Síntese, caracterização de ferritas espinélio com propriedades magnéticas e absorvedoras de microondas

Were synthesized spinel-type ferrites with general formula Ni0,8Mg0.2-xMxFe2O4, where M represents the doping Mn, Co or Mn + Co simultaneously, x ranges for the values 0.02, 0.05 and 0.1. The value of x was divided by 2 in cases where M equals Mn and Co conjugates. We used the citrate precursor method and heat treatment to obtain the phases at 1100°C. The materials were characterized by XRD, TGA/ DTGA, SEM, MAV and reflectivity measurements by the method of waveguide. Powders to 350°C/3.5 h were crystalline and nanosized. According to the results this temperature all powders have a percentage of ferrite phase over 90%. The composition had the addition of Mn and Co simultaneously showed a higher percentage of secondary phase NiO, 5.8%. The TGA/DTGA curves indicate that this sample reached phase (s) crystalline (s) at lowest temperatures. The X-ray diffractograms of the samples calcined at 350°C and 1100°C were treated with the Rietveld refinament technique. The powders calcined at 1100 °C/3h in air show to be 100% except spinel phase composition with 0.02 doping. The micrographs show clusters of particles with sizes smaller than 1 μm in calcination temperature of 1100°C which agreed with the result of Rietveld refinement. In the compositions doped with Mn were higher values of magnetization (45.90 and 53.20 Am2/kg), which did not cause high microwave absorption. The theoretical calculation of magnetization (MT) was consistent with the results, considering that there was agreement between the increase of magnetization experimental and theoretical. It was observed that there was the interrelation of the final effect of absorption with the thickness of MARE, the composition of ferrimagnetic materials and in particular the specific values of frequency. The analysis shows that the reflectivity increases in the concentration of cobalt increased the frequency range and also for absorption 10.17 GHz and 84%, respectively. The best result of chemical homogeneity and the value of 2.96 x 10-2 tesla coercive field were crucial for high performance ferrite absorber with 0.1 cobalt. The Cobalt has high magnetocrystalline anisotropy, it is associated with an increased coercive field, Hc. Therefore, this property improves the results of reflectivity of spinel ferrites

Encapsulação de nanopartículas de magnetita em matriz de poli(metacrilato de metilacoácido metacrílico) por processo de polimerização em miniemulsão

Magnetic particles are systems with potential use in drug delivery systems, ferrofluids, and effluent treatment. In many situations, such as in biomedical applications, it is necessary to cover magnetic particles with an organic material, as polymers. In this work, magnetic particles were obtained through covering magnetite particles with poly(methyl methacrylate‐comethacrylic acid) via miniemulsion polymerization process. The resultant materials were characterized X‐ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), zeta potential (��) measurements and vibrating sample magnetometry (VSM). XRD results showed magnetite as the predominant cristalline phase in all samples and that cristallites had nanometric dimensions. Thermogravimetric analysis revealed an increase in polymer thermal stability as a result of magnetite encapsulation. TGA results showed also that the encapsulation efficiency was directly related to nanoparticles s hidrofobicity degree. VSM measurements showed that magnetic polymeric particles were superparamagnetic, so that they may be potentially used for magnetic (bio)separation

Litoestratigrafia e deformação cenzóica na região de Icapuí, Ceará, e implicações para a estruturação de campos de petróleo na borda ocidental da bacia Potiguar(NE do Brasil)

