Theoretical and experimental study of the phase formation for Ti2YAl and Ti2Y′Ga (Y = Co, Fe; Y′ = Cr, Fe)

The site preference and phase formation of Ti2YAl and Ti2Y′Ga (Y = Co, Fe; Y′ = Cr, Fe) have been investigated by theoretical calculation and experimental study. It has been found that Ti2CoAl and Ti2FeAl are stable in Hg2CuTi-type structure, while Ti2CrGa and Ti2FeGa compounds are most likely to form Cu2MnAl-type structure. These results indicate that not all full-Heusler alloys follow the site preference rule, especially when the transition metals are low-valent metals. The differences of band structures and magnetic properties between Hg2CuTi-type and Cu2MnAl-type structures for the above compounds are also studied by first-principles calculation. It has been predicted that Ti2FeAl, Ti2FeGa and Ti2CoAl are half-metallic compounds in Hg2CuTi-type structure, while their half-metallic properties are completely destroyed as they formed Cu2MnAl-type structure.