UFSMOOC: uma plataforma institucional para cursos online gratuitos

Teaching options aimed at the community, at UFSM (Federal University of Santa Maria), could reach a greater number of people, if it weren't for the absence of a platform for the use of MOOCs (Massive Open Online Courses). Here, the creation of an institutional platform that meets this need is presented; with free courses, from all knowledge areas. The implementation weighed aspects of the system’s usability and design, as well as its functionality and security. In this context, the developed software has shown the potential to become a relevant tool in the democratization of knowledge in Brazil.As opções de extensão focadas no ensino para a comunidade, naUFSM (Universidade Federal de Santa Maria), poderiam alcançar um númeromaior de pessoas, não fosse a ausência de uma plataforma para uso deMOOCs (Massive Open Online Courses). Este artigo apresenta a criação deuma plataforma institucional que supra essa necessidade; com cursosgratuitos, de todas as áreas do conhecimento. A implementação considerouaspectos da usabilidade e design do sistema, bem como sua funcionalidade esegurança. Neste contexto, o software desenvolvido apresentou potencialidadede tornar-se uma ferramenta relevante na democratização do conhecimento noBrasil

Quantum tunneling in magnetic tunneling junctions

This paper reports on the study of ferromagnetic tunneling junctions produced by magnetron sputtering technique and deposited under oxidation conditions that lead to low potential barrier height, low asymmetrical barrier and quantum tunneling as the charge transport mechanism. The exponential growth of the effective area-resistance product with the effective barrier thickness, and the concentration of the tunnel current in small areas of the junctions, were identified by fitting room temperature I-V curves, for each individual sample, with either Simmons’ [J. Appl. Phys. 34, 1793 (1963); 35, 2655 (1964); 34, 2581 (1963)] or Chow’s [J. Appl. Phys. 36, 559 (1965)] model. This result suggests the presence of effective tunneling areas or hot spots, leading to a non-uniform current distribution and showing quantum tunneling as the charge transport mechanism. This mechanism, is also, verified through I-T curves

Observation of recoil magnetization curves outside the major loop in Co, Fe, and Ni films

We report a peculiar magnetization reversal observed in magnetron-sputtered Co, Fe, and Ni films. We found that some recoil (minor) magnetization curves lie entirely and way outside the major loop, a phenomenon referred to here as a recoil-curve overshoot. The greatly enhanced recoil curve’s remanence and coercivity result in an up to 2.5-fold increase of loop’s area. The model of pairs of exchange-coupled grains with misaligned anisotropy axes reproduces, in a very good agreement with the experiment, all key features of the recoil-curve overshoot as well as the kink that some major loops present before saturation. The disclosed features of the ferromagnetic hysteresis provide further insights into this important classical phenomenon

Interações magnéticas e magnetoresistencia em Co/sub 10/ Cu/sub 90/

Foram investigados os efeitos de tratamentos térmicos nas propriedades estruturais, magnéticas e de magnetotransporte eletrônico de fitas de Co10Cu90 rapidamente resfriadas (“melt-spun”) enfatizando o estudo de possíveis relações entre as interações magnéticas entre grãos, camadas e cristais presentes nestes materiais e a magnetoresistência. A análise combinada da evolução estrutural e da intensidade das interações entre os grãos magnéticos mostra claramente o papel de alguns parâmetros estruturais (tamanho e densidade de partículas, distância entre partículas) e da própria intensidade das interações entre as partículas nas propriedades de transporte eletrônico em presença de um campo magnético

Correlation between magnetic interactions and giant magnetoresistance in melt-spun co/sub 10/cu/sub 90/ granular alloys

The effects of annealing on the structural, magnetic, and magnetotransport properties of melt-spun Co10Cu90 granular alloys were investigated. The interaction effects were studied from both remanent magnetization and magnetotransport data, using two different methods to reach the demagnetized state, ac and dc demagnetization. The analysis of the structural evolution and interaction strength between the magnetic clusters clearly shows the role of some structural parameters ~particle size and density, interparticle distance! and the degree of magnetic correlation in the magnetic field response of the resistance in these inhomogeneous systems

Quantum tunneling in magnetic tunneling junctions

This paper reports on the study of ferromagnetic tunneling junctions produced by magnetron sputtering technique and deposited under oxidation conditions that lead to low potential barrier height, low asymmetrical barrier and quantum tunneling as the charge transport mechanism. The exponential growth of the effective area-resistance product with the effective barrier thickness, and the concentration of the tunnel current in small areas of the junctions, were identified by fitting room temperature I-V curves, for each individual sample, with either Simmons’ [J. Appl. Phys. 34, 1793 (1963); 35, 2655 (1964); 34, 2581 (1963)] or Chow’s [J. Appl. Phys. 36, 559 (1965)] model. This result suggests the presence of effective tunneling areas or hot spots, leading to a non-uniform current distribution and showing quantum tunneling as the charge transport mechanism. This mechanism, is also, verified through I-T curves

A comparative study of magnetic properties of large diameter Co nanowires and nanotubes

