In recent years, the ability to design nanostructures and control magnetic properties on a nanometric scale has attracted a lot of attention from researchers, with emphasis on different geometries, such as cubic, rectangular, cylindrical, rings, etc., being studied extensively with the possibility of applications in technologiesdata recording, biomedicine and sensors.From a theoretical point of view, there is interest in the analysis of new magnetic phases, originating from the dipolar field, in nanostructures with dimensions on the order of tens of the exchange length, for applications in magnetic recording systems.In this work, initially a theoretical study was carried out on the impact of dipolar interaction on the magnetic phases of nanocylinders and later on nanorings.Our studies indicated that the effect of dipolar interaction in nanorings is capable of causing significant changes in the magnetic phases in isolated nanostructures.It was shown that through the chosen parameters we can control the vortex nucleation region.There is a difference in the nanostructures detailed in this work, because for nanorings the exchange energy term that was associated with the nucleus is non-existent and for nanocylinders this term is not absent, which favors studying the behavior of magnetic states in nanorings, as it was verifiedthe emergence of multidomain phases contributing to the formation of domain walls.The research was developed through the analysis of the magnetization curves of the remanence phases.An external magnetic field of 5 kOe was applied in different directions until saturating the structure and we gradually removed this field until remanence was reached.

Since the 1990s, with the discovery of the accelerated expansion of the Universe, several attempts have been made to explain the nature of the mechanism that causes this acceleration. To date, cosmological observations reinforce the consolidation of theΛ-Cold Dark Matter (ΛCDM) cosmological model as the most adequate to explain the dynamics of
the Cosmos. This model assumes a negative pressure fluid, the cosmological constant -Λ, driving this accelerated expansion. However, this model is still incipient to satisfactorily explain this mechanism, giving rise to the problem of the cosmological constant, in addition to presenting other problems such as flatness of the universe, for example, impelling the search for alternative cosmological scenarios. In this context, this work seeks to explore the ΛCDM-Rastall cosmological model, derived from Rastall’s non-conservative gravitational theory, alternative to Einstein’s Theory of General Relativity, through statistical tests, involving a data sample composed of 32 ages of galaxies in intermediate and high redshifts. Thus, this model was analyzed by through two tests called Lookback Time and Age. In the first one we assume the age of the Universe t₀= 13.8±0.024 Gyears and H₀= 67.4±0.5 km.s⁻¹.Mpc⁻¹, while for the latter we adopted the following values for the Hubble constant: i) H₀=74±1.4 km.s⁻¹.Mpc^-1 resulting in Ωm=0.29±0.019 and λ=0.5±0.074 and ii) H0= 67.4±0.5 km.s^-1.Mpc^-1 obtaining Ωm=0.36±0.024 and λ=0.5±0.076. We also find the theoretical ages of the Universe for these scenarios.

When a beam of electromagnetic radiation is incident on a surface, the reflected beam may undergo a lateral displacement. This effect is not predicted by geometric optics and is known as the Goos-Hänchen effect, which, in the case of the present work, is due to guided wave excitation, in which the displacement will be dependent on the frequency of the incident radiation. The configuration studied consists of a Si prism, with the angle of incidence within the prism greater than the critical angle for total internal reflection, an air layer and a Si slab with defined thickness. Computer simulations were performed with this geometry and interesting results were obtained. The first one is that, for the frequency band used (255-295 GHz), from calculations assuming a wide beam, we observed that the beam displacement presents different values, presenting maximum and minimum for certain established frequencies coresponding to guided wave excitations. Apart from this result we consider how, for a Gaussian beam of finite width, the intensities of the incident and reflected beam present a displacement. We examine how, when we modify parameters such as the beam width and the thickness of the air layer between the prism and the Si plate, the displacements are greater for wider beams and a larger prism-slab distance.

The magnetocaloric effect (MCE) is a relevant subject of study due to its potential in areas like biotechnology, medicine, and materials engineering. When a magnetic material is subjected to an external magnetic field, its entropy changes. Upon removal of the field, the material undergoes a temperature change, referred to as the magnetocaloric effect. This phenomenon has several innovative applications, such as magnetic refrigeration, magnetic hyperthermia, and data storage.

Magnetic refrigeration is a promising application of the EMC effect due to its eco-friendly nature. It offers a sustainable and efficient alternative to traditional refrigeration methods that rely on harmful gases. This technology has a significant impact, and with increasing concerns about the environment, it provides an excellent solution to the refrigeration needs of various sectors.

Currently, research is focused on discovering new materials and magnetic structures that efficiently present Electromagnetic Compatibility (EMC). Therefore, it is crucial to comprehend the interactions among magnetic moments, temperature, and external fields, as well as the magnetic order of magnetic materials concerning intrinsic and extrinsic parameters, to develop new structures that meet the demands of modern society.

This study aims to investigate the magnetocaloric effect on clusters of ferromagnetic gadolinium (Gd) nanoparticles with ellipsoidal geometry. Additionally, the study will explore the influence of the dipolar field on the thermal stabilization of the magnetic moments of the nanoparticles.

This study analyzed micrometric elliptical clusters of Gd nanoparticles with varying eccentricities, nanoparticle densities, and diameters ranging from 30 nm to 200 nm. The dipolar interaction in the clusters depends upon their anisotropy, which is influenced by their geometry. The analysis was conducted at a fixed magnetic field in the preferred direction of anisotropy (i.e., the ellipse's major axis) in a temperature range of 200 K to 450 K. The isothermal magnetic entropy variation DS_M was calculated under an applied external magnetic field, revealing the normal EMC and the inverse magnetocaloric effect (EMCI) due to the competition between the Zeeman and dipolar interaction energies. Transitional phrases were used to indicate the sequence of the analysis. The technical terms planar susceptibility and out-of-plane angle were also utilized.

