The results of a comprehensive investigation of magnetic and electric properties of $LaMnO_3$-based magnetic semiconductors with Mn ions replaced by ions of 3d metals (Fe, Co, and Ni) are presented. Also discussed are the available literature data on manganites with variously replaced La and Mn ions. The conclusion is drawn that the manganites studied are magnetic semiconductors with a narrow forbidden zone, whose magnitude is comparable with that of the exchange interaction energy. It is shown that the effect of the exchange energy on the structure of energy bands of current carriers results in (a) a correlation of the magnetic and electric properties, (b) anomalous behavior of kinetic effects, (c) a metal-semiconductor transition in the ferromagnetic region at a given temperature upon variation of the composition, and (d) a metal-semiconductor transition in the region of the Curie point.
Department of General Physics for Natural Science Faculties, Faculty of Physics, Moscow State University, Leninskie Gory, Moscow, 119992, Russia
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