I09-Surface and Interface Structural Analysis
|
Adam J.
Jackson
,
Benjamin J.
Parrett
,
Joe
Willis
,
Alex M.
Ganose
,
W. W. Winnie
Leung
,
Yuhan
Liu
,
Benjamin A. D.
Williamson
,
Timur K.
Kim
,
Moritz
Hoesch
,
Larissa S. I.
Veiga
,
Raman
Kalra
,
Jens
Neu
,
Charles A.
Schmuttenmaer
,
Tien-Lin
Lee
,
Anna
Regoutz
,
Tung-Chun
Lee
,
Tim D.
Veal
,
Robert G.
Palgrave
,
Robin
Perry
,
David O.
Scanlon
Diamond Proposal Number(s):
[24449]
Open Access
Abstract: Transparent conducting oxides have become ubiquitous in modern optoelectronics. However, the number of oxides that are transparent to visible light and have the metallic-like conductivity necessary for applications is limited to a handful of systems that have been known for the past 40 years. In this work, we use hybrid density functional theory and defect chemistry analysis to demonstrate that tri-rutile zinc antimonate, ZnSb2O6, is an ideal transparent conducting oxide and to identify gallium as the optimal dopant to yield high conductivity and transparency. To validate our computational predictions, we have synthesized both powder samples and single crystals of Ga-doped ZnSb2O6 which conclusively show behavior consistent with a degenerate transparent conducting oxide. This study demonstrates the possibility of a family of Sb(V)-containing oxides for transparent conducting oxide and power electronics applications.
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Oct 2022
|
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I06-Nanoscience
|
S.
Reimers
,
Y.
Lytvynenko
,
Y. R.
Niu
,
E.
Golias
,
B.
Sarpi
,
L. S. I.
Veiga
,
T.
Denneulin
,
A.
Kovács
,
R. E.
Dunin-Borkowski
,
J.
Bläßer
,
M.
Klaui
,
M.
Jourdan
Diamond Proposal Number(s):
[30141]
Open Access
Abstract: Current pulse driven Néel vector rotation in metallic antiferromagnets is one of the most promising concepts in antiferromagnetic spintronics. We show microscopically that the Néel vector of epitaxial thin films of the prototypical compound Mn2Au can be reoriented reversibly in the complete area of cross shaped device structures using single current pulses. The resulting domain pattern with aligned staggered magnetization is long term stable enabling memory applications. We achieve this switching with low heating of ≈20 K, which is promising regarding fast and efficient devices without the need for thermal activation. Current polarity dependent reversible domain wall motion demonstrates a Néel spin-orbit torque acting on the domain walls.
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Apr 2023
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
J. G.
Vale
,
C. D.
Dashwood
,
E.
Paris
,
L. S. I.
Veiga
,
Mirian
Garcia-Fernandez
,
A.
Nag
,
A.
Walters
,
K.
Zhou
,
I.-M.
Pietsch
,
Anton
Jesche
,
P.
Gegenwart
,
R.
Coldea
,
T.
Schmitt
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[20569]
Abstract: The excitations in honeycomb
α
−
Li
2
IrO
3
have been investigated with high-resolution resonant inelastic x-ray scattering (RIXS) at the O
K
edge. The low-energy response is dominated by a fully resolved ladder of excitations, which we interpret as being due to multiphonon processes in the presence of strong electron-phonon coupling (EPC). At higher energies, the orbital excitations are shown to be dressed by phonons. The high quality of the data permits a quantitative test of the analytical model for the RIXS cross section, which has been proposed to describe EPC in transition-metal oxides (TMOs). We find that the magnitude of the EPC is comparable to that found for a range of
3
d
TMOs. This indicates that EPC may be of equal importance in determining the phenomenology displayed by corresponding
5
d
-based systems.
|
Dec 2019
|
|
I06-Nanoscience
|
Dong
Li
,
Bonan
Zhu
,
Dirk
Backes
,
Larissa S. I.
Veiga
,
Tien-Lin
Lee
,
Hongguang
Wang
,
Qian
He
,
Pinku
Roy
,
Jiaye
Zhang
,
Jueli
Shi
,
Aiping
Chen
,
Peter A.
Van Aken
,
Quanxi
Jia
,
Sarnjeet S.
Dhesi
,
David O.
Scanlon
,
Kelvin H. L.
