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The magnetostriction of Co-Ga alloys: Co-14Ga, Co-24Ga and Co-33Ga (atomic), is studied at room temperature for the first time. All three alloys are ferromagnetic. Co-14Ga microstructure is biphasic, a mixture of e (hcp) and α (fcc) phases. Co-24Ga presents three phases e, α and β (ordered bcc) and Co-33Ga is single β phase alloy. It was found that all three alloys present negative saturation magnetostriction λ s . The most interesting material for applications would be the alloy Co-33Ga since the magnetostriction saturates for a small field.

The room temperature magnetostriction of polycrystalline Fe100– x Cr x alloys annealed at 800 °C was investigated as a function of Cr content varying from 10 to 30 at.% Cr. All alloys exhibited a single bcc $\alpha $ -Fe–Cr phase with a disordered A2 structure. With increasing Cr concentration, the grain shape became very elongated. The greatest total magnetostriction value of $70 \times 10^{-6}$ was obtained in the direction of the elongated grains for 30% of Cr. We also investigated the effect of B addition on the magnetostriction and structural properties of the alloy Fe80Cr20. Although the addition of B was expected to form the Fe2B phase, the B-added Fe–Cr alloy forms a ternary phase (Fe z Cr1– z )2B ( $0 ), a weak magnetic phase.

Cobalt ferrite (CoFe2O4) and manganese substituted cobalt ferrite (Co0,25Mn0,75Fe2O4) were synthesized by coprecipitation and sol–gel methods. X-ray diffraction revealed that manganese ions slightly enlarged the crystal lattice with respect to pure cobalt ferrite. Magnetization, linear magnetostriction, and piezomagnetic coefficient values tended to decrease with the ion substitution. Linear magnetostriction dropped from a value of −111.5 ppm for cobalt ferrite to values of −22.6 and −30.6 ppm for the substituted samples obtained from coprecipitation and sol–gel, respectively. The sample prepared by sol–gel technique resulted in a higher magnetization, magnetostriction, and piezomagnetic coefficient than that synthesized by coprecipitation method.

Hysteresis loops and magnetostriction were measured on ring-shaped ${\rm Fe}_{85}{\rm Ga}_{15}$ samples. The samples were annealed at $T=980^{\circ}{\rm C}$ for 100 h and cooled from annealing temperature in two different ways: one was slowly cooled in an oven and the other one was quenched in cold water. X-ray diffraction results showed a strong texture in these samples, which is dependent on the cooling process. The anisotropy energy and magnetostriction of the samples were calculated based on these determined textures. These results agree qualitatively with magnetization and magnetostriction experiments and support the thermal history influence on the magnetostriction values.

The structural and magnetic properties of polycrystalline Fe100-xMnx alloys with x = 38, 42, 46, 50, and 55 atomic percent were investigated after a heat treatment and a cold rolling process. According to X-ray diffraction (XRD), all samples crystallize into a y -phase. For cold rolled alloys x = 38 and 42, XRD analysis using pole figures showed no texture formation whereas cold rolled alloys with x = 46 and 50 exhibited texture components {110} and with x = 55, {011} . Magnetization measurements clearly demonstrate an antiferromagnetic type of ordering. For both the as-cast as well as the cold rolled materials, magnetostriction measurements at room temperature gave nearly zero magnetostriction.

In this paper, we report magnetostriction measurements and an investigation of structural properties on melt-spun ribbons of Fe85.7Al14.3, Fe81.3Al18.7, and Fe77.7Al22.3 ribbons produced at different wheel speeds. The bcc-disordered A2 structure is obtained for 14.3 and 18.7 at %Al whereas the alloy with 22.3 at %Al exhibits the DO3-type structure. With increasing Al concentration, the saturation magnetization decreases, whereas the average lattice constant, longitudinal, transverse, and volume magnetostriction increase. However for each alloy, the crystallite size, lattice constant, and magnetostriction vary randomly with wheel velocity. While the behavior of the longitudinal magnetostriction versus applied field is similar for all samples, the behavior of the transverse magnetostriction is strongly dependent on the wheel speed. These results indicate that the formed structural disorder and the stresses in the ribbons are different with wheel speed.

