Effect of the structural disorder and short-range order on the electronic structure and magnetic properties of the Fe$_2$VAl Heusler alloy

The Fe$_2$VAl Heusler alloy is of great interest because ab initio calculations predict the absence of magnetization in it and a half-metal behavior with a pseudogap at the Fermi level. At the same time, experimental data (low-temperature specific heat, electrical resistivity, and magnetic properties) show that it is difficult to achieve such characteristics, and Fe$_2$VAl samples usually have the characteristics of a poor magnetic metal. Ab initio calculations have been performed for ordered and disordered (Fe$_{1-x}$V$_x$)$_3$Al Heusler alloys with $x=0.33$. It has been shown that the alloy in a structurally ordered state ($L2_1$ structure) is a half-metal with a deep pseudogap at the Fermi level and does not have magnetization. At the same time, antisite defects in the iron and vanadium sublattices of the disordered alloy ($D0_3$ structure) lead to an increase in the conductivity and to the appearance of spin polarization and magnetization of $(2.1\pm0.1)\mu_{\mathrm{B}}$/f.u. The short-range order in the disordered phase has been generated by increasing the concentration of clusters characteristic of the bcc structure of $\alpha$-Fe, which results in an increase in the magnetization to $(2.5\pm0.1)\mu_{\mathrm{B}}$/f.u.