This thesis deals with the sedimentological/stratigraphic and structural evolution of the sedimentary rocks that occur in the NW continental border of the Potiguar Basin. These rocks are well exposed along coastal cliffs between the localities of Lagoa do Mato and Icapuí, Ceará State (NE Brazil). The sedimentological/stratigraphic study involved, at the outcrop scale, detailed facies descriptions, profile mapping of the vertical succession of different beds, and columnar sections displaying inferred lateral relationships. The approach was complemented by granulometric and petrographic analyses, including the characterization of heavy mineral assemblages. The data set allowed to recognize two kinds of lithological units, a carbonate one of very restricted occurrence at the base of the cliffs, and three younger, distinct siliciclastic units, that predominate along the cliffs, in vertical and lateral extent. The carbonate rocks were correlated to the late Cretaceous Jandaíra Formation, which is covered by the siliciclastic Barreiras Formation. The Barreiras Formation occurs in two distinct structural settings, the usual one with nondeformed, subhorizontal strata, or as tilted beds, affected by strong deformation. Two lithofacies were recognized, vertically arranged or in fault contacts. The lower facies is characterized by silty-argillaceous sandstones with low-angle cross bedding; the upper facies comprises medium to coarse grained sandstones, with conglomeratic layers. The Tibau Formation (medium to coarse-grained sandstones with argillite intercalations) occurs at the NW side of the studied area, laterally interlayered with the Barreiras Formation. Eolic sediments correlated to the Potengi Formation overly the former units, either displaying an angular unconformity, or simply an erosional contact (stratigraphic unconformity). Outstanding structural features, identified in the Barreiras Formation, led to characterize a neocenozoic stress field, which generated faults and folds and/or reactivated older structures in the subjacent late cretaceous (to paleogene, in the offshore basin) section. The structures recognized in the Barreiras Formation comprise two distinct assemblages, namely a main extensional deformation between the localities of Ponta Grossa and Redonda, and a contractional style (succeeded by oblique extensional structures) at Vila Nova. In the first case, the structural assemblage is dominated by N-S (N±20°Az) steep to gently-dipping extensional faults, displaying a domino-style or listric geometry with associated roll-over structures. This deformation pattern is explained by an E-W/WNW extension, contemporaneous with deposition of the upper facies of the Barreiras Formation, during the time interval Miocene to Pleistocene. Strong rotation of blocks and faults generated low-angle distensional faults and, locally, subvertical bedding, allowing to estimate very high strain states, with extension estimates varying between 40% up to 200%. Numerous detachment zones, parallel to bedding, help to acommodate this intense deformation. The detachment surfaces and a large number of faults display mesoscopic features analoguous to the ones of ductile shear zones, with development of S-C fabrics, shear bands, sigmoidal clasts and others, pointing to a hydroplastic deformation regime in these cases. Local occurrences of the Jandaíra limestone are controled by extensional faults that exhume the pre-Barreiras section, including an earlier event with N-S extension. Finally, WNWtrending extensional shear zones and faults are compatible with the Holocene stress field along the present continental margin. In the Vila Nova region, close to Icapuí, gentle normal folds with fold hinges shallowly pluging to SSW affect the lower facies of the Barreiras Formation, displaying an incipient dissolution cleavage associated with an extension lineation at high rake (a S>L fabric). Deposition of the upper facies siliciclastics is controlled by pull-apart graben structures, bordered by N-NE-trending sinistral-normal shear zones and faults, characterizing an structural inversion. Microstructures are compatible with tectonic deformation of the sedimentary pile, burried at shallow depths. The observed features point to high pore fluid pressures during deformation of the sediments, producing hydroplastic structures through mechanisms of granular flow. Such structures are overprinted by microfractures and microfaults (an essentially brittle regime), tracking the change to microfracturing and frictional shear mechanisms accompanying progressive dewatering and sediment lithification. Correlation of the structures observed at the surface with those present at depth was tested through geophysical data (Ground Penetrating Radar, seismics and a magnetic map). EW and NE-trending lineaments are observed in the magnetic map. The seismic sections display several examples of positive flower structures which affect the base of the cretaceous sediments; at higher stratigraphic levels, normal components/slips are compatible with the negative structural inversion characterized at the surface. Such correlations assisted in proposing a structural model compatible with the regional tectonic framework. The strong neogenepleistocene deformation is necessarily propagated in the subsurface, affecting the late cretaceous section (Açu and Jandaíra formations), wich host the hydrocarbon reservoirs in this portion of the Potiguar Basin. The proposed structural model is related to the dextral transcurrent/transform deformation along the Equatorial Margin, associated with transpressive terminations of E-W fault zones, or at their intersections with NE-trending lineaments, such as the Ponta Grossa-Fazenda Belém one (the LPGFB, itself controlled by a Brasiliano-age strike-slip shear zone). In a first step (and possibly during the late Cretaceous to Paleogene), this lineament was activated under a sinistral transpressional regime (antithetic to the main dextral deformation in the E-W zones), giving way to the folds in the lower facies of the Barreiras Formation, as well as the positive flower structures mapped through the seismic sections, at depth. This stage was succeeded (or was penecontemporaneous) by the extensional structures related to a (also sinistral) transtensional movement stage, associated to volcanism (Macau, Messejana) and thermal doming processes during the Neogene-Pleistocene time interval. This structural model has direct implications to hydrocarbon exploration and exploitation activities at this sector of the Potiguar Basin and its offshore continuation. The structure of the reservoirs at depth (Açu Formation sandstones of the post-rift section) may be controlled (or at least, strongly influenced) by the deformation geometry and kinematics characterized at the surface. In addition, the deformation event recognized in the Barreiras Formation has an age close to the one postulated for the oil maturation and migration in the basin, between the Oligocene to the Miocene. In this way, the described structural cenario represents a valid model to understand the conditions of hydrocarbon transport and acummulation through space openings, trap formation and destruction. This model is potentially applicable to the NW region of the Potiguar Basin and other sectors with a similar structural setting, along the brazilian Equatorial Atlantic Margin

