I06-Nanoscience
|
O. J.
Amin
,
S. F.
Poole
,
S.
Reimers
,
L. X.
Barton
,
A.
Dal Din
,
F.
Maccherozzi
,
S. S.
Dhesi
,
V.
Novák
,
F.
Krizek
,
J. S.
Chauhan
,
R. P.
Campion
,
A. W.
Rushforth
,
T.
Jungwirth
,
O. A.
Tretiakov
,
K. W.
Edmonds
,
P.
Wadley
Diamond Proposal Number(s):
[26255, 27845]
Open Access
Abstract: Topologically protected magnetic textures are promising candidates for information carriers in future memory devices, as they can be efficiently propelled at very high velocities using current-induced spin torques. These textures—nanoscale whirls in the magnetic order—include skyrmions, half-skyrmions (merons) and their antiparticles. Antiferromagnets have been shown to host versions of these textures that have high potential for terahertz dynamics, deflection-free motion and improved size scaling due to the absence of stray field. Here we show that topological spin textures, merons and antimerons, can be generated at room temperature and reversibly moved using electrical pulses in thin-film CuMnAs, a semimetallic antiferromagnet that is a testbed system for spintronic applications. The merons and antimerons are localized on 180° domain walls, and move in the direction of the current pulses. The electrical generation and manipulation of antiferromagnetic merons is a crucial step towards realizing the full potential of antiferromagnetic thin films as active components in high-density, high-speed magnetic memory devices.
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May 2023
|
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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.
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May 2023
|
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I06-Nanoscience
|
Allan S.
Johnson
,
Daniel
Perez-Salinas
,
Khalid M.
Siddiqui
,
Sungwon
Kim
,
Sungwook
Choi
,
Klara
Volckaert
,
Paulina E.
Majchrzak
,
Soeren
Ulstrup
,
Naman
Agarwal
,
Kent
Hallman
,
Richard F.
Haglund
,
Christian M.
Günther
,
Bastian
Pfau
,
Stefan
Eisebitt
,
Dirk
Backes
,
Francesco
Maccherozzi
,
Ann
Fitzpatrick
,
Sarnjeet S.
Dhesi
,
Pierluigi
Gargiani
,
Manuel
Valvidares
,
Nongnuch
Artrith
,
Frank
De Groot
,
Hyeongi
Choi
,
Dogeun
Jang
,
Abhishek
Katoch
,
Soonnam
Kwon
,
Sang Han
Park
,
Hyunjung
Kim
,
Simon E.
Wall
Diamond Proposal Number(s):
[22048]
Open Access
Abstract: Using light to control transient phases in quantum materials is an emerging route to engineer new properties and functionality, with both thermal and non-thermal phases observed out of equilibrium. Transient phases are expected to be heterogeneous, either through photo-generated domain growth or by generating topological defects, and this impacts the dynamics of the system. However, this nanoscale heterogeneity has not been directly observed. Here we use time- and spectrally resolved coherent X-ray imaging to track the prototypical light-induced insulator-to-metal phase transition in vanadium dioxide on the nanoscale with femtosecond time resolution. We show that the early-time dynamics are independent of the initial spatial heterogeneity and observe a 200 fs switch to the metallic phase. A heterogeneous response emerges only after hundreds of picoseconds. Through spectroscopic imaging, we reveal that the transient metallic phase is a highly orthorhombically strained rutile metallic phase, an interpretation that is in contrast to those based on spatially averaged probes. Our results demonstrate the critical importance of spatially and spectrally resolved measurements for understanding and interpreting the transient phases of quantum materials.
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Dec 2022
|
|
|
|
Ian
Vidamour
,
Matthew O. A.
Ellis
,
David
Griffin
,
Guru
Venkat
,
Charles
Swindells
,
Richard W. S.
Dawidek
,
Thomas J
Broomhall
,
Nina-Juliane
Steinke
,
Joshaniel
Cooper
,
Francesco
Maccherozzi
,
Sarnjeet
Dhesi
,
Susan
Stepney
,
Eleni
Vasilaki
,
Dan A.
Allwood
,
Tom James
Hayward
Open Access
Abstract: Devices based on arrays of interconnected magnetic nano-rings with emergent magnetization dynamics have recently been proposed for use in reservoir computing applications, but for them to be computationally useful it must be possible to optimise their dynamical responses. Here, we use a phenomenological model to demonstrate that such reservoirs can be optimised for classification tasks by tuning hyperparameters that control the scaling and input-rate of data into the system using rotating magnetic fields. We use task-independent metrics to assess the rings' computational capabilities at each set of these hyperparameters and show how these metrics correlate directly to performance in spoken and written digit recognition tasks. We then show that these metrics, and performance in tasks, can be further improved by expanding the reservoir's output to include multiple, concurrent measures of the ring arrays' magnetic states.
