Effect of double exchange on thermoelectric power of Cu xGa yCr zSe 4

Abstract

A correlation between double exchange magnetic interaction and the thermoelectric power is considered in the ferromagnetically ordered Cu x Ga y Cr z Se 4 nonstoichiometric p-type spinel conductors in the temperature range from 5 to 400 K between y = 0.036 and 0.394. The magnetic and thermopower investigations provide evidence that: (1) the carrier diffusion dominates in the most stoichiometric single crystals and the intensity of diffusion thermopower is five times larger than the intensities of the phonon and magnon excitations, (2) for samples with low gallium content the strong ferromagnetic coupling connected mainly with double exchange mechanism makes easier the spin wave excitations at higher temperatures on one side and the high nonstoichiometry hinders the spin wave excitations on the other, and (3) for samples with higher gallium content, which are more stoichiometric, the ferromagnetic coupling connected here with the weaker double exchange interaction causes a shift of the magnon drag peak into lower temperatures.