I16-Materials and Magnetism
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Dorin
Rusu
,
Jonathan J. P.
Peters
,
Thomas P. A.
Hase
,
James A.
Gott
,
Gareth A. A.
Nisbet
,
Jörg
Strempfer
,
Daniel
Haskel
,
Samuel D.
Seddon
,
Richard
Beanland
,
Ana M.
Sanchez
,
Marin
Alexe
Diamond Proposal Number(s):
[25569]
Open Access
Abstract: Ferroics, especially ferromagnets, can form complex topological spin structures such as vortices1 and skyrmions when subjected to particular electrical and mechanical boundary conditions. Simple vortex-like, electric-dipole-based topological structures have been observed in dedicated ferroelectric systems, especially ferroelectric–insulator superlattices such as PbTiO3/SrTiO3, which was later shown to be a model system owing to its high depolarizing field. To date, the electric dipole equivalent of ordered magnetic spin lattices driven by the Dzyaloshinskii–Moriya interaction (DMi) has not been experimentally observed. Here we examine a domain structure in a single PbTiO3 epitaxial layer sandwiched between SrRuO3 electrodes. We observe periodic clockwise and anticlockwise ferroelectric vortices that are modulated by a second ordering along their toroidal core. The resulting topology, supported by calculations, is a labyrinth-like pattern with two orthogonal periodic modulations that form an incommensurate polar crystal that provides a ferroelectric analogue to the recently discovered incommensurate spin crystals in ferromagnetic materials. These findings further blur the border between emergent ferromagnetic and ferroelectric topologies, clearing the way for experimental realization of further electric counterparts of magnetic DMi-driven phases.
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Feb 2022
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[10248]
Open Access
Abstract: Demonstrating both the intrinsic and extrinsic nature of the giant piezoelectric effect (GPE) in complex solid solutions, near the morphotropic phase boundary, has been extremely challenging until now, because such materials exhibit multiple phases on the order of tens of microns across, meaning important information is lost due to averaging when using established high resolution diffraction techniques to extract three dimensional structural information. We have used a different approach proposed by Nisbet et al. [Acta Crystallogr. Sect. A 71, 20 (2015)], which has been adapted to differentiate between spatially adjacent phases and simultaneously track the evolution of those phases in response to electric fields. As a result, we have identified three environment specific GPEs. The first of these is a GPE which is an order of magnitude greater than previously reported for a given change in field. This is observed during a tetragonal-monoclinic transition in a multiphasic environment. A secondary, large GPE is observed in the neighboring, nontransitioning, monoclinic phase due to stress biasing, and a more typical GPE is observed when the system becomes monophasic. Our results demonstrate the simultaneous and complex interplay of intrinsic and extrinsic factors contributing to the GPE which is likely to have implications for device manufacture and miniaturization.
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Dec 2021
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I16-Materials and Magnetism
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Peter
Finkel
,
Markys G.
Cain
,
Thomas
Mion
,
Margo
Staruch
,
Jakub
Kolacz
,
Sukriti
Mantri
,
Chad
Newkirk
,
Kyril
Kavetsky
,
John
Thornton
,
Junhai
Xia
,
Marc
Currie
,
Thomas
Hase
,
Alex
Moser
,
Paul
Thompson
,
Christopher
Lucas
,
Andy
Fitch
,
Julie M.
Cairney
,
Scott D.
Moss
,
A. Gareth A.
Nisbet
,
John E.
Daniels
,
Samuel E.
Lofland
Diamond Proposal Number(s):
[18924]
Abstract: Electrical switching of ferroelectric domains and subsequent domain wall motion promotes strong piezoelectric activity; however, light scatters at refractive index discontinuities such as those found at domain wall boundaries. Thus, simultaneously achieving large piezoelectric effect and high optical transmissivity is generally deemed infeasible. Here, it is demonstrated that the ferroelectric domains in perovskite Pb(In1/2Nb1/2)O3 Pb(Mg1/3Nb2/3)O3-PbTiO3 domain-engineered crystals can be manipulated by electrical field and mechanical stress to reversibly and repeatably, with small hysteresis, transform the opaque poly-domain structure into a highly transparent mono-domain state. This control of optical properties can be achieved at very low electric fields (less than 1.5 kV cm−1) and is accompanied by a large (>10000 pm V−1) piezoelectric coefficient that is superior to that of linear state-of-the-art materials by a factor of three or more. The coexistence of tunable optical transmissivity and high piezoelectricity paves the way for a new class of photonic devices.
