Person:
Sánchez Santolino, Gabriel

First Name

Gabriel

Last Name

Sánchez Santolino

URI

https://hdl.handle.net/20.500.14352/85624

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Ciencias Físicas

Department

Física de Materiales

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Now showing 1 - 10 of 23

Advanced electron microscopy characterization of complex oxide interfaces
(2015) Sánchez Santolino, Gabriel; Varela del Arco, María; Santamaría Sánchez-Barriga, Jacobo
Pequeños cambios a nivel atómico de la estructura, composición o estado electrónico de un material pueden producir sorprendentes efectos macroscópicos. En particular, en óxidos complejos basados en metales de transición, un gran número de fenómenos físicos como transiciones metal-aislante, magnetorresistencia colosal o multiferroicidad son extremadamente sensibles a estas variaciones. Por tanto, para abordar el estudio de sistemas con tales características, técnicas experimentales con capacidad de analizar materiales a escala atómica y en el espacio real se hacen indispensables. La microscopía electrónica de transmisión con barrido combinada con la espectroscopia de pérdida de energía de electrones (EELS) forman una pareja con posibilidades únicas para estos estudios. Estas técnicas han crecido enormemente desde el desarrollo del corrector de aberración esférica en la última década y su alta resolución espacial nos permite ahora estudiar átomos individuales. El uso de estos equipos supone una herramienta única para el estudio de sistemas complejos, más aún cuando la dimensionalidad se reduce a pocos nanómetros como en películas delgadas o interfaces. En estos casos, técnicas de difracción promediadas macroscópicamente pueden no ser suficientemente sensibles a los parámetros que rigen la física relevante y por tanto, la gran sensibilidad espacial de la microscopía electrónica supone una gran ventaja. El objetivo principal de este trabajo será precisamente establecer la conexión entre los mecanismos a nivel atómico y las propiedades físicas de una serie de sistemas basados en óxidos complejos cuidadosamente escogidos. Analizaremos en el espacio real fluctuaciones mínimas, casi por debajo del umbral de detectabilidad, responsables últimas del comportamiento macroscópico.En primer lugar, se ha estudiado como pequeñas concentraciones de vacantes de oxígeno, tanto inducidas mediante irradiación como intrínsecas al material, pueden determinar las propiedades físicas macroscópicas del sistema. Se ha observado cómo procesos de irradiación dan lugar a la formación de una capa de TiO con alto grado cristalino en la superficie de monocristales de TiO2 y como además pueden producir estados metálicos superficiales en un aislante de bandas como es el SrTiO3. Se ha analizado además como la reestructuración electrónica debida a la presencia de vacantes de oxígeno estructurales explica por primera vez el origen electroestático del bloqueo iónico en fronteras de grano de materiales con importantes aplicaciones energéticas. Se ha abordado también el estudio de pequeñas variaciones estructurales, en particular, distorsiones colectivas de la red de oxígeno en heteroestructuras de óxidos complejos y su relación con la aparición de estados físicos inexistentes en los materiales masivos. Se ha encontrado una correlación entre rotaciones del octaedro de oxígenos producidas por tensiones epitaxiales y la estabilización de una fase interfacial ferromagnética y conductora en superredes formadas por óxidos aislantes. Además, se ha extendido este análisis a sistemas más complejos como uniones túnel multiferroicas donde se ha obtenido la configuración de dominios ferroeléctricos midiendo las distorsiones en la red de oxígenos para cada celda unidad. Este estudio muestra una de las primeras observaciones experimentales de una configuración de dominios ferroeléctricos tipo head-to-head en capas ultra-delgadas. Se ha encontrado además la presencia de una carga de apantallamiento confinada a la pared de dominio que genera estados electrónicos accesibles en el interior de la barrera ferroeléctrica, proporcionando los mecanismos para estabilizar un tuneleamiento cuántico resonante.El continuo desarrollo de estas técnicas experimentales hace vislumbrar un futuro prometedor tanto para la ciencia de materiales como para la microscopía electrónica. La exploración a escala atómica de fenómenos físicos aún por desvelar está ahora, más que nunca a nuestro alcance.
