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50 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I06-Nanoscience	Current-driven skyrmion dynamics and drive-dependent skyrmion hall effect in an ultrathin film Romeo Juge , Soong-geun Je , Dayane De Souza Chaves , Liliana D. Buda-prejbeanu , José Peña-garcia , Jayshankar Nath , Ioan Mihai Miron , Kumari Gaurav Rana , Lucia Aballe , Michael Foerster , Francesca Genuzio , Tevfik Onur Menteş , Andrea Locatelli , Francesco Maccherozzi , Sarnjeet S. Dhesi , Mohamed Belmeguenai , Yves Roussigné , Stéphane Auffret , Stefania Pizzini , Gilles Gaudin , Jan Vogel , Olivier Boulle Physical Review Applied 12 DOI: 10.1103/PhysRevApplied.12.044007 Diamond Proposal Number(s): [14035] Show Abstract ▼ Abstract: Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their current-induced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of Néel skyrmions with diameters in the 100-nm range in an ultrathin Pt / Co / Mg O trilayer. We find that these skyrmions can be driven at a speed of 100 m s − 1 and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties.	Oct 2019
I06-Nanoscience	Mechanism of Néel order switching in antiferromagnetic thin films revealed by magnetotransport and direct imaging L. Baldrati , O. Gomonay , A. Ross , M. Filianina , R. Lebrun , R. Ramos , C. Leveille , F. Fuhrmann , T. R. Forrest , F. Maccherozzi , S. Valencia , F. Kronast , E. Saitoh , J. Sinova , M. Kläui Physical Review Letters 123 DOI: 10.1103/PhysRevLett.123.177201 Diamond Proposal Number(s): [18850, 20698] Show Abstract ▼ Abstract: We probe the current-induced magnetic switching of insulating antiferromagnet–heavy-metal systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one-third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely, the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs.	Oct 2019
I06-Nanoscience	Early-stage dynamics of metallic droplets embedded in the nanotextured Mott insulating phase of V2O3 A. Ronchi , P. Homm , M. Menghini , P. Franceschini , F. Maccherozzi , F. Banfi , G. Ferrini , F. Cilento , F. Parmigiani , S. S. Dhesi , M. Fabrizio , J.-p. Locquet , C. Giannetti Physical Review B 100 DOI: 10.1103/PhysRevB.100.075111 Diamond Proposal Number(s): [16128] Show Abstract ▼ Abstract: Unveiling the physics that governs the intertwining between the nanoscale self-organization and the dynamics of insulator-to-metal transitions (IMTs) is key for controlling on demand the ultrafast switching in strongly correlated materials and nanodevices. A paradigmatic case is the IMT in V 2 O 3 , for which the mechanism that leads to the nucleation and growth of metallic nanodroplets out of the supposedly homogeneous Mott insulating phase is still a mystery. Here, we combine x-ray photoemission electron microscopy and ultrafast nonequilibrium optical spectroscopy to investigate the early-stage dynamics of isolated metallic nanodroplets across the IMT in V 2 O 3 thin films. Our experiments show that the low-temperature monoclinic antiferromagnetic insulating phase is characterized by the spontaneous formation of striped polydomains, with different lattice distortions. The insulating domain boundaries accommodate the birth of metallic nanodroplets, whose nonequilibrium expansion can be triggered by the photoinduced change of the 3 d -orbital occupation. We address the relation between the spontaneous nanotexture of the Mott insulating phase in V 2 O 3 and the timescale of the metallic seeds growth. We speculate that the photoinduced metallic growth can proceed along a nonthermal pathway in which the monoclinic lattice symmetry of the insulating phase is partially retained.	Aug 2019
I06-Nanoscience	Tunability of domain structure and magnonic spectra in antidot arrays of Heusler alloy Sougata Mallick , Sucheta Mondal , Takeshi Seki , Sourav Sahoo , Thomas Forrest , Francesco Maccherozzi , Zhenchao Wen , Saswati Barman , Anjan Barman , Koki Takanashi , Subhankar Bedanta Physical Review Applied 12 DOI: 10.1103/PhysRevApplied.12.014043 Diamond Proposal Number(s): [16582] Show Abstract ▼ Abstract: Materials suitable for magnonic crystals demand low magnetic damping and long spin-wave propagation distance. In this context Co -based Heusler compounds are ideal candidates for magnonic based applications. In this work, antidot arrays (with different shapes) of epitaxial Co 2 Fe 0.4 Mn 0.6 Si Heusler-alloy thin films are prepared using e-beam lithography and sputtering technique. Magneto-optic Kerr effect (MOKE) and ferromagnetic resonance analysis confirm the presence of dominant