1,720,995 research outputs found
Calculation of the Magnetoresistance of YMn2Ge2 and LaMn2Ge2
No full textWe have calculated the diffusive conductivity and ballistic conductance of the layered compounds LaMn2Ge2 and YMn2Ge2 . For the last one we obtain a negative band contribution to the giant magnetoresistance. For LaMn2Ge2 we show that the band contribution can already explain the experimentally observed large positive magnetoresistance if a nearly ferromagnetic structure is considered. Fil: Milano, Julian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes; Argentin
Strain induced anisotropy change in ultrathin Fe films grown on MnAs(110)/GaAs(001)
Get PDFMechanical stress due to a misfit between a thin film and its substrate induces strains which can strongly modify the unstrained thin film properties. One good and interesting example to study strain effects is given by ultrathin films of Fe epitaxially grown on MnAs(110)/GaAs(001). The MnAs(110) films show, at room temperature, coexistence of two structural phases, which organize themselves forming a striped pattern. The Fe epilayer senses the strain effects due to lattice mismatch and to the border constraints given by the striped substrate. In this work, we are concerned with the consequences that this strain has on the magnetic anisotropy of the Fe thin film and try to explain recent experimental results. These experiments indicate an easy axis rotation of the film Fe atoms sitting on one of the striped phases. In order to have an approach to the understanding of the observed phenomenon, we make use of ab initio calculations and of the magnetoelastic model. We find that both the magnetoelastic model and the ab initio calculated spin orbit coupling point towards the strain effects as the most important contribution to the observed easy axis rotation.Fil: Helman, Christian. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin
Diffusion in thorium carbide: A first-principles study
Get PDFThe prediction of the behavior of Th compounds under irradiation is an important issue for the upcoming Generation-IV nuclear reactors. The study of self-diffusion and hetero-diffusion is a central key to fulfill this goal. As a first approach, we obtained, by means of first-principles methods, migration and activation energies of Th and C atoms self-diffusion and diffusion of He atoms in ThC. We also calculate diffusion coefficients as a function of temperature.Fil: Perez Daroca, Diego Raul. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Mosca, Hugo Osvaldo. Universidad Nacional de San Martín. Instituto Sabato; Argentina. Comisión Nacional de Energía Atómica; Argentin
Computational study of protactinium incorporation effects in Th and Th compounds
Get PDFProtactinium contamination is a mayor issue in the thorium fuel cycle. We investigate, in this work, the consequences of Pa incorporation in vacancy defects and interstitials in Th, ThC and ThN. We calculate charge transfers and lattice distortions due to these incorporations as well as migration paths and energies involved in the diffusion of Pa.Fil: Perez Daroca, Diego Raul. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; ArgentinaFil: Mosca, Hugo Osvaldo. Comisión Nacional de Energía Atómica. Centro Atómico Constituyentes. Gerencia de Investigación y Aplicaciones; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentin
From direct to inverse GMR: Introduction of Cr in Fe/Cu superlattices
Get PDFIt is well known that layered systems can present giant magnetoresistance (GMR). Particularly, the multilayers FeN/Cu8/Fe M/Cr/ FeM/Cu8 show inverse GMR. That is, the electrical conductivity decreases with the applied magnetic field. In the most common multilayers the conductivity increases with the applied field and this kind of GMR is called direct. In general the GMR is attributed to spin-dependent scattering in the bulk and mainly at interfaces. In this work we calculate the electronic band contribution to the GMR for Fe3/Cu 4/Fe/Cr/Fe/Cu4 and Fe3/Cu4 multilayers within the semiclassical approximation. The electrical conductivity is obtained in the ballistic and diffusive regimes. The results show a large change in the GMR behavior when one layer of Cr is introduced within the Fe layers. The GMR calculated in the CPP configuration (current flowing perpendicular to layers) of Fe3/Cu4 is of the direct type, with a value of about 40% while that obtained for Fe3/Cu 4/Fe/Cr/Fe/Cu4 is inverse and of the order of 45%. In the CIP configuration (current flowing parallel to the layers) the calculated GMR is direct with a value of about 35% for the system without Cr while, by the introduction of Cr, we obtain also a direct GMR but of about 3%. © 2001 Published by Elsevier Science B.V.Fil: Milano, Julian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad de Buenos Aires; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad de Buenos Aires; Argentin
Electronic structure and properties of NbS2 and TiS2 low dimensional structures
