  Spin-orbit torque facilitates efficient magnetization switching via an
in-plane current in perpendicularly magnetized heavy metal/ferromagnet
heterostructures. The efficiency of spin-orbit-torque-induced switching is
determined by the charge-to-spin conversion arising from either bulk or
interfacial spin-orbit interactions, or both. Here, we demonstrate that the
spin-orbit torque and the resultant switching efficiency in Pt/CoFeB systems
are significantly enhanced by an interfacial modification involving Ti
insertion between the Pt and CoFeB layers. Spin pumping and X-ray magnetic
circular dichroism experiments reveal that this enhancement is due to an
additional interface-generated spin current of the nonmagnetic interface and/or
improved spin transparency achieved by suppressing the proximity-induced moment
in the Pt layer. Our results demonstrate that interface engineering affords an
effective approach to improve spin-orbit torque and thereby magnetization
switching efficiency.
