I16-Materials and Magnetism
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Diamond Proposal Number(s):
[22052, 18967]
Open Access
Abstract: Understanding and controlling the transition between antiferromagnetic states having different symmetry content with respect to time-inversion and space-group operations are fundamental challenges for the design of magnetic phases with topologically nontrivial character. Here, we consider a paradigmatic antiferromagnetic oxide insulator, Ca2RuO4, with symmetrically distinct magnetic ground states and unveil a novel path to guide the transition between them. The magnetic changeover results from structural and orbital reconstruction at the transition metal site that in turn arise as a consequence of substitutional doping. By means of resonant X-ray diffraction we track the evolution of the structural, magnetic, and orbital degrees of freedom for Mn doped Ca2RuO4 to demonstrate the mechanisms which drive the antiferromagnetic transition. While our analysis focuses on a specific case of substitution, we show that any perturbation that can impact in a similar way on the crystal structure, by reconstructing the induced spin–orbital exchange, is able to drive the antiferromagnetic reorganization.
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Jun 2022
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[4073, 1803, 17569]
Abstract: Chirality is a concept first proposed by Lord Kelvin in the 19th century, referring to objects that do not coincide with their mirror image. Chirality can be thought of as ‘handedness’, with the most obvious example being a pair of human hands. Theoretical models suggest that chiral materials will give rise to exotic physical phenomena.
Langasite (lanthanum gallium silicate) is a piezoelectric crystal with optoelectronic applications. An international team of researchers used X-ray scattering and polarised neutrons to investigate the magnetic and structural chirality in a langasite crystal. The crystal has a chiral atomic arrangement. When it orders magnetically, it forms a triangular arrangement of magnetic helices. The triangular configuration adopted by the spins, the rotational direction of the helices and their relationship with the structural chirality were unclear.
Diamond Light Source’s Materials and Magnetism beamline (I16) was perfect for this study. It allows full control of the energy and polarisation of the X-ray beam and analysis of the final polarisation of the diffracted beam. These features are all necessary to study the chiral properties of a crystal. The research team determined the system’s absolute structural and magnetic chirality and the unusual mechanism controlling the direction of rotation of the magnetic helix. Chirality is an elusive property to measure. However, it is robust and can be associated to topological properties. In future, it may be possible to use topologically chiral objects to store information.
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Jul 2021
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I16-Materials and Magnetism
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Byungmin
Sohn
,
Bongju
Kim
,
Se Young
Park
,
Hwan Young
Choi
,
Jae Young
Moon
,
Taeyang
Choi
,
Young Jai
Choi
,
Hua
Zhou
,
Jun Woo
Choi
,
Alessandro
Bombardi
,
Dan. G.
Porter
,
Seo Hyoung
Chang
,
Jung Hoon
Han
,
Changyoung
Kim
Diamond Proposal Number(s):
[22181]
Open Access
Abstract: We observed a humplike feature in Hall effects of
SrRuO
3
ultrathin films, and systematically investigated it by controlling thicknesses, temperatures and magnetic fields. The humplike feature is extremely stable, even surviving as a magnetic field is tilted by as much as
85
∘
. Based on the atomic-level structural analysis of a
SrRuO
3
ultrathin film with a theoretical calculation, we reveal that atomic rumplings at the thin-film surface enhance Dzyaloshinskii-Moriya interaction, which can generate stable chiral spin textures and a humplike Hall effect. Moreover, temperature dependent resonant x-ray measurements at the Ru
L
edge under a magnetic field showed that the intensity modulation of unexpected peaks was correlated with the hump region in the Hall effect. We verify that the two-dimensional property of ultrathin films generates stable noncoplanar spin textures having a magnetic order in a ferromagnetic oxide material.
