B23-Circular Dichroism
I22-Small angle scattering & Diffraction
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Diamond Proposal Number(s):
[29045]
Open Access
Abstract: We investigate two unusual phenomena in self-assembly of anisotropic molecules from isotropic (Iso) melt: a heat-capacity (Cp) maximum, and spontaneous formation of the recently discovered chiral liquid (Iso*). Based on experiments on new non-chiral monomers, dimers and polymers, we construct a statistical theory that shows why many complex mesostructures form in two stages: continuous equilibrium growth of nano-clusters in melt through strong interactions, causing the Cp-maximum, followed by establishment of positional long-range order (LRO) through a weak first-order transition. We also show why many achiral compounds additionally form an intermediate chiral Iso* liquid through what we find is a second-order transition. We propose that the first process is equivalent to “supramolecular polymerization” in solutions, where the lack of inter-cluster interaction rules out LRO. Furthermore, we argue that separation into a broad and a sharp transition is universal in condensed matter where strong interactions by themselves cannot lead to LRO, either because the clusters are 1D or due to strong frustration. Clusters must first grow to critical size when, at Tc, the combined weak interactions reach ~kBTc, prompting LRO formation. A situation similar to that in soft self-assembly is seen in spin ordering in magnetic crystals, but only near 0 K.
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May 2025
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I06-Nanoscience (XPEEM)
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Ian T.
Vidamour
,
Guru
Venkat
,
Charles
Swindells
,
David
Griffin
,
Paul W.
Fry
,
Richard M.
Rowan-Robinson
,
Alexander
Welbourne
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Susan
Stepney
,
Dan A.
Allwood
,
Thomas J.
Hayward
Open Access
Abstract: We describe “RingSim,” a phenomenological agent-based model that allows numerical simulation of magnetic nanowire networks with areas of hundreds of micrometers squared for durations of hundreds of seconds, a practical impossibility for general-purpose micromagnetic simulation tools. In RingSim, domain walls (DWs) are instanced as mobile agents, which respond to external magnetic fields, and their stochastic interactions with pinning sites and other DWs are described via simple phenomenological rules. We first present a detailed description of the model and its algorithmic implementation for simulating the behaviors of arrays of interconnected ring-shaped nanowires, which have previously been proposed as hardware platforms for unconventional computing applications. The model is then validated against a series of experimental measurements of an array’s static and dynamic responses to rotating magnetic fields. The robust agreement between the modeled and experimental data demonstrates that agent-based modeling is a powerful tool for exploring mesoscale magnetic devices, enabling time scales and device sizes that are inaccessible to more conventional magnetic simulation techniques.
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Apr 2025
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B23-Circular Dichroism
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Rituparno
Chowdhury
,
Marco D.
Preuss
,
Hwan-Hee
Cho
,
Joshua J. P.
Thompson
,
Samarpita
Sen
,
Thomi K.
Baikie
,
Pratyush
Ghosh
,
Yorrick
Boeije
,
Xian Wei
Chua
,
Kai-Wei
Chang
,
Erjuan
Guo
,
Joost
Van Der Tol
,
Bart W. L.
Van Den Bersselaar
,
Andrea
Taddeucci
,
Nicolas
Daub
,
Daphne M.
Dekker
,
Scott T.
Keene
,
Ghislaine
Vantomme
,
Bruno
Ehrler
,
Stefan C. J.
Meskers
,
Akshay
Rao
,
Bartomeu
Monserrat
,
E. W.
Meijer
,
Richard H.
Friend
Diamond Proposal Number(s):
[32194]
Abstract: Current organic light-emitting diode (OLED) technology uses light-emitting molecules in a molecular host. We report green circularly polarized luminescence (CPL) in a chirally ordered supramolecular assembly, with 24% dissymmetry in a triazatruxene (TAT) system. We found that TAT assembled into helices with a pitch of six molecules, associating angular momentum to the valence and conduction bands and obtaining the observed CPL. Cosublimation of TAT as the “guest” in a structurally mismatched “host” enabled fabrication of thin films in which chiral crystallization was achieved in situ by thermally triggered nanophase segregation of dopant and host while preserving film integrity. The OLEDs showed external quantum efficiencies of up to 16% and electroluminescence dissymmetries ≥10%. Vacuum deposition of chiral superstructures opens new opportunities to explore chiral-driven optical and transport phenomena.
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Mar 2025
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I06-Nanoscience (XPEEM)
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Yu
Yan
,
Bo
Liu
,
Xianyang
Lu
,
Junlin
Wang
,
Sarnjeet S.
Dhesi
,
Iain G.
Will
,
Vlado K.