Since the beginning of humanity we have been instigated by questions about our existence and our place in the cosmos, based on questions like this and hypotheses, a new area to be studied by stellar astrophysics, the study of exoplanets gives us before nothing more is the certainty that our planetary system is not unique and that a wide range of Possibilities arise as new discoveries are made in this area of study. This one work aims to provide a historical overview of exoplanetology in addition to publicize the advances made in the area, from the first discoveries to future perspectives, show some basic concepts within this area of study such as the definition of what would be exoplanets and present the most used exoplanet detection methods and responsible for the most recent discoveries. A study was also carried out with 20 curves of light, obtained from the Exoplanet Archive, consisting of 10 stars with planets already confirmed by other studies and 10 stars without confirmed planets. For each of these stars the light curve and probability density graph was created in the R studio program, as well as studied the first four moments of statistical distribution for the flow of this star. In the results we obtained expected patterns for the light curves being eclipsed with periods very close to those found in the literature, and constant flows in the light curves of planetless stars. for statistical moments were also expected patterns were found, considering the limitations of the R studio program and the Kepler telescope.

This thesis aims to revisit and innovate the understanding of some phenomena of the primordial Universe from a non-Gaussian perspective. The research is divided into three main topics: non-Gaussian effects in Big Bang nucleosynthesis, hydrogen recombi- nation, particle-antiparticle excess, and Rindler space; primordial plasma acceleration; and evolution of primordial chemical potentials. In the first topic, we determined the non-Gaussian Saha ionization equation for recombination. We defined new binding energy and established new chemical equilibrium conditions. As an application in cosmology, we showed that there is a value q ≠ 1 that provides the same result as the usual case for the nucleosynthesis temperature and the fractional ionization equi- librium temperature, and that recombination necessarily occurs in excited states in a non-Gaussian context. Furthermore, we developed a correction strategy for the Saha ionization equation, allowing the reproduction of the same results for recombination as predicted by the Boltzmann kinetic approach. We derived non-Gaussian expressions for the particle-antiparticle excess in relativistic and non-relativistic limits and analyzed their effects. As an application in gravitation, we showed that the non-Gaussian binding energy in Rindler space has a quadratic dependence on the gravitational field and derived a constraint for this field. Besides, we demonstrated that photoionization and pair production are more intensely suppressed in regions with strong gravitational fields compared to results obtained with classical statistics and derived a constraint im- posed on the electron and positron chemical potentials. Regarding the second topic, we determined the plasma acceleration via the Saha ionization equation in the primordial Universe. We derived the plasma acceleration at the beginning of nucleosynthesis and showed that there is a transition in acceleration around the nucleosynthesis temperature. We also demonstrated that when the deuterium bottleneck is overcome, the plasma acceleration is much higher than the acceleration of the Universe. We showed that the plasma acceleration is negative at the time of recombination, and for z < 380.23 the primordial plasma begins to accelerate. We investigated the possible physical reasons underlying this occurrence. Finally, in the third topic, we revisited the hydrogen recom- bination history from an innovative perspective: the evolution of chemical potentials. We derived expressions for these potentials, which are dependent on the thermal bath temperature and the ionization degree of the Universe. This novel approach revealed a constraint between the chemical potentials of hydrogen and the proton at z ≈ 1200, when the free electron fraction is Xe ≈ 1/3.

Samples with silenite structure of the type Bi25F eO40 doped with manganese (Mn) were produced via solid state reaction, at a temperature of 700◦C, using bismuth ores as precursors, iron and manganese extracted from deposits located in the state of Rio Grande do Norte. The X-ray diffractograms obtained for the specimens confirm the presence of the Bi₂₅FeO₄₀ phase and the BiClO₂Pb spurious phase, in which the former has a weight percentage greater than 90% . Hysteresis curves at room temperature indicate an increase in the coercive field and a decrease in the remanent magnetization with the increase in the concentration of dopant ions in the crystal structure, which may result from a possible contribution of distinct magnetic phases. The values of g factor obtained in the Electronic Paramagnetic Resonance spectra point to resonance signals coming from paramagnetic centers of Fe3+ ions. The band gap energies were calculated for each sample through the absorbance values obtained by UV/Visible Spectrometry and the results varied between 2.24 and 2.27 eV, which indicates that the compounds have potential for applications in photocatalytic activities. Zeta potential analyzes were performed for samples Bi₂₅FeO₄₀, subjected to heat treatment at a temperature of 600 ^oC, and Bi₂₅Fe_(1−x)Mn_xO₄₀ (BMO), with x = 1, calcined at 700◦C, in order to estimate the surface charge of the particles and later apply them in the process of drug adsorption. For a pH of 6.8, the samples exhibited a net negative charge. In the adsorption, the BMO sample showed a better efficiency in removing the drug from the solution.

Keywords: Minerals, Doping, Silenite (Bi25F eO40).

In recent years, the study of thin films and magnetic multilayers
has been important from an academic perspective, revealing great potential for technological applications. In this work, we present a theoretical investigation of the effects of magnetic field, temperature, and size on the magnetic phases in thin films of the rare earth Terbium (Tb).

The theoretical method used to obtain the magnetic phases of Tb films takes into account the contributions of exchange energy, anisotropy energy, Zeeman energy, and thermal energy, which are calculated using an auto-consistent field model.

The self-consistent effective field model uses the constants
associated with the energies involved and their dependence
on temperature, and this dependences are obtained from experimental works.

Our study revealed that, in addition to the previously observed
magnétic phases to Tb in bulk, the Tb films produce a variety of different magnética phases due to competition between the envolved energies (Exchange, Anisotropie, Zeeman, and Thermal) and the
effects of size and surface, produce a variety of different magnetic phases.