No abstract

There are two common methods in generating magnetic resonance in FMs for spin pumping, cavity FMR and microstrip waveguides [3,7,8,12,19]. FMR cavities produce modest-strength, uniform rf fields over a relatively large space (cm-scale); while microstrip waveguides produce rf fields typically in micron to sub-mm scale, and when made very close to the FMs, can generate fairly large h rf [12,19]. Since the magnitude of rf field determines the excitation strength for spin pumping and only a few reports on microstrip spin pumping presented values of h rf [12,19], in this letter, we mainly compare our results with previous reports of spin pumping using cavity FMR. respectively, which reach the resolution limit of conventional high-resolution XRD systems, demonstrating excellent crystalline quality. In this letter, we focus on two 20-nm YIG films (YIG-1 and YIG-2) for FMR and spin pumping measurements.Room-temperature FMR measurements of the YIG films are carried out in a cavity at a microwave frequency f = 9.65 GHz and power P rf = 0.2 mW. Figure 3e shows the angular dependence of V ISHE for Pt/YIG-1 and W/YIG-2 normalized by the maximum magnitude of V ISHE at θ H = 90°.The clear sinusoidal shape is characteristic of ISHE since [15]thus confirming that the observed ISHE voltage arises from FMR spin pumping. The spin pumping signals we observed in insulating YIG cannot be explained by artifacts due to thermoelectric or magnetoelectric effects, such as anisotropic magnetoresistance (AMR) or anomalous Hall effect (AHE) [13,16,32,34,35].While a spin current is generated by transfer of angular momentum from YIG to metal, simultaneously, the coupling between YIG and metal exerts an additional damping to the magnetization precession in YIG, resulting in increased linewidths [10,12], as shown in Fig. 5 4 for the three samples before (∆H 0 ) and after (∆H 1 ) the deposition of where G r , γ, and B are the real part of spin mixing conductance, the gyromagnetic ratio, factor and Bohr magnetron, respectively. Using Eq. (2), we obtain = 4.56× 10 14 and 2.30× 10 14 Ω -1 m -2 for Pt/YIG-2 and W/YIG-2, respectively, which agree with the theoretical calculations [36] and are among the highest of reported experimental values [3,5,8,9].Previously, spin pumping of Pt/YIG excited by similar cavity FMR gave ISHE voltages in the µV range [1,9,11,16]. The large spin pumping signals and high spin mixing conductance observed in our YIG films may be attributed to two possible reasons. First, the small thickness (20 nm) of our films compared to LPE films (100 nm or larger) may play an important role, as suggested by a recent report [7] that a 200-nm YIG film shows much higher spin pumping efficiency than 1-µm and 3-µm films excited by a microstrip waveguide. [7,12]. Further investigation of spin pumping in these thin YIG films using microstrip waveguides will access larger dynamic range of spin pumping. In addition, the mV-level ISHE voltages reported here using a moderate h rf will allow miniaturization of spin pumping structures while m...

We report the manipulation of nitrogen vacancy (NV) spins in diamond when nearby ferrimagnetic insulator, yttrium iron garnet, is driven into precession. The change in NV spin polarization, as measured by changes in photoluminescence, is comparable in magnitude to that from conventional optically detected magnetic resonance, but relies on a distinct mechanism as it occurs at a microwave frequency far removed from the magnetic resonance frequency of the NV spin. This observation presents a new approach to transferring ferromagnetic spin information into a paramagnet and then transducing the response into a robust optical signal. It also opens new avenues for studying ferromagnetism and spin transport at the nanoscale.

