I15-1-X-ray Pair Distribution Function (XPDF)
|
Elsebeth J.
Pedersen
,
Theany
To
,
Søren S.
Sørensen
,
Rasmus
Christensen
,
Johan F. S.
Christensen
,
Lars R.
Jensen
,
Michal
Bockowski
,
Oxana V.
Magdysyuk
,
Maria
Diaz-Lopez
,
Yuanzheng
Yue
,
Morten M.
Smedskjaer
Diamond Proposal Number(s):
[30401]
Abstract: Methods to improve the fracture toughness of oxide glasses are needed since low fracture toughness is a major bottleneck for their applications. To overcome this, it is critically important to investigate the effect of both short- and medium-range structural features on fracture toughness. Recent work reported a record-high fracture toughness for a bulk lithium aluminoborate glass subjected to hot compression. Here, we further explore the structural origin of this high fracture toughness by subjecting different alkali aluminoborate glasses to hot compression. Through a combination of x-ray total scattering experiments and atomistic simulations, we find that hot compression causes significant changes to both the short- and medium-range order structure of the glasses, e.g., increased coordination numbers (CNs) of network forming species and decreased average size of ring-type structures. To this end, we reveal positive correlations between the pressure-induced increase in fracture toughness and (i) the increase in average CN of network forming species and (ii) the area of the first sharp diffraction peak in the structure factor. Our study thus improves the understanding of which structural features benefit intrinsic toughening of oxide glasses.
|
May 2023
|
|
I06-Nanoscience
|
C.
Schmitt
,
L.
Sanchez-Tejerina
,
M.
Filianina
,
F.
Fuhrmann
,
H.
Meer
,
R.
Ramos
,
F.
Maccherozzi
,
D.
Backes
,
E.
Saitoh
,
G.
Finocchio
,
L.
Baldrati
,
M.
Klaui
Diamond Proposal Number(s):
[22448]
Abstract: The understanding of antiferromagnetic domain walls, which are the interface between domains with different Néel order orientations, is a crucial aspect to enable the use of antiferromagnetic materials as active elements in future spintronic devices. In this work, we demonstrate that in antiferromagnetic NiO/Pt bilayers arbitrary-shaped structures can be generated by switching driven by electrical current pulses. The generated domains are T domains, separated from each other by a domain wall whose spins are pointing toward the average direction of the two T domains rather than the common axis of the two planes. Interestingly, this direction is the same for the whole domain wall indicating the absence of strong Lifshitz invariants. The domain wall can be micromagnetically modeled by strain distributions in the NiO thin film induced by the MgO substrate, deviating from the bulk anisotropy. From our measurements we determine the domain-wall width to have a full width at half maximum of
Δ
=
98
±
10
nm, demonstrating strong confinement.
|
May 2023
|
|
Theoretical Physics
|
Open Access
Abstract: The Landau free energy of a compound that benefits from a linear coupling of an electric field and a magnetic field includes a product of the two fields, one polar and time even and one axial and time odd. Evidently, the coefficient of the product of fields is unchanged by a simultaneous change in the directions of space and time, a symmetry operation labeled anti-inversion. Invariance with respect to anti-inversion is the defining symmetry of the linear magnetoelectric (ME) effect included in 58 of 122 magnetic crystal classes, 19 of which prohibit higher-order (nonlinear) contributions to the free energy. In ME compounds, expectation values of some atomic magnetic tensors are invariant with respect to anti-inversion. An invariance shared by the Dirac monopole (an element of charge allowed in Maxwell's equations that has not been observed) and a Zel'dovich anapole, is also known as a Dirac dipole. From the science of materials perspective, it has been established that Dirac multipoles contribute to the diffraction of x rays and neutrons. We identify Dirac monopoles in bulk magnetic properties of iron tellurate (
Fe
2
Te
O
6
) and a spin ladder (
Sr
Fe
2
S
2
O
). They are visible in the diffraction of light using an iron electric dipole–magnetic dipole absorption event. Both cited compounds present a simple antiferromagnetic configuration of axial dipoles, and their different magnetic crystal classes allow a linear ME effect. However, the Kerr effect is symmetry allowed in the spin ladder and forbidden in iron tellurate. Anapoles are forbidden in iron tellurate and allowed in the spin ladder compound, a difference evident in diffraction patterns fully informed by symmetry. More generally, we identify a raft of Dirac multipoles, and axial multipoles beyond dipoles, visible in future experiments using standard techniques with beams of neutrons or x rays tuned in energy to an iron atomic resonance. ME invariance imposes a phase relationship between nuclear (charge) and magnetic contributions to neutron (x-ray) diffraction amplitudes. In consequence, intensities of Bragg spots in an x-ray pattern do not change when helicity in the primary beam is reversed. A like effect occurs in the magnetic diffraction of polarized neutrons.
|
Apr 2023
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Andrea
Amorese
,
Philipp
Hansmann
,
Andrea
Marino
,
Peter
Körner
,
Thomas
Willers
,
Andrew
Walters
,
Ke-Jin
Zhou
,
Kurt
Kummer
,
Nicholas B.
