Anomalous hopping magnetoresistance in semiconductors with complex magnetic structure: Application to lightly doped La 2CuO 4
A mechanism of hopping magnetoresistance (MR) due to the interaction of localized carriers' spins and and spins of magnetic subsystem in magnetic semiconductors is proposed. The external magnetic field H affects resistance R indirectly: H governs the order in magnetic subsystem, which in its turn affects the hopping probabilities. The arising magnetoresistance is unusual: it may be negative and may have jumps or kinks at magnetic phase transitions. The experimental data on MR of La 2CuO 4 is interpreted. It is shown that for the quantitative agreement the assumption of a polaronic effect in this substance is required.