Thermopower of magnetoresistive composites based on La0,7Sr0,3MnO3

Abstract

The paper studies the dependence of the magnetoresistance and Seebeck coefficient of the composite magnetoresistive composition near the percolation threshold of 80%La0,7Sr0,3MnO3/20%GeO2 on the constant magnetic field strength up to 3,8 kOe and temperature in the range from 25°C to 150°C. The 80%La0,7Sr0,3MnO3/20%GeO2 samples have the p-type conductivity, a the positive sign of the Seebeck coefficient and a dielectric character of the change in the electrical resistance with temperature. The activation energy of such compositions is of about 0,35 eV. The magnetoresistance of such a composition decreases with an increase in the temperature difference between the hot and cold edges and disappears in the region of the phase transition temperatures of 90°C. It was found that in a constant external magnetic field of 3,8 kOe, a decrease in the Seebeck coefficient of the 80%La0,7Sr0,3MnO3/20%GeO2 compositions by 11% is observed at a temperature difference of 10 K. The dependence of the Seebeck coefficient on the magnetic field decreases with an increase in the hot edge temperature and also disappears in the temperature range of 90°C, which is associated with the ferromagnetic-paramagnetic phase transition of lanthanum manganite La0,7Sr0,3MnO3 and the suppression of spin-dependent electron tunneling.

Keywords

• seebeck coefficient
• magnetoresistive composite
• constant magnetic field
• lanthanum- strontium manganite
• percolation