Spin to Charge Conversion at the Conducting TiO₂Surface

Abstract

The insulating TiO2 (100) surface was transformed into conducting state after Ar+ ion irradiation, which is due to the formation of oxygen vacancies. The thickness of the conducting layer is about 5 nm according to the transmission electron microscopy, and its surface with a spatial asymmetry hosts Rashba spin–orbit coupling. A permalloy (Py) thin film was then deposited onto the irradiated TiO2 by magnetron sputtering. In this Py/TiO2 sample, an inverse Rashba–Edelstein effect (IREE) induced voltage was detected, which converted the spin current injected from Py by spin pumping into the charge current (voltage) due to the spin–orbit coupling. Through the two‐step measurement with sample flipping, the voltages of the IREE at different microwave frequency and power are separated from the spin rectification effect in the Py films. The inverse Rashba–Edelstein length λIREE, which is used to characterize the spin‐to‐charge current conversion efficiency, is calculated to be about 0.58 nm in this work. From the similarity of the parameter, we may conclude that the effect is universal in these two dimensional electron gas hosted by the surfaces or interfaces.

Spin Rectification dc Voltage Spectra via Sweeping Frequency

“…Further studies have even found that dc current and dc voltage can be generated by the rectification effect of high‐frequency magnetization dynamics. This so‐called spin rectification effect (SRE), which is due to nonlinear coupling between an oscillating current and an oscillating resistance in magnetic structures, provides a novel technique for the study of magnetization dynamics by electrical detection. Due to its high sensitivity and feasibility, the SRE has been widely employed to study ferromagnetic resonance (FMR), spin wave resonance, and domain‐wall resonance in different ferromagnetic materials.…”