Histerese térmica de sistemas magnéticos nanoestruturados

We report a theoretical investigation of thermal hysteresis in magnetic nanoelements. Thermal hysteresis originates in the existence of meta-stable states in temperature intervals which may be tuned by small values of the external magnetic field, and are controlled by the systems geometric dimensions as well as the composition. Two systems have been investigated. The first system is a trilayer consisting of one antiferromagnetic MnF2 film, exchange coupled with two Fe lms. At low temperatures the ferromagnetic layers are oriented in opposite directions. By heating in the presence of an external magnetic field, the Zeeman energy induces a gradual orientation of the ferromagnets with the external field and the nucleation of spin- op-like states in the antiferromagnetic layer, leading eventually, in temperatures close to the Neel temperature, to full alignment of the ferromagnetic films and the formation of frustrated exchange bonds in the center of the antiferromagnetic layer. By cooling down to low temperatures, the system follows a different sequence of states, due to the anisotropy barriers of both materials. The width of the thermal hysteresis loop depends on the thicknesses of the FM and AFM layers as well as on the strength of the external field. The second system consists in Fe and Permalloy ferromagnetic nanoelements exchange coupled to a NiO uncompensated substrate. In this case the thermal hysteresis originates in the modifications of the intrinsic magnetic

Superparamagnetismo em Jacobsitas sintéticas

In this experimental study sintetic samples of Jacobsites (MnFe2O4) were synthesized by the Pechini method and calcined within ambient atmosphere and afterwards in the vacuum from 400 to 700ºC, the range of calcination temperatures. The X-Ray Diffraction (XRD) and the Scanning Electronic Microscopy (SEM) analysis have shown that the samples treated at 400ºC temperature are composed by a simple type of spinel phase, with a crystallite size of 8:8nm for the sample calcined in ambient atmosphere and 20; 1nm for the sample treated in the vacuum, showing that the cristallite average size can be manipulated by the atmosphere control. The hysteresis loops for the sample calcined at 400ºC in ambient atmosphere reveal features of superparamagnetic behavior with magnetization 29:3emu=g at the maximum field of 1:2T. The sample calcined in 400oC under vacuum show magnetization = 67emu=g at the maximum field of 1:5T. The sample treated at 500oC, under ambient atmosphere, has shown besides the spinel phase, secondary phases of hematite (Fe2O3) and bixbyite (FeMnO3). The hysteresis loops demonstrate a sharp drop of the magnetization compared to the previous sample. The analysis has revealed that for the samples treated in higher temperatures (600ºC and 700ºC) its observed the absence of the spinel phase and the maintenance of the bixbyite and hematite. The hysteresis loops for those samples in accordance to the external magnetic field are straight lines crossing the origin, consistent with the antiferromagnetic behavior of the phases.The Mössbauer espectroscopy show to the sample calcined at 400ºC within ambiente atmosphere two sextet and one doublet. The two sextets are assigned to the hyperfine fields related to the magnetic deployment in the nuclei of Fe3+ ions, at the tetraedric and octaedric sites. The doublet is assigned to superparamagnetic behavior of the particles with smaller diameter than dc . Now the sample calcined at 400ºC under vacuum only show two sextet

