Arantxa Fraile Rodríguez

Institut de Nanociència i Nanotecnologia de la Universitat de Barcelona

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Co-Authors

F. Nolting

Paul Scherrer Institute

A. Labarta

Universitat de Barcelona

X. Batlle

Universitat de Barcelona

L. J. Heyderman

Paul Scherrer Institute

Armin Kleibert

Paul Scherrer Institute

A. López‐Echarri

University of the Basque Country

Carlos Moya

Universitat de Barcelona

I. Ruiz‐Larrea

University of the Basque Country

Mariona Escoda-Torroella

Universitat de Barcelona

A. Asenjo

Instituto de Ciencia de Materiales de Madrid

Cooperative Institutions

Paul Scherrer Institute

Centre National de la Recherche Scientifique

Consejo Superior de Investigaciones Científicas

Lawrence Berkeley National Laboratory

Swiss Light Source

École Polytechnique Fédérale de Lausanne

Instituto de Ciencia de Materiales de Madrid

University of California, Berkeley

Universitat de Barcelona

Argonne National Laboratory

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Selective anisotropic growth of Bi₂S₃ nanoparticles with adjustable optical properties

Physical Chemistry Chemical Physics (2022)

Mariona Escoda-Torroella Carlos Moya José A. Ruiz-Torres Arantxa Fraile Rodríguez A. Labarta

We report on the controlled synthesis and functionalization in two steps of elongated Bi2S3 nanoparticles within a wide range of sizes. First, we show the effect of the temperature and reaction time on the synthesis of two series of nanoparticles by the reaction of thioacetamide with bismuth(III) neodecanoate in the presence of organic surfactants. At 105 °C and long reaction times, nanoneedles of about 45 nm in length containing larger crystallites are obtained, while highly crystalline nanorods of about 30 nm in length are dominant at 165 °C, regardless of the reaction time. The optical properties of both types of nanoparticles show an enhancement of the band gap compared to bulk Bi2S3. This is likely to arise from quantum confinement effects caused by the small particle dimensions relative to the typical exciton size, together with an increase in near-infrared absorption due to the anisotropic particle shape. Second, a ligand exchange approach has been developed to transfer the Bi2S3 nanoparticles to aqueous solutions by grafting dimercaptosuccinic acid onto the surface of the particles. The as-prepared coated nanoparticles show good stability in water, in a wide biological pH range, and in phosphate-buffered saline solutions. Overall, this work highlights the controlled design at all levels - from the inorganic core to the organic surface coating - of elongated Bi2S3 nanoparticles, leading to a tunable optical response by tuning their morphology and size.

Nanorod

Surface Modification

Particle (ecology)

10.1039/d2cp05437j

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Thin Cr₂O₃ Films for Magnetoelectric Data Storage Deposited by Reactive E-beam Evaporation

Ferroelectrics (2008)

Pavel Borisov A. Hochstrat Vladimir V. Shvartsman W. Kleemann T. Eimüller

Magnetoelectric materials are proposed for use in magnetic memory applications. The main idea of the Magnetoelectric Random Access Memory (MERAM) is to enable electrical data writing in a magnetoelectric antiferromagnet, while the principle of the magnetoresistive data reading remains. As a possible medium for magnetoelectric data storage Cr 2 O 3 is proposed. Thin films of Cr 2 O 3 have been grown on a [0001] sapphire substrate by reactive e-beam evaporation of Cr 2 O 3 in an O 2 atmosphere. The out-of plane orientation of the thin Cr 2 O 3 films and the chemical environment of Cr 3+ ions are evidenced by X-Ray diffractometry and absorption spectroscopy. Surface characterization has been done by atomic force microscopy. At decreasing temperature the conductivity shows an exponentional decrease, which is probably due to hopping via small amounts of Cr 3 O 4 .

Characterization

10.1080/00150190802384518

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Citations (18)

Relationship between Nonadiabaticity and Damping in Permalloy Studied by Current Induced Spin Structure Transformations

Physical Review Letters (2008)

L. Heyne Mathias Kläui D. Backes T. A. Moore S. Krzyk

By direct imaging we determine spin structure changes in Permalloy wires and disks due to spin transfer torque as well as the critical current densities for different domain wall types. Periodic domain wall transformations from transverse to vortex walls and vice versa are observed, and the transformation mechanism occurs by vortex core displacement perpendicular to the wire. The results imply that the nonadiabaticity parameter beta does not equal the damping alpha, in agreement with recent theoretical predictions. The vortex core motion perpendicular to the current is further studied in disks revealing that the displacement in opposite directions can be attributed to different polarities of the vortex core.