Electrolyte gated synaptic transistor based on an ultra-thin film of La0.7Sr0.3MnO3
(Advanced Electronic Materials, 2023) López Montes, Alejandro; Tornos Castillo, Javier; Peralta, Andrea; Barbero, Isabel; Fernandez Canizares, Francisco; Sánchez Santolino, Gabriel; Varela Del Arco, María; Rivera Calzada, Alberto Carlos; Camarero, Julio; León Yebra, Carlos; Santamaría Sánchez-Barriga, Jacobo; Romera, Miguel; Romera Rabasa, Miguel Álvaro
Developing electronic devices capable of reproducing synaptic functionality is essential in the context of implementing fast, low-energy consumption neuromorphic computing systems. Hybrid ionic/electronic three-terminal synaptic transistors are promising as efficient artificial synapses since they can process information and learn simultaneously. In this work, an electrolyte-gated synaptic transistor is reported based on an ultra-thin epitaxial La0.7Sr0.3MnO3 (LSMO) film, a half-metallic system close to a metal-insulator transition. The dynamic control of oxygen composition of the manganite ultra-thin film with voltage pulses applied through the gate terminal allows reversible modulation of its electronic properties in a non-volatile manner. The conductance modulation can be finely tuned with the amplitude, duration, and number of gating pulses, providing different alternatives to gradually update the synaptic weights. The transistor implements essential synaptic features such as excitatory postsynaptic potential, paired-pulse facilitation, long-term potentiation/depression of synaptic weights, and spike-time-dependent plasticity. These results constitute an important step toward the development of neuromorphic computing devices leveraging the tunable electronic properties of correlated oxides, and pave the way toward enhancing future device functionalities by exploiting the magnetic (spin) degree of freedom of the half metallic transistor channel.
Anisotropic magnetotransport in SrTiO3 surface electron gases generated by Ar+ irradiation
(Physical Review B, 2011) Bruno, Flavio Yair; Tornos Castillo, Javier; Gutiérrez del Olmo, M.; Sánchez Santolino, Gabriel; Nemes, Norbert Marcel; García-Hernández, M.; Méndez, B.; Piqueras, J.; Antorrena, G.; Morellón, L.; Teresa, J. M. de; Clement, M.; Iborra, E.; León Yebra, Carlos; Santamaría Sánchez-Barriga, Jacobo
Metallic surface layers are fabricated by doping (100) SrTiO3 (STO) single crystals with oxygen vacancies generated by bombardment with Ar ions from an rf plasma source. The presence of oxygen vacancies is confirmed by cathodoluminescence and x-ray photoemission spectroscopy. This technique produces a surface electron gas with high values of the sheet carrier density (n2D = 2.45×1017 cm−2). A strong increase (300%) of the low-temperature magnetoresistance is observed when the magnetic field is rotated away from the surface, characteristic of orbital effects of confined electrons. We estimate the width of the confinement region to be in the 200–300 nm range. When a magnetic field is applied in the surface plane and parallel to the current direction, a large negative magnetoresistance is found below the structural transition of the STO, which is discussed in terms of spin-orbit scattering. On further reduction of temperature, there is a change to a positive magnetoresistance regime due to the scattering of charge carriers at the disordered surface region.
Direct Transformation of Crystalline MoO3 into Few-Layers MoS2
(Materials, 2020) Carrascoso, Felix; Sánchez Santolino, Gabriel; Hsu, Chun-wei; Nemes, Norbert Marcel; Castellanos-Gomez, Andres; Torres Pardo, María De La Almudena; Gant, Patricia; Mompeán, Federico J.; Kalantar-zadeh, Kourosh; Alonso, José A.; García Hernández, Mar; Frisenda, Riccardo
We fabricated large-area atomically thin MoS2 layers through the direct transformation of crystalline molybdenum trioxide (MoO3) by sulfurization at relatively low temperatures. The obtained MoS2 sheets are polycrystalline (~10–20 nm single-crystal domain size) with areas of up to 300 × 300 µm2, 2–4 layers in thickness and show a marked p-type behavior. The synthesized films are characterized by a combination of complementary techniques: Raman spectroscopy, X-ray diffraction, transmission electron microscopy and electronic transport measurements.