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Nov 2021
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[20485]
Abstract: We present measurements of the polarization dependencies of the x-ray signal photons generated by the effect of parametric down-conversion of x rays into ultraviolet radiation. The results exhibit pronounced discrepancies with the classical model for the nonlinearity but qualitatively agree with a recently developed quantum mechanical theory for the nonlinear interaction. Our work shows that the reconstruction of the atomic scale charge distribution of valence electrons in crystals by using nonlinear interaction between x rays and longer wavelength radiation, as was suggested in previous works, requires the knowledge of polarization of the generated x-ray signal beam. The results presented in this work indicate a methodology for the study of properties of the Wannier functions in crystals.
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Aug 2021
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[17527, 22041]
Open Access
Abstract: Nonlinear interactions between X-rays and long wavelength radiation can be used as a powerful atomic-scale probe for light-matter interactions and for properties of valence electrons. However, reported X-ray nonlinear effects were small and their observations required tremendous efforts. Here we report the observation of strong nonlinearities in parametric down-conversion (PDC) of X-rays to long wavelength radiation in gallium arsenide and lithium niobate crystals, with efficiencies about 4 orders of magnitude stronger than the efficiencies measured in any material studied before. Furthermore, we show that the efficiency in the ferroelectric phase of strontium barium niobite is two orders of magnitude stronger than in its paraelectric phase. This observation suggests that the lack of inversion symmetry is the origin for the strong observed nonlinearity. Additionally, we demonstrate the ability to use the effect for the investigation of the spectral response of non-centrosymmetric materials at wavelengths ranging from infrared to soft X-rays.
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Dec 2019
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I16-Materials and Magnetism
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C. T.
Koops
,
S. B.
Hrkac
,
M.
Abes
,
P.
Jordt
,
J.
Stettner
,
A.
Petraru
,
H.
Kohlstedt
,
V.
Hrkac
,
N.
Wolff
,
L.
Kienle
,
O. H.
Seeck
,
G.
Nisbet
,
O. M.
Magnussen
,
B. M.
Murphy
Abstract: The elastic coupling in multiferroic materials and even more so in magnetoelectric composites plays an important role for the properties and function. In this study, the electrically induced strain at the epitaxial interface of 0.72Pb(Mn1/3Nb2/3)O3–0.28PbTiO3—CoFe2O4, a magnetoelectric composite, is characterized by in situ X-ray scattering experiment and transmission electron microscopy study. For the measured range all strain induced lattice changes are reversible ruling out plastic deformation. The surprisingly non-perfect elastic coupling of 87 ± 7% in this epitaxial system can be explained by the presence of planar defects in the CFO film.
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Sep 2019
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[14024]
Open Access
Abstract: We study the magnetic structure of the “stuffed” (Tb-rich) pyrochlore iridate Tb2+xIr2−xO7−y, using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L3 and Tb M5 edges, which provide selective sensitivity to Ir 5d and Tb 4f magnetic moments, respectively. At the Ir L3 edge, we found the onset of long-range k = 0 magnetic order below TIr N ∼71K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS crosssections, we estimate an ordered magnetic moment of µIr 5d ≈ 0.34(3)µB at 5K. At the Tb M5 edge,long-range k = 0 magnetic order appeared below ∼ 40K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M5 edge in applied magnetic fields up to 6T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which TIr N = 130K and µIr 5d = 0.56µB, indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.
