  Spin-orbit torques (SOT) allow the electrical control of magnetic states.
Current-induced SOT switching of the perpendicular magnetization is of
particular technological importance. The SOT consists of damping-like and
field-like torques so that the efficient SOT switching requires to understand
combined effects of the two torque-components. Previous quasi-static
measurements have reported an increased switching probability with the width of
current pulses, as predicted with considering the damping-like torque only.
Here we report a decreased switching probability at longer pulse-widths, based
on time-resolved measurements. Micromagnetic analysis reveals that this
anomalous SOT switching results from domain wall reflections at sample edges.
The domain wall reflection is found to strongly depend on the field-like torque
and its relative sign to the damping-like torque. Our result demonstrates a key
role of the field-like torque in the deterministic SOT switching and notifies
the importance of sign correlation of the two torque-components, which may shed
light on the SOT switching mechanism.
