Temperature Dependence of Spin-Orbit Torques Exerted by a 2DEG in CoFeB/LaTiO₃/SrTiO₃ Thin-Film Heterostructures

Rashba-type spin-orbit coupling in 2D electron gases (2DEGs) such as LaAlO₃/SrTiO₃ is of great interest for efficient charge to spin conversion. LaTiO₃/SrTiO₃ (LTO/STO) also gives rise to a 2DEG at its interface and has been shown previously to exhibit giant Rashba spin-orbit coupling. Therefore, the 2DEG arising from the LTO/STO interface is also a promising platform for demonstrating efficient charge to spin conversion. For this reason, we fabricated CoFeB/LaTiO₃/SrTiO₃ heterostructures to understand how spin currents generated in the 2DEG exert torques on a neighboring magnet as a function of temperature, where the LaTiO₃ is conductive as a result of the strain induced by the STO substrate. Spin torque ferromagnetic resonance measurements show an increasingly large damping-like torque as temperature decreases. Second harmonic Hall measurements support this temperature dependence, with a large damping-like torque measured. We also observe a unidirectional magnetoresistance resulting from nonreciprocal charge transport in the 2DEG, confirming the large Rashba spin-orbit coupling. Our results provide more information on how the 2DEG at the LTO/STO interface exerts spin-orbit torques on neighboring magnetic layers.