Room-temperature voltage-controlled spin-orbit torques in perpendicular 2DEG/Ti/CoFeB heterostructure

Two-dimensional electron gas (2DEG) emerged at the oxide interface has aroused great interest for its many fascinating properties, such as high mobility (μ), superconductivity, ferromagnetism, and strong Rashba spin-orbit coupling (SOC). The large Rashba-Edelstein effect and its inverse effect have been explored in 2DEG by using spin-torque ferromagnetic resonance (ST-FMR) and spin-pumping techniques. However, the 2DEG sandwiched between oxides requires state-of-art material engineering and limits its device design, in which direct contact of functional layer with 2DEG cannot be achieved. Here, we successfully created 2DEG at SrTiO₃ interface by utilizing the argon ions (Ar⁺) irradiation. Subsequently, the perpendicular magnetized Ti/CoFeB/MgO multilayers have been deposited on top of the 2DEG. The transmission electron microscopy (TEM) image shows the sharp interfaces and negligible inter-diffusion between layers in the 2DEG/Ti/CoFeB/MgO heterostructure. Gate voltage (V_g) dependence of longitudinal resistance (R_xx) and carrier density (n_H) at T = 300 K for the 2DEG/SiO₂ sample indicates that V_g can efficiently manipulate oxygen vacancies (OV). The magnetoresistance (ΔR_xx) at different angles (θ_H) for 2DEG/Ti/CoFeB/MgO heterostructure at T = 10 K exhibits the 2DEG characteristic. The sign change of ΔR_xx suggests that the magnetic field (H)-induced transition of interaction between the electrons and the Kondo-shielded magnetic impurities. The first (V_1f) and second (V_2f) harmonic Hall voltage at various V_g and the corresponding damping-like effective field (H_L), field-like effective field (H_T), and effective spin-torque efficiency (θ_‖,⊥) fitted from V_2f reveal that a large modulation of SOT about 550% has been achieved via V_g in 2DEG/Ti/CoFeB/MgO heterostructure. The voltage-controlled SOT in 2DEG opens the way for a new generation of spintronics devices.