We define Δ V ASP as the amplitude of the symmetric Lorentzian fitting of Δ V. Although, the symmetric ASP component still contains contributions from both IEE and AMR, we can determine that our signal is largely dominated by IEE, since IEE signal is odd under magnetization reversal and AMR is even under magnetization reversal 23 (see the supplementary material). 22 We first separate the symmetric ASP component from the asymmetric component by the Lorentzian fitting. We can analyze their contributions by fitting analysis the IEE signal has only symmetric Lorentzian shape and the AMR signal has both symmetric and asymmetric Lorentzian shape. 9 Δ V is mainly from the sum of the voltage coming from IEE and anisotropic magnetoresistance (AMR). Since the ISHE is negligible in our device, the spin pumping signal is mainly caused by the IEE. We detect the generated electric voltage via IEE at the maximum A-FMR field angles θ = 45 ° and − 135 °, as shown in Fig. The generated spin current is converted to a charge current at the interface between Cu and Bi 2O 3 via IEE. The A-FMR in the Ni layer generates spin current into the Cu layer by the ASP. 19,20 The schematic illustration of our device is shown in Fig. Consequently, the generated spin current is converted to charge current at the interface via IEE. The SAW excites A-FMR, i.e., the precessional magnetization dynamics in a bottom Ni layer, which causes a diffusive spin current pumped into the Cu/Bi 2O 3 Rashba interface. We fabricated a Ni (10 nm)/Cu (20 nm)/Bi 2O 3 (20 nm) trilayer stripe of 49.2 × 276 μm 2 by using electron beam evaporation and photolithography. 8,10 The distance between an IDT and reflector gratings d is set to d = 7.2 μm, which is integer multiple of λ SAW. 18 With the velocity of SAW on LiNbO 3 v SAW = 3440 m/s, 8 the resonance frequency of SAW f SAW can be calculated as f SAW = v SAW / λ SAW = 2.86 GHz. The period of the IDT gratings gives the wavelength of the SAW λ SAW = 1.2 μm. After lithography, we deposited Ti (5 nm) and Au (20 nm) using a thermal evaporation for IDTs and reflectors.
Reflector gratings comprise metallic wires with the same width and the distance between the closest gratings. The dimensions of metallic electrodes in all IDTs are 300 nm in width, 25 nm in thickness, and the distance in-between metallic electrodes in all IDTs is 300 nm. For the generation of SAWs, we used a LiNbO 3 substrate on which we fabricated IDTs and reflector gratings using electron beam lithography.
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