Generación de texturas de espín y paredes de dominio en nanoestructuras de óxidos correlacionados

El capítulo 1 es una introducción general sobre los óxidos fuertemente correlacionados y los materiales que se van a estudiar. Se describen los aspectos físicos que hay detrás de las manganitas en general y el LSMO en particular, con especial atención a los efectos de espín como la magnetorresistencia. Se introduce también la superconductividad de tipo II con el YBCO como ejemplo paradigmático y el modelo de estado crítico de Bean. El capítulo 2 describe las técnicas experimentales que se utilizan en este trabajo. Se explica el crecimiento por pulverización catódica o sputtering, el análisis estructural de las muestras con difracción de rayos X, el análisis morfológico con microscopía de fuerzas atómicas (AFM) y de magnetrotrasporte en criostato de ciclo cerrado de He. Por su importancia, se desarrolla el proceso de fabricación de nanoestructuras con litografía por haz de electrones, el ataque y la deposición de contactos metálicos con litografía óptica. Finalmente se detallan las dos técnicas de caracterización magnética en la escala nanométrica utilizadas, las imágenes de dicroísmo circular magnético (XMCD) en el microscopio de fotoemisión de electrones (PEEM) y el microscopio de fuerzas magnéticas (MFM). En el capítulo 3 se describe el estudio de la nucleación y manipulación de paredes de dominio en nanohilos de LSMO diseñados para tener una región donde compiten diferentes anisotropías de forma. Se explican los detalles particulares de la fabricación, y se hace un amplio estudio magnético y de transporte de los dispositivos, que permite entender la formación y el movimiento de las paredes de dominio de 180º al invertir el campo. Se fabrican nanodispositivos diseñados para modificar la dinámica de las paredes, consiguiendo mejorar su magnetorresistencia para su aplicación práctica..

Photodiodes based in La0.7Sr0.3MnO3/single layer MoS2 hybrid vertical heterostructures

The fabrication of artificial materials by stacking of individual two-dimensional (2D) materials is amongst one of the most promising research avenues in the field of 2D materials. Moreover, this strategy to fabricate new man-made materials can be further extended by fabricating hybrid stacks between 2D materials and other functional materials with different dimensionality making the potential number of combinations almost infinite. Among all these possible combinations, mixing 2D materials with transition metal oxides can result especially useful because of the large amount of interesting physical phenomena displayed separately by these two material families. We present a hybrid device based on the stacking of a single layer MoS2 onto a lanthanum strontium manganite (La0.7Sr0.3MnO3) thin film, creating an atomically thin device. It shows a rectifying electrical transport with a ratio of 103, and a photovoltaic effect with Voc up to 0.4 V. The photodiode behaviour arises as a consequence of the different doping character of these two materials. This result paves the way towards combining the efforts of these two large materials science communities.Comment: 1 table, 4 figures (+9 supp. info. figures

Photodiodes based in La0.7Sr0.3MnO3/single layer MoS2 hybrid vertical heterostructures

The fabrication of artificial materials by stacking of individual two-dimensional (2D) materials is amongst one of the most promising research avenues in the field of 2D materials. Moreover, this strategy to fabricate new man-made materials can be further extended by fabricating hybrid stacks between 2D materials and other functional materials with different dimensionality making the potential number of combinations almost infinite. Among all these possible combinations, mixing 2D materials with transition metal oxides can result especially useful because of the large amount of interesting physical phenomena displayed separately by these two material families. We present a hybrid device based on the stacking of a single layer MoS onto a lanthanum strontium manganite (LaSrMnO) thin film, creating an atomically thin device. It shows a rectifying electrical transport with a ratio of 10, and a photovoltaic effect with V up to 0.4 V. The photodiode behaviour arises as a consequence of the different doping character of these two materials. This result paves the way towards combining the efforts of these two large materials science communities.Work at IMDEA was supported by MINECO (Ramón y Cajal 2014 program RYC-2014-01406, MAT2014-58399-JIN, FIS2015-67367-C2-1-P), the Comunidad de Madrid (MAD2D-CM Program (S2013/MIT-3007)) and NANOFRONTMAG-CM program (S2013/MIT-2850) and the European Commission under the Graphene Flagship (contract CNECTICT-604391) and FP7 ITN MOLESCO (project no. 606728). RF acknowledges support from the Netherlands Organisation for Scientific Research (NWO) through the research program Rubicon with project number 680-50-1515. YN acknowledges the grant from the China Scholarship Council (File NO. 201506120102). Work at UCM supported by Spanish MINECO through grants MAT2014-52405-C02-01 and by CAM through grant CAM S2013/MIT-2740. Work at ICMM is supported by Spanish MINECO through grant MAT2014-52405-C02-02

Ferroelectric control of interface spin filtering in multiferroic tunnel junctions

The electronic reconstruction occurring at oxide interfaces may be the source of interesting device concepts for future oxide electronics. Among oxide devices, multiferroic tunnel junctions are being actively investigated as they offer the possibility to modulate the junction current by independently controlling the switching of the magnetization of the electrodes and of the ferroelectric polarization of the barrier. In this Letter, we show that the spin reconstruction at the interfaces of a La_0.7Sr_0.3MnO_3/BaTiO_3/La_0.7Sr_0.3MnO_3 multiferroic tunnel junction is the origin of a spin filtering functionality that can be turned on and off by reversing the ferroelectric polarization. The ferroelectrically controlled interface spin filter enables a giant electrical modulation of the tunneling magnetoresistance between values of 10% and 1000%, which could inspire device concepts in oxides-based low dissipation spintronics