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253 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
I19-Small Molecule Single Crystal Diffraction	An electric field cell for performing in situ single-crystal synchrotron X-ray diffraction Lucy K. Saunders , Hamish H.-M. Yeung , Mark Warren , Peter Smith , Stuart Gurney , Stephen F. Dodsworth , Inigo Vitorica-Yrezabal , Adrian Wilcox , Paul V. Hathaway , Geoff Preece , Paul Roberts , Sarah A. Barnett , David R. Allan Journal Of Applied Crystallography 54 DOI: 10.1107/S1600576721007469 Diamond Proposal Number(s): [19670, 22964] Open Access Show Abstract ▼ Abstract: With the recent increase in research into ferroelectric, anti-ferroelectric and piezoelectric materials, studying the solid-state properties in situ under applied electric fields is vital in understanding the underlying processes. Where this behaviour is the result of atomic displacements, crystallographic insight has an important role. This work presents a sample environment designed to apply an electric field to single-crystal samples in situ on the small-molecule single-crystal diffraction beamline I19, Diamond Light Source (UK). The configuration and operation of the cell is described as well as its application to studies of a proton-transfer colour-change material.	Oct 2021
	BaBi2O6: A promising n-type thermoelectric oxide with the pbsb2o6crystal structure Kieran B. Spooner , Alex M. Ganose , W. W. Winnie Leung , John Buckeridge , Benjamin A. D. Williamson , Robert G. Palgrave , David O. Scanlon Chemistry Of Materials 12 DOI: 10.1021/acs.chemmater.1c02164 Show Abstract ▼ Abstract: Thermoelectric materials offer the possibility of enhanced energy efficiency due to waste heat scavenging. Based on their high-temperature stability and ease of synthesis, efficient oxide-based thermoelectrics remain a tantalizing research goal; however, their current performance is significantly lower than the industry standards such as Bi2Te3 and PbTe. Among the oxide thermoelectrics studied thus far, the development of n-type thermoelectric oxides has fallen behind that of p-type oxides, primarily due to limitations on the overall dimensionless figure of merit, or ZT, by large lattice thermal conductivities. In this article, we propose a simple strategy based on chemical intuition to discover enhanced n-type oxide thermoelectrics. Using state-of-the-art calculations, we demonstrate that the PbSb2O6-structured BaBi2O6 represents a novel structural motif for thermoelectric materials, with a predicted ZT of 0.17–0.19. We then suggest two methods to enhance the ZT up to 0.22, on par with the current best earth-abundant n-type thermoelectric at around 600 K, SrTiO3, which has been much more heavily researched. Our analysis of the factors that govern the electronic and phononic scattering in this system provides a blueprint for optimizing ZT beyond the perfect crystal approximation.	Sep 2021
I11-High Resolution Powder Diffraction	Hole and electron doping of topochemically reduced Ni(I)/Ru(II) insulating ferromagnetic oxides Zheying Xu , Lun Jin , Julius-Konstantin Backhaus , Felicity Green , Michael A. Hayward Inorganic Chemistry 2 DOI: 10.1021/acs.inorgchem.1c02265 Diamond Proposal Number(s): [13284] Show Abstract ▼ Abstract: LaxSr2–xNiRuO6, LaxSr4–xNiRuO8, and LaxSr3–xNiRuO7 are, respectively, the n = ∞, 1, and 2 members of the (Lax/2Sr1–(x/2))nSr(Ni0.5Ru0.5)nO3n+1 compositional series. Reaction with CaH2, in the case of the LaxSr2–xNiRuO6 perovskite phases, or Zr oxygen getters in the case of the LaxSr4–xNiRuO8 and LaxSr3–xNiRuO7 Ruddlesden–Popper phases, yields the corresponding topochemically reduced (Lax/2Sr1–(x/2))nSr(Ni0.5Ru0.5)nO3n–1 compounds (LaxSr2–xNiRuO4, LaxSr4–xNiRuO6, and LaxSr3–xNiRuO5), which contain Ni and Ru cations in square-planar coordination sites. The x = 1 members of each series (LaSrNiRuO4, LaSr3NiRuO6, and LaSr2NiRuO5) exhibit insulating ferromagnetic behavior at low temperature, attributable to exchange couplings between the Ni1+ and Ru2+ centers they contain. Increasing the La3+ concentration (x > 1) leads to a reduction of some of the Ru2+ centers to Ru1+ centers and a suppression of the ferromagnetic state (lower Tc, reduced saturated ferromagnet moment). In contrast, increasing the Sr2+ concentration (x < 1) oxidizes some of the Ru2+ centers to Ru3+ centers and enhances the ferromagnetic coupling (increased Tc, increased saturated ferromagnet moment) for the n = ∞ and n = 2 samples but appears to have no influence on the magnetic ordering temperature of the n = 1 samples. The magnetic couplings and influence of doping are discussed on the basis of superexchange and direct exchange couplings between the square-planar Ni and Ru centers.	Sep 2021
