Magnetic relaxation in a model of interacting nanoparticles in terms of microscopic energy barriers

TL;DR

This study uses Monte Carlo simulations to analyze magnetic relaxation in interacting nanoparticle systems, revealing a transition from logarithmic to power-law relaxation due to changing energy barrier distributions influenced by dipolar interactions.

Contribution

It extends the $T ext{ln}(t/ au_0)$ method to interacting systems and links relaxation behavior to effective energy barrier distributions.

Findings

Transition from logarithmic to power-law relaxation with increased interactions

Effective energy barriers decrease due to local dipolar fields

Small energy barriers emerge as interactions strengthen

Abstract

Monte Carlo simulations are used to study the magnetic relaxation of a system of single domain particles with dipolar interactions modeled by a chain of Heisenberg classical spins. We show that the so-called $T\ln(t/\tau_0)$ method can be extended to interacting systems and how, from the computed master relaxation curves, the effective energy barrier distributions responsible for the relaxation can be obtained. A transition from a quasi-logarithmic to power-law behavior of the relaxation as the interaction strength is in-creased is found. By direct computation of the effective energy barriers of the system, we show that this is due to the appearance of an increasing number of small energy barriers caused by the reduction of the anisotropy energy barriers as the local dipolar fields increase.