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Jun 2021
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I16-Materials and Magnetism
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Stephan
Geprags
,
Bjorn Erik
Skovdal
,
Monika
Scheufele
,
Matthias
Opel
,
Didier
Wermeille
,
Paul
Thompson
,
Alessandro
Bombardi
,
Virginie
Simonet
,
Stephane
Grenier
,
Pascal
Lejay
,
Gilbert Andre
Chahine
,
Diana Lucia
Quintero-Castro
,
Rudolf
Gross
,
Danny
Mannix
Diamond Proposal Number(s):
[12770]
Abstract: We report on a comprehensive investigation of the effects of strain and film thickness on the structural and magnetic properties of epitaxial thin films of the prototypal
J
eff
=
1
/
2
compound
Sr
2
IrO
4
by advanced x-ray scattering. We find that the
Sr
2
IrO
4
thin films can be grown fully strained up to a thickness of 108 nm. By using x-ray resonant scattering, we show that the out-of-plane magnetic correlation length is strongly dependent on the thin film thickness, but independent of the strain state of the thin films. This can be used as a finely tuned dial to adjust the out-of-plane magnetic correlation length and transform the magnetic anisotropy from two-dimensional to three-dimensional behavior by incrementing film thickness. These results provide a clearer picture for the systematic control of the magnetic degrees of freedom in epitaxial thin films of
Sr
2
IrO
4
and bring to light the potential for a rich playground to explore the physics of
5
d
transition-metal compounds.
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Dec 2020
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I16-Materials and Magnetism
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N.
Qureshi
,
A.
Bombardi
,
S.
Picozzi
,
P.
Barone
,
E.
Lelièvre-Berna
,
X.
Xu
,
C.
Stock
,
D. F.
Mcmorrow
,
A.
Hearmon
,
F.
Fabrizi
,
P. G.
Radaelli
,
S.-W.
Cheong
,
L. C.
Chapon
Diamond Proposal Number(s):
[4073, 1803, 17569]
Abstract: We present a combined polarized neutron and x-ray scattering study on two enantiopure langasite single crystals aimed at the determination of their absolute structural and magnetic chiralities and the coupling between them. Our respective data sets unambiguously reveal two samples of opposite structural chirality, where the magnetic handedness is pinned by the structural one. Simple energy considerations of the magnetic exchange and single-ion anisotropy parameters reveal that it is not the Dzyaloshinskii-Moriya interaction but the local single-ion anisotropy on a triangular plaquette which plays a key role in stabilizing one of the two magnetic helices.
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Aug 2020
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I16-Materials and Magnetism
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Priscila
Rosa
,
Yuanfeng
Xu
,
Marein
Rahn
,
Jean
Souza
,
Satya
Kushwaha
,
Larissa
Veiga
,
Alessandro
Bombardi
,
Sean
Thomas
,
Marc
Janoschek
,
Eric
Bauer
,
Mun
Chan
,
Zhijun
Wang
,
Joe
Thompson
,
Neil
Harrison
,
Pascoal
Pagliuso
,
Andrei
Bernevig
,
Filip
Ronning
Diamond Proposal Number(s):
[18991]
Open Access
Abstract: Here we investigate antiferromagnetic Eu5In2Sb6, a nonsymmorphic Zintl phase. Our electrical transport data show that Eu5In2Sb6 is remarkably insulating and exhibits an exceptionally large negative magnetoresistance, which is consistent with the presence of magnetic polarons. From ab initio calculations, the paramagnetic state of Eu5In2Sb6 is a topologically nontrivial semimetal within the generalized gradient approximation (GGA), whereas an insulating state with trivial topological indices is obtained using a modified Becke−Johnson potential. Notably, GGA + U calculations suggest that the antiferromagnetic phase of Eu5In2Sb6 may host an axion insulating state. Our results provide important feedback for theories of topological classification and highlight the potential of realizing clean magnetic narrow-gap semiconductors in Zintl materials.
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Jul 2020
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[17731, 19890, 20778, 21376]
Abstract: An experimental setup to perform high-pressure resonant X-ray scattering (RXS) experiments at low temperature on I16 at Diamond Light Source is presented. The setup consists of a membrane-driven diamond anvil cell, a panoramic dome and an optical system that allows pressure to be measured in situ using the ruby fluorescence method. The membrane cell, inspired by the Merrill–Bassett design, presents an asymmetric layout in order to operate in a back-scattering geometry, with a panoramic aperture of 100° in the top and a bottom half dedicated to the regulation and measurement of pressure. It is specially designed to be mounted on the cold finger of a 4 K closed-cycle cryostat and actuated at low-temperature by pumping helium into the gas membrane. The main parts of the body are machined from a CuBe alloy (BERYLCO 25) and, when assembled, it presents an approximate height of 20–21 mm and fits into a 57 mm diameter. This system allows different materials to be probed using RXS in a range of temperatures between 30 and 300 K and has been tested up to 20 GPa using anvils with a culet diameter of 500 µm under quasi-cryogenic conditions. Detailed descriptions of different parts of the setup, operation and the developed methodology are provided here, along with some preliminary experimental results.
