Investigations on Selected Cobalt-based Quaternary Heusler Alloys for Spintronic Applications

Abstract

Systematic experimental and theoretical investigations have been conducted to explore the structural, magnetic, and electronic properties of bulk Co2-xMnVxAl (x = 0.0, 0.25, and 0.5) and Co2-xFeTixAl (x = 0.00, 0.25, 0.50, 0.75, and 1.00) Heusler alloys. These investigations explored the impact of V and Ti substitution for Co in Co2-xMnVxAl and Co2-xFeTixAl Heusler alloys, respectively. These studies demonstrated a viable approach to attain 100% spin polarization (P) by tuning the minority spin bandgap at Fermi level (EF) while retaining the ferromagnetic character. After achieving high P, the next step was to comprehend impact of P on Gilbert damping constant (α) to ascertain the efficiency of the free ferromagnetic layer in magnetoresistance devices. In this regard, off-stoichiometric compositions of the promising Co2FeGa0.5Ge0.5 Heusler alloy was considered. Off-stoichiometric Co1.77Fe1.23Ga0.56Ge0.44 Heusler alloy thin film was heat treated at different annealing temperature (Tan) to improve its atomic ordering. Effect of improvement in atomic ordering on intrinsic contribution to  and its correlation with P was then analysed. This investigation revealed remarkably low α in the Co1.77Fe1.23Ga0.56Ge0.44 film annealed at Tan = 600 ℃. It also clarified that atomic disorder significantly influences α, and α decreases with increasing P resulting from improved atomic ordering. To assess the potential of the spin-orbit torque mechanism for achieving energy-efficient switching of the magnetization in the free ferromagnetic layer, spin mixing conductance (𝑔eff↑↓) across the interface of Co2.06Fe0.99Ga0.53Ge0.42/Pt bilayers was evaluated. Furthermore, a detailed investigation was carried out to assess the effect of ultrathin Cu, Ni, Ru, Ta, and Cr insertion layers on 𝑔eff↑↓ of Co2.06Fe0.99Ga0.53Ge0.42/Pt bilayer film after ensuring that there are no insertion-layer-induced changes in the atomic structure of the Pt layer.