Relation of Giant Thermo-EMF, Magnetothermo-EMF, Magnetoresistance, and Magnetization to Magnetic Impurity States in Manganites Nd(1–x)SrxMnO3 and Sm(1–x)SrxMnO3

Resumo

Thermo-EMF, magnetothermo-EMF, magnetoresistance, and magnetization of single-crystal samples of Nd_(1–x)Sr_xMnO₃ and Sm_(1–x)Sr_xMnO₃ with 0 ≤ x ≤ 0.3 have been studied experimentally. A sharp increase in the thermo-EMF and giant magnetothermo-EMF and magnetoresistance has been observed near the Curie point T_C in compounds with 0.15 ≤ x ≤ 0.3. At the same time, no peculiarities have been found in compositions with x = 0. Since compounds with x > 0 consist of ferromagnetic clusters of the ferron type that reside in an antiferromagnetic A-type matrix, this means that the sharp increase in the thermo-EMF near T_C is caused by ferrons. Indeed, the disappearance of ferrons due to a magnetic field or heating above T_C leads to an abrupt decrease in the thermo-EMF. Therefore, thermo-EMF in alloyed magnetic semiconductors has been determined by the impurity concentration and the sample volume.