Person: Casola, Francesco
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Casola
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Francesco
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Casola, Francesco
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Publication Magnetostatic twists in room-temperature skyrmions explored by nitrogen-vacancy center spin texture reconstruction(Springer Science and Business Media LLC, 2018-07-13) Dovzhenko, Yuliya; Casola, Francesco; Schlotter, S.; Zhou, T. X.; Büttner, F.; Walsworth, R. L.; Beach, G. S. D.; Yacoby, AmirMagnetic skyrmions are two-dimensional non-collinear spin textures characterized by an integer topological number. Room-temperature skyrmions were recently found in magnetic multilayer stacks, where their stability was largely attributed to the interfacial Dzyaloshinskii–Moriya interaction. The strength of this interaction and its role in stabilizing the skyrmions is not yet well understood, and imaging of the full spin structure is needed to address this question. Here, we use a nitrogen-vacancy centre in diamond to measure a map of magnetic fields produced by a skyrmion in a magnetic multilayer under ambient conditions. We compute the manifold of candidate spin structures and select the physically meaningful solution. We find a Néel-type skyrmion whose chirality is not left-handed, contrary to preceding reports. We propose skyrmion tube-like structures whose chirality rotates through the film thickness. We show that NV magnetometry, combined with our analysis method, provides a unique tool to investigate this previously inaccessible phenomenon.Publication NMR technique for determining the depth of shallow nitrogen-vacancy centers in diamond(American Physical Society (APS), 2016) Pham, Linh; DeVience, Stephen J.; Casola, Francesco; Lovchinsky, Igor; Sushkov, Alexander; Bersin, Eric; Lee, Junghyun; Urbach, Elana; Cappellaro, Paola; Park, Hongkun; Yacoby, Amir; Lukin, Mikhail; Walsworth, RonaldWe demonstrate a robust experimental method for determining the depth of individual shallow nitrogen-vacancy (NV) centers in diamond with ∼1 nm uncertainty. We use a confocal microscope to observe single NV centers and detect the proton nuclear magnetic resonance (NMR) signal produced by objective immersion oil, which has well understood nuclear spin properties, on the diamond surface. We determine the NV center depth by analyzing the NV NMR data using a model that describes the interaction of a single NV center with the statistically polarized proton spin bath. We repeat this procedure for a large number of individual, shallow NV centers and compare the resulting NV depths to the mean value expected from simulations of the ion implantation process used to create the NV centers, with reasonable agreement.Publication Nanoscale NMR spectroscopy and imaging of multiple nuclear species(Nature Publishing Group, 2015) DeVience, Stephen J.; Pham, Linh; Lovchinsky, Igor; Sushkov, Alexander; Bar-Gill, Nir; Belthangady, Chinmay; Casola, Francesco; Corbett, Madeleine; Zhang, Huiliang; Lukin, Mikhail; Park, Hongkun; Yacoby, Amir; Walsworth, RonaldNuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI) provide non-invasive information about multiple nuclear species in bulk matter, with wide-ranging applications from basic physics and chemistry to biomedical imaging1. However, the spatial resolution of conventional NMR and MRI is limited2 to several micrometres even at large magnetic fields (>1 T), which is inadequate for many frontier scientific applications such as single-molecule NMR spectroscopy and in vivo MRI of individual biological cells. A promising approach for nanoscale NMR and MRI exploits optical measurements of nitrogen–vacancy (NV) colour centres in diamond, which provide a combination of magnetic field sensitivity and nanoscale spatial resolution unmatched by any existing technology, while operating under ambient conditions in a robust, solid-state system3, 4, 5. Recently, single, shallow NV centres were used to demonstrate NMR of nanoscale ensembles of proton spins, consisting of a statistical polarization equivalent to ∼100–1,000 spins in uniform samples covering the surface of a bulk diamond chip6, 7. Here, we realize nanoscale NMR spectroscopy and MRI of multiple nuclear species (1H, 19F, 31P) in non-uniform (spatially structured) samples under ambient conditions and at moderate magnetic fields (∼20 mT) using two complementary sensor modalities.Publication Nanometre-scale probing of spin waves using single-electron spins(Nature Publishing Group, 2015) van der Sar, Toeno; Casola, Francesco; Walsworth, Ronald; Yacoby, AmirPushing the frontiers of condensed-matter magnetism requires the development of tools that provide real-space, few-nanometre-scale probing of correlated-electron magnetic excitations under ambient conditions. Here we present a practical approach to meet this challenge, using magnetometry based on single nitrogen-vacancy centres in diamond. We focus on spin-wave excitations in a ferromagnetic microdisc, and demonstrate local, quantitative and phase-sensitive detection of the spin-wave magnetic field at ~50 nm from the disc. We map the magnetic-field dependence of spin-wave excitations by detecting the associated local reduction in the disc’s longitudinal magnetization. In addition, we characterize the spin–noise spectrum by nitrogen-vacancy spin relaxometry, finding excellent agreement with a general analytical description of the stray fields produced by spin–spin correlations in a 2D magnetic system. These complementary measurement modalities pave the way towards imaging the local excitations of systems such as ferromagnets and antiferromagnets, skyrmions, atomically assembled quantum magnets, and spin ice.Publication Control and local measurement of the spin chemical potential in a magnetic insulator(American Association for the Advancement of Science (AAAS), 2017-07-13) Du, Chunhui; van der Sar, Toeno; Zhou, Tony X.; Upadhyaya, Pramey; Casola, Francesco; Zhang, Huiliang; Onbasli, Mehmet C.; Ross, Caroline A.; Walsworth, Ronald; Tserkovnyak, Yaroslav; Yacoby, AmirThe spin chemical potential characterizes the tendency of spins to diffuse. Probing this quantity could provide insight into materials such as magnetic insulators and spin liquids and aid optimization of spintronic devices. Here we introduce single-spin magnetometry as a generic platform for nonperturbative, nanoscale characterization of spin chemical potentials. We experimentally realize this platform using diamond nitrogen-vacancy centers and use it to investigate magnons in a magnetic insulator, finding that the magnon chemical potential can be controlled by driving the system's ferromagnetic resonance. We introduce a symmetry-based two-fluid theory describing the underlying magnon processes, measure the local thermomagnonic torque, and illustrate the detection sensitivity using electrically controlled spin injection. Our results pave the way for nanoscale control and imaging of spin transport in mesoscopic systems.