cubic and moderate uniaxial magnetic anisotropies in the thin film. Domain imaging via x-ray photoemission electron microscopy on the antidot arrays reveals chainlike switching or correlated bigger domains for different antidot shapes. Time-resolved MOKE microscopy is performed to study the precessional dynamics and magnonic modes of the antidots with different shapes. We show that the optically induced spin-wave spectra in such antidot arrays can be tuned by changing the shape of the holes. The variation in internal-field profiles, pinning energy barrier, and anisotropy modifies the spin-wave spectra dramatically within the antidot arrays with different shapes. We further show that by combining the magnetocrystalline anisotropy with the shape anisotropy, an extra degree of freedom can be achieved to control the magnonic modes in such antidot lattices.	Jul 2019
I06-Nanoscience	Shear-strain-mediated magnetoelectric effects revealed by imaging M. Ghidini , R. Mansell , F. Maccherozzi , X. Moya , L. C. Phillips , W. Yan , D. Pesquera , C. H. W. Barnes , R. P. Cowburn , J.-m. Hu , S. S. Dhesi , N. D. Mathur Nature Materials 38 DOI: 10.1038/s41563-019-0374-8 Diamond Proposal Number(s): [8876] Show Abstract ▼ Abstract: Large changes in the magnetization of ferromagnetic films can be electrically driven by non-180° ferroelectric domain switching in underlying substrates, but the shear components of the strains that mediate these magnetoelectric effects have not been considered so far. Here we reveal the presence of these shear strains in a polycrystalline film of Ni on a 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 substrate in the pseudo-cubic (011)pc orientation. Although vibrating sample magnetometry records giant magnetoelectric effects that are consistent with the hitherto expected 90° rotations of a global magnetic easy axis, high-resolution vector maps of magnetization (constructed from photoemission electron microscopy data, with contrast from X-ray magnetic circular dichroism) reveal that the local magnetization typically rotates through smaller angles of 62–84°. This shortfall with respect to 90° is a consequence of the shear strain associated with ferroelectric domain switching. The non-orthogonality represents both a challenge and an opportunity for the development and miniaturization of magnetoelectric devices.	May 2019
I06-Nanoscience	Redox behaviour of a ceria-zirconia inverse model catalyst Michael Allan , David Grinter , Simran Dhaliwal , Chris Muryn , Thomas Forrest , Francesco Maccherozzi , Sarnjeet S. Dhesi , Geoff Thornton Surface Science 682, 8-13 DOI: 10.1016/j.susc.2018.12.005 Diamond Proposal Number(s): [17343] Show Abstract ▼ Abstract: The redox behaviour modification following the addition of zirconia to ceria nanostructures supported on Rh(111) has been investigated using a combination of Low Energy Electron Diffraction (LEED) and X-ray Photoemission Electron Microscopy (XPEEM). Soft X-ray irradiation was employed to reduce ZrO2-x(111) supported on Rh(111) and, by introducing oxygen, the reoxidation process of the thin film was monitored. CeO2(111) was then deposited on zirconia/Rh(111) and, using XPEEM, we determined that the mixed metal oxide formed a phase-separated structure with CeO2(111) nanoparticles on top of the zirconia. Upon exposure of CeO2-x/ZrO2-x/Rh(111) to X-ray illumination, the zirconia no longer undergoes any observable reduction while at the same time the ceria is reduced. Our results indicate a synergy between the zirconia and ceria in the phase-separated system expected in the working catalyst, with oxygen transfer between the metal oxides. This sheds light on the mechanism of the enhancement of catalytic properties seen with the addition of zirconia to ceria and highlights the oxygen storage and release ability of ceria.	Apr 2019
I06-Nanoscience	Imaging of current induced Néel vector switching in antiferromagnetic Mn 2 Au S. Yu. Bodnar , M. Filianina , S. P. Bommanaboyena , T. Forrest , F. Maccherozzi , A. A. Sapozhnik , Y. Skourski , M. Klaui , M. Jourdan Physical Review B 99 DOI: 10.1103/PhysRevB.99.140409 Diamond Proposal Number(s): [20534] Show Abstract ▼ Abstract: The effects of current induced Néel spin-orbit torques on the antiferromagnetic domain structure of epitaxial Mn2Au thin films were investigated by x-ray magnetic linear dichroism–photoemission electron microscopy.We observed current induced switching of antiferromagnetic domains essentially corresponding to morphological features of the samples. Reversible as well as irreversible Néel vector reorientation was obtained in different parts of the samples and the switching of up to 30% of all domains in the field of view of 10 μm is demonstrated. Our direct microscopical observations are compared to and fully consistent with anisotropic magnetoresistance effects previously attributed to current induced Néel vector switching in Mn2Au.	Apr 2019
