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Abstract: Fe x Ni100−x thin films were produced by galvanostatic electrodeposition on Si (100), nominal thickness 2800nm, and x ranging 7–20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature 57Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization. [Copyright &y& Elsevier]

The magnetic behavior of the pseudo-binary system Fe2(Nb1-xMnx) is investigated by means of the experimental techniques of X-ray diffraction (XRD), Mössbauer Spectroscopy (MS) and magnetization studies. The XRD results indicate that, up to x=0.3, all samples are single phase with hcp structure. This corresponds to the solubility limit of manganese in this phase. Above x=0.3, all prepared samples present the coexistence of three phases, two with hcp structure and one fcc. The magnetization measurements at low temperatures indicate that the transition temperature increases with the addition of Mn atoms in the Fe2Nb host (TN=10 K) up to 58 K for x=0.1. The Mössbauer spectra were fitted with a quadrupole splitting distribution, which indicates that the average quadrupolar splitting increases slightly with the increase of the manganese concentration. [ABSTRACT FROM AUTHOR]

A series of Mn x Fe 1 - x Nb 2 O 6 compounds ( 0 ⩽ x ⩽ 1 ) is investigated by both X-ray and neutron powder diffraction, as well as specific-heat and magnetic measurements. The samples present orthorhombic Pbcn crystal symmetry, and exhibit weakly coupled magnetic chains. These chains are of Heisenberg type (weak anisotropy) on the Mn-rich side, and Ising-like (strong anisotropy) on the Fe-rich side. Except for 100% Fe ( x = 0 ) , which has weakly-interacting ferromagnetic Ising chains, a negative Curie-Weiss temperature is obtained from the magnetic susceptibility, indicating dominant antiferromagnetic interactions. At the lowest probed temperature, T = 1.5 K , true long-range magnetic order is only observed for x = 1 , 0.8, and 0. Although the ordering is globally antiferromagnetic in all cases, the first two are characterized by a two-sublattice structure with propagation vector k = ( 0 , 0 , 0 ) , while the latter presents alternatingly oriented ferromagnetic chains described by k = ( 0 , 1 2 , 0 ) . For other compositions, short-range magnetic correlations are extracted from diffuse neutron-scattering data. [ABSTRACT FROM AUTHOR]

We have synthesized composites of the type Fex(Al2O3)100−x by arc-melting compacted pellets of iron and alumina powders with starting compositions of x=0.4, 2, 3, 5, 10, 20, 40 and 60. Aluminas of two different nominal grades (99.7% and 99.99%) were used in the preparation of the composites. The samples were characterized by X-ray diffractometry, magnetization and Mo¨ssbauer spectroscopy. The results revealed the formation of the spinel FeAl2O3+z (hercynite phase) and of metallic iron partially nanostructured by this melting process. The Mo¨ssbauer subspectral areas of the formed phases were plotted against x, showing that increasing the starting iron content of the mixed powders favors the hercynite reaction. It was also observed that when the more pure alumina is used for cast, more hercynite is formed or, alternatively, less iron nanocrystallites precipitate, when compared to the less pure oxide. An arc-melted sample (x=2) was annealed at 1200°C in a hydrogen atmosphere, revealing hercynite reduction and phase separation of metallic iron. [Copyright &y& Elsevier]

Abstract: We report results on the structural and magnetic properties of the Co x Ni1−x Ta2O6 series of compounds by X-ray powder diffraction, magnetic susceptibility and magnetization measurements. X-ray refinements carried out by the Rietveld method show that these compounds crystallize in a P42/mnm tetragonal structure. Magnetic susceptibility curves show a broadened maximum witnessing that these compounds exhibit two-dimensional antiferromagnetic behaviors. All the Co x Ni1−x Ta2O6 compounds order below 10K and present a large ion anisotropy. The magnetic properties have been determined in both the paramagnetic and antiferromagnetic state. In the hypothesis of two dimensional AF ordering, the near neighbor exchange constants (J 1) and the next near neighbor exchange constants for two different paths (J 2 and J'' 2) were determined. The composition dependence of the magnetic properties including ordering temperature, exchange constants and anisotropy factors are discussed. The drastic reduction of the ordering temperature for x=0.20 for Co x Ni1−x Ta2O6, suggest the hypothesis of a peculiar magnetic behavior for this composition. [Copyright &y& Elsevier]

Abstract: We report on a detailed investigation of magnetic properties of CoTa2O6 using several techniques: neutron and X-ray diffraction, specific-heat, magnetic susceptibility, and magnetization measurements. The compound shows quasi-two-dimensional behavior due to its layered structure of alternating Co–O and Ta–O planes. We find that all magnetic moments lie entirely in the Co–O planes, along easy axes determined by the orientations of oxygen octahedra that surround the Co ions. The easy axes in successive magnetic planes have relative orientations that differ by 90°. Antiferromagnetic ordering is observed below 6.6K, with propagation vectors (1/4,1/4,1/4) associated to the two non-equivalent sets of Co2+ ions, whose magnetic moments are perpendicularly oriented. [Copyright &y& Elsevier]