I09-Surface and Interface Structural Analysis
|
Gian Marco
Pierantozzi
,
Alessandro
De Vita
,
Chiara
Bigi
,
Xin
Gui
,
Hung-Ju
Tien
,
Debashis
Mondal
,
Federico
Mazzola
,
Jun
Fujii
,
Ivana
Vobornik
,
Giovanni
Vinai
,
Alessandro
Sala
,
Cristina
Africh
,
Tien-Lin
Lee
,
Giorgio
Rossi
,
Tay-Rong
Chang
,
Weiwei
Xie
,
Robert J.
Cava
,
Giancarlo
Panaccione
Diamond Proposal Number(s):
[24968]
Open Access
Abstract: We unravel the interplay of topological properties and the layered (anti)ferromagnetic ordering in EuSn2P2, using spin and chemical selective electron and X-ray spectroscopies supported by first-principle calculations. We reveal the presence of in-plane long-range ferromagnetic order triggering topological invariants and resulting in the multiple protection of topological Dirac states. We provide clear evidence that layer-dependent spin-momentum locking coexists with ferromagnetism in this material, a cohabitation that promotes EuSn2P2 as a prime candidate axion insulator for topological antiferromagnetic spintronics applications.
|
Jan 2022
|
|
I09-Surface and Interface Structural Analysis
|
F.
Offi
,
K.
Yamauchi
,
S.
Picozzi
,
V.
Lollobrigida
,
A.
Verna
,
C.
Schlueter
,
T.-L.
Lee
,
A.
Regoutz
,
D. J.
Payne
,
A.
Petrov
,
G.
Vinai
,
G. M.
Pierantozzi
,
T.
Pincelli
,
G.
Panaccione
,
F.
Borgatti
Diamond Proposal Number(s):
[11322]
Abstract: Hybridization of electronic states and orbital symmetry in transition metal oxides are generally considered key ingredients in the description of both their electronic and magnetic properties. In the prototypical case of
La
0.65
Sr
0.35
MnO
3
(LSMO), a landmark system for spintronics applications, a description based solely on Mn
3
d
and O
2
p
electronic states is reductive. We thus analyzed elemental and orbital distributions in the LSMO valence band through a comparison between density functional theory calculations and experimental photoelectron spectra in a photon energy range from soft to hard x rays. We reveal a number of hidden contributions, arising specifically from La
5
p
, Mn
4
s
, and O
2
s
orbitals, considered negligible in previous analyses; our results demonstrate that all these contributions are significant for a correct description of the valence band of LSMO and of transition metal oxides in general.
|
Oct 2021
|
|
I06-Nanoscience
|
Federico
Motti
,
G.
Vinai
,
Valentina
Bonanni
,
Vincent
Polewczyk
,
Paola
Mantegazza
,
Thomas
Forrest
,
Francesco
Maccherozzi
,
Stefania
Benedetti
,
Christian
Rinaldi
,
Matteo
Cantoni
,
Damiano
Cassese
,
Stefano
Prato
,
Sarnjeet S.
Dhesi
,
Giorgio
Rossi
,
Giancarlo
Panaccione
,
Piero
Torelli
Diamond Proposal Number(s):
[18810]
Abstract: A ferromagnetic (FM) thin film deposited on a substrate of
Pb
(
Mg
1
/
3
Nb
2
/
3
)
O
3
−
PbTiO
3
(PMN-PT) is an appealing heterostructure for the electrical control of magnetism, which would enable nonvolatile memories with ultralow-power consumption. Reversible and electrically controlled morphological changes at the surface of PMN-PT suggest that the magnetoelectric effects are more complex than the commonly used “strain-mediated” description. Here we show that changes in substrate morphology intervene in magnetoelectric coupling as a key parameter interplaying with strain. Magnetic-sensitive microscopy techniques are used to study magnetoelectric coupling in Fe/PMN-PT at different length scales, and compare different substrate cuts. The observed rotation of the magnetic anisotropy is connected to the changes in morphology, and mapped in the crack pattern at the mesoscopic scale. Ferroelectric polarization switching induces a magnetic field-free rotation of the magnetic domains at micrometer scale, with a wide distribution of rotation angles. Our results show that the relationship between the rotation of the magnetic easy axis and the rotation of the in-plane component of the electric polarization is not straightforward, as well as the relationship between ferroelectric domains and crack pattern. The understanding and control of this phenomenon is crucial to develop functional devices based on FM/PMN-PT heterostructures.
|
Nov 2020
|
|
I09-Surface and Interface Structural Analysis
|
Chiara
Bigi
,
Zhenkun
Tang
,
Gian Marco
Pierantozzi
,
Pasquale
Orgiani
,
Pranab Kumar
Das
,
Jun
Fujii
,
Ivana
Vobornik
,
Tommaso
Pincelli
,
Alessandro
Troglia
,
Tien-Lin
Lee
,
Regina
Ciancio
,
Goran
Drazic
,
Alberto
Verdini
,
Anna
Regoutz
,
Phil D. C.
