Sign of thermoelectric power in Co/Cu and Fe/Cr multilayers

Abstract

We analyze the thermoelectric power (TEP) of Co/Cu and Fe/Cr multilayers in terms of the Mott formula, which relates TEP and energy dependent electric conductivity. The conductivity of the multilayers is treated using the model proposed by Tsymbal and Pettifor, Phys. Rev. B 54, 15 314 (1996). The model is based on a quantum-mechanical formulation for the electron transport within a realistic spd tight-binding approximation for the band structure and spin-independent disorder in the on-site atomic energy levels. We find that for a disorder, producing a realistic resistivity of the multilayers, the thermoelectric power is positive for Fe/Cr multilayers, but negative for Co/Cu multilayers, which is consistent with experiments. The difference in the sign of TEP is explained in terms of the difference in the electronic band structures for Co/Cu and Fe/Cr multilayers. We also show that the model accounts for the experimentally observed sign of the magnetothermoelectric power at room temperature, when the magnetizations of the consecutive ferromagnetic layers change their alignment.