Accounting for quantum thermal effects in atomistic spin dynamics

One of the most effective tools for the study of magnetism dynamics and equilibrium magnetic properties accounting for thermal fluctuations is classical atomistic spin dynamics (ASD). Despite proving extremely successful for a variety of applications, they however run into some limitations, particularly at low temperatures. Here, we present two approaches to effectively incorporate quantum effects into ASD simulations, thus enhancing their low temperature predictions.

First, we show how the quantum behaviour of spins can be accurately reproduced by classical spins at an effective temperature. This effective temperature is determined a priori from the microscopic properties of the system and can be incorporated into ASD simulations at no additional cost to improve the predictions.

Second, we take an open system approach accounting for strong coupling to the environment. By treating the environment semi-classically, we are able to obtain magnetisation values that match experimental data qualitatively at low temperature, and further give more accurate predictions of the critical temperature. The parameters that characterise this model can be calculated ab initio or extracted from experiments.

These results are a substantial step forward towards effectively including quantum aspects of the spin dynamics in magnetism simulations. When implemented in a large scale ASD framework, we believe would provide a far more accurate description of the magnetism dynamics and low temperature behaviour.