Microstructure and spin polarization of quaternary Co2Cr1−xVxAl, Co2V1−xFexAl and Co2Cr1−xFexAl Heusler alloys

The microstructures, magnetic properties and spin polarization of quaternary Co2Cr1−xVxAl, Co2V1−xFexAl and Co2Cr1−xFexAl alloys were investigated. Phase separation into A2 and B2/L21 structure occurs in Co2CrAl and Co2Cr0.6Fe0.4Al, 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 Co2Cr1−xVxAl alloy changes from 1.4 to 2.0 μB when x increases from 0.0 to 0.5 and then becomes 1.4 μB for x = 1.0. This behavior can be attributed to the variation in the local magnetic moment of Co atoms. The saturation magnetization of Co2V1−xFexAl and Co2Cr1−xFexAl alloys increases with increasing Fe concentration. The spin polarization decreases from 0.62 to 0.56 with increasing x for Co2Cr1−xFexAl alloy. Also, the spin polarization decreases with increasing x for Co2Fe1−xVxAl and Co2Cr1−xVxAl alloys. Possible reasons for the reduced spin polarization in these alloys are discussed.