I06-Nanoscience (XPEEM)
|
Diamond Proposal Number(s):
[35404]
Open Access
Abstract: Antiferromagnets (AFs) are characterized by spin structures that are resistant to external magnetic fields, rendering them ideal for persistent information storage but challenging to control. This study demonstrates that a thin ferromagnetic adlayer can serve as a magnetic âleverâ to provide a strong handle on the spin texture of an adjacent antiferromagnet. In bilayers composed of NiO(001) and Co, the expected exchange bias effectâa unidirectional shift in the Co hysteresis due to coupling with NiOâis notably absent. Instead, a strong interfacial coupling is observed, causing the NiO to partially follow the magnetization of Co under an applied magnetic field. Using x-ray magnetic linear dichroism, we detect an inversion of dichroism, indicating a reorientation of the NĂ©el vector in NiO. X-ray spectromicroscopy imaging further reveals a direct correlation between ferromagnetic and antiferromagnetic domain structures. These findings are explained using a toy model that distinguishes between stable and unstable AF domains, highlighting the dynamic interplay between NiO and the Co adlayer in the presence of a magnetic field.
|
Jan 2025
|
|
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.
Ć mejkal
,
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.
|
Dec 2024
|
|
I06-Nanoscience (XPEEM)
|
Denis
Gentili
,
Gabriele
Calabrese
,
Eugenio
Lunedei
,
Francesco
Borgatti
,
Seyed A.
Mirshokraee
,
Vasiliki
Benekou
,
Giorgio
Tseberlidis
,
Alessio
Mezzi
,
Fabiola
Liscio
,
Andrea
Candini
,
Giampiero
Ruani
,
Vincenzo
Palermo
,
Francesco
Maccherozzi
,
Maurizio
Acciarri
,
Enrico
Berretti
,
Carlo
Santoro
,
Alessandro
Lavacchi
,
Massimiliano
Cavallini
Open Access
Abstract: Defects are inherent in transition metal dichalcogenides and significantly affect their chemical and physical properties. In this study, surface defect electrochemical nanopatterning is proposed as a promising method to tune in a controlled manner the electronic and functional properties of defective MoSâ thin films. Using parallel electrochemical nanolithography, MoSâ thin films are patterned, creating sulphur vacancy-rich active zones alternated with defect-free regions over a centimetre scale area, with sub-micrometre spatial resolution. The patterned films display tailored optical and electronic properties due to the formation of sulphur vacancy-rich areas. Moreover, the effectiveness of defect nanopatterning in tuning functional properties is demonstrated by studying the electrocatalytic activity for the hydrogen evolution reaction.
|
Nov 2024
|
|
I06-Nanoscience (XPEEM)
|
M.
Lowe
,
A.
Al-Mahboob
,
D.
Ivarsson
,
M.
ArmbrĂŒster
,
J.
Ardini
,
G.
Held
,
F.
Maccherozzi
,
A.
Bayer
,
V.
Fournee
,
J.
Ledieu
,
J. T.
Sadowski
,
R.
Mcgrath
,
H. R.
Sharma
Open Access
Abstract: The intermetallic compound ZnPd has been found to have desirable characteristics as a catalyst for the steam reforming of methanol. The understanding of the surface structure of ZnPd is important to optimize its catalytic behavior. However, due to the lack of bulk single-crystal samples and the complexity of characterizing surface properties in the available polycrystalline samples using common experimental techniques, all previous surface science studies of this compound have been performed on surface alloy samples formed through thin-film deposition. In this study, we present findings on the chemical and atomic structure of the surfaces of bulk polycrystalline ZnPd studied by a variety of complementary experimental techniques, including scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), low energy electron microscopy (LEEM), photoemission electron microscopy (PEEM), and microspot low-energy electron diffraction (đ-LEED). These experimental techniques, combined with density functional theory (DFT)-based thermodynamic calculations of surface free energy and detachment kinetics at the step edges, confirm that surfaces terminated by atomic layers composed of both Zn and Pd atoms are more stable than those terminated by only Zn or Pd layers. DFT calculations also demonstrate that the primary contribution to the tunneling current arises from Pd atoms, in agreement with the STM results. The formation of intermetallics at surfaces may contribute to the superior catalyst properties of ZnPd over Zn or Pd elemental counterparts.
|
Oct 2024
|
|
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.
|
Oct 2024
|
|
I06-Nanoscience (XPEEM)
|
Sonka
Reimers
,
Olena
Gomonay
,
Oliver J.
Amin
,
Filip
Krizek
,
Luke X.
Barton
,
Yaryna
Lytvynenko
,
Stuart F.