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May 2019
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I16-Materials and Magnetism
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Open Access
Abstract: The project to upgrade the I16 polarisation analyser was necessary to increase its functionality and to introduce a more robust construction. The requirement that the analyser was to be mounted on a diffractometer meant the construction needed to be as lightweight and as compact as possible. This provided opportunities to explore new collaborative ways of working with both in-house and external suppliers. The paper describes the approach taken to develop lightweight aluminium vacuum chambers working with a company specialising in additive layer manufacturing. In addition, the design of lightweight and compact slit assemblies are detailed; these were developed in collaboration with a supplier of driven linear stages. A novel requirement for the analyser is to have a detector mounted on a rotation axis in vacuum. The results of working with the in-house detector group to develop a design to with all the necessary thermal and electrical connections are described. The paper also describes further use of additive layer manufacturing to produce prototypes that allows the design of a cable management system to be optimised where previously using 3d CAD models had proved unsatisfactory.
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Dec 2018
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I16-Materials and Magnetism
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N.
Gurung
,
N.
Leo
,
S. P.
Collins
,
G.
Nisbet
,
G.
Smolentsev
,
M.
Garcia-Fernandez
,
K.
Yamaura
,
L. J.
Heyderman
,
U.
Staub
,
Y.
Joly
,
D. D.
Khalyavin
,
S. W.
Lovesey
,
V.
Scagnoli
Diamond Proposal Number(s):
[12459, 14853]
Abstract: The 5d transition-metal oxides offer further opportunities to test our understanding of the interplay of correlation effects and spin-orbit interactions in materials in the absence of a single dominant interaction. The subtle balance between solid-state interactions can result in mechanisms that minimize the interaction energy, and in material properties of potential use for applications. We focus here on the 5d transition-metal oxide NaOsO3, a strong candidate for the realization of a magnetically driven transition from a metallic to an insulating state exploiting the so-called Slater mechanism. Experimental results are derived from nonresonant and resonant x-ray single-crystal diffraction at the Os L edges. A change in the crystallographic symmetry does not accompany the metal-insulator transition in the Slater mechanism and, indeed, we find no evidence of such a change in NaOsO3. An equally important experimental observation is the emergence of the (300) Bragg peak in the resonant condition with the onset of magnetic order. The intensity of this space-group-forbidden Bragg peak continuously increases with decreasing temperature in line with the square of intensity observed for an allowed magnetic Bragg peak. Our main experimental results, the absence of crystal symmetry breaking, and the emergence of a space-group-forbidden Bragg peak with developing magnetic order, support the use of the Slater mechanism to interpret the metal-insulator transition in NaOsO3. We successfully describe our experimental results with simulations of the electronic structure and with an atomic model based on the established symmetry of the crystal and magnetic structure.
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Sep 2018
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I10-Beamline for Advanced Dichroism
I16-Materials and Magnetism
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D.
Pincini
,
Federica
Fabrizi
,
G.
Beutier
,
G.
Nisbet
,
H.
Elnaggar
,
V. E.
Dmitrienko
,
M. I.
Katsnelson
,
Y. O.
Kvashnin
,
A. I.
Lichtenstein
,
V. V.
Mazurenko
,
E. N.
Ovchinnikova
,
O. V.
Dimitrova
,
S. P.
Collins
Diamond Proposal Number(s):
[12479, 13608, 16227, 12478, 15987]
Open Access
Abstract: The orbital contribution to the magnetic moment of the transition-metal ion in the isostructural weak ferromagnets ACO3 (A= Mn,Co,Ni) and FeBO3 was investigated by a combination of first-principles calculations, nonresonant x-ray magnetic scattering, and x-ray magnetic circular dichroism. A nontrivial evolution of the orbital moment as a function of the 3d orbitals filling is revealed, with a particularly large value found in the Co member of the family. Here, the coupling between magnetic and lattice degrees of freedom produced by the spin-orbit interaction results in a large single-ion anisotropy and a peculiar magnetic-moment-induced electron cloud distortion, evidenced by the appearance of a subtle scattering amplitude at space-group-forbidden reflections and significant magnetostrictive effects. Our results, which complement a previous investigation on the sign of the Dzyaloshinskii-Moriya interaction across the series, highlight the importance of spin-orbit coupling in the physics of weak ferromagnets and prove the ability of modern first-principles calculations to predict the properties of materials where the Dzyaloshinskii-Moriya interaction is a fundamental ingredient of the magnetic Hamiltonian.
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Sep 2018
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