I05-ARPES
|
Liam
Trzaska
,
Lei
Qiao
,
Matthew D.
Watson
,
Monica
Ciomaga Hatnean
,
Igor
Markovic
,
Edgar
Abarca Morales
,
Tommaso
Antonelli
,
Cephise
Cacho
,
Geetha
Balakrishnan
,
Wei
Ren
,
Silvia
Picozzi
,
Phil D. C.
King
Diamond Proposal Number(s):
[21986, 25564]
Open Access
Abstract: The recent discovery of the persistence of long-range magnetic order when van der Waals magnets are thinned towards monolayers provides a tunable platform for engineering of novel magnetic structures and devices. Here, we study the evolution of the electronic structure of CrGeTe3 as a function of surface electron doping. From angle-resolved photoemission, we observe spectroscopic fingerprints that this electron doping drives a marked increase in TC, reaching values more than double that of the undoped material, in agreement with recent studies using electrostatic gating. Together with density functional theory calculations and Monte Carlo simulations, we show that, surprisingly, the increased TC is mediated by the population of spin-minority Cr t2g states, forming a half-metallic 2D electron gas. This promotes a novel variant of double exchange, and unlocks a significant influence of Ge – which was previously thought to be electronically inert in this system – in mediating Cr-Cr exchange.
|
Jan 2025
|
|
I10-Beamline for Advanced Dichroism - scattering
|
M.
Gomilšek
,
T. j.
Hicken
,
M. n.
Wilson
,
K. J. A.
Franke
,
B. M.
Huddart
,
A.
Štefančič
,
S. J. R.
Holt
,
G.
Balakrishnan
,
D. A.
Mayoh
,
M. t.
Birch
,
S. H.
Moody
,
H.
Luetkens
,
Z.
Guguchia
,
M. t. F.
Telling
,
P. J.
Baker
,
S. J.
Clark
,
T.
Lancaster
Open Access
Abstract: Skyrmions are particlelike vortices of magnetization with nontrivial topology, which are usually stabilized by Dzyaloshinskii-Moriya interactions (DMI) in noncentrosymmetric bulk materials. Exceptions are centrosymmetric Gd- and Eu-based skyrmion-lattice (SL) hosts with zero DMI, where both the SL stabilization mechanisms and magnetic ground states remain controversial. We address these here by investigating both the static and dynamical spin properties of the centrosymmetric SL host Gd2PdSi3 using muon spectroscopy. We find that spin fluctuations in the noncoplanar SL phase are highly anisotropic, implying that spin anisotropy plays a prominent role in stabilizing this phase. We also observe strongly anisotropic spin dynamics in the ground-state (IC-1) incommensurate magnetic phase of the material, indicating that it hosts a meronlike multi-𝑞 structure. In contrast, the higher-field, coplanar IC-2 phase is found to be single 𝑞 with nearly isotropic spin dynamics.
|
Jan 2025
|
|
I08-1-Soft X-ray Ptychography
|
Jeffrey
Neethirajan
,
Benedikt J,
Daurer
,
Marisel
Di Pietro Martinez
,
Ales
Hrabec
,
Luke
Turnbull
,
Rikako
Yamamoto
,
Marina
Raboni Ferreira
,
Ales
Stefancic
,
Daniel A.
Mayoh
,
Geetha
Balakrishnan
,
Zhaowen
Pei
,
Pengfei
Xue
,
Liao
Chang
,
Emilie
Ringe
,
Richard
Harrison
,
Sergio
Valencia
,
Majid
Kazemian
,
Burkhard
Kaulich
,
Claire
Donnelly
Diamond Proposal Number(s):
[32984, 33254]
Open Access
Abstract: Imaging of nanoscale magnetic textures within extended material systems is of critical importance to both fundamental research and technological applications. While high-resolution magnetic imaging of thin nanoscale samples is well established with electron and soft x-ray microscopy, the extension to micrometer-thick systems currently requires hard x rays, which limits high-resolution imaging to rare-earth magnets. Here, we overcome this limitation by establishing soft x-ray magnetic imaging of micrometer-thick systems using the pre-edge phase x-ray magnetic circular dichroism signal, thus making possible the study of a wide range of magnetic materials. By performing dichroic spectroptychography, we demonstrate high spatial resolution imaging of magnetic samples up to 1.7 μm thick, an order of magnitude higher than conventionally possible with soft x-ray absorption-based techniques. We demonstrate the applicability of the technique by harnessing the pre-edge phase to image thick chiral helimagnets, and naturally occurring magnetite particles, gaining insight into their three-dimensional magnetic configuration. This new regime of magnetic imaging makes possible the study of extended non-rare-earth systems that have until now been inaccessible, including magnetic textures for future spintronic applications, non-rare-earth permanent magnets for energy harvesting, and the magnetic configuration of giant magnetofossils.
|
Aug 2024
|
|
I10-Beamline for Advanced Dichroism - scattering
|
M. T.
Littlehales
,
S. H.
Moody
,
P. J.
Bereciartua
,
D. A.
Mayoh
,
Z. B.
Parkin
,
T. J.
Blundell
,
E.
Unsworth
,
S.
Francoual
,
G.
Balakrishnan
,
D.
