Person:
Pérez García, Lucas

First Name

Lucas

Last Name

Pérez García

URI

https://hdl.handle.net/20.500.14352/75170

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

Area

Física Aplicada

Identifiers

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Now showing 1 - 10 of 23

Mixed effects of the atomic arrangement and surface chemistry on the electrodeposition of Bi thin films on n-GaAs substrates
(Journal of physical chemistry C, 2016) Prados Díaz, Alicia; Pérez García, Lucas; Guzmán, Alvaro; Ranchal Sánchez, Rocío
We have studied the electrodeposition of Bi thin films on two GaAs orientations with different atomic arrangement and chemical composition, (110) and (111)B. The electrochemical properties of each substrate have been analyzed by means of cyclic voltammetries and current transients. Then, X-ray diffraction has been used to determine the crystal structure and quality of the Bi films, and atomic force microscopy images have provided information about the surface morphology. Finally, the Bi/GaAs interface has been electrically characterized by means of capacitance-voltage and current-voltage curves. In this study, we have been able to discriminate between the effect of surface chemistry and the arrangement of surface atoms. The former has a direct effect on the reduction process of Bi(III) ions and on the electrical properties of the Bi/GaAs interface, whereas the atoms arrangement at the substrate surface determines the texture and morphology of the Bi films.
Epsilon iron oxide: Origin of the high coercivity stable low Curie temperature magnetic phase found in heated archeological materials
(Geochemistry geophysics geosystems, 2017) López Sánchez, Jesús; McIntosh, G.; Osete López, María Luisa; Campo García, A. del; Villalain, J.J.; Pérez García, Lucas; Kovacheva, M.; Rodríguez de la Fuente, Óscar
The identification of epsilon iron oxide (-Fe2O3) as the low Curie temperature high coercivity stable phase (HCSLT) carrying the remanence in heated archeological samples has been achieved in samples from two archeological sites that exhibited the clearest evidence of the presence of the HCSLT. This uncommon iron oxide has been detected by Confocal Raman Spectroscopy (CRS) and characterized by rock magnetic measurements. Large numbers of -Fe2O3 microaggregates (in CO) or isolated clusters (in HEL) could be recognized, distributed over the whole sample, and embedded within the ceramic matrix, along with hematite and pseudobrookite and with minor amounts of anatase, rutile, and maghemite. Curie temperature estimates of around 170 degrees C for CO and 190 degrees C for HEL are lower than for pure, synthetic -Fe2O3 (227 degrees C). This, together with structural differences between the Raman spectra of the archeologically derived and synthetic samples, is likely due to Ti substitution in the -Fe2O3 crystal lattice. The -Fe2O3--Fe2O3--Fe2O3 transformation series has been recognized in heated archeological samples, which may have implications in terms of their thermal history and in the factors that govern the formation of -Fe2O3.
Small Fluxgate Magnetometers: Development and Future Trends in Spain
(Sensors, 2010) Ciudad, David; Díaz Michelena, Marina; Pérez García, Lucas; Aroca, Claudio
In this paper, we give an overview of the research on fluxgate magnetometers carried out in Spain. In particular we focus in the development of the planar-type instruments. We summarize the fabrication processes and signal processing developments as well as their use in complex systems and space.
Formation of a magnetite/hematite epitaxial bilayer generated with low energy ion bombardment
(Applied physics letters, 2017) Ruiz Gómez, Sandra; Serrano, A.; Carabias,, I.; Garcıa, M. A.; Hernando Grande, Antonio; Mascaraque Susunaga, Arantzazu; Pérez García, Lucas; González Barrio, Miguel Ángel; Rodríguez de la Fuente, Óscar
We have used a low-energy ion bombardment to fabricate an epitaxial single-crystalline magnetite/hematite bilayer grown on Au(111). This non-conventional fabrication method involves the transformation of the upper layers of a single-crystalline hematite thin film to single-crystalline magnetite, a process driven by the preferential sputtering of oxygen atoms and favoured by the good structural matching of both phases. We show the reversibility of the transformation between hematite and magnetite, always keeping the epitaxial and single- crystalline character of the films. The magnetic characterization of the bilayer grown using this method shows that the magnetic response is mainly determined by the magnetite thin film, exhibiting a high coercivity. Published by AIP Publishing.
Role of the surface states in the magnetotransport properties of ultrathin bismuth films
(Physical review B, 2010) Marcano, N.; Sangiao, S.; Magén, C.; Morellon, L.; Ibarra,, M. R.; Plaza, M.; Pérez García, Lucas
We have investigated the magnetotransport properties of ultrathin films of Bi grown on thermally oxidized Si(001) substrates with thickness ranging from 10 to 100 nm at temperatures down to 2 K and in magnetic fields up to 90 kOe. Remarkable differences both in temperature and field dependence of the Hall resistivity are found for the films with thickness above and below 20 nm. These observations can be explained due to the presence of surface states, which play an important role in determining the electronic transport properties of the thinnest films. The estimated surface carrier density 4 x 10^(13) cm^(-2) at room temperature correlates well with that recently reported from angle-resolved photoemission spectroscopy on ultrathin Bi(001) films.
Magnetic behaviour of multisegmented FeCoCu/Cu electrodeposited nanowires
(Journal of physics D: applied physics, 2017) Núñez, A.; Pérez García, Lucas; Abuin Herráez, Manuel; Araujo, J. P.; Proenca, M. P.
