Impact of planar defects on the reversal time of single magnetic domain nanoparticles

TL;DR

This paper develops an analytical model using Langer's theory to predict how planar defects in single magnetic nanoparticles influence their magnetic relaxation times, emphasizing the role of microstructural defects in magnetic stability.

Contribution

It introduces a new analytical expression for relaxation time that accounts for planar defects and system size, advancing understanding of magnetic relaxation in nanoparticles.

Findings

Relaxation time depends exponentially on system size and defect count.

Both Arrhenius exponential and prefactor are affected by microstructural defects.

Model aligns with experimental data on magnetic nanoparticle stability.

Abstract

Recent experimental investigations of individual magnetic nanoparticles reveal a diverse range of magnetic relaxation times which cannot be explained by considering their size, shape, and surface anisotropy, suggesting other factors associated with the internal microstructure of the particles are at play. In this letter, we apply Langer's theory of thermal activation to single magnetic domain fcc Co nanoparticles, whose experimental microstructures are characterized by planar defects, and derive an analytic expression for the relaxation time. The obtained Arrhenius exponential and its prefactor, which is often assumed to be a constant, are here found to both depend exponentially on system size and the number of defects. Together they provide a quantitative prediction of the experimental findings, and more generally highlight the importance of structural defects when considering magnetic stability.