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(a) Simplified scheme of the scanning probe magnetometer. A 20 nm diamond nanocrystal hosting a single NV defect is grafted at the end of an AFM tip. A confocal microscope placed on top of the tip allows us both to excite and collect the NV defect spin-dependent PL. A microwave field is generated by an antenna approached in the vicinity of the NV defect. (b) PL raster scan of the AFM tip showing a bright PL spot at its apex. White dashed lines indicate the shadow of the tip. (c) Second-order autocorrelation function recorded from the bright emission spot using a Hanbury Brown and Twiss interferometer. A strong anticorrelation effect, , is observed at zero delay. More than photons/s can be detected from the single NV defect when excited at saturation, with a signal-to-background ratio greater than 10. (d) Optically detected ESR spectra recorded for different magnetic field magnitudes. For these experiments, the ESR contrast is , the linewidth MHz, and the average rate of detected photons cnt/s, with an optical pumping power W. The zero-field splitting parameters are D = 2.87 GHz and E = 5 MHz.
Measurements of the magnetic field distribution created by a commercial magnetic hard disk for a probe-to-sample distance d = 250 nm. All images correspond to pixels, with a 13-nm pixel size. (a) Geometry of the magnetic bits. (b) Single iso-magnetic field image. Dark areas correspond to a null component, and the red arrow indicates the NV defect axis, along which the magnetic field projection is measured. (c) Dual iso-magnetic field image recorded by measuring the PL difference for two fixed MW frequencies applied consecutively. Dark (respectively, bright) areas correspond to (respectively, mT). (d) Complete magnetic field distribution of the same area recorded by using the lock-in method. The panel on the right shows a line-cut taken along the white dashed line. For images (b)–(d), the acquisition time per pixel is 5 ms, 60 ms, and 110 ms, respectively.
(a) Simulation of the off-axis magnetic field component for a random distribution of bit magnetizations and a probe-to-sample distance d = 30 nm. (b) PL image recorded with the NV scanning probe magnetometer operating in tapping mode, without applying any microwave field. The image corresponds to pixels, with a 8-nm pixel size and a 20-ms acquisition time per pixel. (c) Line-cut corresponding to the white dashed line in (b). A possible configuration of the bit magnetization is schematically depicted in (d).
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