Análise do Efeito Goos-Hanchen e Não-reciprocidade do fluxo de potência em antiferromagnéticos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior

Nucleação de vortices e paredes de domínio em nanoestruturas magnéticas

We report a theoretical investigation of the magnetic phases and hysteresis of exchange biased ferromagnetic (F) nanoelements for three di erent systems: exchange biased nanoparticles, exchange biased narrow ferromagnetic stripes and exchange biased thin ferromagnetic lms. In all cases the focus is on the new e ects produced by suitable patterns of the exchange energy coupling the ferromagnetic nanoelement with a large anisotropy antiferromagnetic (AF) substrate. We investigate the hysteresis of iron and permalloy nanoparticles with a square basis, with lateral dimensions between 45 nm and 120 nm and thickness between 12 nm and 21 nm. Interface bias is aimed at producing large domains in thin lms. Our results show that, contrary to intuition, the interface exchange coupling may generate vortex states along the hysteresis loop. Also, the threshold value of the interface eld strength for vortex nucleation is smaller for iron nanoelements. We investigate the nucleation and depinning of an array of domain walls pinned at interface defects of a vicinal stripe/AF bilayer. The interface exchange eld displays a periodic pattern corresponding to the topology of the AF vicinal substrate. The vicinal AF substrate consists of a sequence of terraces, each with spins from one AF subalattice, alternating one another. As a result the interface eld of neighboring terraces point in opposite direction, leading to the nucleation of a sequence of domain walls in the ferromagnetic stripe. We investigated iron an permalloy micrometric stripes, with width ranging from 100 nm and 300 nm and thickness of 5 nm. We focused in domain wall sequences with same chirality and alternate chirality. We have found that for 100nm terraces the same chiraility sequence is more stable, requiring a larger value of the external eld for depinning. The third system consists of an iron lm with a thickness of 5 nm, exchange coupled to an AF substrate with a periodic distribution of islands where the AF spins have the opposite direction of the spins in the background. This corresponds to a two-sublattice noncompensated AF plane (such as the surface of a (100) FeF2 lm), with monolayer-height islands containing spins of one sublattice on a surface containing spins of the opposite sublattice. The interface eld acting in the ferromagnetic spins over the islands points in the opposite direction of that in the spins over the background. This a model system for the investigation of interface roughness e ects. We have studied the coercicivity an exchange bias hysteresis shift as a function of the distance between the islands and the degree of interface roughness. We have found a relevant reduction of coercivity for nearly compensated interfaces. Also the e ective hysteresis shift is not proportional to the liquid moment of the AF plane. We also developed an analytical model which reproduces qualitatively the results of numerical simulations

Excitações elementares em super-redes quasiperiódicas com simetria espelho

In this thesis, we investigated the magnonic and photonic structures that exhibit the so-called deterministic disorder. Speci cally, we studied the effects of the quasiperiodicity, associated with an internal structural symmetry, called mirror symmetry, on the spectra of photonics and magnonics multilayer. The quasiperiodicity is introduced when stacked layers following the so-called substitutional sequences. The three sequences used here were the Fibonacci sequence, Thue-Morse and double-period, all with mirror symmetry. Aiming to study the propagation of light waves in multilayer photonic, and spin waves propagation in multilayer magnonic, we use a theoretical model based on transfer matrix treatment. For the propagation of light waves, we present numerical results that show that the quasiperiodicity associated with a mirror symmetry greatly increases the intensity of transmission and the transmission spectra exhibit a pro le self-similar. The return map plotted for this system show that the presence of internal symmetry does not alter the pattern of Fibonacci maps when compared with the case without symmetry. But when comparing the maps of Thue-Morse and double-time sequences with their case without the symmetry mirror, is evident the change in the pro le of the maps. For magnetic multilayers, we work with two di erent systems, multilayer composed of a metamagnetic material and a non-magnetic material, and multilayers composed of two cubic Heisenberg ferromagnets. In the rst case, our calculations are carried out in the magnetostatic regime and calculate the dispersion relation of spin waves for the metamgnetic material considered FeBr2. We show the e ect of mirror symmetry in the spectra of spin waves, and made the analysis of the location of bulk bands and the scaling laws between the full width of the bands allowed and the number of layers of unit cell. Finally, we calculate the transmission spectra of spin waves in quasiperiodic multilayers consisting of Heisenberg ferromagnets. The transmission spectra exhibit self-similar patterns, with regions of scaling well-de ned in frequency and the return maps indicates only dependence of the particular sequence used in the construction of the multilayer

