Hall-bar-width dependence of the field-like spin-orbit torque in NiFe/Pt bilayers

Current-induced spin-orbit torques (SOTs) can cause an obvious manipulation of magnetization in a heavy metal/ferromagnetic metal bilayer. We report here the peculiarities of field-like SOT by a planar Hall effect (PHE) measurement for a number of stripe samples with various widths ( w ), consisting of a thermally oxidized Si sub./NiFe/Pt. The separation of interfacial spin-orbit effective field, bulk spin-orbit effective field, and Oersted field was performed by using the longitudinal and transverse PHE configurations. The interfacial effective field is much larger and plays a dominant role than the bulk one in the films. All the effective fields follow the 1/w dependence and obey the linear relationship with the current density. Furthermore, both the interfacial and bulk SOT coefficients remain constant and are independence of Hall-bar-width. The dominant interfacial spin-orbit effective field in the NiFe/Pt bilayers suggests the necessity of further analysis of interfacial effect on the current-induced manipulation of magnetization.