Theory of spin magnetohydrodynamics

TL;DR

This paper develops a comprehensive hydrodynamic framework for spin magnetohydrodynamics, elucidating the reciprocal effects of spin-transfer torque and Berry-phase gauge fields, and analyzing dissipation and resistivity in magnetic textures.

Contribution

It introduces a phenomenological theory coupling magnetic precession with electric currents, including new coefficients and equations for spin-magnetohydrodynamics.

Findings

Derived general magnetohydrodynamic equations.

Identified lower bounds on magnetic-texture resistivity.

Analyzed dissipation mechanisms in coupled magnetic-electronic systems.

Abstract

We develop a phenomenological hydrodynamic theory of coherent magnetic precession coupled to electric currents. Exchange interaction between electron spin and collective magnetic texture produces two reciprocal effects: spin-transfer torque on the magnetic order parameter and the Berry-phase gauge field experienced by the itinerant electrons. The dissipative processes are governed by three coefficients: the ohmic resistance, Gilbert damping of the magnetization, and the "beta coefficient" describing viscous coupling between magnetic dynamics and electric current, which stems from spin mistracking of the magnetic order. We develop general magnetohydrodynamic equations and discuss the net dissipation produced by the coupled dynamics. The latter in particular allows us to determine a lower bound on the magnetic-texture resistivity.