Zhang
,
Weiwei
Li
Diamond Proposal Number(s):
[25425, 26901, 29616]
Abstract: Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of
La
0.9
Ba
0.1
MnO
3
thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn
e
g
orbitals can be switched from the
d
3
z
2
−
r
2
orbital to the
d
x
2
−
y
2
orbital by varying the strain from compressive to tensile. The change of orbital occupancy associated with Mn
3
d
-O
2
p
hybridization leads to dramatic modulation of the magnetic and electronic properties of strained
La
0.9
Ba
0.1
MnO
3
thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the
La
0.9
Ba
0.1
MnO
3
system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.
|
Apr 2022
|
|
I16-Materials and Magnetism
|
D.
Pincini
,
S.
Boseggia
,
R.
Perry
,
Ma. J.
Gutmann
,
S.
Ricco
,
L. S. I.
Veiga
,
C. D.
Dashwood
,
S. P.
Collins
,
G.
Nisbet
,
A.
Bombardi
,
D. G.
Porter
,
F.
Baumberger
,
A. T.
Boothroyd
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[15323, 15952, 15867, 18934]
Abstract: The chemical and magnetic structures of the series of compounds Ca2−xLaxRuO4 [x=0, 0.05(1), 0.07(1), 0.12(1)] have been investigated using neutron diffraction and resonant elastic x-ray scattering. Upon La doping, the low-temperature S-Pbca space group of the parent compound is retained in all insulating samples [x≤0.07(1)], but with significant changes to the atomic positions within the unit cell. These changes can be characterized in terms of the local
RuO6 octahedral coordination: with increasing doping, the structure, crudely speaking, evolves from an orthorhombic unit cell with compressed octahedra to a quasitetragonal unit cell with elongated ones. The magnetic structure on the other hand, is found to be robust, with the basic k=(0,0,0), b-axis antiferromagnetic order of the parent compound preserved below the critical La doping concentration of x≈0.11. The only effects of La doping on the magnetic structure are to suppress the A-centred mode, favoring the B mode instead, and to reduce the Néel temperature somewhat. Our results are discussed with reference to previous experimental reports on the effects of cation substitution on the d4 Mott insulator Ca2RuO4, as well as with regard to theoretical studies on the evolution of its electronic and magnetic structure. In particular, our results rule out the presence of a proposed ferromagnetic phase, and suggest that the structural effects associated with La substitution play an important role in the physics of the system.
|
Jul 2018
|
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I21-Resonant Inelastic X-ray Scattering (RIXS)
|
C. D.
Dashwood
,
A.
Geondzhian
,
J. G.
Vale
,
A. C.
Pakpour-Tabrizi
,
C. A.
Howard
,
Q.
Faure
,
L. S. I.
Veiga
,
D.
Meyers
,
G. S.
Chiuzbaian
,
A.
Nicolaou
,
N.
Jaouen
,
R. B.
Jackman
,
A.
Nag
,
M.
Garcia-Fernandez
,
Ke-Jin
Zhou
,
A. C.
Walters
,
K.
Gilmore
,
D. F.
Mcmorrow
,
M. P. M.
Dean
Diamond Proposal Number(s):
[22695]
Open Access
Abstract: Interactions between electrons and lattice vibrations are responsible for a wide range of material properties and applications. Recently, there has been considerable interest in the development of resonant inelastic x-ray scattering (RIXS) as a tool for measuring electron-phonon (
e
-ph) interactions. Here, we demonstrate the ability of RIXS to probe the interaction between phonons and specific electronic states both near to, and away from, the Fermi level. We perform carbon
K
-edge RIXS measurements on graphite, tuning the incident x-ray energy to separately probe the interactions of the
π
∗
and
σ
∗
electronic states. Our high-resolution data reveal detailed structure in the multiphonon RIXS features that directly encodes the momentum dependence of the
e
-ph interaction strength. We develop a Green’s-function method to model this structure, which naturally accounts for the phonon and interaction-strength dispersions, as well as the mixing of phonon momenta in the intermediate state. This model shows that the differences between the spectra can be fully explained by contrasting trends of the
e
-ph interaction through the Brillouin zone, being concentrated at the
Γ
and
K
points for the
π
∗
states while being significant at all momenta for the
σ
∗
states. Our results advance the interpretation of phonon excitations in RIXS and extend its applicability as a probe of
e
-ph interactions to a new range of out-of-equilibrium situations.
|
Dec 2021
|
|
I06-Nanoscience
|
S. P.
Bommanaboyena
,
D.
