Quantum Brownian motion for magnets

Abstract Spin precession in magnetic materials is commonly modelled with the classical phenomenological Landau–Lifshitz–Gilbert (LLG) equation. Based on a quantized three-dimensional spin + environment Hamiltonian, we here derive operator equation of motion that describes and includes general form damping consistently accounts for memory, coloured noise quantum statistics. The LLG recovered as its classical, Ohmic approximation. We further introduce resonant Lorentzian system–reservoir couplings allow systematic comparison dynamics between non-Ohmic regimes. Finally, simulate full non-Markovian semi-classical limit. At low temperatures, our numerical results demonstrate characteristic reduction flattening steady state alignment an external field, caused by statistics environment. provide powerful framework to explore dissipation thermodynamics.