Ferromagnetism in undoped manganites

Hotta, Takashi

Progress in Ferromagnetism Research, p.19 - 38, 2006/00

In manganites, the appearance of the ferromagnetic (FM) metallic phase has been usually rationalized by the so-called double-exchange mechanism, based on a strong Hund's rule coupling between mobile electrons and localized spins. Then, it has been believed for a long time that hole-doping is indispensable for explaining the FM metallic phase in manganites. However, it has been theoretically pointed out that a novel metal-insulator transition in the FM state can occur even for undoped manganites based on the -orbital degenerate Hubbard model tightly coupled to Jahn-Teller distortions. In this article, the result is reviewed in detail.