Tuning magnetocrystalline anisotropy of Fe$_{3}$Sn by alloying

TL;DR

This study investigates how alloying Fe$_{3}$Sn with various elements can modify its magnetocrystalline anisotropy from planar to uniaxial, aiming to improve its potential as a permanent magnet material.

Contribution

It demonstrates the effect of different dopants on Fe$_{3}$Sn's anisotropy and provides experimental validation for Sb and Mn doping to achieve uniaxial anisotropy.

Findings

Dopants like Sb and Mn can reverse the anisotropy from planar to uniaxial.

Small structural changes significantly influence magnetic anisotropy.

Fe$_{3}$Sn-Sb with Mn is stable and shows promising magnetic properties.

Abstract

The electronic structure, magnetic properties and phase formation of hexagonal ferromagnetic Fe$_{3}$Sn-based alloys have been studied from first principles and by experiment. The pristine Fe$_{3}$Sn compound is known to fulfill all the requirements for a good permanent magnet, except for the magnetocrystalline anisotropy energy (MAE). The latter is large, but planar, i.e. the easy magnetization axis is not along the hexagonal c direction, whereas a good permanent magnet requires the MAE to be uniaxial. Here we consider Fe$_{3}$Sn$_{0.75}$M$_{0.25}$, where M= Si, P, Ga, Ge, As, Se, In, Sb, Te and Bi, and show how different dopants on the Sn sublattice affect the MAE and can alter it from planar to uniaxial. The stability of the doped Fe$_{3}$Sn phases is elucidated theoretically via the calculations of their formation enthalpies. A micromagnetic model is developed in order to estimate the energy density product (BH)max and coercive field $\mu_{0}$H$_{c}$ of a potential magnet made of Fe$_{3}$Sn$_{0.75}$Sb$_{0.25}$, the most promising candidate from theoretical studies. The phase stability and magnetic properties of the Fe$_{3}$Sn compound doped with Sb and Mn has been checked experimentally on the samples synthesised using the reactive crucible melting technique as well as by solid state reaction. The Fe$_{3}$Sn-Sb compound is found to be stable when alloyed with Mn. It is shown that even small structural changes, such as a change of the c/a ratio or volume, that can be induced by, e.g., alloying with Mn, can influence anisotropy and reverse it from planar to uniaxial and back.