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

Instruments / Technical Area	Publication Details	Published
I10-Beamline for Advanced Dichroism - scattering	Influence of an ultrathin Mn 'spy layer' on the static and dynamic magnetic coupling within FePt/NiFe bilayers David G. Newman , Andreas Frisk , David M. Burn , Barat Achinuq , Emily Heppell , Graham J. Bowden , Maciej Dabrowski , Gerrit Van Der Laan , Thorsten Hesjedal , Robert J. Hicken Journal Of Physics D: Applied Physics DOI: 10.1088/1361-6463/ad89d0 Diamond Proposal Number(s): [2333] Open Access Show Abstract ▼ Abstract: We explore whether insertion of an ultrathin Mn 'spy layer' within a magnetic hard/soft bilayer can enable depth-sensitive element-specific measurements of the static and dynamic magnetization, while avoiding significant disruption of the original magnetic state. MgO(110)/FePt(100 Å)/NiFe(200 Å)/Mn(tMn Å)/NiFe(200 Å) samples with Mn thicknesses of tMn=0, 5, and 10Å were fabricated by magnetron sputtering and studied by element-selective x-ray magnetic circular dichroism (XMCD), vector network analyzer ferromagnetic resonance (VNA-FMR), and x-ray detected ferromagnetic resonance (XFMR). For tMn= 5 Å, the magnetic reversal properties remain broadly similar to tMn= 0 Å. For tMn=10 Å, the two NiFe layers decouple with XMCD hysteresis loops at the Mn edge showing two switching events that suggest the presence of two distinct Mn-containing regions. While the Mn moments within each region have ferromagnetic order, their relative alignment is antiparallel at high field. Analysis of the magnetic data and additional scanning transmission electron microscopy (STEM) measurements point to the presence of a Mn layer at the lower NiFe/Mn interface, and the formation of a NiFeMn alloy at the upper Mn/NiFe interface. The Mn moments of the former region lie antiparallel to those of the underlying NiFe layer. The VNA-FMR data suggests that for tMn= 5 and 10 Å, the interfacial exchange coupling at the FePt/NiFe is suppressed and the in-plane uniaxial magnetic anisotropy of the NiFe is increased, perhaps due to migration of Mn towards the buried interface. The above findings show that Mn is a problematic magnetic spy, and that a Mn thickness of less than 5Å would be required.	Oct 2024
I06-Nanoscience (XPEEM)	Quantitative atomic order characterization of a Mn2FeAl Heusler epitaxial thin film S. Kurdi , Y. Sakuraba , K. Masuda , H. Tajiri , B. Nair , G. F. Nataf , M. E. Vickers , G. Reiss , M Meinert , S. S. Dhesi , Massimo Ghidini , Z H Barber Journal Of Physics D: Applied Physics DOI: 10.1088/1361-6463/ac4e32 Diamond Proposal Number(s): [18932] Open Access Show Abstract ▼ Abstract: In this work, we investigate the effect of anti-site disorder on the half-metallic properties of a Mn2FeAl Heusler alloy thin film. The film was grown on TiN-buffered MgO 001 substrates via magnetron sputtering. A detailed structural characterization using X-ray diffraction (XRD) and anomalous XRD showed that the film crystallizes in the partially disordered L21B structure with 33% disorder between the Mn(B) and Al(D) sites. We measure a positive anisotropic magnetoresistance in the film, which is an indication of non-half metallic behaviour. Our X-ray magnetic circular dichroism sum rules analysis shows that Mn carries the magnetic moment in the film, as predicted, with a positive Fe moment. Experimentally determined moments correspond most closely with those found by density functional calculated ones for the L21B structure with Mn(B) and Al(D) site disorder, matching the experimental structural analysis. We thus attribute the deviation from half-metallic behaviour to the formation of the L21B structure, which we support by density functional theory calculations. To realize a half-metallic Mn2FeAl film it is important that the inverse Heusler XA structure is stabilized with minimal anti-site atomic disorder.	Jan 2022
