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.

We demonstrate optical detection of a broad spectrum of ferromagnetic excitations using nitrogenvacancy (NV) centers in an ensemble of nanodiamonds. Our recently developed approach exploits a straightforward CW detection scheme using readily available diamond detectors, making it easily implementable. The NV center is a local detector, giving the technique spatial resolution, which here is defined by our laser spot, but in principle can be extended far into the nanoscale. Among the excitations we observe are propagating dipolar and dipolar-exchange spinwaves, as well as dynamics associated with the multi-domain state of the ferromagnet at low fields. These results offer an approach, distinct from commonly used ODMR techniques, for spatially resolved spectroscopic study of magnetization dynamics at the nanoscale.PACS numbers: 07.79.-v, 72.25.-b, 85.75.-d Spintronic [1,2] and magnonic devices [3][4][5] are receiving intense scientific attention due to their promise to deliver new technologies that can revolutionize computing and provide greater energy efficiency. In particular, tools for understanding phenomena such as angular momentum transfer across interfaces [6][7][8][9][10], spin wave propagation in low dimensional and nanoscale systems [11,12], domain wall motion [13][14][15], microwaveassisted switching [16], and relaxation and damping in small structures [17] are needed. There is current interest in materials with more novel magnetic textures than simple ferromagnets, such as skyrmions [18]. Electrical detection has been widely used for studying domain wall motion, but does not have imaging capabilities. Optical techniques such as Brillouin light scattering (BLS) [12] and the magneto-optic Kerr effect (MOKE) [19] are also widely used but are ultimately limited by the optical diffraction limit. Scanned probe techniques can provide high spatial resolution but can be perturbative and may require a more challenging set-up such as vacuum and cryogenic environment to achieve high sensitivity.Nitrogen-vacancy (NV) centers in diamond have emerged as an attractive tool to study magnetic phenomena at the nanoscale, and they offer a way to convert magnonic signals into optical signals. NV centers offer a powerful magnetometry tool due to a potent combination of optical and magnetic properties that make the intensity of their photoluminescence (PL) dependent on their spin state. This has allowed detection of just a few resonant nuclear spins and nuclear magnetic resonance imaging with resolutions of tens of nanometers, all under ambient conditions and at room temperature [20][21][22]. NV centers have also been used to study domain wall hopping [23], the helical phase in FeGe [24], * hammel@physics.osu.edu* † bhallamudi.1@osu.edu* and spinwave modes in permalloy [25]. High sensitivity to detect dynamic fields has been achieved by finding optimal NV centers with long lifetimes and manipulating them (and sometimes the target spins) with intricate microwave and optical pulse sequences.We have recently demonstrated a ne...

We observe a dependence of the damping of a confined mode of precessing ferromagnetic magnetization on the size of the mode. The micron-scale mode is created within an extended, unpatterned YIG film by means of the intense local dipolar field of a micromagnetic tip. We find that damping of the confined mode scales like the surface-to-volume ratio of the mode, indicating an interfacial damping effect (similar to spin pumping) due to the transfer of angular momentum from the confined mode to the spin sink of ferromagnetic material in the surrounding film. Though unexpected for insulating systems, the measured intralayer spin-mixing conductance g ↑↓ = 5.3×10 19 m −2 demonstrates efficient intralayer angular momentum transfer.

Auto-oscillation of a ferromagnet due to spin-orbit torques in response to a dc current is of wide interest as a flexible mechanism for generating controllable high frequency magnetic dynamics. However, spin wave mode degeneracies and nonlinear magnon-magnon scattering impede coherent precession. Discretization of the spin wave modes can reduce this scattering. Spatial localization of the spin wave modes by the strongly inhomogeneous dipole magnetic field of a nearby spherical micromagnet provides variable spatial confinement, thus offering the option of systematic tunability of magnon spectrum for studying multi-mode interactions. Here we demonstrate that field localization generates a discrete spin wave mode spectrum observable as a series of well-resolved localized modes in the presence of imposed spin currents arising from the spin Hall effect (SHE) in a permalloy/platinum (Py/Pt) microstrip. The observation of linewidth reduction through damping control in this micromagnetically engineered spectrum demonstrates that localized modes can be controlled efficiently, an important step toward continuously tunable SHE driven auto-oscillators.

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.