Tailoring of the magneto-transport properties, half-metallicity and vacancy-induced structural disorder in Co2ZrSn for spintronics

In spintronics, the ability of half-metallic ferromagnets (HMF) to achieve 100 % spin-polarization is essential to develop next-generation magnetic tunnel-junctions. In this work, the effect of Co-vacancy point-defects on the half metallicity and magneto-transport properties of the promising Co2ZrSn Heusler alloy are studied. The alloy is synthesized via several processing routes, involving different cooling rates and degrees of metastability. Polycrystalline samples are analyzed by synchrotron X-ray diffraction. The occupancy and the disorder of Co-sites in the crystal structure, evaluated by Rietveld refinement, are responsible for significant changes in such properties, such as the shrinking of the half-metallic band-gap, reduction of saturation magnetization and electrical conductivity. The electrical resistivity, R, measured at low temperature (below 300 K) show a change of regime from a T2 to a Tx dependency, which is interpreted as a change of electron scattering mechanisms due to a crossover from a half-metallic to an itinerant ferromagnetic state. The thermoelectric figure of merit zT is here experimentally determined for the first time. Ab-initio calculated properties, both on pristine and defective structures, are in quantitative agreement with experiments and linearly scale with the Co-site occupancy, which does not affect the half-metallic ground state. Lastly, phonon and thermal properties are discussed in the framework of Slack's model..