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	Operando characterisation of alumina-supported bimetallic Pd-Pt catalysts during methane oxidation in dry and wet conditions Alexander Large , Jake Seymour , Wilson Quevedo Garzon , Kanak Roy , Federica Venturini , David C. Grinter , Luca Artiglia , Emily Brooke , Martha Briceno De Gutierrez , Agnes Raj , Kevin Lovelock , Roger A. Bennett , Tugce Eralp-Erden , Georg Held Journal Of Physics D: Applied Physics DOI: 10.1088/1361-6463/abde67 Diamond Proposal Number(s): [19464, 20952, 22702, 24584] Open Access Show Abstract ▼ Abstract: Near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to study the chemical states of a range of alumina-supported monometallic Pd and bimetallic Pd-Pt nanocatalysts, under methane oxidation conditions. It has been suggested before that for optimal complete methane oxidation, palladium needs to be in an oxidised state. These experiments, combining NAP-XPS with a broad range of characterisation techniques, demonstrate a clear link between Pt presence, Pd oxidation, and catalyst activity under stoichiometric reaction conditions. Under oxygen-rich conditions this behaviour is less clear, as all of the palladium tends to be oxidised, but there are still benefits to the addition of Pt in place of Pd for complete oxidation of methane.	Jan 2021
B07-C-Versatile Soft X-ray beamline: Ambient Pressure XPS and NEXAFS	A combined laboratory and synchrotron in-situ photoemission study of the rutile TiO2 (110) / water interface Conor Byrne , Khadisha Marie Zahra , Simran Dhaliwal , David C. Grinter , Kanak Roy , Wilson Garzon , Georg Held , Geoff Thornton , Alex Walton Journal Of Physics D: Applied Physics DOI: 10.1088/1361-6463/abddfb Diamond Proposal Number(s): [23855] Open Access Show Abstract ▼ Abstract: In-situ analysis of the TiO2 / water interface via NAP-XPS is demonstrated in both a lab based system (NAP-cell configuration) and synchrotron endstation (backfill configuration). Ultra-thin wetting layers (UTWL) of liquid water (~10 nm) are formed on a rutile TiO2 surface with minimal contamination present in addition to unique insight during the growth of the liquid films as indicated via NAP-XPS, in-situ sample temperature and background vapour pressure monitoring. Chemical changes at the solid / liquid interface are also demonstrated via healing of Ti3+ surface defect states. Photon depth profiling of the as grown liquid layers indicate that the formed films are ultra-thin (~10 nm) and likely to be continuous in nature. This work demonstrates a novel and flexible approach for studying the solid / liquid interface via NAP-XPS which is readily integrated with any form of NAP-XPS system, thereby making a critical interface of study available to a wide audience of researchers for use in operando electrochemical and photocatalytic research.	Jan 2021
I06-Nanoscience (XPEEM)	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
I10-Beamline for Advanced Dichroism - scattering	Etching induced formation of interfacial FeMn in IrMn/CoFe bilayers D. O'Donnell , S. Hassan , Y. Du , N. Gauquelin , D Krishnan , J. Verbeeck , R. Fan , P. Steadman , P. Bencok , A. N. Dobrynin Journal Of Physics D: Applied Physics 52 DOI: 10.1088/1361-6463/ab03bd Show Abstract ▼ Abstract: The effect of ion etching on exchange bias in IrMn3/Co70Fe30 bilayers is investigated. In spite of the reduction of saturation magnetization caused by the embedding of Ir from the capping layer into the Co70Fe30 layer during the etching process, the exchange bias in samples with the same thickness of the Co70Fe30 layer is reducing in proportion to the etching power. X-ray magnetic circular dichroism measurements revealed the emergence of an uncompensated Mn magnetization after etching, which is antiferromagnetically coupled to the ferromagnetic layer. This suggests etching induced formation of small interfacial FeMn regions which leads to the decrease of effective exchange coupling between ferromagnetic and antiferromagnetic layers.	Apr 2019
I06-Nanoscience (XPEEM)	Voltage control of magnetic single domains in Ni discs on ferroelectric BaTiO3 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 Journal Of Physics D: Applied Physics 51, 22 DOI: 10.1088/1361-6463/aabf77 Diamond Proposal Number(s): [9590] Show Abstract ▼ 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.	May 2018
