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 Focusing mainly on the authors’ own work, but not exclusively, published/unpublished XPEEM and MFM images of ferroic domains and complex magnetic textures (involving vortices and phase separation) are presented.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.
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Mar 2022
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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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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.
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Sep 2021
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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.
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Mar 2021
|
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I06-Nanoscience
|
Richard W.
Dawidek
,
Thomas J.
Hayward
,
Ian T.
Vidamour
,
Thomas J.
Broomhall
,
Guru
Venkat
,
Mohanad Al
Mamoori
,
Aidan
Mullen
,
Stephan J.
Kyle
,
Paul W.
Fry
,
Nina-Juliane
Steinke
,
Joshaniel F. K.
Cooper
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Lucia
Aballe
,
Michael
Foerster
,
Jordi
Prat
,
Eleni
Vasilaki
,
Matthew O. A.
Ellis
,
Dan A.
Allwood
Diamond Proposal Number(s):
[24205]
Open Access
Abstract: Emergent behaviors occur when simple interactions between a system's constituent elements produce properties that the individual elements do not exhibit in isolation. This article reports tunable emergent behaviors observed in domain wall (DW) populations of arrays of interconnected magnetic ring‐shaped nanowires under an applied rotating magnetic field. DWs interact stochastically at ring junctions to create mechanisms of DW population loss and gain. These combine to give a dynamic, field‐dependent equilibrium DW population that is a robust and emergent property of the array, despite highly varied local magnetic configurations. The magnetic ring arrays’ properties (e.g., non‐linear behavior, “fading memory” to changes in field, fabrication repeatability, and scalability) suggest they are an interesting candidate system for realizing reservoir computing (RC), a form of neuromorphic computing, in hardware. By way of example, simulations of ring arrays performing RC approaches 100% success in classifying spoken digits for single speakers.
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Feb 2021
|
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I06-Nanoscience
|
Hariom
Jani
,
Jheng-Cyuan
Lin
,
Jiahao
Chen
,
Jack
Harrison
,
Francesco
Maccherozzi
,
Jonathon
Schad
,
Saurav
Prakash
,
Chang-Beom
Eom
,
A.
Ariando
,
Thirumalai
Venkatesan
,
Paolo G.
Radaelli
Diamond Proposal Number(s):
[23857, 20317]
Abstract: In the quest for post-CMOS (complementary metal–oxide–semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic ‘whirls’ such as skyrmions and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices. However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures, and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus, but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe2O3—an Earth-abundant oxide insulator—capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble–Zurek mechanism2, we stabilize exotic merons and antimerons (half-skyrmions)8 and their pairs (bimerons), which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature.
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Feb 2021
|
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I06-Nanoscience
|
Diamond Proposal Number(s):
[23819]
Abstract: Tm
Fe
O
3
(TFO) is a canted antiferromagnet that undergoes a spin reorientation transition (SRT) with temperature between 82 and 94 K in single crystals. In this temperature region, the Néel vector continuously rotates from the crystallographic
c
axis (below 82 K) to the
a
axis (above 94 K). The SRT allows for a temperature control of distinct antiferromagnetic states without the need for a magnetic field, making it apt for applications working at terahertz frequencies. For device applications, thin films of TFO are required as well as an electrical technique for read-out of the magnetic state. Here, we demonstrate that orthorhombic TFO thin films can be grown by pulsed laser deposition and the detection of the SRT in TFO thin films can be accessed by making use of the all-electrical spin Hall magnetoresistance, in good agreement for the temperature range where the SRT occurs in bulk crystals. Our results demonstrate that one can electrically detect the SRT in insulators.
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Jan 2021
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