Longitudinal and transverse magnetostriction measurements were performed on polycrystalline Fe100- xTix alloys, for a large Ti concentration range, from x = 8.8 to 34.7 at.%. Our results showed that substituting Fe by Ti does not significantly enhance the magnetostriction. For all Ti concentrations in the magnetically saturated state, the longitudinal magnetostriction values vary from -2 ×10-6 to 6 × 10-6. On the other hand, Fe100-xTix alloys exhibit a large forced volume magnetostriction, which increases with increasing Ti-concentration. The magnetostriction behavior could be explained considering investigations of the hyteresis loops and the microstructure .

We report the effect of a short-time vacuum annealing (1073 K during 10 minutes) on structural phase transition temperatures and magneto-structural properties of as-quenched ribbons of the Heusler alloy Ni50.6Mn34.5In14.9. This alloy crystallizes in a single phase cubic B2-type austenite with a Curie point of TCA=284 K that with the lowering in temperature transforms into a martensite with TCM185 K. The direct and reverse martensitic phase transition temperatures were MS=257 K, Mf = 221 K, AS = 239 K, and Af = 266 K. After annealing austenite shows the highly ordered L21-type structure while the average chemical composition as well as the structural and magnetic transition temperatures were shifted to Ni50.2Mn34.3In15.5 and MS = 253 K, Mf = 238 K, AS = 257 K, Af = 265 K, ΔT = 13 K, TCA = 299 K and TCM207 K. In the annealed samples the magnetization changes associated to the magnetic and structural transitions are more abrupt and magnetization isotherms in both the austenitic and martensitic existence region show higher initial magnetic susceptibility and faster approach to saturation. Field-cooled hysteresis loops at 10 K were shifted along the negative H-axis for both samples, but a significant anomaly was evident on the left side of the hysteresis loop for as-quenched ribbons.

In order to investigate the effect of the quenching rate on the magnetostriction of Fe82.5Ga17.5 alloy, a set of ribbons was prepared by varying the wheel velocities from 7.5 up to 25 m/s. Additionally Fe85Al15, Fe81Al19 and Fe75Al25 ribbons were prepared under similar conditions. The microstructure shows generally columnar particles and (100) texture perpendicular to the surface of the ribbons. For Fe-Al ribbons, the lattice constant and magnetostriction (which shows volume magnetostriction effect for the higher Al concentrations) increase and saturation magnetization decreases with Al content. However, the average grains size and the lattice constants of Fe82.5Ga17.5 and Fe-Al alloys, show large fluctuations with the wheel velocity. For Fe82.5Ga17.5, ribbons the magnetostriction values and its character with applied field depend strongly on the quenching rate. The dependence of the longitudinal magnetostriction with wheel speed exhibits a maximum of about 116 ppm at 15 m/s, which is related to the higher degree of (100) texture.

Nanocrystalline YCo5 powders with high coercivity were prepared by mechanical milling and subsequent heat treatment at 820 °C for different annealing times, ta = 2.5, 3.0, 3.5 and 4.5 min, obtaining average crystallite sizes of  17, 19, 32 and 39 nm., respectively. The coercivity values were determined from the hysteresis loops measured at maxima fields of Hm = 5 and 20 T. The highest coercivity was obtained for the sample exhibiting  19 nm, where at room temperature and Hm = 5 T, the coercivity value is of 9.0 kOe. At 77 K and Hm = 5 T, the coercivity increase to 11.8 kOe and for Hm = 20 T, a higher value such as 13.1 kOe was found. The Ms/Mr ratio is enhanced to 0.62 indicating the occurrence of exchange interaction among nanocrystalline magnets.

A new system for measuring magnetic viscosity in bulk hard magnetic materials base on a pulsed field method is presented. After the magnetizing field pulse, the stray field of the sample, which is proportional to the magnetic moment, is measured with a compensated set of two Hall probes. The set of Hall probes is driven with an AC voltage source and the Hall voltage is detected using a lock-in amplifier. By this method the system is able to measure the time dependence of the magnetization (viscosity). The magnetic viscosity coefficient (S) is obtained through a linear fitting of the magnetization decay versus ln t. Two typical Nd-Fe-B samples were measured and good agreement with the results from the traditional viscosity experiment was obtained.

