Exchange interactions and Curie temperatures in Fe2 NiZ compounds

Using the spin-polarized relativistic Korringa-Kohn-Rostoker method, we study the exchange interactions and Curie temperatures of Fe 2 Ni Z ( Z = Al, Ga, Si, Ge) with the Hg 2 CuTi structure. The Heisenberg exchange coupling parameters and Curie temperatures are obtained by calculating the exchange interactions between the constituents. It is found the nearest neighbor exchanges play a leading role in interactions, the calculated Curie temperatures, which are higher than the room temperature, decrease when changing Z from III to IV group. In addition, we study the influence of lattice constant on magnetic moments and Curie temperatures. It is found the Fe magnetic moments become more larger due to the reduction of atomic orbital overlap as the expansion of lattice parameters. Only small changes are observed for the moment of Ni atom, while for the Z atom, the magnetic moment is nearly constant. Finally, the Curie temperatures of Fe 2 Ni Z compounds under different lattice constants are acquired by using the mean-field approximation.