Phase diagram description of the CaCu3Fe4O12 double perovskite

CaCu3Fe4O12 exhibits a temperature-induced transition from a ferrimagnetic-insulating phase, in which Fe appears charge disproportionated, as Fe 3 + and Fe 5 +, to a paramagnetic-metallic phase at temperatures above 210 K, with Fe 4 + present. To describe it, we propose a microscopic effective model with two interpenetrating sublattices of Fe (4 - δ) + + and Fe (4 + δ) + +, respectively, δ being a measure of the Fe-charge disproportionation. We include all 3d-Fe orbitals: t 2 g localized orbitals, with spin 3/2 and magnetically coupled, plus two degenerate itinerant eg orbitals with local and nearest-neighbor (NN) electron correlations, and hopping between NN eg orbitals of the same symmetry. Allub and Alascio [J. Phys.: Condens. Matter 24(49), 495601 (2012)] previously proposed a model to describe the phase transition in LaCu3Fe4O12 from a paramagnetic-metal to an antiferromagnetic-insulator, induced by temperature or pressure, involving charge transfer between Fe and Cu ions, in contrast to Fe-charge disproportionation. With the model proposed for CaCu3Fe4O12, modified to account for this difference between the two compounds, the density of states of the itinerant Fe orbitals was obtained, using Green´s function methods. The phase diagram of CaCu3Fe4O12 was calculated, including phases exhibiting Fe-charge disproportionation, where the two eg orbitals in each site are symmetrically occupied, as well as novel phases exhibiting local orbital selectivity/asymmetric occupation of eg orbitals. Both kinds of phases may exhibit paramagnetism and ferromagnetism. We determined the model parameters which best describe the phase transition observed in CaCu3Fe4O12 and found other phases in different parameter ranges, which might be relevant for other compounds of the ACu3Fe4O12 family, presenting Fe-charge disproportionation and intersite charge transfer Fe-Cu.Fil: Buitrago Piñeros, Ivon Rocio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Universidad Nacional de Cuyo; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Ventura, Cecilia Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Universidad Nacional de Río Negro; ArgentinaFil: Allub, Roberto Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentin

Gender dysphoria: an overview

Gender dysphoria, gender identity disorder or transsexualism is a psychological condition that requires care and multiple health professionals; endocrinologists, surgeons and psychiatrists are just some of the professionals needed to address these situations. The following article is a summary of what transsexuality means, its history and treatment, as more and more people request our services with a therapeutic approach

Strategies for COVID-19 vaccination under a shortage scenario: a geo-stochastic modelling approach

In a world being hit by waves of COVID-19, vaccination is a light on the horizon. However, the roll-out of vaccination strategies and their influence on the pandemic are still open questions. In order to compare the effect of various strategies proposed by the World Health Organization and other authorities, a previously developed SEIRS stochastic model of geographical spreading of the virus is extended by adding a compartment for vaccinated people. The parameters of the model were fitted to describe the pandemic evolution in Argentina, Mexico and Spain to analyze the effect of the proposed vaccination strategies. The mobility parameters allow to simulate different social behaviors (e.g. lock-down interventions). Schemes in which vaccines are applied homogeneously in all the country, or limited to the most densely-populated areas, are simulated and compared. The second strategy is found to be more effective. Moreover, under the current global shortage of vaccines, it should be remarked that immunization is enhanced when mobility is reduced. Additionally, repetition of vaccination campaigns should be timed considering the immunity lapse of the vaccinated (and recovered) people. Finally, the model is extended to include the effect of isolation of detected positive cases, shown to be important to reduce infections.Fil: Barreiro, Nadia Luisina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; ArgentinaFil: Ventura, Cecilia Ileana. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Govezensky, T.. Universidad Nacional Autónoma de México; MéxicoFil: Nuñez, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Bolcatto, Pablo Guillermo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Matemática Aplicada del Litoral. Universidad Nacional del Litoral. Instituto de Matemática Aplicada del Litoral; Argentina. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; ArgentinaFil: Barrio, R. A.. Universidad Nacional Autónoma de México; Méxic

Estrategias de vacunación contra la pandemia en México

Estrategias de vacunación contra la pandemia en México.Fil: Barrio, Rafael. Universidad Nacional Autónoma de México; MéxicoFil: Barreiro, Nadia. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; ArgentinaFil: Bolcatto, P.. Ministerio de Defensa. Instituto de Investigaciones Científicas y Técnicas para la Defensa; ArgentinaFil: Garcia, Alberto. Universidad Nacional Autónoma de México; MéxicoFil: Govezensky, T.. Universidad Nacional Autónoma de México; MéxicoFil: Nuñez, Matias. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Ventura, Cecilia Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Renormalized spin waves in the AF Heisenberg-Kondo model for heavy fermions.

