Half-metallic properties ofCo2(Cr1−xFex)GaHeusler alloys

Abstract

Magnetic and half-metallic properties of ${\mathrm{Co}}_{2}({\mathrm{Cr}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x})\mathrm{Ga}$ Heusler alloys have been investigated. In the entire concentration range, the $L{2}_{1}$-type ordered phase is obtained. The saturation magnetic moment ${M}_{s}$ at $4.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $x=0.0$ $(\ensuremath{\equiv}{\mathrm{Co}}_{2}\mathrm{Cr}\mathrm{Ga})$ is $3.01{\ensuremath{\mu}}_{B}∕\mathrm{f.u.}$, in agreement with the generalized Slater-Pauling line and consistent with the theoretical value. The experimental value of ${M}_{s}$ increases with increasing $x$, slightly larger than that of the theoretical value above $x=0.60$. The Curie temperature ${T}_{C}$ also increases with $x$, and qualitatively accords with the theoretical values estimated from the effective exchange constant ${J}_{0}$. The present theoretical results disclose that not only the $L{2}_{1}$-type ordered phase but also the $B2$-type phase exhibits high values of the spin polarization ratio $P$ in a low concentration range of $x$. The ratio $P$ of the $L{2}_{1}$- and $B2$-type phases decreases with increasing $x$, because the large peak of the density of states at the Fermi energy for Cr in the majority spin band becomes smaller and a strong hybridization between $\mathrm{Co}\text{\ensuremath{-}}3d$ and $\mathrm{Fe}\text{\ensuremath{-}}3d$ makes a gap narrower in the minority spin band.