Spin-relaxation based coupling between NV centers and ferromagnetic dynamics*

We and others have recently reported optical detection of magnetic resonance that avoids the need for resonant overlap of the target and nitrogen-vacancy (NV) sensor spins by exploiting target-spin induced NV spin relaxation. The relaxation is due to fluctuating magnetic fields which, in the case of ferromagnets (FM), result from the decay of the coherently driven mode into spinwaves. This provides a sensitive approach to measuring damping at the nanoscale. Here we describe systematic investigations of NV-spin relaxation by spinwaves in which: 1) the NV-FM separation is controlled by a wedge-shaped spacer; 2) the applied magnetic field alters the wavevectors of spinwaves that are resonant with the NV spins; and 3) various FMs and mode-confinement produce modes with differing dispersions. We report on our progress in applying this approach to understanding damping of localized modes.