I06-Nanoscience
|
Romeo
Juge
,
Soong-geun
Je
,
Dayane De Souza
Chaves
,
Liliana D.
Buda-prejbeanu
,
José
Peña-garcia
,
Jayshankar
Nath
,
Ioan Mihai
Miron
,
Kumari Gaurav
Rana
,
Lucia
Aballe
,
Michael
Foerster
,
Francesca
Genuzio
,
Tevfik Onur
Menteş
,
Andrea
Locatelli
,
Francesco
Maccherozzi
,
Sarnjeet S.
Dhesi
,
Mohamed
Belmeguenai
,
Yves
Roussigné
,
Stéphane
Auffret
,
Stefania
Pizzini
,
Gilles
Gaudin
,
Jan
Vogel
,
Olivier
Boulle
Diamond Proposal Number(s):
[14035]
Abstract: Magnetic skyrmions are chiral spin textures that hold great promise as nanoscale information carriers. Since their first observation at room temperature, progress has been made in their current-induced manipulation, with fast motion reported in stray-field-coupled multilayers. However, the complex spin textures with hybrid chiralities and large power dissipation in these multilayers limit their practical implementation and the fundamental understanding of their dynamics. Here, we report on the current-driven motion of Néel skyrmions with diameters in the 100-nm range in an ultrathin
Pt
/
Co
/
Mg
O
trilayer. We find that these skyrmions can be driven at a speed of
100
m
s
−
1
and exhibit a drive-dependent skyrmion Hall effect, which is accounted for by the effect of pinning. Our experiments are well substantiated by an analytical model of the skyrmion dynamics as well as by micromagnetic simulations including material inhomogeneities. This good agreement is enabled by the simple skyrmion spin structure in our system and a thorough characterization of its static and dynamical properties.
|
Oct 2019
|
|
I06-Nanoscience
|
A.
Ronchi
,
P.
Homm
,
M.
Menghini
,
P.
Franceschini
,
F.
Maccherozzi
,
F.
Banfi
,
G.
Ferrini
,
F.
Cilento
,
F.
Parmigiani
,
S. S.
Dhesi
,
M.
Fabrizio
,
J.-p.
Locquet
,
C.
Giannetti
Diamond Proposal Number(s):
[16128]
Abstract: Unveiling the physics that governs the intertwining between the nanoscale self-organization and the dynamics of insulator-to-metal transitions (IMTs) is key for controlling on demand the ultrafast switching in strongly correlated materials and nanodevices. A paradigmatic case is the IMT in
V
2
O
3
, for which the mechanism that leads to the nucleation and growth of metallic nanodroplets out of the supposedly homogeneous Mott insulating phase is still a mystery. Here, we combine x-ray photoemission electron microscopy and ultrafast nonequilibrium optical spectroscopy to investigate the early-stage dynamics of isolated metallic nanodroplets across the IMT in
V
2
O
3
thin films. Our experiments show that the low-temperature monoclinic antiferromagnetic insulating phase is characterized by the spontaneous formation of striped polydomains, with different lattice distortions. The insulating domain boundaries accommodate the birth of metallic nanodroplets, whose nonequilibrium expansion can be triggered by the photoinduced change of the
3
d
-orbital occupation. We address the relation between the spontaneous nanotexture of the Mott insulating phase in
V
2
O
3
and the timescale of the metallic seeds growth. We speculate that the photoinduced metallic growth can proceed along a nonthermal pathway in which the monoclinic lattice symmetry of the insulating phase is partially retained.
|
Aug 2019
|
|
I06-Nanoscience
|
M.
Ghidini
,
R.
Mansell
,
F.
Maccherozzi
,
X.
Moya
,
L. C.
Phillips
,
W.
Yan
,
D.
Pesquera
,
C. H. W.
Barnes
,
R. P.
Cowburn
,
J.-m.