Permalloy

Domain wall (magnetism)

Spin-transfer torque

10.1103/physrevlett.100.066603

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Citations (85)

Domain Wall Propagation and Pinning Induced by Current Pulses in Cylindrical Modulated Nanowires

arXiv (Cornell University) (2022)

C. Bran Jose Ángel Fernández-Roldán Julián A. Moreno Arantxa Fraile Rodríguez R. P. del Real

The future developments of three-dimensional magnetic nanotechnology require the control of domain wall dynamics by means of current pulses. While this has been extensively studied in planar magnetic strips (planar nanowires), few reports exist in cylindrical geometry, where Bloch point domain walls are expected to have intriguing properties. Here we report this investigation in cylindrical magnetic Ni nanowires with geometrical notches. Experimental work based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with photoemission electron microscopy (PEEM) indicates that large current densities induce domain wall nucleation while smaller currents move domain walls preferably against the current direction. In the region where no pinning centers are present we found domain wall velocity of about 1 km/s. The domain wall motion along current was also detected in the vicinity of the notch region. Pinning of domain walls has been observed not only at geometrical constrictions but also outside of them. Thermal modelling indicates that large current densities temporarily raise the temperature in the nanowire above the Curie temperature leading to nucleation of domain walls during the system cooling. Micromagnetic modelling with spin-torque effect shows that for intermediate current densities Bloch point domain walls with chirality parallel to the Oersted field propagate antiparallel to the current direction. In other cases, domain walls can be bounced from the notches and/or get pinned outside their positions. We thus find that current is not only responsible for the domain wall propagation but is also a source of pinning due to the Oersted field action.

Domain wall (magnetism)

Photoemission electron microscopy

Antiparallel (mathematics)

10.48550/arxiv.2210.01480

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Analog control of electrical conductivity in La0.5Sr0.5FeO3-{\delta} through oxygen deficiency induced magnetic transition

arXiv (Cornell University) (2024)

Paul Nizet Francesco Chiabrera Nicolau López‐Pintó Nerea Alayo Philipp Langner

Switchability of materials properties by applying controlled stimuli such as voltage pulses is an emerging field of study with applicability in adaptive and programmable devices like neuromorphic transistors or non-emissive smart displays. One of the most exciting approaches to modulate materials performance is mobile ion/vacancy insertion for inducing changes in relevant electrical, optical, or magnetic properties, among others. Unveiling the interplay between changes in the concentration of mobile defects (like oxygen vacancies) and functional properties in relevant materials represents a step forward for underpinning the emerging oxide iontronics discipline. In this work, electrochemical oxide-ion pumping cells were fabricated for an analog control of the oxygen stoichiometry in thin films of mixed ionic-electronic conductor La0.5Sr0.5FeO3-{\delta}. We demonstrate over more than 4 orders of magnitude electronic conductivity control within the same crystallographic phase through the precise and continuous voltage control of the oxygen stoichiometry. We show that behind the modification of the transport properties of the material lays a paramagnetic-to-antiferromagnetic transition. We exploit such magnetoelectric coupling to show control over the exchange interaction between La0.5Sr0.5FeO3-{\delta} and a ferromagnetic Co layer deposited on top.

Oxygen deficiency

10.48550/arxiv.2408.02539

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Imaging of magnetic nanodots on self-organized semiconductor substrates

Physical Review B (2005)

A. M. Mulders Arantxa Fraile Rodríguez D. Arvanitis Christina Hofer Christian Teichert

Arrays of magnetic nanodots have been prepared by evaporation in ultrahigh vacuum onto self-organized templates consisting of nanometric pyramids of SiGe alloy previously grown on Si(001). Co was deposited by molecular beam epitaxy at grazing incidence, so that preferential deposition occurs on the island facets facing the Co flux. The films' structural and magnetic morphology has been characterized by means of mirror electron microscopy and x-ray photoemission electron microscopy with magnetic circular dichroism. The morphology of the Co deposit is dictated by the surface template. The Co dots are elongated along the direction perpendicular to deposition due to geometrical factors of the surface at grazing incidence and via steering by the surface steps, and this promotes an uniaxial magnetic anisotropy in this direction. The dots are ferromagnetic and single domain at room temperature. Macroscopic magnetic domains composed of several dots are observed. This indicates that the dipolar interaction between them is stronger than the coercivity and the exchange interaction is minimized.

