Tailoring hard magnetic properties of Fe2MnSn Heusler alloy via interstitial modification: A first-principles approach

TL;DR

This study uses first-principles calculations to demonstrate that interstitial doping of Fe2MnSn Heusler alloy with light elements can significantly enhance its magnetic properties, offering a sustainable route to rare-earth-free permanent magnets.

Contribution

It introduces interstitial engineering as a novel method to improve magnetic properties of Fe2MnSn alloy, identifying specific dopants that induce desirable magnetic anisotropy and high Curie temperatures.

Findings

Interstitial doping enhances structural stability and magnetization.

Certain dopants induce a transition from in-plane to out-of-plane magnetic anisotropy.

N-doped Fe2MnSn exhibits the highest uniaxial anisotropy and magnetic hardness.

Abstract

We employ first-principles calculations to explore interstitial engineering as a strategy to tailor the hard magnetic properties of Fe2MnSn Heusler alloy, establishing its potential as a rare-earth-free permanent magnet. By introducing light interstitial elements -- B, C, H, N, O, and F -- at varying concentrations (1.56-12.5 at%), we uncover significant enhancements in structural stability, magnetization, Curie temperature, and magnetocrystalline anisotropy. These dopants preferentially occupy octahedral interstitial sites in the hexagonal phase of Fe2MnSn, leading to localized lattice distortions that enhance its magnetic characteristics. Notably, at 12.5 at% doping, B, C, N, and O induce a critical transition from in-plane to out-of-plane magnetic anisotropy -- achieved without 5d or rare-earth elements -- highlighting a sustainable pathway to high-performance magnets. Among these, N-doped Fe2MnSn exhibits the highest uniaxial anisotropy (0.61 MJ/m^3), followed by the B-doped (0.44 MJ/m^3) alloy. The magnetization of the doped compounds surpasses that of conventional ferrites and gap magnets like MnAl and MnBi. The Curie temperature sees a substantial boost, reaching 1058 K for O-doped Fe2MnSn and 1000 K for the C-doped alloy. Although N-doping results in a modest increase in Tc (744 K vs. 729 K for the pristine alloy), it delivers superior hard magnetic properties, with the highest magnetic hardness (0.65) and an enhanced maximum energy product (0.36 MJ/m^3), making it a strong candidate for gap magnet applications. These findings highlight interstitial doping as a viable route to engineer rare-earth-free permanent magnets with optimized magnetic performance.