Understanding spin currents from magnon dispersion and polarization; Spin-Seebeck effect and neutron scattering study on TbFeO

Kawamoto, Yo*; Kikkawa, Takashi; Saito, Eiji; 9 of others*

Magnon spin currents in the ferrimagnetic garnet TbFeO with 4 electrons were examined through the spin-Seebeck effect and neutron scattering measurements. The compound shows a magnetic compensation, where the spin-Seebeck signal reverses above and below = 249.5(4) K. Unpolarized neutron scattering unveils two major magnon branches with finite energy gaps, which are well explained in the framework of spin-wave theory. Their temperature dependencies and the direction of the precession motion of magnetic moments, i.e., magnon polarization, defined using polarized neutrons, explain the reversal at and decay of the spin-Seebeck signals at low temperatures. We illustrate an example that momentum- and energy-resolved microscopic information is a prerequisite to understand the magnon spin current.