Brookes
,
Hong-Ji
Lin
,
Chien-Te
Chen
,
Pascal
Lejay
,
Maurits W.
Haverkort
,
Liu Hao
Tjeng
,
Andrea
Severing
Diamond Proposal Number(s):
[18447]
Open Access
Abstract: We investigated the electronic structure of the enigmatic
CeRh
3
B
2
using resonant inelastic scattering and x-ray absorption spectroscopy in combination with ab initio density functional calculations. We find that the
Rh
4
d
states are irrelevant for the high-temperature ferromagnetism and the Kondo effect. We also find that the
Ce
4
f
crystal-field strength is too small to explain the strong reduction of the Ce magnetic moment. The data revealed instead the presence of two different active
Ce
4
f
orbitals, with each coupling selectively to different bands in
CeRh
3
B
2
. The intersite hybridization of the
∣
∣
J
=
5
2
,
J
z
=
±
1
2
⟩
crystal-field state and
Ce
5
d
band combined with the intrasite
Ce
4
f
–
5
d
exchange creates the strong ferromagnetism, while hybridization between the
∣
∣
J
=
5
2
,
J
z
=
±
5
2
⟩
and the B
s
p
in the
a
b
-plane contributes to the Kondo interaction, which causes the moment reduction. This orbital selective coupling explains the unique and seemingly contradictory properties of
CeRh
3
B
2
.
|
Mar 2023
|
|
I05-ARPES
|
Q. Q.
Zhang
,
Y.
Shi
,
K. Y.
Zhai
,
W. X.
Zhao
,
X.
Du
,
J. S.
Zhou
,
X.
Gu
,
R. Z.
Xu
,
Y. D.
Li
,
Y. F.
Guo
,
Z. K.
Liu
,
C.
Chen
,
S.-K.
Mo
,
T. K.
Kim
,
C.
Cacho
,
J. W.
Yu
,
W.
Li
,
Y. L.
Chen
,
J.-H.
Chu
,
L. X.
Yang
Diamond Proposal Number(s):
[22375]
Abstract: EuTe
4
is a van der Waals material exhibiting a charge density wave (CDW) with a large thermal hysteresis in the resistivity and CDW gap. In this paper, we systematically study the electronic structure and transport properties of
EuTe
4
using high-resolution angle-resolved photoemission spectroscopy (ARPES), magnetoresistance (MR) measurements, and scanning tunneling microscopy (STM). We observe a CDW gap of
∼
200
meV
at low temperatures that persists up to 400 K, suggesting that the CDW transition occurs at a much higher temperature. The ARPES intensity near the Fermi level shows large thermal hysteretic behavior, consistent with the resistivity measurement. The hysteresis in the resistivity measurement does not change under a magnetic field up to 7 T, excluding the thermal magnetic hysteretic effect. Instead, the surface topography measured with STM shows surface domains with different CDW trimerization directions, which may be important for the thermal hysteretic behavior. Interestingly, we reveal a large negative MR at low temperatures that can be associated with the canting of magnetically ordered Eu spins. Our results shed light on the understanding of magnetic, transport, and electronic properties of
EuTe
4
.
|
Mar 2023
|
|
I21-Resonant Inelastic X-ray Scattering (RIXS)
|
Abstract: Spinel oxides are well-known functional materials but rarely show superconductivity. Recently, emergent superconductivity was discovered in
MgTi
2
O
4
, which is attributed to the increase of electron doping and the suppression of orbital order. Here, we utilized Ti
L
-edge resonant inelastic x-ray scattering to study the orbital excitations in superconducting (SC) and insulating
MgTi
2
O
4
films. We find that the spectral weight of orbital excitations is enhanced and the energy of
t
2
g
intraband excitation is softened in the SC film compared to the insulating one, suggesting higher electron doping and a suppressed orbital order gap in the SC sample. These observations were further supported by our multiplet calculations using the minimal two-site model. Our results provide spectroscopic evidence for the competition between orbital order and superconductivity in
MgTi
2
O
4
and shed light on searching for novel superconductors in spinel oxides.