Recent neutron measurements in CeIn_3 and CePd_2Si_3 evidenced spin wave excitations at low temperatures. These heavy fermion compounds exhibit AF long range order, but a strong competition between the RKKY interaction and Kondo effect is evidenced by their nearly equal N?el and Kondo temperatures. Our aim is to show how magnons in the AF phase of these compounds can be dexribed by a microscopic Heisenberg-Kondo model [J. Iglesias et al. PRB 56, 11820 (1997)] introduced before for the non-magnetic phase. The model includes the correlated Ce 4f electrons hybridized with the conduction band, and we consider competing RKKY and Kondo AF couplings. Carrying on a series of unitary transformations we perturbatively derive an effective Hamiltonian which, projected onto the AF electron ground state, describes the spin wave excitations, renormalized by their interaction with the correlated itinerant electrons. We numerically study how the different parameters of the model influence the renormalization of the magnons and compare our results with available experimental data, finding good agreement with the spin wave measurements in cubic CeIn_

Generic model of the colossal magnetoresistance pyrochlore Tl/sub 2/Mn/sub 2/O/sub 7/

The colossal magnetoresistance (CMR) exhibited by the pyrochlore compound Tl₂Mn₂O₇ was discovered in 1996. Important differences with CMR Mn-perovskite compounds regarding crystal structure and electronic properties were soon realized, indicating the possibility of different mechanisms for CMR being present. Recently, new pyrochlore compounds exhibiting CMR were prepared. The larger experimental background now existent, has received diverse interpretations. In the present work, we aim to contribute to the understanding of the properties of Tl₂Mn₂O₇ through the study of a generic model for the compound, including Hund and superexchange couplings as well as hybridization effects (HS model). The model includes two kinds of electronic orbitals, as widely believed to be present: one, directly related to the magnetism of the compound, involves localized Mn moments, represented by spins, and a narrow band strongly Hund coupled to them. Also, more extended electronic orbitals, related to the carriers in Tl₂Mn₂O₇, appear and hybridize with the narrow band. The possibility of a superexchange coupling between the localized spins is also allowed for. This generic model allows exploration of many of the proposals put forward by other researchers for Tl₂Mn₂O₇. As a first approach to the problem, here we employ a mean field approximation to study the magnetic phase diagram and electronic structure of the HS model, for various sets of parameters mentioned before in connection with the compound. Furthermore, we are able to exhibit similarities with predictions obtained before using an intermediate valence model for Tl₂Mn₂O₇, if appropriate sets of parameters are used. In particular, we show here many common features which can be obtained for the electronic structure around the Fermi level in the ferromagnetic phase. Due to the simplifications adopted in the present treatment the comparison between the models could not be extended to higher temperatures here

Formation of non-substitutional beta-Sn defects in Ge1-x Snx alloys

Although group IV semiconductor alloys are expected to form substitutionally, in Ge1xSnx this is true only for low concentrations (x < 0.13). The use of these alloys as a narrow gap semiconductor depends on the ability to produce samples with the high quality required for optoelectronic device applications. In a previous paper, we proposed the existence of a non-substitutional complex defect (b-Sn), consisting of a single Sn atom in the center of a Ge divacancy, which may account for the segregation of Sn at large x. Afterwards, the existence of this defect was confirmed experimentally. In this paper we study the local environment and the interactions of the substitutional defect (a-Sn), the vacancy in Ge, and the b-Sn defect by performing extensive numerical ab initio calculations. Our results confirm that a b-Sn defect can be formed by natural diffusion of a vacancy around the substitutional a-Sn defect, since the energy barrier for the process is very small.Fil: Fuhr, Javier Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); ArgentinaFil: Ventura, Cecilia Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Rio Negro. Sede Andina; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); ArgentinaFil: Barrio, Rafael A. . Universidad Nacional Autónoma de México; Méxic

Normal state electronic properties of LaO1−xFxBiS2 superconductors

A good description of the electronic structure of BiS2-based superconductors is essential to understand their phase diagram, normal state and superconducting properties. To describe the first reports of normal state electronic structure features from angle resolved photoemission spectroscopy (ARPES) in LaO1-xFxBiS2, we used a minimal microscopic model to study their low energy properties. It includes the two effective tight-binding bands proposed by Usui et al., Phys. Rev. B, 86, 2012, 220501(R), and we added moderate intra- A nd inter-orbital electron correlations related to Bi-(pY, pX) and S-(pY, pX) orbitals. We calculated the electron Green's functions using their equations of motion, which we decoupled in second-order of perturbations on the correlations. We determined the normal state spectral density function and total density of states for LaO1-xFxBiS2, focusing on the description of the k-dependence, effect of doping, and the prediction of the temperature dependence of spectral properties. Including moderate electron correlations, improves the description of the few experimental ARPES and soft X-ray photoemission data available for LaO1-xFxBiS2. Our analytical approximation enabled us to calculate the spectral density around the conduction band minimum at k→0=(0.45π,0.45π), and to predict the temperature dependence of the spectral properties at different BZ points, which might be verified by temperature-dependent ARPES.Fil: Querales Flores, Jose Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Ventura, Cecilia Ileana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; ArgentinaFil: Citro, R.. Universidad Nacional de Río Negro; ArgentinaFil: Rodríguez Núñez, J. J.. Universidad de Carabobo; Venezuel