This paper gives an overview about the basic ideas of magnetoelectric materials. Up to now single-phase materials show the magnetoelectric effect only below room temperature. Mixing a magnetostrictive with a piezoelectric component is a way to overcome this limitation. This delivers a composite which can exhibit a magnetoelectric effect even at room temperature and higher. Possible candidates for these composites (piezoelectric as well as magnetostrictive) are shown, examples from literature and own results are given. The most important coupling mechanism (magnetization, magnetostriction, local stress, charge) between the magnetostrictive and the piezoelectric phase are discussed. Hints for a direct coupling between the electric polarization and the magnetization are also presented. Different measurement methods for determining the magnetoelectric coefficient are discussed. Representative results as obtained on a technical useful composite between 50% Co-Ferrite+50% BaTiO 3 are given. The behavior of a simple “mixed” structure with that of a “core-shell” structure is compared. The later gives a 20-times larger magnetoelectric coefficient.

X-ray diffraction and transmission electron microscopy (TEM) experiments were performed in heat-treated Sm(Co,Cu) 5 samples with different Co/Cu content. The major phase observed in the diffraction patterns exhibits a hexagonal CaCu 5 type structure in all the studied compositions. The behavior of the diffraction profiles, as function of the Cu content, is believed to be due to an inhomogeneous distribution of Co and Cu through out the samples. Heavily planar faulted regions have been observed by means of TEM and are also associated with Sm and Co rich phases within the matrix. A CaCu 5 type structure with local Sm rich regions seems to be responsible for the observed magnetic behavior.

The modified oxalate precursor method was used for the preparation of nanocrystalline CoFe2O4. Structural investigations of as-produced powders performed by means of high-resolution transmission electron microscopy and X-ray diffraction revealed an average particle size of 8 nm. The nanocrystallites are pure CoFe2O4 and present a well crystallized spinel structure with lattice constant of 8.3583 Å. The particles are superparamagnetic exhibiting a blocking temperature around room temperature. The magnetization and the coercive field values obtained at 9 T are 56.8 emu · g−1 and 17.0 kOe (at 4.2 K), respectively. The crystalline anisotropy determined from the coercive field as a function of temperature is 8.0 × 105 J · m−3, which is much higher than that of bulk materials.

The temperature dependence of the hysteresis loop, saturation magnetization, and saturation magnetostriction of rapidly quenched ribbons of the compositions Fe/sub 100-x/Si/sub x/ (x=12.1, 13.8, 20.0) and of FINEMET-type material with compositions Fe/sub 73.6/Cu/sub 1/Nb/sub 3/Si/sub 13.5/B/sub 9/ Fe/sub 73.5/Cu/sub 1/Nb/sub 3/Si/sub 16.5/B/sub 6/ were measured between room temperature and 400/spl deg/C. This paper analyzes the temperature dependence of the saturation magnetostriction and the saturation magnetization of the FINEMET ribbons after various heat treatments, assuming a superposition of the properties of the nanocrystalline Fe-Si and of the remaining amorphous phase. The behavior of the coercivity of Fe-Si prepared by rapid solidification follows roughly that of the (absolute value) of the magnetostriction. The Curie temperature of the remaining amorphous phase is enhanced.

The coercive field of the as-cast Fe 68 Si 20 Nb 12 and Fe 60 Si 20 Nb 20 ribbons decreases with increasing temperature abruptly up to 35 K, then slowly up to around 200 K. Above this temperature the coercive field increases. Qualitatively this is attributed to the point that this unusual coercive field curve behavior is related mainly to the nano-crystalline material containing two nanocrystalline phases (BCC Fe–Si and hexagonal NbFe 2 - y Si y ), where exchange interactions among these small particles occur. The fraction of the hexagonal phase increases with increasing Nb and after annealing decomposes in two hexagonal phases with similar composition. For the Fe 60 Si 20 Nb 20 alloy the quantity of NbFe 2 - y Si y nanocrystallites is almost the same of that BCC Fe–Si particles.

