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
9 results
Search Results
Now showing 1 - 9 of 9
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 Electrodeposited magnetic nanowires with radial modulation of composition(Nanomaterials, 2022) Fernández González, Claudia; Guedeja-Marrón Gil, Alejandra; Rodilla González, Beatriz Loreto; Arché Nuñez, Ana; Corcuera, Rubén; Lucas, Irene; González, María Teresa; Varela del Arco, María; Presa Muñoz del Toro, Patricia de la; Aballe, Lucía; Pérez García, Lucas; Ruíz Gómez, SandraIn the last few years, magnetic nanowires have gained attention due to their potential implementation as building blocks in spintronics applications and, in particular, in domain-wall- based devices. In these devices, the control of the magnetic properties is a must. Cylindrical magnetic nanowires can be synthesized rather easily by electrodeposition and the control of their magnetic properties can be achieved by modulating the composition of the nanowire along the axial direction. In this work, we report the possibility of introducing changes in the composition along the radial direction, increasing the degrees of freedom to harness the magnetization. In particular, we report the synthesis, using template-assisted deposition, of FeNi (or Co) magnetic nanowires, coated with a Au/Co (Au/FeNi) bilayer. The diameter of the nanowire as well as the thickness of both layers can be tuned at will. In addition to a detailed structural characterization, we report a preliminary study on the magnetic properties, establishing the role of each layer in the global collective behavior of the system.Item Asymmetrical magnetization processes induced by compositional gradients in ferromagnetic nanowires(Scripta Materialia, 2024) Fernández-González, Claudia; Berja, Alba; Álvaro-Gómez, Laura; Martín-Rubio, Carolina; Mascaraque Susunaga, Arantzazu; Aballe, Lucía; Sanz, Ruy; Ruiz-Gómez, Sandra; Pérez García, LucasElectrodeposited nanowires are an excellent scenario to study and control magnetic domain wall motion in nanostructures. In particular, the introduction of local changes in composition during the growth procedure has been proven to be very efficient for controlling the magnetization dynamics. In this work, we show the possibility of introducing compositional gradients in FeNi electrodeposited nanowires by gradually changing the Fe/Ni ratio along their axis. These compositional gradients produce an asymmetrical landscape for domain wall motion which is reflected in asymmetrical magnetization processes under an applied magnetic field. By studying nanowires with different compositional gradients we were able to correlate composition and magnetic asymmetry. Our results pave the way towards full control of the movement of domain walls along the nanowires.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.