High spin polarization in a two phase quaternary Heusler alloy Co2MnAl1−XSnX

We have investigated the structure and the spin polarization of Co2MnAl, Co2MnSn, and Co2MnAl0.5Sn0.5 alloys. The structures of the Co2MnAl and Co2MnSn alloys that were annealed for four days at 450°C were B2 and L21, respectively. Co2MnAl0.5Sn0.5 had a dendrite microstructure that was formed by the phase separation into Al-enriched B2 and Sn-enriched L21 phases during solidification. The saturation magnetization values of Co2MnAl, Co2MnAl0.5Sn0.5, and Co2MnSn were 3.66μB, 4.3μB, and 4.9μB, respectively, which are slightly lower than the theoretical values of 4μB, 4.5μB, and 5μB due to the low degree of L21 ordering. The spin polarization P measured by the point contact Andreev reflection technique were 0.56 for B2-Co2MnAl, 0.6 for L21-Co2MnSn, and interestingly, a higher value of 0.63 for the two phase Co2MnAl0.5Sn0.5 alloy.