University Nac Of Cuyo

San Carlos de Bariloche, Argentina

University Nac Of Cuyo

San Carlos de Bariloche, Argentina
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Carreira S.J.,Comision Nacional de la Energia Atomica | Carreira S.J.,CONICET | Aviles Felix L.,CONICET | Aviles Felix L.,Bariloche Atomic Center | And 7 more authors.
Applied Physics Letters | Year: 2016

We report on the interlayer exchange coupling across insulating barriers observed on Ni80Fe20/Ba0.05Sr0.95TiO3/La0.66Sr0.33MnO3 (Py/BST0.05/LSMO) trilayers. The coupling mechanism has been analyzed in terms of the barrier thickness, samples' substrate, and temperature. We examined the effect of MgO (MGO) and SrTiO3 (STO) (001) single-crystalline substrates on the magnetic coupling and also on the magnetic anisotropies of the samples in order to get a deeper understanding of the magnetism of the structures. We measured a weak coupling mediated by spin-dependent tunneling phenomena whose sign and strength depend on barrier thickness and substrate. An antiferromagnetic (AF) exchange prevails for most of the samples and smoothly increases with the barrier thicknesses as a consequence of the screening effects of the BST0.05. The coupling monotonically increases with temperature in all the samples and this behavior is attributed to thermally assisted mechanisms. The magnetic anisotropy of both magnetic components has a cubic symmetry that in the case of permalloy is added to a small uniaxial component. © 2016 Author(s).

Aviles-Felix L.,Bariloche Atomic Center | Butera A.,Bariloche Atomic Center | Butera A.,University Nac Of Cuyo | Gomez J.E.,Bariloche Atomic Center
Applied Physics Letters | Year: 2017

We report the observation of spin pumping and inverse spin Hall effects in antiferromagnetically coupled [Co/Ru/Co]/Pt heterostructures. The “spin-flop” magnetization process observed in antiferromagnetically exchange coupled Co layers combined with spin pumping and inverse spin Hall effects allowed us to detect both transversal and longitudinal charge accumulations. By controlling the exchange coupling strength and the spin flop transition in the magnetization process, it was possible to produce spin currents polarized in different directions. © 2017 Author(s).

Querales-Flores J.D.,Bariloche Atomic Center | Querales-Flores J.D.,University Nac Of Cuyo | Ventura C.I.,Bariloche Atomic Center | Ventura C.I.,University Nac Of Rio Negro | And 3 more authors.
Journal of Applied Physics | Year: 2016

The existence of non-substitutional β-Sn defects in Ge1-xSnx alloys was confirmed by emission channeling experiments [Decoster et al., Phys. Rev. B 81, 155204 (2010)], which established that, although most Sn enters substitutionally (α-Sn) in the Ge lattice, a second significant fraction corresponds to the Sn-vacancy defect complex in the split-vacancy configuration (β-Sn), in agreement with our previous theoretical study [Ventura et al., Phys. Rev. B 79, 155202 (2009)]. Here, we present the electronic structure calculations for Ge1-xSnx, including the substitutional α-Sn as well as the non-substitutional β-Sn defects. To include the presence of the non-substitutional complex defects in the electronic structure calculation for this multi-orbital alloy problem, we extended the approach for the purely substitutional alloy by Jenkins and Dow [Phys. Rev. B 36, 7994 (1987)]. We employed an effective substitutional two-site cluster equivalent to the real non-substitutional β-Sn defect, which was determined by a Green's functions calculation. We then calculated the electronic structure of the effective alloy purely in terms of substitutional defects, embedding the effective substitutional clusters in the lattice. Our results describe the two transitions of the fundamental gap of Ge1-xSnx as a function of the total Sn-concentration: namely, from an indirect to a direct gap, first, and the metallization transition at a higher x. They also highlight the role of β-Sn in the reduction of the concentration range, which corresponds to the direct-gap phase of this alloy of interest for the optoelectronics applications. © 2016 Author(s).

