Origin of the magnetic ground state developed upon Si, Ge, and Sb-substitution at Sn site in Fe2TiSn

Abstract

A nonmagnetic full Heusler alloy, Fe2TiSn, was substituted with Si, Ge, and Sb at the Sn site with a primary aim of investigating the physical properties of these compositions that are much anticipated to result in a high thermoelectric power factor and generate a half-metallic ground state. The X-ray diffraction (XRD) study carried out using the synchrotron source confirms the solubility limit of substituent atoms to be a mere 5% for Si and Ge and 60% for Sb that results in a pure L21 Heusler phase. Rietveld refinement of the XRD profiles yields the lattice parameters. Despite the fact that chemical substitution should lead to atomic disorder and an increase in the scattering of charge carriers, resistivity measurements show a significant decrease in the magnitude with as little as 5% substitution of Sn by Si or Ge. The weak localization present in Fe2TiSn seems to drastically reduce in the substituted compositions, and the long range magnetic order seems to affect the transport of the charge carriers. The origin of magnetic interactions is investigated using extended X-ray absorption fine structure spectroscopy. The changes in the local crystal structure in terms of the Fe–Fe bond distance are determined. The inference drawn from the experimental study is further complemented with exchange coupling parameter, Jij, and orbital projected density of states calculations, thus presenting an overall understanding of the origin of magnetic interactions in these technologically relevant compositions.