Em defesa da liberdade acadêmica e da autonomia: apresentação ao dossiê “Autonomia Universitária no Brasil, 30 anos (1988-2018): história, projetos e impasses”

Prólogo al dossier “Autonomia Universitária no Brasil, 30 anos (1988-2018): história, projetos e impasses”Introduction to the Dossier “Autonomia Universitária no Brasil, 30 anos (1988-2018): história, projetos e impasses”Apresentação ao dossiê “Autonomia Universitária no Brasil, 30 anos (1988-2018): história, projetos e impasses

Estudo do desenvolvimento de materiais nanocristalinos : magnetismo e estrutura

Orientador: Reiko Sato TurtelliTese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb WataghinResumo: Neste trabalho são realizados estudos de diversas propriedades magnéticas e estruturais no processo de desenvolvimento da microestrutura nanocristalina formada a partir de uma liga amorfa de composição Fe73.5CU1Nb3Si13.5B9.Após tratamentos térmicos específicos, formam-se cristais nanométricos imersos em uma matriz amorfa, que são os responsáveis pelas excelentes propriedades magnéticas que esses materiais apresentam. O processo de cristalização é analisado utilizando as seguintes técnicas: Espectroscopía Mõssbauer, difração de raios-x, relaxação da permeabilidade magnética, magnetostrição, curvas de histerese, permeabilidade inicial, campo de pinning e temperatura de Curie. É verificado que a formação dos cristais nanométricos influencia drasticamente os graus de liberdade dos defeitos presentes na estrutura amorfa, ocorrendo um quase completo desaparecimento do fenômeno de relaxação magnética nesses materiais. Tal fato pode ser verificado separando a contribuição das duas componentes estruturais, utilizando os resultados obtidos através de Espectroscopía Mõssbauer. A análise dos espectros Mõssbauer fornece ainda a evolução composicional e a estrutura dos cristais formados. Tais resultados, em conjunto com os dados obtidos das linhas de difração de raios-x, fornecem uma visão completa da microestrutura desses novos materiais. Através das medidas magnéticas macroscópicas comprovam-se as excelentes propriedades magnéticas dos materiais nanocristalinos. Dessas investigações é verificado que o estado nanocristalino final é dependente do grau de desordem topológica da fita amorfa inicial. Para um estudo mais sistemático desse efeito, são desenvolvidas técnicas indiretas para a caracterização da estrutura amorfa. Como resultado final, é verificado que a permeabilidade do material nanocristalino depende fortemente da taxa de resfriamento na qual a amostra amorfa foi produzidaAbstract: In this work, several magnetic and structural investigations have been performed during the development of a nanocrystalline state from an amorphous ribbon of nominal composition Fe73.5Cu1Nb3Si13.5B9. After specific thermal treatments, the material consist on nanometer sized crystallites embedded in an amorphous matrix, which are responsible for the excellent magnetic properties achieved. The crystallization process is analyzed using the following techniques: Mõssbauer spectroscopy, x-ray diffraction, magnetic aftereffect, hysteresis loops, initial permeability , pinning field, magnetostriction, Curie temperature. It is observed that the formation of the nanocrystals influences drastically the degree of freedom of the defects present in the amorphous phase, occurring an almost complete suppression of relaxation effects in these materials. This fact can be verified separating the contribution of the two structural phases using the results obtained from Mossbauer spectroscopy. The analysis of Mõssbauer spectra gives also information about compositional evolution and structure of the crystal1ine grains. This results, in addition with data extracted from x-ray diffraction, offer a complete view of the microstructure of these new materials. From macroscopic magnetic measurements the excellent soft magnetic properties are verified. It is observed that the final nanocrystal1ine state is dependent on the degree of topological disorder of the initial amorphous ribbons. In order to perform a systematic study concerning this point, several methods to characterize the amorphous structure are developed. As a final result it is observed that the magnetic permeability is highly dependent on the quenching rate at which the amorphous ribbons are produced.DoutoradoFísicaDoutor em Ciência

