Atomic site occupation determined by magnetism in the Heusler alloy Mn2CoGa doped with Cr

The atomic configuration and magnetic properties of Mn2CoMxGa1−x (M=Cr and Ni) Heusler alloys have been investigated by experiments and calculations. Doping with Ni leads to a magnetic moment change of 5.92 μB/atom, giving rise to a local FM structure in the ferrimagnetic matrix. On the other hand, a moment change of 3.61 μB/atom is experimentally observed in Cr-doped alloys, which is very large compared with the atomic moment of about 2 μB/Cr atom in other Heusler alloys. Electronic-structure calculations are presented which indicate that, in contrast with Ni-doped alloys, the magnetism favors the doped Cr atoms to occupy unusual atomic sites. This is opposite to the effect of the covalent bonding in Ni-doped alloys and disobeys the empirical site-occupation rule for Heusler alloys. Due to the difference in electronegativity of the dopants, the covalent bonding in Mn2CoGa doped with Ti, V and Cr is weaker than in alloys doped with Fe, Co and Ni. Because Cr has a higher magnetic moment than Ti and V, the magnetism determines, in this weak-covalent environment, an atomic site occupation by Cr which does not obey the empirical rule. This provides clear evidence for the impact of magnetism on the crystalline structure of Heusler alloys.