Understanding the magnetic behaviour of multisegmented nanowires (NWs) is a major key for the application of such structures in future devices. In this work, magnetic/non-magnetic arrays of FeCoCu/Cu multilayered NWs electrodeposited in nanoporous alumina templates are studied. Contrarily to most reports on multilayered NWs, the magnetic layer thickness was kept constant (30 nm) and only the non-magnetic layer thickness was changed (0 to 80 nm). This allowed us to tune the interwire and intrawire interactions between the magnetic layers in the NW array creating a three-dimensional (3D) magnetic system without the need to change the template characteristics. Magnetic hysteresis loops, measured with the applied field parallel and perpendicular to the NWs' long axis, showed the effect of the non-magnetic Cu layer on the overall magnetic properties of the NW arrays. In particular, introducing Cu layers along the magnetic NW axis creates domain wall nucleation sites that facilitate the magnetization reversal of the wires, as seen by the decrease in the parallel coercivity and the reduction of the perpendicular saturation field. By further increasing the Cu layer thickness, the interactions between the magnetic segments, both along the NW axis and of neighbouring NWs, decrease, thus rising again the parallel coercivity and the perpendicular saturation field. This work shows how one can easily tune the parallel and perpendicular magnetic properties of a 3D magnetic layer system by adjusting the non-magnetic layer thickness.
Geometrically defined spin structures in ultrathin Fe₃O₄ with bulk like magnetic properties
(Nanoscale, 2018) Ruiz Gómez, Sandra; Pérez García, Lucas; Mascaraque Susunaga, Arantzazu; Quesada, Adrian; Prieto, Pilar; Palacio, Irene; Martín García, Laura; Foerster, Michael; Aballe, Lucía; Figuera, Juan de la
We have grown high quality magnetite microcrystals free from antiphase boundaries on Ru(0001) by reactive molecular beam epitaxy, conserving bulk magnetic properties below 20 nm thickness. Magnetization vector maps are obtained by X-ray spectromicroscopy and compared with micromagnetic simulations. The observed domain configurations are dictated purely by shape anisotropy, overcoming the possible influences of (magneto) crystalline anisotropy and defects, thus demonstrating the possibility of designing spin structures in ultrathin, magnetically soft magnetite at will.
Use of magnets for reversible restoration in sculpture. The case of the "Virgen de los Desamparados" in Valencia (Spain)
(Journal of cultural heritage, 2018) Azahara Rodríguez, M.; Ruiz Gómez, Sandra; Pérez García, Lucas; Mas Barberà, Xavier
In this paper, we present the use of a magnetic system for restoring a real piece of art: the Virgen de los Desamparados sculpture (1954) by the Valencian sculptor Silvestre d'Edeta (Valencia, Spain). This sculpture is made of artificial stone reinforced with iron rods in the matrix and, before the intervention, showed a high degree of degradation due to various physical, chemical and biological processes causing internal strain, cracks and fragmentation. Several non-destructive imaging techniques (photography, photogrammetry, digital radiography and 3D virtual reconstruction) have been used to study the original status of the artwork. The materials to produce the prosthesis to restore the sculpture, and the procedure to attach them with magnets and various adhesives, have been addressed in this study. Different theoretical models and simulations have been developed to help the restorer to select the most appropriate magnets and their optimal position. The restoration returns legibility to the piece by restoring the missing head-hair-crown section.
Tailoring the magnetization states in 2D arrays of multiresponse ferromagnetic nanomagnets
(Journal of physics D: applied physics, 2017) Abuin Herráez, Manuel; Maicas, Marco; García, M Ángel; Pérez García, Lucas; Mascaraque Susunaga, Arantzazu
We have fabricated Fe52-54Co46-48 nanomagnet arrays as a function of several geometrical parameters like the spacing between nanostructures, the aspect ratio and the layers thicknesses. The nanomagnets consist in two magnetic layers, separated by a non magnetic interlayer, that interact through magnetostatic coupling. They present a multiresponse hysteresis loops with two different switching fields. We have performed micromagnetic simulations to discern the role play by the different interactions. The spacing in the array strongly modifies the saturating field along the short axis and the magnetization reversal mechanisms from coherent rotation to domain wall nucleation. A small asymmetry between the two magnetic layers favors a magnetization reversal mechanism along the long axis with two different switching fields. These fields can be tailored through the thickness of the layers or the inter-element spacing in the array. In trilayers with the same magnetic layer thicknesses, the asymmetry can be induced by growing the two magnetic layers with a different anisotropy. The well-defined reversal fields make these nanomagnets potentially useful for magnetic tagging.
Structure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy
(Scientific reports, 2018) Ruiz Gómez, Sandra; Pérez García, Lucas; Mandziak, Anna; Figuera, Juan de la; Delgado Soria, Guiomar; Prieto Recio, Pilar; Quesada, Adrián; Foerster, Michael; Aballe, Lucía
We demonstrate the preparation of ultrathin Fe-rich nickel ferrite (NFO) islands on a metal substrate. Their nucleation and growth are followed in situ by low-energy electron microscopy (LEEM). A comprehensive characterization is performed combining LEEM for structural characterization and PEEM (PhotoEmission Electron Microscopy) with synchrotron radiation for chemical and magnetic analysis via X-ray Absorption Spectroscopy and X-ray Magnetic Circular Dichroism (XAS-PEEM and XMCD-PEEM, respectively). The growth by oxygen-assisted molecular beam epitaxy takes place in two stages. First, islands with the rocksalt structure nucleate and grow until they completely cover the substrate surface. Later three-dimensional islands of spinel phase grow on top of the wetting layer. Only the spinel islands show ferromagnetic contrast, with the same domains being observed in the Fe and Ni XMCD images. The estimated magnetic moments of Fe and Ni close to the islands surface indicate a possible role of the bi-phase reconstruction. A significant out-of-plane magnetization component was detected by means of XMCD-PEEM vector maps.