Site-specific spectroscopic measurement of spin and charge in (LuFeO3)m/(LuFe2O4)1 multiferroic superlattices

Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO3)m/(LuFe2O4)1 superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ → Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe2O4 layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement.Fil: Fan, Shiyu. University of Tennessee; Estados UnidosFil: Das, Hena. Cornell University; Estados UnidosFil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Smith, Kevin. University of Tennessee; Estados UnidosFil: Mundy, Julia. Harvard University; Estados Unidos. Cornell University; Estados UnidosFil: Brooks, Charles. Cornell University; Estados UnidosFil: Holtz, Megan E.. Cornell University; Estados UnidosFil: Muller, David A.. Cornell University; Estados UnidosFil: Fennie, Craig J.. Cornell University; Estados UnidosFil: Ramesh, Ramamoorthy. Lawrence Berkeley National Laboratory; Estados Unidos. University of California at Berkeley; Estados UnidosFil: Schlom, Darrell G.. Cornell University; Estados UnidosFil: McGill, Stephen. National High Magnetic Field Laboratory; Estados UnidosFil: Musfeldt, Janice L.. University of Tennessee; Estados Unido

La renovación de la palabra en el bicentenario de la Argentina : los colores de la mirada lingüística

El libro reúne trabajos en los que se exponen resultados de investigaciones presentadas por investigadores de Argentina, Chile, Brasil, España, Italia y Alemania en el XII Congreso de la Sociedad Argentina de Lingüística (SAL), Bicentenario: la renovación de la palabra, realizado en Mendoza, Argentina, entre el 6 y el 9 de abril de 2010. Las temáticas abordadas en los 167 capítulos muestran las grandes líneas de investigación que se desarrollan fundamentalmente en nuestro país, pero también en los otros países mencionados arriba, y señalan además las áreas que recién se inician, con poca tradición en nuestro país y que deberían fomentarse. Los trabajos aquí publicados se enmarcan dentro de las siguientes disciplinas y/o campos de investigación: Fonología, Sintaxis, Semántica y Pragmática, Lingüística Cognitiva, Análisis del Discurso, Psicolingüística, Adquisición de la Lengua, Sociolingüística y Dialectología, Didáctica de la lengua, Lingüística Aplicada, Lingüística Computacional, Historia de la Lengua y la Lingüística, Lenguas Aborígenes, Filosofía del Lenguaje, Lexicología y Terminología

Realistic indirect spin interactions between magnetic impurities on a metallic Pb(110) surface

Motivated by recent experiments, here we study the indirect interactions between magnetic impurities deposited on top of a clean Pb(110) surface, induced by the underlying conduction electrons. Our approach makes use of ab initio calculations to characterize the clean Pb(110) surface and avoids self-consistency, a feature that greatly reduces the computational cost. In combination with second-order perturbation theory in the microscopic s-d exchange parameter Jsd between a magnetic adatom and the conduction electrons, we are able to systematically derive the Ruderman-Kittel-Kasuya-Yosida, the Dzyaloshinskii-Moriya, and the anisotropic tensor interactions emerging at the Pb(110) surface between magnetic impurities. The only adjustable parameter is Jsd, which is fitted to reproduce the experiments. Our results show important anisotropy effects arising both from the rectangular geometry of the (110) unit cell and from the strong Rashba spin-orbit interaction due to the broken inversion symmetry at the Pb(110) surface. In addition to Pb(110), the characterization of the indirect spin interactions described here could be extended to other realistic metallic surfaces for weakly coupled impurities and would enable us to fabricate atomic-size nanostructures with engineered interactions and on-demand magnetic properties, anticipating useful applications in nanotechnology.Fil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Lobos, Alejandro Martin. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Interdisciplinario de Ciencias Básicas. - Universidad Nacional de Cuyo. Instituto Interdisciplinario de Ciencias Básicas; Argentin

Multiferroic properties of three-layer Aurivillius compound Bi4TiFeNbO12: A first-principles and experimental study

