Nd16Co72-xRu xC11B boro-carbides have been prepared by arc melting and studied by X-ray diffraction and magnetization measurements. X-ray diffraction results confirm that all the prepared alloys possess the tetragonal 2:14:1 (P4(2)/mmm) hard magnetic phase. The observed decrease of the magnetization and Curie temperature indicate the development of antiferromagnetic spin correlations with the increase of the Ru content. The combined addition of B and C is favorable to the formation and stabilization of the tetragonal phase in these compounds. At lower Ru contents the Curie temperature is higher than in the corresponding Co-based boride in spite of larger cell volumes.

Co2+x+yMn1-xAl1-y intermetallic compounds have been prepared by arc melting and studied with X-ray diffraction and magnetization measurements to ascertain the effect of deviations of composition from the stoichiometry on the ferromagnetism of this system. Hysteresis loops registered at room temperature show a soft ferromagnetic behavior in excess Co. In off-stoichiometric alloys the saturation magnetization is lower than in Co2MnAl, whereas the Curie temperature T C is higher in all the studied alloys. T C varies substantially with variations in composition and increases with the Mn content. In the source of this behavior a volume effect is inferred which is expected to lead to strengthened ferromagnetic exchanges.

The Nd16Co76-xRu xC7B system has been investigated to assess the effect of boron-carbon combined addition on the ferromagnetic behavior of these intermetallic compounds. The results indicate that the addition of 1 at.% B favors the formation of the tetragonal magnetic phase 2:14:1 in these alloys. With the increase of the Ru concentration is observed an expansion of the lattice in the basal plane as well as a contraction along the c direction of the tetragonal unit cell. The Curie temperature decreases from 432 K at x = 6 to 421 K for x = 27, whereas the saturation magnetization has a steep decrease. The highest T C value has been verified for the alloy with the largest c parameter, despite its a parameter is the smallest one. In comparison to isotypic borides and pure carbides, a loss of coercivity and remanence is observed.

The electronic structure of the A15 compounds A3B A=Nb; B=Al,Ga,Ge,Sn and In is studied by means of fully relativistic full-potential linearized augmented-plane wave (FP-LAPW) calculations within the formalism of the density functional theory. Band structures and densities of states are determined for all the studied compounds. From the calculations are obtained the theoretical lattice constants, the Fermi energy E F, the density of states at the Fermi level N(E F) which is used to estimate the electronic specific heat coefficient gamma and the electron-phonon coupling parameter lambda for the Nb3In compound. Generally, a good agreement between results of the calculations and experiments is found.

The first-principles molecular cluster discrete variational method (DV) is used to investigate the electronic structure and local magnetic properties of Cr impurities in bcc iron and Fe/Cr interfaces. The spin polarized case is considered within the framework of the local-spin-density approximation of the density function theory. The effect on the local moment and hyperfine magnetic field (Fermi contact term) of adding Cr atoms in the vicinity of Fe atoms is investigated. For a Cr impurity in bcc iron the calculated magnetic moment and hyperfine field is -0.62 µB and -300 kG, respectively. For pure chromium we obtained -0.49 µB and -67 kG. The Fe moment is sensitive to the separation between Cr atoms in the first shell of neighbors.

We performed a Mössbauer spectroscopy study of the iron meteorite Soledade. This meteorite, which consists of a metallic matrix, is an octahedrite with polycrystalline troilite, cohenite, schreibersite and rhabdites as major constituents. A chemical analysis indicates 6.78 % Ni, 0.46% Co, besides traces of Cu, Cr, Ga, Ge, As, Sb, W, Re, Ir and Au. No traces of silicates have been found and no oxygen was detected. Iron is appearing in the austhenitic phase and alloyed with nickel. An analysis of the Mössbauer spectra at room temperature indicates that the Fe-Ni phase is homogeneously distributed in the matrix, although variations in the composition between different regions are observed.

As argilas encontradas em amostras de solos, provenientes de Terras Indígenas do planalto médio do Rio Grande do Sul, foram caracterizadas com o intuito de fornecer dados e parâmetros técnicos para seu uso como matéria prima de produtos cerâmicos. O estudo mineralógico efetuado nas amostras utilizando a técnica de difração de raios X demonstrou que o argilomineral predominante é a caulinita. Outros minerais, como quartzo e rutilo, encontram-se presentes em menor quantidade. As análises químicas demonstram que as quantidades de óxido de Mg, Mn, K, Na, Ca, Cu e Zn são baixas (a soma das porcentagens é menor que 0,97 %). As amostras foram analisadas por espectroscopia Mössbauer de 57Fe. Os espectros Mössbauer obtidos na temperatura ambiente confirmam a presença do mineral caulinita. Os espectros a 77 K revelam a existência dos minerais goetita e hematita, na forma de partículas magnéticas ultrafinas (nanopartículas) em estado superparamagnético. Os testes físicos efetuados nas amostras indicam que os solos são finos e apresentam características granulométricas e de plasticidade, que podem ser aproveitadas para a produção de materiais cerâmicos para construção ou objetos ornamentais.

Clay samples collected from soils of indian territories of the middle plateau in Rio Grande do Sul were analyzed with the aim to obtain characterization data and technical parameters for their potential use as raw material for ceramic products. The mineralogical study in samples by using the X-ray diffraction technique demonstrated that the predominant clay mineral is kaolinite. Others minerals as quartz and rutile also are present in small amounts. Chemical analysis shows low percentages for oxides of Mg, Mn, K, Na, Ca, Cu and Zn (overall percentages smaller than 0.97%). The samples also were analyzed with the 57Fe Mössbauer spectroscopy. The Mössbauer spectra at room temperature confirm the presence of the mineral kaolinite. At 77 K they reveal the existence of the minerals goethite and hematite as ultrafine magnetic particles in a superparamagnetic state. The physical tests performed in the samples show that these soils are very fine material and present appropriate granulometric characteristics and plasticity, which can be taken in advantage for the production of materials for construction or production of ornamental artifacts.