Ruestes C.J.,University of Mendoza | Ruestes C.J.,University Nac Of Cuyo | Ruestes C.J.,University of California at San Diego | Bringa E.M.,University of Mendoza | And 5 more authors.
Computational Materials Science | Year: 2014

Nanoporous materials, can present an outstanding range of mechanical properties. Both molecular dynamics and dislocation analysis were used to evaluate and quantify the evolution of plasticity in a porous Ta single crystal containing randomly placed voids with 3.3 nm radii and average initial porosity of 4.1%, when subjected to uniaxial compressive strain. Nanovoids act as effective sources for dislocation emission. Dislocation shear loops nucleate at the surface of the voids and expand by the advance of the edge component. The evolution of dislocation configuration and densities were predicted by the molecular dynamics calculations and successfully compared to an analysis based on Ashby's concept of geometrically-necessary dislocations. Resolved shear stress calculations were performed for all bcc slip systems and used to identify the operating Burgers vectors in the dislocation loops. The temperature excursion during plastic deformation was used to estimate the mobile dislocation density which is found to be less than 10% of the total dislocation density. © 2014 Elsevier B.V. All rights reserved.

Querales Flores J.D.,Bariloche Atomic Center | Querales Flores J.D.,University Nac Of Cuyo | Ventura C.I.,Bariloche Atomic Center | Ventura C.I.,University Nac Of Rio Negro | And 3 more authors.
Physics Letters, Section A: General, Atomic and Solid State Physics | Year: 2016

Using a second-order perturbative Green's functions approach we determined the normal state spectral function A(k→,ω) employing a minimal model for ferropnictides. Used before to study magnetic fluctuations and superconducting properties, it includes the two effective bands related to Fe-3d orbitals proposed by S. Raghu et al. [Phys. Rev. B 77 (2008) 220503(R)], and local intra- and inter-orbital correlations for the effective orbitals. Here, we focus on the normal state electronic properties, in particular the temperature and doping dependence of the total density of states, A(ω), and of A(k→,ω) in different Brillouin zone regions, comparing them with existing angle resolved photoemission spectroscopy (ARPES) and theoretical results. We obtain an asymmetric effect of electron and hole doping, quantitative agreement with the experimental chemical potential shifts, as well as spectral weight redistributions near the Fermi level with temperature consistent with the available experiments. In addition, we predict a non-trivial dependence of A(ω) with temperature, exhibiting clear renormalization effects by correlations. Interestingly, investigating the origin of this predicted behavior by analyzing the evolution with temperature of the k-dependent self-energy obtained in our approach, we could identify a number of Brillouin zone points, not probed by ARPES yet, where the largest non-trivial effects of temperature on the renormalization are predicted for the parent compounds. © 2016 Elsevier B.V.

Buitrago I.R.,University Nac Of Cuyo | Ventura C.I.,Bariloche Atomic Center
Journal of Superconductivity and Novel Magnetism | Year: 2013

We investigate magnetic excitations in half-doped colossal magnetoresistance manganites. In particular, we focus on spin excitations in the CE phase originally proposed by Goodenough (Phys. Rev. 100:564, 1955). Using a localized spin model, we calculated magnons for 3D-perovskite compounds such as La1-x Mx MnO3, where M=Ca, Sr, Ba, and for their 2D-laminar counterparts. We compared them with predictions for the spin excitations corresponding to other phases proposed. For the laminar half-doped manganite La0.5Sr1.5MnO4, for which magnon measurements by inelastic neutron scattering exist, as well as an estimation of the magnetic couplings, our calculations agree well with the experimental data. © 2012 Springer Science+Business Media, LLC.

Buitrago I.R.,Bariloche Atomic Center | Buitrago I.R.,University Nac Of Cuyo | Ventura C.I.,Bariloche Atomic Center | Ventura C.I.,University Nac Of Rio Negro | Manuel L.O.,CONICET
IEEE Transactions on Magnetics | Year: 2013

