Investigation of atomic anti-site disorder and ferrimagnetic order in the half-metallic Heusler alloy Mn₂V Ga

Abstract

The band structure calculation for the compound Mn(2)VGa carried out using the plane wave self-consistent field package with generalized gradient approximation shows that the compound is nearly half-metallic at the equilibrium lattice parameter. However, theoretical investigations have shown that a certain percentage of atomic anti-site disorder can destroy the half-metallic nature of the sample. Hence it is important to quantify the site disorder in these systems. We have deduced the percentage of atomic anti-site disorder from the refinement of the higher angle room temperature (300 K) neutron diffraction (ND) pattern and it was observed to be roughly 8% in our sample. The field variation of resistance recorded at different temperatures shows a positive slope at low temperatures and a negative slope at higher temperatures, indicating the half-metallic character at low temperatures. The ab initio calculations predict a ferrimagnetic ground state for this system. The analysis of the magnetic structure from ND data measured at 6 K yields magnetic moment values of 1.28 μ(B) and -0.7 μ(B) for Mn and V, respectively, confirming the ferrimagnetic ordering.

Neutron diffraction and ab initio studies on the fully compensated ferrimagnetic characteristics of Mn2V1−x Co x Ga Heusler alloys

“…which is close to the S-P value. The obtained moment value is in agreement with the earlier report [18].…”

“…Earlier ND studies showed that Mn 2 VGa alloy crystallizes in the cubic L2 1 structure [18]. Therefore in our previous report on the structural and magnetic properties of the Mn 2 V 1−x Co x Ga (x = 0, 0.25, 0.5, 0.75, 1) alloys, Rietveld refinement of XRD patterns was carried out by assuming the L2 1 structure.…”

Near total magnetic moment compensation with high Curie temperature in Mn2V0.5Co0.5Z (Z = Ga,Al) Heusler alloys

“…But for the A2 disorder, all three scattering terms would become equal causing the absence of both the superlattice reflections. However the earlier report on the neutron diffraction studies of Mn 2 VGa alloy has shown the presence of huge superlattice reflections even though they were absent in the XRD pattern [19]. They attributed the lack of these peaks in the XRD pattern to the similar atomic scattering factors of x-ray for the elements Mn,V and Ga.…”

“…is comparable with the earlier reported value of 1.85 µ B /f.u. [19]. The small deviation of experimental magnetic moments from the S-P value could be due to the atomic anti-site disorder present in the system.…”

“…Researchers have attempted to synthesize HMFCF in the bulk form by substituting Co at the Mn site of Mn 2 VZ (Z = Ga,Al) Heusler alloys. The half-metallicity and ferrimagnetic characteristics of the parent Mn 2 VGa alloy has been experimentally proven by magnetic, transport and neutron diffraction studies [18,19]. Ramesh Kumar et al have reported the compensation behavior for Mn 2−x Co x VGa for x = 1 for which the valence electron count is 24 [20].…”