Anomalous influence of an external magnetic field on spin fluctuations in magnetic semiconductors with strong p - d hybridization and the colossal magnetoresistance effect

The colossal magnetoresistance effect in magnetic semiconductors based on lanthanum manganites has been investigated in terms of the model allowing for the effects of p-d hybridization and electronelectron Coulomb correlations. The influence of an external magnetic field on spin fluctuations has been considered under the conditions where the chemical potential is in a narrow heavy-fermion band formed in the hybridization gap. It has been shown that, in the vicinity of the Curie point T C, the strong spin anharmonicity leads to an anomalously strong suppression of spin fluctuations by the external magnetic field, a phenomenon contributing significantly to the formation of colossal negative magnetoresistance.