Possible half-metallic behavior of Co2−xCrxFeGe Heusler alloys: Theory and experiment

Abstract

This paper reports a combined experimental and theoretical study of structural, electronic, magnetic, and mechanical properties of quaternary Heusler alloys ${\mathrm{Co}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}\mathrm{FeGe}$ prepared by arc-melting with Cr concentrations $0\ensuremath{\le}x\ensuremath{\le}1$. Single-phase microstructures are observed for Cr compositions from $x=0.25$ to $x=1$. Lower Cr concentrations are multiphased. X-ray diffraction patterns at room temperature reveal a face-centered cubic crystal structure in all single-phase samples. The low-temperature saturation magnetic moments, as determined from magnetization measurements, agree fairly well with our theoretical results and also obey the Slater-Pauling rule for half-metals, a prerequisite for half-metallicity. All alloys are observed to have high Curie temperatures that scale linearly with the saturation magnetic moments. Relatively high mechanical hardness values are also observed. First-principles calculations also predict a finite band gap in the minority spin channel of the alloys, increasing in size with increasing Cr concentration. Cr substitution brings the Fermi level toward the center of this gap while also increasing the majority spin density of states near the Fermi level. As a whole, ${\mathrm{Co}}_{2\ensuremath{-}x}{\mathrm{Cr}}_{x}\mathrm{FeGe}$ shows great promise as a half-metal with 100% spin polarization.