Engineering a driven-dissipative bath of altermagnetic quantum magnons for controlling classical dynamics of spins hosting spin waves, domain walls, or skyrmions

TL;DR

This paper develops a theoretical framework using Schwinger-Keldysh field theory to engineer a nonequilibrium bosonic bath of quantum magnons in altermagnetic insulators, enabling control over classical spin dynamics in multilayer spintronic systems.

Contribution

It introduces a novel nonequilibrium quantum magnon bath model that modifies the classical Landau-Lifshitz-Gilbert equation with nonlocal, anisotropic, and non-Markovian damping terms.

Findings

The extended LLG equation includes spatially nonlocal damping effects.

The model allows tuning of spin wave, domain wall, and skyrmion dynamics.

Demonstrates control of classical spin phenomena via engineered quantum magnon baths.

Abstract

Using Schwinger-Keldysh field theory (SKFT), we engineer a dissipative and driven (i.e., out of equilibrium) bosonic bath acting on classical localized spins within a ferromagnetic insulator (FI) layer whose dynamics is governed by the Landau-Lifshitz-Gilbert equation, as is usually assumed in spintronics and magnonics. The bosonic bath is comprised of quantum magnons within a layer of altermagnetic insulator (AMI) that is attached to a conventional FI layer, often one of the key ingredients within spintronic and magnonic multilayers, so that interaction between slow classical (in the FI layer) and fast quantum (in the AMI layer) localized spins ensues. Such a bath, including its driving to produce a nonequilibrium distribution of altermagnetic magnons, generates a rich structure of the SKFT-derived extended LLG equation for classical spins within the FI layer. Our LLG equation contains two damping terms, both of which are spatially nonlocal and anisotropic, while one of them is also intrinsically non-Markovian, i.e., nonlocal in time. We demonstrate how to exploit these terms for tuning spintronic and magnonic effects within the FI layer of AMI/FI bilayers that involve spin wave or domain wall propagation, as well as skyrmion annihilation.