Backes
,
L. S. I.
Veiga
,
S. S.
Dhesi
,
Y. R.
Niu
,
B.
Sarpi
,
T.
Denneulin
,
A.
Kovács
,
T.
Mashoff
,
O.
Gomonay
,
J.
Sinova
,
K.
Everschor-Sitte
,
D.
Schönke
,
R. M.
Reeve
,
M.
Klaui
,
H.-J.
Elmers
,
M.
Jourdan
Diamond Proposal Number(s):
[29305]
Open Access
Abstract: In antiferromagnetic spintronics, the read-out of the staggered magnetization or Néel vector is the key obstacle to harnessing the ultra-fast dynamics and stability of antiferromagnets for novel devices. Here, we demonstrate strong exchange coupling of Mn2Au, a unique metallic antiferromagnet that exhibits Néel spin-orbit torques, with thin ferromagnetic Permalloy layers. This allows us to benefit from the well-established read-out methods of ferromagnets, while the essential advantages of antiferromagnetic spintronics are only slightly diminished. We show one-to-one imprinting of the antiferromagnetic on the ferromagnetic domain pattern. Conversely, alignment of the Permalloy magnetization reorients the Mn2Au Néel vector, an effect, which can be restricted to large magnetic fields by tuning the ferromagnetic layer thickness. To understand the origin of the strong coupling, we carry out high resolution electron microscopy imaging and we find that our growth yields an interface with a well-defined morphology that leads to the strong exchange coupling.
|
Nov 2021
|
|
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
|
|
I16-Materials and Magnetism
|
Diamond Proposal Number(s):
[14024]
Open Access
Abstract: We study the magnetic structure of the “stuffed” (Tb-rich) pyrochlore iridate Tb2+xIr2−xO7−y, using resonant elastic x-ray scattering (REXS). In order to disentangle contributions from Tb and Ir magnetic sublattices, experiments were performed at the Ir L3 and Tb M5 edges, which provide selective sensitivity to Ir 5d and Tb 4f magnetic moments, respectively. At the Ir L3 edge, we found the onset of long-range k = 0 magnetic order below TIr N ∼71K, consistent with the expected signal of all-in all-out (AIAO) magnetic order. Using a single-ion model to calculate REXS crosssections, we estimate an ordered magnetic moment of µIr 5d ≈ 0.34(3)µB at 5K. At the Tb M5 edge,long-range k = 0 magnetic order appeared below ∼ 40K, also consistent with an AIAO magnetic structure on the Tb site. Additional insight into the magnetism of the Tb sublattice is gleaned from measurements at the M5 edge in applied magnetic fields up to 6T, which is found to completely suppress the Tb AIAO magnetic order. In zero applied field, the observed gradual onset of the Tb sublattice magnetisation with temperature suggests that it is induced by the magnetic order on the Ir site. The persistence of AIAO magnetic order, despite the greatly reduced ordering temperature and moment size compared to stoichiometric Tb2Ir2O7, for which TIr N = 130K and µIr 5d = 0.56µB, indicates that stuffing could be a viable means of tuning the strength of electronic correlations, thereby potentially offering a new strategy to achieve topologically non-trivial band crossings in pyrochlore iridates.
|
May 2019
|
|
I16-Materials and Magnetism
|
C. D.
Dashwood
,
L. S. I.
Veiga
,
Q.
Faure
,
J. G.
Vale
,
D. G.
Porter
,
S. P.
Collins
,
P.
Manuel
,
D. D.
Khalyavin
,
F.
Orlandi
,
R. S.
Perry
,
R. D.
Johnson
,
D. F.
Mcmorrow
Diamond Proposal Number(s):
[23580]
Abstract: We show how complex modulated order can spontaneously emerge when magnetic interactions compete in a metal with polar lattice distortions. Combining neutron and resonant x-ray scattering with symmetry analysis, we reveal that the spin reorientation in
Ca
3
Ru
2
O
7
is mediated by a magnetic cycloid whose eccentricity evolves smoothly but rapidly with temperature. We find the cycloid to be highly sensitive to magnetic fields, which appear to continuously generate higher harmonic modulations. Our results provide a unified picture of the rich magnetic phases of this correlated, multiband polar metal.
|
Nov 2020
|
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