Searching for magnetically hard monoborides (and finding a few): A first-principles investigation

TL;DR

This study uses first-principles calculations to explore a wide range of transition metal boride alloys, identifying promising candidates with high magnetic hardness for rare-earth-free hard magnetic materials.

Contribution

It systematically investigates the magnetic properties of MnB, FeB, and their alloys with transition metals, revealing new potential hard magnetic materials.

Findings

(Fe-Co)B alloys show magnetic hardness exceeding five.

MnB alloys with certain transition metals are classified as soft or semi-hard.

FeB alloys with specific elements are identified as magnetically hard.

Abstract

New hard magnetic materials with zero or low rare earth content are in demand due to the high prices of the rare earth metals. Among the candidates for such materials, we consider MnB, FeB and their alloys, because previous experiments suggest that FeB has a relatively high magnetic hardness of about 0.83 at room temperature. Using first-principles calculations, we examine the full range of alloys from CrB, through MnB, FeB, to CoB. Furthrmore, we consider alloys of MnB and FeB with substitutions of 3$d$, 4$d$ and 5$d$ transition metals. For the above ninety compositions, we determine magnetic moment, magnetocrystalline anisotropy energy and magnetic hardness. For (Fe-Co)B alloys, the calculated values of magnetic hardness exceed five, which is an exceptionally high. While these values are inflated by the virtual crystal approximation used, we still expect actual magnetic hardnesses well above unity. Furthermore, we classify considered MnB alloys substituted with transition metals as magnetically soft or semi-hard and FeB alloys with Sc, Ti, V, Zr, Nb, Mo, Hf, Ta or W as magnetically hard (with magnetic hardness exceeding unity).