Detecting and Imaging of Magnons at Nanoscale with van der Waals Quantum Sensor

Magnonic devices are extensively studied for energy-efficient information processing. High spatial resolution and high accuracy measurement is required to characterize the excitation and distribution of magnons. Here, sensing and imaging of magnons in the magnetic insulator Y3Fe5O12$\rm Y_3 Fe_5 O_{12}$ (YIG) is realized with negatively charged boron vacancy (VB-$V_{\rm {B}}<^>-$) spin defects in 2D hexagonal boron nitride (hBN). Thermal magnon noise is studied through spin relaxometry, illustrating the nanometers proximity of the 2D quantum sensor over a large area. The small probe-sample standoff distance helps to detect weak signals with diffraction-limited spatial resolution. The uniform out-of-plane symmetry axis of VB-$V_{\rm {B}}<^>{-}$ is further utilized to study perpendicular magnetic anisotropy (PMA). It effectively extracts the stray field of microwave-excited magnons from the direct stripline field. The distributions of propagating and localized magnons in different structures are subsequently imaged and analyzed. The work provides the strategy for utilizing the distinctive advantages of the van der Waals quantum sensor in magnetic imaging. The results will promote the development of magnonic devices for diverse applications. VB-$V_{\rm {B}}<^>{-}$ color center in hBN film is explored as 2D quantum sensor to detect the near-surface magnon stray field. With nanometers probe-sample distance and the uniform out-of-plane axis of spin sensor, the excitation and propagation of magnons in magnetic insulators are revealed with high accuracy and diffraction-limited spatial resolution. image