Poole
,
Vit
NovĂĄk
,
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 CuâąMnâąAs 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.
|
Jun 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
âŒ
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
âŒ
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.
|
Apr 2024
|
|
I06-Nanoscience (XPEEM)
|
Ryuji
Fujita
,
Gautam
Gurung
,
Mohamadâassaad
Mawass
,
Alevtina
Smekhova
,
Florian
Kronast
,
Alexander Kang-Jun
Toh
,
Anjan
Soumyanarayanan
,
Pin
Ho
,
Angadjit
Singh
,
Emily
Heppell
,
Dirk
Backes
,
Francesco
Maccherozzi
,
Kenji
Watanabe
,
Takashi
Taniguchi
,
Daniel A.
Mayoh
,
Geetha
Balakrishnan
,
Gerrit
Van Der Laan
,
Thorsten
Hesjedal
Diamond Proposal Number(s):
[31730]
Open Access
Abstract: The van der Waals interaction enables atomically thin layers of exfoliated 2D materials to be interfaced in heterostructures with relaxed epitaxy conditions, however, the ability to exfoliate and freely stack layers without any strain or structural modification is by no means ubiquitous. In this work, the piezoelectricity of the exfoliated van der Waals piezoelectric α-In2Se3 is utilized to modify the magnetic properties of exfoliated Fe3GeTe2, a van der Waals ferromagnet, resulting in increased domain wall density, reductions in the transition temperature ranging from 5 to 20 K, and an increase in the magnetic coercivity. Structural modifications at the atomic level are corroborated by a comparison to a graphite/α-In2Se3 heterostructure, for which a decrease in the Tuinstra-Koenig ratio is found. Magnetostrictive ferromagnetic domains are also observed, which may contribute to the enhanced magnetic coercivity. Density functional theory calculations and atomistic spin dynamic simulations show that the Fe3GeTe2 layer is compressively strained by 0.4%, reducing the exchange stiffness and magnetic anisotropy. The incorporation of α-In2Se3 may be a general strategy to electrostatically strain interfaces within the paradigm of hexagonal boron nitride-encapsulated heterostructures, for which the atomic flatness is both an intrinsic property and paramount requirement for 2D van der Waals heterojunctions.
|
Mar 2024
|
|
I06-Nanoscience (XPEEM)
|
Chengwu
Qiu
,
Yaroslav I.
Odarchenko
,
Qingwei
Meng
,
Hongyang
Dong
,
Ines
Lezcano Gonzalez
,
Monik
Panchal
,
Paul
Olalde-Velasco
,
Francesco
Maccherozzi
,
Laura C.
Zanetti-Domingues
,
Marisa L.
Martin-Fernandez
,
Andrew M.
Beale
Diamond Proposal Number(s):
[24409]
Open Access
Abstract: The nanoparticle (NP) redox state is an important parameter in the performance of cobalt-based FischerâTropsch synthesis (FTS) catalysts. Here, the compositional evolution of individual CoNPs (6â24 nm) in terms of the oxide vs metallic state was investigated in situ during CO/syngas treatment using spatially resolved X-ray absorption spectroscopy (XAS)/X-ray photoemission electron microscopy (X-PEEM). It was observed that in the presence of CO, smaller CoNPs (i.e., â€12 nm in size) remained in the metallic state, whereas NPs â„ 15 nm became partially oxidized, suggesting that the latter were more readily able to dissociate CO. In contrast, in the presence of syngas, the oxide content of NPs â„ 15 nm reduced, while it increased in quantity in the smaller NPs; this reoxidation that occurs primarily at the surface proved to be temporary, reforming the reduced state during subsequent UHV annealing. O K-edge measurements revealed that a key parameter mitigating the redox behavior of the CoNPs were proximate oxygen vacancies (Ovac). These results demonstrate the differences in the reducibility and the reactivity of Co NP size on a Co/TiO2 catalyst and the effect Ovac have on these properties, therefore yielding a better understanding of the physicochemical properties of this popular choice of FTS catalysts.
|
Nov 2023
|
|
I06-Nanoscience (XPEEM)
|
Diamond Proposal Number(s):
[24373]
Open Access
Abstract: Pointed magnetic elements are introduced as an improvement upon rectangular strips currently employed in composite element magnetic barcodes. The coercivity of these elements, as measured using the magneto-optic Kerr effect, is found to strictly adhere to a single power law relationship with the element width, where the power law exponent is dependent on the length of the pointed region and takes values between â
0.98 and â
0.91. The steeper gradients here, along with the absence of the crossover region seen in rectangular devices, present these structures as a strict improvement in terms of potential device applications. These improvements are found to be present for all structures where the pointed region is as long as, or longer than, the magnetic element is wide. The remanent magnetization configuration, imaged using photo-emission microscopy with contrast from x-ray magnetic circular dichroism (XMCD-PEEM), is compared to the results of micromagnetic simulations. It is found to cant inward in the pointed section of the strip, aligning with the edges of the point, pinning the magnetization and giving a consistent magnetization reversal behavior for all element widths investigated.
|
Oct 2023
|
|
