follow what they were doing almost on daily basis. He would suggest leads to them. So, this was very close, very supportive, collaborative kind of activity, and he just moved right into it. He didn't expect anything from anyone else that he wouldn't do himself, but he certainly expected — he worked all the time, in his office where he was at that time almost all the time. He might come in at eight in the morning, went home for dinner at six or something and then came back to work in the evening to work on his book. I know because sometimes I would be here in the evening in the laboratory and if something would happen that I thought he'd be interested in I knew he was there and I'd go up and tell him. He didn't mind the interruption. But, that was his book that he would work on in the evening, I think for a year and a half or two years he was in every evening to do it. With his group, I think, they had some outing together. This was the period when he and (???) had a moderate amount of entertaining for visitors and they would invite members of the group to their home. So, this was a close kind of interaction. He wanted to develop a group, an important theoretical group and he understood very well that the personal element was important and we wanted to foster that as well. I think, his students, theoretical students particularly, were really very close to him. Experimental group was more removed from him. Of the experimentalist I was closest to him. Partly because I had this interaction with him early, partly because I really was interested in theoretical physics and even though I decided not to be a theorist I really wanted to do some analyses of experimental work and Kittel certainly encourage that and supported me. (Now we go back and discuss the beginnings of Portis' interest in physics) Physics teacher was instrumental in developing his interest. No family traditions in academic type of occupation. Museum of Science and Industry. Never interested in military implications of modern technology. Wanted to become a high school physics teacher. Study at Chicago. Influence of Robert Hutchinson on the way of teaching at the University of Chicago (Quite a long story). Bachelor of Philosophy degree. Did not meet Clyde Hutchison until later when he came to visit Berkeley.

Szymborski:

First experiments on ESR of color centers.

Portis:

I think it was simply a matter of getting really high concentrations of color centers. We just made a little container with a crystal in it, which we got from Harshaw and some alkali metal and just cooked it for a very long time. We had a copy of Slichter's thesis and looked at it, but it was kind of sophisticated for us. Kittel really wanted to do something different. I mean, he wasn't interested in studying sophisticated relaxation problems, and wasn't interested in local field things as the Oxford school was doing. But he really wanted to see whether we can look at new materials. Find a resonance in materials in which it hadn't been done before. He had things in mind, and it was really remarkable things that occurred to him and the things that he had us do. It was almost weekly that he would say "look at this" or “that."

Szymborski:

Was the development of ESR techniques the outcome of the war-time improvement of the microwave techniques?

Portis:

Absolutely, I think absolutely. Purcell was very actively involved in the microwave development (at the Rad Lab) and I am sure that that easy transition from nuclear resonance to microwave resonance was possible because of this experience. I don't know if that was the case but I would guess that Bleaney would have some association with war-time radar work as well. I suppose those were two first groups. There is, I guess, one credited work in the Soviet Union first in terms of observing the ESR. But I don't know if that was really followed up. There was this work at Bell on resonance in ferrites that Jaeger and Gold and Kittel were involved with. That was microwave work, but the color centers work was just one of the numbers of things that were going on here and I got involved in the resonance aspects of it, in the saturation behavior and all that, and that was fun to do. But what I was doing was really phenomenological — it was a kind of an interesting story, I was fussing around doing an awful lot of things that you know, could be thrown away later, but I became convinced that the only way that once the saturation behavior was for the line-width to be associated with ab inhomogeneity, and it couldn't simply be dipole broadening of Hutchison. Kittel, independently of this have had the idea that the line-width could have arisen from the hyperfine interaction. He did some theoretical estimates of that, the numbers looked very promising — there was a weekly journal club in the evening for the faculty, and occasionally some of the graduate students would go as well, and Kittel gave a report of this to this journal club, and someone, I’d think Ed MacMillan said "Well, if you're right you ought to be able to do some isotopic separation and see different line-width.” This is not something that had occurred to us, because those were people that knew about Spedding (?) and the group at Ames and all this business with isotopic substitution. So, we arranged to get another isotope of Potassium and, I guess, they were willing to provide it for us as potassium chloride and we put F-centers to it…

Szymborski:

That was the famous Kip-Kittel-Levy-Portis paper?

Portis:

There was an interesting thing you know, that came out of the idea of the isotopic substitution. It really came out of the faculty meeting with a group of nuclear physicists who suggested this. You know, with all Kittel's following things that would’ve never occurred to him, I think.

