[26p-E201-1~12] 10.2 Fundamental and exploratory device technologies for spin

▲ [26p-E201-2] Determination of orbital torque efficiency in ferromagnet/Cu/Oxide thin films

〇Junyeon Kim¹, Dongwook Go^2,3, Daegeun Jo⁴, Hyun-Woo Lee⁴, YoshiChika Otani^1,5 (1.RIKEN, 2.PGI-IAS, 3.Univ. Mainz, 4.POSTECH, 5.ISSP, Univ. Tokyo)

Keywords:orbital torque, Spin manipulation, Rashba effect

The utilization of orbital angular momentum (OAM) provides a promising path for low-power-consumption spin manipulation. Recent studies show that an interaction between Cu and oxygen at an interface/surface such as Cu/Al₂O₃ leads to strong OAM polarization through the orbital Rashba effect, giving rise to a non-trivial torque (orbital torque, OT), 10-100 times more efficient than the conventional spin torque by the spin conversion [1,2]. Nevertheless, we still encounter plenty of issues to be addressed for further spintronic applications because of unconventional features of the OT.
We studied the OT for CoFe/Cu/OX (OX=MgO, SiO₂, TiO₂) ultrathin films. All the samples are prepared by the electron beam evaporation technique and photo-lithography. We measured the OT using the spin torque ferromagnetic resonance (ST-FMR) technique and found sizeable OT for all films (Fig. 1). Nonetheless, the magnitude of the OT varies depending on the capped oxide layer, and maximum OT appears for the SiO₂ capped films. Considering pronounced OAM polarization at the Cu/OX interfaces, we speculate that the different Cu-oxygen interaction depending on the capped layer provides a critical role in determining the OT efficiency. Further information will be given during the meeting.
[1] J. Kim et al., Phys. Rev. B, 103, L020407 (2021).
[2] D. Go et al., Phys. Rev. B, 103, L121113 (2021).