I06-Nanoscience (XPEEM)
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Purnima P.
Balakrishnan
,
Hemian
Yi
,
Zi-Jie
Yan
,
Wei
Yuan
,
Andreas
Suter
,
Christopher J.
Jensen
,
Pascal
Manuel
,
Fabio
Orlandi
,
Takayasu
Hanashima
,
Christy J.
Kinane
,
Andrew J.
Caruana
,
Dirk
Backes
,
Padraic
Shafer
,
Brian B.
Maranville
,
Zaher
Salman
,
Thomas
Prokscha
,
Cui-Zu
Chang
,
Alexander J.
Grutter
Diamond Proposal Number(s):
[42224]
Abstract: The search for chiral topological superconductivity in magnetic topological insulator (TI)-FeTe heterostructures is a key frontier in condensed matter physics, with potential applications in topological quantum computing. The combination of ferromagnetism, superconductivity, and topologically nontrivial surface states brings together the key elements required for chiral Majorana physics. In this work, we examine the interplay between magnetism and superconductivity at the interfaces between FeTe and a series of Te-based TI overlayers. In both Te/FeTe and superconducting MnBi2Te4/FeTe, any interfacial suppression of antiferromagnetism must affect at most a few nanometers. On the other hand, (Bi,Sb)2Te3/FeTe layers exhibit near-total suppression of antiferromagnetic ordering. Ferromagnetic Cr𝑥(Bi,Sb)2−𝑥Te3 (CBST)/FeTe bilayers exhibit net magnetization in both CBST and FeTe layers, with evidence of interactions between superconductivity and ferromagnetism. These observations identify magnetic TI/FeTe interfaces as an exceptionally robust platform to realize chiral topological superconductivity.
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Oct 2025
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I06-Nanoscience (XPEEM)
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M.
Boldrin
,
A.
Bagri
,
D.
Barlettani
,
E.
Teather
,
L.
Squillantini
,
M.
De Souza
,
R. B.
Pontes
,
A. G.
Silva
,
T. J. A.
Mori
,
R.
Perry
,
R.
Lora-Serrano
,
E.
Granado
,
E. M.
Bittar
,
L. S. I.
Veiga
,
L.
Bufaiçal
Diamond Proposal Number(s):
[35100]
Abstract: The La2CoMnO6 (LCMO) perovskite has received a lot of attention due to its near-room-temperature magnetodielectric effect. Despite the recent efforts, the mechanism ruling the correlation between its magnetic and dielectric properties is not yet fully understood. In order to address this issue, we conducted a detailed investigation of the coupling between the structural, electronic, and magnetic properties of a polycrystalline LCMO sample. Using magnetic field-dependent x-ray powder diffraction and measurements with a capacitive dilatometer, we show that applying an external magnetic field decreases the unit cell volume, thereby modifying the octahedral distortions. Experiments involving temperature and field-dependent x-ray absorption spectroscopy at the Co-𝐿2,3 edges provide further evidence that the spin-orbit interaction of outermost Co 3𝑑 orbital and the field-induced enhancement of covalence effects are the key contributors to the magnetostrictive effects. From a detailed analysis using multiplet and density functional theory calculations, we propose that the field-induced modulations of the orbital hybridization and the ligand-to-metal charge transfer are responsible for the changes in the dielectric response of LCMO, thus enabling a direct coupling between magnetic, elastic, and dielectric properties in this material.
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Sep 2025
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E02-JEM ARM 300CF
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Diamond Proposal Number(s):
[16952]
Open Access
Abstract: Atomic resolution imaging is key to understanding thin film growth and how a particular set of conditions influences properties. Whilst such imaging in the scanning transmission electron microscope (STEM) has had a transformative impact in nanoscience, it forms projection images and provides no direct information about displacements perpendicular to the image plane. In this article, we show that it is possible to make atomic resolution maps of the direction and magnitude of La displacements at ∼30∘ to the imaging plane in a La2CoMnO6 thin film on (111) LSAT (LaAlO3−La(Sr,Ta)O3) using a four-dimensional STEM (4DSTEM) methodology. This reveals that the La modulation lies preferentially in the interface plane, and is strongly suppressed close to the epitaxial interface, and further reveals how the modulation varies with distance from the interface with unit cell resolution. These details would be completely invisible to all prior techniques in electron microscopy and this sheds light on why this particular substrate in this orientation best promotes double perovskite cation ordering, and the consequent optimal magnetic ordering for this thin film system. The approach used herein of fitting atomic resolution 4DSTEM data to determine crystal parameters opens the door for a new era of atomic-resolution crystallography.
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Sep 2025
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I09-Surface and Interface Structural Analysis
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Rajesh
Dutta
,
Prajwal M.