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Aug 2022
|
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I06-Nanoscience
|
Diamond Proposal Number(s):
[24409]
Open Access
Abstract: Improving both the extent of metallic Co nanoparticle (Co NP) formation and their stability is necessary to ensure good catalytic performance, particularly for Fischer–Tropsch synthesis (FTS). Here, we observe how the presence of surface oxygen vacancies (Ovac) on TiO2 can readily reduce individual Co3O4 NPs directly into CoO/Co0 in the freshly prepared sample by using a combination of X-ray photoemission electron microscopy (X-PEEM) coupled with soft X-ray absorption spectroscopy. The Ovac are particularly good at reducing the edge of the NPs as opposed to their center, leading to smaller particles being more reduced than larger ones. We then show how further reduction (and Ovac consumption) is achieved during heating in H2/syngas (H2 + CO) and reveal that Ovac also prevents total reoxidation of Co NPs in syngas, particularly the smallest (∼8 nm) particles, thus maintaining the presence of metallic Co, potentially improving catalyst performance.
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Jul 2022
|
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I06-Nanoscience
|
Andrea
Ronchi
,
Paolo
Franceschini
,
Andrea
De Poli
,
Pia
Homm
,
Ann
Fitzpatrick
,
Francesco
Maccherozzi
,
Gabriele
Ferrini
,
Francesco
Banfi
,
Sarnjeet S.
Dhesi
,
Mariela
Menghini
,
Michele
Fabrizio
,
Jean-Pierre
Locquet
,
Claudio
Giannetti
Diamond Proposal Number(s):
[18897, 21700]
Open Access
Abstract: Mott transitions in real materials are first order and almost always associated with lattice distortions, both features promoting the emergence of nanotextured phases. This nanoscale self-organization creates spatially inhomogeneous regions, which can host and protect transient non-thermal electronic and lattice states triggered by light excitation. Here, we combine time-resolved X-ray microscopy with a Landau-Ginzburg functional approach for calculating the strain and electronic real-space configurations. We investigate V2O3, the archetypal Mott insulator in which nanoscale self-organization already exists in the low-temperature monoclinic phase and strongly affects the transition towards the high-temperature corundum metallic phase. Our joint experimental-theoretical approach uncovers a remarkable out-of-equilibrium phenomenon: the photo-induced stabilisation of the long sought monoclinic metal phase, which is absent at equilibrium and in homogeneous materials, but emerges as a metastable state solely when light excitation is combined with the underlying nanotexture of the monoclinic lattice.
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Jun 2022
|
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I06-Nanoscience
|
Diamond Proposal Number(s):
[19060]
Open Access
Abstract: The authors describe and compare two complementary techniques that are habitually used to image ferromagnetic and ferroelectric materials with sub-micron spatial resolutions (typically 50 nm, at best 10 nm). The first technique is variable-temperature photoemission electron microscopy with magnetic/antiferromagnetic/polar contrast from circularly/linearly polarized incident X-rays (XPEEM). The second technique is magnetic force microscopy (MFM). Focusing mainly on the authors’ own work, but not exclusively, published/unpublished XPEEM and MFM images of ferroic domains and complex magnetic textures (involving vortices and phase separation) are presented. Highlights include the use of two XPEEM images to create 2D vector maps of in-plane (IP) magnetization, and the use of imaging to detect electrically driven local reversals of magnetization. The brief and simple descriptions of XPEEM and MFM should be useful for beginners seeking to employ these techniques in order to understand and harness ferroic materials.
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May 2022
|
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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.
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Apr 2022
|
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Cyril
Leveille
,
Erick
Burgos-Parra
,
Yanis
Sassi
,
Fernando
Ajejas
,
Valentin
Chardonnet
,
Emanuele
Pedersoli
,
Flavio
Capotondi
,
Giovanni
De Ninno
,
Francesco
Maccherozzi
,
Sarnjeet
Dhesi
,
David M.
Burn
,
Gerrit
Van Der Laan
,
Oliver S.
Latcham
,
Andrey V.
Shytov
,
Volodymyr V.
Kruglyak
,
Emmanuelle
Jal
,
Vincent
Cros
,
Jean-Yves
Chauleau
,
Nicolas
Reyren
,
Michel
Viret
,
Nicolas
Jaouen
Open Access
Abstract: Non-collinear spin textures in ferromagnetic ultrathin films are attracting a renewed interest fueled by possible fine engineering of several magnetic interactions, notably the interfacial Dzyaloshinskii-Moriya interaction. This allows for the stabilization of complex chiral spin textures such as chiral magnetic domain walls (DWs), spin spirals, and magnetic skyrmions among others. We report here on the behavior of chiral DWs at ultrashort timescale after optical pumping in perpendicularly magnetized asymmetric multilayers. The magnetization dynamics is probed using time-resolved circular dichroism in x-ray resonant magnetic scattering (CD-XRMS). We observe a picosecond transient reduction of the CD-XRMS, which is attributed to the spin current-induced coherent and incoherent torques within the continuously varying spin texture of the DWs. We argue that a specific demagnetization of the inner structure of the DW induces a flow of spins from the interior of the neighboring magnetic domains. We identify this time-varying change of the DW texture shortly after the laser pulse as a distortion of the homochiral Néel shape toward a transient mixed Bloch-Néel-Bloch texture along a direction transverse to the DW.
|
Mar 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.
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Feb 2022
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