Estruturação da seqüência vulcano-sedimentar Rio Mata Cavalo (Morro do Pilar, MG, Brasil) baseada na análise qualitativa de dados geofísicos

Geofísica terrestre (magnetometria e radiometria) foi utilizada como ferramenta de apoio ao mapeamento geológico em uma área de pesquisa mineral da Companhia Mineradora de Minas Gerais (COMIG), denominada Alvo Bueiro, localizada a sudeste da cidade de Morro do Pilar, na Serra do Espinhaço, Estado de Minas Gerais. A integração de informações de geologia de superfície com os dados geofísicos correspondentes permitiu definir quatro zonas: A, B, C e D. A Zona A, caracterizada por altos valores de susceptibilidade magnética e baixos valores de radiometria, é composta por itabiritos do Grupo Serra da Serpentina. A Zona B, pertencente ao mesmo grupo, é constituída por filitos cinza e metassiltitos e mostra baixa susceptibilidade magnética; interrupções nas linhas de contorno foram interpretadas como decorrentes de falhas de empurrão. A Zona C, relacionada à Seqüência Vulcano-Sedimentar Rio Mata Cavalo, é caracterizada por uma expressiva anomalia do campo magnético total em xistos máficos e ultramáficos com lentes de formações ferríferas e filitos carbonosos negros; esta zona hospeda as mais importantes anomalias geoquímicas de ouro conhecidas na área em estudo. A Zona D, correspondente a ortognaisses cisalhados do Complexo Dona Rita, mostra os mais elevados valores de radiometria do Alvo Bueiro e baixas respostas magnéticas.

Integração de métodos geofísicos na modelagem crustal da Bacia de Santos

A Bacia de Santos é uma bacia de margem passiva gerada durante o Neocomiano, associado com o evento de ruptura do Supercontinente de Gondwana. A espessura da seção sedimentar pode alcançar 15 km, incluindo a seqüência rifte, e foi depositada sobre uma crosta afinada cuja espessura original era de cerca de 35 km. Foi realizada uma modelagem crustal em 8 linhas, aproximadamente perpendiculares ao mergulho deposicional da bacia, objetivando o reconhecimento da geometria da fase rifte e a estimativa do estiramento crustal. Foram utilizados durante a modelagem quatro horizontes sísmicos em profundidade, mapas magnético e gravimétrico além de dados da profundidade do embasamento magnético. Foi reconhecido um pronunciado estiramento crustal em toda a bacia (fatores de estiramento crustal variando entre 1.2 e 3.1), evidenciando ampla acomodação da deformação. Os resultados da modelagem necessitaram, ainda, de espessas e contínuas camadas de rochas vulcânicas para ajuste do modelo. Estas cunhas de rochas vulcânicas, limitadas lateralmente por falhas normais, são feições comuns em bacias rifte. Os resultados da modelagem foram confrontados com dados da profundidade do embasamento magnético, obtidos anteriormente, e evidenciaram forte correlação, sobretudo nas áreas rasas da bacia.

Medida da permeabilidade magnética em fio delgado ferromagnético

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Nanopartículas magnéticas: o cobalto

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Construcción de ambientes favorables para el desarrollo de competencias laborales: tres estudios sectoriales

Incluye Bibliografía

Ministerio del Interior y la planificación regional en el Brasil

Incluye Bibliografía

Influência da ionosfera no posicionamento GPS: estimativas dos resíduos no contexto de duplas diferenças e eliminação dos efeitos de 2ª e 3ª ordem

Pós-graduação em Ciências Cartográficas - FCT