Nanodot

Photoemission electron microscopy

10.1103/physrevb.71.214422

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Citations (12)

Tunable circular dichroism through absorption in coupled optical modes of twisted triskelia nanostructures

Scientific Reports (2022)

Javier Rodríguez-Álvarez Antonio García‐Martín Arantxa Fraile Rodríguez X. Batlle A. Labarta

We present a system consisting of two stacked chiral plasmonic nanoelements, so-called triskelia, that exhibits a high degree of circular dichroism. The optical modes arising from the interactions between the two elements are the main responsible for the dichroic signal. Their excitation in the absorption cross section is favored when the circular polarization of the light is opposite to the helicity of the system, so that an intense near-field distribution with 3D character is excited between the two triskelia, which in turn causes the dichroic response. Therefore, the stacking, in itself, provides a simple way to tune both the value of the circular dichroism, up to 60%, and its spectral distribution in the visible and near infrared range. We show how these interaction-driven modes can be controlled by finely tuning the distance and the relative twist angle between the triskelia, yielding maximum values of the dichroism at 20{\deg} and 100{\deg} for left- and right-handed circularly polarized light, respectively. Despite the three-fold symmetry of the elements, these two situations are not completely equivalent since the interplay between the handedness of the stack and the chirality of each single element breaks the symmetry between clockwise and anticlockwise rotation angles around 0{\deg}. This reveals the occurrence of clear helicity-dependent resonances. The proposed structure can be thus finely tuned to tailor the dichroic signal for applications at will, such as highly efficient helicity-sensitive surface spectroscopies or single-photon polarization detectors, among others.

Dichroic glass

Helicity

Dichroism

Linear dichroism

Chirality

10.1038/s41598-021-03908-2

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Citations (4)

Geometric frustration in a hexagonal lattice of plasmonic nanoelements

Optics Express (2018)

Ana Conde‐Rubio Arantxa Fraile Rodríguez Xavier Borrisé Francesc Pérez‐Murano X. Batlle

We introduce the concept of geometric frustration in plasmonic arrays of nanoelements. In particular, we present the case of a hexagonal lattice of Au nanoasterisks arranged so that the gaps between neighboring elements are small and lead to a strong near-field dipolar coupling. Besides, far-field interactions yield higher-order collective modes around the visible region that follow the translational symmetry of the lattice. However, dipolar excitations of the gaps in the hexagonal array are geometrically frustrated for interactions beyond nearest neighbors, yielding the destabilization of the low energy modes in the near infrared. This in turn results in a slow dynamics of the optical response and a complex interplay between localized and collective modes, a behavior that shares features with geometrically frustrated magnetic systems.

Hexagonal Lattice

Lattice (music)

Translational symmetry

10.1364/oe.26.020211

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Citations (5)

Selective Control over the Morphology and the Oxidation State of Iron Oxide Nanoparticles

Langmuir (2020)

Mariona Escoda-Torroella Carlos Moya Arantxa Fraile Rodríguez X. Batlle A. Labarta

Iron oxide nanoparticles (NPs) have been extensively used for both health and technological applications. The control over their morphology, crystal microstructure, and oxidation state is of great importance to optimize their final use. However, while mature in understanding, it is still far from complete. Here we report on the effect of the amount of 1,2-hexadecanediol and/or 1-octadecene in the reaction mixture on the thermal decomposition of iron(III) acetylacetonate in oleic acid for two series of iron oxide NPs with sizes ranging from 6 to 48 nm. We show that a low amount of either compound leads to both large, mixed-phase NPs composed of magnetite (Fe3O4) and wüstite (FeO) and high reaction yields. In contrast, a higher amount of either 1,2-hexadecanediol or 1-octadecene gives rise to smaller, single-phase NPs with moderate reaction yields. By infrared spectroscopy, we have elucidated the role of 1,2-hexadecanediol, which mediates the particle nucleation and growth. Finally, we have correlated the magnetic response and the structural features of the NPs for the two series of samples.

Wüstite

Iron oxide nanoparticles

Oxidation state

Morphology

Particle (ecology)

10.1021/acs.langmuir.0c02221

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Citations (23)

Probing ferroelectricity inPbZr0.2Ti0.8O3with polarized soft x rays

Physical Review B (2010)

Elke Arenholz G. van der Laan Arantxa Fraile Rodríguez Pu Yu Qing He

The reduction in symmetry associated with the onset of ferroelectric order in ${\text{PbZr}}_{0.2}{\text{Ti}}_{0.8}{\text{O}}_{3}$ (PZT) thin films leads to a pronounced difference at the $\text{Ti}\text{ }{L}_{3,2}$ absorption edges between spectra measured with the x-ray linear polarization perpendicular and parallel to the ferroelectric polarization. We introduce a general method to analyze the observed difference spectra using atomic multiplet calculations. Moreover, we find experimental evidence for structural changes in PZT induced by the reversal of the ferroelectric polarization.

Multiplet

10.1103/physrevb.82.140103

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Citations (43)