Integrated ab initio modelling of atomic order and magnetic anisotropy for rare-earth-free magnet design: effects of alloying additions in $\mathrm{L}1_0$ FeNi

TL;DR

This paper presents a comprehensive ab initio modelling framework to predict atomic order and magnetic properties in multicomponent materials, demonstrated on alloyed FeNi systems for potential rare-earth-free magnets.

Contribution

The study introduces a unified ab initio approach to simultaneously predict atomic ordering, magnetic anisotropy, and critical temperatures in complex alloys, advancing materials design.

Findings

Alloying additions significantly influence atomic ordering and magnetic properties.

Magnetic field and temperature conditions can promote tetragonal order in FeNi alloys.

Predicted magnetic properties suggest potential for rare-earth-free permanent magnets.

Abstract

We describe an integrated modelling approach to accelerate the search for novel, single-phase, multicomponent materials with high magnetocrystalline anisotropy (MCA). For a given system we predict the nature of atomic ordering, its dependence on the magnetic state, and then proceed to describe the consequent MCA, magnetisation, and magnetic critical temperature (Curie temperature). Crucially, within our modelling framework, the same ab initio description of the material's electronic structure determines all aspects. We demonstrate this holistic method by studying the effects of alloying additions in FeNi, examining systems with the general stoichiometries Fe$_4$Ni$_3X$ and Fe$_3$Ni$_4X$, for additives including X= Pt, Pd, Al, and Co. The atomic ordering behaviour predicted on adding these elements, fundamental for determining a material's MCA, is rich and varied. Equiatomic FeNi has been reported to require ferromagnetic order to establish the tetragonal L10 order suited for significant MCA. Our results show that when alloying additions are included in this material, annealing in an applied magnetic field and/or below a material's Curie temperature may also promote tetragonal order, along with an appreciable effect on the predicted hard magnetic properties.