I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[19173]
Abstract: We present an investigation on the structural and magnetic properties of the interfaces of
Fe
3
O
4
/
MgO
(
001
)
and
Fe
3
O
4
/
NiO
/
MgO
(
001
)
by extracting cation-selective magneto-optical depth profiles by means of x-ray resonant magnetic reflectivity in combination with charge-transfer multiplet simulations of x-ray magnetic circular dichroism data. For
Fe
3
O
4
/
MgO
(
001
)
, the magneto-optical depth profiles at the
Fe
2
+
oct
and the
Fe
3
+
oct
resonant energies follow exactly the structural profile, while the magneto-optical depth profile at the
Fe
3
+
tet
resonance is offset by
3.2
±
1.3
Å from the interface, consistent with a
B
-site interface termination of
Fe
3
O
4
with fully intact magnetic order. In contrast, for
Fe
3
O
4
/
NiO
(
001
)
, the magneto-optical depth profiles at the
Fe
2
+
oct
and the
Ni
2
+
resonances agree with the structural profile, but the interface positions of the magneto-optical depth profiles at the
Fe
3
+
oct
and the
Fe
3
+
tet
resonances are spatially shifted by
3.3
±
1.4
and
2.7
±
0.9
Å, respectively, not consistent with a magnetically ordered stoichiometric interface. This may be related to an intermixed
(
Ni
,
Fe
)
O
layer at the interface. The dichroic depth profile at the Ni
L
3
edge might hint at uncompensated magnetic moments throughout the NiO film.
|
Jun 2022
|
|
I10-Beamline for Advanced Dichroism
|
Xiaoqian
Zhang
,
Wenqing
Liu
,
Wei
Niu
,
Qiangsheng
Lu
,
Wei
Wang
,
Ali
Sarikhani
,
Xiaohua
Wu
,
Chunhui
Zhu
,
Jiabao
Sun
,
Mitchel
Vaninger
,
Paul. F.
Miceli
,
Jianqi
Li
,
David J.
Singh
,
Yew San
Hor
,
Yue
Zhao
,
Chang
Liu
,
Liang
He
,
Rong
Zhang
,
Guang
Bian
,
Dapeng
Yu
,
Yongbing
Xu
Diamond Proposal Number(s):
[22532]
Abstract: One of the most promising avenues in 2D materials research is the synthesis of antiferromagnets employing 2D van der Waals (vdW) magnets. However, it has proven challenging, due in part to the complicated fabrication process and undesired adsorbates as well as the significantly deteriorated ferromagnetism at atomic layers. Here, the engineering of the antiferromagnetic (AFM) interlayer exchange coupling between atomically thin yet ferromagnetic CrTe2 layers in an ultra-high vacuum-free 2D magnetic crystal, Cr5Te8 is reported. By self-introducing interstitial Cr atoms in the vdW gaps, the emergent AFM ordering and the resultant giant magnetoresistance effect are induced. A large negative magnetoresistance (10%) with a plateau-like feature is revealed, which is consistent with the AFM interlayer coupling between the adjacent CrTe2 main layers in a temperature window of 30 K below the Néel temperature. Notably, the AFM state has a relatively weak interlayer exchange coupling, allowing a switching between the interlayer AFM and ferromagnetic states at moderate magnetic fields. This work represents a new route to engineering low-power devices that underpin the emerging spintronic technologies, and an ideal laboratory to study 2D magnetism.
|
May 2022
|
|
B23-Circular Dichroism
|
Diamond Proposal Number(s):
[123352]
Open Access
Abstract: Structure-function relationships of biological macromolecules, in particular proteins, provide crucial insights for fundamental biochemistry, medical research and early drug discovery. However, production of recombinant proteins, either for structure determination, functional studies, or to be used as biopharmaceutical products, is often hampered by their instability and propensity to aggregate in solution in vitro. Protein samples of poor quality are often associated with reduced reproducibility as well as high research and production expenses. Several biophysical methods are available for measuring protein aggregation and stability. Yet, discovering and developing means to improve protein behaviour and structure-function integrity remains a demanding task. Here, we discuss workflows that are made possible by adapting established biophysical methods to high-throughput screening approaches. Rapid identification and optimisation of conditions that promote protein stability and reduce aggregation will support researchers and industry to maximise sample quality, stability and reproducibility, thereby reducing research and development time and costs.
