Connection of Thermopower, Magneto Thermopower with Resistivity and Magnetoresistivity in Nd (1-x)Sr xMnO 3 and Sm (1-x)Sr xMnO 3 Manganites

An experimental study of thermopower, magneto thermopower, magnetoresistivity and magnetization of Nd (1-x)Sr xMnO 3 and Sm (1-x)Sr xMnO 3 with 0 ≤ х ≤ 0.3 was conducted. A steep rise of thermopower as well as giant values of magneto thermopower and magnetoresistivity were observed near Curie temperature ТС in compounds with 0.15 ≤ х ≤ 0.3. On the other hand, no special features were found in case of х = 0. It has been known that compounds with 0.1 ≤ х ≤ 0.3 consist of ferromagnetic clusters of ferron (magnetic polaron) type located in A-type antiferromagnetic matrix. An increase of thermopower near ТС is caused by ferrons as with the application of magnetic field or temperatures higher than ТС thermopower falls sharply due to the destruction of ferrons. So, the value of thermopower is directly connected to the number of magnetic polarons in sample. Therefore, thermopower in doped magnetic semiconductors is determined by level of doping and volume of the sample.