Spontaneous Nernst coefficient of ferromagnets from the interplay of electron scattering and Berry curvature

We employ the Boltzmann transport approach to derive the spontaneous Nernst coefficient for ferromagnetic metals, explicitly treating the transverse current density due to Berry curvature as a Fermi surface property. We find that the spontaneous Nernst coefficient is proportional to the inverse of the scattering time constant, implying that efficient spontaneous Nernst materials should exhibit relatively strong scattering, a stark contrast to ordinary Nernst materials. Furthermore, we establish a direct connection between the strength and sign of the spontaneous Nernst coefficient and the itinerant contribution to orbital angular momentum density arising from the Bloch bands. Finally, we construct a rigid two-band model to evaluate the thermoelectric coefficients by which we find a good agreement with the signs and orders of magnitude of the experimental coefficients of magnetic 3 d transition metal ferromagnets. We finally propose some practical recipes for maximizing the spontaneous Nernst effect through electronic band structure tailoring.