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PLUM Seminar : Thursday,  11th May 2023 at 2:00 pm

Samer Kurdi  (University of Delft)

Title: Scanning Nitrogen Vacancy Magnetometry: A Novel Spin Wave Imaging Platform


Institut Néel, Room F418 (Erwin Bertaut)

Abstract : Magnetometry based on nitrogenvacancy (NV) spins in diamond has recently emerged as a powerful tool for probing spin waves1 the elementary excitations of coupled spins in magnetically ordered materials. In this talk I will focus on how we utilize scanning NV magnetometry in which we use a NV sensor spin(s) that are shallowly embedded in the tip of a diamond scanning probe to image spin waves in a thin film magnetic insulator. I will focus on two studies:

(1) I will show how microwave excitation of lowwavenumber spin waves leads to a highdensity and, most surprising, a unidirectional gas of incoherent magnons2. We find that the enhanced magnon density extends unidirectionally over hundreds of micrometres from the excitation stripline. Furthermore, we demonstrate how the spatial decay of the stray fields reveals the wavenumber content of both coherently excited spin waves with a well defined wavenumber as that of the incoherent magnon gas.

(2) I will show how we can use our singleNV sensor as a wavelength filter to characterize frequency degenerate spin wave modes3. With the NV probe in contact with the magnet we observe a mixture of thermal and coherently driven spin waves and when we retract our tip we suppressed the smallwavelength modes, leaving only the coherently driven mode visible. We also show that our incontact scans at low microwave drive power surprisingly show occupation of the entire isofrequency contour of the twodimensional spinwave dispersion despite our one dimensional microstrip geometry.

These results reveal the power of scanning NVmagnetometry as a tool for spinwave probing. Whilst showcasing that (1) coherently driven, lowwavenumber spin waves are efficient generators of a nonequilibrium magnon gas in target directions and that (2) nanoscale control over the NVsample distance enables wavenumberselective imaging of magnetization oscillations. Our results open new avenues for local control of spin transport and for imaging other coherent spinwave modes.

[1] I. Bertelli et al. Sci. Adv. 6 eabd3556 (2020).
[2] B. G Simon*, S. Kurdi* et al. Nano Lett. 21 8213 (2021).
[3] B. G Simon*, S. Kurdi* et al. Nano Lett. 22 9198 (2022).
[4] B. A. McCullian et al. Nat. Comm. 11 5229 (2020).