Magnetic properties and structural evolution of the melt-spun Fe 80 - x Si 20 Cr x and Fe 87.1 - x Si 12.9 Cr x with Cr concentration are investigated for the as-cast and annealed samples. The coercivity at 300 K of the as-cast alloys decreases and that of the annealed ones increases with Cr concentration. For both as-cast and annealed samples, the saturation magnetization and the magnetic ordering temperature decrease, although heat treatments cause an increase of these magnetic properties. We have explained the behavior of these concentration dependence based on the structural analysis. Low-Cr region displays a discontinuity in the coercivity curve of the annealed alloys, which can be attributed to the change of the short-range order to the transient long-range ordered state.

We present magnetostriction and magnetization measurements of a cobalt ferrite Co0.8Fe2.2O4 single crystal. We observe unusual behaviour in the magnetic hard axis of the single crystal which manifests in a jump of the magnetization curve at a critical field. This first order magnetization process (FOMP) which is explained as an anisotropy driven transition is visible at temperatures lower than 150 K. By analyzing the anisotropy constants we found that the higher order anisotropy constant K2 dominates the anisotropy energy. In the magnetostriction measurements the FOMP is clearly visible as a huge jump in the [111] direction, which can be explained by means of a geometric model., Comment: This Paper is already accepted for the conference proceedings of the MMM 2011 (http://www.magnetism.org). The proceedings will be published in April 2012 in Journal of Applied Physics

The aim of this work was to study the influence of the Ni content in Fe 86− x Ni x Zr 7 Cu 1 B 6 ( x =5–86 at% ) alloys on the magnetic properties after annealing at various temperatures. The annealing temperatures were estimated from DSC measurements. It was found that the first crystallization peak T x 1 decreases with increasing Ni content. The composition dependence of the coercivity and the magnetization at room temperature were investigated, too. After the heat treatment, the magnetization J max ( x ) decreases with increasing Ni content in contrary to the bell-shaped dependence of J max ( x ) in the as cast state. The concentration dependence (5–65 at% Ni ) of the coercivity H C ( x ) of annealed samples shows the same bell-type behaviour like those in the amorphous state. The coercivity of the annealed sample with 5 at% of Ni is smaller than H C ( x ) of the as-cast state. For higher concentrations of Ni the coercivity increases with annealing. The change of the coercivity was investigated for 25, 33, 43 at% of Ni at various annealing temperatures. In those cases, the coercivity increases with increasing annealing temperature up to temperatures corresponding to the first crystallization peak at which the coercivity reaches the maximum value.

A system for magnetic characterization of soft magnetic materials in low field is described. Fields of 0.02 A/m can be applied and a good sensibility is achieved by means of a Lock-In amplifier. Signals of 1 nV can be measured, and magnetic characterization with external stresses can be made. The measurements can be done from room temperature up to 973 K. The system allows to perform permeability, pinning field, Curie temperature and disaccommodation measurements automatically. >

In order to investigate the effect of boron additions in the magnetostrictive behavior of Fe72Ga28 alloy, this alloy was doped with 0.5, 1.0, 1.5 and 2.0 at.% of boron. The results have shown that boron additions of 0.5 and 1.0% improve significantly the magnetostriction, the values being about two-fold higher compared to the undoped alloy. Microstructural evaluations suggest that boron additions suppress partially the D03 phase ordering, retaining the α-phase. Furthermore, the increase of lattice parameters of the α and D03 phases indicates that boron enters interstitially in the cubic lattice of these phases. Both effects are considered to be responsible for the increased magnetostriction observed in the (Fe0.72Ga0.28)99.5B0.5 and Fe0.72Ga0.28)99.0B1.0 alloys.