King
,
Deepnarayan
Biswas
,
Giorgio
Rossi
,
Giancarlo
Panaccione
,
Annabella
Selloni
Diamond Proposal Number(s):
[16041]
Abstract: Two-dimensional (2D) metallic states induced by oxygen vacancies (
V
O
s
) at oxide surfaces and interfaces provide opportunities for the development of advanced applications, but the ability to control the behavior of these states is still limited. We used angle resolved photoelectron spectroscopy combined with density-functional theory (DFT) to study the reactivity of
V
O
-induced states at the (001) surface of anatase
TiO
2
, where both 2D metallic and deeper lying in-gap states (IGs) are observed. The 2D and IG states exhibit remarkably different evolutions when the surface is exposed to molecular
O
2
: while IGs are almost completely quenched, the metallic states are only weakly affected. DFT calculations indeed show that the IGs originate from surface
V
O
s
and remain localized at the surface, where they can promptly react with
O
2
. In contrast, the metallic states originate from subsurface vacancies whose migration to the surface for recombination with
O
2
is kinetically hindered on anatase
TiO
2
(001), thus making them much less sensitive to oxygen dosing.
|
Feb 2020
|
|
I09-Surface and Interface Structural Analysis
|
G.
Vinai
,
C.
Bigi
,
A.
Rajan
,
M. D.
Watson
,
T.-L.
Lee
,
F.
Mazzola
,
S.
Modesti
,
S.
Barua
,
M.
Ciomaga Hatnean
,
G.
Balakrishnan
,
P. D. C.
King
,
P.
Torelli
,
G.
Rossi
,
G.
Panaccione
Diamond Proposal Number(s):
[21429]
Abstract: Among transition-metal dichalcogenides, mono and few-layers thick
VSe
2
has gained much recent attention following claims of intrinsic room-temperature ferromagnetism in this system, which have nonetheless proved controversial. Here, we address the magnetic and chemical properties of
Fe
/
VSe
2
heterostructure by combining element sensitive x-ray absorption spectroscopy and photoemission spectroscopy. Our x-ray magnetic circular dichroism results confirm recent findings that both native mono/few-layer and bulk
VSe
2
do not show intrinsic ferromagnetic ordering. Nonetheless, we find that ferromagnetism can be induced, even at room temperature, after coupling with a Fe thin film layer, with antiparallel alignment of the moment on the V with respect to Fe. We further consider the chemical reactivity at the
Fe
/
VSe
2
interface and its relation with interfacial magnetic coupling.
|
Jan 2020
|
|
I09-Surface and Interface Structural Analysis
|
Anna
Regoutz
,
Alex M.
Ganose
,
Lars
Blumenthal
,
Christoph
Schlueter
,
Tien-Lin
Lee
,
Gregor
Kieslich
,
Anthony K.
Cheetham
,
Gwilherm
Kerherve
,
Ying-Sheng
Huang
,
Ruei-San
Chen
,
Giovanni
Vinai
,
Tommaso
Pincelli
,
Giancarlo
Panaccione
,
Kelvin H. L.
Zhang
,
Russell G.
Egdell
,
Johannes
Lischner
,
David O.
Scanlon
,
David J.
Payne
Diamond Proposal Number(s):
[12673]
Abstract: Theory and experiment are combined to gain an understanding of the electronic properties of OsO2, a poorly studied metallic oxide that crystallizes in the rutile structure. Hard and soft valence-band x-ray photoemission spectra of OsO2 single crystals are in broad agreement with the results of density-functional-theory calculations, aside from a feature shifted to high binding energy of the conduction band. The energy shift corresponds to the conduction electron plasmon energy measured by reflection electron energy loss spectroscopy. The plasmon satellite is reproduced by many-body perturbation theory.
|
Feb 2019
|
|
|
|
Pranab Kumar
Das
,
Jagoda
Sławińska
,
Ivana
Vobornik
,
Jun
Fujii
,
Anna
Regoutz
,
Juhan M.
Kahk
,
David O.
Scanlon
,
Benjamin J.
Morgan
,
Cormac
Mcguinness
,
Evgeny
Plekhanov
,
Domenico
Di Sante
,
Ying-Sheng
Huang
,
Ruei-San
Chen
,
Giorgio
Rossi
,
Silvia
Picozzi
,
William R.
Branford
,
Giancarlo
Panaccione
,
David J.