I09-Surface and Interface Structural Analysis	Design and realization of topological Dirac fermions on a triangular lattice Maximilian Bauernfeind , Jonas Erhardt , Philipp Eck , Pardeep K. Thakur , Judith Gabel , Tien-Lin Lee , Jörg Schäfer , Simon Moser , Domenico Di Sante , Ralph Claessen , Giorgio Sangiovanni Nature Communications 12 DOI: 10.1038/s41467-021-25627-y Diamond Proposal Number(s): [26419, 25151] Open Access Show Abstract ▼ Abstract: Large-gap quantum spin Hall insulators are promising materials for room-temperature applications based on Dirac fermions. Key to engineer the topologically non-trivial band ordering and sizable band gaps is strong spin-orbit interaction. Following Kane and Mele’s original suggestion, one approach is to synthesize monolayers of heavy atoms with honeycomb coordination accommodated on templates with hexagonal symmetry. Yet, in the majority of cases, this recipe leads to triangular lattices, typically hosting metals or trivial insulators. Here, we conceive and realize “indenene”, a triangular monolayer of indium on SiC exhibiting non-trivial valley physics driven by local spin-orbit coupling, which prevails over inversion-symmetry breaking terms. By means of tunneling microscopy of the 2D bulk we identify the quantum spin Hall phase of this triangular lattice and unveil how a hidden honeycomb connectivity emerges from interference patterns in Bloch px ± ipy-derived wave functions.	Sep 2021
Theoretical Physics	Determination of spin chirality using x-ray magnetic circular dichroism Gerrit Van Der Laan Physical Review B 104 DOI: 10.1103/PhysRevB.104.094414 Open Access Show Abstract ▼ Abstract: A threefold symmetric kagome lattice that has negative spin chirality can give a nonzero x-ray magnetic circular dichroism (XMCD) signal, despite the total spin moment amounting to zero. In order to explain this, I present here a rule for the rotational symmetry invariance of the XMCD signal. A necessary condition is the existence of an anisotropic XMCD signal for the local magnetic atom, which can arise from a spin anisotropy either in the ground state or the final state. The angular dependence of the XMCD as a function of the beam direction has an unusual behavior. The maximum dichroism is not aligned along the spin direction, but depends on the relative orientation of the spin with respect to the atomic orientation. Therefore, different geometries can result in the same angular dependence, and the spin direction can only be determined if the atomic orientation is known. The consequences for the x-ray magneto-optical sum rules are given. The integrated XMCD signals are proportional to the anisotropy in the orbital moment and the magnetic dipole term, where the isotropic spin moment drops out.	Sep 2021
I05-ARPES	Pseudogap in a crystalline insulator doped by disordered metals Sae Hee Ryu , Minjae Huh , Do Yun Park , Chris Jozwiak , Eli Rotenberg , Aaron Bostwick , Keun Su Kim Nature 596, 68 - 73 DOI: 10.1038/s41586-021-03683-0 Diamond Proposal Number(s): [25869] Show Abstract ▼ Abstract: Key to our understanding of how electrons behave in crystalline solids is the band structure that connects the energy of electron waves to their wavenumber. Even in phases of matter with only short-range order (liquid or amorphous solid), the coherent part of electron waves still has a band structure. Theoretical models for the band structure of liquid metals were formulated more than five decades ago, but, so far, band-structure renormalization and the pseudogap induced by resonance scattering have remained unobserved. Here we report the observation of the unusual band structure at the interface of a crystalline insulator (black phosphorus) and disordered dopants (alkali metals). We find that a conventional parabolic band structure of free electrons bends back towards zero wavenumber with a pseudogap of 30–240 millielectronvolts from the Fermi level. This is wavenumber renormalization caused by resonance scattering, leading to the formation of quasi-bound states in the scattering potential of alkali-metal ions. The depth of this potential tuned by different kinds of disordered alkali metal (sodium, potassium, rubidium and caesium) allows the classification of the pseudogap of p-wave and d-wave resonance. Our results may provide a clue to the puzzling spectrum of various crystalline insulators doped by disordered dopants, such as the waterfall dispersion observed in copper oxides.	Aug 2021
