I06-Nanoscience
|
Filip
Krizek
,
Sonka
Reimers
,
Zdeněk
Kašpar
,
Alberto
Marmodoro
,
Jan
Michalička
,
Ondřej
Man
,
Alexander
Edström
,
Oliver J.
Amin
,
Kevin W.
Edmonds
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Jan
Zubáč
,
Domink
Kriegner
,
Dina
Carbone
,
Jakub
Železný
,
Karel
Výborný
,
Kamil
Olejník
,
Vít
Novák
,
Jan
Rusz
,
Juan-Carlos
Idrobo
,
Peter
Wadley
,
Tomas
Jungwirth
Diamond Proposal Number(s):
[22437]
Open Access
Abstract: The interest in understanding scaling limits of magnetic textures such as domain walls spans the entire field of magnetism from its physical fundamentals to applications in information technologies. Here, we explore antiferromagnetic CuMnAs in which imaging by x-ray photoemission reveals the presence of magnetic textures down to nanoscale, reaching the detection limit of this established microscopy in antiferromagnets. We achieve atomic resolution by using differential phase-contrast imaging within aberration-corrected scanning transmission electron microscopy. We identify abrupt domain walls in the antiferromagnetic film corresponding to the Néel order reversal between two neighboring atomic planes. Our work stimulates research of magnetic textures at the ultimate atomic scale and sheds light on electrical and ultrafast optical antiferromagnetic devices with magnetic field–insensitive neuromorphic functionalities.
|
Apr 2022
|
|
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
|
|
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
|
|
I06-Nanoscience
|
Sonka
Reimers
,
Dominik
Kriegner
,
Olena
Gomonay
,
Dina
Carbone
,
Filip
Krizek
,
Vit
Novák
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Alexander
Bjorling
,
Oliver J.
Amin
,
Luke X.
Barton
,
Stuart F.
Poole
,
Khalid A.
Omari
,
Jan
Michalička
,
Ondřej
Man
,
Jairo
Sinova
,
Tomáš
Jungwirth
,
Peter
Wadley
,
Sarnjeet S.
Dhesi
,
Kevin W.
Edmonds
Diamond Proposal Number(s):
[22437, 2714]
Open Access
Abstract: Efficient manipulation of antiferromagnetic (AF) domains and domain walls has opened up new avenues of research towards ultrafast, high-density spintronic devices. AF domain structures are known to be sensitive to magnetoelastic effects, but the microscopic interplay of crystalline defects, strain and magnetic ordering remains largely unknown. Here, we reveal, using photoemission electron microscopy combined with scanning X-ray diffraction imaging and micromagnetic simulations, that the AF domain structure in CuMnAs thin films is dominated by nanoscale structural twin defects. We demonstrate that microtwin defects, which develop across the entire thickness of the film and terminate on the surface as characteristic lines, determine the location and orientation of 180∘ and 90∘ domain walls. The results emphasize the crucial role of nanoscale crystalline defects in determining the AF domains and domain walls, and provide a route to optimizing device performance.
|
Feb 2022
|
|
I06-Nanoscience
|
S.
Kurdi
,
Y.
Sakuraba
,
K.
Masuda
,
H.
Tajiri
,
B.
Nair
,
G. F.
Nataf
,
M. E.
Vickers
,
G.
Reiss
,
M
Meinert
,
S. S.
Dhesi
,
Massimo
Ghidini
,
Z H
Barber
Diamond Proposal Number(s):
[18932]
Open Access
Abstract: In this work, we investigate the effect of anti-site disorder on the half-metallic properties of a Mn2FeAl Heusler alloy thin film. The film was grown on TiN-buffered MgO 001 substrates via magnetron sputtering. A detailed structural characterization using X-ray diffraction (XRD) and anomalous XRD showed that the film crystallizes in the partially disordered L21B structure with 33% disorder between the Mn(B) and Al(D) sites. We measure a positive anisotropic magnetoresistance in the film, which is an indication of non-half metallic behaviour. Our X-ray magnetic circular dichroism sum rules analysis shows that Mn carries the magnetic moment in the film, as predicted, with a positive Fe moment. Experimentally determined moments correspond most closely with those found by density functional calculated ones for the L21B structure with Mn(B) and Al(D) site disorder, matching the experimental structural analysis. We thus attribute the deviation from half-metallic behaviour to the formation of the L21B structure, which we support by density functional theory calculations. To realize a half-metallic Mn2FeAl film it is important that the inverse Heusler XA structure is stabilized with minimal anti-site atomic disorder.
