11:45 AM - 12:00 PM
▼ [20a-E216-11] Crystallinity dependence of spin-orbit torque in electrically-conductive RuO2
Keywords:Spin-current, Spin-orbit torque
Spin-orbit (SO) torque generated by the spin Hall effect (SHE) or Rashba-Edelstein effect(REE) is expected to effectively perform magnetization switching in an adjacent ferromagnet. To increase conversion efficiency or functionality, recently there has been interest in synthesizing SO materials such as oxides. CuOX was successfully observed to have finite spin torque efficiency through oxidation from pure Cu, which has negligible SO interaction interestingly. However, the mechanism for this generation in oxides is still controversial. Basically, a finite SO interaction could generate the SO torque via the SHE or the REE, and gives different types of spin relaxation in different crystallinities in the materials .To unveil the systematic mechanism of the SO torque generation in SO oxides, we have studied polycrystalline and epitaxial electrically-conductive RuO2 based on the above background by means of spin-torque ferromagnetic resonance in this study. First of all, we deposited two kinds of 10 nm-thick RuO2 film onto Al2O3(11-02) and Si/SiO2 substrates by using reactive magnetron RF sputtering with a pure Ru target with 0.06 Pa-oxygen partial pressure. The substrate temperature was increased to 400 °C during sputtering for epitaxial RuO2. After the deposition, we checked the crystallinity as shown in Figs. (a), (b), and (c) by means of reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD), and deposited Co(5nm)/AlOX(2nm) in-situ onto the RuO2 layer. Finally, we prepared devices for ST-FMR measurement by photo-lithography and Ar-ion milling. In the measurement, we surprisingly found an enhancement of the spin-torque efficiency ξST in the epitaxial RuO2 (ξST = 14.3 ± 2.0 %) compared with the polycrystalline film (ξST =10.2 ± 1.7 %). We discuss the detailed mechanism for the enhancement in this meeting.