We study spin-orbit-torque-driven ferromagnetic resonance (FMR) in ferromagnetic (FM) bilayers, consisting of Co and permalloy (Py), sandwiched between Pt and MgO layers. We find that the FM layer in contact with the Pt layers dominantly determines that spin Hall angle, which is consistent with the spin-transparency model. By contrast, the FMR linewidths are considerably influenced not only by the spin-pumping effect across the Pt|FM in terface but also by the spin relaxation such as two-magnon scattering at the FMMgO interface.The CoMgO interface leads to notably increased FMR linewidths, while the Py|MgO interface has less effect. This different contribution of each interface to the spin Hall angel and dissipation parameter suggests that the stack configuration of Pt|Co|Py|MgO requires less writing energy than Pt|Py|Co|MgO in spin-orbit-torque-driven magnetic switching. Our approach offers a promising method to optimize material parameters by engineering either interfaces in contact with the heavy-metal or the oxide layer.
@article{arxiv.1801.05131,
title = {Spin-orbit-torque and magnetic damping in tailored ferromagnetic bilayers},
author = {DongJoon Lee and JongHyuk Kim and HeeGyum Park and Kyung-Jin Lee and Byeong-Kwon Ju and Hyun Cheol Koo and Byoung-Chul Min and OukJae Lee},
journal= {arXiv preprint arXiv:1801.05131},
year = {2018}
}