Thermal vacancy formation in Co-based Heusler-type alloys Co2MnZ (ZÂ =Â Si, Ge, Sn)

Thermal vacancy formation was studied for the Heusler-type ferromagnetic alloys Co2MnZ (Z = Si, Ge, Sn) as a function of temperature (773-1273 K) by the density, electrical resistivity and positron annihilation measurements. The vacancy concentration increased with increase in quenching temperature and particularly, a high vacancy concentration exceeding 2% was observed in Co2MnGe and Co2MnSn. Estimated vacancy formation and migration energies were comparable with those for B2-type FeAl and CoGa alloys with high vacancy concentration. Further, the vacancy type and the vacancy site were examined for alloys quenched from 773 K. As a result, it was suggested that the mono-vacancies are randomly distributed over the lattice sites.