Imaging Harmonic Generation in Permalloy using Scanning Nitrogen Vacancy Center Magnetometry

Harmonic generation is the process by which a driven system emits responses at integer multiples of the excitation frequency, arising from its inherent nonlinear susceptibility. It has been studied in many systems including nonlinear optics, superconductors, and magnetic materials with application to frequency conversion and materials characterization. Previous experiments have measured up to 60 harmonics of coherent harmonic generation via driven magnons in permalloy using an ensemble of nitrogen-vacancy (NV) centers in nanodiamonds [1,2]. In this work, we use a scanning NV center magnetometer to image the strong spatial dependence of the harmonic generation. Also, we measure a difference in amplitudes of harmonic generation for the two NV transitions, revealing a chirality in the resulting harmonic generation. We have reconstructed the magnetization in our sample via corresponding scanning stray field measurements and discuss the relationship between local magnetic texture and localized harmonic generation.

[1] Koerner, C. et al., Science 375, 1165-1169 (2022)

[2] Lan, G. et al. Nat. Commun. 16, 1178 (2025)