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Mar 2020
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I16-Materials and Magnetism
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Han Gyeol
Lee
,
Lingfei
Wang
,
Liang
Si
,
Xiaoyue
He
,
Daniel G.
Porter
,
Jeong Rae
Kim
,
Eun Kyo
Ko
,
Jinkwon
Kim
,
Sung Min
Park
,
Bongju
Kim
,
Andrew Thye Shen
Wee
,
Alessandro
Bombardi
,
Zhicheng
Zhong
,
Tae Won
Noh
Diamond Proposal Number(s):
[22181]
Abstract: The metal–insulator transition (MIT) in transition‐metal‐oxide is fertile ground for exploring intriguing physics and potential device applications. Here, an atomic‐scale MIT triggered by surface termination conversion in SrRuO3 ultrathin films is reported. Uniform and effective termination engineering at the SrRuO3(001) surface can be realized via a self‐limiting water‐leaching process. As the surface termination converts from SrO to RuO2, a highly insulating and nonferromagnetic phase emerges within the topmost SrRuO3 monolayer. Such a spatially confined MIT is corroborated by systematic characterizations on electrical transport, magnetism, and scanning tunneling spectroscopy. Density functional theory calculations and X‐ray linear dichroism further suggest that the surface termination conversion breaks the local octahedral symmetry of the crystal field. The resultant modulation in 4d orbital occupancy stabilizes a nonferromagnetic insulating surface state. This work introduces a new paradigm to stimulate and tune exotic functionalities of oxide heterostructures with atomic precision.
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Dec 2019
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[15087]
Abstract: The presence of domains in ferroic materials can negatively affect their macroscopic properties and hence their usefulness in device applications. From an experimental perspective, the measurement of materials comprising multiple domains can complicate the interpretation of the material properties and their underlying mechanisms. In general,
Bi
Fe
O
3
films tend to grow with multiple magnetic domains and often contain multiple ferroelectric- and ferroelastic-domain variants. By growing (111)-oriented
Bi
Fe
O
3
films on an orthorhombic
Tb
Sc
O
3
substrate, we are able to overcome this and, by exploiting the magnetoelastic coupling between the magnetic and crystal structures, bias the growth of a given magnetic-, ferroelectric-, and structural-domain film. We further demonstrate the coupling of the magnetic structure to the ferroelectric polarization by showing that the magnetic polarity in this domain is inverted upon
180
∘
ferroelectric switching.
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Feb 2019
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I16-Materials and Magnetism
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Diamond Proposal Number(s):
[16576, 17569, 18967]
Open Access
Abstract: We review the magnetic and orbital ordered states in Ca2RuO4 by performing resonant elastic x-ray scattering (REXS) at the Ru L2,3 edges. In principle, the point symmetry at Ru sites does not constrain the direction of the magnetic moment below TN. However early measurements reported the ordered moment entirely along the b orthorhombic axis. Taking advantage of the large resonant enhancement of the magnetic scattering close to the Ru L2 and L3 absorption edges, we monitored the azimuthal, thermal, and energy dependence of the REXS intensity and find that a canting (m_c≃0.1 m_b) along the c-orthorhombic axis is present. No signal was found for m_a despite this component also being allowed by symmetry. Such findings are interpreted by a microscopic model Hamiltonian and pose new constraints on the parameters describing the model. Using the same technique we reviewed the accepted orbital ordering picture. We detected no symmetry breaking associated with the signal increase at the “so-called” orbital ordering temperature (≃260K). We did not find any changes of the orbital pattern even through the antiferromagnetic transition, suggesting that, if any, only a complex rearrangement of the orbitals, not directly measurable using linearly polarized light, can take place.
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Sep 2018
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