Alba Venero
,
P. D.
Hatton
Diamond Proposal Number(s):
[34192]
Open Access
Abstract: The Eu(Ga1−𝑥Al𝑥)4 series is composed of centrosymmetric structures which exhibit a wide range of rich topological phenomena, including some members hosting magnetic skyrmions. In this letter, we investigate the previously unreported intermediate compound EuGa2.4Al1.6, which hosts two distinct phase transitions under zero applied magnetic field. We have used resonant elastic x-ray scattering with full linear polarization analysis to unambiguously determine the zero-field magnetic structures, which consist of a transition between a basal plane transverse spin density wave at higher temperatures into a noncollinear helical ground state. Furthermore, we demonstrate a phase coexistence regime below the transition and reveal an elliptically modulated helical magnetic structure emerging from wavevector splitting.
|
Jul 2024
|
|
I05-ARPES
I09-Surface and Interface Structural Analysis
|
Brendan
Edwards
,
Darius-A.
Deaconu
,
Philip A. E.
Murgatroyd
,
Sebastian
Buchberger
,
Tommaso
Antonelli
,
Daniel
Halliday
,
Gesa-R.
Siemann
,
Andela
Zivanovic
,
Liam
Trzaska
,
Akhil
Rajan
,
Edgar
Abarca Morales
,
Daniel A.
Mayoh
,
Amelia E.
Hall
,
Rodion V.
Belosludov
,
Matthew D.
Watson
,
Timur K.
Kim
,
Deepnarayan
Biswas
,
Tien-Lin
Lee
,
Craig M.
Polley
,
Dina
Carbone
,
Mats
Leandersson
,
Geetha
Balakrishnan
,
Mohammad Saeed
Bahramy
,
Phil D. C.
King
Diamond Proposal Number(s):
[32937, 30125, 31465]
Open Access
Abstract: The addition of metal intercalants into the van der Waals gaps of transition metal dichalcogenides has shown great promise as a method for controlling their functional properties. For example, chiral helimagnetic states, current-induced magnetization switching, and a giant valley-Zeeman effect have all been demonstrated, generating significant renewed interest in this materials family. Here, we present a combined photoemission and density-functional theory study of three such compounds:
V1/3NbS2
,
Cr1/3NbS2
, and
Fe1/3NbS2
, to investigate chemical trends of the intercalant species on their bulk and surface electronic structure. Our resonant photoemission measurements indicate increased hybridization with the itinerant NbS2-derived conduction states with increasing atomic number of the intercalant, leading to pronounced mixing of the nominally localized intercalant states at the Fermi level. Using spatially and angle-resolved photoemission spectroscopy, we show how this impacts surface-termination-dependent charge transfers and leads to the formation of new dispersive states of mixed intercalant-Nb character at the Fermi level for the intercalant-terminated surfaces. This provides an explanation for the origin of anomalous states previously reported in this family of compounds and paves the way for tuning the nature of the magnetic interactions in these systems via control of the hybridization of the magnetic ions with the itinerant states.
|
Jul 2024
|
|
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.
|
Jul 2024
|
|
I10-Beamline for Advanced Dichroism - scattering
|
Diamond Proposal Number(s):
[30616, 31619]
Open Access
Abstract: Spintronic devices incorporating magnetic skyrmions have attracted significant interest recently. Such devices traditionally focus on controlling magnetic textures in 2D thin films. However, enhanced performance of spintronic properties through the exploitation of higher dimensionalities motivates the investigation of variable-thickness skyrmion devices. We report the demonstration of a skyrmion injection mechanism that utilizes charge currents to drive skyrmions across a thickness step and, consequently, a metastability barrier. Our measurements show that under certain temperature and field conditions skyrmions can be reversibly injected from a thin region of an FeGe lamella, where they exist as an equilibrium state, into a thicker region, where they can only persist as a metastable state. This injection is achieved with a current density of 3 × 108 A m–2, nearly 3 orders of magnitude lower than required to move magnetic domain walls. This highlights the possibility to use such an element as a skyrmion source/drain within future spintronic devices.
|
May 2024
|
|
I06-Nanoscience (XPEEM)
|
Ryuji
Fujita
,
Gautam
Gurung
,
Mohamad‐assaad
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
|
|
I10-Beamline for Advanced Dichroism - scattering
|
Diamond Proposal Number(s):
[30613]
Open Access
Abstract: Magnetic chiral soliton lattices (CSLs) emerge from the helical phase in chiral magnets when magnetic fields are applied perpendicular to the helical propagation vector, and they show great promise for next-generation magnetic memory applications. These one-dimensional structures are previously observed at low temperatures in samples with uniaxial symmetry. Here, it is found that in-plane fields are the key to stabilizing the CSL in cubic Co8Zn10Mn2 over the entire temperature range from 15 K to below the Curie temperature (365 K). Using small-angle resonant elastic X-ray scattering, it is observed that the CSL is stabilized with an arbitrary in-plane propagation vector, while its thin plate geometry plays a deciding role in the soliton wavelength as a function of applied field. This work paves the way for high temperature, real world applications of soliton physics in future magnetic memory devices.
|
Apr 2023
|
|
I10-Beamline for Advanced Dichroism - scattering
|
Diamond Proposal Number(s):
[30616, 31619]
Abstract: https://meetings.aps.org/Meeting/MAR23/Session/W54.7
|
Mar 2023
|
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