Semiconducting Magnets at High Temperature

For water the melting temperature is where crystal turns to liquid. For magnets the Curie temperature is the point above which the lined-up spins of a ferromagnet fall out of alignment and the material becomes nonmagnetic. Recently the calcium-boron compound CaB6, doped with lanthanum, was observed to retain a modest ferromagnetism at temperatures as high as 900 K, surprising for a compound not containing the traditional magnetic metals such as nickel or iron.

Now physicists in The Netherlands (Paul Kelly, University of Twente, p.j.kelly@tn.utwente.nl, 31-53-489-3166) suggest that CaB6 is not a metal, as has been thought, but actually a semiconductor. One obstacle so far to the realization of spintronics, the kind of electronics in which electron spin and not just electron charge plays a part, has been the difficulty of mixing semiconductors and magnetic metals. Hence the value of a semiconductor that starts out as a magnet and remains magnetic well above room temperature. Spintronics analogues of typical semiconductor functions, such as rectification and amplification, would now be possible.. In addition to magnetic sensor and memory applications, entirely new possibilities such as reprogrammable logic might be brought within reach. (Tromp et al., Physical Review Letters, 2 July 2001; text at Physics News Select).