Magnetisation Dynamics

a figure showing different curves for equilibrium magnetization, utilizing classical and quantum noise.

Picture: M. Berritta et al., Phys. Rev. B 109, 174441 (2024)

The most widely used equation to describe magnetisation dynamics is the Landau-Lifshitz-Gilbert (LLG) equation, which predicts the precession and relaxation of a classical spin vector. In our group we study a generalised LLG equation which takes into account physically relevant additions to the LLG paradigm: coloured noise and memory effects. Our research explores how the dynamics and the equilibrium state of the spin vector is affected. In particular, we show how to successfully integrate quantum effects into classical spin dynamics. At low temperatures, this gives magnetisation predictions that are much closer to experimental observations (see figure) than the predictions of the standard LLG equation.

If you want to read more about the topic, you can start here:

Quantum Brownian Motion for Magnets, J. Anders et al., New J. Phys. 24 033020 (2022)
SpiDy.jl: open-source Julia package for the study of non-Markovian stochastic dynamics S. Scali et al., J. Open Source Softw. 9(97), 6263 (2024)
Accounting for quantum effects in atomistic spin dynamics M. Berritta et al., Phys. Rev. B 109, 174441 (2024)
Anisotropic signatures in the spin-boson model, F. Hartmann et al., Phys. Rev. B 108, 184402 (2023)