High frequency ferromagnetic spectroscopy enabled by coupling pairs of magnons to NV spins

Coupling NV center defects in diamond to ferromagnetic dynamics is of interest for both quantum sensing and for NV spin manipulation. We have used NV relaxometry to detect driven ferromagnetic dynamics in a low-damping insulating ferrimagnet, nickel zinc aluminum ferrite. We determine that NV coupling to driven magnetization has two regimes: first, when the uniform mode FMR frequency is less than the NV spin resonance frequency, and the converse. A driven spinwave instability in the nickel ferrite populates the magnons far above thermal levels. The spectral response of NV-ferromagnet coupling in the first regime can be understood from the spinwave instability physics. The second regime of NV-ferromagnet coupling can be understood via a two-magnon relaxation process. These results further the understanding of how driven ferromagnetic dynamics lead to NV spin relaxation, and demonstrate the potential to detect magnons with frequencies well above the NV frequency.