Single spins localized at nitrogen–vacancy defects in diamond are currently being investigated as sensitive magnetometers with nanoscale spatial resolution. Vincent Jacques and colleagues at the Ecole Normale Supérieure de Cachan, Université Paris-Sud and CNRS have now used nitrogen–vacancy magnetometry to image magnetic vortices — magnetic nanostructures with a curling in-plane magnetization and an out-of-plane magnetized core — in thin ferromagnetic films (Nature Commun. 4, 2279; 2013). The technique provides quantitative, vectorial information on the three-dimensional distribution of stray magnetic fields above the magnetic nanostructures, in good agreement with the results of the simulations.

The researchers combined an optical confocal microscope with an atomic force microscope, and attached a diamond nanocrystal containing a single nitrogen–vacancy defect to the tip of the atomic force microscope. As the sample is scanned by the probe, spin-dependent photoluminescence is collected and analysed to extract information on the value of the local magnetic field in a given direction. By using different orientations of the nitrogen–vacancy defect, it is possible to image various components of the magnetic field.

The images (edge of red square, 5 μm; scale bars, 1 μm) show maps of the out-of-plane component of the stray field of magnetic vortices in a permalloy thin film. The pixel brightness is proportional to the intensity of the magnetic field, with black corresponding to zero field. The experimental images (a,c) are recorded at a probe-to-sample distance of 300 nm and can be quite accurately reproduced by micromagnetic simulations (b,d). The field of a single magnetic vortex is shown in a,b where the vortex core is located at the centre. Panels c,d are maps of the field distribution in a higher-order magnetization state, with four vortices around an anti-vortex at the centre of the images.

Credit: © 2013 NPG