Volume dependence of the exchange interaction and Curie temperature in Co_2MGa (M = Ti and Fe): A first-principles study

摘要

Magnetic moment, exchange interaction and Curie temperature (T_C) have been calculated for Co_2TiGa and Co_2FeGa by a first-principles density functional calculation combined with a linear response method. The exchange interaction is dominated by Co-Co pairs in Co_2TiGa while that of Co_2FeGa is mainly contributed by Fe-Co pairs. Based on the mean field multiple-sublattices model, the estimated T_C is about 114 K for M = Ti and 1270 K for M = Fe, calculated with the experimental lattice constant, in good agreement with the experimental values (128 K and 1093 K for M = Ti and Fe, respectively). With increasing lattice constant, a, from 95% to 105% of the experimental value (a_(exp)), the moment per formula unit m_(f.u.) changes from 0.43 μ_B to 1.0 μ_B and T_C increases from 27 K to 142 K in Co_2TiGa. However, m_(f.u.) increases slightly from 4.98 μ_B to 5.40 μ_B while T_C decreases from 1330 K to 1190 K with increasing a from 95% to 105% of a_(exp) in Co_2FeGa. These different volume dependences of T_C are ascribed to the weak ferromagnetism in Co_2TiGa and the strong ferromagnetism in Co_2FeGa.