Investigation of magnetotransport properties on Fe<sub>2</sub>TiSn<sub>1-x</sub>Sb<sub>x</sub> with 0 ≤ x ≤ 0.6 are presented in this paper. The substitution of Sb in place of Sn decreases the antisite disorder as evident from X ray diffraction patterns as well as from transport properties measurement. The much-disputed upturn in low temperature electrical resistivity of Fe<sub>2</sub>TiSn has been demonstrated to be a result of weak localization induced by antisite disorder. With increased Sb substitution (≥ 25%) the metallic transport behaviour of Fe<sub>2</sub>TiSn changes to semiconductor-like. At low temperature the carrier transport in such compositions occur via variable range hopping mechanism. Moreover, a systematic increase in the anomalous Hall voltage is observed with increasing Sb content, attributable to a side jump or Berry phase curvature effect. Electrical resistivity in the high temperature regime hints towards half metallicity of the system. Our Ab-initio electronic structure calculations using the GGA formalism further supports the results of our magnetotransport study.
Band structure tailoring has been a great avenue to achieve the half-metallic electronic ground state in materials. Applying this approach to the full Heusler alloy Fe2TiSn, Cr is introduced systematically at Ti site that conforms to the chemical formula $${\text{Fe}}_{2} {\text{Ti}}_{{1 - x}} {\text{Cr}}_{x}$$ Fe 2 Ti 1 - x Cr x Sn. Compositions so obtained have been investigated for its electronic, magnetic, and electrical transport properties with an aim to observe the half-metallic ferromagnetic ground state, anticipated theoretically for Fe2CrSn. Our experimental study using synchrotron X-ray diffraction reveals that only compositions with $$x \le$$ x ≤ 0.25 yield phase pure L2$$_1$$ 1 cubic structures. The non-magnetic ground state of Fe2TiSn gets dramatically affected upon inclusion of Cr giving rise to a localized magnetic moment in the background of Ruderman–Kittel–Kasuya–Yosida (RKKY) correlations. The ferromagnetic interactions begin to dominate for x = 0.25 composition. Results of its resistivity and magnetoresistance (MR) measurement point towards a half-metallic ground state. The calculation of exchange coupling parameter, $$\hbox {J}_{{ij}}$$ J ij , and orbital projected density of states that indicate a change in hybridization between 3d and 5p orbital, support the observations made from the study of local crystal structure made using the extended X-ray absorption fine structure spectroscopy. Our findings here highlight an interesting prospect of finding half-metallicity via band structure tailoring for wide application in spintronics devices.
With an aim to control the anti-site disorder between Fe and Ti atoms in the full Heusler alloy, FeTiSn, we substitute a small percentage of Ti at Fe site to form the FeTiSn () series. Using the incident x-rays tuned to the Fe K-edge absorption energy, we record the high resolution synchrotron x-ray diffraction profiles and unambiguously show the reduction in anti-site disorder. In particular, the Fe–Ti anti-site disorder decreases up to an excess Ti content of 0.07; further increase of Ti content leads to disorder between Ti–Sn sites. Detailed characterization vis-á-vis the excess Ti content has been carried out in terms of its thermal and electrical transport, and magnetic properties. Signatures of strong spin fluctuation are seen in all the physical properties reported here. The much disputed high value of the Sommerfeld constant has been shown to be a resultant of such strong spin fluctuations, thus ruling out the long standing controversy of heavy fermionic nature of FeTiSn. Magnetization and the Seebeck coefficient show clear dependence on the disorder. Both dc and ac magnetic measurements reveal the low temperature superparamagnetic nature of this system, comprising of large magnetic clusters 3 nm in size.
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