  Current induced spin-orbit torques (SOTs) in ferromagnet/non-magnetic metal
heterostructures open vast possibilities to design spintronic devices to store,
process and transmit information in a simple architecture. It is a central task
to search for efficient SOT-devices, and to quantify the magnitude as well as
the symmetry of current-induced spin-orbit magnetic fields (SOFs). Here, we
report a novel approach to determine the SOFs based on magnetization dynamics
by means of time-resolved magneto-optic Kerr microscopy. A microwave current in
a narrow Fe/GaAs (001) stripe generates an Oersted field as well as SOFs due to
the reduced symmetry at the Fe/GaAs interface, and excites standing spin wave
(SSW) modes because of the lateral confinement. Due to their different
symmetries, the SOFs and the Oersted field generate distinctly different mode
patterns. Thus it is possible to determine the magnitude of the SOFs from an
analysis of the shape of the SSW patterns. Specifically, this method, which is
conceptually different from previous approaches based on lineshape analysis, is
phase independent and self-calibrated. It can be used to measure the current
induced SOFs in other material systems, e.g., ferromagnetic metal/non-magnetic
metal heterostructures.
