High spin polarization in a two phase quaternary Heusler alloy Co_2MnAl_(1-x)Sn_x

摘要

We have investigated the structure and the spin polarization of Co_2MnAl, Co_2MnSn, and Co_2MnAl_(0.5)Sn_(0.5) alloys. The structures of the Co_2MnAl and Co_2MnSn alloys that were annealed for four days at 450℃ were B2 and L2_1, respectively. Co_2MnAl_(0.5)Sn_(0.5) had a dendrite microstructure that was formed by the phase separation into Al-enriched B2 and Sn-enriched L2_1 phases during solidification. The saturation magnetization values of Co_2MnAl, Co_2MnAl_(0.5)Sn_(0.5), and Co_2MnSn were 3.66μ_B, 4.3μ_B, and 4.9μ_B, respectively, which are slightly lower than the theoretical values of 4μ_B, 4.5μ_B, and 5μ_B due to the low degree of L2_1 ordering. The spin polarization P measured by the point contact Andreev reflection technique were 0.56 for B2-Co_2MnAl, 0.6 for L2_1-Co_2MnSn, and interestingly, a higher value of 0.63 for the two phase Co_2MnAl_(0.5)Sn_(0.5) alloy.