Thermal Spin Waves from Accelerating Domain Walls via the Unruh Effect

Abstract

We consider a wire consisting of a conducting ferromagnetic layer and an insulating antiferromagnetic layer that are coupled. The ferromagnet hosts a domain wall, which is dynamically driven by a charge current. We show that for a specific time-dependent current, the domain wall moves according to a Rindler trajectory. This motion excites spin waves in the antiferromagnetic insulator, and their emission spectrum is characterised by an effective temperature analogous to the Unruh temperature, $T_U = \hbar a/2\pi c k_B$, with a the acceleration of the domain wall, c the maximum antiferromagnetic spin wave velocity, and kB the Boltzmann constant. This thermal signature is a direct consequence of the Unruh effect and could be experimentally observed. Our results establish magnetism as a promising platform for probing relativistic quantum field phenomena. Moreover, since the Unruh effect is inherently linked to entanglement, our proposal provides a route for entangling magnetic domain walls via relativistic effects.