Laxmeesha
,
Tarush
Tandon
,
Tessa D.
Tucker
,
Sharup
Sheikh
,
Uditha M.
Jayathilake
,
Wei
Tian
,
Adam A.
Aczel
,
Tien-Lin
Lee
,
Alexander X.
Gray
,
Steven J.
May
Abstract: We have investigated the electronic and magnetic structures of topological kagome Fe1−𝑥Mn𝑥Sn (0≤𝑥≤0.3) thin films via neutron diffraction, electronic transport measurements, and ab initio density functional theory (DFT) to understand the interplay between hole doping, magnetism, and the electronic structures. Temperature-dependent neutron diffraction measurements on parent FeSn reveal the Néel temperature to be 𝑇N∼355 K and the underlying A-type antiferromagnetic ordering is associated with a wave vector 𝒒=(001/2). Upon Mn doping to 𝑥=0.15, 𝑇N decreases slightly while the magnetic ordering vector remains the same. Resistivity measurements show metallic characteristics and in-plane anisotropy down to 10 K for all the investigated samples. The effects of hole doping are mapped in terms of electronic ground state calculations via DFT which show that the Dirac point is moved closer to the Fermi level (𝐸F) and the flat bands get pushed away from 𝐸F upon hole doping. However, a comparison between hole-doped Fe1−𝑥Mn𝑥Sn and electron-doped Fe1−𝑥Co𝑥Sn indicates that the Néel temperature does not scale with the position of 𝐸F relative to the flat band. Our results establish the antiferromagnetic state of FeSn and Fe1−𝑥Mn𝑥Sn films at room temperature, laying the groundwork for future studies of magnetism in kagome heterostructures.
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Jul 2025
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I11-High Resolution Powder Diffraction
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Diamond Proposal Number(s):
[36397]
Abstract: Here we demonstrate the floating zone crystal growth of the 𝐽eff=1/2 Mott insulator Sr2IrO4. Historically, the growth of iridates from a ternary melt has been precluded by the extreme vapor pressure of the metal oxide species and the difficulty of maintaining the correct oxidation state of Ir at high temperatures. Here, we show that the application of a high-pressure oxygen growth environment stabilizes the Sr2IrO4 phase, leading to the first demonstration of cm3-scale crystals. In contrast with the conventional SrCl2 flux growth method, where poor control over disorder leads to strong sample dependence, the high-pressure floating zone growth enables active control over the homogeneity of the melt. Crystals grown via this technique possess qualitatively similar properties to those grown via flux, with a relatively sharp onset of antiferromagnetic order observed in temperature-dependent magnetization. Furthermore, we demonstrate that by tuning the mixing rate of the melt, we are able to grow natively hole-doped Sr2Ir1−𝑦O4, which exhibits a strongly modified magnetic and electronic response.
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May 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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I06-Nanoscience (XPEEM)
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Diamond Proposal Number(s):
[35404]
Open Access
Abstract: Antiferromagnets (AFs) are characterized by spin structures that are resistant to external magnetic fields, rendering them ideal for persistent information storage but challenging to control. This study demonstrates that a thin ferromagnetic adlayer can serve as a magnetic ‘lever’ to provide a strong handle on the spin texture of an adjacent antiferromagnet. In bilayers composed of NiO(001) and Co, the expected exchange bias effect—a unidirectional shift in the Co hysteresis due to coupling with NiO—is notably absent. Instead, a strong interfacial coupling is observed, causing the NiO to partially follow the magnetization of Co under an applied magnetic field. Using x-ray magnetic linear dichroism, we detect an inversion of dichroism, indicating a reorientation of the Néel vector in NiO. X-ray spectromicroscopy imaging further reveals a direct correlation between ferromagnetic and antiferromagnetic domain structures. These findings are explained using a toy model that distinguishes between stable and unstable AF domains, highlighting the dynamic interplay between NiO and the Co adlayer in the presence of a magnetic field.
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Jan 2025
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I06-Nanoscience (XPEEM)
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M.
Lowe
,
A.
Al-Mahboob
,
D.
Ivarsson
,
M.
Armbrüster
,
J.
Ardini
,
G.
Held
,
F.
Maccherozzi
,
A.
Bayer
,
V.
Fournee
,
J.
Ledieu
,
J. T.
Sadowski
,
R.