The structure of annealed Sm(Co0.6Cu0.4)5 compounds, prepared with different Sm excess content, has been investigated by means of high resolution x-ray diffraction and scanning electron microscopy. The samples were also magnetically characterized by thermomagnetic analysis and M versus H curves at room temperature. Increasing Sm excess improves the compositional order of the 1?:?5 phase. The coercivity (HC) and the Curie temperature (TC) are both changed as a function of Sm excess content. The decrease in the structural defects density, resulting from the compositional order, is responsible for the observed magnetic behaviour.

We report measurement of the luminescence spectra of highly photoexcited semiconductor samples of GaAs, CdTe and InP. The experiments were performed under similar conditions as those imposed on the systems in previous work devoted to the observation of inelastic (Doppler - Raman) scattering of light. We show that our results are fully consistent with the interpretation of the macroscopic thermodynamic state of the system in terms of a hot excitation model.

Orientadores: Rogério Cézar de Cerqueira Leite, Antonio Rubens Britto de Castro Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Neste trabalho mediu-se o espalhamento de luz por plasmas e por fonons ópticos foto-excitádos em várias amostras de GaiAs usando radiação infra-vermelha do laser de Nd:YAG. O mesmo feixe era utilizado para excitar o plasma e para medir o espalhamento Raman. Foram obsevadas distribuições não equitibradas de elétrons e buracos mas não se pode verificar nenhuma variação na relação das componentes Stokes e anti-Stokes atribuível a distribuições não equilibradas de fónons ópticos longitudinais, em condições de alta intensidade de excitação. Calculou-se a secção de choque de espalhamento no plasma duplo de elétrons e buracos não equilibrados usando o conceito de quase-partículas de Landau. A não homogeneidade do feixe do laser no interior do cristal foi levada em conta. Este cálculo permitiu estimar a densidade de portadores foto-excitados nas amostras de alta resistividade, analisando-se os desvios do perfil Gaussiano do espectro Raman ,dos portadores quentes. Estes desvios são explicados pelo efeito de muitos corpos. Sob excitação máxima, foi estabelecido um limite inferior igual a 1x1016 cm-3 para a densidade de portadores foto-excitados. Este valor resultou do ajuste da secção de espalhamento teórica aos dados experimentais. Levando-se em conta o deslocamento em energia da linha correspondente ao fonon LO, estabeleceu-se um limite superior 2x1016 cm-3. Até a maxíma potência disponível, não se observou sinal de saturação na densidade de portadores foto-excitados. Conclui-se então que um limite inferior para manifestação de efeitos de saturaçao e 1x1016 elétrons por cm3. Um alargamento na linha dos fonons LO foi observado sob condições de altas potências de pico de laser. Isto foi explicado como resultado da redução de tempo de vida na presença de excesso de populações dos fonons LO Abstract: Not informed Doutorado Física Doutor em Ciências

Orientador: Rogério Cézar de Cerqueira Leite Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Fisica Gleb Wataghin Resumo: Não informado Abstract: Not informed Mestrado Física Mestre em Física