NONE-No attached Diamond beamline	Topological defect-mediated skyrmion annihilation in three dimensions Max T. Birch , David Cortés-Ortuño , Nguyen D. Khanh , Shinichiro Seki , Ales Stefancic , Geetha Balakrishnan , Yoshinori Tokura , Peter D. Hatton Communications Physics 4 DOI: 10.1038/s42005-021-00675-4 Open Access Show Abstract ▼ Abstract: The creation and annihilation of magnetic skyrmions are mediated by three-dimensional topological defects known as Bloch points. Investigation of such dynamical processes is important both for understanding the emergence of exotic topological spin textures, and for future engineering of skyrmions in technological applications. However, while the annihilation of skyrmions has been extensively investigated in two dimensions, in three dimensions the phase transitions are considerably more complex. We report field-dependent experimental measurements of metastable skyrmion lifetimes in an archetypal chiral magnet, revealing two distinct regimes. Comparison to supporting three-dimensional geodesic nudged elastic band simulations indicates that these correspond to skyrmion annihilation into either the helical and conical states, each exhibiting a different transition mechanism. The results highlight that the lowest energy magnetic configuration of the system plays a crucial role when considering the emergence and stability of topological spin structures via defect-mediated dynamics.	Aug 2021
I11-High Resolution Powder Diffraction I12-JEEP: Joint Engineering, Environmental and Processing	Intercalates of Bi2Se3 studied in situ by time-resolved powder X-ray diffraction and neutron diffraction Machteld E. Kamminga , Simon J. Cassidy , Partha P. Jana , Mahmoud Elgaml , Nicola D. Kelly , Simon J. Clarke Dalton Transactions 7 DOI: 10.1039/D1DT00960E Diamond Proposal Number(s): [18786, 20375] Open Access Show Abstract ▼ Abstract: Intercalation of lithium and ammonia into the layered semiconductor Bi2Se3 proceeds via a hyperextended (by >60%) ammonia-rich intercalate, to eventually produce a layered compound with lithium amide intercalated between the bismuth selenide layers which offers scope for further chemical manipulation.	Aug 2021
I11-High Resolution Powder Diffraction	Directed synthesis of a hybrid improper magnetoelectric multiferroic material Tong Zhu , Fabio Orlandi , Pascal Manuel , Alexandra S. Gibbs , Weiguo Zhang , P. Shiv Halasyamani , Michael A. Hayward Nature Communications 12 DOI: 10.1038/s41467-021-25098-1 Diamond Proposal Number(s): [13284] Open Access Show Abstract ▼ Abstract: Preparing materials which simultaneously exhibit spontaneous magnetic and electrical polarisations is challenging as the electronic features which are typically used to stabilise each of these two polarisations in materials are contradictory. Here we show that by performing low-temperature cation-exchange reactions on a hybrid improper ferroelectric material, Li2SrTa2O7, which adopts a polar structure due to a cooperative tilting of its constituent TaO6 octahedra rather than an electronically driven atom displacement, a paramagnetic polar phase, MnSrTa2O7, can be prepared. On cooling below 43 K the Mn2+ centres in MnSrTa2O7 adopt a canted antiferromagnetic state, with a small spontaneous magnetic moment. On further cooling to 38 K there is a further transition in which the size of the ferromagnetic moment increases coincident with a decrease in magnitude of the polar distortion, consistent with a coupling between the two polarisations.	Aug 2021
I10-Beamline for Advanced Dichroism	Electronic and spin control in functional oxide heterostructures Ronja Anika Hinz DOI: 10.17877/DE290R-22350 Show Abstract ▼ Abstract: Transition metal oxides exhibit a variety of physical properties due to their high tunability of spin, orbital, and charge degrees of freedom. This thesis studies two complex, transition metal oxide thin film/substrate systems, the NiFe2O4/Nb:SrTiO3 (NFO/STO) and the La0.3Sr0.7MnO3/Nb:SrTiO3 (LSMO/ STO). NFO is a ferrimagnetic insulator. LSMO is a ferromagnetic half metal and below a critical thickness transitions to an insulator. However, the physical properties of those complex oxides heterostructures are often directly linked to the quality of the thin oxide film and the interactions between the oxide thin film and its substrate at the interface. In this thesis the ultra thin NFO film growth via pulsed laser deposition is optimized. First those optimized, smooth and single crystalline NFO films are studied with lab measurement methods to ensure a high film quality. In a next step their stoichiometry and crystalline occupancy is studied via hard X-ray photoemission (HAXPES) and X-ray absorption spectroscopy, which were recorded at the large scale synchrotron BESSY II, PETRA III and the DIAMOND Light source. The stoichiometry and occupancy is found to match the theoretical expectations of the NFO oxide in the inverse spinel structure. The magnetic response of the NFO/STO heterostructure is researched with the element selective X-ray magnetic circular dichroism (XMCD). Due to the proximity effect the Ti signal mimics the ferrimagnetic response of the NFO thin film. The electronic properties of Au/NFO/STO and Pt/LSMO/STO devices were investigated via in-operando HAXPES measurements. In-operando HAXPES is recording HAXPES spectra during a voltage is applied to the sample. The band alignment and band bending are investigated by applying Kraut' s method to the HAXPES spectra.	Aug 2021

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