title: Quantifying interface and bulk contributions to spin-orbit torque in magnetic bilayers.
abstract: Spin-orbit interaction-driven phenomena such as the spin Hall and Rashba effect in ferromagnetic/heavy metal bilayers enables efficient manipulation of the magnetization via electric current. However, the underlying mechanism for the spin-orbit interaction-driven phenomena remains unsettled. Here we develop a sensitive spin-orbit torque magnetometer based on the magneto-optic Kerr effect that measures the spin-orbit torque vectors for cobalt iron boron/platinum bilayers over a wide thickness range. We observe that the Slonczewski-like torque inversely scales with the ferromagnet thickness, and the field-like torque has a threshold effect that appears only when the ferromagnetic layer is thinner than 1 nm. Through a thickness-dependence study with an additional copper insertion layer at the interface, we conclude that the dominant mechanism for the spin-orbit interaction-driven phenomena in this system is the spin Hall effect. However, there is also a distinct interface contribution, which may be because of the Rashba effect.
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Fan
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Halise
authors.initials: H
authors.lastname: Celik
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Materials Science and Engineering, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Chaoying
authors.initials: C
authors.lastname: Ni
authors.affiliation: 1] Department of Materials Science and Engineering, Korea University, Seoul 136-701, Republic of Korea [2] KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul 136-713, Republic of Korea.
authors.forename: Kyung-Jin
authors.initials: KJ
authors.lastname: Lee
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: Virginia O
authors.initials: VO
authors.lastname: Lorenz
authors.affiliation: Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA.
authors.forename: John Q
authors.initials: JQ
authors.lastname: Xiao