Effect of Co substitution for Mn on spin polarization and magnetic properties of ferrimagnetic Mn₂VAl

Bulk (Mn_1-xCo_x)₂VAl (x = 0, 0.25, 0.50) alloys in highly ordered L2₁ structure with a very small amount of B2 disorder have been prepared and their magnetic properties have been measured. The value of saturation magnetizations of the alloys with x = 0, 0.25 and 0.50 are 1.88 μ_B, 0.84 μ_B and 0.07 μ_B, respectively, being consistent with 2.00 μ_B, 1.00 μ_B and 0 μ_B, respectively, predicted by the Slater-Pauling rule. This indicates that the stoichiometric MnCoVAl alloy is a fully compensated ferrimagnet (FCF). Spin polarization measurements using point contact Andreev reflection technique showed that the quaternary alloys exhibited higher intrinsic spin polarization than the parent ternary composition. The spin polarization of 0.60 deduced for the MnCoVAl alloy suggests that spin-polarized current can be extracted from FCF. Curie temperature (T_C) and the effective anisotropy constant of (Mn_1-xCo_x)₂VAl alloys decrease with increase in Co content.