  In this work, we report the successful synthesis of a Fe-based novel
half-metallic quaternary Heusler alloy FeMnVGa and its structural, magnetic and
transport properties probed through different experimental methods and
theoretical technique. Density functional theory (DFT) calculations performed
on different types of structure reveal that Type-2 ordered structure (space
group: F-43m, Ga at 4a, V at 4b, Mn at 4c and Fe at 4d) possess minimum energy
among all the ordered variants. Ab-initio simulations in Type 2 ordered
structure further reveal that the compound is half-metallic ferromagnet (HMF)
having a large spin-polarization (89.9 %). Neutron diffraction reveal that the
compound crystalizes in disordered Type-2 structure (space group: Fm-3m) in
which Ga occupy at 4a, V at 4b and Fe/Mn occupy 4c/4d sites with 50:50
proportions. The structural disorder is further confirmed by X-ray diffraction
(XRD), extended X-ray absorption fine structure (EXAFS),57Fe Mossbauer
spectrometry results and DFT calculations. Magnetisation studies suggest that
the compound orders ferromagnetically below TC ~ 293 K and the saturation
magnetization follows Slater-Pauling rule. Mossbauer spectrometry, along with
neutron diffraction suggest that Mn is the major contributor to the total
magnetism in the compound consistent with the theoretical calculations. First
principle calculations indicate that spin-polarization remain high (81.3 %)
even in the presence of such large atomic disorder. The robustness of the HMF
property in presence of disorder is a quite unique characteristic over other
reported HMF in literature and make this compound quiet promising for
spintronics applications.
