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 ...

Using electrical detection of a strongly coupled spin-photon system comprised of a microwave cavity mode and two magnetic samples, we demonstrate the long distance manipulation of spin currents. This distant control is not limited by the spin diffusion length, instead depending on the interplay between the local and global properties of the coupled system, enabling systematic spin current control over large distance scales (several centimeters in this work). This flexibility opens the door to improved spin current generation and manipulation for cavity spintronic devices.

We experimentally examine the topological nature of a strongly coupled spin-photon system induced by damping. The presence of both spin and photonic losses results in a non-Hermitian system with a variety of exotic phenomena dictated by the topological structure of the eigenvalue spectra and the presence of an exceptional point (EP), where the coupled spin-photon eigenvectors coalesce. By controlling both the spin resonance frequency and the spin-photon coupling strength we observe a resonance crossing for cooperativities above one, suggesting that the boundary between weak and strong coupling should be based on the EP location rather than the cooperativity. Furthermore we observe dynamic mode switching when encircling the EP and identify the potential to engineer the topological structure of coupled spin-photon systems with additional modes. Our work therefore further highlights the role of damping within the strong coupling regime, and demonstrates the potential and great flexibility of spin-photon systems for studies of non-Hermitian physics.

A pure spin current driven by spin pumping is converted to a DC voltage and detected electrically in a Py/Pt bilayer sample. This DC voltage mixes with a DC voltage produced through spin rectification. The ferromagnetic resonance line shape strongly depends on the microwave magnetic h field distribution. We have systematically studied the line shapes by changing the external magnetic field orientation in plane of a Pt/Py bilayer. A method is demonstrated which allows us to calculate the microwave h field vector distribution, and distinguish spin pumping from spin rectification. V C 2013 AIP Publishing LLC. [http://dx.Spin pumping is a recently developed method for generating spin currents (others include DC injection and optical excitation) and has recently attracted much attention. 1-7 The process of spin pumping drives a pure spin current from a ferromagnetic metal (FM) into a normal metal (NM) via ferromagnetic resonance (FMR); this current is then converted to a DC voltage in the Pt through the inverse spin Hall effect (ISHE) and detected electrically.

We report room temperature electrical detection of spin injection from a ferromagnetic insulator (YIG) into a ferromagnetic metal (Permalloy, Py). Non-equilibrium spins with both static and precessional spin polarizations are dynamically generated by the ferromagnetic resonance of YIG magnetization, and electrically detected by Py as dc and ac spin currents, respectively. The dc spin current is electrically detected via the inverse spin Hall effect of Py, while the ac spin current is converted to a dc voltage via the spin rectification effect of Py which is resonantly enhanced by dynamic exchange interaction between the ac spin current and the Py magnetization. Our results reveal a new path for developing insulator spintronics, which is distinct from the prevalent but controversial approach of using Pt as the spin current detector.Developing new methods for generating and detecting spin currents has been the central task of spintronics. In the pioneering work of Johnson and Silsbee [1], the generation and detection of spin-polarized currents were both achieved through the use of ferromagnetic metals (FM). Recent breakthroughs reveal ferromagnetic insulators (FI) to be promising spin current sources, in which spin currents can be generated without the presence of any charge current [2,3]. In the ground-breaking experiment performed 3 years ago by Kajiwara et al.[2], electrical detection of the spin current generated by yttrium iron garnet (Y 3 Fe 5 O 12 , YIG) was achieved by utilizing the heavy normal metal platinum (Pt), in which spin current was detected via the inverse spin Hall effect (ISHE). Since then, nearly the entire insulator-spintronics community has followed suit and used Pt as the standard spin detector. But so far, consensus has not yet been achieved on a few critical spin-dependent material issues of Pt [4][5][6][7]. Given the fact that ferromagnetic metals are broadly used as spin detectors in both semiconductor [8,9] and metallic spintronics devices [1,10,11], it is noteworthy that the appealing topic of how a FM material may detect the spin current generated by a FI has barely been investigated. Elucidating this issue is of broad interest for making insulator-spintronics device compatible with both semiconductor and metallic spintronics devices.In this letter, we report room temperature detection of spin current generated in YIG by feromagnetic resonance (FMR). Distinct from the popular approach of using Pt as the spin detector, we use the ferromagnetic metal Permalloy (Py) instead, and demonstrate that Py not only detects the dc spin current from YIG, but most strikingly, it also detects the recently predicted ac spin current [12] by directly converting it into a dc voltage, which makes Py a superior spin detector compared to Pt. Two very recent experiments make this work possible: (i) the discovery of the ISHE in Py [13], and (ii) the establishment of a universal method for clearly separating spin rectification from spin pumping [14].We begin by highlighting the basic ideas. As shown in Fig.