Magnetic properties and identification of Griffiths-like phase in Mn₂FeSi Heusler antiferromagnet

Materials having low magnetic moments with high spin polarization are promising for spintronic applications. Among these materials, Mn-based Heusler alloys are attractive candidates due to the antiferromagnetic alignment of Mn atoms. Theoretical calculations predict Mn2FeSi to have an inverse Heusler (XA) structure with a magnetic moment of 2 mu(B)/f.u. However, no experimental reports exist on a phase-pure composition of this material. In this study, our first principle calculations demonstrate the effect of various types of disorder on the electronic and magnetic properties of Mn2FeSi. The B2-type disorder seems responsible for forming secondary phases in stoichiometric Mn2FeSi. We verify this by conducting theoretical calculations for different configurations of the atomic disorders permissible in a Heusler phase. We substantiate our theoretical investigation with an experimental study wherein we first stabilize the phase-pure Mn2FeSi in an inverse Heusler structure by substituting Al at the Si site. Amongst the prepared Mn2FeSi1_xAlx (x = 0, 0.1, 0.15), the compositions with x = 0 and 0.15 show a clear presence of a secondary phase, identified as the beta - Mn phase with a lattice constant of 6.24 angstrom. Analysis of the back-scattered electron spectroscopy images and X-ray diffraction patterns confirm the formation of a pure Heusler phase in x = 0.1 composition. Magnetization measurements reveal an antiferromagnetic behavior in all compositions, with a N e el temperature of similar to 50 K. However, deviation from CurieWeiss law was observed for x = 0.1, suggesting competing magnetic interactions. Further investigation into the magnetic properties of this composition displays signatures of Griffiths phase, possibly caused by antisite disorder in the compound.