Spin-orbit torque in a Ni-Fe single layer

We evaluated the self-induced spin-orbit torque (SOT) in a single ferromagnetic layer. Spin-torque ferromagnetic resonance (ST-FMR) was measured for the very thin Ni-Fe (permalloy, Py) layers with and without structural inversion symmetry: asymmetric and symmetric Py layers. For both structures, the fieldlike component coming from the Oersted field clearly appeared. On the other hand, the dampinglike component was observed only for asymmetric Py with thickness ≤30.16em0exnm. This dampinglike torque is attributable to the significant spatial change in the properties of Py. We propose a toy model to analyze the self-induced SOT.