Atomic disorder and magnetic property in Co-based Heusler alloys Co2MnZ (Z=Si, Ge, Sn)

Co-type and Mn–Z-type atomic disorder and magnetic property are investigated for Co-based Heusler alloys Co 2 MnZ (Z = Si, Ge, Sn) as a function of quenching temperature. It is shown that the Co-type disorder preferentially proceeds with increase in quenching temperature in Co 2 MnSi, while the Mn–Ge-type disorder preferentially proceeds in Co 2 MnGe. In Co 2 MnSn, only the Mn–Sn-type disorder proceeds. On the other hand, the mean magnetic moment decreases with increase in quenching temperature for Co 2 MnSi and Co 2 MnGe, while it remains almost constant in Co 2 MnSn. Relation between the atomic disorder and the magnetic behavior is discussed. It is concluded that the Co-type disorder leads to degradation of the magnetism as observed in Co 2 MnSi and Co 2 MnGe, while the Mn–Z-type disorder affects hardly the magnetism as in Co 2 MnSn. Atomic disorder behaviors found in the present alloys are examined by thermodynamic approach based on the Bragg–Williams approximation.