Unraveling the charge-to-spin conversion from 2DEGs at SrTiO₃ based interfaces

The formation of two-dimensional electron gases (2DEGs), especially the ones created at the interface of two insulating oxides [1], has led to a paradigm shift in designing the next generation materials with high charge-to-spin conversion efficiency, θ_CS for spintronics based memory devices. Here, we gain insight into the θ_CS at the 2DEGs, created on two distinct types of SrTiO₃/amorphous insulator, namely the SrTiO₃/AlN and SrTiO₃/Al₂O₃, respectively. The underlying mechanism of the contribution of oxygen vacancy that directly correlates with the θ_CS has been overlooked in these two distinct amorphous insulators, so far. We unravel the directionality of spin-torques by angular dependent ST-FMR measurements [2]. The resultant θ_CS/t , where t is the thickness of the 2DEG, is estimated to be 0.244 nm^-1 and 0.101 nm^-1 for the SrTiO₃/AlN and SrTiO₃/ Al₂O₃ systems, respectively, and they are strikingly comparable to their crystalline counterparts. Furthermore, we also observe a large direct current modulation of resonance linewidth in SrTiO₃/AlN samples, confirming its high θ_CS­ and supporting us to propose an oxygen-vacancy-enabled charge-to-spin conversion.

[1] A. Ohtomo, and H. Y. Hwang, Nature 427, 423 (2004).

[2] U. Shashank et. al., Appl. Phys. Lett. 118, 252406 (2021).