Pressure dependence of Curie temperature and resistivity in complex Heusler alloys

Using first-principles electronic structure calculations, we have studied the dependence of the Curie temperature on external hydrostatic pressure for random Ni₂MnSn Heusler alloys doped with Cu and Pd atoms, over the entire range of dopant concentrations. The Curie temperatures are calculated by applying random-phase approximation to the Heisenberg Hamiltonian whose parameters are determined using the linear response and multiple scattering methods, based on density-functional theory. In (Ni_1-x,Pd_x)₂MnSn alloys, the Curie temperature is found to increase with applied pressure over the whole concentration range. The crossover from the increase to the decrease of the Curie temperature with pressure takes place for Cu concentrations larger than about 70% in (Ni_1-x,Cu_x)₂MnSn Heusler alloys. The results for the reference Ni₂MnSn Heusler alloy agree well with a previous theoretical study of E. Sasioglu, L. M. Sandratskii, and P. Bruno, Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.71.214412 71, 214412 (2005) and also reasonably well with available experimental data. Results for the spin-disorder-induced part of the resistivity in (Ni_1-x,Pd_x)₂MnSn Heusler alloys, calculated by using the disordered local moment model, are also presented. Finally, a qualitative understanding of the results, based on Anderson's superexchange interaction and Stearn's model of the indirect exchange interaction between localized and itinerant d electrons, is provided.