Electronic structure, magnetism and disorder in the Heusler compound Co₂TiSn

Polycrystalline samples of the Heusler compound Co₂TiSn have been prepared and studied using bulk techniques (x-ray diffraction and magnetization) as well as local probes (¹¹⁹Sn Mössbauer spectroscopy and ⁵⁹Co nuclear magnetic resonance spectroscopy) in order to determine how disorder affects the half-metallic behaviour and also to establish the joint use of Mössbauer and NMR spectroscopies as a quantitative probe of local atom ordering in these compounds. Additionally, density functional electronic structure calculations on ordered and partially disordered Co₂TiSn compounds have been carried out at a number of different levels of theory in order to simultaneously understand how the particular choice of DFT scheme as well as disorder affects the computed magnetization. Our studies suggest that a sample which seems well ordered by x-ray diffraction and magnetization measurements can possess up to 10% of antisite (Co/Ti) disordering. Computations similarly suggest that even 12.5% antisite Co/Ti disorder does not destroy the half-metallic character of this material. However, the use of an appropriate level of non-local DFT is crucial.