We present a first-principles and experimental study of the structural, ferroelectric, and magnetic properties of the potentially multiferroic three-layer Aurivillius compound Bi4TiFeNbO12. This system can be realized by inserting a BiFeO3 formula unit into the two-layer Aurivilius Bi3TiNbO9 matrix. The calculations are performed using the PBEsol exchange–correlation functional within the DFT+U framework. First we search for potential cation site preference by comparing the relative stability of different Fe, Nb and Ti arrangements. We find a preference for the Fe3＋ ions to occupy the inner site within the pseudoperovskite block. This configuration exhibits a band gap of 1.2 eV (UFe=4eV) and ferroelectric and magnetic orders. A value of 66 μC/cm2 is obtained for the spontaneous polarization, which is similar to the one obtained for Bi4Ti3O12 (BIT). The magnetic ground state of this system is characterized by a strong antiferromagnetic coupling between the Fe3＋ ions located in the central layer. By mapping to a Heisenberg model, the superexchange antiferromagnetic coupling between nearest-neighbor Fe3＋ cations is estimated to be J=53 meV. Finally, we synthesize Bi3.25La0.75TiFeNbO12 ceramics by the solid-state reaction method. Their structural, electric and magnetic properties are confronted with the theoretical predictions.Fil: Lavado, Cristian. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Rébola, Alejandro Federico. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Machado, Rodrigo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Stachiotti, Marcelo Gabriel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentin

First-principles study of the atomic and electronic structures of misfit-layered calcium cobaltite (Ca2CoO3)(CoO2)1.62 using rational approximants

The atomic and electronic structures of the misfit-layered thermoelectric oxide material Ca3Co4O9 are investigated using detailed first-principles computations performed within the framework of density functional theory (DFT) and its DFT+U extension to account for electron correlations. The structure of Ca3Co4O9, composed of two incommensurate subsystems—a distorted rocksalt-type Ca2CoO3 layer sandwiched between hexagonal CoO2 layers—is modeled by means of Fibonacci rational approximants with systematically increasing unit cells.We show that good agreement with photoemission and transport experiments can be obtained regarding the contribution of the two subsystems to states near the Fermi level, when electron correlations are taken into account with a Hubbard U. The size of the rational approximant plays a secondary role in the analysis; the relatively “small” structure of composition (Ca2CoO3)6(CoO2)10 represents a good model for investigating the atomic and electronic properties of Ca3Co4O9. Within the DFT+U formalism, the metallic conductivity of Ca3Co4O9 is shown to result from itinerant holes in the hexagonal CoO2 layers, in which the Co atoms are predicted to have a mixed valence of Co4+ with ∼30% concentration and Co3+ with ∼70% concentration, both in low-spin configurations. In most cases, the resulting electronic structures show very good agreement with available data from transport and magnetic measurements

Site-specific spectroscopic measurement of spin and charge in (LuFeO3)m/(LuFe2O4)1 multiferroic superlattices.

Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO3)m/(LuFe2O4)1 superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ →  Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe2O4 layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement

Site-specific spectroscopic measurement of spin and charge in (LuFeO3)m/(LuFe2O4)1 multiferroic superlattices.

Interface materials offer a means to achieve electrical control of ferrimagnetism at room temperature as was recently demonstrated in (LuFeO3)m/(LuFe2O4)1 superlattices. A challenge to understanding the inner workings of these complex magnetoelectric multiferroics is the multitude of distinct Fe centres and their associated environments. This is because macroscopic techniques characterize average responses rather than the role of individual iron centres. Here, we combine optical absorption, magnetic circular dichroism and first-principles calculations to uncover the origin of high-temperature magnetism in these superlattices and the charge-ordering pattern in the m = 3 member. In a significant conceptual advance, interface spectra establish how Lu-layer distortion selectively enhances the Fe2+ →  Fe3+ charge-transfer contribution in the spin-up channel, strengthens the exchange interactions and increases the Curie temperature. Comparison of predicted and measured spectra also identifies a non-polar charge ordering arrangement in the LuFe2O4 layer. This site-specific spectroscopic approach opens the door to understanding engineered materials with multiple metal centres and strong entanglement

Procesos y metodologías participativas : reflexiones y experiencias para la transformación social

Las metodologías participativas de investigación y acción social - IAP con su fuerte propuesta epistemológica de investigar para la acción, y para y con sus actores sociales protagonistas- suman en este libro, en tiempos de su expansión, otro grano de arena con esta iniciativa. La obra refleja bien esa multiplicación y proliferación de su utilización, y a la vez pone sobre la mesa una vez más, también amenazas, límites y contradicciones de lo que se intenta hacer desde lo participativo. Los lectores podrán sondear el grado de los desfases, las continuidades y discontinuidades, las dicciones y contradicciones, los valores y ambivalencias, las emergencias de explicaciones que como obra heterogénea respecto a sus autores, localización de experiencias y procedencias, posicionamientos, y uso de las metodologías y técnicas participativas, el libro encierra en diálogo y disputa