I06-Nanoscience
|
D.
Pesquera
,
E.
Khestanova
,
M.
Ghidini
,
S.
Zhang
,
A. P.
Rooney
,
F.
Maccherozzi
,
P.
Riego
,
S.
Farokhipoor
,
J.
Kim
,
X.
Moya
,
M. E.
Vickers
,
N. A.
Stelmashenko
,
S. J.
Haigh
,
S. S.
Dhesi
,
N. D.
Mathur
Diamond Proposal Number(s):
[14745]
Open Access
Abstract: Epitaxial films may be released from growth substrates and transferred to structurally and chemically incompatible substrates, but epitaxial films of transition metal perovskite oxides have not been transferred to electroactive substrates for voltage control of their myriad functional properties. Here we demonstrate good strain transmission at the incoherent interface between a strain-released film of epitaxially grown ferromagnetic La0.7Sr0.3MnO3 and an electroactive substrate of ferroelectric 0.68Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 in a different crystallographic orientation. Our strain-mediated magnetoelectric coupling compares well with respect to epitaxial heterostructures, where the epitaxy responsible for strong coupling can degrade film magnetization via strain and dislocations. Moreover, the electrical switching of magnetic anisotropy is repeatable and non-volatile. High-resolution magnetic vector maps reveal that micromagnetic behaviour is governed by electrically controlled strain and cracks in the film. Our demonstration should inspire others to control the physical/chemical properties in strain-released epitaxial oxide films by using electroactive substrates to impart strain via non-epitaxial interfaces.
|
Jun 2020
|
|
I06-Nanoscience
|
M.
Wang
,
C.
Andrews
,
S.
Reimers
,
O. J.
Amin
,
P.
Wadley
,
R. P.
Campion
,
S. F.
Poole
,
J.
Felton
,
K. W.
Edmonds
,
B. L.
Gallagher
,
A. W.
Rushforth
,
O.
Makarovsky
,
K.
Gas
,
M.
Sawicki
,
D.
Kriegner
,
J.
Zubáč
,
K.
Olejník
,
V.
Novák
,
T.
Jungwirth
,
M.
Shahrokhvand
,
U.
Zeitler
,
S. S.
Dhesi
,
F.
Maccherozzi
Diamond Proposal Number(s):
[11846, 20793]
Abstract: We report magnetic-field-induced rotation of the antiferromagnetic Néel vector in epitaxial CuMnAs thin films. First, using soft x-ray magnetic linear dichroism spectroscopy as well as magnetometry, we demonstrate spin-flop switching and continuous spin reorientation in films with uniaxial and biaxial magnetic anisotropies, respectively, for applied magnetic fields of the order of 2 T. The remnant antiferromagnetic domain configurations are determined using x-ray photoemission electron microscopy. Next, we show that the Néel vector reorientations are manifested in the longitudinal and transverse anisotropic magnetoresistance. Dependencies of the electrical resistance on the orientation of the Néel vector with respect to both the electrical current direction and the crystal symmetry are identified, including a weak fourth-order term evident at high magnetic fields. The results provide characterization of key parameters including the anisotropic magnetoresistance coefficients, magnetocrystalline anisotropy, and spin-flop field in epitaxial films of tetragonal CuMnAs, a candidate material for antiferromagnetic spintronics.
|
Mar 2020
|
|
I06-Nanoscience
|
Massimo
Ghidini
,
Rhodri
Mansell
,
Raffaele
Pellicelli
,
David
Pesquera
,
Bhaskaran
Nair
,
Xavier
Moya
,
Saeedeh
Farokhipoor
,
Francesco
Maccherozzi
,
Crispin
Barnes
,
Russell
Cowburn
,
Sarnjeet
Dhesi
,
Neil
Mathur
Diamond Proposal Number(s):
[11843]
Abstract: Using photoemission electron microscopy (PEEM) to image ferromagnetism in polycrystalline Ni disks, and ferroelectricity in their single-crystal BaTiO3 substrates, we find that voltage-driven 90 ferroelectric domain switching serves to reversibly annihilate each magnetic vortex via uniaxial compressive strain, and that the orientation of the resulting bi domain reveals the chirality of the annihilated vortex. (Micromagnetic simulations reveal that only 60% of this strain was required for annihilation.) Voltage control of magnetic vortices is novel, and should be energetically favourable with respect to the use of a magnetic field or an electrical current. In future, stray field from bi domains could be exploited to read vortex chirality. Given that core polarity can already be read via stray field, our work represents a step towards four-state low power memory applications.
