Magnetic interactions and spin-reversal mechanism in ErMn1-xCoxO3-delta samples

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

Morphotropic phase boundary and electrical properties of 1-x[Bi 0.5Na0.5]TiO3 -xBa[Zr0.25Ti 0.75]O3 lead-free piezoelectric ceramics

Lead-free solid solutions (1-x)Bi0.5Na0.5TiO 3 (BNT)-xBaZr0.25Ti0.75O3 (BZT) (x=0, 0.01, 0.03, 0.05, and 0.07) were prepared by the solid state reaction method. X-ray diffraction (XRD) and Rietveld refinement analyses of 1-x(BNT)-x(BZT) solid solution ceramic were employed to study the structure of these systems. A morphotropic phase boundary (MPB) between rhombohedral and cubic structures occured at the composition x=0.05. Raman spectroscopy exhibited a splitting of the (TO3) mode at x=0.05 and confirmed the presence of MPB region. Scanning electron microcopy (SEM) images showed a change in the grain shape with the increase of BZT into the BNT matrix lattice. The temperature dependent dielectric study showed a gradual increase in dielectric constant up to x=0.05 and then decrease with further increase in BZT content. Maximum coercive field, remanent polarization and high piezoelectric constant were observed at x=0.05. Both the structural and electrical properties show that the solid solution has an MPB around x=0.05. © 2012 Elsevier Ltd and Techna Group S.r.l.

Fenton-like processes and adsorption using iron oxide-pillared clay with magnetic properties for organic compound mitigation

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

DNA Psi-condensation and reentrant decondensation: Effect of the PEG degree of polymerization

psi-Condensation of DNA fragments of about 4 kbp was induced by poly(ethylene glycol) (PEG), with degrees of polymerization ranging from 45 to 182, and univalent salt (NaCl). Using circular dichroism spectroscopy, we were able to accurately determine the critical amount of PEG needed to induce condensation, as a function of the NaCl concentration. A significant dependence on the PEG degree of polymerization was found. Phase boundaries determined for the multimolecular condensation were very similar to those observed previously for the monomolecular collapse, with two asymptotic regimes at low and high salt concentrations. We analyze our data using a theoretical model that properly takes into account both the polyelectrolyte nature of the DNA and the liquid crystallinity of the condensed phase. The model assumes that all PEG is excluded from the condensates and shows reentrant decondensation only at low salt. We also systematically study reentrant decondensation and find a very strong dependence on PEG molecular weight. At low PEG molecular weight, decondensation occurs at relatively low concentrations of PEG, and over a wide range of salt concentrations. This suggests that in the reentrant decondensation the flexible polymers used are not completely excluded from the condensed phase.

Spherical particles of phenolic resin treated with iron oxide

This paper describes the preparation and characterization of phenolic resins' thermospheres covered by a magnetic phase of iron oxide. The thermospheres were prepared by allowing phenol and formaldehyde to react under dispersion polymerization conditions and the iron oxide phase was incorporated in situ onto the phenolic resin particles by adding concentrated NH3 to FeCl2 in DMSO. This reaction was conducted at 70 degrees C under nitrogen atmosphere in a controlled temperature vessel, and the modified resin was isolated and dried in vacuo. Both pure and modified resins were characterized by DRX, TG- DTA, and MEV/ EDX. The modified particles were attracted by a magnetic field, indicating the fixation of magnetic iron oxide. No diffraction peaks were observed in DRX analysis; thermal analysis ( DTA) of both pure and modified resins presented exothermic events between 300 and 680 degrees C, and 300 and 570 degrees C, respectively, indicating the microstructure of the resin was modified after the treatment. Thermogravimetric analysis ( TGA) of the pure resin registered a 2.0% residue, compared to 8.0% for the modified resin. These residues correspond to about 7.0% of fixed iron oxide. MEV/ EDX analyses confirm the modification of the resins by the process of fixing iron oxide.

Fases magnéticas em compostos Er'Co IND. x''Mn IND. 1-x''O IND> 3+ou - δ'

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Estudo de percolação de clusters de Monte Carlo para o modelo de Ising bidimensional

Pós-graduação em Física - IFT

A discrete finite-dimensional phase space approach for the description of Fe8 magnetic clusters: Wigner and Husimi functions

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Outlining precision boundaries among areas with different variability standards using magnetic susceptibility and geomorphic surfaces

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

Structural, electronic structure and magnetic studies of SmFe1-xNixO3 (x <= 0.5)

We present the structural, electronic structure and magnetic studies of Ni doped SmFeO3. The X-ray diffraction (XRD) studies confirm the single phase nature of the samples having orthorhombic Pbnm structure and the unit-cell volume is decreasing with the increase of Ni concentration. X-ray absorption spectroscopy (XAS) studies on O K. Fe L-3.2, Ni L-3.2 and Sm M-5.4 edges of SmFe1-xNixO3 (x <= 0.5) samples along with the reference compounds revealed the homo-valence state of Fe and Ni in these materials. From magnetization studies it has been observed the materials exhibit ferromagnetic and anti-ferromagnetic sub-lattices, which are strongly dependent on the thermo-magnetic state of the system. (C) 2010 Elsevier B.V. All rights reserved.

Structural, electronic structure and magnetic studies of GdFe1-xNixO3 (x <= 0.5)

The structural, electronic structure and magnetic properties of Ni doped GdFeO3 perovskite materials have been studied. A decreasing trend in volume with the increasing Ni concentration without any structural change is confirmed from X-ray diffraction studies. The electronic structural studies show that the competing ions within the ensemble have +3 oxidation states, which includes the Gd, Fe and Ni ions, and also confirms the octahedral symmetry of the Fe/Ni ions. The magnetic properties clearly depict that the Ni doping can tailor the phase transitions arising due to temperature/field dependence having a heavy impact on spin dynamics. (C) 2012 Elsevier B.V. All rights reserved.

Solid-liquid transition in Nb powder determined by third harmonic susceptibility

Measurements of the third harmonic of the AC-susceptibility were employed to determine the boundaries of the linear regime of the magnetic response of Nb powder. Non-linear contributions to the magnetic response reveal the occurrence of a structured phase, disappearing as the vortex lattice melts to the liquid state. A systematic study of the third harmonic was conducted to determine how its onset temperature depends on experimental parameters, such as the frequency and amplitude of the excitation field. The melting line (ML) has been extracted from the onset temperature measured at low-frequencies and low-excitation fields in the presence of DC magnetic fields. The study indicates that the ML can be described by a 3D vortex-glass model, except at lower fields, where the system experiences a depinning crossover, and the best description of the experimental data is provided by a 3D Bose-glass model. (c) 2008 Elsevier B. V. All rights reserved.

Kondo-attractive-Hubbard model for the ordering of local magnetic moments in superconductors

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

The Schrodinger and Pauli-Dirac Oscillators in Noncommutative Phase Space

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Finite-momentum condensate of magnetic excitons in a bilayer quantum Hall system

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