Person: Pérez García, Lucas
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First Name
Lucas
Last Name
Pérez García
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Físicas
Department
Física de Materiales
Area
Física Aplicada
Identifiers
42 results
Search Results
Now showing 1 - 10 of 42
Item 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, RocíoWe 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.Item 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, ÓscarThe 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.Item Small Fluxgate Magnetometers: Development and Future Trends in Spain(Sensors, 2010) Ciudad, David; Díaz Michelena, Marina; Pérez García, Lucas; Aroca, ClaudioIn 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.Item 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, ÓscarWe 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.Item 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, LucasWe 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.Item Helical surface magnetization in nanowires: the role of chirality(Nanoscale, 2020) Ruiz Gómez, Sandra; Fernández González, Claudia; Martínez, Eduardo; Raposo, Víctor; Sorrentino, Andrea; Foerster, Michael; Aballe, Lucía; Mascaraque Susunaga, Arantzazu; Ferrer, Salvador; Pérez García, LucasNanomagnetism is nowadays expanding into three dimensions, triggered by the discovery of new magnetic phenomena and their potential use in applications. This shift towards 3D structures should be accompanied by strategies and methodologies to map the tridimensional spin textures associated. We present here a combination of dichroic X-ray transmission microscopy at different angles and micromagnetic simulations allowing to determine the magnetic configuration of cylindrical nanowires. We have applied it to permalloy nanowires with equispaced chemical barriers that can act as pinning sites for domain walls. The magnetization at the core is longitudinal and generates at the surface of the wire helical magnetization. Different types of domain walls are found at the pinning sites, which respond differently to applied fields depending on the relative chirality of the adjacent domains.Item 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.Item Large magnetoresistance of isolated domain walls in La_(0.7)Sr(0.3)MnO_3 nanowires(Advanced Materials, 2023) Orfila Rodríguez, Gloria; Sanchez-Manzano, David; Arora, Ashima; Cuéllar Jiménez, Fabian Andrés; Ruiz Gómez, Sandra; Rodriguez-Corvillo, Sara; López, Sandra; Peralta, Andrea; Carreira, Santiago J.; Gallego, Fernando; Tornos Castillo, Javier; Rouco Gómez, Víctor; Riquelme, Juan J.; Munuera, Carmen; Mompean, Federico J.; Garcia-Hernandez, Mar; Sefrioui Khamali, Zouhair; Villegas Hernández, Javier Eulogio; Pérez García, Lucas; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Valencia, Sergio; Santamaría Sánchez-Barriga, JacoboGeneration, manipulation, and sensing of magnetic domain walls are cornerstones in the design of efficient spintronic devices. Half-metals are amenable for this purpose as large low field magnetoresistance signals can be expected from spin accumulation at spin textures. Among half metals, La1−xSrxMnO3 (LSMO) manganites are considered as promising candidates for their robust half-metallic ground state, Curie temperature above room temperature (Tc = 360 K, for x = 1/3), and chemical stability. Yet domain wall magnetoresistance is poorly understood, with large discrepancies in the reported values and conflicting interpretation of experimental data due to the entanglement of various source of magnetoresistance, namely, spin accumulation, anisotropic magnetoresistance, and colossal magnetoresistance. In this work, the domain wall magnetoresistance is measured in LSMO cross-shape nanowires with single-domain walls nucleated across the current path. Magnetoresistance values above 10% are found to be originating at the spin accumulation caused by the mistracking effect of the spin texture of the domain wall by the conduction electrons. Fundamentally, this result shows the importance on non-adiabatic processes at spin textures despite the strong Hund coupling to the localized t2g electrons of the manganite. These large magnetoresistance values are high enough for encoding and reading magnetic bits in future oxide spintronic sensors.Item 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 laWe 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.Item 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, XavierIn 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.