J. Phys. Colloques
Volume 41, Numéro C5, Juillet 1980Colloque International du C.N.R.S sur les Semiconducteurs Magnétiques / Magnetic Semiconductors
|Page(s)||C5-51 - C5-58|
J. Phys. Colloques 41 (1980) C5-51-C5-58
II. PHASE TRANSITIONN.F. Mott
THE CONDUCTION PROCESSES IN MAGNETIC AND IN INTERMEDIATE VALENCY COMPOUNDS
A comparison is made between two classes of material in which d or f orbitals show intermediate valencies ; in one group is Fe3O4 and Ti4O7, in the other SmS (above 6 kbar), SmB6 and TmSe. It is pointed out that the electrons do not order in the former if the ratio of electrons to sites differs from 0.5 due to alloying by more than a few per cent. The electron gas in the latter case, and above the Verwey temperature in the former, is described as a "Wigner glass". Some speculations are added about Eu3S4 and Sm3S4. In SmS and SmB6 the Coqblin-Blandin model is developed further, and the nature of hybridisation Between an f-band and a conduction band is defined. In contrast to Fe3O4 the two charge states do not order, and the reason for this is discussed.