Hu
,
S. S.
Dhesi
,
N. D.
Mathur
Diamond Proposal Number(s):
[8876]
Abstract: Large changes in the magnetization of ferromagnetic films can be electrically driven by non-180° ferroelectric domain switching in underlying substrates, but the shear components of the strains that mediate these magnetoelectric effects have not been considered so far. Here we reveal the presence of these shear strains in a polycrystalline film of Ni on a 0.68Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 substrate in the pseudo-cubic (011)pc orientation. Although vibrating sample magnetometry records giant magnetoelectric effects that are consistent with the hitherto expected 90° rotations of a global magnetic easy axis, high-resolution vector maps of magnetization (constructed from photoemission electron microscopy data, with contrast from X-ray magnetic circular dichroism) reveal that the local magnetization typically rotates through smaller angles of 62–84°. This shortfall with respect to 90° is a consequence of the shear strain associated with ferroelectric domain switching. The non-orthogonality represents both a challenge and an opportunity for the development and miniaturization of magnetoelectric devices.
|
May 2019
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[17343]
Abstract: The redox behaviour modification following the addition of zirconia to ceria nanostructures supported on Rh(111) has been investigated using a combination of Low Energy Electron Diffraction (LEED) and X-ray Photoemission Electron Microscopy (XPEEM). Soft X-ray irradiation was employed to reduce ZrO2-x(111) supported on Rh(111) and, by introducing oxygen, the reoxidation process of the thin film was monitored. CeO2(111) was then deposited on zirconia/Rh(111) and, using XPEEM, we determined that the mixed metal oxide formed a phase-separated structure with CeO2(111) nanoparticles on top of the zirconia. Upon exposure of CeO2-x/ZrO2-x/Rh(111) to X-ray illumination, the zirconia no longer undergoes any observable reduction while at the same time the ceria is reduced. Our results indicate a synergy between the zirconia and ceria in the phase-separated system expected in the working catalyst, with oxygen transfer between the metal oxides. This sheds light on the mechanism of the enhancement of catalytic properties seen with the addition of zirconia to ceria and highlights the oxygen storage and release ability of ceria.
|
Dec 2018
|
|
I06-Nanoscience
|
G.
Mattoni
,
N.
Manca
,
M.
Hadjimichael
,
Pavlo
Zubko
,
A. J. H.
Van Der Torren
,
C.
Yin
,
S.
Catalano
,
M.
Gibert
,
F.
Maccherozzi
,
Y.
Liu
,
S. S.
Dhesi
,
A. D.
Caviglia
Diamond Proposal Number(s):
[13081, 10428]
Abstract: Strongly correlated materials show unique solid-state phase transitions with rich nanoscale phenomenology that can be controlled by external stimuli. Particularly interesting is the case of light–matter interaction in the proximity of the metal–insulator transition of heteroepitaxial nickelates. In this work, we use near-infrared laser light in the high-intensity excitation regime to manipulate the nanoscale phase separation in NdNiO3. By tuning the laser intensity, we can reproducibly set the coverage of insulating nanodomains, which we image by photoemission electron microscopy, thus semipermanently configuring the material state. With the aid of transport measurements and finite element simulations, we identify two different timescales of thermal dynamics in the light–matter interaction: a steady-state and a fast transient local heating. These results open interesting perspectives for locally manipulating and reconfiguring electronic order at the nanoscale by optical means.
|
Aug 2018
|
|
I06-Nanoscience
|
Massimo
Ghidini
,
Bonan
Zhu
,
Rhodri
Mansell
,
Raffaele
Pellicelli
,
Arnaud
Lesaine
,
Xavier
Moya
,
Sam
Crossley
,
Bhasi
Nair
,
Francesco
Maccherozzi
,
Crispin H. W.
Barnes
,
Russell P.
Cowburn
,
Sarnjeet
Dhesi
,
Neil D.
Mathur
Diamond Proposal Number(s):
[9590]
Abstract: For 1 microm-diameter Ni discs on a BaTiO3 substrate, the local
magnetization direction is determined by ferroelectric domain
orientation as a consequence of growth strain, such that single-domain
discs lie on single ferroelectric domains. On applying a voltage across
the substrate, ferroelectric domain switching yields non-volatile
magnetization rotations of 90°, while piezoelectric effects that are
small and continuous yield non-volatile magnetization reversals that
are non-deterministic. This demonstration of magnetization reversal
without ferroelectric domain switching implies reduced fatigue, and
therefore represents a step towards applications.
|
May 2018
|
|
I06-Nanoscience
|
Peter
Wadley
,
Sonka
Reimers
,
Michal J.
