Nonlinear relaxation between magnons and phonons in insulating ferromagnets

TL;DR

This paper presents a theoretical study of nonlinear relaxation processes between magnons and phonons in insulating ferromagnets, highlighting the microscopic mechanisms and potential applications in spintronics and thermoelectric devices.

Contribution

It introduces a microscopic calculation of nonlinear magnon-phonon heat transfer using Cherenkov phonon radiation, extending understanding of spin-lattice relaxation in insulators.

Findings

Derived the nonlinear heat current formula between magnons and phonons.

Compared magnon-phonon relaxation with electron-phonon processes in metals.

Discussed implications for spin-pumping and thermoelectric applications.

Abstract

Nonlinear relaxation between spin waves (magnons) and the crystal lattice (phonons) in an insulating ferromagnet is investigated theoretically. Magnons and phonons are described by the equilibrium Bose-Einstein distributions with different temperatures. The nonlinear heat current from magnons to phonons is calculated microscopically in terms of the Cherenkov radiation of phonons by magnons. The results are discussed in comparison with the well-known theoretical results on the nonlinear electron-phonon relaxation in metals [Kaganov, Lifshitz, Tanatarov, J. Exp. Theor. Phys. 31, 232 (1956)]. The elaborated theoretical description is relevant for spin-pumping experiments and thermoelectric devices in which the magnon temperature is essentially higher than the phonon one.