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122 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	Voltage-driven displacement of magnetic vortex cores M. Ghidini , R. Pellicelli , R. Mansell , D. Pesquera , B. Nair , X. Moya , S. Farokhipoor , F. Maccherozzi , C. H. W. Barnes , R. P. Cowburn , S. S. Dhesi , N. D. Mathur Journal Of Physics D: Applied Physics 53 DOI: 10.1088/1361-6463/aba01d Diamond Proposal Number(s): [11843] Open Access Show Abstract ▼ Abstract: Magnetic vortex cores in polycrystalline Ni discs underwent non-volatile displacements due to voltage-driven ferroelectric domain switching in single-crystal BaTiO3. This behaviour was observed using photoemission electron microscopy to image both the ferromagnetism and ferroelectricity, while varying in-plane sample orientation. The resulting vector maps of disc magnetization match well with micromagnetic simulations, which show that the vortex core is translated by the transit of a ferroelectric domain wall, and thus the inhomogeneous strain with which it is associated. The non-volatility is attributed to pinning inside the discs. Voltage-driven displacement of magnetic vortex cores is novel, and opens the way for studying voltage-driven vortex dynamics.	Oct 2020
I05-ARPES I06-Nanoscience	Spectral functions of CVD grown MoS2 monolayers after chemical transfer onto Au surface Sung Won Jung , Sangyeon Pak , Sanghyo Lee , Sonka Reimers , Saumya Mukherjee , Pavel Dudin , Timur K. Kim , Mattia Cattelan , Neil Fox , Sarnjeet S. Dhesi , Cephise Cacho , Seungnam Cha Applied Surface Science DOI: 10.1016/j.apsusc.2020.147390 Diamond Proposal Number(s): [24367, 22901] Show Abstract ▼ Abstract: The recent rise of van der Waals (vdW) crystals has opened new prospects for studying versatile and exotic fundamental physics with future device applications such as twistronics. Even though the recent development on Angle-resolved photoemission spectroscopy (ARPES) with Nano-focusing optics, making clean surfaces and interfaces of chemically transferred crystals have been challenging to obtain high-resolution ARPES spectra. Here, we show that by employing nano-ARPES with submicron sized beam and polystyrene-assisted transfer followed by annealing process in ultra-high vacuum environment, remarkably clear ARPES spectral features such as spin-orbit splitting and band renormalization of CVD-grown, monolayered MoS2 can be measured. Our finding paves a way to exploit chemically transferred crystals for measuring high-resolution ARPES spectra to observe exotic quasi-particles in vdW heterostructures.	Jul 2020
I06-Nanoscience	Large magnetoelectric coupling in multiferroic oxide heterostructures assembled via epitaxial lift-off D. Pesquera , E. Khestanova , M. Ghidini , S. Zhang , A. P. Rooney , F. Maccherozzi , P. Riego , S. Farokhipoor , J. Kim , X. Moya , M. E. Vickers , N. A. Stelmashenko , S. J. Haigh , S. S. Dhesi , N. D. Mathur Nature Communications 11 DOI: 10.1038/s41467-020-16942-x Diamond Proposal Number(s): [14745] Open Access Show Abstract ▼ Abstract: Epitaxial films may be released from growth substrates and transferred to structurally and chemically incompatible substrates, but epitaxial films of transition metal perovskite oxides have not been transferred to electroactive substrates for voltage control of their myriad functional properties. Here we demonstrate good strain transmission at the incoherent interface between a strain-released film of epitaxially grown ferromagnetic La0.7Sr0.3MnO3 and an electroactive substrate of ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 in a different crystallographic orientation. Our strain-mediated magnetoelectric coupling compares well with respect to epitaxial heterostructures, where the epitaxy responsible for strong coupling can degrade film magnetization via strain and dislocations. Moreover, the electrical switching of magnetic anisotropy is repeatable and non-volatile. High-resolution magnetic vector maps reveal that micromagnetic behaviour is governed by electrically controlled strain and cracks in the film. Our demonstration should inspire others to control the physical/chemical properties in strain-released epitaxial oxide films by using electroactive substrates to impart strain via non-epitaxial interfaces.	Jun 2020
I06-Nanoscience	Exchange-bias via nanosegregation in novel Fe 2–x Mn 1+x Al ( x = –0.25, 0, 0.25) Heusler films Samer Kurdi , Massimo Ghidini , Giorgio Divitini , Bhaskaran Nair , Ahmed Kursumovic , Paola Tiberto , Sarnjeet Dhesi , Zoe Barber Nanoscale Advances DOI: 10.1039/C9NA00689C Diamond Proposal Number(s): [17563] Open Access Show Abstract ▼ Abstract: Exchange-bias has been reported in bulk nanocrystalline Fe2MnAl, but individual thin films of this Heusler alloy have never been studied so far. Here we study the structural and magnetic properties of nanocrystalline thin films of Fe2–xMn1+xAl (x = –0.25, 0, 0.25) obtained by sputtering and ex-situ post-deposition annealing. We find that Fe2MnAl films display exchange-bias, and that varying Mn concentration determines the magnitude of the effect, which can be either enhanced (in Fe1.75Mn1.25Al) or suppressed (in Fe2.25Mn0.75Al). X-ray diffraction (XRD) shows that our films present a mixed L21-B2 Heusler structure where increasing Mn concentration favors the partial transformation of the L21 phase into the B2 phase. Scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDX) reveal that this composition-driven L21→B2 transformation is accompanied by phase segregation at the nanoscale. As a result, the Fe2–xMn1+xAl films that show exchange-bias (x = 0, 0.25) are heterogeneous, with nanograins of an Fe-rich phase embedded in a Mn-rich matrix (a non-negative matrix factorisation algorithm was used to give an indication of the phase composition from EDX data). Our comparative analysis of XRD, magnetometry and X-ray magnetic circular dichroism (XMCD), shows that Fe-rich nanograins and Mn-rich matrix are composed of a ferromagnetic L21 phase and an antiferromagnetic B2 phase, respectively, thus revealing that exchange-coupling between these two phases is the cause of the exchange-bias effect. Our work should inspire the development of single-layer, environmentally-friendly spin valve devices based on nanocomposite Heusler films.	May 2020
I06-Nanoscience	Nanoscale magnetoelectric effects revealed by imaging M. Ghidini , S. S. Dhesi , N. D. Mathur Journal Of Magnetism And Magnetic Materials DOI: 10.1016/j.jmmm.2020.167016 Diamond Proposal Number(s): [8876, 6230] Show Abstract ▼ Abstract: We review our work on continuous Ni films coupled via strain to ferroelectric substrates of BaTiO3 (BTO) and 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 (PMN-PT). We show that magnetic force microscopy (MFM) and photoemission electron microscopy (PEEM) of the Ni films (during or after electrical treatment) permit to reveal nanoscale converse magnetoelectric effects (CMEs) that are novel and elude macroscopic measurements. As examples, we discuss magnetization reversal without applied field in multilayer capacitors (MLCs), shear-strain-mediated CMEs in thin Ni films on PMN-PT and reversible switching of perpendicular magnetization from out-of-plane to in-plane in Ni films on BTO. In this latter case, we show that PEEM can be used to measure both magnetic and ferroelectric domains, thus providing key mechanistic insight in the magnetoelectric coupling mechanism.	May 2020
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	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	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	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

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