Magnetization relaxation and geometric forces in a Bose ferromagnet

TL;DR

This paper develops a hydrodynamic theory for spin 1/2 Bose gases, incorporating geometric forces and magnetization dynamics, and explores phenomena like the topological Hall effect and magnetization relaxation.

Contribution

It introduces a comprehensive hydrodynamic framework for Bose ferromagnets at arbitrary temperatures, including geometric forces and topological effects.

Findings

Geometric forces influence particle dynamics in the system.

Topological Hall effect affects collective modes.

Magnetization relaxation is fourth order in spatial gradients.

Abstract

We construct the hydrodynamic theory for spin 1/2 Bose gases at arbitrary temperatures. This theory describes the coupling between the magnetization, and the normal and superfluid components of the gas. In particular, our theory contains the geometric forces on the particles that arise from their spin's adiabatic following of the magnetization texture. The phenomenological parameters of the hydrodynamic theory are calculated in the Bogoliubov approximation and using the Boltzmann equation in the relaxation-time approximation. We consider the topological Hall effect due to the presence of a skyrmion, and show that this effect manifests itself in the collective modes of the system. The dissipative coupling between the magnetization and the normal component is shown to give rise to magnetization relaxation that is fourth order in spatial gradients of the magnetization direction.