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 Ni${}_2$MnSn 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${}_x$)${}_2$MnSn 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${}_x$)${}_2$MnSn Heusler alloys. The results for the reference Ni${}_2$MnSn Heusler alloy agree well with a previous theoretical study of E. Sasioglu, L. M. Sandratskii, and P. Bruno, Phys. Rev. B 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${}_x$)${}_2$MnSn 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.

Figure 1

The Mn-Mn exchange interactions in the Ni${}_2$MnSn Heusler alloy as functions of the relative interatomic distance $d/a$ where $a$ is the fcc lattice parameter: (a) the effective interactions $J_{ij}$ calculated from Eq. (2), (b) the bare interactions $J_{ij}^{\mathrm{bare}}$ defined by Eq. (3). The cases of ambient pressure (open circles) and the pressure corresponding to the 3% reduction of the lattice constant (filled circles) are shown.

Figure 2

The concentration-dependence of Curie temperatures (RPA) for (Ni${}_{1-x}$,Pd${}_x$)${}_2$MnSn alloys for ambient pressure and for the pressure corresponding to the reduction of the alloy lattice constant by 3%. Model assumes electron correlations on Ni sites treated in the framework of the LSDA $+$ U method.

Figure 3

The concentration-dependence of Curie temperatures (RPA) for (Ni${}_{1-x}$,Cu${}_x$)${}_2$MnSn alloys for ambient pressure and for set of pressures corresponding to indicated reductions of the alloy lattice constant. Model assumes electron correlations on Ni sites treated in the framework of the LSDA $+$ U method.

Figure 4

The temperature-dependence of the resistivity of the (Ni${}_{1-x}$,Pd${}_x$)${}_2$MnSn alloys for ambient pressure (full symbols) and the pressure corresponding to the reduction of the alloy lattice constant by 3% (open symbols): (a) $x=0$, (b) $x=0.5$, (c) $x=1$.