Structural analysis of magnetic nanocomposites based on chitosan

This work investigates the structure and magnetic properties of chitosan based films with different contents of magnetic nanoparticles (MNPs) of around 10 nm as well as the effects of the addition of glycerol as plasticizer. Synthesized MNPs were dispersed in the chitosan film forming solution by ultrasonication and then composite films were obtained by casting. From the morphological analysis, a bimodal distribution of clusters was detected; the larger ones seem to be present mostly in the plasticized samples. Regarding the mechanical behavior of the samples, for the non-plasticized samples the outstanding increase in modulus and strength with the increasing content of MNP was explained by a strong interfacial adhesion and very good particles dispersion into the chitosan matrix. This fact was also supported by the model applyed to the strength as a function of the volume fraction of MNP. Regarding magnetic properties, all nanocomposite films evidenced systems with particles of strong dipolar interactions that lead to blocking and irreversibility temperatures close to room temperature (RT). Even though the isothermal magnetization results showed that the particles in the nanocomposite films behave as super-paramagnetic at the highest analyzed temperature (RT). Langevin model as well as FESEM and SAXS analysis supported the hypothesis that the formation of aggregates with different features dominates the magnetic response through collective behavior, mainly in the plasticized films.Fil: Kloster, Gianina Andrea. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Muraca, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Físicas de Mar del Plata. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Físicas de Mar del Plata; ArgentinaFil: Moscoso Londoño, Oscar. Universidade Estadual de Campinas; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Knobel, Marcelo. Universidade Estadual de Campinas; BrasilFil: Marcovich, Norma Esther. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Mosiewicki, Mirna Alejandra. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentin

Characterization of the magnetic interactions of multiphase magnetocaloric materials using first-order reversal curve analysis

In order to understand the magnetocaloric response of materials, it is important to analyze the interactions between the different phases present in them. Recent models have analyzed the influence of these interactions on the magnetocaloric response of composites, providing an estimate value of the interaction field that is consistent with experimental results. This paper analyzes to which extent magnetization first-order reversal curve (FORC) method can be used to calculate these interactions. It is shown that the different field ranges that are explored using these techniques (inside the hysteretic region for FORC; close to magnetic saturation for magnetocaloric effect) produce interaction field values that differ in order of magnitude, with FORC being sensitive to the lower values of the interaction field and magnetocaloric analysis accounting for the larger interactions

Synthesis and magnetic properties of cobalt-iron/cobalt-ferrite soft/hard magnetic core/shell nanowires

A straightforward method for the synthesis of CoFe2.7/CoFe2O4 core/shell nanowires is described. The proposed method starts with a conventional pulsed electrodeposition procedure on alumina nanoporous template. The obtained CoFe2.7 nanowires are released from the template and allowed to oxidize at room conditions over several weeks. The effects of partial oxidation on the structural and magnetic properties were studied by x-ray spectrometry, magnetometry, and scanning and transmission electron microscopy. The results indicate that the final nanowires are composed of 5 nm iron-cobalt alloy nanoparticles. Releasing the nanowires at room conditions promoted surface oxidation of the nanoparticles and created a CoFe2O4 shell spinel-like structure. The shell avoids internal oxidation and promotes the formation of bi-magnetic soft/hard magnetic core/shell nanowires. The magnetic properties of both the initial single-phase CoFe2.7 nanowires and the final core/shell nanowires, reveal that the changes in the properties from the array are due to the oxidation more than effects associated with released processes (disorder and agglomeration).Fil: Londoño Calderon, Cesar Leandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnología en Polímeros y Nanotecnología. Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnología en Polímeros y Nanotecnología; ArgentinaFil: Moscoso Londoño, Oscar. Universidade Estadual de Campinas; Brasil. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Muraca, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidade Estadual de Campinas; Brasil. Brazilian Center for Research in Energy and Materials. Brazilian Nanotechnology National Laboratory; BrasilFil: Arzuza, Luis. Universidade Estadual de Campinas; BrasilFil: Carvalho, Peterson. Universidade Estadual de Campinas; BrasilFil: Pirota, Kleber Roberto. Universidade Estadual de Campinas; BrasilFil: Knobel, Marcelo. Universidade Estadual de Campinas; BrasilFil: Pampillo, Laura Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Martinez Garcia, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Formosa. Facultad de Recursos Naturales; Argentin

Significant coercivity enhancement at low temperatures in magnetically oriented cobalt ferrite nanoparticles

