Self-consistent solution of magnetic and friction energy losses of a magnetic nanoparticle

TL;DR

This paper introduces a simple yet rich simulation model for analyzing magnetic and frictional energy losses in magnetic nanoparticles within viscous fluids under alternating magnetic fields, revealing complex steady-state behaviors.

Contribution

It develops a macrospin simulation approach coupling Landau-Lifshitz-Gilbert and mechanical equations to analyze loss mechanisms in nanoparticles, highlighting different regimes and steady states.

Findings

Identifies regimes dominated by Néel relaxation and frictional losses.

Shows energy increases continuously across regime boundaries.

Demonstrates dependence of steady states on initial particle orientation.

Abstract

We present a simple simulation model for analysing magnetic and frictional losses of magnetic nano-particles in viscous fluids subject to alternating magnetic fields. Assuming a particle size below the single-domain limit, we use a macrospin approach and solve the Landau-Lifshitz-Gilbert equation coupled to the mechanical torque equation. Despite its simplicity the presented model exhibits surprisingly rich physics and enables a detailed analysis of the different loss processes depending on field parameters and initial arrangement of the particle and the field. Depending on those parameters regions of different steady states emerge: a region with dominating N\'eel relaxation and high magnetic losses and another region region with high frictional losses at low fields or low frequencies. The energy increases continuously even across regime boundaries up to frequencies above the Brownian relaxation limit. At those higher frequencies the steady state can also depend on the initial orientation of the particle in the external field. The general behavior and special cases and their specific absorption rates are compared and discussed.