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Hélène
Ginestet
,
Rachel J.
Husband
,
Nicolas
Jaisle
,
Eric
Edmund
,
Zuzana
Konôpková
,
Cornelius
Strohm
,
Madden S.
Anae
,
Daniele
Antonangeli
,
Karen
Appel
,
Orianna B.
Ball
,
Marzena
Baron
,
Silvia
Boccato
,
Khachiwan
Buakor
,
Julien
Chantel
,
Hyunchae
Cynn
,
Anand P.
Dwivedi
,
Heinz
Graafsma
,
Egor
Koemets
,
Torsten
Laurus
,
Hauke
Marquardt
,
Bernhard
Massani
,
James D.
Mchardy
,
Malcolm I.
Mcmahon
,
Vitali
Prakapenka
,
Jolanta
Sztuk-Dambietz
,
Minxue
Tang
,
Tianqi
Xie
,
Zena
Younes
,
Ulf
Zastrau
,
Alexander F.
Goncharov
,
Clemens
Prescher
,
Agnes
Dewaele
,
R. Stewart
Mcwilliams
,
Guillaume
Morard
,
Sébastien
Merkel
Open Access
Abstract: The development of pulsed intense x-ray sources, such as free electron laser, offers new avenues for high pressure experiments. Here, we study the feasibility and metrology of x-ray heating in diamond anvil cells at the European x-ray free electron laser. This method enables one to volumetrically heat the sample while inhibiting chemical migration and probing the crystallographic structure of the sample throughout the heating with a high repetition rate. We focus our study on iron, whose phase diagram is well established up to 100 GPa, to explore the possibilities and limitations of this technique. We volumetrically heat iron samples at starting pressures ranging from 10 to 138 GPa, using the x-ray beam pulsed at 4.5 MHz in a serial pump-and-probe experimental design. Experimental challenges arise from temperature gradients within the sample, changes in temperature at the 100 ns timescale, the difficulty of direct temperature estimates, the effect of thermal pressure, and the presence of metastable crystallites due to rapid cycles of heating and cooling. Hence, we develop a multi-crystal-like data processing method that allows us to account for sample heterogeneity in probed conditions. We then calibrate our measurements using known physical properties of iron under pressure. Thermal pressure in our experiments increases from 4% of the isochoric prediction at 10 GPa to 23% at 138 GPa, and we show that our data are in agreement with most previous observations of iron in this pressure range. The method can now be implemented at higher pressures and temperatures and on materials with unknown phase diagrams.
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Jan 2026
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Optics
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Faiyaz
Mollick
,
Maheswar
Nayak
,
Ajay
Kumar Kashyap
,
Jitendra
Kumar
,
Arindam
Majhi
,
Nageswararao
Pothana
,
Parasmani
Rajput
,
Manoj
Kumar Tiwari
,
Sanjay
Kumar Rai
,
Manvendra
Narayan Singh
,
Archna
Sagdeo
Open Access
Abstract: The comprehensive structure, stress, and optical property correlation of high performance x-ray multilayer (ML) mirrors based on Mo/Si and W/B4C material systems is systematically investigated for hard x-ray applications in the 10–20 keV range. All MLs are deposited by magnetron sputtering with carefully tuned periodicities and number of layer pairs to optimize for either high photon flux or high spectral resolution. Structural properties are probed using x-ray reflectivity and diffuse scattering, while residual stress and crystallite characteristics of metallic layer are analyzed by grazing incidence x-ray diffraction. The Mo/Si MLs, with relatively large periods (∼6.53 and 9.43 nm), exhibit interlayer formation and demonstrate high reflectivity up to ∼92% along with very high integrated reflectivity, making them suitable for high-flux applications. In contrast, short and ultra-short period (∼3.74 and 1.85 nm) W/B4C MLs show sharp interfaces, supporting their use in high-resolution optics with relative energy resolution down to ∼1.2%.
