About the significance of the driving current direction in ferromagnetic resonance experiments

We present an experimental study of the effects of driving current direction on ferromagnetic resonance in NiFe foils. The rf driving current was applied to NiFe foils of different shapes. In rectangular samples with a close-to-uniform flow of the applied current along the long edge of the sample we find the resonance field to follow a simple 'cos' dependence on the angle between the current and external dc magnetic field, similar to the one observed previously in NiFe wires [1]. We argue that this behavior cannot be explained by in-plane demagnetizing fields of the rectangular foil. In triangular samples where the current partially flows along all three sample edges we observed three independent 'cos' features. The latter suggests individual contributions from different areas with different current directions. We were able to switch off one of these contributions by covering one edge of the triangular sample with a conducting overlayer and thereby effectively short-circuiting the corresponding current path. Our findings highlight the significance of driving current distributions in ferromagnetic resonance experiments. [1] Q. Gao, M. Tsoi, J. Magn. Magn. Mater. 580, 170947 (2023).