Structure, magnetic property, and spin polarization of $Co2FeAlxSi1−x$ Heusler alloys

We report the spin polarization of $Co2FeAlxSi1−x$ (⁠$x=0.0$⁠, 0.3, 0.5, 0.7) bulk alloys measured by the point contact Andreev reflection method. All the $Co2FeAlxSi1−x$ alloys had an $L21$ structure along with $A2$- and $B2$-type disorder. Several off-stoichiometric alloys $(CoxFeyAl0.5Si0.5)$ were prepared to understand the effect of the compositional deviation from the stoichiometry on the spin polarization. By substituting Al for Si, the spin polarization changed from $0.57±0.01$ for $x=0.0$ to a maximum value of $0.60±0.01$ for $x=0.5$⁠. The off-stoichiometric alloys had spin polarizations of $0.57−0.60±0.01$⁠. Ab initio calculations were performed to interpret the effect of Al addition as well as the effect of disorder on the magnetic properties and on the electronic structure.