Ferromagnetic resonance (FMR) driven spin pumping of pure spin currents from a ferromagnet (FM) into a nonmagnetic material (NM) promises new spin-functional devices with low energy consumption [1-6]. The mechanism of spin pumping is under intense investigation and it is widely believed that exchange interaction between the FM and NM is responsible for this phenomenon [2-5, 7]. We observe a thousand-fold exponential decay of the spin pumping from 20-nm thick Y 3 Fe 5 O 12 (YIG) films to platinum across insulating barriers, from which the exponential decay lengths of 0.16 and 0.23 nm are extracted for oxide barriers with band gaps of 4.93 eV and 2.36 eV, respectively. This prototypical signature of quantum tunneling through a barrier underscores the importance of exchange coupling for spin pumping and reveals its dependence on the characteristics of the barrier material. Generation and manipulation of spin currents is key to spintronic applications [1]. FMR driven spin pumping has been demonstrated to inject a pure spin current through angular 2 momentum transfer from an FM to an adjacent NM [2-6]. General belief assumes a dynamic coupling via exchange interaction between the precessing magnetization (M) of the FM and the conduction electrons of the NM at the NM/FM interface. This mechanism will lead to a short, atomic-scale coupling that decays exponentially with separation between the FM and NM. However, this has not been experimentally confirmed, partially due to the large dynamic range needed to measure such rapidly decaying spin pumping signal [6, 8]. Our recent demonstration of large spin pumping in Pt/YIG bilayers with mV-level inverse spin Hall effect (ISHE) voltage, V ISHE , offers a material platform with signal-to-noise ratio sufficient to quantitatively characterize the coupling range, enabling detailed insights into the spin pumping mechanism. We use three different barrier materials, including two oxide insulators and Si, to systematically investigate the barrier thickness t dependence of spin pumping in Pt/barrier(t)/YIG heterostructures. The clear exponential decays of ISHE voltage with characteristic lengths of ~0.2 nm for the oxide barriers provide decisive evidence for the predicted exchange coupling model for spin pumping. Our experiments utilize YIG thin films grown on (111)-oriented Gd 3 Ga 5 O 12 (GGG) substrates by an off-axis sputtering technique we developed for epitaxial film growth of complex materials [9-12]. Figure 1a shows a high resolution x-ray diffraction (XRD) scan of a 20-nm YIG film near the YIG (444) peak with clear Laue oscillations, indicating high uniformity throughout the film. The XRD rocking curve in the inset to Fig. 1a gives a full width at half maximum (FWHM) of 0.0185, demonstrating excellent crystalline quality. Figure 1b shows a representative FMR derivative spectrum for a 20 nm YIG film taken at radio-frequency (rf) f = 9.65 GHz and microwave power P rf = 0.2 mW with an in-plane magnetic field, from which the peak-to-peak linewidth (H) of 10 Oe is obtained [13]...

Highly ordered epitaxial films of ferrimagnetic semiconductor Sr2CrReO6 (SCRO) have been fabricated by off-axis magnetron sputtering, and characterized as a function of the oxygen partial pressure. In this Letter, we report 18 000% modulation in electrical resistivity at T = 7K (60% at room temperature) from a 1% modulation in the oxygen partial pressure during film growth. The growth window was centered at peak saturation magnetization, which drops due to both increasing and decreasing oxygen growth pressure. The results suggest that n-type doping due to oxygen vacancies plays a dominant role in the electrical properties and modulation of Sr2CrReO6 thin films.

Highly ordered epitaxial Sr2CrReO6 films of 20-nm and 175-nm thicknesses were deposited on SrTiO3 and (LaAlO3)0.3(Sr2AlTaO6)0.7 substrates and Sr2CrNbO6 buffer layers. Electronic measurements and scanning transmission electron microscopy images clearly show that the Sr2CrNbO6 buffer layers facilitate Cr/Re ordering near the interface, thus minimizing the number of defect states in the films. Arrhenius fits of the resistivity data give activation energies of 7.3–32 meV for films grown on non-buffered substrates, suggesting defect states are more conducting than Sr2CrReO6, whereas films grown on the Sr2CrNbO6 buffer layer have activation energies in the narrow range 38.6–42.1 meV.

We report on the efficiency of spin pumping from parametrically excited propagating high-k spinwaves in a YIG(25 nm)/Pt(5 nm) bilayer. We observe clear signals, detected using the inverse spin Hall effect. The measured spin pumping efficiency and microwave thresholds needed for parametric excitation indicate that spin pumping is insensitive to the spinwave wavevector magnitude and propagation direction in the range 0≤k≲20 μm−1. This finding is consistent with the fact that for thin films, the variation of spin wave amplitude across the film thickness is only weakly dependent on the wavevector. Our results are promising for the development of spin-based devices operated by spinwaves.