Apresentaremos uma série de estudos realizados sobre o tema anisotropias magnéticas induzidas (Kind) em 1igas amorfas. Foram usados vários tipos de tratamentos térmico, com o objetivo de obtermos uma visão amp1a do assunto. A análise teórica dos dados de Kind e de \"after-effect\" magnético (MAE) foi feita com um modelo baseado em sistemas de dois níveis (TLS). A partir da análise dos dados experimentais obtém-se um largo espectro de energias de ativação. Estas energias estão relacionadas aos tempos de re1axação, através da equação de Arrhenius: = 0 exp (E/kT), onde o pré-fator 0 é da ordem do inverso da frequência de Debye. Construiu-se um forno para tratamentos térmicos em ligas amorfas, que opera em um eletroimã de 6 kOe e desenvolveu-se os programas para análise de dados experimentais. Essas facilidades, associadas ao traçador de curvas de histerese, permitiram os seguintes estudos de anisotropias induzidas em ligas amorfas ferromagnéticas: 1. Estudo da cinética de indução de anisotropia por tratamentos térmicos na faixa de temperatura de 190 a 250 °C, para fitas amorfas \"as cast\" de composição C070.4Fe4.6 Si15B10. Com o modelo TLS pode-se obter o espectro de energias de ativação, que se apresentou na faixa de energia de 1.50 a 1.85eV, com 0 = 1.6 x 10-13s. 2. Realizou-se também o estudo da indução de anisotropia na presença de um campo magnético de 5 kOe, para amostras pré-tratadas a 400 °C por 10 minutos. Estas são de composição Co77-X Mnx Si14 B9, com X = 2 e 6 e foram submetidas a tratamentos isotérmicos a temperaturas entre 240 e 325 °C. Neste caso pode-se verificar que para as duas composiQ6es 0 pré-fator é maior ( 10-8S). Quanto ao espectro de energias de ativação, em ambos os casos, apresenta-se na faixa de energias de 1.10 a 1.55 eV. 3.Outro experimento, neste caso com amostras de composição Co67Fe4Mo1Si12B16 consistiu na aplicação, à temperatura ambiente, de tensão mecânica ( 800 MPa) na fita, enquanto se monitorava a energia de anisotropia magnética. Pudemos então observar uma variação continua dessa propriedade e posteriormente uma recuperação completa da condição inicial, com a remoção da tensão aplicada, mostrando um processo de caráter anelástico. Procuramos estudar os efeitos de tensões mecânicas sobre as propriedades magnéticas de amostras com composição Co67Fe4Mo1Si12B16. Duas linhas de trabalho foram adotadas: 4) Numa olhou-se para a isotropia induzida em amostras pré-tratadas, quando submetidas a tratamentos térmicos na faixa de temperatura de 200 a 400 °C, sob tensão mecânica de 500 MPa e posteriormente na ausência de tensão. A partir desses ensaios foi possível se separar uma componente plástica e outra anelástica na anisotropia induzida. 5) Noutra, obteve-se o comportamento do MAE, para amostras com e sem tensão mecânica aplicada, no intervalo de 300 a 500 K. Os resultados obtidos demonstram a não existência de efeitos plásticos ou anelásticos nas energias de ativação dos processos envolvidos no \"after-effect\". Por outro lado verificamos uma grande alteração na intensidade do MAE, devido à tensão. In this thesis we will present a series of studies related to induced magnetic anisotropies (Kind) in amorphous alloys. In order to get a more general view of this theme, we used several different kinds of annealings. The theoretical analysis of the data of Kind and magnetic after-effect (MAE) was performed using a model based on two-level systems (TLS). From the analysis of the experimental data we get a large actiyation energy spectrum. These energies are related to the relaxation times, through the Arrheniu \'s expression: = 0 exp(E/kT), where the pre-factor 0 is of the order of the inverse of the Debye frequency . We constructed a furnace for thermal annealing of the amorphous alloys, which operates within an electromagnet producing 6 kOe. We also wrote, the computer programs for the analysis of the experimental data. These facilities, together with the hysteresis loop tracer permitted the followings studies of the induced anisotropies in amorphous alloys: 1) A study of the kinetics of the induced anisotropy by annealing in the temperature range from 190 to 250 °C, in as cast amorphous ribbons of composition Co70.4Fe4.6Si15B10. Using the TLS model we obtained the activation energy spectrum. It presents two peaks in the energy range from 1.50 to 1.85eV and a pre-factor 0= 1.6x10-13 s. 2) Using a 5 KOe magnetic field we studied the effects of a Field annealing treatment in samples pre-annealed at 400 °C for 10 minutes. The isothermal annealings were made in Co70-XMnXSi14B9 with x = 2 and 6, in the temperature range from 240 to 325 °C. In this case we observed for these two compositions a larger pre-factor ( 10-8s) than before. The activation-energy spectra, for the both composition, are found in the energy range from 1.10 to 1.55eV. 3) Another experiment was done using samples of Co67Fe4Mo1Si12B16. We applied a tensile stress (800MPa) to the ribbon and measured the magnetic anisotropy energy. We observed a continuous variation of this energy and, after removal of the stress, the sample recuperated its initial condition, showing a process characteristically anelastic. We studied the effects of mechanic stress on the magnetic properties of samples of composition Co67Fe4Mo1Si12B16. We worked in two directions: 4) We studied the induced anisotropy in pre-annealed samples, submitted to annealing in the range from 200 to 400 °C, under a tensile stress of 500MPa and without applied stress. From these resul ts we can separate a plastic and an anelastic component in the induced anisotropy. 5) In other, we studied the behavior of the MAE, for samples with and with and without applied tensile stress, in the range from 300 to 500 K. The results obtained show neither plastic nor anelastic effects on the activation energies of the processes involved in the MAE. On the other h~nd we can see a strong alteration in the intensity of the MAE, due the stress.

