[5p-C18-8~21] 【CS.10】10.1 & 10.2 & 10.3 Code-sharing session

▲ [5p-C18-21] Origin of Threshold Current Density for Asymmetric Magnetoresistance in Pt/Py Bilayers

〇TIAN LI¹, Sanghoon kim¹, Seung-Jae Lee², Seo-Won Lee², Tomohiro Koyama³, Daichi Chiba³, Takahiro Moriyama¹, Kyung-Jin Lee², Kab-Jin Kim^1,4, Teruo Ono^1,5 (1.Kyoto Univ., 2.Korea Univ., 3.Univ. of Tokyo, 4.KAIST, 5.CSRN)

Keywords:spintronics, magnetoresistance, magnon

An asymmetric magnetoresistance (MR) in Py/Pt bilayer has been recently reported to originate from the electron-magnon scattering due to terahertz (THz) magnon generated in a spin-flip process [1]. As the current density increases, the asymmetric MR increases linearly up to a threshold, and above the threshold it increases more rapidly. The existence of the threshold current density in the asymmetric MR implies that different mechanisms govern the asymmetric MR below and above threshold current density. To reveal the origin of the threshold behavior of asymmetric MR, we investigate the current density dependence of asymmetric MR under various magnetic fields [2]. The results demonstrate that asymmetric MR below the threshold is not affected by the external magnetic field up to 8.9 T, which is consistent with the scenario of THz magnon generation: THz magnons have an energy of a few meV, which is much larger than the Zeeman energy induced by the magnetic field of 8.9 T (~1 meV computed from gμ_BB with g = 2). On the other hand, the rapid increase of the asymmetric MR above the threshold is strongly suppressed by magnetic field, suggesting that the magnetic excitations with a lower energy scale are involved in the asymmetric MR above threshold. Micromagnetic simulation reveals that the spin-torque-induced inhomogeneous magnetization excitation, lying in gigahertz (GHz) frequency scale, is responsible for the rapid increase of asymmetric MR above threshold current density. Our results therefore suggest that the asymmetric MR has two origins: the spin-torque-induced GHz inhomogeneous magnon excitation above the threshold and the spin-flip-induced THz magnon excitation independent of the threshold.
[1] K. -J. Kim et al., arXiv:1603.08746.
[2] T. Li et al., Appl. Phys. Express 10, 073001 (2017).