Abstract
Magnetic moment, exchange interaction and Curie temperature (TC) have been calculated for Co2TiGa and Co2FeGa by a first-principles density functional calculation combined with a linear response method. The exchange interaction is dominated by Co-Co pairs in Co2TiGa while that of Co2FeGa is mainly contributed by Fe-Co pairs. Based on the mean field multiple-sublattices model, the estimated TC 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 (aexp.), the moment per formula unit mf.u. changes from 0.43 μB to 1.0 μB and TC increases from 27 K to 142 K in Co2TiGa. However, mf.u. increases slightly from 4.98 μB to 5.40 μB while TC decreases from 1330 K to 1190 K with increasing a from 95% to 105% of aexp. in Co2FeGa. These different volume dependences of TC are ascribed to the weak ferromagnetism in Co2TiGa and the strong ferromagnetism in Co2FeGa.
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