|
Mar 2023
|
|
I10-Beamline for Advanced Dichroism
|
Xiaodong
Xie
,
Kejing
Ran
,
Yizhou
Liu
,
Raymond
Fan
,
Wancong
Tan
,
Haonan
Jin
,
Manuel
Valvidares
,
Nicolas
Jaouen
,
Haifeng
Du
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
,
Shilei
Zhang
Diamond Proposal Number(s):
[20437, 26148, 22629]
Abstract: We identify a three-dimensional skyrmion side-face state in chiral magnets that consists of a thin layer of modulated surface spirals and an array of phase-locked skyrmion screws. Such chiral spin structures lead to a characteristic X-shaped magnetic diffraction pattern in resonant elastic x-ray scattering, reminiscent of Photo 51 of the DNA double-helix diffraction. By measuring both thin plates and bulk
Cu
2
OSeO
3
crystals in the field-in-plane geometry, we unambiguously identify the modulated skyrmion strings by retrieving their chirality and helix angle. The breaking of the translational symmetry along the side faces suppresses the bulk-favored conical state, providing a stabilization mechanism for the skyrmion lattice phase that has been overlooked so far.
|
Feb 2023
|
|
I15-Extreme Conditions
I19-Small Molecule Single Crystal Diffraction
|
David M.
Jarvis
,
Matthew J.
Coak
,
Hayrullo
Hamidov
,
Charles R. S.
Haines
,
Giulio I.
Lampronti
,
Cheng
Liu
,
Shiyu
Deng
,
Dominik
Daisenberger
,
David R.
Allan
,
Mark R.
Warren
,
Andrew R.
Wildes
,
Siddharth S.
Saxena
Diamond Proposal Number(s):
[15949, 23524]
Abstract: FePS
3
is a layered magnetic van der Waals compound that undergoes a Mott insulator-metal transition under applied pressure. The transition has an associated change in the crystal symmetry and magnetic structure. Understanding the underlying physics of these transitions requires a detailed understanding of the crystal structure as a function of pressure. Two conflicting models have previously been proposed for the evolution of the structure with pressure. To settle the disagreement, we present a study of the pressure-dependent crystal structures using both single-crystal and powder x-ray diffraction measurements. We show unambiguously that the highest-pressure transition involves a collapse of the interplanar spacing, along with an increase in symmetry from a monoclinic to a trigonal space group, to the exclusion of other models. Our collected results are crucial for understanding high-pressure behavior in these materials and demonstrate a clear and complete methodology for exploring complex two-dimensional material structures under pressure.
|
Feb 2023
|
|
I15-1-X-ray Pair Distribution Function (XPDF)
I15-Extreme Conditions
|
Ge
Wang
,
Tengfei
Hu
,
Wenxuan
Zhu
,
Zhilun
Lu
,
Annette
Kleppe
,
Maria
Diaz Lopez
,
Antonio
Feteira
,
Derek C.
Sinclair
,
Zhengqian
Fu
,
Houbing
Huang
,
Dawei
Wang
,
Ian M.
Reaney
Diamond Proposal Number(s):
[21714, 27500]
Abstract: For the first time, the origin of large electrostrain in pseudocubic
BiFeO
3
-based ceramics is verified with direct structural evidence backed by appropriate simulations. We employ advanced structural and microstructural characterizations of
BiFeO
3
-based ceramics that exhibit large electrostrain (
>
0.4
%
) to reveal the existence of multiple, nanoscale local symmetries, dominantly tetragonal or orthorhombic, which have a common, averaged direction of polarization over larger, meso- or microscale regions. Phase-field simulations confirm the existence of local nanoscale symmetries, thereby providing a new vision for designing high-performance lead-free ceramics for high-strain actuators.
|
Feb 2023
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[14135]
Abstract: The size of the orbital moment in
Fe
3
O
4
has been the subject of a long-standing and contentious debate. In this paper, we make use of ferromagnetic resonance (FMR) spectroscopy and x-ray magnetic circular dichroism (XMCD) to provide complementary determinations of the size of the orbital moment in “bulklike” epitaxial
Fe
3
O
4
films grown on yttria-stabilized zirconia (111) substrates. Annealing the 100 nm as-grown films to
1100
∘
C
in a reducing atmosphere improves the stoichiometry and microstructure of the films, allowing for bulklike properties to be recovered as evidenced by x-ray diffraction and vibrating sample magnetometry. In addition, in-plane angular FMR spectra exhibit a crossover from a fourfold symmetry to the expected sixfold symmetry of the (111) surface, together with an anomalous peak in the FMR linewidth at
∼
10
GHz; this is indicative of low Gilbert damping in combination with two-magnon scattering. For the bulklike annealed sample, a spectroscopic splitting factor
g
≈
2.18
is obtained using both FMR and XMCD techniques, providing evidence for the presence of a finite orbital moment in
Fe
3
O
4
.
|
Feb 2023
|
|
