Insight into the important role of antisite disorder in the magnetic properties of Mn2CuAl

Mn2CuAl is a full Heusler alloy characterized by four sets of interpenetrating face centered cubic sublattices designated A, B, C, and D and a spin gapless semiconductor. With the motivation to explore and explain the origin of the great discrepancy between the experimental molecular moment (Mexp. = 1.44 μB/f.u.) and the calculated molecular moment (Mcal. = 0.22 μB/f.u.), theoretical calculation and related experiments for Mn2CuAl were performed. All the evidence coming from calculated and experimental results point to the fact that the type of disorder is AC disorder and the degree of atomic disorder (DAD) is ∼50%. This type of disorder is unexpected in Heusler alloys. Furthermore, it is found that increasing annealing time can effectively reduce the DAD of the system while changing the method of preparation has little effect on the DAD.