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 x 10(7) A/cm(2). After inserting 0.8-nm-thick Co2FeAl and Co, the J(c) becomes 5 x 10(7) A/cm(2) and 9 x 10(7) A/cm(2), 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.