We have been studying a broad class of relevant physical properties of Heusler alloys, in particular, their magnetic structure as a function of temperature and disorder. We calculate magnetic moments, magnon spectra, the spin-stiffness constant, and critical (Curie) temperatures, as well as the transport properties. Besides that we investigate Heusler alloys at the hydrostatic pressure with the aim of deeper understanding of their properties. The transport properties, in particular, are very sensitive to the presence of any kind of disorder and to temperature. We therefore plan to determine not only the residual resistivity due to impurities, but also its temperature-dependence due to the spin-disorder and the transport properties in the presence of magnetic field like, e.g., anisotropic magnetoresistivity and anomalous Hall effect. All above mentioned physical properties will be calculated in the framework of a unified model based on the density-functional theory. Our approach differs from existing ones by a systematic inclusion of the effect of substitutional disorder and, first of all, by evaluating a broad class of physical properties in the framework of a unified theoretical description.
Received results:
Semi-Heusler quaternary alloys (Cu,Ni)MnSb: according to experiments the transition from the ferromagnetic state (NiMnSb) to the antiferromagnetic state (CuMnSb) gives rise to an abrupt change of the magnetic moments and resistivities at about 70 percent of Cu while the Curie temperature is a smooth function of the Cu-content. We explain this peculiar behavior by the onset of disorder in orientations of the Mn-spins. A simple account of magnetic disorder provides a good quantitative understanding of available experimental data. The origin of the observed magnetic phase transition is also discussed.
J. Kudrnovský, V. Drchal, I. Turek, and P. Weinberger: Electronic, magnetic, and transport properties and magnetic phase transition in quaternary (Cu,Ni)MnSb Heusler alloys,
Phys. Rev. B 78 (2008) 054441.
Full Heusler Ni2MnSn alloys doped with Cu- and Pd-atoms: While the magnetic moments depend only weakly on the alloy composition, the Curie temperatures exhibit strongly non-linear behavior with respect to Cu-doping in contrast to an almost linear concentration dependence in the case of Pd-doping. A detailed analysis of exchange interactions provided a deeper understanding of this problem. The dominating contribution to the temperature-dependent resistivity is due to thermodynamical fluctuations originating from the spin-disorder, which, according to our calculations, can be described reasonably well via the so-called disordered local moments model.
Calculated concentration trends of magnetic moments, Curie temperatures, spin-stiffness, as well as the temperature-dependent resistivity agree well with experiment.
S. K. Bose, J. Kudrnovský, V. Drchal, and I. Turek: Magnetism of mixed quaternary Heusler alloys: (Ni1-xTx)2MnSn (T=Cu,Pd) as a case study, Phys. Rev. B 82 (2010) 174402.
