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
8 results
Search Results
Now showing 1 - 8 of 8
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 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 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, 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.Item Direct x-ray detection of the spin hall effect in CuBi(Physical review X, 2022) Ruiz Gómez, Sandra; Guerrero, Rubén; Khaliq, Muhammad W; Fernández González, Claudia; Prat, Jordi; Valera, Andrés; Finizio, Simone; Perna, Paolo; Camarero, Julio; Pérez García, Lucas; Aballe, Lucía; Foerster, MichaelThe spin Hall effect and the inverse spin Hall effect are important spin-charge conversion mechanisms. The direct spin Hall effect induces a surface spin accumulation from a transverse charge current due to spin-orbit coupling even in nonmagnetic conductors. However, most detection schemes involve additional interfaces, leading to large scattering in reported data. Here we perform interface-free x-ray spectroscopy measurements at the Cu L_(3;2) absorption edges of highly Bi-doped Cu (Cu_(95)Bi_5). The detected x-ray magnetic circular dichroism signal corresponds to an induced magnetic moment of (2.2 + 0.5) x 10^(-12) mu(B) A^(-1) cm^(2) per Cu atom averaged over the probing depth, which is of the same order of magnitude as found for Pt measured by magneto-optics. The results highlight the importance of interface-free measurements to assess material parameters and the potential of CuBi for spin-charge conversion applications.Item Scaling up the production of electrodeposited nanowires: a roadmap towards applications(Nanomaterials, 2021) Fernández González, Claudia; Guzmán Mínguez, Jesús C.; Guedeja-Marrón Gil, Alejandra; García Martín, Eduardo; Foerster, Michael; Niño, Miguel Ángel; Aballe, Lucía; Quesada, Adrian; Pérez García, Lucas; Ruiz Gómez, SandraThe use of metallic nanowires is mostly reduced to scientific areas where a small quantity of nanostructures are needed. In order to broaden the applicability of these nanomaterials, it is necessary to establish novel synthesis protocols that provide a larger amount of nanowires than the conventional laboratory fabrication processes at a more competitive cost. In this work, we propose several modifications to the conventional electrochemical synthesis of nanowires in order to increase the production with considerably reduced production time and cost. To that end, we use a soft anodization procedure of recycled aluminum at room temperature to produce the alumina templates, followed by galvanostatic growth of CoFe nanowires. We studied their morphology, composition and magnetic configuration, and found that their properties are very similar to those obtained by conventional methods.Item Initial stages of the growth of mixed iron-cobalt oxides on Ru(0001)(Physics procedia, 2016) Martín García, Laura; Quesadab, Adrian; Pérez García, Lucas; Foerster, Michael; Aballe, Lucia; Figuera, Juan de laMixed iron-cobalt oxides have been grown on a Ru(0001) single crystal substrate by reactive molecular beam epitaxy. The growth has been followed by low-energy electron microscopy and diffraction. Chemical characterization has been performed by selected area x-ray absorption spectroscopy. As previously known, iron grows into a wetting layer of FeO. In contrast, cobalt grows into three-dimensional islands of CoO, of either with a (111) –most common-or a (100) orientation. For mixed compositions, flat 2D growth is regained. Depending on temperature, either segregation into two FeCo compositions or a single phase is detected. In all cases the structure corresponds to an in-plane expanded (111)-oriented halite one. When only one phase is observed or for the Co-rich phase in the two phase film, its crystal structure is rotated by 30. relative to the Ru substrate, unlike the Co-poor phase which appears aligned with the substrate.Item Highly Bi-doped Cu thin films with large spin-mixing conductance(APL Materials, 2018) 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.Item Observation of a topologically protected state in a magnetic domain wall stabilized by a ferromagnetic chemical barrier(Scientific reports, 2018) Ruiz Gómez, Sandra; Mascaraque Susunaga, Arantzazu; Pérez García, Lucas; Foerster, Michael; Aballe, Lucía; Proenca, M. P.; Lucas, Irene; Prieto, José Luis; Figuera, Juan de la; Quesada, AdriánThe precise control and stabilization of magnetic domain walls is key for the development of the next generation magnetic nano-devices. Among the multitude of magnetic configurations of a magnetic domain wall, topologically protected states are of particular interest due to their intrinsic stability. In this work, using XMCD-PEEM, we have observed a topologically protected magnetic domain wall in a ferromagnetic cylindrical nanowire. Its structure is stabilized by periodic sharp alterations of the chemical composition in the nanowire. The large stability of this topologically protected domain wall contrasts with the mobility of other non-protected and non-chiral states also present in the same nanowire. The micromagnetic simulations show the structure and the conditions required to find the topologically protected state. These results are relevant for the design of future spintronic devices such as domain wall based RF oscillators or magnetic memories.