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Nov 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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I10-Beamline for Advanced Dichroism - scattering
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Open Access
Abstract: In transition metal oxides, electron–electron interaction and lattice degree of freedom are basic ingredients of emergent phenomena, such as metal-to-insulator transition (MIT) and superconductivity. Perovskite rare-earth nickelates are largely studied for their temperature-driven MIT, which is accompanied by a breathing-mode distortion and associated with a bond-disproportionation of the expanded (3d8L0) and compressed (3d8L2) NiO6 octahedra. Steric effects control the onset temperature of the MIT, the latter being concomitant or not with a complex antiferromagnetic spin arrangement depending upon the choice of the rare-earth ion (TMIT ≥ TNéel). Interface engineering of oxygen octahedra tilting, as imposed by the symmetry and orientation of the substrate, has resulted in an efficient pathway to modify both TMIT and TNéel, hence suggesting a key role of the electron–phonon coupling for both transport and magnetic properties in nickelate thin films. Here, via a combination of resonant elastic x-ray scattering and transport experiments, we show control over both TMIT and TNéel in heteroepitaxial PbZr0.2Ti0.8O3(d)/NdNiO3(7 nm)//SrTiO3 heterostructures, which are characterized by different strains and polarization states of the PbZr0.2Ti0.8O3 layer grown at different thicknesses d. We found the expected NdNiO3 bulk behavior (TMIT = TNéel), for a fully relaxed PbZr0.2Ti0.8O3 layer showing a monodomain polarization state. On the other side, an almost 30 K difference (TMIT > TNéel), is found for a fully strained PbZr0.2Ti0.8O3 characterized by a multidomain texture of the polarization state. We discuss our results in terms of an altered breathing distortion pattern of the underlying nickelate layer as supported by x-ray absorption spectroscopy measurements. We infer that locally different polar distortions controlled by a combination of polarization direction and strength of the strain state play the main role in the observed TMIT and TNéel variations.
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Mar 2025
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[8699]
Open Access
Abstract: The mechanisms contributing to the electromechanical response of piezoelectric ceramics in shear mode have been investigated using high energy synchrotron x-ray diffraction. Soft lead zirconate titanate ceramic specimens were subjected to an electric field in the range 0.2 to 3.0 MV m-1, perpendicular to that of the initial poling direction, while XRD patterns were recorded in transmission. At low electric field levels, the axial strains remained close to zero but a significant shear strain occurred due to the reversible shear-mode piezoelectric coefficient. Both the axial and shear strains increased substantially at higher field levels due to irreversible ferroelectric domain switching. Eventually, the shear strain decreased again as the average remanent polarization became oriented towards the electric field direction. The lattice strain and domain orientation distributions follow the form of the total strain tensor, enabling the domain switching processes to be monitored by the rotation of the principal strain axis. Reorientation of this axis towards the electric field direction occurred progressively above 0.6 MV m-1, while the angle of rotation increased from 0° to approximately 80° at the maximum field of 3.0 MV m-1. A strong correlation was established between the effective strains associated with different crystallographic directions, which was attributed to the effects of elastic coupling between grains in the polycrystal.
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Nov 2024
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I10-Beamline for Advanced Dichroism - scattering
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Diamond Proposal Number(s):
[31755]
Open Access
Abstract: The soft X-ray reflectivity technique is frequently utilized for studying magnetization reversal in thin films due to its elemental and depth sensitivity. The characteristic hysteresis loops measured with this technique are dependent on both the magnetization direction in magnetic materials and the incident soft X-ray polarization. In this note, we have discussed these magneto-optical effects in soft X-ray reflectivity measurements. These effects can be exploited to probe magnetization reversal mechanisms driven by stimuli beyond conventional means of magnetic field. To demonstrate this, we have presented our investigations on current-induced magnetization switching in ferromagnet/heavy metal (FM/HM) heterostructures.
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Sep 2024
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[31704]
Open Access
Abstract: The functional properties of piezoelectric ceramic materials, such as barium titanate, are highly dependent on grain size. Lead-free polycrystalline Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) samples were prepared with a combination of the hydrothermal method and spark plasma sintering to achieve grain sizes from 100 nm to 10 μm by varying the maximum sintering temperature. In this range, a transition from a nearly linear dielectric to a ferroelectric response can be seen in macroscopic electromechanical measurements, demonstrating the importance of grain size on functional properties in BCZT. Furthermore, in situ electric field-dependent synchrotron x-ray diffraction measurements were performed to quantify the intrinsic and extrinsic strain contributions and their variations with grain size. At lower grain sizes, the data revealed a significant loss of extrinsic contributions in the piezoelectric behavior, limiting the response to intrinsic contribution associated with lattice strain. For BCZT, a critical grain size between approximately 0.08 and 0.18 μm is proposed, below which no piezoelectric response was observed.
