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 41

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.
Influence of coating and size of magnetic nanoparticles on cellular uptake for in vitro MRI
(Nanomaterials, 2021) Cortés Llanos, Belén; Ocampo, Sandra M.; Cueva, Leonor de la; Calvo, Gabriel F.; Belmonte Beitia, Juan; Pérez García, Lucas; Salas, Gorka; Ayuso Sacido, Ángel
Iron oxide nanoparticles (IONPs) are suitable materials for contrast enhancement in magnetic resonance imaging (MRI). Their potential clinical applications range from diagnosis to therapy and follow-up treatments. However, a deeper understanding of the interaction between IONPs, culture media and cells is necessary for expanding the application of this technology to different types of cancer therapies. To achieve new insights of these interactions, a set of IONPs were prepared with the same inorganic core and five distinct coatings, to study their aggregation and interactions in different physiological media, as well as their cell labelling efficiency. Then, a second set of IONPs, with six different core sizes and the same coating, were used to study how the core size affects cell labelling and MRI in vitro. Here, IONPs suspended in biological media experience a partial removal of the coating and adhesion of molecules. The FBS concentration alters the labelling of all types of IONPs and hydrodynamic sizes & GE; 300 nm provide the greatest labelling using the centrifugation-mediated internalization (CMI). The best contrast for MRI results requires a core size range between 12-14 nm coated with dimercaptosuccinic acid (DMSA) producing R_2^* values of 393.7 s_(-1) and 428.3 s_(-1), respectively. These findings will help to bring IONPs as negative contrast agents into clinical settings.
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, Michael
The 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.
Tailoring magnetic anisotropy at will in 3d interconnected nanowire networks
(Physica status solidi-rapid research letters, 2019) Ruiz Clavijo, Alejandra; Ruiz Gómez, Sandra; Caballero Calero, Olga; Pérez García, Lucas; Martín González, Marisol
The control of magnetic anisotropy has been the driving force for the development of magnetic applications in a wide range of technological fields from sensing to spintronics. In recent years, the possibility of tailoring the magnetic properties goes together with a need for new 3D materials to expand the applications to a new generation of devices. Herein, the possibility of designing the magnetic anisotropy of 3D magnetic nanowire networks is shown just by modifying the geometry of the structure or by composition. It is also shown that this is possible when the magnetic properties of the structure are governed by magnetostatic anisotropy. The present approach can guide systematic tuning of the magnetic easy axis and coercivity in the desired direction at the nanoscale. Importantly, this can be achieved on virtually any magnetic material, alloy, or multilayers that can be prepared inside porous alumina. These results are promising for engineering novel magnetic devices that exploit tailored magnetic anisotropy using metamaterials concept.
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, Sandra
The 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.
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; Aballe, Lucía; Pérez García, Lucas; Presa Muñoz De Toro, Patricia Marcela De La; Ruiz Gómez, Sandra
In 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.
Polystyrene nanopillars with inbuilt carbon nanotubes enable synaptic modulation and stimulation in interfaced neuronal networks
(Advanced materials interfaces, 2021) Calaresu, Ivo; Hernández, Jaime; Rauti, Rossana; Rodilla, Beatriz L.; Arché-Núñez, Ana; Pérez García, Lucas; Camarero, Julio; Miranda, Rodolfo; González, M. Teresa; Rodríguez, Isabel; Scaini, Denis; Ballerini, Laura
The use of nanostructured materials and nanosized-topographies has the potential to impact the performance of implantable biodevices, including neural interfaces, enhancing their sensitivity and selectivity, while reducing tissue reactivity. As a result, current trends in biosensor technology require the effective ability to improve devices with controlled nanostructures. Nanoimprint lithography to pattern surfaces with high-density and high aspect ratio nanopillars (NPs) made of polystyrene (PS-NP, insulating), or of a polystyrene/carbon-nanotube nanocomposite (PS-CNT-NP, electrically conductive) are exploited. Both substrates are challenged with cultured primary neurons. They are demonstrated to support the development of suspended synaptic networks at the NPs' interfaces characterized by a reduction in proliferating neuroglia, and a boost in neuronal emergent electrical activity when compared to flat controls. The authors successfully exploit their conductive PS-CNT-NPs to stimulate cultured cells electrically. The ability of both nanostructured surfaces to interface tissue explants isolated from the mouse spinal cord is then tested. The integration of the neuronal circuits with the NP topology, the suspended nature of the cultured networks, the reduced neuroglia formation, and the higher network activity together with the ability to deliver electrical stimuli via PS-CNT-NP reveal such platforms as promising designs to implement on neuro-prosthetic or neurostimulation devices.
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, Adrián
The 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.
Sub-nT resolution of single layer sensor based on the AMR effect in La_2/_3Sr_1/_3MnO_3 Thin Films
(IEEE transactions on magnetics, 2022) Enger, Luiz Guilherme; Flament, Stephane; Bhatti, Imtiaz-Noor; Guillet, Bruno; Sing, Marc Lam Chok; Pierron, Victor; Lebargy, Sylvain; Díez, Jose Manuel; Vera, Arturo; Martínez, Isidoro; Guerrero, Rubén; Pérez García, Lucas; Perna, Paolo; Camarero, Julio; Miranda, Rodolfo; González, María Teresa; Mechin, Laurence
Single-layer magnetoresistive sensors were designed in a Wheatstone bridge configuration using La_2/_3Sr_1/_3MnO_3 ferromagnetic oxide thin film. Uniaxial anisotropy was induced by performing epitaxial deposition of the films on top of vicinal SrTiO_3 substrate. X-ray scan confirms the high crystalline quality of the films and the magnetic anisotropy was checked by magneto-optical Kerr effect measurements. Thanks to the anisotropic magnetoresistive effect and the very low noise measured in the devices, sub-nT resolution was achieved above 100 Hz at 310 K.
Micromagnetics of magnetic chemical modulations in soft-magnetic cylindrical nanowires
(Physical review B, 2022) Álvaro Gómez, Laura; Ruiz Gómez, Sandra; Fernández González, Claudia; Schobitz, M.; Mille, N.; Hurst, J.; Tiwari, D.; De Riz, A.; Andersen, I. M.; Bachmann, J.; Cagnon, L.; Foerster, M.; Belkhou, R.; Toussaint, J-C; Thirion, C.; Masseboeuf, A.; Gusakova, D.; Pérez García, Lucas; Fruchart, O.
We analyze the micromagnetics of short longitudinal modulations of a high-magnetization material in cylindrical nanowires made of a soft-magnetic material of lower magnetization such as permalloy, combining magnetic microscopy, analytical modeling, and micromagnetic simulations. The mismatch of magnetization induces curling of magnetization around the axis in the modulations, in an attempt to screen the interfacial magnetic charges. The curling angle increases with modulation length, until a plateau is reached with nearly full charge screening for a specific length scale delta(mod), larger than the dipolar exchange length of any of the two materials. The curling circulation can be switched by the Oersted field arising from a charge current with typical magnitude 10(12) A/m(2) for a diameter of similar to 100 nm, and reaching a maximum for delta(mod).