I06-Nanoscience
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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
Diamond Proposal Number(s):
[8876]
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.
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May 2019
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I06-Nanoscience
|
Diamond Proposal Number(s):
[17343]
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.
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Dec 2018
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I06-Nanoscience
|
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
Diamond Proposal Number(s):
[13081, 10428]
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.
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Aug 2018
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I06-Nanoscience
|
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
Diamond Proposal Number(s):
[9590]
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.
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May 2018
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I06-Nanoscience
|
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
Diamond Proposal Number(s):
[16376]
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.
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Mar 2018
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I06-Nanoscience
Optics
|
Open Access
Abstract: Insertion devices are utilized at synchrotron radiation facilities around the world for their capability to provide a high-brilliance X-ray beam. APPLE-II type undulators are especially important for their capacity to switch between a variety of photon beam polarization states. A high-precision soft X-ray polarimeter has been used to investigate the polarization calibration of an APPLE-II undulator (period length λu = 64 mm) installed on beamline I06 at Diamond Light Source. Systematic measurement of the beam polarization state at a range of linear arbitrary angles has been compared with the expected result for a given set of undulator gap and row phase parameters calculated from theory. Determination of the corresponding Stokes–Poincaré parameters from the measured data reveals a discrepancy between the two. The limited number of energy/polarization combinations included in the undulator calibration tables necessitates the use of interpolated values for the missing points which is expected to contribute to the discrepancy. However, by modifying the orbit of the electron beam through the undulator by at least 160 µm it has been found that for certain linear polarizations the discrepancies can be corrected. Overall, it is suggested that complete correction of the Stokes–Poincaré parameters for all linear angles would require alteration of both these aspects.
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Mar 2018
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I06-Nanoscience
|
Diamond Proposal Number(s):
[9309]
Abstract: The growth and reactive dewetting of ultra-thin films of iron oxides supported on Re(0001) surfaces have been imaged in-situ in real time. Initial growth forms a non-magnetic stable FeO (wüstite like) layer in a commensurate network upon which high aspect ratio nanowires of several microns length but less than 40nm width can be fabricated. The nanowires are closely aligned with the substrate crystallography and imaging by X-ray magnetic circular dichroism shows that each contain a single magnetic domain. The driving force for dewetting appears to be the minimization of strain energy of the Fe3O4 crystallites and follows the Tersoff and Tromp model in which strain is minimized at constant height by extending in one epitaxially matched direction. Such wires are promising in spintronic applications and we predict that the growth will also occur on other hexagonal substrates.
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Mar 2018
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I06-Nanoscience
|
Diamond Proposal Number(s):
[10361, 12565, 14135]
Abstract: The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (>×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect.
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Feb 2018
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I06-Nanoscience
|
W.
Saenrang
,
B. A.
Davidson
,
F.
Maccherozzi
,
J. P.
Podkaminer
,
J.
Irwin
,
R. D.
Johnson
,
J. W.
Freeland
,
J.
Íñiguez
,
J. L.
Schad
,
K.
Reierson
,
J. C.
Frederick
,
C. A. F.
Vaz
,
L.
Howald
,
T. H.
Kim
,
S.
Ryu
,
M. V.
Veenendaal
,
P. G.
Radaelli
,
S. S.
Dhesi
,
M. S.
Rzchowski
,
C. B.
Eom
Diamond Proposal Number(s):
[12084, 13225, 11589]
Open Access
Abstract: Exploiting multiferroic BiFeO3 thin films in spintronic devices requires deterministic and robust control of both internal magnetoelectric coupling in BiFeO3, as well as exchange coupling of its antiferromagnetic order to a ferromagnetic overlayer. Previous reports utilized approaches based on multi-step ferroelectric switching with multiple ferroelectric domains. Because domain walls can be responsible for fatigue, contain localized charges intrinsically or via defects, and present problems for device reproducibility and scaling, an alternative approach using a monodomain magnetoelectric state with single-step switching is desirable. Here we demonstrate room temperature, deterministic and robust, exchange coupling between monodomain BiFeO3 films and Co overlayer that is intrinsic (i.e., not dependent on domain walls). Direct coupling between BiFeO3 antiferromagnetic order and Co magnetization is observed, with ~ 90° in-plane Co moment rotation upon single-step switching that is reproducible for hundreds of cycles. This has important consequences for practical, low power non-volatile magnetoelectric devices utilizing BiFeO3.
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Nov 2017
|
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I06-Nanoscience
|
Elisabeth M.
Bothschafter
,
Elsa
Abreu
,
Laurenz
Rettig
,
Teresa
Kubacka
,
Sergii
Parchenko
,
Michael
Porer
,
Christian
Dornes
,
Yoav William
Windsor
,
Mahesh
Ramakrishnan
,
Aurora
Alberca
,
Sebastian
Manz
,
Jonathan
Saari
,
Seyed M.
Koohpayeh
,
Manfred
Fiebig
,
Thomas
Forrest
,
Philipp
Werner
,
Sarnjeet S.
Dhesi
,
Steven L.
Johnson
,
Urs
Staub
Diamond Proposal Number(s):
[13355, 13926]
Abstract: We investigate the demagnetization dynamics of the cycloidal and sinusoidal phases of multiferroic TbMnO3 by means of time-resolved resonant soft x-ray diffraction following excitation by an optical pump. The use of orthogonal linear x-ray polarizations provides information on the contribution from the different magnetic moment directions, which can be interpreted as signatures from multiferroic cycloidal spin order and sinusoidal spin order. Tracking these signatures in the time domain enables us to identify the transient magnetic phase created by intense photoexcitation of the electrons and subsequent heating of the spin system on a picosecond time scale. The transient phase is shown to exhibit mostly spin density wave character, as in the adiabatic case, while nevertheless retaining the wave vector of the cycloidal long-range order. Two different pump photon energies, 1.55 and 3.1 eV, lead to population of the conduction band predominantly via intersite d−d or intrasite p−d transitions, respectively. We find that the nature of the optical excitation does not play an important role in determining the dynamics of magnetic order melting. Further, we observe that the orbital reconstruction, which is induced by the spin ordering, disappears on a time scale comparable to that of the cycloidal order, attesting to a direct coupling between magnetic order and orbital reconstruction. Our observations are discussed in the context of recent theoretical models of demagnetization dynamics in strongly correlated systems, revealing the potential of this type of measurement as a benchmark for such theoretical studies.
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Nov 2017
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