Modulated switching current density and spin-orbit torques in MnGa/Ta films with inserting ferromagnetic layers

We report modulated switching current density and spin-orbit torques (SOT) in MnGa/Ta films with inserting very thin Co₂FeAl and Co layers. Ferromagnetic coupling has been found in MnGa/Co₂FeAl/Ta, resulting in a decreased effective anisotropy field. On the contrary, in MnGa/Co/Ta, antiferromagnetic coupling plays a dominant role. The switching current density J_c in MnGa/Ta is 8.5 × 10⁷ A/cm². After inserting 0.8-nm-thick Co₂FeAl and Co, theJ_c becomes 5 × 10⁷ A/cm² and 9 × 10⁷ A/cm², respectively. By performing adiabatic harmonic Hall voltage measurements, it is demonstrated that the inserted Co₂FeAl layer has mainly enhanced the field-like torques, while in MnGa/Co/Ta the damping-like torques have been enhanced. Finally, the enhanced spin Hall effect (SHE) has also been studied using the spin Hall magnetoresistance measurement. The modulated J_c and SOT are ascribed to the combination of magnetic coupling, Rashba effect and SHE at the interfaces.