|
May 2022
|
|
B23-Circular Dichroism
|
Diamond Proposal Number(s):
[9156]
Open Access
Abstract: The aim of this work was to test polyamines as potential natural substrates of the Acinetobacter baumannii chlorhexidine efflux protein AceI using near-UV synchrotron radiation circular dichroism (SRCD) spectroscopy. The Gram-negative bacterium A. Baumannii is a leading cause of hospital-acquired infections and an important foodborne pathogen. A. Baumannii strains are becoming increasingly resistant to antimicrobial agents, including the synthetic antiseptic chlorhexidine. AceI (144-residues) was the founding member of the recently recognised PACE family of bacterial multidrug efflux proteins. Using the plasmid construct pTTQ18-aceI(His6) containing the A. baumannii aceI gene directly upstream from a His6-tag coding sequence, expression of AceI(His6) was amplified in E. coli BL21(DE3) cells. Near-UV (250–340 nm) SRCD measurements were performed on detergent-solubilised and purified AceI(His6) at 20 °C. Sample and SRCD experimental conditions were identified that detected binding of the triamine spermidine to AceI(His6). In a titration with spermidine (0–10 mM), this binding was saturable and fitting of the curve for the change in signal intensity produced an apparent binding affinity (KD) of 3.97 ± 0.45 mM. These SRCD results were the first experimental evidence obtained for polyamines as natural substrates of PACE proteins.
|
May 2022
|
|
I10-Beamline for Advanced Dichroism
|
Sheng
Jiang
,
Zhaocong
Huang
,
Qi
An
,
Wen
Zhang
,
Yuli
Yin
,
Dong
Zhang
,
Jun
Du
,
Biao
You
,
Jian-Guo
Zheng
,
Wenqing
Liu
,
Ya
Zhai
Abstract: The significance of spin transport over an interface in energy-efficient spintronic devices has stimulated interest in the spintronic society during the last few decades. Here, interfaces of
permalloy
/
Cu
1
−
x
Tb
x
(Py/Cu-Tb) were investigated in depth. As the Cu-Tb thickness increases, we found that the saturation magnetization of the bilayers falls and then plateaus. Element-specific x-ray magnetic circular dichroism studies suggest that the Tb moment aligns opposite to the Fe and Ni moments, forming a self-assembled antiferromagnetic interface. As a result, the Cu-Tb adjacent layer to Py and the interface have a significant impact on spin transport. Relevant parameters, such as spin mixing conductance, spin diffusion length, and damping, can be tuned by inserting a thin Cu layer between Py and Tb or varying the compositions of Cu-Tb alloys. Using rare-earth Tb, we provide an effective method for controlling the spin transport and magnetism of ferromagnet/normal-metal interfaces. This approach is expected to have a great deal of potential in spintronic applications.
|
May 2022
|
|
I06-Nanoscience
|
G.
Awana
,
R.
Fujita
,
A.
Frisk
,
P.
Chen
,
Q.
Yao
,
A. J.
Caruana
,
C. J.
Kinane
,
N.-J.
Steinke
,
S.
Langridge
,
P.
Olalde-Velasco
,
S. S.
Dhesi
,
G.
Van Der Laan
,
X. F.
Kou
,
S. L.
Zhang
,
T.
Hesjedal
,
D.
Backes
Diamond Proposal Number(s):
[23748]
Open Access
Abstract: An elegant approach to overcome the intrinsic limitations of magnetically doped topological insulators is to bring a topological insulator in direct contact with a magnetic material. The aspiration is to realize the quantum anomalous Hall effect at high temperatures where the symmetry-breaking magnetic field is provided by a proximity-induced magnetization at the interface. Hence, a detailed understanding of the interfacial magnetism in such heterostructures is crucial, yet its distinction from structural and magnetic background effects is a rather nontrivial task. Here, we combine several magnetic characterization techniques to investigate the magnetic ordering in
MnTe
/
Bi
2
Te
3
heterostructures. A magnetization profile of the layer stack is obtained using depth-sensitive polarized neutron reflectometry. The magnetic constituents are characterized in more detail using element-sensitive magnetic x-ray spectroscopy. Magnetotransport measurements provide additional information about the magnetic transitions. We find that the supposedly antiferromagnetic MnTe layer does not exhibit an x-ray magnetic linear dichroic signal, raising doubt that it is in its antiferromagnetic state. Instead, Mn seems to penetrate into the surface region of the
Bi
2
Te
3
layer. Furthermore, the interface between MnTe and
Bi
2
Te
3
is not abrupt, but extending over
∼
2.2
nm. These conditions are the likely reason that we do not observe proximity-induced magnetization at the interface. Our findings illustrate the importance of not solely relying on one single technique as proof for proximity-induced magnetism at interfaces. We demonstrate that a holistic, multitechnique approach is essential to gain a more complete picture of the magnetic structure in which the interface is embedded.
|
May 2022
|
|
I06-Nanoscience
|
X.
Gu
,
C.
Chen
,
W. S.
Wei
,
L. L.
Gao
,
J. Y.
Liu
,
X.
