Imaging Magnon Emission from a Ferromagnetic Vortex with Scanning NV Magnetometry

There is a great deal of interest in the development of nanoscale magnonic devices, necessitating the generation of nanometer-scale wavelength spin waves. However, there is a dearth of techniques to image them – conventional optical techniques cannot directly measure sub-diffraction limit wavelengths, and, while X-ray techniques overcome this limit, they require a beamline, making them less accessible to researchers. Here, we demonstrate the use of scanning nitrogen-vacancy (NV) center magnetometry to probe short wavelength spin waves emitted from a vortex in a soft ferromagnetic disc. We directly image the static and microwave stray fields of the disc, utilizing the latter's height dependence to quantitatively measure the wavenumber of vortex-emitted magnons. Furthermore, we demonstrate a 40x enhancement in Rabi oscillation frequency of our NV center near the vortex core, an order of magnitude higher than previously reported in vortex-mediated qubit driving schemes, showcasing an advantage of the technique for device characterization.