Size effect on the structural and magnetic phase transformations of iron nanoparticles

TL;DR

This study investigates how the size of iron nanoparticles influences their structural and magnetic phase transformations, revealing that surface effects significantly enhance magnetism and alter transition temperatures.

Contribution

We developed a novel atomic-scale model combining tight-binding and Monte Carlo methods to analyze size-dependent magnetic and structural transformations in Fe nanoparticles.

Findings

Magnetism is strongly reinforced at the surface of nanoparticles.

Decreasing size increases the Curie temperature.

Structural transition temperatures behave differently from magnetic ones.

Abstract

Iron nanoparticles are among the most promising low-dimensional materials in terms of applications. This particularity is attributable to the magnetic properties of these nanoparticles, which exhibit different allotropes as a function of temperature. In this work, we sought to characterise at the atomic scale how their structural and magnetic transformations can be affected by the size. To achieve this objective, we developed a tight-binding model incorporating a magnetic contribution via a Stoner term implemented in a Monte Carlo code to relax the structure and the magnetic state. Using our approach, we show that magnetism is strongly reinforced by the surface, which leads to increase the Curie temperature as the size of the particle decreases contrary to the solid-solid transition temperature. Our work thus provides a deep understanding at the atomic scale of the key factors that determines the structural and magnetic properties of Fe nanoparticles, shedding more light on their unique character which is crucial for further applications.