I10-Beamline for Advanced Dichroism - scattering	Tailoring the interfacial exchange coupling of perpendicularly magnetized Co/L10-Mn1.5Ga bilayers J. X. Xiao , J. Lu , W. Q. Liu , Y. W. Zhang , H. L. Wang , L. J. Zhu , H. X. Deng , D. H. Wei , Y. B. Xu , J. H. Zhao Journal Of Physics D: Applied Physics 49 DOI: 10.1088/0022-3727/49/24/245003 Show Abstract ▼ Abstract: We have studied the magnetic properties of Co (2–12 MLs)/L10-Mn1.5Ga (15 nm) bilayers without and with annealing at 300 °C by a combination of superconducting quantum interference device (SQUID) magnetometry and x-ray magnetic circular dichroism (XMCD). We find that the Co layer can remain perpendicularly magnetized when its thickness is less than six monolayers due to the coupling between Co and L10-Mn1.5Ga layers, which is doubly confirmed by both SQUID and XMCD measurements. Such an exchange coupling between L10-Mn1.5Ga and Co layers changes from ferromagnetic coupling to antiferromagnetic coupling after the annealing process. Furthermore, the magnetic coupling can also be tailored from ferromagnetic to antiferromagnetic by changing the L10-Mn1.5Ga surface from Mn-rich to Ga-rich. The first-principles calculations show that the interfacial coupling type is ferromagnetic for a Mn-terminated L10-Mn1.5Ga bilayer, while antiferromagnetic for a Ga-terminated bilayer. The spin and orbital moments of Co in the Co/L10-Mn1.5Ga bilayers are calculated according to the sum rules and the ratio of the orbital to spin magnetic moments for Co is not enhanced like other perpendicularly magnetized Co-based multilayers such as Co/Pd and Co/Pt.	Jun 2016
	Charge transport optimization in CZT ring-drift detectors V. Boothman , A. Alruhaili , V. Perumal , P. Sellin , A. Lohstroh , K. Sawhney , S. Kachanov Journal Of Physics D: Applied Physics 48 DOI: 10.1088/0022-3727/48/48/485101 Show Abstract ▼ Abstract: Ring-drift design has been applied to large (7.5 mm × 7.5 mm × 2.3 mm) cadmium zinc telluride (CZT) devices. This low-noise, single-carrier-sensing configuration is the gold standard for spectroscopic silicon x-ray detectors. By combining the advantages of ring- drift with the high quantum efficiency and room-temperature operating capabilities of CZT, a simple and compact device for high-resolution spectroscopy of x-rays in the range 50–500 keV can be created. Quality of CZT crystals has improved greatly in recent years and electron-only sensing overcomes the problem of inherently poor hole transport in II–VI semiconductors. The spatial response of our 3-ring CZT device was studied by microbeam scanning while the voltages applied to all electrodes were systematically varied. Maximum active radius extended to 2.3 mm, beyond the second ring. Resolution was limited by electronic noise. Our results show that the lateral field and its ratio to the bulk field exert a crucial influence on active area, peak position and sensitivity. CZT and the device geometry were modelled in 3D with Sentaurus TCAD. Line scans were simulated and trends in performance with bias conditions matched experimental data, validating the model. We aimed to optimize the resolution, sensitivity and active radius of the device. Fields and charge drift were visualized and the active volume was mapped in 3D to improve understanding of the factors governing performance including number of rings, their widths, positions and bias.	Dec 2015
	Microscopic origin of the reduced magnetocrystalline anisotropy with increasing oxide content in Co80Pt20:oxide thin films Wen Zhang , Simon A. Morton , P. K. Johnny Wong , Bin Lu , Yongbing Xu , Michel P. De Jong , Wilfred G. Van Der Wiel , Gerrit Van Der Laan Journal Of Physics D: Applied Physics 46 (40), 405001 DOI: 10.1088/0022-3727/46/40/405001 Show Abstract ▼ Abstract: Angle-dependent x-ray magnetic circular dichroism at the Co L2.3 edges has been utilized to systematically study Co80Pt20 :WO3 perpendicular magnetic recording thin films, in which the magnetocrystalline anisotropy significantly drops as the oxide volume fraction increases. The microscopic origin of this phenomenon in the studied films can be mainly attributed to an increase in orbital moment normal to the grainoxide interface, with increasing oxide volume fraction, which arises from a more pronounced effect of symmetry breaking at the grainoxide interface in smaller grains.	Oct 2013

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