Spin pumping is a mechanism that generates spin currents from ferromagnetic resonance over macroscopic interfacial areas, thereby enabling sensitive detection of the inverse spin Hall effect that transforms spin into charge currents in nonmagnetic conductors. Here we study the spin-pumping-induced voltages due to the inverse spin Hall effect in permalloy/normal metal bilayers integrated into coplanar waveguides for different normal metals and as a function of angle of the applied magnetic field direction, as well as microwave frequency and power. We find good agreement between experimental data and a theoretical model that includes contributions from anisotropic magnetoresistance and inverse spin Hall effect. The analysis provides consistent results over a wide range of experimental conditions as long as the precise magnetization trajectory is taken into account. The spin Hall angles for Pt, Pd, Au, and Mo were determined with high precision to be 0.013Ϯ 0.002, 0.0064Ϯ 0.001, 0.0035Ϯ 0.0003, and −0.0005Ϯ 0.0001, respectively.

Spin transfer appears to be a promising tool for improving spintronics devices. Experiments that quantitatively access the magnitude of the spin transfer are required for a fundamental understanding of this phenomenon. By inductively measuring spin waves propagating along a permalloy strip subjected to a large electrical current, we observed a current-induced spin wave Doppler shift that we relate to the adiabatic spin transfer torque. Because spin waves provide a well-defined system for performing spin transfer, we anticipate that they could be used as an accurate probe of spin-polarized transport in various itinerant ferromagnets.

We report a complete study of spin-wave transduction combining microwave measurements performed over a frequency range of ͓1-15͔ GHz on Permalloy strips ͑thickness= 10-20 nm, width=2-8 m͒ and an accurate modeling of the experiment. This technique has been used recently to assess the spin polarization of the electrical current by measuring a current-induced spin-wave Doppler shift. We present here an electromagnetism calculation based on the magnetostatic wave theory combined with the Gilbert form of the damping that can be used directly as an optimization tool for future spin-wave experiments.

The spin diffusion length of Pt at room temperature and at 8 K is experimentally determined via spin pumping and spin Hall effect in permalloy/Pt bilayers. Voltages generated during excitation of ferromagnetic resonance from the inverse spin Hall effect and anisotropic magnetoresistance effect were investigated with a broadband approach. Varying the Pt layer thickness gives rise to an evolution of the voltage line shape due to the superposition of the above two effects. By studying the ratio of the two voltage components with the Pt layer thickness, the spin diffusion length of Pt can be directly extracted. We obtain a spin diffusion length of ∼1.2 nm at room temperature and ∼1.6 nm at 8 K.

We develop a method for universally resolving the important issue of separating spin pumping (SP) from spin rectification (SR) signals in bilayer spintronics devices. This method is based on the characteristic distinction of SP and SR, as revealed in their different angular and field symmetries. It applies generally for analyzing charge voltages in bilayers induced by the ferromagnetic resonance (FMR), independent of FMR line shape. Hence, it solves the outstanding problem that device specific microwave properties restrict the universal quantification of the spin Hall angle in bilayer devices via FMR experiments. Furthermore, it paves the way for directly measuring the nonlinear evolution of spin current generated by spin pumping. The spin Hall angle in a Py/Pt bilayer is thereby directly measured as 0.021±0.015 up to a large precession cone angle of about 20• . [3][4][5]. Soon after, a consensus was formed that quantitatively, such FMR voltages in FM/NM bilayers involve in general not only the contribution from spin pumping (SP), but also that from spin rectification (SR), where the magnetization dynamics driven by either the microwave field [6] or the spin transfer torque [7] rectifies the microwave current flowing in the FM layer. In 2010, a method based on line shape analysis of the FMR voltage was established for quantitatively separating the two contributions of SP and SR [8]. Although such a line shape analysis is useful and enabled the first quantification of the spin Hall angle via FMR measurement [8], as discussed in a few follow-up studies [9][10][11], it is important to be aware that it only applies on specially designed devices measured under proper configurations which fulfil three conditions: (1) Microwave currents in the non-magnetic metallic layer should be minimized so that contributions from spin transfer torque induced spin rectification can be neglected [7]. (2) The measurement configuration and microwave phase should be such that the spin rectification either makes no contribution to the Lorentzian part † Current affiliation: Colegio de Ciencias e Ingenieria, Universidad San Francisco de Quito, Quito, Ecuador of the electrically detected FMR line shape or can be calibrated [9][10][11]. (3) The cone angle of the magnetization precession should be small so that the FMR line shape is free from nonlinear distortion [12]. These strict conditions limit the broad application of the line shape method for generally analyzing the spin pumping and spin Hall effect in bilayer spintronic devices [13,14]. So far, developing a universal method independent of device-specific microwave properties remains a significant challenge. In particular, there is no applicable method for quantifying the spin pumping effect in the nonlinear regime, where the technologically important question of how efficient a large spin current may be generated by high power microwaves remains open.In this letter, we establish such a universal method based on general symmetry consideration. This method enables the pure spin pumping ...

Voltages generated from inverse spin Hall and anisotropic magneto--resistance effects via spin pumping in ferromagnetic (F)/non--magnetic (N) bilayers are investigated by means of a broadband ferromagnetic resonance approach. Varying the non--magnetic layer thickness enables the determination of the spin diffusion length in Pd of 5.5 ± 0.5 nm. We also observe a systematic change of the voltage lineshape when reversing the stacking order of the F/N bilayer, which is qualitatively consistent with expectations from spin Hall effects. However, even after independent calibration of the precession angle, systematic quantitative discrepancies in analyzing the data with spin Hall effects remain.

Growth of nm-thick yttrium iron garnet (YIG) films by sputtering and ferromagnetic resonance (FMR) properties in the films were studied. The FMR linewidth of the YIG film decreased as the film thickness was increased from several nanometers to about 100 nm. For films with very smooth surfaces, the linewidth increased linearly with frequency. In contrast, for films with big grains on the surface, the linewidth-frequency response was strongly nonlinear. Films in the 7–26 nm thickness range showed a surface roughness between 0.1 nm and 0.4 nm, a 9.48-GHz FMR linewidth in the 6–10 Oe range, and a damping constant of about 0.001.

The spatial variation of the spin pumping–inverse spin Hall effect was studied in a palladium/permalloy bilayer via a coplanar waveguide ferromagnetic resonance (CPW-FMR) broadband technique. The inverse spin Hall signal is both inhomogeneous and asymmetric with respect to both the position along the CPW and the excitation port. Based on this observation, we show how the inverse spin Hall effect can be used as a sensitive probe for mapping the microwave magnetic field distribution in the FMR frequency range.