Mcgrath
,
H. R.
Sharma
Open Access
Abstract: The intermetallic compound ZnPd has been found to have desirable characteristics as a catalyst for the steam reforming of methanol. The understanding of the surface structure of ZnPd is important to optimize its catalytic behavior. However, due to the lack of bulk single-crystal samples and the complexity of characterizing surface properties in the available polycrystalline samples using common experimental techniques, all previous surface science studies of this compound have been performed on surface alloy samples formed through thin-film deposition. In this study, we present findings on the chemical and atomic structure of the surfaces of bulk polycrystalline ZnPd studied by a variety of complementary experimental techniques, including scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), low energy electron microscopy (LEEM), photoemission electron microscopy (PEEM), and microspot low-energy electron diffraction (𝜇-LEED). These experimental techniques, combined with density functional theory (DFT)-based thermodynamic calculations of surface free energy and detachment kinetics at the step edges, confirm that surfaces terminated by atomic layers composed of both Zn and Pd atoms are more stable than those terminated by only Zn or Pd layers. DFT calculations also demonstrate that the primary contribution to the tunneling current arises from Pd atoms, in agreement with the STM results. The formation of intermetallics at surfaces may contribute to the superior catalyst properties of ZnPd over Zn or Pd elemental counterparts.
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Oct 2024
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I09-Surface and Interface Structural Analysis
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Pablo
Vezzoni Vicente
,
Tobias
Weiss
,
Dennis
Meier
,
Wenchao
Zhao
,
Birce Sena
Tömekçe
,
Marc
G. Cuxart
,
Benedikt P.
Klein
,
David A.
Duncan
,
Tien-Lin
Lee
,
Anthoula C.
Papageorgiou
,
Matthias
Muntwiler
,
Ari Paavo
Seitsonen
,
Willi
Auwärter
,
Peter
Feulner
,
Johannes V.
Barth
,
Francesco
Allegretti
Diamond Proposal Number(s):
[25907]
Abstract: In light of the recent research interest in low-dimensional bismuth structures as spin-active materials and topological insulators, we present a comprehensive characterization of the Bi/Au(111) interface. The nuanced evolution of Bi phases upon deposition in ultrahigh vacuum (UHV) on a Au(111) surface is investigated from semidisordered clusters to few-layer Bi(110) thin films. Particular attention is devoted to the high-coverage, submonolayer phases, commonly grouped under the (𝑃×√3) nomenclature. We bring forth a new model, refining the current understanding of the Bi/Au(111) interface and demonstrating the existence of submonolayer moiré superstructures, whose geometry and superperiodicity depend on their coverage. This tuneable periodicity paves the way for their use as tailored buffer and templating layers for epitaxial growth of thin films on Au(111). Finally, we clarify the growth mode of multilayer Bi(110) as bilayer-by-bilayer, allowing precise thickness control of anisotropically strained thin films. This holistic understanding of the structural properties of the material was enabled by the synergy of several experimental techniques, namely low-energy electron diffraction (LEED), x-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy and spectroscopy (STM, STS), and x-ray standing waves (XSW), further corroborated by density functional theory (DFT) simulations.
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Oct 2024
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B18-Core EXAFS
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A.
Bandyopadhyay
,
S.
Lee
,
D. T.
Adroja
,
M. R.
Lees
,
G. B. G.
Stenning
,
P.
Aich
,
L.
Tortora
,
C.
Meneghini
,
G.
Cibin
,
A.
Berlie
,
R. A.
Saha
,
D.
Takegami
,
A.
Meléndez-Sans
,
G.
Poelchen
,
M.
Yoshimura
,
K. D.
Tsuei
,
Z.
Hu
,
T.-S.
Chan
,
S.
Chattopadhyay
,
G. S.
Thakur
,
K.-Y.
Choi
Diamond Proposal Number(s):
[33369]
Open Access
Abstract: We present an experimental investigation of the magnetic ground state in Ba4NbIr3O12, a fractional valent trimer iridate. X-ray absorption and photoemission spectroscopy show that the Ir valence lies between 3+ and 4+ while Nb is pentavalent. Combined dc/ac magnetization, specific heat, and muon spin rotation/relaxation (µSR) measurements reveal no magnetic phase transition down to 0.05 K. Despite a significant Weiss temperature (ΘW∼−15 to −25 K) indicating antiferromagnetic correlations, a quantum spin-liquid (QSL) phase emerges and persists down to 0.1 K. This state likely arises from geometric frustration in the edge-sharing equilateral triangle Ir network. Our µSR analysis reveals a two-component depolarization, arising from the coexistence of rapidly (90%) and slowly (10%) fluctuating Ir moments. Powder x-ray diffraction and Ir-L3edge x-ray absorption fine structure spectroscopy identify 8–10% Nb/Ir site-exchange, reducing frustration within part of the Ir network, and likely leading to the faster muon spin relaxation, while the structurally ordered Ir ions remain highly geometrically frustrated, giving rise to the rapidly spin-fluctuating QSL ground state. At low temperatures, the magnetic specific heat varies as 𝛾𝑇+𝛼𝑇2, indicating gapless spinon excitations, and possible Dirac QSL features with linear spinon dispersion, respectively.
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Jul 2024
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