First-principles study of magnetic and spin-dependent transport properties of Mn 2 V Z ( Z = Al, Ga) with negative spin polarization using a disordered local moment approach at finite temperatures

First-principles studies were performed on two Mn-based ferrimagnetic Heusler compounds with L 2 1 and B 2 structures, that is, Mn 2 V Z ( Z = Al or Ga). The aim was to investigate their magnetic properties, electronic structures, and spin-resolved longitudinal conductivity at both zero and elevated temperatures. Density functional theory and functional integral theory were used. This approach incorporates transverse spin fluctuations through a disordered local moment method and the coherent potential approximation. In most cases, the calculated theoretical Curie temperatures were lower than the experimental values. Alloys with a B 2 structure exhibit higher Curie temperatures compared to compounds with an L 2 1 structure. Calculations of the temperature dependence of the density of states (DOS) indicate that the half-metallic electronic structure collapses due to self-energy effects that reflect spin disorder at nonzero temperature. In other words, transverse spin fluctuations are renormalized in the electronic structure. However, the spin-resolved longitudinal conductivities demonstrated an improved spin polarization, particularly for Mn 2 VGa with an L 2 1 structure. The competition between the half-metal-to-normal-metal transitions, which are caused by a modification of the DOS, and scattering coming from spin-disorder explains this behavior of conductivities. Both of these effects are induced by transverse spin fluctuations. Additionally, the results show that the spin polarizations defined in terms of the conductivities and of the DOS do not follow the same trends at T > 0 . Their temperature dependencies are not the same, particularly for the L 2 1 structures, although they are related to each other. Finally, the total energy landscape of the paramagnetic state was calculated using the fixed spin moment method to investigate the strength of the longitudinal spin fluctuations. These results suggest that the alloys may exhibit strong longitudinal spin fluctuations.