Szymborski:

What kind of collaboration was there between the four authors of the paper?

Portis:

Kittel had the idea, Kip really managed… This was sort of... I think, what we did we just worked on things that occurred to Kittel and if they developed, fine, if not we did something else. And when it was time to write a thesis we kind of put together the things that we had done, that developed and so, along the way, color centers was something that we did. I got little more involved in it that I might have because of this theoretical aspect. Levy was just getting started and this was one of the first things that he did. Kittel was feeling that the authorship… I mean, if somebody was involved in a substantial way he should get some recognition for it, and so, this was not something to which Bob Levy made a major contribution —

Szymborski:

You acknowledged in your paper "fruitful discussions" with Alvarez, Segre, Esterman, Knight, and Seitz...

Portis:

This, you know, I bet these were all discussions that Kittel had, and I think that Kittel is just very generous about acknowledgements, and if he talked to someone about something and this person made a couple of remarks that turned out to be useful even if only to lead Kittel towards something else, he would acknowledge it. I think that may have been Segre who suggested the isotopic thing but if he did it was just in this journal club. I could've been Alvarez.

Szymborski:

What about Estermann?

Portis:

He might have been with LNR at this period. He could as well been with the Office of Naval Research. He did spend a period at ONR, and it may have been that the connection was through that. Kittel certainly knew about the work in color centers, knew about Seitz's interests — if it was something that Seitz was interested in we would have to pay attention to it — he saw the Hutchison paper and thought it and said it cannot be the dipole broadening, and so we were just off and running. I don't think it took an awful lot more than that.

Szymborski:

Can you tell me little more about the saturation?

Portis:

…What normally happens when resonance is saturated is that when you increase the power you get smaller signal. I don't think I was looking for anything but I just was looking at signal as a function of power level and what I found was that the signal was independent of power level. So, it was intermediate. Was it a saturated case or wasn't it a traditional saturated case? What I found was that at very large power level there was this signal, quite strong, the absorption was a constant in the level. But if I wasn’t careful I would get a dispersive signal, and it was quite large. Then I decided, I better measure carefully and what I found was the absorption part was constant with power and the dispersive part increased with power as if there were no saturation at all. The lines did not broaden in width, so this was quite unusual, quite different from anything that anyone had reported, and I just sort of fooled around with that for a couple of month and finally came up with the realization that if one had a resonance that was broadened by something external to the resonant system, that is not by interaction between spins, but by, say, magnetic field of inhomogeneity, this was what someone should expect… Blumbergen... Noble later did that… Kittel then did all the theoretical work on the line-width and shape and all that.

Szymborski:

That was one of the cases when theory really helped in experimental work...

Portis:

I don't think anybody in solid state physics would argue about that. I think the fact that there was a theoretical program and an experimental program and there was a lot of interaction between them that meant a great deal. Beyond that, the fact that Kittel, as you know, was interested in color centers and ferromagnetism and semiconductors alkali metals and saw these as materials on which experiments could be done, but also a theory could be done. He would have Yaco (?) Yaffet looking at relaxation processes of electron spins in alkali metals, well George Feher was really doing a very broad survey of electron spin resonance in (???) metals…

Szymborski:

Was he here?

Portis:

Yes. He was, I think, just a year behind me. He had been an undergraduate student of Electrical Engineering and then came into physics department and started to do research about a year later than me. There was again some Russian work on spin resonance in metals that had caught Kittel's attention and Kittel wanted George to simply survey, to repeat all of that and see what he can find. George did — his field was electrical engineering and he built well designed, high sensitivity system, though it took longer than Kittel would have liked. I guess the alkali metals really produced results. (digression on Slichter and conduction electrons resonance) Do you want to have the Dyson connection? You should read it. Dyson came for summer to work with Kittel. I was a graduate student when he came out, I think maybe two summers anyway; the first summer KR he worked on spin waves and the temperature dependence of the magnetization. And then the second summer — I guess I was leaving or had left — he worked on the line shape of (???) that George Feher had found in the alkali metals and showed that this arose from diffusion of electron in and out of the skin-depth. It was a remarkable thing. Dyson is a phenomenal applied mathematician with no critical sense of what important solid state physics problems were, and so Kittel basically (fed this to him?) He said, here is something that is curious and that no one else was able to solve. Kittel had the sense that Dyson could do it, and here were these two instances where Dyson would go, do the problem, he would come back give us a talk, and we could barely understand what he was saying. His language wasn't ours at all. But it was tremendously productive, and spin waves were one problem, line-shape another. I’m pretty sure that Slichter interest developed after that.

