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18 items found (0 items not approved), displaying 1 to 10.[First/Prev] 1, 2 [Next/Last]

Instruments / Technical Area	Publication Details	Published
B18-Core EXAFS I10-Beamline for Advanced Dichroism - scattering	Biosynthesis and characterization of copper nanoparticles using Shewanella oneidensis: application for click chemistry Richard Kimber , Edward A. Lewis , Fabio Parmeggiani , Kurt Smith , Heath Bagshaw , Toby Starborg , Nimisha Joshi , Adriana Figueroa , Gerrit Van Der Laan , Giannantonio Cibin , Diego Gianolio , Sarah J. Haigh , Richard A. D. Pattrick , Nicholas J. Turner , Jonathan R. Lloyd Small 116, 1703145 DOI: 10.1002/smll.201703145 Diamond Proposal Number(s): [15476, 16136] Open Access Show Abstract ▼ Abstract: Copper nanoparticles (Cu-NPs) have a wide range of applications as heterogeneous catalysts. In this study, a novel green biosynthesis route for producing Cu-NPs using the metal-reducing bacterium, Shewanella oneidensis is demonstrated. Thin section transmission electron microscopy shows that the Cu-NPs are predominantly intracellular and present in a typical size range of 20–40 nm. Serial block-face scanning electron microscopy demonstrates the Cu-NPs are well-dispersed across the 3D structure of the cells. X-ray absorption near-edge spectroscopy and extended X-ray absorption fine-structure spectroscopy analysis show the nanoparticles are Cu(0), however, atomic resolution images and electron energy loss spectroscopy suggest partial oxidation of the surface layer to Cu2O upon exposure to air. The catalytic activity of the Cu-NPs is demonstrated in an archetypal “click chemistry” reaction, generating good yields during azide-alkyne cycloadditions, most likely catalyzed by the Cu(I) surface layer of the nanoparticles. Furthermore, cytochrome deletion mutants suggest a novel metal reduction system is involved in enzymatic Cu(II) reduction and Cu-NP synthesis, which is not dependent on the Mtr pathway commonly used to reduce other high oxidation state metals in this bacterium. This work demonstrates a novel, simple, green biosynthesis method for producing efficient copper nanoparticle catalysts.	Jan 2018
I10-Beamline for Advanced Dichroism - scattering	Anisotropic magnetic switching along hard [110]-type axes in Er-doped DyFe2/YFe2 thin films G. B. G. Stenning , G. J. Bowden , G. Van Der Laan , A. I. Figueroa , P. Bencok , P. Steadman , T. Hesjedal Journal Of Magnetism And Magnetic Materials DOI: 10.1016/j.jmmm.2017.05.007 Diamond Proposal Number(s): [8213, 13758] Show Abstract ▼ Abstract: Epitaxial-grown DyFe2/YFe2 multilayer thin films form an ideal model system for the study of magnetic exchange springs. Here the DyFe2 (YFe2) layers are magnetically hard (soft). In the presence of a magnetic field, exchange springs form in the YFe2 layers. Recently, it has been demonstrated that placing small amounts of Er into the centre of the YFe2 springs generates substantial changes in magnetic behavior. In particular, (i) the number of exchange-spring states is increased dramatically, (ii) the resulting domain-wall states cannot simply be described as either Néel or Bloch walls, (iii) the Er and Dy magnetic loops are strikingly different, and (iv) it is possible to engineer Er-induced magnetic exchange-spring collapse. Here, results are presented for Er-doped (110)-oriented DyFe2(60Å)/YFe2(240Å)15(60Å)/YFe2(240Å)15 multilayer films, at 100 K in fields of up to 12 T. In particular, we contrast magnetic loops for fields applied along seemingly equivalent hard-magnetic [110]-type axes. MBE-grown cubic Laves thin films offer the unique feature of allowing to apply the magnetic field along (i) a hard out-of-plane [110]-axis (the growth axis) and (ii ) a similar hard in-plane [View the MathML source1¯10]-axis. Differences are found and attributed to the competition between the crystal-field interaction at the Er site and the long-range dipole-dipole interaction. In particular, the out-of-plane [110] Er results show the existence of a new magnetic exchange spring state, which would be very difficult to identify without the aid of element-specific technique of x-ray magnetic circular dichroism (XMCD).	May 2017
I10-Beamline for Advanced Dichroism - scattering	X-ray magnetic circular dichroism study of Dy-doped Bi2Te3 topological insulator thin films A. I. Figueroa , A. A. Baker , S. E. Harrison , K. Kummer , G. Van Der Laan , T. Hesjedal Journal Of Magnetism And Magnetic Materials DOI: 10.1016/j.jmmm.2016.08.063 Diamond Proposal Number(s): [10207] Open Access Show Abstract ▼ Abstract: Magnetic doping of topological insulators (TIs) is crucial for unlocking novel quantum phenomena, paving the way for spintronics applications. Recently, we have shown that doping with rare earth ions introduces large magnetic moments and allows for high doping concentrations without the loss of crystal quality, however no long range magnetic order was observed. In Dy-doped Bi2Te3 we found a band gap opening above a critical doping concentration, despite the paramagnetic bulk behavior. Here, we present a surface-sensitive x-ray magnetic circular dichroism (XMCD) study of an in-situ cleaved film in the cleanest possible environment. The Dy M4,5 absorption spectra measured with circularly polarized x-rays are fitted using multiplet calculations to obtain the effective magnetic moment. Arrott-Noakes plots, measured by the Dy M5 XMCD as a function of field at low temperatures, give a negative transition temperature. The evaporation of a ferromagnetic Co thin film did not introduce ferromagnetic ordering of the Dy dopants either; instead a lowering of the transition temperature was observed, pointing towards an antiferromagnetic ordering scenario. This result shows that there is a competition between the magnetic exchange interaction and the Zeeman interaction. The latter favors the Co and Dy magnetic moments to be both aligned along the direction of the applied magnetic field, while the exchange interaction is minimized if the Dy and Co atoms are antiferromagnetically coupled, as in zero applied field.	Nov 2016
I10-Beamline for Advanced Dichroism - scattering	Spin pumping in magnetic trilayer structures with an MgO barrier A. Baker , A. Figueroa-Garcia , D. Pingstone , V. K. Lazarov , G. Van Der Laan , T. Hesjedal Scientific Reports 6 DOI: 10.1038/srep35582 Diamond Proposal Number(s): [11501] Open Access Show Abstract ▼ Abstract: We present a study of the interaction mechanisms in magnetic trilayer structures with an MgO barrier grown by molecular beam epitaxy. The interlayer exchange coupling, Aex, is determined using SQUID magnetometry and ferromagnetic resonance (FMR), displaying an unexpected oscillatory behaviour as the thickness, tMgO, is increased from 1 to 4 nm. Transmission electron microscopy confirms the continuity and quality of the tunnelling barrier, eliminating the prospect of exchange arising from direct contact between the two ferromagnetic layers. The Gilbert damping is found to be almost independent of the MgO thickness, suggesting the suppression of spin pumping. The element-specific technique of x-ray detected FMR reveals a small dynamic exchange interaction, acting in concert with the static interaction to induce coupled precession across the multilayer stack. These results highlight the potential of spin pumping and spin transfer torque for device applications in magnetic tunnel junctions relying on commonly used MgO barriers.	Oct 2016
I10-Beamline for Advanced Dichroism - scattering	Size dependent microbial oxidation and reduction of magnetite nano- and micro-particles James M. Byrne , Gerrit Van Der Laan , Adriana Figueroa-Garcia , Odeta Qafoku , Chongmin Wang , Carolyn Pearce , Michael Jackson , Joshua Feinberg , Kevin M. Rosso , Andreas Kappler Scientific Reports 6, 30969 DOI: 10.1038/srep30969 Diamond Proposal Number(s): [9565] Open Access Show Abstract ▼ Abstract: The ability for magnetite to act as a recyclable electron donor and acceptor for Fe-metabolizing bacteria has recently been shown. However, it remains poorly understood whether microbe-mineral interfacial electron transfer processes are limited by the redox capacity of the magnetite surface or that of whole particles. Here we examine this issue for the phototrophic Fe(II)-oxidizing bacteria Rhodopseudomonas palustris TIE-1 and the Fe(III)-reducing bacteria Geobacter sulfurreducens, comparing magnetite nanoparticles (d ≈ 12 nm) against microparticles (d ≈ 100–200 nm). By integrating surface-sensitive and bulk-sensitive measurement techniques we observed a particle surface that was enriched in Fe(II) with respect to a more oxidized core. This enables microbial Fe(II) oxidation to occur relatively easily at the surface of the mineral suggesting that the electron transfer is dependent upon particle size. However, microbial Fe(III) reduction proceeds via conduction of electrons into the particle interior, i.e. it can be considered as more of a bulk electron transfer process that is independent of particle size. The finding has potential implications on the ability of magnetite to be used for long range electron transport in soils and sediments.	Aug 2016
I10-Beamline for Advanced Dichroism - scattering	On the temperature dependence of spin pumping in ferromagnet-topological insulator-ferromagnet spin valves A. A. Baker , A. I. Figueroa-Garcia , G. Van Der Laan , T. Hesjedal Results In Physics DOI: 10.1016/j.rinp.2016.05.007 Diamond Proposal Number(s): [9210] Open Access Show Abstract ▼ Abstract: Topological insulators (TIs) have a large potential for spintronics devices owing to their spin-polarized, counter-propagating surface states. Recently, we have investigated spin pumping in a ferromagnet-TI-ferromagnet structure at room temperature. Here, we present the temperature-dependent measurement of spin pumping down to 10 K, which shows no variation with temperature.	Jul 2016
