Exploring magnetic excitations in the condensed matter using single electron spins

Pushing the frontiers of condensed-matter magnetism requires tools to probe magnetic excitations on the nanometer scale. We have developed a new approach to exploring magnetic excitations in correlated-electron systems [1], using magnetometry based on single electron spins in diamond. We demonstrate the power of this approach by detecting spin-wave excitations in a ferromagnetic microdisc with nanoscale spatial sensitivity over a broad range of frequencies and magnetic fields. In addition, we show how spin-wave resonances can be exploited for on-chip amplification of microwave magnetic fields, allowing strongly increased spin manipulation rates and single-spin magnetometry with enhanced sensitivity. These results can be directly applied to nanoscale magnetic imaging of spin-wave propagation and magnetic vortex/skyrmion dynamics, and open the way towards spin-spin coupling via ferromagnets.\\[4pt] [1] T.~van~der~Sar, F.~Casola, R.~Walsworth, and A.~Yacoby, arXiv:1410.6423 (2014).