I06-Nanoscience (XPEEM)
|
Yu
Yan
,
Bo
Liu
,
Xianyang
Lu
,
Junlin
Wang
,
Sarnjeet S.
Dhesi
,
Iain G.
Will
,
Vlado K.
Lazarov
,
Jun
Du
,
Jing
Wu
,
Rong
Zhang
,
Yongbing
Xu
Abstract: Fe/GaAs is a prototype system of spin injection at room temperature. The interfacial strain and oriented bonds are both considered the origin of the Fe in-plane uniaxial magnetic anisotropy (UMA), which remains decisive. Here, by the x-ray magnetic circular dichroism (XMCD) and the vibrating sample magnetometer measurements, this study shows that in the Fe/Cr(t)/GaAs structure, the in-plane UMA of Fe originates from the chemical bonding between the Fe and the GaAs substrate by varying Cr thickness, t. The UMA drops as the Cr coverage increases, characterized by a decrease in the saturation field from 2400 to 57 Oe. The XMCD studies reveal that the Fe orbital moment, a signature of chemical bonds, decreases from 0.216 μB at Cr = 0 ML to 0.138 μB at Cr = 5 ML. The reduction of the Fe orbital moment and the UMA are qualitatively consistent, establishing a link between the UMA and the interfacial chemical bonds. The decreased UMA remains unchanged at t > 5 ML, above which Fe and GaAs are fully separated by a continuous Cr layer. Our findings provide clear experimental evidence that the UMA in the Fe/GaAs system originates from the oriented interface bonds, clarifying the UMA origin in this prototype system.
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Mar 2025
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I06-Nanoscience (XPEEM)
|
O. J.
Amin
,
A.
Dal Din
,
E.
Golias
,
Y.
Niu
,
A.
Zakharov
,
S. C.
Fromage
,
C. J. B.
Fields
,
S. L.
Heywood
,
R. B.
Cousins
,
F.
Maccherozzi
,
J.
Krempasky
,
J. H.
Dil
,
D.
Kriegner
,
B.
Kiraly
,
R. P.
Campion
,
A. W.
Rushforth
,
K. W.
Edmonds
,
S. S.
Dhesi
,
L.
Šmejkal
,
T.
Jungwirth
,
P.
Wadley
Diamond Proposal Number(s):
[36317]
Open Access
Abstract: Nanoscale detection and control of the magnetic order underpins a spectrum of condensed-matter research and device functionalities involving magnetism. The key principle involved is the breaking of time-reversal symmetry, which in ferromagnets is generated by an internal magnetization. However, the presence of a net magnetization limits device scalability and compatibility with phases, such as superconductors and topological insulators. Recently, altermagnetism has been proposed as a solution to these restrictions, as it shares the enabling time-reversal-symmetry-breaking characteristic of ferromagnetism, combined with the antiferromagnetic-like vanishing net magnetization. So far, altermagnetic ordering has been inferred from spatially averaged probes. Here we demonstrate nanoscale imaging of altermagnetic states from 100-nanometre-scale vortices and domain walls to 10-micrometre-scale single-domain states in manganese telluride (MnTe). We combine the time-reversal-symmetry-breaking sensitivity of X-ray magnetic circular dichroism12 with magnetic linear dichroism and photoemission electron microscopy to achieve maps of the local altermagnetic ordering vector. A variety of spin configurations are imposed using microstructure patterning and thermal cycling in magnetic fields. The demonstrated detection and controlled formation of altermagnetic spin configurations paves the way for future experimental studies across the theoretically predicted research landscape of altermagnetism, including unconventional spin-polarization phenomena, the interplay of altermagnetism with superconducting and topological phases, and highly scalable digital and neuromorphic spintronic devices.
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Dec 2024
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I06-Nanoscience (XPEEM)
|
Tuhin
Maity
,
Manisha
Bansal
,
Nives
Strkalj
,
Kapildeb
Dolui
,
Di
Zhang
,
Zihao
He
,
Guillaume F
Nataf
,
Adam
Lovett
,
Massimo
Ghidini
,
Sarnjeet S.
