Microscopic theory of magnon-drag thermoelectric transport in ferromagnetic metals

A theoretical study of the magnon-drag Peltier and Seebeck effects in ferromagnetic metals is presented. A magnon heat current is described perturbatively from the microscopic viewpoint with respect to electron-magnon interactions and the electric field. Then, the magnon-drag Peltier coefficient Γ _mag is obtained as the ratio between the magnon heat current and the electric charge current. We show that Γ _mag = C _magT ^5/2 at a low temperature T; that the coefficient C _mag is proportional to the spin polarization P of the electric conductivity; and that P > 0 for C _mag < 0, but P < 0 for C _mag > 0. From experimental results for magnon-drag Peltier effects, we estimate that the strength of the electron-magnon interaction is about 0.3 eV·Å ^3/2 for permalloy.