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

Abstract

We report the spin polarization of ${\text{Co}}_2{\text{FeAl}}_x{\text{Si}}_{1-x}$ ($x=0.0$ , 0.3, 0.5, 0.7) bulk alloys measured by the point contact Andreev reflection method. All the ${\text{Co}}_2{\text{FeAl}}_x{\text{Si}}_{1-x}$ alloys had an $L{2}_1$ structure along with $A2$ - and $B2$ -type disorder. Several off-stoichiometric alloys $\left({\text{Co}}_x{\text{Fe}}_y{\text{Al}}_{0.5}{\text{Si}}_{0.5}\right)$ 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 $0.57\pm 0.01$ for $x=0.0$ to a maximum value of $0.60\pm 0.01$ for $x=0.5$ . The off-stoichiometric alloys had spin polarizations of $0.57-0.60\pm 0.01$ . 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.