At half doping, the ground state of three-dimensional manganite perovskite oxides like R1-xCax MnO3, where R is a trivalent ion such as La, Pr, etc., is still unclear. Many experimental findings agree better with the combined magnetic, charge, and orbital order characteristic of the 'intermediate phase', introduced by Efremov et 2004 [Nat. Mater., 3, 853]. This phase consists of spin dimers (thus incorporating aspects of the Zener polaron phase (ZP) proposed in 2002 by Daoud-Aladine et al. [Phys. Rev. Lett., 89, 097205]), though formed by a pair of parallel Mn spins of different magnitude, in principle (thereby allowing for a degree of Mn charge disproportionation: not necessarily as large as that of Mn3+ -Mn4+ in Goodenough's original CE phase [Phys. Rev. 100, 564 (1955)]). In the intermediate phase, consecutive spin dimers localed along the planar zig-zag chains are oriented at a constant relative angle φ between them. Varying Mn-charge disproportionation and φ, the intermediate phase should allow to continuously interpolate between the two limiting cases of the CE phase and the dimer phase denoted as 'orthogonal intermediate π/2-phase'. It is not easy to find a microscopic model able to describe the phenomenological intermediate phase adequately for the spin, charge, and orbital degrees of freedom simultaneously. Here, we study the quantum spin excitations of a planar model of interacting localized spins, which we found can stabilize the intermediate phase classically. We compare the quantum magnons of the intermediate phase with those of the CE and orthogonal π/2 phases, in the context of recent experimental results. © 1965-2012 IEEE.

Sesma F.G.,University Nac Of Cuyo | Larochette P.A.,University Nac Of Cuyo | Larochette P.A.,Bariloche Atomic Center | Pelegrina J.L.,University Nac Of Cuyo | Pelegrina J.L.,Bariloche Atomic Center
Journal of Alloys and Compounds | Year: 2010

The shift of the martensitic transformation temperatures has been measured in a Cu-Zn-Al alloy as a function of the quenching temperature using different experimental techniques. Results from temperature and stress induced transformations were compared. It was found that the spread of the results is related to the geometry as also to the preparation time characteristic of each experimental method. The evidence of Zn loss by volatilization during the high temperature anneals is also reported. © 2010 Elsevier B.V.

Sirena M.,University Nac Of Cuyo | Sirena M.,CONICET | Kaul E.,University Nac Of Cuyo | Kaul E.,CONICET | And 6 more authors.
Journal of Applied Physics | Year: 2011

The La0.75Sr0.25MnO3 (LSMO)/Ba 0.7Sr0.3TiO3 (BSTO) superlattices and bilayers, where LSMO is ferromagnetic and BSTO is ferroelectric, were grown by dc sputtering. X-ray diffraction indicates that the samples present a textured growth with the c axis perpendicular to the substrate. Magnetization measurements show a decrease of the sample's magnetization for decreasing ferromagnetic thickness. This effect could be related to the presence of biaxial strain and a magnetic dead layer in the samples. Conductive atomic force microscopy indicates that the samples present a total covering of the ferromagnetic layer for a ferroelectric thickness higher than four unit cells. Transport tunneling of the carriers seems to be the preferred conduction mechanism through the ferroelectric layer. These are promising results for the development of multiferroic tunnel junctions. © 2011 American Institute of Physics.

Clavijo S.,University Nac Of Cuyo | Membrives F.,University Nac Of Cuyo | Quiroga G.,University Nac Of Cuyo | Boccaccini A.R.,Friedrich - Alexander - University, Erlangen - Nuremberg | And 2 more authors.
Ceramics International | Year: 2016

Electrophoretic deposition (EPD) method has been developed for the fabrication of chitosan/Bioglass® and chitosan/Bioglass®/TiO2 composite coatings on stainless steel substrates for biomedical applications. Microstructure, thickness, and mechanical properties, such as Vickers microhardness, compressive strength, and elastic modulus were determined. The use of chitosan enabled the co-EPD of Bioglass® and TiO2 particles and offered the advantage of room temperature processing typical of EPD. The coating composition was varied by the combination of Bioglass® and TiO2 concentrations in the chitosan solutions used for EPD. The cathodic deposition yield was studied at constant voltage for various deposition times. The coatings were microstructurally characterized by scanning electron microscopy (SEM) and energy dispersive spectroscopy(EDS). Homogeneous chitosan/Bioglass® coatings on stainless steel substrates were obtained at constant voltage condition using aqueous suspensions based on 0.016 wt% chitosan and 2 wt% Bioglass®. The addition of TiO2 nanopowder to the composite coating was confirmed to improve the hardness, Young's modulus and compressive strength of the base chitosan/Bioglass® coating. © 2016 Elsevier Ltd and Techna Group S.r.l.

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