Thermal Stoner-Wohlfarth Model for Magnetodynamics of Single Domain Nanoparticles: Implementation and Validation

TL;DR

This paper introduces and validates a thermal Stoner-Wohlfarth model for simulating the magnetodynamics of single domain nanoparticles, effectively capturing equilibrium and dynamic behaviors in magnetic soft matter systems.

Contribution

The paper develops and validates a thermal Stoner-Wohlfarth model that accounts for thermal effects and relaxation mechanisms in magnetic nanoparticles, enhancing simulation accuracy.

Findings

tSW model accurately reproduces equilibrium properties for anisotropy > 5 times thermal fluctuations.

Model effectively captures dynamic properties without dipole-dipole interactions.

Applicable to systems where anisotropy dominates thermal fluctuations.

Abstract

We present the thermal Stoner-Wohlfarth (tSW) model and apply it in the context of Molecular Dynamics simulations. The model is validated against an ensemble of immobilized, randomly oriented uniaxial particles (solid superparamagnet) and a classical dilute ferrofluid for different combinations of anisotropy strength and magnetic field/moment coupling, at a fixed temperature. We compare analytical and simulation results to quantify the viability of the tSW model in reproducing the equilibrium (with and without dipole-dipole interactions) and dynamic (without dipole-dipole interactions) properties of magnetic soft matter systems. We show that if the anisotropy of a particle is more than five times higher than the thermal fluctuations, tSW is applicable and efficient. This approach allows one to consider the interplay between N\'eel and Brownian relaxation, often neglected in the fixed point-dipole representation-based magnetic soft matter theoretical investigations.