Dhesi
,
Ping
Lu
,
Haiyan
Wang
,
Weiwei
Li
,
Judith L.
Macmanus-Driscoll
Diamond Proposal Number(s):
[22427]
Open Access
Abstract: We investigate the emergence and optimization of conventional exchange bias (EB) in ultrathin (<10 nm) ferroelectric (FE) BaTiO3 (BTO)/ferromagnetic (FM) La0.67Sr0.33MnO3 (LSMO) epitaxial bilayers without an antiferromagnetic (AFM) material. The EB originates from the electronic orbital reconstruction at the FE-FM interface due to the ferroelectric polarization. We achieve maximum EB of approximately 42 Oe with single-domain polarization in nine-unit-cell-thick BTO, setting the BTO thickness above the critical threshold for ferroelectricity yet below the thickness of strain relaxation and multidomain breakdown. Furthermore, the LSMO layer needs to be thick enough to sustain both the FM layer and polarization-induced AFM spin configuration at the LSMO/BTO interface, yet as thin as possible to enable the EB loop shift. The temperature, training, field, and thickness dependence of the EB confirm that the LSMO/BTO interface exhibits conventional EB despite its unconventional origin. Using x-ray magnetic circular dichroism, scanning transmission electron microscopy, and density-functional-theory calculations, we confirm that the macroscopic EB effect originates from the interfacial AFM spin configuration in LSMO driven by FE-induced d-orbital modifications in interfacial Mn ions. Thus, we engineer strong interfacial EB coupling in artificial multiferroics without a conventional AFM material by controlling FE polarization, highlighting the potential for advanced spintronic applications.
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Nov 2024
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I06-Nanoscience (XPEEM)
|
Alessandra
Milloch
,
Ignacio
Figueruelo-Campanero
,
Wei-Fan
Hsu
,
Selene
Mor
,
Simon
Mellaerts
,
Francesco
Maccherozzi
,
Larissa S. I.
Veiga
,
Sarnjeet S.
Dhesi
,
Mauro
Spera
,
Jin Won
Seo
,
Jean-Pierre
Locquet
,
Michele
Fabrizio
,
Mariela
Menghini
,
Claudio
Giannetti
Diamond Proposal Number(s):
[27218, 31711, 34455]
Open Access
Abstract: Avalanche resistive switching is the fundamental process that triggers the sudden change of the electrical properties in solid-state devices under the action of intense electric fields. Despite its relevance for information processing, ultrafast electronics, neuromorphic devices, resistive memories and brain-inspired computation, the nature of the local stochastic fluctuations that drive the formation of metallic regions within the insulating state has remained hidden. Here, using operando X-ray nano-imaging, we have captured the origin of resistive switching in a V2O3-based device under working conditions. V2O3 is a paradigmatic Mott material, which undergoes a first-order metal-to-insulator phase transition together with a lattice transformation that breaks the threefold rotational symmetry of the rhombohedral metallic phase. We reveal a new class of volatile electronic switching triggered by nanoscale topological defects appearing in the shear-strain based order parameter that describes the insulating phase. Our results pave the way to the use of strain engineering approaches to manipulate such topological defects and achieve the full dynamical control of the electronic Mott switching. Topology-driven, reversible electronic transitions are relevant across a broad range of quantum materials, comprising transition metal oxides, chalcogenides and kagome metals.
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Oct 2024
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I06-Nanoscience (XPEEM)
|
Raul
Lopez-Martin
,
Chris
Binns
,
Benito
Santos Burgos
,
Peter S.
Normile
,
Jose A.
De Toro
,
Andrew
Pratt
,
Toby
Bird
,
Maha
Alotaibi
,
Jack
Pearce
,
David
Hesp
,
Connor
Fields
,
Shengfu
Yang
,
Hanqing
Liu
,
Larissa S. I.
