Macrospin model of an assembly of magnetically coupled core-shell nanoparticles

TL;DR

This paper develops a multi-stage Monte Carlo model to analyze the magnetic properties of core-shell ferrite nanoparticles, successfully matching experimental hysteresis and cooling curves, and advancing understanding of their internal spin interactions.

Contribution

It introduces a hierarchical modeling approach for core-shell nanoparticles, incorporating internal structure and magnetic interactions, which improves interpretation of experimental magnetic data.

Findings

Hysteresis loops match experimental data well.

Zero-field cooling and field cooling curves agree with measurements.

Model elucidates internal spin interactions in nanoparticles.

Abstract

Highly sophisticated synthesis methods and experimental techniques allow for precise measurements of magnetic properties of nanoparticles that can be reliably reproduced using theoretical models. Here, we investigate the magnetic properties of ferrite nanoparticles by using theoretical techniques based on Monte Carlo methods. We introduce three stages of sophistication in the macromagnetic model. First, by using tailor-made hamiltonians we study single nanoparticles. In a second stage, the internal structure of the nanoparticle is taken into consideration by defining an internal (core) and external (shell) region, respectively. In the last stage, an assembly of core/shell NPs are considered. All internal magnetic couplings such as inter and intra-atomic exchange interactions or magnetocrystalline anisotropies have been estimated. Moreover, the hysteresis loops of the aforementioned three cases have been calculated and compared with recent experimental measurements. In the case of the assembly of nanoparticles, the hysteresis loops together with the zero-field cooling and field cooling curves are shown to be in a very good agreement with the experimental data. The current model provides an important tool to understand the internal structure of the nanoparticles together with the complex internal spin interactions of the core-shell ferrite nanoparticles.