Atomic order induced reduction of Gilbert damping constant and enhancement of half-metallicity in off-stoichiometric Co2FeGa0.5Ge0.5 Heusler alloy thin films

Abstract

The development of energy-efficient spintronic devices with enhanced magnetoresistance demands materials with low Gilbert damping constant (α) and high half-metallicity. In this study, we report a very low α in sputter-deposited off-stoichiometric Co2FeGa0.5Ge0.5 (CFGG) Heusler alloy thin films and investigate the relation between α and atomic ordering and half-metallicity. CFGG thin films with a composition of Co44.3Fe30.7Ga13.9Ge11.1 were epitaxially deposited on MgO (001) substrates by magnetron sputtering followed by in situ annealing. The density of states calculations revealed that this composition has higher half-metallicity than the stoichiometric composition, owing to Fermi energy tuning. As-deposited and 400 °C-annealed samples exhibited B2-type partially disordered structure, while annealing above 500 °C induced a L21-type ordered structure. The improvement in atomic order resulted in the reduction of α, as demonstrated by ferromagnetic resonance measurement, and enhancement in half-metallicity, as revealed by anisotropic and ordinary magnetoresistance measurements. The 600 °C-annealed samples exhibited an intrinsic α of (3.5 ± 0.3) × 10−4, the low value reported for metallic ferromagnetic materials, demonstrating the potential for its use in energy-efficient spintronic devices.