  Recent studies rediscovered the crucial role of field-like spin orbit torque
(SOT) in nanosecond-timescale SOT dynamics. However, there is not yet an
effective way to control its relative amplitude. Here, we experimentally
modulate the field-like SOT in W/CoFeB/MgO trilayers through tuning the
interfacial spin accumulation. By performing spin Hall magnetoresistance
measurement, we find that the CoFeB with enhanced spin dephasing, either
generated from larger layer thickness or from proper annealing, can distinctly
boost the spin absorption and enhance the interfacial spin mixing conductance
G_r. While the damping-like torque efficiency increases with G_r, the
field-like torque efficiency turns out to decrease with it. The results suggest
that the interfacial spin accumulation, which largely contributes to a
field-like torque, is reduced by higher interfacial spin transparency. Our work
shows a new path to further improve the performance of SOT-based magnetic
devices.
