Half-metallic magnetism in Ti3Co5-xFexB2

Rohit Pathak,Imran Ahamed,Arti Kashyap,Ralph Skomski,D J Sellmyer,W Y Zhang,Shah Vallopilly

doi:10.1063/1.4976302

Rohit Pathak, Imran Ahamed + Show 5 more

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https://doi.org/10.1063/1.4976302

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Abstract

Bulk alloys and thin films of Fe-substituted Ti3Co5B2 have been investigated by first-principle density-functional calculations. The series, which is of interest in the context of alnico magnetism and spin electronics, has been experimentally realized in nanostructures but not in the bulk. Our bulk calculations predict paramagnetism for Ti3Co5B2, Ti3Co4FeB2 and Ti3CoFe4B2, whereas Ti3Fe5B2 is predicted to be ferromagnetic. The thin films are all ferromagnetic, indicating that moment formation may be facilitated at nanostructural grain boundaries. One member of the thin-film series, namely Ti3CoFe4B2, is half-metallic and exhibits perpendicular easy-axis magnetic anisotropy. The half-metallicity reflects the hybridization of the Ti, Fe and Co 3d orbitals, which causes a band gap in minority spin channel, and the limited equilibrium solubility of Fe in bulk Ti3Co5B2 may be linked to the emerging half-metallicity due to Fe substitution.

Highlights

The tetragonal intermetallic compound Ti3Co5B21 has long been known to be non-magnetic (Pauli paramagnetic), but recent experimental research has found that Fe substitution makes the alloy ferromagnetic.[2]
The melt-spun samples considered in Ref. 2 form part of ongoing efforts to create magnetocrystalline anisotropy in alnico-type permanent magnets.[3,4]
The tetragonal crystal structure of the alloy supports uniaxial anisotropy, which is much stronger than the cubic anisotropy of the main magnetic bcc-type Fe-Co phase and may complement the shape anisotropy of the material

Summary

Introduction

The tetragonal intermetallic compound Ti3Co5B21 has long been known to be non-magnetic (Pauli paramagnetic), but recent experimental research has found that Fe substitution makes the alloy ferromagnetic.[2] This is important in two contexts. Any additional magnetocrystalline anisotropy would substantially enhance the coercivity, which is the performance bottleneck in an otherwise very good permanent-magnet material. The search for new magnetic materials with uniaxial anisotropy is a key aspect of the ongoing development of spin-electronics materials.[5,6,7,8] Among the desired properties for spin-electronics applications are a high spin polarization at the Fermi level, ideally half-metallicity,[9,10,11,12,13,14,15,16,17] and some noncubic anisotropy.[18,19,20,21]

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