Payne
Abstract: The delicate interplay of electronic charge, spin, and orbital degrees of freedom is in the heart of many novel phenomena across the transition metal oxide family. Here, by combining high-resolution angle-resolved photoemission spectroscopy and first principles calculations (with and without spin-orbit coupling), the electronic structure of the rutile binary iridate, IrO2, is investigated. The detailed study of electronic bands measured on a high-quality single crystalline sample and use of a wide range of photon energy provide a huge improvement over the previous studies. The excellent agreement between theory and experimental results shows that the single-particle DFT description of IrO2 band structure is adequate, without the need of invoking any treatment of correlation effects. Although many observed features point to a 3D nature of the electronic structure, clear surface effects are revealed. The discussion of the orbital character of the relevant bands crossing the Fermi level sheds light on spin-orbit-coupling-driven phenomena in this material, unveiling a spin-orbit-induced avoided crossing, a property likely to play a key role in its large spin Hall effect.
|
Jun 2018
|
|
I09-Surface and Interface Structural Analysis
|
T.
Pincelli
,
V.
Lollobrigida
,
F.
Borgatti
,
A.
Regoutz
,
B.
Gobaut
,
C.
Schlueter
,
T.-L.
Lee
,
D. J.
Payne
,
M.
Oura
,
K.
Tamasaku
,
A. Y.
Petrov
,
P.
Graziosi
,
F. Miletto
Granozio
,
M.
Cavallini
,
G.
Vinai
,
R.
Ciprian
,
C.
Back
,
G.
Rossi
,
M.
Taguchi
,
H.
Daimon
,
G.
Van Der Laan
,
G.
Panaccione
Diamond Proposal Number(s):
[11322]
Abstract: In the rapidly growing field of spintronics, simultaneous control of electronic and magneticproperties is essential, and the perspective of building novel phases is directly linked to the control of tuning parameters, for example, thickness and doping. Looking at the relevanteffects in interface-driven spintronics, the reduced symmetry at a surface and interface corresponds to a severe modification of the overlap of electron orbitals, that is, to a change of electron hybridization. Here we report a chemically and magnetically sensitive depth-dependent analysis of two paradigmatic systems, namely La1xSrxMnO3 and (Ga,Mn)As. Supported by cluster calculations, we find a crossover between surface and bulk in the electron hybridization/correlation and we identify a spectroscopic fingerprint of bulk metallic character and ferromagnetism versus depth. The critical thickness and the gradient of hybridization are measured, setting an intrinsic limit of 3 and 10 unit cells from the surface,respectively, for (Ga,Mn)As and La1xSrxMnO3, for fully restoring bulk properties.
|
Jul 2017
|
|
I09-Surface and Interface Structural Analysis
|
Anna
Regoutz
,
Isha
Gupta
,
Alexantrou
Serb
,
Ali
Khiat
,
Francesco
Borgatti
,
Tien-Lin
Lee
,
Christoph
Schlueter
,
Piero
Torelli
,
Benoit
Gobaut
,
Mark
Light
,
Daniela
Carta
,
Stuart
Pearce
,
Giancarlo
Panaccione
,
Themistoklis
Prodromakis
Diamond Proposal Number(s):
[0240]
Open Access
Abstract: TiO2 is commonly used as the active switching layer in resistive random access memory. The electrical characteristics of these devices are directly related to the fundamental conditions inside the TiO2 layer and at the interfaces between it and the surrounding electrodes. However, it is complex to disentangle the effects of film “bulk” properties and interface phenomena. The present work uses hard X-ray photoemission spectroscopy (HAXPES) at different excitation energies to distinguish between these regimes. Changes are found to affect the entire thin film, but the most dramatic effects are confined to an interface. These changes are connected to oxygen ions moving and redistributing within the film. Based on the HAXPES results, post-deposition annealing of the TiO2 thin film was investigated as an optimisation pathway in order to reach an ideal compromise between device resistivity and lifetime. The structural and chemical changes upon annealing are investigated using X-ray absorption spectroscopy and are further supported by a range of bulk and surface sensitive characterisation methods. In summary, it is shown that the management of oxygen content and interface quality is intrinsically important to device behavior and that careful annealing procedures are a powerful device optimisation technique.
|
Jan 2016
|
|
I10-Beamline for Advanced Dichroism
|
Diamond Proposal Number(s):
[8571]
Abstract: Diluted magnetic semiconductors, and particularly (Ga,Mn)As, have been the subject of considerable debate regarding the nature of the interplay between their electronic and magnetic properties. Here, we review the recent insights and advances offered by synchrotron-based x-ray spectroscopies studies of these materials, with a particular focus on x-ray magnetic circular dichroism and hard x-ray photoelectron spectroscopy. Such measurements offer a combined probe of the element-specific magnetic order and the local densities of states, revealing detailed information about the hybridization of diluted magnetic ions and the host crystal.
|
Apr 2015
|
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