Grzybowski
,
Carl
Andrews
,
Mu
Wang
,
Jasbinder S.
Chauhan
,
Bryan L.
Gallagher
,
Richard P.
Campion
,
Kevin W.
Edmonds
,
Sarnjeet S.
Dhesi
,
Francesco
Maccherozzi
,
Vit
Novak
,
Joerg
Wunderlich
,
Tomas
Jungwirth
Diamond Proposal Number(s):
[16376]
Abstract: Antiferromagnets have several favourable properties as active elements in spintronic devices, including ultra-fast dynamics, zero stray fields and insensitivity to external magnetic fields1. Tetragonal CuMnAs is a testbed system in which the antiferromagnetic order parameter can be switched reversibly at ambient conditions using electrical currents2. In previous experiments, orthogonal in-plane current pulses were used to induce 90° rotations of antiferromagnetic domains and demonstrate the operation of all-electrical memory bits in a multi-terminal geometry3. Here, we demonstrate that antiferromagnetic domain walls can be manipulated to realize stable and reproducible domain changes using only two electrical contacts. This is achieved by using the polarity of the current to switch the sign of the current-induced effective field acting on the antiferromagnetic sublattices. The resulting reversible domain and domain wall reconfigurations are imaged using X-ray magnetic linear dichroism microscopy, and can also be detected electrically. Switching by domain-wall motion can occur at much lower current densities than those needed for coherent domain switching.
|
Mar 2018
|
|
I06-Nanoscience
Optics
|
Open Access
Abstract: Insertion devices are utilized at synchrotron radiation facilities around the world for their capability to provide a high-brilliance X-ray beam. APPLE-II type undulators are especially important for their capacity to switch between a variety of photon beam polarization states. A high-precision soft X-ray polarimeter has been used to investigate the polarization calibration of an APPLE-II undulator (period length λu = 64 mm) installed on beamline I06 at Diamond Light Source. Systematic measurement of the beam polarization state at a range of linear arbitrary angles has been compared with the expected result for a given set of undulator gap and row phase parameters calculated from theory. Determination of the corresponding Stokes–Poincaré parameters from the measured data reveals a discrepancy between the two. The limited number of energy/polarization combinations included in the undulator calibration tables necessitates the use of interpolated values for the missing points which is expected to contribute to the discrepancy. However, by modifying the orbit of the electron beam through the undulator by at least 160 µm it has been found that for certain linear polarizations the discrepancies can be corrected. Overall, it is suggested that complete correction of the Stokes–Poincaré parameters for all linear angles would require alteration of both these aspects.
|
Mar 2018
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[9309]
Abstract: The growth and reactive dewetting of ultra-thin films of iron oxides supported on Re(0001) surfaces have been imaged in-situ in real time. Initial growth forms a non-magnetic stable FeO (wüstite like) layer in a commensurate network upon which high aspect ratio nanowires of several microns length but less than 40nm width can be fabricated. The nanowires are closely aligned with the substrate crystallography and imaging by X-ray magnetic circular dichroism shows that each contain a single magnetic domain. The driving force for dewetting appears to be the minimization of strain energy of the Fe3O4 crystallites and follows the Tersoff and Tromp model in which strain is minimized at constant height by extending in one epitaxially matched direction. Such wires are promising in spintronic applications and we predict that the growth will also occur on other hexagonal substrates.
|
Mar 2018
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[10361, 12565, 14135]
Abstract: The magnetoelectric effect in M-type Ti-Co doped strontium hexaferrite has been studied using a combination of magnetometry and element specific soft X-ray spectroscopies. A large increase (>×30) in the magnetoelectric coefficient is found when Co2+ enters the trigonal bi-pyramidal site. The 5-fold trigonal bi-pyramidal site has been shown to provide an unusual mechanism for electric polarization based on the displacement of magnetic transition metal (TM) ions. For Co entering this site, an off-centre displacement of the cation may induce a large local electric dipole as well as providing an increased magnetostriction enhancing the magnetoelectric effect.
|
Feb 2018
|
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