Du
,
D.
Pei
,
J. S.
Zhou
,
R. Z.
Xu
,
Z. X.
Yin
,
W. X.
Zhao
,
Y. D.
Li
,
C.
Jozwiak
,
A.
Bostwick
,
E.
Rotenberg
,
D.
Backes
,
L. S. I.
Veiga
,
S.
Dhesi
,
T.
Hesjedal
,
G.
Van Der Laan
,
H. F.
Du
,
W. J.
Jiang
,
Y. P.
Qi
,
G.
Li
,
W. J.
Shi
,
Z. K.
Liu
,
Y. L.
Chen
,
L. X.
Yang
Diamond Proposal Number(s):
[27482]
Abstract: Crystal geometry can greatly influence the emergent properties of quantum materials. As an example, the kagome lattice is an ideal platform to study the rich interplay between topology, magnetism, and electronic correlation. In this work, combining high-resolution angle-resolved photoemission spectroscopy and ab initio calculation, we systematically investigate the electronic structure of
X
Mn
6
Sn
6
(
X
=
Dy
,
Tb
,
Gd
,
Y
)
family compounds. We observe the Dirac fermion and the flat band arising from the magnetic kagome lattice of Mn atoms. Interestingly, the flat band locates in the same energy region in all compounds studied, regardless of their different magnetic ground states and
4
f
electronic configurations. These observations suggest a robust Mn magnetic kagome lattice across the
X
Mn
6
Sn
6
family, thus providing an ideal platform for the search for, and investigation of, new emergent phenomena in magnetic topological materials.
|
Apr 2022
|
|
B23-Circular Dichroism
|
Diamond Proposal Number(s):
[29153]
Abstract: Circularly polarized organic light-emitting diodes (CP-OLEDs) that demonstrate both state-of-the-art efficiency and strongly circularly polarized (CP) electroluminescence have proved a considerable technical challenge. Furthermore, multiple factors – from film thickness to device structure – have been shown to influence the sign of the emitted CP light, independent of the handedness (absolute stereochemistry) of the chiral emitter. Here we report CP-OLEDs using a blend of poly(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and a chiral small molecule additive (1-aza[6]helicene, aza[6]H). We demonstrate CP-OLEDs with an impressive electroluminescence dissymmetry (gEL) > 0.3 and a current efficiency of 0.53 cd A−1 and brightness of 3023 cd m−2. While at low aza[6]H loadings, F8T2 blends are consistent with previous observations of CP dissymetric inversion as a function of film thickness/excitation mode, a higher loading of aza[6]H (∼40 wt%) removes such dependencies while retaining excellent g-factors. The materials disclosed will allow for further mechanistic studies of chiral polymeric materials and provide new opportunities for chiroptical optimisation in films and devices.
|
Mar 2022
|
|
B23-Circular Dichroism
|
Diamond Proposal Number(s):
[23764, 25489]
Open Access
Abstract: The tau protein, a soluble protein associated with microtubules, which is involved in the assembly and stabilization of cytoskeletal elements, was found to form neurofibrillary tangles in different neurodegenerative diseases. Insoluble tau aggregates were observed to be organized in paired helical filaments (PHFs) and straight filaments (SFs). Recently, two small sequences (306–311 and 275–280) in the microtubule-binding region (MTBR), named PHF6 and PHF6*, respectively, were found to be essential for tau aggregation. Since a possible therapeutic approach consists of impairing amyloid formation either by stabilizing the native proteins or reducing the level of amyloid precursors, here we use synchrotron radiation circular dichroism (SRCD) at Diamond B23 beamline to evaluate the inhibitory effects of two small molecules, trehalose and ceftriaxone, against the aggregation of a small peptide containing the PHF6* sequence. Our results indicate that both these molecules, ceftriaxone and trehalose, increased the stability of the peptide toward aggregation, in particular that induced by heparin. With trehalose being present in many fruits, vegetables, algae and processed foods, these results support the need to investigate whether a diet richer in trehalose might exert a protective effect toward pathologies linked to protein misfolding.
|
Mar 2022
|
|
B23-Circular Dichroism
|
Diamond Proposal Number(s):
[22017, 26044]
Open Access
Abstract: Thin films of a chiral diketopyrrolopyrrole derivative were imaged with spatially-defined Mueller Matrix Polarimetry, focussing on the Circular Dichroism signal, giving unique insight into the impact that deposition techniques and thermal annealing can have on chiral supramolecular structures in the solid state, where homogeneity was observed for spun-coated films while drop-coating afforded chiroptical diversity in the material, a feature invisible to absorption spectroscopy or optical microscopy.
|
Mar 2022
|
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