|
Feb 2020
|
|
I06-Nanoscience
|
Diamond Proposal Number(s):
[13723]
Abstract: A novel method of measuring the core level binding energies of multiple sized nanoparticles on the same substrate is demonstrated using the early stage of Au nanoparticle growth on reduced r-TiO2(110). This method employed in situ scanning tunneling microscopy (STM) and microfocused X-ray photoemission spectroscopy. An STM tip-shadowing method was used to synthesize patterned areas of Au nanoparticles on the substrate with different coverages and sizes. Patterns were identified and imaged using a UV photoelectron emission microscope. The Au 4f core level binding energies of the nanoparticles were investigated as a function of Au nanoparticle coverage and size. A combination of initial and final state effects modifies the binding energies of the Au 4f core levels as the nanoparticle size changes. When single Au atoms and Au3 clusters are present, the Au 4f7/2 binding energy, 84.42 eV, is similar to that observed at a high coverage (1.8 monolayer equivalent), resulting from a cancellation of initial and final state effects. As the coverage is increased, there is a decrease in binding energy, which then increases at a higher coverage to 84.39 eV. These results are consistent with a Volmer-Weber nucleation-growth model of Au nanoparticles at oxygen vacancies, resulting in electron transfer to the nanoparticles.
|
Jan 2020
|
|
I06-Nanoscience
|
L.
Baldrati
,
O.
Gomonay
,
A.
Ross
,
M.
Filianina
,
R.
Lebrun
,
R.
Ramos
,
C.
Leveille
,
F.
Fuhrmann
,
T. R.
Forrest
,
F.
Maccherozzi
,
S.
Valencia
,
F.
Kronast
,
E.
Saitoh
,
J.
Sinova
,
M.
Kläui
Diamond Proposal Number(s):
[18850, 20698]
Abstract: We probe the current-induced magnetic switching of insulating antiferromagnet–heavy-metal systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one-third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely, the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs.
|
Oct 2019
|
|
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
|
Sougata
Mallick
,
Sucheta
Mondal
,
Takeshi
Seki
,
Sourav
Sahoo
,
Thomas
Forrest
,
Francesco
Maccherozzi
,
Zhenchao
Wen
,
Saswati
Barman
,
Anjan
Barman
,
Koki
Takanashi
,
Subhankar
Bedanta
Diamond Proposal Number(s):
[16582]
Abstract: Materials suitable for magnonic crystals demand low magnetic damping and long spin-wave propagation distance. In this context
Co
-based Heusler compounds are ideal candidates for magnonic based applications. In this work, antidot arrays (with different shapes) of epitaxial
Co
2
Fe
0.4
Mn
0.6
Si
Heusler-alloy thin films are prepared using e-beam lithography and sputtering technique. Magneto-optic Kerr effect (MOKE) and ferromagnetic resonance analysis confirm the presence of dominant cubic and moderate uniaxial magnetic anisotropies in the thin film. Domain imaging via x-ray photoemission electron microscopy on the antidot arrays reveals chainlike switching or correlated bigger domains for different antidot shapes. Time-resolved MOKE microscopy is performed to study the precessional dynamics and magnonic modes of the antidots with different shapes. We show that the optically induced spin-wave spectra in such antidot arrays can be tuned by changing the shape of the holes. The variation in internal-field profiles, pinning energy barrier, and anisotropy modifies the spin-wave spectra dramatically within the antidot arrays with different shapes. We further show that by combining the magnetocrystalline anisotropy with the shape anisotropy, an extra degree of freedom can be achieved to control the magnonic modes in such antidot lattices.
|
Jul 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.
|
Apr 2019
|
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