Abstract

A critical review is given of the physics of colossal magnetoresistance (CMR) materials (manganites and other degenerate ferromagnetic semiconductors). The basic idea is that their specific properties (the resistivity peak close to T_C, CMR and so on) are not related to the electron{lattice interaction but are caused by static fluctuations of the magnetisation induced by ionised donors or acceptors. Their screening by charge carriers causes fluctuations of their density and, hence, fluctuations of the intensity of indirect exchange via them. The fluctuations of the magnetisation induced by the latter are maximally close to T_C, which explains the specific features of these materials.