The Spin Seebeck effect induced by the crystal field excitations in TbFeO

森 道康  ; Tomasello, B.*; Ziman, T.*

Mori, Michiyasu; Tomasello, B.*; Ziman, T.*

The spin Seebeck effect is a phenomenon of thermoelectric generation that occurs in a device consisting of a bilayer of a metal and a ferromagnet. When ferrimagnetic TbFeO (TbIG) is substituted for the ferromagnet, the effect goes to zero at low temperatures, yet it increases to positive values by applying a magnetic field. This is opposite to the expectation that the SSE should be suppressed by a magnetic field due to the increase in the magnon gap. In this talk, the crystal-field excitations (CFE) in TbIG are calculated within a mean field theory using the Stevens parameters of TbGaO (TGG) obtained by the neutron-scattering experiment. The primitive cell of TbIG hosts twelve Tb sites with six inequivalent magnetic sublattices, but due to the net [111] molecular field from the tetrahedral and octahedral Fe ions, these can be classified into two distinct groups, the C and the C' sites, which account for the double umbrella magnetic structure. We show that when an external magnetic field is applied along the [111] direction of the crystal, the lowest CFE of the C sublattices decreases. As a consequence of the magnetic field dependence of the lowest CFE, we find that at low temperatures the SSE in TbIG can be enhanced by an applied magnetic field.