Abstract: Electrical control of magnetism has been energized by recent observation of spin-orbit torques in magnetic bilayers made of a heavy metal (HM) and ferromagnet (FM). It has been demonstrated that the spin-orbit torques driven by an in-plane current can switch magnetization, manipulate magnetic domains and excite magnetization auto-oscillation. However, the microscopic mechanism for the spin-orbit torques is still under debate. The question being whether the dominating spin-orbit interaction (SOI) arises from the HM/FM interface due to the Rashba effect or arises in the bulk of HM due to the spin Hall effect, or a combination of the two. It has been theoretically demonstrated that both the Rashba effect and the spin Hall effect generate a spin-orbit effective field (SOF) and spin-orbit effective torque (SOT) on the magnetization, with only quantitative differences. Therefore, an accurate method to determine the SOF and SOT with various thicknesses of the FM and HM are needed. We present a newly developed, magneto-optic-Kerr-effect based spin-orbit torque magnetometer that measures both in-plane and out-of-plane spin-orbit torques, which can have both spatial and time resolution. Through the thickness dependence study, we are able to observe the interface contributions to the spin-orbit torques.

About the Speaker: John Q. Xiao, a Fellow of American Physical Society, received his BS degree in physics from Nanjing University, China. He received his MS and Ph.D degrees in physics from the Johns Hopkins University in 1989 and 1993, respectively. Between 1993 and 1995, he was a post doctoral fellow at the Department of Physics and Astronomy at the Johns Hopkins University. He joined the University of Delaware as an Assistant Professor in 1995 and he is now a Unidel professor of physics and affiliated professor at the Center of Composite Materials and Department of Electrical and Computer Engineering at the University of Delaware. He also serves as the director of the Nanofabrication Core Facility at the University of Delaware. His current research interests ranges over spintronics, soft magnetic materials, magnetic sensors, and microwave magnetic materials and devices.