  Spin-orbit torques in ferromagnetic (FM)/non-magnetic (NM) heterostructures
offer more energy-efficient means to realize spin-logic devices; however, their
strengths are determined by the heterostructure interface. This work examines
crystal orientation impact on the spin-orbit torque efficiency in different
Fe/Pd bilayer systems. Spin torque ferromagnetic measurements evidence that the
damping-like torque efficiency is higher in epitaxial than in polycrystalline
bilayer structures while the field-like torque is negligible in all bilayer
structures. The strength of the damping-like torque decreases with
deterioration of the bilayer epitaxial quality. The present finding provides
fresh insight for the enhancement of spin-orbit torques in magnetic
heterostructures.