Large intrinsic anomalous Hall effect in SrIrO_3 induced by magnetic proximity effect
(Nature communications, 2021) Yoo, Myoung-Woo; Tornos Castillo, Javier; Sander, A.; Lin, Ling-Fang; Mohanta, Narayan; Peralta Somoza, Andrea; Sánchez Manzano, David; Gallego Toledo, Fernando; Haskel, D.; Freeland, J. W.; Keavney, D. J.; Choi, Y.; Strempfer, J.; Wang, X.; Cabero Piris, Mariona; Vasili, Hari Babu; Valvidares, Manuel; Sánchez Santolino, Gabriel; González Calbet, José María; Rivera Calzada, Alberto Carlos; León Yebra, Carlos; Rosenkranz, S.; Bibes, M.; Barthelemy, A.; Anane, A.; Dagotto, E.; Okamoto, S.; te Velthuis, S. G. E.; Santamaría Sánchez-Barriga, Jacobo
The anomalous Hall effect (AHE) is an intriguing transport phenomenon occurring typically in ferromagnets as a consequence of broken time reversal symmetry and spin-orbit interaction. It can be caused by two microscopically distinct mechanisms, namely, by skew or side-jump scattering due to chiral features of the disorder scattering, or by an intrinsic contribution directly linked to the topological properties of the Bloch states. Here we show that the AHE can be artificially engineered in materials in which it is originally absent by combining the effects of symmetry breaking, spin orbit interaction and proximity-induced magnetism. In particular, we find a strikingly large AHE that emerges at the interface between a ferromagnetic manganite (La_(0.7)Sr_(0.3)MnO_3) and a semimetallic iridate (SrIrO_3). It is intrinsic and originates in the proximity-induced magnetism present in the narrow bands of strong spin-orbit coupling material SrIrO_3, which yields values of anomalous Hall conductivity and Hall angle as high as those observed in bulk transition-metal ferromagnets. These results demonstrate the interplay between correlated electron physics and topological phenomena at interfaces between 3d ferromagnets and strong spin-orbit coupling 5d oxides and trace an exciting path towards future topological spintronics at oxide interfaces. The anomalous Hall effect (AHE) occurs in ferromagnets caused by intrinsic and extrinsic mechanisms. Here, Yoo et al. report large anomalous Hall conductivity and Hall angle at the interface between a ferromagnet La_(0.7)Sr_(0.3M)nO_3 and a semimetallic SrIrO_3, due to the interplay between correlated physics and topological phenomena.
Formation of titanium monoxide (001) single-crystalline thin film induced by ion bombardment of titanium dioxide (110)
(Nature communications, 2015) Martínez Pabón, María Beatriz; Beltrán Fínez, Juan Ignacio; Sánchez Santolino, Gabriel; Palacio, I.; López Sánchez, Jesús; Rubio Zuazo, J.; Rojo Alaminos, Juan Manuel; Ferrer, P.; Mascaraque Susunaga, Arantzazu; Muñoz, María del Carmen; Varela Del Arco, María; Castro, G. R.; Rodríguez De La Fuente, Óscar
A plethora of technological applications justify why titanium dioxide is probably the most studied oxide, and an optimal exploitation of its properties quite frequently requires a controlled modification of the surface. Low-energy ion bombardment is one of the most extended techniques for this purpose and has been recently used in titanium oxides, among other applications, to favour resistive switching mechanisms or to form transparent conductive layers. Surfaces modified in this way are frequently described as reduced and defective, with a high density of oxygen vacancies. Here we show, at variance with this view, that high ion doses on rutile titanium dioxide (110) induce its transformation into a nanometric and single-crystalline titanium monoxide (001) thin film with rocksalt structure. The discovery of this ability may pave the way to new technical applications of ion bombardment not previously reported, which can be used to fabricate heterostructures and interfaces.
Project number: PIMCD355/23-24
Métodos innovativos en la docencia en el ámbito de electromagnetismo usando la herramienta Wooclap
