Spin Pumping and Temperature-Resolved Ferromagnetic Resonance in Permalloy-Topological Insulator Nanostructured Bilayers

The huge spin–orbit coupling inherent to 3D topological insulators makes bilayers of the topological insulator—ferromagnetic metal type very attractive for topological spintronics. We study spin pumping due to ferromagnetic resonance in permalloy ferromagnet—topological insulator bismuth selenide (Bi₂Se₃) bilayers. We study cases of both uniform and nanostructured bilayers, where the permalloy layer is in the form of an array of nanocylinders with industry-relevant geometries. We measure the dc voltage signal caused by conversion of the spin current into the charge current in the bulk of topological insulator due to the inverse spin Hall effect. Our results show that the pumped signal for uniform and nanostructured bilayers is comparable, which is important for prospective applications in information and communication technologies. We report the temperature dependencies of a resonance magnetic field for the uniform sample. To obtain theoretical insight into the experimental results, we use a method which involves micromagnetic modeling for estimation of effective constants and dc voltages in experiments with similar nanostructured bilayers.