Microstructure and spin polarization of quaternary Co₂Cr_1-xV_xAl, Co₂V_1-xFe_xAl and Co₂Cr_1-xFe_xAl Heusler alloys

The microstructures, magnetic properties and spin polarization of quaternary Co₂Cr_1-xV_xAl, Co₂V_1-xFe_xAl and Co₂Cr_1-xFe_xAl alloys were investigated. Phase separation into A2 and B2/L2₁ structure occurs in Co₂CrAl and Co₂Cr_0.6Fe_0.4Al, whereas Co₂FeAl exhibits a single-phase B2 structure. The ordered L2₁ structure becomes more stable with increasing vanadium concentration (x ≥ 0.35). The saturation magnetization measured at 5 K for Co₂Cr_1-xV_xAl alloy changes from 1.4 to 2.0 μ_B when x increases from 0.0 to 0.5 and then becomes 1.4 μ_B for x = 1.0. This behavior can be attributed to the variation in the local magnetic moment of Co atoms. The saturation magnetization of Co₂V_1-xFe_xAl and Co₂Cr_1-xFe_xAl alloys increases with increasing Fe concentration. The spin polarization decreases from 0.62 to 0.56 with increasing x for Co₂Cr_1-xFe_xAl alloy. Also, the spin polarization decreases with increasing x for Co₂Fe_1-xV_xAl and Co₂Cr_1-xV_xAl alloys. Possible reasons for the reduced spin polarization in these alloys are discussed.