Szymborski:

In 1955 or so you left for some time to work in Pittsburgh…

Portis:

That's right. I think that David Halliday was building up that department at Pittsburgh and wanted to have the solid state program. He had been in touch with Kittel because he knew this was the place that was producing… David Halliday had begun to do ESR. His background had been in the nuclear physics, he’d done a textbook in nuclear physics, and then he began to do some work in ESR; not very much, but a little. He became a chairman of the department and wanted there to be a group... Fred Kaffer (?) went there the year before I did as a theorist and around that time although I wasn't committed, I wasn't committed that early, they were certainly interested in attracting an experimentalist from Berkeley to join Kaffer (?). Although I made a tour of the country and considered some other possibilities the attraction of the Pittsburgh thing was that I kind of emerged full-grown, that that this would be a regular faculty position. They wanted to build that department and had assurance of support; there were students there who wanted to work…

Szymborski:

Who else was there?

Portis:

At Pittsburgh? In solid state physics we were, Fred Kaffer and I and Christopher Dean who had been a graduate student at Harvard…

Szymborski:

Carnegie Tech was also there.

Portis:

Oh, yes. Sam Friedburg was doing low temperature physics and studies of materials, Jack Aldlin (?) was there and had a magnetic group. Smoluchowski was there too, but his work was more toward metallurgy and physical properties of materials, although we went to their seminars and knew him there wasn't really a lot of interaction. There was some with Samuel Goldman, moderate amount with Sam Friedburg. Fred Kaffer and I both had the association with the Westinghouse and this was through Clarence Zener who had left Chicago to head the research laboratory and had connections with Kittel. And so that was again through Kittel. Zener arranged for Kaffer and me to spend some time at Westinghouse as consultants, to just kind of talk to people there. (After a break, a short talk about military applications of physics) I'll tell little about cyclotron resonance because I think it is interesting.

Szymborski:

It will be fine, but first I want to ask you some more questions about Pittsburgh. You did some work on alkali halides there.

Portis:

I don't remember an awful lot about it; he already (who?) had been admitted to Pittsburgh as a Master's student. I had come to set up really an experimental group in solid state physics and we got a grant and the department bought a good bit of microwave equipment for me. I mean, we did some things, irradiated alkali halides, saw some resonances, and I don't think we published a paper but we submitted an abstract. It wasn't anything terribly compelling for me. I found myself there teaching courses, involved with the Westinghouse thing, getting an experimental program together, but looking back on it it may've been — this is just personal — a little bit more responsibility for me that I should've taken. I thought, you know, that maybe I would've done better to go into a group that was just doing research and interacting with other researchers, or maybe a post-doctoral kind of thing. So, I don't feel that an awful lot was accomplished. I interacted with Kaffer, I did other things… I never thought of myself as a color center person. I never really knew that much about it. My feeling about it was that the color center thing was not what I was terribly interested in. I was more interested in the relaxation work and processes and kinds of things that I've done since then... I never really went back to color centers. Other people did, Feher did.

Szymborski:

You published something on the Faraday rotation in 1960…

Portis:

Yes. It wasn't very important. I was thinking about the Faraday rotation in Pittsburgh and did that in a number of things when we got back to Berkeley.

Szymborski:

What about this rapid passage work?

Portis:

That was a new development. It grew largely, I think, out of work that George Feher had done at Bell Labs. That was in other area, the rapid passage and spin diffusion — that led to some nice developments. This again goes back to this inhomogeneous broadening, a special kind of situation in color centers in alkali halides. What I had studied here was the saturation behavior. George Feher was looking at electron spin resonance in silicon and at donor levels. He found some very peculiar kinds of transient effects that had not been observed before. It occurred to me that that resonance might also be in homogenously broadened (part omitted) This was then of some use to Feher in analyzing his own results. Also Meyer Weger (?) who during the same period, I guess, spent some time at Bell Labs, did some related work. I never published it because I thought… I wrote a report.

Szymborski:

What was going on at Berkeley at the time you were at Pittsburgh?