Veiga
,
Sarnjeet S.
Dhesi
Diamond Proposal Number(s):
[33064]
Open Access
Abstract: Nanostructured FeCo films comprising small (2.1 nm mean diameter) Co nanoparticles deposited into an Fe matrix are investigated by magnetometry, transmission electron microscopy and X-ray Magnetic Circular Dichroism (XMCD). Similar films were previously reported to possess a saturation magnetisation of up to 3 µB/atom, thus exceeding the Slater-Pauling limit by a significant margin. The present work confirms the previous findings by magnetometry and demonstrates that the Co nanoparticles maintain their particulate identity within the film while adopting the crystallographic structure of the Fe matrix. The films show no evidence for voids or porosity (they exhibit the bulk density). An important factor in the high magnetisation in the films is an enhanced magnetic moment on the Co atoms, which XMCD indicates to be at least 2.21 µB, i.e., 30 % larger than the bulk value for metallic cobalt.
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Oct 2024
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I06-Nanoscience (XPEEM)
|
Diamond Proposal Number(s):
[27482]
Open Access
Abstract: We present a spectroscopic study of the magnetic properties of Fe3-δGeTe2 single crystals with varying Fe content, achieved by tuning the stoichiometry of the crystals. We carried out x-ray absorption spectroscopy and analyzed the x-ray circular magnetic dichroism spectra using the sum rules, to determine the orbital and spin magnetic moments of the materials. We find a clear reduction of the spin and orbital magnetic moment with increasing Fe deficiency. Magnetic susceptibility measurements show that the reduction in magnetization is accompanied by a reduced Curie temperature. Multiplet calculations reveal that the Fe2+ state increasingly mixes with a higher valence state when the Fe deficiency is increased. This effect is correlated with the weakening of the magnetic moment. As single crystals are the base material for exfoliation processes, our results are relevant for the assembly of 2D magnetic heterostructures.
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Jul 2024
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I06-Nanoscience (XPEEM)
|
Sonka
Reimers
,
Olena
Gomonay
,
Oliver J.
Amin
,
Filip
Krizek
,
Luke X.
Barton
,
Yaryna
Lytvynenko
,
Stuart F.
Poole
,
Vit
Novák
,
Richard P.
Campion
,
Francesco
Maccherozzi
,
Gerardina
Carbone
,
Alexander
Bjorling
,
Yuran
Niu
,
Evangelos
Golias
,
Dominik
Kriegner
,
Jairo
Sinova
,
Mathias
Klaui
,
Martin
Jourdan
,
Sarnjeet S.
Dhesi
,
Kevin W.
Edmonds
,
Peter
Wadley
Diamond Proposal Number(s):
[22437, 27146]
Abstract: Antiferromagnetic materials hold potential for use in spintronic devices with fast operation frequencies and field robustness. Despite the rapid progress in proof-of-principle functionality in recent years, there has been a notable lack of understanding of antiferromagnetic domain formation and manipulation, which translates to either incomplete or nonscalable control of the magnetic order. Here, we demonstrate simple and functional ways of influencing the domain structure in CuMnAs and Mn2Au, two key materials of antiferromagnetic spintronics research, using device patterning and strain engineering. Comparing x-ray microscopy data from two different materials, we reveal the key parameters dictating domain formation in antiferromagnetic devices and show how the nontrivial interaction of magnetostriction, substrate clamping, and edge anisotropy leads to specific equilibrium domain configurations. More specifically, we observe that patterned edges have a significant impact on the magnetic anisotropy and domain structure over long distances and we propose a theoretical model that relates short-range edge anisotropy and long-range magnetoelastic interactions. The principles invoked are of general applicability to the domain formation and engineering in antiferromagnetic thin films at large, which will hopefully pave the way toward realizing truly functional antiferromagnetic devices.