A comparative study of the magnetic properties of the arrays of Co nanowires and nanotubes with large external diameters (180 nm) has been carried out. The nanowires/nanotubes were grown by electrodeposition into the self-assembled pores of anodic alumina membranes. The experimental study of their magnetic behavior was focused on the angular dependence of hysteresis loops and their parameters. In both nanowire and nanotube arrays, from the analysis of experimental data, effective longitudinal magnetic anisotropy is concluded, which is stronger in the case of the nanotube array. In addition, the extremely small remanence observed for all loops indicates the important role played by magnetostatic interactions. Micromagnetic simulations were first performed considering intrinsic shape and magnetocrystalline anisotropy terms, together with an effective easy-plane anisotropy to account for those magnetostatic interactions. A qualitative agreement between experiments and simulations is found despite the complexity introduced by the intrinsic and extrinsic array properties (i.e., large diameters, grain structure, and array configuration). In addition, simulations were also carried out for individual nanowire/nanotube with a particular emphasis to understand their differences at the remanence, due to pure geometry contribution.This work was supported by the Spanish Ministry of Economy, Industry and Competitiveness (MINECO) under the grants MAT2016-76824-C3-1-R and FIS2016-78591-C3-3-R, and the Regional Government of Madrid under project under project S2013/MIT2850 NANOFRONTMAG-CM.; D.C. and L.S.D. acknowledge Brazilian PDSE Doctoral Programme and Bolsista da CAPES - Proc. n° BEX 7845/14-6.; L.S.D. acknowledges support from Brazilian agency CNPq (Grant 302950/2017-6). J.A. F.-R. acknowledges the support from MINECO and European Social Fund though fellowship BES-2014-068789.Peer reviewe

El Eco de Santiago : diario independiente: Año VIII Número 1605 - 1903 Septiembre 02

This paper reports on the study of deposited (Ni81Fe19/AlOx /Co) magnetic tunnel junctions by magnetron sputtering, with the insulating layer obtained by plasma oxidation of Al. Concentration of the tunnel current in small areas of the junctions and low potential barrier heights were identified by fitting, for each individual sample, the room temperature I-V curves with either Simmons’ [J. Appl. Phys. 34, 1793 1963 ; 35, 2655 (1964) ; 34, 2581 (1963)] or Chow’s [J. Appl. Phys. 36, 559 (1965)] model. A fast decrease of the tunnel magnetoresistance as a function of the bias voltage is observed, with an inversion of its signal above a critical value. The results are discussed in terms of the quantum coherence factor for low height insulating barriers

Magnetism in dilute magnetic oxide thin films based on SnO/sub 2/

Thin films of SnO2 prepared by pulsed-laser deposition on R-cut sapphire substrates exhibit ferromagnetic properties at room temperature when they are doped with Cr, Mn, Fe, Co, or Ni, but not with other 3d cations. Extrapolated Curie temperatures are generally in excess of 500 K. The moment of the films is roughly independent of doping level, from 0.1–15 at. %, with a value per unit substrate area of 200±100u B nm−2. When magnetization is expressed as a moment per 3d dopant ion, it varies from more than the spin-only value at low concentrations to less than 0.2u B/ion near the percolation threshold. Greatest values are found for iron. The magnetization of the films is highly anisotropic with values when the field is applied perpendicular to the substrate more than double the in-plane values. There is little hysteresis except at high doping levels. The oxides are degenerate n-type semiconductors with a Hall mobility of 100 cm2 V−1 s−1 and 1.4 1019 carriers cm−3 in a one-band model, but no anomalous Hall effect or magnetoresistance was observed at room temperature. The data are discussed in relation to (a) the donor impurity-band model of ferromagnetism in semiconductors and (b) the magnetic defect model

Tungsten oxide thin films grown by thermal evaporation with high resistance to leaching

Óxidos de tungstênio apresentam diferentes estequiometrias, estruturas cristalinas e morfologias. Estas características são importantes principalmente quando se deseja utilizá-los como fotocatalisadores. Neste trabalho foram obtidos filmes finos de óxido de tungstênio por evaporação térmica sobre substratos de silício (100) recobertos com ouro, aquecidos a 350 e 600 °C. A estequiometria dos filmes formados, morfologia, estrutura cristalina e resistência à lixiviação foram caracterizadas por espectroscopia de fotoelétrons de raios X, espectroscopia micro-Raman, microscopias eletrônicas de varredura e transmissão, difratometria de raios X, espectrometria de retroespalhamento Rutherford e reação nuclear ressonante O16(α,α´)O16. Os filmes apresentam estrutura nanométrica, cuja forma torna-se bem definida com o aumento da temperatura. O sistema apresenta-se na forma de WO3.1 e cristaliza principalmente na fase hexagonal, sendo obtidas também estruturas de óxido de tungstênio hidratadas. Os filmes obtidos através de evaporação térmica apresentam resistência à lixiviação em ambiente aquoso e excelente atividade fotocatalítica, que foi testada na degradação do corante alaranjado de metila.Tungsten oxides show different stoichiometries, crystal lattices and morphologies. These characteristics are important mainly when they are used as photocatalysts. In this work tungsten oxide thin films were obtained by thermal evaporation on (100) silicon substrates covered with gold and heated at 350 and 600 °C, with different deposition times. The stoichiometry of the films, morphology, crystal structure and resistance to leaching were characterized through X-ray photoelectron spectroscopy, micro-Raman spectroscopy, scanning and transmission electron microscopy, X-ray diffractometry, Rutherford backscattering spectrometry and O16(α,α´)O16 resonant nuclear reaction. Films obtained at higher temperatures show well-defined spherical nanometric structure; they are composed of WO3.1 and the presence of hydrated tungsten oxide was also observed. The major crystal structure observed is the hexagonal. Thin films obtained through thermal evaporation present resistance to leaching in aqueous media and excellent performance as photocatalysts, evaluated through the degradation of the methyl orange dye