Dipolar-glass behaviour of an insulating film containing nanogranular Fe particles

TL;DR

This study uses Monte Carlo simulations to demonstrate that insulating films with nanogranular Fe particles exhibit dipolar-glass behavior, characterized by spin-glass features such as a freezing temperature and specific thermodynamic signatures.

Contribution

It provides the first simulation-based evidence of dipolar-glass behavior in insulating nanogranular magnetic films with dipolar interactions.

Findings

Identification of a spin-glass freezing temperature T_f

Observation of maximum in susceptibility and specific heat at T_f

Correlation between local field variance and spin auto-correlation

Abstract

We perform Metropolis Monte Carlo simulations of the behaviour of a film of insulating material containing a distribution of magnetic nanoparticles. We assume that these particles only interact through dipolar forces and we find that their behaviour at low T shows characteristics of a spin-glass with a freezing T_f at which the linear susceptibility and the specific heat show a maximum. We obtain the spin glass order parameter as a function of temperature and we also calculate the time auto-correlation of the spin at the center of the system. We find that these results are consistent with the temperature dependence of the variance and the mean of the local field at the central spin.