Spin hydrodynamics in amorphous magnets

Abstract

Spin superfluidity, i.e., coherent spin transport mediated by topologically stable textures, is limited by parasitic anisotropies rooted in relativistic interactions and spatial inhomogeneities. Since structural disorder in amorphous magnets can average out the effect of these undesired couplings, we propose this class of materials as platforms for superfluid spin transport. We establish nonlinear equations describing the hydrodynamics of spin in insulating amorphous magnets, where the currents are defined in terms of coherent rotations of a noncollinear texture. Our theory includes dissipation and nonequilibrium torques at the interface with metallic reservoirs. This framework allows us to determine different regimes of coherent dynamics and their salient features in nonlocal magneto-transport measurements. Our work paves the way for future studies on macroscopic spin dynamics in materials with frustrated interactions.