Lazarov
,
Jun
Du
,
Jing
Wu
,
Rong
Zhang
,
Yongbing
Xu
Abstract: Fe/GaAs is a prototype system of spin injection at room temperature. The interfacial strain and oriented bonds are both considered the origin of the Fe in-plane uniaxial magnetic anisotropy (UMA), which remains decisive. Here, by the x-ray magnetic circular dichroism (XMCD) and the vibrating sample magnetometer measurements, this study shows that in the Fe/Cr(t)/GaAs structure, the in-plane UMA of Fe originates from the chemical bonding between the Fe and the GaAs substrate by varying Cr thickness, t. The UMA drops as the Cr coverage increases, characterized by a decrease in the saturation field from 2400 to 57 Oe. The XMCD studies reveal that the Fe orbital moment, a signature of chemical bonds, decreases from 0.216 μB at Cr = 0 ML to 0.138 μB at Cr = 5 ML. The reduction of the Fe orbital moment and the UMA are qualitatively consistent, establishing a link between the UMA and the interfacial chemical bonds. The decreased UMA remains unchanged at t > 5 ML, above which Fe and GaAs are fully separated by a continuous Cr layer. Our findings provide clear experimental evidence that the UMA in the Fe/GaAs system originates from the oriented interface bonds, clarifying the UMA origin in this prototype system.
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Mar 2025
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I06-Nanoscience (XPEEM)
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Diamond Proposal Number(s):
[32492]
Open Access
Abstract: The effect of thermal surface cleaning on the Gilbert damping (
) of yttrium iron garnet (YIG), before capping with a metallic layer, has been investigated. Our results show that
is strongly affected by relatively mild annealing conditions (T = 300 °C) when performed in a vacuum. This increase needs to be taken into account when obtaining the spin-mixing conductance from spin pumping measurements. We measure an increase in
by a factor of
8 when the YIG is vacuum annealed at 300 °C. No such changes in
are observed when annealed at the same temperature in 1
10−1 mbar of oxygen. We suggest that the main driver for the increase in
is the reduction of Fe3+ to Fe2+, as demonstrated by soft x-ray magnetic spectroscopy.
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Mar 2025
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B23-Circular Dichroism
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Leah E. M.
White
,
Tiberiu-M.
Gianga
,
F.
Pradaux-Caggiano
,
Chiara
Faverio
,
Andrea
Taddeucci
,
Henry S.
Rzepa
,
Christian
Jonhannesen
,
Lauren E.
Hatcher
,
Giuliano
Siligardi
,
David R.
Carbery
,
G. Dan
Pantos
Diamond Proposal Number(s):
[33876]
Open Access
Abstract: The ability to synthesise lemniscular molecules to allow for the study and application of their chiroptical properties is a notable technical challenge. Herein, we report the design and synthesis of enantiomers of a [5]helicenoid derived molecular lemniscate, in which two homochiral helicenes are linked via the formation of two azine motifs. We demonstrate that these molecules, and their helicenoid constituents, are also excellent chiral dopants that induce dissymmetry in the ground and excited states of the achiral emissive polymer F8BT, leading to high CPL activity. The ability to control the handedness of the helicenoid dopants via enantiopure synthesis affords control of the sign of CP emission. This manipulation of circularly polarised light is of great interest for optoelectronic technologies.
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Mar 2025
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I05-ARPES
I10-Beamline for Advanced Dichroism - scattering
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E. L.
Arnold
,
J. M.
Riley
,
L. B.
Duffy
,
A. I.
Figueroa
,
R.
Held
,
K. M.
Shen
,
D. G.
Schlom
,
P. D. C.
King
,
M.
Hoesch
,
G.
Van Der Laan
,
T.
Hesjedal
Diamond Proposal Number(s):
[16162, 15481]
Open Access
Abstract: We present a detailed x-ray magnetic circular dichroism (XMCD) study of the magnetic properties of Gd-doped EuO thin films, synthesized via molecular-beam epitaxy with Gd doping levels up to over 12%. The impact of Gd doping on the electronic and magnetic behavior of EuO is studied using XMCD and magnetometry. Gd doping significantly enhances the Curie temperature (𝑇C) from 69 K in undoped EuO to over 120 K, driven by increased carrier density, while preserving the high quality of the single-crystalline films. At higher doping levels, a plateau in 𝑇C is observed, which is attributed to the formation of Eu-Gd nearest-neighbor pairs that limit dopant activation. We also observe a distinctive “double-dome” structure in the temperature-dependent magnetization, which we attribute to both the ferromagnetic ordering of Eu 4𝑓 moments at lower temperatures and the influence of conduction electrons via 4𝑓−5𝑑 exchange interactions at higher temperatures. These findings provide key insights into the mechanisms of carrier-induced magnetic transitions.
