Identification of disorder and effect of annealing on physical properties of half-metallic Fe–Ti–Sn based Heusler alloys

One notable yet typical characteristic of Heusler compounds is their susceptibility to antisite defects and disorders. Concerning this, the Fe2TiSn Heusler compound has been an exciting and disputed candidate, where the ground state properties are highly affected by antisite disorder. Attempts to manipulate the extent of the disorder via doping or substitution are well-documented. This study presents qualitative evidence for significant modification of the disorder, achievable through careful heat treatment of the compositions. Polycrystalline compositions of Fe2TiSn, Fe2Ti0.75Cr0.25Sn, and Fe2TiSn0.5Sb0.5 are investigated for its electrical transport and magnetic properties by separately investigating the samples of each composition in its “as-prepared” state and after post-annealing treatment. Temperature-dependent neutron diffraction has been recorded on the as-prepared compositions to estimate the antisite disorder in these compositions. The structural refinement of the neutron diffraction data confirms the presence of approximately 5% Fe–Ti antisite disorder in these compositions. An additional 10% Fe–Sb disorder is found to exist in Fe2TiSn0.5Sb0.5. The secondary heat treatment of all the compositions leads to a noticeable decrease in antisite disorder, which is seen to drastically affect its electrical resistivity and magnetization. These findings highlight the effectiveness of heat treatment in improving the ordering of the crystal structure of the compositions, with implications for their suitability in spintronics application.