Magnon Drag Thermoelectric Power in Magnetic Graphite Intercalation Compounds

Abstract

Thermoelectric power (TEP) of first-stage non-magnetic graphite acceptor intercalation compounds drops rapidly to a negligibly small value below 7 K. In contrast to the non-magnetic GICs, the magnetic compounds such as first-stage FeCl₃- and CoCl₂-GICs exhibit much larger TEP, which is expected to be due to the magnon drag effect. This prediction is confirmed theoretically in this article. The present calculation is carried out for CoCl₂-GIC, since its magnetic properties have been extensively studied. The dispersion relation for the long wavelength magnons is phonon-like. This is due to the 2D-character of the spin system. By solving the coupled Boltzmann equation for carriers and magnons the magnon drag TEP is calculated and the calculated temperature dependence is proportional to T at low temperatures, which is consistent with the measurement. The calculated value has the same order of magnitude as the observed one.