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

We present a simple simulation model for analyzing magnetic and frictional losses of magnetic nanoparticles 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 magnetic 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 viscous 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.

Automated summary

We propose a simple simulation model to study magnetic and frictional losses of magnetic nanoparticles in viscous fluids under alternating magnetic fields. The model is based on a macrospin approach and solves the Landau-Lifshitz-Gilbert equation coupled with the mechanical torque equation. Despite its simplicity, the model reveals rich physics and allows for a detailed analysis of different loss processes depending on field parameters and initial particle-field arrangement. The model demonstrates the emergence of different steady states depending on these parameters, with regions dominated by magnetic relaxation and high losses or high frictional losses at low fields or frequencies. The energy continuously increases even across regime boundaries, surpassing the viscous relaxation limit. At higher frequencies, the steady state can also depend on the initial particle orientation in the external field. We compare and discuss the general behavior and specific absorption rates for different cases.