Person: Ruiz Gómez, Sandra
Universidad Complutense de Madrid
Faculty / Institute
Física de Materiales
Now showing 1 - 10 of 15
- PublicationNanomateriales para almacenamiento magnético de información(Universidad Complutense de Madrid, 2020-11-10) Ruiz Gómez, Sandra; Mascaraque Susunaga, Arantzazu; Pérez García, LucasEn los últimos años, la llegada de las nuevas tecnologías y la digitalización ha llevado asociada un aumento exponencial de la cantidad de datos generados. Desde un punto de vista tecnológico esto plantea nuevos retos que abordar. Un aumento exponencial de la cantidad de datos no puede suponer un aumento también exponencial del espacio en el que almacenarlos. Es evidente que se necesitan sistemas con una densidad mayor de almacenamiento de información. A su vez, el aumento de los datos almacenados lleva ligado un aumento del tiempo de acceso por lo que es necesario aumentar también la velocidad de acceso. Pero además, mantener la información guardada y trabajar con ella está empezando a suponer un problema serio de consumo de energía que es necesario afrontar...
- PublicationHighly Bi-doped Cu thin films with large spin-mixing conductance(American Institute of Physics, 2018-10-22) Ruiz Gómez, Sandra; González Barrio, Miguel Ángel; Mascaraque Susunaga, Arantzazu; Pérez García, Lucas; Serrano, Aída; Guerrero, Rubén; Muñoz, Manuel; Lucas, Irene; Foerster, Michael; Aballe, LucíaThe spin Hall effect (SHE) provides an efficient tool for the production of pure spin currents, essentially for the next generation of spintronics devices. Giant SHE has been reported in Cu doped with 0.5% Bi grown by sputtering, and larger values are predicted for larger Bi doping. In this work, we demonstrate the possibility of doping Cu with up to 10% of Bi atoms without evidence of Bi surface segregation or cluster formation. In addition, YIG/BiCu structures have been grown, showing a spin mixing conductance larger that the one shown by similar Pt/YIG structures, reflecting the potentiality of these newmaterials.
- PublicationGraphene foam functionalized with electrodeposited nickel hydroxide for energy applications(Elsevier Science SA, 2015-08) Ruiz Gómez, Sandra; Boscá, Alberto; Pérez García, Lucas; Pedrós, Jorge; Martínez, Javier; Páez, Antonio; Calle de la Rosa, Lucia de la; Calle, FernandoThe need of new systems for the storage and conversion of renewable energy sources is fueling the research in supercapacitors. In this work, we propose a low temperature route for the synthesis of electrodes for these supercapacitors: electrodeposition of a transition metal hydroxide-Ni(OH)₂ on a graphene foam. This electrode combines the superior mechanical and electrical properties of graphene, the large specific surface area of the foam and the large pseudocapacitance of Ni(OH)₂. We report a specific capacitance up to 900 F/g as well as specific power and energy comparable to active carbon electrodes. These electrodes are potential candidates for their use in energy applications.
- PublicationFormation of a magnetite/hematite epitaxial bilayer generated with low energy ion bombardment(American Institute of Physics, 2017-02-27) 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.
- PublicationHelical surface magnetization in nanowires: the role of chirality(Royal Society of Chemistry, 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.
- PublicationGeometrically defined spin structures in ultrathin Fe₃O₄ with bulk like magnetic properties(Royal Society of Chemistry, 2018-03-28) 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.
- PublicationStructure and magnetism of ultrathin nickel-iron oxides grown on Ru(0001) by high-temperature oxygen-assisted molecular beam epitaxy(Nature publishing group, 2018-12-19) Ruiz Gómez, Sandra; Pérez García, Lucas; Mandziak, Anna; Figuera, Juan de la; Delgado Soria, Guiomar; Prieto Recio, Pilar; Quesada, Adrián; Foerster, Michael; Aballe, LucíaWe 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.
- PublicationUse of magnets for reversible restoration in sculpture. The case of the "Virgen de los Desamparados" in Valencia (Spain)(Elsevier, 2018-05) 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.
- PublicationDense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process(Elsevier Science SA, 2022-05-21) García Martín, Eduardo; Granados Miralles, Cecilia; Ruiz Gómez, Sandra; Pérez García, Lucas; Campo, Adolfo del; Guzmán Mínguez, Jesús C.; Julián Fernández, César de; Quesada, Adrián; Fernández, José F.; Serrano, AidaThe use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post annealing at 1100 degrees C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage <= 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets.
- PublicationEpitaxial integration of CoFe₂O₄ thin films on Si (001) surfaces using TiN buffer layers(Elsevier Science B. V., 2018-04-01) Prieto, Pilar; Marco, F.; Prieto, José E.; Ruiz Gómez, Sandra; Pérez García, Lucas; Perez del Real, Rafael; Velazquez, Manuel; De laFiguera, JuanEpitaxial cobalt ferrite thin films with strong in-plane magnetic anisotropy have been grown on Si (001) substrates using a TiN buffer layer. The epitaxial films have been grown by ion beam sputtering using either metallic, CoFe₂, or ceramic, CoFe₂2O₄, targets. X-ray diffraction (XRD) and Rutherford spectrometry (RBS) in random and channeling configuration have been used to determine the epitaxial relationship CoFe₂O₄ /TiN /Si . Mossbauer spectroscopy, in combination with XRD and RBS, has been used to determine the composition and structure of the cobalt ferrite thin films. The TiN buffer layer induces a compressive strain in the cobalt ferrite thin films giving rise to an in-plane magnetic anisotropy. The degree of in- plane anisotropy depends on the lattice mismatch between CoFe₂O₂ and TiN, which is larger for CoFe₂O₄ thin films grown on the reactive sputtering process with ceramic targets.