Incoherent ferromagnetic spinwave spectroscopy using defect spins in diamond*

Optically detected spin transitions in nitrogen vacancy (NV) centers in diamond sensitively detect fluctuating fields at NV transition frequencies. Applied to ferromagnetic dynamics, this has enabled sensing of thermally occupied spinwaves as well as broadband, off-resonant spectroscopy of driven uniform-mode ferromagnetic resonance. We measure the relaxation rates of NV sensor spins to detect thermally excited spinwaves from a thin film of permalloy (Py). Analytical calculations and micromagnetic simulations demonstrate good agreement with measured NV relaxation rate as a function of NV-Py separation and applied field strength. Notably, NV sensors detect field noise from Py at a separation of up to 450 nm, thus demonstrating the suitability of NV probes in the GHz frequency range and submicron length scales of interest for communication and information devices.