(2024) Biskup Zaja, Nevenko; Nemes, Norbert Marcel; León Yebra, Carlos; Santamaría Sánchez-Barriga, Jacobo; Sánchez Santolino, Gabriel; Sefrioui Khamali, Zouhair; Schmidt, Rainer; Varela Del Arco, María; Azcondo Sánchez, M. Teresa; Rivera Calzada, Alberto Carlos; Scimemi, Ignacio; Barbero Velasco, Isabel; Zamora Castro, Victor; Ternero Villar, Isabel; Romero de Paz, Julio
Anisotropic magnetotransport in SrTiO_3 surface electron gases generated by Ar^+ irradiation
(Physical review B, 2011) Bruno, Flavio Yair; Tornos, J.; Gutierrez del Olmo, M.; Sánchez Santolino, Gabriel; Nemes, Norbert Marcel; Gárcia Hernández, M.; Méndez Martín, María Bianchi; Piqueras De Noriega, Francisco Javier; Antorrena, G.; Morellon, L.; De Teresa, J. M.; Clement, M.; Iborra, E.; León, C.; Santamaría Sánchez-Barriga, Jacobo
Metallic surface layers are fabricated by doping (100) SrTiO_3 (STO) single crystals with oxygen vacancies generated by bombardment with Ar ions from an rf plasma source. The presence of oxygen vacancies is confirmed by cathodoluminescence and x-ray photoemission spectroscopy. This technique produces a surface electron gas with high values of the sheet carrier density (n_(2D) = 2.45x10^17 cm^(-2)). A strong increase (300%) of the low-temperature magnetoresistance is observed when the magnetic field is rotated away from the surface, characteristic of orbital effects of confined electrons. We estimate the width of the confinement region to be in the 200-300 nm range. When a magnetic field is applied in the surface plane and parallel to the current direction, a large negative magnetoresistance is found below the structural transition of the STO, which is discussed in terms of spin-orbit scattering. On further reduction of temperature, there is a change to a positive magnetoresistance regime due to the scattering of charge carriers at the disordered surface region.
Thermally assisted tunneling transport in La_(0.7)Ca_(0.3)MnO_(3)/SrTiO_(3):Nb Schottky-like heterojunctions
(Physical review B, 2012) Cuéllar Jiménez, Fabian Andrés; Sánchez Santolino, Gabriel; Varela Del Arco, María; Clement, M.; Iborra, E.; Sefrioui, Zouhair; Santamaría Sánchez-Barriga, Jacobo; León Yebra, Carlos
We report on the electrical transport properties of all-oxide La_(0.7)Ca_(0.3)MnO_(3)/SrTiO_(3):Nb heterojunctions with lateral size of just a few micrometers. The use of lithography techniques to pattern manganite pillars ensures perpendicular transport and allows exploration of the microscopic conduction mechanism through the interface. From the analysis of the current-voltage characteristics in the temperature range 20–280 K we find a Schottky-like behavior that can be described by a mechanism of thermally assisted tunneling if a temperature-dependent value of the dielectric permittivity of SrTiO_(3):Nb (NSTO) is considered. We determine the Schottky energy barrier at the interface, qVB = 1.10 ± 0.02 eV, which is found to be temperature independent, and a value of ξ = 17 ± 2 meV for the energy of the Fermi level in NSTO with respect to the bottom of its conduction band.
Reversible electric-field control of magnetization at oxide interfaces
(Nature communications, 2014) Nemes, Norbert Marcel; Sánchez Santolino, Gabriel; Varela Del Arco, María; Sefrioui, Zouhair; León Yebra, Carlos; Santamaría Sánchez-Barriga, Jacobo
Electric-field control of magnetism has remained a major challenge which would greatly impact data storage technology. Although progress in this direction has been recently achieved, reversible magnetization switching by an electric field requires the assistance of a bias magnetic field. Here we take advantage of the novel electronic phenomena emerging at interfaces between correlated oxides and demonstrate reversible, voltage-driven magnetization switching without magnetic field. Sandwiching a non-superconducting cuprate between two manganese oxide layers, we find a novel form of magnetoelectric coupling arising from the orbital reconstruction at the interface between interfacial Mn spins and localized states in the CuO2 planes. This results in a ferromagnetic coupling between the manganite layers that can be controlled by a voltage. Consequently, magnetic tunnel junctions can be electrically toggled between two magnetization states, and the corresponding spin-dependent resistance states, in the absence of a magnetic field.