Large magnetic anisotropy predicted for rare-earth free Fe16-xCoxN2 alloys

TL;DR

This study predicts that substituting Fe with Co in Fe16N2 significantly enhances magnetic anisotropy, with the highest value found in Fe12Co4N2, suggesting potential for rare-earth free magnetic materials.

Contribution

The paper demonstrates that Co substitution in Fe16N2 dramatically increases magnetic anisotropy and reveals a structural transition from tetragonal to cubic phases as Co content increases.

Findings

Magnetocrystalline anisotropy energy reaches 3.18 MJ/m3 in Fe12Co4N2.

Structural transition from tetragonal to cubic occurs with increasing Co.

Enhanced magnetic properties in Co-rich alloys suggest potential for rare-earth free magnets.

Abstract

Structures and magnetic properties of Fe16-xCoxN2 are studied using adaptive genetic algorithm and first-principles calculations. We show that substituting Fe by Co in Fe16N2 with Co/Fe ratio smaller than 1 can greatly improve the magnetic anisotropy of the material. The magnetocrystalline anisotropy energy from first-principles calculations reaches 3.18 MJ/m3 (245.6 {\mu}eV per metal atom) for Fe12Co4N2, much larger than that of Fe16N2 and is one of the largest among the reported rare-earth free magnets. From our systematic crystal structure searches, we show that there is a structure transition from tetragonal Fe16N2 to cubic Co16N2 in Fe16-xCoxN2 as the Co concentration increases, which can be well explained by electron counting analysis. Different magnetic properties between the Fe-rich (x < 8) and Co-rich (x > 8) Fe16-xCoxN2 is closely related to the structural transition.