Spin wave generator via oscillating vortex-antivortex core pairs at zero external field

We demonstrate that the radiation of spin waves can be generated from an oscillating vortex-antivortex core pair. The emission of spin waves was produced by the oscillation of nanoscale magnetic vortex-antivortex core pair in a NiFe disk-film composite structure. The sample consists of a 20-nm-thick, 4 micron long and 1 micron wide NiFe magnonic waveguide, located at the gap of a single-end GS coplanar waveguide circuit, and magnetic disk with thickness 50 nm and diameter 500 nm on top. The vortex cores in the disk was excited by an out of plane radio frequency magnetic field. The dynamic behaviors of the magnetization were studied using a micro-focused Brillouin light scattering spectroscopy (BLS) setup. In addition to the discrete ferromagnetic resonance (FMR) signals above external dc saturation magnetic field, we observed clear signals at zero magnetic field where vortex cores are present. We have found an ultra- flexible mechanism for consistent excitation of propagating spin waves. The frequencies of the spin waves excited are coherently tunable by the driving frequencies from 5 GHz up to 15 GHz. The short wavelength down to 80 nm for 15 GHz was observed.