I10-Beamline for Advanced Dichroism - scattering	Magnetic ordering in Ho-doped Bi2Te3 topological insulator A. Figueroa-Garcia , S. E. Harrison , L. Collins-Mcintyre , G. Van Der Laan , T. Hesjedal Physica Status Solidi (rrl) - Rapid Research Letters DOI: 10.1002/pssr.201600061 Diamond Proposal Number(s): [10207] Show Abstract ▼ Abstract: We investigate the magnetic properties of Ho-doped Bi2Te3 thin films grown by molecular beam epitaxy. Analysis of the polarized X-ray absorption spectra at the Ho M5 absorption edge gives an effective 4f magnetic moment which is ∼45% of the Hund's rule ground state value. X-ray magnetic circular dichroism (XMCD) shows no significant anisotropy, which suggests that the reduced spin moment is not due to the crystal field effects, but rather the presence of non-magnetic or antiferromagnetic Ho sites. Extrapolating the temperature dependence of the XMCD measured in total electron yield and fluorescence yield mode in a field of 7 T gives a Curie–Weiss temperature of ϑCW ≈ –30 K, which suggests antiferromagnetic ordering, in contrast to the paramagnetic behavior observed with SQUID magnetometry. From the anomaly of the XMCD signal at low temperatures, a Néel temperature TN between 10 K and 25 K is estimated.	Apr 2016
B18-Core EXAFS	Oxidation effects in rare earth doped topological insulator thin films A. Figueroa , G. Van Der Laan , S. E. Harrison , G. Cibin , T. Hesjedal Scientific Reports 6 DOI: 10.1038/srep22935 Diamond Proposal Number(s): [11119] Open Access Show Abstract ▼ Abstract: The breaking of time-reversal symmetry (TRS) in topological insulators is a prerequisite for unlocking their exotic properties and for observing the quantum anomalous Hall effect (QAHE). The incorporation of dopants which exhibit magnetic long-range order is the most promising approach for TRS-breaking. REBiTe3, wherein 50% of the Bi is substitutionally replaced by a RE atom (RE = Gd, Dy, and Ho), is a predicted QAHE system. Despite the low solubility of REs in bulk crystals of a few %, highly doped thin films have been demonstrated, which are free of secondary phases and of high crystalline quality. Here we study the effects of exposure to atmosphere of rare earth-doped Bi2(Se, Te)3 thin films using x-ray absorption spectroscopy. We demonstrate that these RE dopants are all trivalent and effectively substitute for Bi3+ in the Bi2(Se, Te)3 matrix. We find an unexpected high degree of sample oxidation for the most highly doped samples, which is not restricted to the surface of the films. In the lowdoping limit, the RE-doped films mostly show surface oxidation, which can be prevented by surface passivation, encapsulation, or in-situ cleaving to recover the topological surface state.	Mar 2016
I10-Beamline for Advanced Dichroism - scattering	Anisotropic absorption of pure spin currents A. A. Baker , A. I. Figueroa-Garcia , C. j. Love , S. A. Cavill , T. Hesjedal , G. Van Der Laan Physical Review Letters 116, 047201 DOI: 10.1103/PhysRevLett.116.047201 PMID: 26871353 Diamond Proposal Number(s): [11501] Open Access Show Abstract ▼ Abstract: Spin transfer in magnetic multilayers offers the possibility of ultrafast, low-power device operation. We report a study of spin pumping in spin valves, demonstrating that a strong anisotropy of spin pumping from the source layer can be induced by an angular dependence of the total Gilbert damping parameter, alpha, in the spin sink layer. Using lab- and synchrotron-based ferromagnetic resonance, we show that an in-plane variation of damping in a crystalline Co50Fe50 layer leads to an anisotropic alpha in a polycrystalline Ni81Fe19 layer. This anisotropy is suppressed above the spin diffusion length in Cr, which is found to be 8 nm, and is independent of static exchange coupling in the spin valve. These results offer a valuable insight into the transmission and absorption of spin currents, and a mechanism by which enhanced spin torques and angular control may be realized for next-generation spintronic devices.	Jan 2016
I10-Beamline for Advanced Dichroism - scattering	Engineering helimagnetism in MnSi thin films S. L. Zhang , R. Chalasani , A. A. Baker , N. J. Steinke , A. I. Figueroa-Garcia , A. Kohn , G. Van Der Laan , T. Hesjedal Aip Advances 6, 015217 DOI: 10.1063/1.4941316 Diamond Proposal Number(s): [9234] Open Access Show Abstract ▼ Abstract: Magnetic skyrmion materials have the great advantage of a robust topological magnetic structure, which makes them stable against the superparamagnetic effect and therefore a candidate for the next-generation of spintronic memory devices. Bulk MnSi, with an ordering temperature of 29.5 K, is a typical skyrmion system with a propagation vector periodicity of ∼18 nm. One crucial prerequisite for any kind of application, however, is the observation and precise control of skyrmions in thin films at room-temperature. Strain in epitaxial MnSi thin films is known to raise the transition temperature to 43 K. Here we show, using magnetometry and x-ray spectroscopy, that the transition temperature can be raised further through proximity coupling to a ferromagnetic layer. Similarly, the external field required to stabilize the helimagnetic phase is lowered. Transmission electron microscopy with element-sensitive detection is used to explore the structural origin of ferromagnetism in these Mn-doped substrates. Our work suggests that an artificial pinning layer, not limited to the MnSi/Si system, may enable room temperature, zero-field skyrmion thin-film systems, thereby opening the door to device applications.	Jan 2016

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