I06-Nanoscience	Light control of the nanoscale phase separation in heteroepitaxial nickelates G. Mattoni , N. Manca , M. Hadjimichael , Pavlo Zubko , A. J. H. Van Der Torren , C. Yin , S. Catalano , M. Gibert , F. Maccherozzi , Y. Liu , S. S. Dhesi , A. D. Caviglia Physical Review Materials 2 DOI: 10.1103/PhysRevMaterials.2.085002 Diamond Proposal Number(s): [13081, 10428] Show Abstract ▼ Abstract: Strongly correlated materials show unique solid-state phase transitions with rich nanoscale phenomenology that can be controlled by external stimuli. Particularly interesting is the case of light–matter interaction in the proximity of the metal–insulator transition of heteroepitaxial nickelates. In this work, we use near-infrared laser light in the high-intensity excitation regime to manipulate the nanoscale phase separation in NdNiO3. By tuning the laser intensity, we can reproducibly set the coverage of insulating nanodomains, which we image by photoemission electron microscopy, thus semipermanently configuring the material state. With the aid of transport measurements and finite element simulations, we identify two different timescales of thermal dynamics in the light–matter interaction: a steady-state and a fast transient local heating. These results open interesting perspectives for locally manipulating and reconfiguring electronic order at the nanoscale by optical means.	Aug 2018
I06-Nanoscience	Voltage control of magnetic single domains in Ni discs on ferroelectric BaTiO3 Massimo Ghidini , Bonan Zhu , Rhodri Mansell , Raffaele Pellicelli , Arnaud Lesaine , Xavier Moya , Sam Crossley , Bhasi Nair , Francesco Maccherozzi , Crispin H. W. Barnes , Russell P. Cowburn , Sarnjeet Dhesi , Neil D. Mathur Journal Of Physics D: Applied Physics 51, 22 DOI: 10.1088/1361-6463/aabf77 Diamond Proposal Number(s): [9590] Show Abstract ▼ Abstract: For 1 microm-diameter Ni discs on a BaTiO3 substrate, the local magnetization direction is determined by ferroelectric domain orientation as a consequence of growth strain, such that single-domain discs lie on single ferroelectric domains. On applying a voltage across the substrate, ferroelectric domain switching yields non-volatile magnetization rotations of 90°, while piezoelectric effects that are small and continuous yield non-volatile magnetization reversals that are non-deterministic. This demonstration of magnetization reversal without ferroelectric domain switching implies reduced fatigue, and therefore represents a step towards applications.	May 2018
I06-Nanoscience	Current polarity-dependent manipulation of antiferromagnetic domains Peter Wadley , Sonka Reimers , Michal J. Grzybowski , Carl Andrews , Mu Wang , Jasbinder S. Chauhan , Bryan L. Gallagher , Richard P. Campion , Kevin W. Edmonds , Sarnjeet S. Dhesi , Francesco Maccherozzi , Vit Novak , Joerg Wunderlich , Tomas Jungwirth Nature Nanotechnology 11 DOI: 10.1038/s41565-018-0079-1 Diamond Proposal Number(s): [16376] Show Abstract ▼ Abstract: Antiferromagnets have several favourable properties as active elements in spintronic devices, including ultra-fast dynamics, zero stray fields and insensitivity to external magnetic fields1. Tetragonal CuMnAs is a testbed system in which the antiferromagnetic order parameter can be switched reversibly at ambient conditions using electrical currents2. In previous experiments, orthogonal in-plane current pulses were used to induce 90° rotations of antiferromagnetic domains and demonstrate the operation of all-electrical memory bits in a multi-terminal geometry3. Here, we demonstrate that antiferromagnetic domain walls can be manipulated to realize stable and reproducible domain changes using only two electrical contacts. This is achieved by using the polarity of the current to switch the sign of the current-induced effective field acting on the antiferromagnetic sublattices. The resulting reversible domain and domain wall reconfigurations are imaged using X-ray magnetic linear dichroism microscopy, and can also be detected electrically. Switching by domain-wall motion can occur at much lower current densities than those needed for coherent domain switching.	Mar 2018

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