|
Jan 2022
|
|
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
|
Diamond Proposal Number(s):
[24373]
Open Access
Abstract: The remanent domain structures of composite element magnetic barcodes have been imaged using photo-emission electron microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM) and analysed with reference to the results of micromagnetic simulations. The magnetisation configuration at the end of wide strips is found to be perpendicular to the majority magnetisation direction. This transitions to an incomplete rotation for nominal strip widths below 300 nm and is found to affect the mechanics of magnetisation reversal for nominal strip widths below 200 nm, owing to a difference in magnetisation orientation when an external magnetic field is applied that is just smaller than the magnetic coercivity of the structures and a corresponding change in reversal dynamics. This change in domain structure as strip width decreases is consistent with both the influence of shape anisotropy and with measurements of magnetic hysteresis. The magnetisation reversal characteristics of composite element structures are found to be dependent on the relative magnetisation configurations of neighbouring strips, which in turn are found to vary stochastically upon the application and removal of a magnetic field along the easy axis of the structure. It is found that the application of a canted field is necessary to ensure sharp, consistent magnetisation reversal of bits when writing a binary code. These results confirm that either improved lithography of narrower strips or non-rectangular elements would be necessary to further increase the number of individually programmable bits in a barcode.
|
Sep 2021
|
|
I06-Nanoscience
|
Abstract: Antiferromagnets are of potential use in spintronic devices due to their ultrafast dynamics, insensitivity to external magnetic fields and absence of magnetic stray fields. Researchers have observed large, transient changes in the electrical resistance in some antiferromagnetic thin film devices after applying electrical or optical pulses. Although the origin of these effects was unknown, it is now understood that they are related to the magnetic order.
Researchers from the Czech Academy of Sciences and Charles University in Prague, the University of Nottingham, ETH Zurich, the University of Regensburg in Germany and Diamond Light Source investigated the micro-scale antiferromagnetic order in CuMnAs films before and after applying current pulses. They aimed to relate changes in the electrical resistance to changes in the magnetic microstructure. Using the X-PEEM End station on Diamond’s Nanoscience beamline (I06) enabled them to take images of the antiferromagnetic structures in microscale device structures. Electrical contacts on the sample allowed them to probe the magnetic state before and after applying current pulses.
The results show that a fragmentation of micrometre-scale antiferromagnetic domains accompanies the changes in the electrical resistance. The resulting textured structure has lengthscales comparable to, or even smaller than, the 30 nm spatial resolution of the X-PEEM End station. Their results establish a clear relationship of the electrical resistance changes with changes in the micromagnetic structure. The electrical switching and relaxation behaviour they observed can potentially mimic the characteristics of neural network components, offering the potential to develop efficient and high-speed neuromorphic computing applications that mimic neuro-biological architectures present in the human nervous system.
|
Jul 2021
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[1658]
Abstract: The physical properties of nanostructured thin films and multilayers depend crucially on their interfaces. The precise knowledge of the interface morphology at the atomic scale is mandatory to reliably understand their macroscopic response. These details become even more critical when dealing with magnetic thin films as the finest structural and/or compositional local changes may affect the magnetic coupling and alter the macroscopic response. Soft X-ray Resonant Magnetic Reflectivity (SXRMR) is a suitable technique in this field, combining specific aspects of x-ray absorption and x-ray scattering processes to simultaneously obtain complementary structural and magnetic information on thin films and multilayers. Here, we present a case study on a MgO/Co/MgO trilayer in which the combined use of SXRMR, x-ray absorption spectroscopy and x-ray magnetic circular dichroism has allowed to reconstruct the elemental and magnetic depth profiles with sub-nanometric resolution and to distinguish fine compositional defects at the Co-on-MgO and MgO-on-Co interfaces.
|
May 2021
|
|
I06-Nanoscience
|
C.
Schmitt
,
L.
Baldrati
,
L.
Sanchez-Tejerina
,
F.
Schreiber
,
A.
Ross
,
M.
Filianina
,
S.
Ding
,
F.
Fuhrmann
,
R.
Ramos
,
F.
Maccherozzi
,
D.
Backes
,
M.-A.
Mawass
,
F.
Kronast
,
S.
Valencia
,
E.
Saitoh
,
G.
Finocchio
,
M.
Klaui
Diamond Proposal Number(s):
[22448]
Abstract: Understanding the electrical manipulation of the antiferromagnetic order is a crucial aspect to enable the design of antiferromagnetic devices working at THz frequencies. Focusing on collinear insulating antiferromagnetic
Ni
O
/
Pt
thin films as a materials platform, we identify the crystallographic orientation of the domains that can be switched by currents and quantify the Néel-vector direction changes. We demonstrate electrical switching between different T domains by current pulses, finding that the Néel-vector orientation in these domains is along [
±
5
±
5
19], different compared to the bulk
⟨
112
⟩
directions. The final state of the in-plane component of the Néel vector
n
IP
after switching by current pulses
j
along the
[
1
±
1
0
]
directions is
n
IP
∥
j
. By comparing the observed Néel-vector orientation and the strain in the thin films, assuming that this variation arises solely from magnetoelastic effects, we quantify the order of magnitude of the magnetoelastic coupling coefficient as
b
0
+
2
b
1
=
3
×
10
7
J
/
m
3
. This information is key for the understanding of current-induced switching in antiferromagnets and for the design and use of such devices as active elements in spintronic devices.
|
Mar 2021
|
|