Get PDFTransition metal dichalcogenides have a laminar structure, weakly bound through van der Waals interactions. Due to their technological applications in catalytic processes the bulk structure of many of them has been widely studied in the last 30 years. Some of them, such as NbTe2 and TiSe2, show superconductivity and have been, therefore, the subject of intense study. Novoselov et al. (2005) achieved to isolate not only graphene but also other bidimensional crystals, among them layers of some dichalcogenides. These bidimensional crystals preserve their monocrystallinity under normal ambient conditions, keeping the crystal structure of the bulk. In this contribution we calculate the magnetic and electronic properties of 2D layers of NbS2 (non-magnetic metal in 3D) and TiS2 (non-magnetic semimetal in 3D) as well as quasi 1D chains cut out from these layers.Fil: Güller, F.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; ArgentinaFil: Helman, Christian. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin
Adsorbed 3d transition-metal atoms and dimers on Au(111): Signatures derived from one-electron calculations
Get PDFThe spectroscopic characteristics of systems with adsorbed d impurities on noble metal surfaces should depend on the number and geometric arrangement of the adsorbed atoms and also on their d band filling. Recent experiments using scanning tunneling microscopy (STM) have probed the electronic structure of all 3d transition-metal impurities and also of Co dimers adsorbed on Au(111). In this contribution we correlate those experimental results with ab initio calculations and try to establish necessary conditions for observing a Kondo resonance when using the single-impurity Anderson model. We find that the relevant orbitals at the STM tip position, when it is on top of an impurity, are the d orbitals with m=0 and that the energy of these levels with respect to the Fermi level determines the possibility of observing a spectroscopic feature due to the impurity.Fil: Weissmann, Mariana Dorotea. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentin
Phonon spectrum, mechanical and thermophysical properties of thorium carbide
Get PDFIn this work, we study, by means of density functional perturbation theory and the pseudopotential method, mechanical and thermophysical properties of thorium carbide. These properties are derived from the lattice dynamics in the quasi-harmonic approximation. The phonon spectrum of ThC presented in this article, to the best authors' knowledge, have not been studied, neither experimentally, nor theoretically. We compare mechanical properties, volume thermal expansion and molar specific capacities with previous results and find a very good agreement. © 2013 Elsevier B.V. All rights reserved.Fil: Perez Daroca, Diego Raul. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Jaroszewicz, Sebastian. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Mosca, Hugo Osvaldo. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentin
Mechanism to generate a two-dimensional electron gas at the surface of the charge-ordered semiconductor BaBiO3
Get PDFIn this Letter, we find by means of first-principles calculations a new physical mechanism to generate a two-dimensional electron gas, namely, the breaking of charge ordering at the surface of a charge-ordered semiconductor due to the incomplete oxygen environment of the surface ions. The emergence of the 2D gas is independent of the presence of oxygen vacancies or polar discontinuities; this is a self-doping effect. This mechanism might apply to many charge-ordered systems, in particular, we study the case of BaBiO 3(001). Our calculations show that the outer layer of the Bi-terminated simulated surface turns more cubiclike and metallic while the inner layers remain in the insulating monoclinic state that the system present in the bulk form. On the other hand, the metallization does not occur for the Ba termination, a fact that makes this system appealing for nanostructuring. Finally, in view of the bulk properties of this material under doping, this particular finding sets another possible route for future exploration: the potential scenario of 2D superconductivity at the BaBiO3 surface.Fil: Vildosola, Veronica Laura. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Güller, Francisco. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Comisión Nacional de Energía Atómica; Argentin
A first-principles study of He, Xe, Kr and O incorporation in thorium carbide
Get PDFThorium-based materials are currently being investigated in relation with their potential utilization in Generation-IV reactors as nuclear fuels. Understanding the incorporation of fission products and oxygen is very important to predict the behavior of nuclear fuels. A first approach to this goal is the study of the incorporation energies and stability of these elements in the material. By means of first-principles calculations within the framework of density functional theory, we calculate the incorporation energies of He, Xe, Kr and O atoms in Th and C vacancy sites, in tetrahedral interstitials and in Schottky defects along the 〈111〉 and 〈100〉 directions. We also analyze atomic displacements, volume modifications and Bader charges. This kind of results for ThC, to the best authors' knowledge, have not been obtained previously, neither experimentally, nor theoretically. This should deal as a starting point towards the study of the complex behavior of fission products in irradiated ThC.Fil: Perez Daroca, Diego Raul. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Llois, Ana Maria. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Mosca, Hugo Osvaldo. Comisión Nacional de Energía Atómica; Argentina. Universidad Nacional de San Martín. Instituto Sabato; Argentin
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