Portis:

Well, Kip's group was doing the cyclotron resonance. The cyclotron resonance started just in the last weeks that I was here. That program went on for next year or two. I was away for three years. Bob Levy went on to the alkali metals in liquid ammonia solutions; Art Kip took on a couple additional students. Something that I had been interested in: manganese and copper, both nuclear resonance and electron resonance was pursued. John Ellen (?) came over from England and did some of that. Walter Knight collaborated with Kip and, I guess, with Kittel on the copper resonance, copper nuclear resonance in those alloys. The group tended really to go more to metals. The feeling, I think, well, Kittel's feeling, Art's, I guess, mine is that the insulators were — well, we did this thing in the color centers — there were plenty of other people working on insulators and characterizing various kinds of paramagnetic sites. We were more interested in relaxation and transport.

Szymborski:

Who were the other people you said were working on these problems?

Portis:

I really didn't know much. I knew what Gordon Noble was doing, I certainly knew about Kanzig’s work and knew about Jordan Markham. I knew about all this, but I'd never been interested in the optical stuff. I found metals more interesting and later magnetic materials. I guess it was the same with Kittel. You know, my taste was formed by that association. I was just much more interested in the processes, in dynamic kind of situation and not so much interested in the structure.

Szymborski:

Now, what about this story of the cyclotron resonance?

Portis:

Oh, I think that's an interesting story. One of Kittel's graduate students (well, I think it happened this way), Elihu Abrahams, was working on the motion of the electrons in bands and what he realized was that if the carrier moves through the band and under the action of an electric field, without any scattering, the motion will be periodic in the band. It would go to the end of the band, will be Bragged-reflected and go, and so on. Now, I don't think Kittel had really realized that and he thought much about it, he talked to Bill Shockley about it. The Kittel-Shockley connection is an interesting one that you might want to explore. (Partly it was Shockley who thought it might be an interesting experience, and, you know, Kahn with Kittel. Shockley told Kittel about some ideas (this is the best of my recollection) that Shockley had had about the cyclotron resonance. He was interested in the periodic motion, and was thinking about the periodic motion in the field… Kittel (???) that that was an interesting idea, but what Shockley had in mind for doing — I just don't remember what it was — was just kind of too complicated and difficult (digression) I think, Kittel had the idea that all you had to do was to put the semiconductor sample in a microwave electric field, and with the small number of carriers — there will be no skin-depth problems and you can just excite the resonance. I think he might have had the idea of shining the light on the sample to produce carriers. This was in the summer of 1953 and he got very excited about it and got the whole group interested and doing something with it. They wanted me to stay on. I was to go to the University of Pittsburgh like August or September to begin setting up a lab and to begin teaching, and they wanted me to stay on and work on this, if only for a couple of weeks. And I thought — oh, it's a long project, and would get out of my life. And so, Jim Dresselhaus, who was a theoretical student of Kittel's (??? with his hands), went down to the lab to work with Art Kip on the cyclotron resonance. I just went off. We drove across the country and by the time I got to Pittsburgh waiting for me was a draft of a letter to Phys. Rev. Letters announcing, you know, that they discovered cyclotron resonance in semiconductors.

Szymborski:

How did you feel?

Portis:

Oh... Happy for them, really; feeling that it would've been nice to participate in that, but, you know, they did the work, and in any case I felt, well, if I were interested in just collecting publications it would've been fun to do, of course, it would've been nice, it would've been lovely to have this publication, but, you know.

Szymborski:

This was, as far as I know the first direct measurement of the effective mass in silicon.

Portis:

Yeah, I think, let's see, there had been, sure, we had made an estimate from the electron spin susceptibility of what the masses have to be. Masses were inferred from other things. The band structure was known, but there were no number... You know, people had very vague ideas what the band structure was from magneto resistance measurements. But I think that in terms of any kind of precise, unambiguous measurement of masse: there is no question that this was the first one. (Digression on theory) Herman's work was tremendously difficult and elaborate and, I mean, probably beyond... Now, one can do that much more easily — by semi empirical techniques (Marvin Cohen if you talk to him might tell you more). But this was tremendously elaborate kind of business. The interesting thing, I think, you should ask Kip about the cyclotron resonance in metals is that this was his own undertaking. That was not with the collaboration with Kittel. He went to a conference in the Soviet Union and, I guess, to report on the cyclotron resonance business work. If I am not mistaken Kittel had been invited and couldn't and didn't go. And Kip met Azbel (this would've been '55, something like that) Maybe Art will tell you the whole story and I shouldn't spoil it. But Azbel said, we think you can do it in metals. Kaner and I have done this work and we want to tell you about it and to encourage you to do this — Art came back and — I think this is really the first thing that he did in which Kittel was not the collaborator; it had been suggested to him and he didn't feel and I think that in the rest of his professional activity from then for ten, fifteen years (he worked independently).

