Analysis of the temperature dependence of the thermal conductivity of insulating single crystal oxides

The temperature dependence of the thermal conductivity of 27 different single crystal oxides is reported from ≈20 K to 350 K. These crystals have been selected among the most common substrates for growing epitaxial thin-film oxides, spanning over a range of lattice parameters from ≈3.7 Å to ≈12.5 Å. Different contributions to the phonon relaxation time are discussed on the basis of the Debye model. This work provides a database for the selection of appropriate substrates for thin-film growth according to their desired thermal properties, for applications in which heat management is importantThis work was supported by the European Research Council (Grant No. ERC StG-259082, 2DTHERMS), and MINECO of Spain (Project No. MAT2013-44673-R) and Xunta de Galicia (Project No. EM2013/037). V.P. acknowledges support from the Ramon y Cajal Program (No. RYC-2011-09024) and E.F.V. from Xunta de Galicia through the I2C planS

Tunnel Magnetoresistance in Self-Assemblies of Exchange-Coupled Core/Shell Nanoparticles

We report the precise control of tunneling magnetoresistance (TMR) in devices of self-assembled core-shell Fe3O4/Co1-xZnxFe2O4 nanoparticles (0≤x≤1). Adjusting the magnetic anisotropy through the content of Co2+ in the shell, provides an accurate tool to control the switching field between the bistable states of the TMR. In this way, different combinations of soft-hard and hard-soft core/shell configurations can be envisaged for optimizing devices with the required magnetotransport response.Fil: Fabris, Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Lima, Enio Junior. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Quinteros, Cynthia Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Neñer, Lucas. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Granada, Mara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Sirena, Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Zysler, Roberto Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Troiani, Horacio Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Leborán, Victor. Universidad de Santiago de Compostela; EspañaFil: Rivadulla, Francisco. Universidad de Santiago de Compostela; EspañaFil: Winkler, Elin Lilian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin

Large thermoelectric power variations in epitaxial thin films of layered perovskite GdBaCo₂O_5.5±δwith a different preferred orientation and strain

This work describes the growth of thin epitaxial films of the layered perovskite material GdBaCo2O5.5±δ (GBCO) on different single crystal substrates SrTiO3 (STO), (LaAlO3)0.3(Sr2TaAlO6)0.7 (LSAT) and LaAlO3 (LAO) as an approach to study changes in the thermoelectric properties by means of the induced epitaxial strain. In addition to strain changes, the films grow with considerably different preferred orientations and domain microstructures: GBCO films on STO are purely c-axis oriented (c⊥) with an average 0.18% in-plane tensile strain; GBCO on LSAT is composed of domains with a mixed orientation (c‖ and c⊥) with an average 0.71% in-plane compressive strain; while on LAO it is b-axis oriented (c‖) with an average 0.89% in-plane compressive strain. These differences result in important cell volume changes, as well as in the orthorhombicity of the a–b plane of the GBCO structure, which in turn induce a change in the sign and temperature dependence of the thermopower, while the electrical conductivity remains almost unchanged. In general, compressively strained films show negative S thermopower (n-type) while tensile strained films show a positive S (p-type) at low temperatures, probing the adaptive nature of the GdBaCo2O5.5±δ compound. These results point to the spontaneous generation of oxygen vacancies to partially accommodate the epitaxial stress as the main cause for this effect.This work was supported by the projects: MINECO ref. MAT2016-77100-C2-1-P and CNRS-CSIC PICS Project ref. 261091, the EU for funding through project H2020-MSCA-RISE-2014 ref. 645658, and the AGAUR agency for 2017SGR327. ICN2 is funded by the CERCA programme/Generalitat de Catalunya and by the Severo Ochoa programme of the Spanish Ministry of Economy, Industry and Competitiveness (MINECO, grant no. SEV-2017-0706). CMS and ECA acknowledge support from the support from the Spanish MICINN project SIP (PGC2018-101743-B-I00). AC particularly acknowledges the support of the Severo Ochoa programme and ICN2 for his PhD grant. FR acknowledges support from MAT2016-80762-R, Xunta de Galicia (Centro singular de investigación de Galicia accreditation 2016–2019, ED431G/09), by the European Union (European Regional Development Fund-ERDF) and the European Commission through the Horizon H2020 funding by H2020-MSCA-RISE-2016-Project No. 734187 – SPICOLOST.Peer reviewe