Stripline ͑SL͒, vector network analyzer ͑VNA͒, and pulsed inductive microwave magnetometer ͑PIMM͒ techniques were used to measure the ferromagnetic resonance ͑FMR͒ linewidth for a series of Permalloy films with thicknesses of 50 and 100 nm. The SL-FMR measurements were made for fixed frequencies from 1.5 to 5.5 GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6 to 8 kA/ m ͑20-100 Oe͒. The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter ␣ value of 0.007 and zero frequency intercepts in the 160-320 A / m ͑2-4 Oe͒ range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

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We report the observation of ferromagnetic resonance-driven spin pumping signals at room temperature in three-dimensional topological insulator thin films -Bi 2 Se 3 and (Bi,Sb) 2 Te 3 -deposited by molecular beam epitaxy on Y 3 Fe 5 O 12 thin films. By systematically varying the Bi 2 Se 3 film thickness, we show that the spin-charge conversion efficiency, characterized by the inverse RashbaEdelstein effect length (λ IREE ), increases dramatically as the film thickness is increased from 2 quintuple layers, saturating above 6 quintuple layers. This suggests a dominant role of surface states in spin and charge interconversion in topological insulator/ferromagnet heterostructures.Our conclusion is further corroborated by studying a series of Y 3 Fe 5 O 12 /(Bi,Sb) 2 Te 3 heterostructures. Finally, we use the ferromagnetic resonance linewidth broadening and the inverse RashbaEdelstein signals to determine the effective interfacial spin mixing conductance and λ IREE .

Strong damping enhancement in nm-thick yttrium iron garnet (YIG) films due to Pt capping layers was observed. This damping is substantially larger than the expected damping due to conventional spin pumping, is accompanied by a shift in the ferromagnetic resonance field, and can be suppressed by the use of a Cu spacer in between the YIG and Pt films. The data indicate that such damping may originate from the ferromagnetic ordering in Pt atomic layers near the YIG/Pt interface and the dynamic exchange coupling between the ordered Pt spins and the spins in the YIG film.