The present work describes a synthesis and characterization strategy employed to study the magnetic anisotropic properties of a diluted nanoparticulate system. The system under analysis is composed of monodisperse and highly crystalline 16 nm Co0.5Fe2.5O4 nanoparticles (NPs), homogenously dispersed in 1-octadecene. Owing to the liquid nature of the matrix at room temperature, the relative orientation of the nanoparticle easy axis can be controlled by an external magnetic field, enabling us to measure how the magnetic properties are modified by the alignment of the particles within the sample. In turn, by employing this strategy, we have found a significant hardness and squareness enhancement of the hysteresis loop in the magnetically oriented system, with the coercive field reaching a value as high as 30.2 kOe at low temperatures. In addition, the magnetic behavior associated with the system under study was supported by additional magnetic measurements, which were ascribed to different events expected to take place throughout the sample characterization, such as the melting process of the 1-octadecene matrix or the NP relaxation under the Brownian mechanism at high temperatures.Fil: Tancredi, Pablo. Instituto Nacional de Tecnología Industrial; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long". Universidad de Buenos Aires. Facultad de Ingeniería. Instituto de Tecnologías y Ciencias de la Ingeniería "Hilario Fernández Long"; ArgentinaFil: Rivas Rojas, Patricia Carolina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Moscoso Londoño, Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Muraca, Diego. Universidade Estadual de Campinas; BrasilFil: Knobel, Marcelo. Universidade Estadual de Campinas; BrasilFil: Socolovsky, Leandro Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Tecnológica Nacional. Facultad Regional Santa Cruz. Centro de Investigaciones y Transferencia de Santa Cruz. Universidad Nacional de la Patagonia Austral. Centro de Investigaciones y Transferencia de Santa Cruz; Argentin

Domain wall propagation tuning in magnetic nanowires through geometric modulation

The magnetic behavior of nickel modulated nanowires embedded in porous alumina membranes is investigated. Their diameters exhibit a sharp transition between below (35 nm) and above (52 nm) the theoretical limit for transverse and vortex domain walls. Magnetic hysteresis loops and first-order reversal curves (FORCs) were measured on several ordered nanowire arrays with different wide-narrow segment lengths ratio and compared with those from homogenous nanowires. The experimental magnetic response evidences a rather complex susceptibility behavior for nanowires with modulated diameter. Micromagnetic simulations on isolated and first-neighbors arrays of nanowires show that the domain wall structure, which depends on the segment diameter, suffers a transformation while crossing the diameter modulation, but without any pinning. The experimental array magnetic behavior can be ascribed to a heterogeneous stray field induced by the diameter modulation, yielding a stronger interaction field at the wide extremity than at the narrow one. The results evidence the possibility to control the domain wall propagation and morphology by modulating the lateral aspect of the magnetic entity

Compact Ag@fe3o4 Core-shell Nanoparticles By Means Of Single-step Thermal Decomposition Reaction.

A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.4683

Iron oxide nanosized clusters embedded in porous nanorods: A new colloidal design to enhance capabilities of MRI contrast agents

“This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, © 2010 American Chemical Society after peer review and technical editing by the publisher. To acces final work see “Iron oxide nanosized clusters embedded in porous nanorods: A new colloidal design to enhance capabilities of MRI contrast agents”, ACS Nano 4.4 (2010): 2095-2103, https://doi.org/10.1021/nn9013388"Development of nanosized materials to enhance the image contrast between the normal and diseased tissue and/or to indicate the status of organ functions or blood flow is essential in nuclear magnetic resonance imaging (MRI). Here we describe a contrast agent based on a new iron oxide design (superparamagnetic iron oxide clusters embedded in antiferromagnetic iron oxide porous nanorods). We show as a proof-of-concept that aqueous colloidal suspensions containing these particles show enhanced-proton relaxivities (i.e., enhanced MRI contrast capabilities). A remarkable feature of this new design is that large scale production is possible since aqueous-based routes are used, and porosity and iron oxide superparamagnetic clusters are directly developed from a single phase. We have also proved with the help of a simple model that the physical basis behind the increase in relaxivities lies on both the increase of dipolar field (interactions within iron oxide clusters) and the decrease of proton-cluster distance (porosity favors the close contact between protons and clusters). Finally, a list of possible steps to follow to enhance capabilities of this contrast agent is also included (partial coating with noble metals to add extra sensing capacity and chemical functionality, to increase the amount of doping while simultaneously carrying out cytotoxicity studies, or to find conditions to further decrease the size of the nanorods and to enhance their stability)We acknowledge financial support from the Spanish Ministerio de Ciencia e innovación trough MAT2008-03224/NAN and from the Comunidad Autónoma de Madrid under Project S-0505/MAT/019