[7a-C18-1~9] 10.2 Fundamental and exploratory device technologies for spin

▲ [7a-C18-3] Inverse spin Hall effect in surface oxidized Cu layer in Cu-based lateral spin valves

〇Akiyoshi Yamada¹, Taisei Ariki², Kohei Ohnishi², Yuichiro Ando¹, Takashi Kimura², Masashi Shiraishi¹ (1.Kyoto Univ., 2.Kyushu Univ.)

Keywords:Inverse spin Hall effect, Cu Oxide, spin valves

A significant enhancement of the spin Hall angle in copper (Cu) film due to surface oxidization was detected by spin-transfer-torque ferromagnetic resonance (STT-FMR) measurements.[1] Such an enhancement of the SOC without employing heavy metals is a promising way to realize further enhancement of spin-charge interconversion efficiency using the spin Hall effect (SHE) and the inverse spin Hall effect (ISHE). However, a microscopic origin of the enhancement of the spin Hall angle is still not fully understood. In this study, we investigated the ISHE in the oxidized Cu layer by using electrical spin injection and detection in lateral spin valves (LSVs). Cu based LSVs equipped with two CoFeAl (13 nm in thick) ferromagnetic electrodes and a naturally oxidized Cu (Cu_xO) electrode (30 nm in thick ) for the ISHE measurements were fabricated, as schematically shown in the inset of Fig. 1(a). [2] After fabrication of the CoFeAl electrodes, a cross-shaped Cu film was deposited to form the Cu channel and the Cu_xO electrode, simultaneously. Then the LSVs were covered by a 30 nm thick SiO₂ layer except for the CuxO electrode region, to form a naturally oxidized layer only in the specified region. Clear nonlocal spin signals were detected at various temperatures from 3.4 to 300 K as shown in Fig. 1(a), indicating considerable spin accumulation in the Cu channel. The nonlocal voltage under application of an external magnetic field along y-direction shown in the inset of Fig. 1(b) revealed that the magnetization was sufficiently aligned along y-direction at ±2000 Oe. However, no clear ISHE signals were obtained at 3.4 K. The considerably small ISHE signal might be due to insufficient spin current injected into the Cu_xO layer or unexpectedly small spin Hall angle in our Cu_xO layer. In the presentation, we discuss the precise origin of the small ISHE signals and results of the ISHE signals with different oxidation procedures or device structures.