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Optical detection of magnetic resonance using quantum spin sensors (QSSs) provides a spatially local and sensitive technique to probe spin dynamics in magnets. However, its utility as a probe of antiferromagnetic resonance (AFMR) remains an open question. We report the experimental demonstration of optically detected AFMR in layered van der Waals antiferromagnets (AFM) up to frequencies of 24 gigahertz. We leverage QSS spin relaxation due to low-frequency magnetic field fluctuations arising from collective dynamics of magnons excited by the uniform AFMR mode. First, through AFMR spectroscopy, we characterize the intrinsic exchange fields and magnetic anisotropies of the AFM. Second, using the localized sensitivity of the QSS, we demonstrate magnon transport over tens of micrometers. Last, we find that optical detection efficiency increases with increasing frequency. This showcases the dual capabilities of QSS as detectors of high-frequency magnetization dynamics and magnon transport, paving the way for understanding and controlling the magnetism of antiferromagnets. 

Ferromagnetic resonance force microscopy (FMRFM) is a powerful scanned probe technique that uses sub-micrometer-scale, spatially localized standing spin wave modes (LMs) to perform local ferromagnetic resonance (FMR) measurements. Here, we show the spatially resolved imaging of Gilbert damping in a ferromagnetic material (FM) using FMRFM. Typically damping is measured from the FMR linewidth. We demonstrate an approach to image the spatial variation of Gilbert damping utilizing the LM resonance peak height to measure the LM resonance cone angle. This approach enables determination of damping through field-swept FMRFM at a single excitation frequency. The extreme force sensitivity of ∼2 fN at room temperature can resolve changes of Gilbert damping as small as ∼2×10−4 at 2 GHz, corresponding to ∼0.16 Oe in FMR linewidth resolution. This high sensitivity, high spatial resolution, and single frequency imaging of Gilbert damping creates the opportunity to study spin interactions at the interface between an insulating FM and a small volume of nonmagnetic material such as atomically thin two-dimensional materials.