Itinerant magnetism, electronic properties and half-metallicity of Co2ZrSn and Co2HfSn Heusler alloys

Half-metallic ferromagnetic alloys are attracting considerable interest for their potential applications in spintronic devices. Co-based Heusler alloys are considered to be promising half-metallic compounds as they combine suitable magnetic, electronic and transport properties with compositional versatility and high thermal stability. In this work, Co2ZrSn and Co2HfSn Heusler alloys were studied by combining experimental and ab-initio investigations in order to accurately estimate their electronic density of states in proximity of the Fermi level and to determine their magnetic and electronic properties. Magnetization measurements, performed between 2 K and 550 K, suggest for both alloys a gradual transition from localized ferromagnetism to weak itinerant ferromagnetism with increasing temperature, well described by a simple mean field model up to the Curie temperature (454 K in Co2ZrSn and 432 K in Co2HfSn) and beyond. Ab-initio calculations were performed using two exchange-correlational functionals, PBE and PBE optimized for solids (PBEsol), in order to assess the reproducibility of theoretical results. Overall, band structures and density of states (DOS) diagrams indicated, for both compounds, the presence of a half-metallic band gap in the minority spin sub-band. The dependence of magnetic moments and band gap width on cell parameters is discussed in detail. Calculated magnetic moments and cell parameters satisfactorily match the experimental results obtained in this work and previously reported in the literature.