Este trabalho interdisciplinar apresenta três novas aplicações de diferentes métodos biomagnéticos para estudar características físicas da motilidade gástrica humana. Empregou-se um biosusceptômetro AC para medir a atividade mecânica de contração gástrica através do acompanhamento temporal dos traçadores magnéticos previamente ingeridos com um alimento teste (80 ml de iogurte e 3 g de ferrita em pó). Os registros gráficos foram obtidos de forma bastante satisfatória, mostrando ser esse método uma alternativa viável para a detecção e seguimento temporal dessa atividade, em condições normais e sob o efeito de drogas. Através do processo de relaxação de partículas previamente magnetizadas no interior do estômago e com o auxílio de um magnetômetro de saturação de fluxo, estudou-se o processo de mistura de um alimento teste no estômago. Um pulso de campo magnético de aproximadamente 600 G é aplicado sobre a região gástrica do voluntário contendo o alimento teste (80 ml de iogurte e 3 g de magnetita em pó), e o campo remanente é medido e acompanhado no tempo. Os resultados preliminares indicam que esse método apresenta um grande potencial para um maior entendimento das características físicas da função de mistura do estômago e também da atividade de contração do estômago. Novos estudos sob condições variadas de alimentação e drogas podem fornecer subsídios para uma melhor interpretação desse processo. Utilizando-se um magnetômetro supercondutor (SQUID-DC) mediu-se a atividade elétrica gástrica obtendo-se bons traçados temporais na maioria das medidas. Os registros indicam que através desse sistema podem-se realizar experimentos no intuito de diferenciar as atividades elétricas e também observar seu comportamento frente a diferentes condições clínicas. Os dados obtidos nesse trabalho mostram ser este enfoque um valioso instrumento que pode contribuir para um melhor entendimento das características físicas da motilidade gástrica e também possibilitar novos estudos sobre o sistema gastrointestinal This interdisciplinary work presents three new applications of different biomagnetic methods to study physical characteristics of human gastric motility. A biosusceptometer was used to measure the mechanical activity of gastric contraction through a time to time checking of the magnetic tracers previously ingested by a volunteer along with a test food (80 ml of yogurt and 3g of ferrite in powder). Results in graphical recording were very satisfactory, indicating this method as a possible alternative to detect and also follow up that gastric activity, besides allowing the evaluation of related activity under the effect of drugs. Through the observation of the relaxation of previously magnetized particles in the stomach, measured with a fluxgate magnetometer, the process of mixing of the test food in stomach was studied. A strong pulse of magnetic field (600G) is applied externally to the stomach region of the volunteer who have already ingested the mentioned food test, whereas the remanent field is measured and followed up in time. Preliminary results indicate that this method provides a good understanding of the physical characteristics of the mixture of food and also of the stomach contraction activity. New studies of different types of food and drugs may provide further information on the process. A superconductor magnetometer (SQUID-DC) was used to measure the gastric electrical activity, and good temporal tracers were obtained for the majority of measurements. Recordings were of satisfactory quality, indicating that through that system, experiments can be carried out in order to differentiate the electrical activities and also to observe its behavior for different clinical conditions. Results obtained in this thesis to measure the gastric electromagnetic activity, indicate this to be a valuable tool to understand the physical characteristics of gastric motility, as well as to open new ways for studying the gastrointestinal system

MAGNETOSTRICCAO E RELAXACAO TERMICA EM LIGAS AMORFAS FERROMAGNETICAS MAGNETOSTRICATION AND THERMAL RELAXATION IN AMORPHIC FERROMAGNETIC ALLOYS