Accounting for Quantum Effects in Atomistic Spin Dynamics

TL;DR

This paper introduces two methods to incorporate quantum effects into atomistic spin dynamics simulations, improving their accuracy at low temperatures by using effective temperature adjustments and a semi-classical model with quantum-like environment interactions.

Contribution

It presents two novel approaches to include quantum effects in classical ASD simulations, enhancing their low-temperature predictive capabilities.

Findings

Effective temperature approach reproduces quantum low-temperature behavior.

Semi-classical model with quantum-like environment matches experimental temperature dependence.

Methods can be integrated into existing ASD simulations without added complexity.

Abstract

Atomistic spin dynamics (ASD) is a standard tool to model the magnetization dynamics of a variety of materials. The fundamental dynamical model underlying ASD is entirely classical. In this paper, we present two approaches to effectively incorporate quantum effects into ASD simulations, thus enhancing their low temperature predictions. The first allows to simulate the magnetic behavior of a quantum spin system by solving the equations of motion of a classical spin system at an effective temperature relative to the critical temperature. This effective temperature is determined a priori from the microscopic properties of the system. The second approach is based on a \semi model where classical spins interact with an environment with a quantum-like power spectrum. The parameters that characterize this model can be calculated ab initio or extracted from experiments. This semi-classical model quantitatively reproduces the absolute temperature behavior of a magnetic system, thus accounting for the quantum mechanical aspects of its dynamics, even at low temperature. The methods presented here can be readily implemented in current ASD simulations with no additional complexity cost.