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Feb 2025
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B23-Circular Dichroism
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Maryam
Abooali
,
Stephanie
Schlichtner
,
Xi
Lei
,
Nijas
Aliu
,
Sabrina
Ruggiero
,
Sonia
Loges
,
Martin
Ziegler
,
Franziska
Hertel
,
Anna-Lena
Volckmar
,
Albrecht
Stenzinger
,
Petros
Christopoulos
,
Michael
Thomas
,
Elena
Klenova
,
N. Helge
Meyer
,
Stergios
Boussios
,
Nigel
Heaton
,
Yoh
Zen
,
Ane
Zamalloa
,
Shilpa
Chokshi
,
Luca
Urbani
,
Sophie
Richard
,
Kavitha
Kirubendran
,
Rohanah
Hussain
,
Giuliano
Siligardi
,
Dietmar
Cholewa
,
Steffen M.
Berger
,
Inna M.
Yasinska
,
Elizaveta
Fasler-Kan
,
Vadim V.
Sumbayev
Diamond Proposal Number(s):
[24509, 20755, 21202]
Open Access
Abstract: V-domain Ig-containing suppressor of T cell activation (VISTA) is a unique immune checkpoint protein, which was reported to display both receptor and ligand activities. However, the mechanisms of regulation of VISTA activity and functions by factors of tumour microenvironment (TME) remain unclear and understanding these processes is required in order to develop successful personalised cancer immunotherapeutic strategies and approaches. Here we report for the very first time that VISTA interacts with another immune checkpoint protein galectin-9 inside the cell most likely facilitating its interaction with TGF-β-activated kinase 1 (TAK1). This process is required for protection of lysosomes, which is crucial for many cell types and tissues. We found that VISTA expression can be differentially controlled by crucial factors present in TME, such as transforming growth factor beta type 1 (TGF-β) and hypoxia as well as other factors activating hypoxic signalling. We confirmed that involvement of these important pathways modulated by TME differentially influences VISTA expression in different cell types. These networks include: TGF-β-Smad3 pathway, TAK1 (TGF-β-activated kinase 1) or apoptosis signal-regulating kinase 1 (ASK1)-induced activation of activating transcription factor 2 (ATF-2) and hypoxic signalling pathway. Based on this work we determined the five critical functions of VISTA and the role of TME factors in controlling (modulating or downregulating) VISTA expression.
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Feb 2025
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I10-Beamline for Advanced Dichroism - scattering
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Abstract: Depth resolved characterization of structural and magnetic profiles of antiferromagnetic/ferromagnetic (AFM/FM) system upon annealing was performed in this work. We studied systems comprising of AFM IrMn
and FM (Co, Fe, Co70Fe30) bilayer structures using magnetometry, polarized neutron reflectometry, soft X-ray magnetic circular dichroism and secondary neutral spectrometry. Structural depth profiles obtained from neutron reflectometry indicate non-homogeneity of the AFM layer even before annealing, which is associated with the migration of manganese to the surface of the sample. Annealing of samples with CoFe and Co layers leads to a slight increase (
5 %) in the migration of manganese, which, however, does not lead to significant degradation of the exchange coupling at the AFM/FM interface. A significantly different picture was observed in the Fe/IrMn
systems where a strong migration of iron into the AFM layer was observed upon annealing of the sample, leading to erosion of the magnetic profile, the formation of a non-magnetic alloy and degradation of the pinning strength. This study can be useful in the optimization of AFM/FM systems in different spintronics devices, including HDD read heads, where thermal annealing is applied at different stages of the device manufacturing process.
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Jan 2025
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I10-Beamline for Advanced Dichroism - scattering
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Diamond Proposal Number(s):
[32078]
Open Access
Abstract: This study reports the structural and magnetic properties of Mn-doped Bi2Te3
thin films grown by magnetron sputtering. The films exhibit a ferromagnetic response that depends on the Mn doping concentration, as revealed by X-ray magnetic circular dichroism measurements. At an Mn concentration of ∼6.0%, a magnetic moment of (3.48 ± 0.25) μB
/Mn was determined. Structural analysis indicated the presence of a secondary MnTe𝑥
phase, which complicates the interpretation of the magnetic properties. Additionally, the incorporation of Mn ions within the van der Waals gap and substitutional doping on Bi sites contributes to the observed complex magnetic properties. Intriguingly, a decrease in magnetic moment per Mn was observed with increasing Mn concentration, which is consistent with the formation of the intrinsic magnetic topological insulator MnBi2Te4
.
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Jan 2025
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