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May 2024
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I15-Extreme Conditions
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Diamond Proposal Number(s):
[28469]
Open Access
Abstract: Palladium is one of the most important technological materials, yet its phase diagram remains poorly understood. At ambient conditions, its solid phase is face-centered cubic (fcc). However, another solid phase of Pd, body-centered cubic (bcc), was very recently predicted in two independent theoretical studies to occur at high pressures and temperatures. In this work, we report an experimental study on the room-temperature equation of state (EOS) of Pd to a pressure of 80 GPa, as well as a theoretical study on the phase diagram of Pd including both fcc-Pd and bcc-Pd. Our theoretical approach consists in ab initio quantum molecular dynamics (QMD) simulations based on the Z methodology which combines both direct Z method for the simulation of melting curves and inverse Z method for the calculation of solid–solid phase transition boundaries. We obtain the melting curves of both fcc-Pd and bcc-Pd and an equation for the fcc–bcc solid–solid phase transition boundary as well as the thermal EOS of Pd which is in agreement with experimental data and QMD simulations. We uncover the presence of another solid phase of Pd on its phase diagram, namely, random hexagonal close-packed (rhcp), and estimate the location of the rhcp-bcc solid–solid phase transition boundary and the rhcp–fcc–bcc triple point. We also discuss the topological similarity of the phase diagrams of palladium and silver, the neighbor of Pd in the periodic table. We argue that Pd is a reliable standard for shock-compression studies and present the analytic model of its principal Hugoniot in a wide pressure range.
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Feb 2024
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Abstract: Tetrahedrite, Cu12Sb4S13, an eco-friendly thermoelectric material with earth-abundant and low-cost constituents, has garnered global interest. This study investigated the thermoelectric characteristics of Ag-added tetrahedrites, which were prepared through solid-state synthesis and subsequently hot-pressed. The minimal temperature dependence of the transport coefficient indicated the presence of strong electron–phonon coupling in the samples. It was observed that Ag addition in tetrahedrite could successfully scatter acoustic phonons, reducing the lattice thermal conductivity while minimally affecting the power factor. The enhanced anharmonicity induced by Ag addition is the primary cause of reduced lattice thermal conductivity. Raman spectroscopy data showed that Ag addition could weaken the Sb–S bond, further supporting the previous argument. Consequently, the lattice thermal conductivity was lowered to ∼0.27 W m−1 K−1 and obtained for the composition Ag0.025 added Cu11.975Sb4S13. A relatively high power factor of ∼1.3 mW m−1 K−2 was obtained for the same composition. Owing to the lowest total thermal conductivity ∼1.09 W m−1 K−1, the sample with composition Ag0.025 added Cu11.975Sb4S13 showed the highest thermoelectric figure of merit of 0.87 at 738 K.
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Dec 2023
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I06-Nanoscience (XPEEM)
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Diamond Proposal Number(s):
[24373]
Open Access
Abstract: Pointed magnetic elements are introduced as an improvement upon rectangular strips currently employed in composite element magnetic barcodes. The coercivity of these elements, as measured using the magneto-optic Kerr effect, is found to strictly adhere to a single power law relationship with the element width, where the power law exponent is dependent on the length of the pointed region and takes values between −
0.98 and −
0.91. The steeper gradients here, along with the absence of the crossover region seen in rectangular devices, present these structures as a strict improvement in terms of potential device applications. These improvements are found to be present for all structures where the pointed region is as long as, or longer than, the magnetic element is wide. The remanent magnetization configuration, imaged using photo-emission microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM), is compared to the results of micromagnetic simulations. It is found to cant inward in the pointed section of the strip, aligning with the edges of the point, pinning the magnetization and giving a consistent magnetization reversal behavior for all element widths investigated.
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Oct 2023
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