Szymborski:

Did Russians do the experiment too?

Portis:

Art will tell you, but I think, Azbel said, "I don't have anyone here to do it.” And Art said "I'll do it.” The interesting story would be, if you can get it from Kittel, on what El Abrahamson has done, and then that connection with Shockley, because that's how it got started.

Szymborski:

Other people who worked in the field were Benjamin Lax and others at MIT. Did they start at the same time?

Portis:

I think you have to get that from them. I am sure they were thinking about it, and they were very close. They had been doing optical studies and once the group here announced that they found it at the microwave frequencies Lax group moved into it very fast. There was really a kind of competition. Both groups produced major papers at about the same time, and I am sure independently of each other.

Szymborski:

When you came back you started working with Teaney, I think...

Portis:

That's right. Still in Pittsburgh I got interested in the idea of making Hall Effect measurement in microwave frequencies and had designed a microwave cavity that would make that possible. Then, with Teaney we did some studies on the antiferromagnetic using this, using the cavity as a part of a highly sensitive super heterodyne. It was an interesting experimental development. The antiferromagnetic work did not really amount to anything, but I think, the development of the cavity and its application to the Hall Effect measurements (meant something). A lot of people have used it since, particularly in biological materials to measure Hall Effect. I think, what's nice about it is that one can make transport measurements in a sample without really making electrical contacts to it. That's important for biological systems and for finely divided materials, things like that. The really exciting development that I was involved in was the nuclear resonance in ferromagnetic alloys. This is the separate line of development. This was stimulated by Nicklaus Curti who had done gamma-ray anisotropy from cobalt. He was here as a visitor for a year and decided to set up a program heat capacity of cobalt. He said to us "look, I can tell you the magnetic field, the hyperfine field in the cobalt, and you might try to do the nuclear resonance.” I guess he talked to Kip about this, I mean to Kittel, rather, and Kittel certainly encouraged him to suggest it new to me. So, I had a graduate student, Arthur Gossart build equipment in that frequency range. We were very worried that resonance would be very broad, because the field was in homogenous, so I encouraged Gossart to do a really careful job of building the spectrometer, sort of a la George Feher. It was going slowly, but I realized (normally you excite resonance in a static field and the transverse oscillating field) that if you put the radio-frequency field under the ferromagnet the whole magnetization will move back and forth, which means that you get a very much larger radio-frequency field than you would otherwise get. And this is a tremendous enhancement, and so the absorption should be very much larger than what otherwise would be the case. I went in to Art Gossart and I said "Art, I think your spectrometer is sensitive enough. You should put a sample in it and look." And he did that right away and we got a gigantic resonance, even larger than I had estimated from this domain rotation mechanism. We submitted I think with the help of Kittel we decided that this was the domain wall motion and that we really were exciting just these nuclei which were in the domain walls. Phil Anderson independently said when he saw our letter in Phys. Rev. Letters — they really understand what they saw, it's really domain walls. (part omitted) That turned out to be really an exciting development, this nuclear resonance in ferromagnets. Other people picked it up and there was a lot of work done on alloys and… We did cobalt and nickel later, would've done iron but most of other people did it first. Things that I did after I came back were really my own. I interacted in some with Kittel, but I was really on my own. He, I think, at that point (Kip was doing cyclotron resonance and was pretty much on his own) pretty much moved back from any very active participation and collaboration in experimental program and worked on exclusively with his theoretical students. Kittel is, I mean, a very compelling person. He is not abrasive at all, but his associations tend to be kind of intense. I don't think Art Kip is going to talk to you about that… Chicago connection Volker Heine was here as a post-doc of Kittel, but working on the theory of cyclotron resonance with Kip. That was a kind of collaboration in that period. Walter Marshall, who came here with a remarkable group of people who came here to work with Kittel, who is here, worked on the theory of… field in ferromagnetic materials. That was tied to Curti's work and to our antiferromagnetic resonance work.