First-principles study of magnetic and spin-dependent transport properties of Mn2VZ (Z = Al, Ga) with negative spin polarization using a disordered local moment approach at finite temperatures

TL;DR

This study uses first-principles calculations to explore the magnetic and spin transport properties of Mn2VZ (Z=Al, Ga) Heusler compounds, revealing temperature-dependent electronic structures and spin polarization effects.

Contribution

It introduces a disordered local moment approach combined with DFT to analyze finite-temperature magnetic and transport properties of Mn-based Heusler alloys, highlighting the inconsistency of half-metallicity at finite temperatures.

Findings

Higher Curie temperatures in B2 structures compared to L21.

Collapse of half-metallic electronic structure at finite temperatures.

Enhanced spin polarization in Mn2VGa with L21 structure.

Abstract

First-principles studies were performed on two Mn-based ferrimagnetic Heusler compounds with L21 and B2 structures, that is, Mn2VZ (Z = Al or Ga). The aim was to investigate their magnetic properties, electronic structures, and spin-resolved longitudinal conductivity at finite temperatures. Density functional theory (DFT) and functional integral theory were used. This approach incorporates transverse spin fluctuations through a disordered local moment method and the coherent potential approximation. In all cases, the calculated theoretical Curie temperatures were lower than the experimental values. Alloys with a B2 structures exhibit higher Curie temperatures compared to compounds with an L21 structures. Calculations of the temperature dependence of the density of states (DOS) indicate that the half-metallic electronic structure collapses owing to the renormalization of transverse spin fluctuations at a finite temperatures. However, the spin-resolved longitudinal conductivities demonstrated an improved spin polarization, particularly for Mn2VGa with an L21 structure. This result contradicts predictions based on the temperature-dependent DOS. The competition between the metallic transitions, which are caused by a modification of the DOS, and scattering coming from spin-disorder explains this phenomenon. Both of these effects are induced by transverse spin fluctuations. Additionally, the results show that half-metallicity, as defined by the DOS or conductivity, is inconsistent at finite temperatures. 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.