Ferromagnetic order in dipolar systems with anisotropy: application to magnetic nanoparticle supracrystals

TL;DR

This study uses Monte Carlo simulations to explore how dipolar interactions and anisotropy influence ferromagnetic order in assemblies of magnetic nanoparticles arranged on a lattice, revealing conditions for ferromagnetic phase stability.

Contribution

It introduces a detailed simulation analysis of dipolar and anisotropic effects on magnetic nanoparticle assemblies with fcc symmetry, focusing on low anisotropy regimes.

Findings

Dipolar interactions can induce ferromagnetic order in nanoparticle assemblies.

Anisotropy introduces disorder that can suppress ferromagnetic long-range order.

The study identifies conditions under which ferromagnetic phases are stable or vanish.

Abstract

Single domain magnetic nanoparticles (MNP) interacting through dipolar interactions (DDI) in addition to the magnetocrystalline energy may present a low temperature ferromagnetic (SFM) or spin glass (SSG) phase according to the underlying structure and the degree of order of the assembly. We study, from Monte Carlo simulations in the framework of the effective one-spin or macrospin models, the case of a monodisperse assembly of single domain MNP fixed on the sites of a perfect lattice with fcc symmetry and randomly distributed easy axes. We limit ourselves to the case of a low anisotropy, namely the onset of the disappearance of the dipolar long-range ferromagnetic (FM) phase obtained in the absence of anisotropy due to the disorder introduced by the latter.