The study on spin-orbit torque using metallic disordered atomic structure of metallic glass

摘要

Large spin-charge conversion in metastaole disordered atomic structure of metallic glass was reported recently. The anomalous temperature dependence of inverse spin-Hall effect can be explained by the phonon skew scattering contribution due to the nature of metastable atomic structure. However, charge-spin conversion as well as spin-orbit torque using metallic glass has never been studied so far. In this study, we focused on spin-orbit torque using Pd-Si binary alloy metallic glass which is known to show large glass forming ability.Figure 1 shows schematic illustration of this study. Spin current generated by charge-spin conversion in nonmagnetic metallic glass layer injects into ferromagnetic layer and exerts spin-orbit torque. Spin-orbit torque ferromagnetic resonance measurement was performed to evaluate charge-spin conversion efficiency quantitatively. Figure 2 shows typical ferromagnetic resonance spectrum observed for Si / SiO_2 sub. / Pd-Si (5) / Ni-Fe (4) / Al_2O_3 (3) sample (thickness is in nm). The signal is fitted by summation of symmetric and anti-symmetric Lorentzian function as shown in solid curves in the figure. Effective spin-Hall angle was evaluated to be 0.20 ±0.03, which is obtained by modulation of ferromagnetic resonance linewidth induced by direct current. Charge-spin conversion efficiency is found to be enhanced by a factor of ~10 compared with Pd, whereas electrical resistivity is increased by a factor of only ~3. Detailed experimental results will be discussed in the presentation.