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117 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2, 3, 4, 5, 6, 7, 8 [Next/Last]

Instruments / Technical Area	Publication Details	Published
I06-Nanoscience	Spin flop and crystalline anisotropic magnetoresistance in CuMnAs M. Wang , C. Andrews , S. Reimers , O. J. Amin , P. Wadley , R. P. Campion , S. F. Poole , J. Felton , K. W. Edmonds , B. L. Gallagher , A. W. Rushforth , O. Makarovsky , K. Gas , M. Sawicki , D. Kriegner , J. Zubáč , K. Olejník , V. Novák , T. Jungwirth , M. Shahrokhvand , U. Zeitler , S. S. Dhesi , F. Maccherozzi Physical Review B 101 DOI: 10.1103/PhysRevB.101.094429 Diamond Proposal Number(s): [11846, 20793] Show Abstract ▼ Abstract: We report magnetic-field-induced rotation of the antiferromagnetic Néel vector in epitaxial CuMnAs thin films. First, using soft x-ray magnetic linear dichroism spectroscopy as well as magnetometry, we demonstrate spin-flop switching and continuous spin reorientation in films with uniaxial and biaxial magnetic anisotropies, respectively, for applied magnetic fields of the order of 2 T. The remnant antiferromagnetic domain configurations are determined using x-ray photoemission electron microscopy. Next, we show that the Néel vector reorientations are manifested in the longitudinal and transverse anisotropic magnetoresistance. Dependencies of the electrical resistance on the orientation of the Néel vector with respect to both the electrical current direction and the crystal symmetry are identified, including a weak fourth-order term evident at high magnetic fields. The results provide characterization of key parameters including the anisotropic magnetoresistance coefficients, magnetocrystalline anisotropy, and spin-flop field in epitaxial films of tetragonal CuMnAs, a candidate material for antiferromagnetic spintronics.	Mar 2020
I06-Nanoscience	Probing the local distortion of Fe sites in Fe3 O4 thin films using enhanced symmetry selection in XMLD Hebatalla Elnaggar , Rupan Wang , Mahnaz Ghiasi , Maria Yañez , Mario U. Delgado-jaime , Mai Hussein Hamed , Amélie Juhin , Sarnjeet S. Dhesi , Frank De Groot Physical Review Materials 4 DOI: 10.1103/PhysRevMaterials.4.024415 Diamond Proposal Number(s): [17588] Show Abstract ▼ Abstract: Magnetite ( Fe 3 O 4 ) thin-films are among the most stimulating systems for electronic applications, in particular given that their electric and magnetic properties can be controlled by substrate strain. Here we investigate the electronic structure of a 38 nm Fe 3 O 4 / SrTiO 3 ( 001 ) thin-film by a unique set of x-ray magnetic linear dichroism (XMLD) measurements. We show that it is only possible to uncover the orbital character of the Fe sites in Fe 3 O 4 by a systematic analysis of the XMLD angular distribution. The local symmetry of the Fe 2 + B site in the thin-film is found to be trigonally distorted. Our results highlight that the combination of state-of-the-art XMLD measurements and theoretical simulations is indispensable for investigating the electronic structure of oxide thin-films and heterostructures.	Feb 2020
I06-Nanoscience	Voltage-driven annihilation and creation of magnetic vortices in Ni discs Massimo Ghidini , Rhodri Mansell , Raffaele Pellicelli , David Pesquera , Bhaskaran Nair , Xavier Moya , Saeedeh Farokhipoor , Francesco Maccherozzi , Crispin Barnes , Russell Cowburn , Sarnjeet Dhesi , Neil Mathur Nanoscale DOI: 10.1039/C9NR08672B Diamond Proposal Number(s): [11843] Show Abstract ▼ Abstract: Using photoemission electron microscopy (PEEM) to image ferromagnetism in polycrystalline Ni disks, and ferroelectricity in their single-crystal BaTiO3 substrates, we find that voltage-driven 90 ferroelectric domain switching serves to reversibly annihilate each magnetic vortex via uniaxial compressive strain, and that the orientation of the resulting bi domain reveals the chirality of the annihilated vortex. (Micromagnetic simulations reveal that only 60% of this strain was required for annihilation.) Voltage control of magnetic vortices is novel, and should be energetically favourable with respect to the use of a magnetic field or an electrical current. In future, stray field from bi domains could be exploited to read vortex chirality. Given that core polarity can already be read via stray field, our work represents a step towards four-state low power memory applications.	Feb 2020
I06-Nanoscience	Photoemission core level binding energies from multiple sized nanoparticles on the same support: TiO 2 (110)/Au Andrew Mellor , Axel Wilson , Chi L. Pang , Chi M. Yim , Francesco Maccherozzi , Sarnjeet S. Dhesi , Christopher A. Muryn , Hicham Idriss , Geoff Thornton The Journal Of Chemical Physics 152 DOI: 10.1063/1.5135760 Diamond Proposal Number(s): [13723] Show Abstract ▼ Abstract: A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO2(110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au3 clusters are present, the Au 4f7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.	Jan 2020
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	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	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	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

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