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Jun 2024
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I06-Nanoscience (XPEEM)
|
A.
Hariki
,
A.
Dal Din
,
O. j.
Amin
,
T.
Yamaguchi
,
A.
Badura
,
D.
Kriegner
,
K. W.
Edmonds
,
R. p.
Campion
,
P.
Wadley
,
D.
Backes
,
L. S. I.
Veiga
,
S. S.
Dhesi
,
G.
Springholz
,
L.
Šmejkal
,
K.
Výborný
,
T.
Jungwirth
,
J.
Kuneš
Diamond Proposal Number(s):
[33456, 36317]
Abstract: Altermagnetism is a recently identified magnetic symmetry class combining characteristics of conventional collinear ferromagnets and antiferromagnets, that were regarded as mutually exclusive, and enabling phenomena and functionalities unparalleled in either of the two traditional elementary magnetic classes. In this work we use symmetry, ab initio theory, and experiments to explore x-ray magnetic circular dichroism (XMCD) in the altermagnetic class. As a representative material for our XMCD study we choose
α
-MnTe with compensated antiparallel magnetic order in which an anomalous Hall effect has been already demonstrated. We predict and experimentally confirm a characteristic XMCD line shape for compensated moments lying in a plane perpendicular to the light propagation vector. Our results highlight the distinct phenomenology in altermagnets of this time-reversal symmetry breaking response, and its potential utility for element-specific spectroscopy and microscopy.
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Apr 2024
|
|
I06-Nanoscience (XPEEM)
|
C. E. A.
Barker
,
K.
Fallon
,
C.
Barton
,
E.
Haltz
,
T. P.
Almeida
,
S.
Villa
,
C.
Kirkbride
,
F.
Maccherozzi
,
B.
Sarpi
,
S. S.
Dhesi
,
D.
Mcgrouther
,
S.
Mcvitie
,
T. A.
Moore
,
O.
Kazakova
,
C. H.
Marrows
Diamond Proposal Number(s):
[28586]
Open Access
Abstract: In synthetic antiferromagnets (SAFs), antiferromagnetic (AFM) order and synthesis using conventional sputtering techniques is combined to produce systems that are advantageous for spintronics applications. Here we present the preparation and study of SAF multilayers possessing both perpendicular magnetic anisotropy and the Dzyaloshinskii-Moriya interaction. The multilayers have an antiferromagnetically aligned ground state but can be forced into a full ferromagnetic (FM) alignment by applying an out-of-plane field
∼
100
mT. We study the spin textures in these multilayers in their ground state as well as around the transition point between the AFM and FM states at fields
∼
40 mT by imaging the spin textures using complementary methods: photoemission electron, magnetic force, and Lorentz transmission electron microscopies. The transformation into a FM state by field proceeds by a nucleation and growth process, where skyrmionic nuclei form and then broaden into regions containing a ferromagnetically aligned labyrinth pattern that eventually occupies the whole film. Remarkably, this process occurs without any significant change in the net magnetic moment of the multilayer. The mix of antiferromagnetically and ferromagnetically aligned regions on the micron scale in the middle of this transition is reminiscent of a first-order phase transition that exhibits phase coexistence. These results are important for guiding the design of spintronic devices whose operation is based on spin textures in perpendicularly magnetized SAFs.
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Apr 2024
|
|
|
|
Gianluigi A.
Botton
,
Peter
Coll
,
Andrew J.
Dent
,
Sarnjeet
Dhesi
,
Sky
French
,
David R.
Hall
,
Joseph
Hriljac
,
Sarah
Macdonell
,
Sofia
Diaz-Moreno
,
Chris
Nicklin
,
Paul
Quinn
,
Robert
Rambo
,
Kawal
Sawhney
,
Richard P.
Walker
,
Martin A.
Walsh
,
Molly
Pekarik-Fry
Open Access
Abstract: A look at the Diamond-II upgrade programme
|
Mar 2024
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