Filtering and Imaging of Frequency-Degenerate Spin Waves Using Nanopositioning of a Single-Spin Sensor

Abstract

Nitrogen-vacancy (NV) magnetometry is a new technique for imaging spin waves in magnetic materials. It detects spin waves by their microwave magnetic stray fields, which decay evanescently on the scale of the spin-wavelength. Here, we use nanoscale control of a single-NV sensor as a wavelength filter to characterize frequency-degenerate spin waves excited by a microstrip in a thin-film magnetic insulator. With the NV probe in contact with the magnet, we observe an incoherent mixture of thermal and microwave-driven spin waves. By retracting the tip, we progressively suppress the small-wavelength modes until a single coherent mode emerges from the mixture. In-contact scans at low drive power surprisingly show occupation of the entire isofrequency contour of the two-dimensional spin-wave dispersion despite our one-dimensional microstrip geometry. Our distance-tunable filter sheds light on the spin-wave band occupation under microwave excitation and opens opportunities for imaging magnon condensates and other coherent spin-wave modes.

Mapping of Spin‐Wave Transport in Thulium Iron Garnet Thin Films Using Diamond Quantum Microscopy

“…Spin-wave interference is observed in 240 nm thick YIG/GGG film when using very weak MW powers, [33] i.e., 500 times less than the MW power used in our experiments. The lower MW power regime prevents broadening and saturating the NV ODMR peaks in the presence of spin waves (Figure 3e), and therefore allows imaging of complex rich patterns of spin waves excited in different directions.…”

“…[28] Future measurements by using NV-diamond scanning probe microscopy (SPM) [56,57] could push down the spatial resolution from ≈500 nm (confocal geometry) to below 50 nm (SPM) and provide more accuracy in filtering and imaging spin waves in ferrimagnetic insulators. [33] Particularly, TmIG with PMA is suggested to host topological spin textures [8,15] and therefore opens the door for NV magnetometry to study the complex interaction between topological spin textures such as skyrmions and magnons.…”

“…The lower MW power regime prevents broadening and saturating the NV ODMR peaks in the presence of spin waves (Figure 3e), and therefore allows imaging of complex rich patterns of spin waves excited in different directions. [33]…”

“…[28] An alternative technique has recently emerged for nanoscale measurement of spin waves based on optical detection of the electron spin resonances of nitrogen-vacancy (NV) centers in diamond. [29][30][31][32][33] Negatively charged NVs, composed of substitutional nitrogen adjacent to a vacancy site, are bright and stable emitters that exhibit optically detected magnetic resonance (ODMR) and millisecond spin coherence at ambient conditions, [34] making them an ideal platform to investigate SW properties in REIG magnetic insulators. NV magnetometry has been utilized to probe magnetic dynamic excitations in ferromagnetic thin films and microstructures, [35][36][37][38] deduce the chemical potential of the SW bath in YIG, [30] and study the effect of propagating surface SW modes in YIG to amplify externally applied microwave (MW) to excite remote NV locations from the MW source.…”