Electronic and magnetic properties of Ti and Fe on graphene

The structural, electronic and magnetic properties of Fe and Ti atomic wires and the complete covering when adsorbed on graphene are presented through ab initio calculations based on density functional theory. The most stable configurations are investigated for Fe and Ti in different concentrations adsorbed on the graphene surface, and the corresponding binding energies are calculated. The results show a tendency of the Ti atoms to cover uniformly the graphene surface, whereas the Fe atoms form clusters. The adsorption of the transition metal on the graphene surface changes significantly the electronic density of states near the graphene Fermi region. In all arrangements studied, a charge transfer is observed from the adsorbed species to the graphene surface due to the high hybridizations between the systems.

Ni-Zn-Sm nanopowder ferrites: Morphological aspects and magnetic properties

Ni-Zn ferrites have been widely used in components for high-frequency range applications due to their high electrical resistivity, mechanical strength and chemical stability. Ni-Zn ferrite nanopowders doped with samarium with a nominal composition of Ni0.5Zn0.5Fe2-xSmxO4 (x = 0.0, 0.05, and 0.1 mol) were obtained by combustion synthesis using nitrates and urea as fuel. The morphological aspects of Ni-Zn-Sm ferrite nanopowders were investigated by X-ray diffraction, nitrogen adsorption by BET, sedimentation, scanning electron microscopy and magnetic properties. The results indicated that the Ni-Zn-Sm ferrite nanopowders were composed of soft agglomerates of nanoparticles with a high surface area (55.8-64.8 m(2)/g), smaller particles (18-20 nm) and nanocrystallite size particles. The addition of samarium resulted in a reduction of all the magnetic parameters evaluated, namely saturation magnetization (24-40 emu/g), remanent magnetization (2.2-3.5 emu/g) and coercive force (99.3-83.3 Oe). (c) 2007 Elsevier B. V. All rights reserved.

Crystal growth and magnetic properties of tin selenide-doped europium Sn(1-x)Eu(x)Se

The growth and magnetic properties of Tin Selenide (SnSe) doped with Eu(2+) Sn(1-x)Eu(x)Se (x=2.5%) were investigated. Q-band (34 GHz) electron paramagnetic resonance measurements show that the site symmetry of Eu(2+) at 4.2 K is orthorhombic and the Lande factor was determined to be g=1.99 +/- 0.01. The exchange coupling between nearest-neighbor (NN) Eu(2+) ions was estimated from magnetization and magnetic-susceptibility measurements using a model that takes into account the magnetic contributions of single ions, pairs and triplets. The exchange interaction between Eu(2+) nearest neighbors was found to be antiferromagnetic with an estimated average value of J(p)/k(B) =-0.18 +/- 0.03 K. (C) 2009 Elsevier B.V. All rights reserved.

Effect of urea and glycine fuels on the combustion reaction synthesis of Mn-Zn ferrites: Evaluation of morphology and magnetic properties

The goal of this study is to evaluate the influence of the urea and glycine fuels on the synthesis of Mn-Zn ferrite by combustion reaction The morphology and magnetic properties of the resulting powders were investigated. The powders were characterized by X-ray diffraction (XRD), nitrogen adsorption (BET), scanning and transmission electron microscopy (SEM and TEM), and magnetic measurement of M x H curves. The X-lay diffraction patterns indicated that the samples containing urea resulted in the formation of crystalline powders and the presence of hematite as a secondary phase The samples containing glycine presented only the formation of crystalline and monophases (Mn,Zn)Fe(2)O(4). The average crystallite size was 18 and 35 nm and saturation magnetization was 3.6 and 75 emu/g, respectively, for the samples containing urea and glycine. The samples synthesized with glycine fuel showed better magnetic properties for application as soft magnetic devices. (C) 2009 Elsevier B.V All rights reserved

Hyperfine and magnetic properties of Fe-Cu clusters and Fe precipitates embedded in a Cu matrix

Using the first-principles real-space linear muffin-tin orbital method within the atomic sphere approximation (RS-LMTO-ASA) we study hyperfine and local magnetic properties of substituted pure Fe and Fe-Cu clusters in an fcc Cu matrix. Spin and orbital contributions to magnetic moments, hyperfine fields and the Mossbauer isomer shifts at the Fe sites in Fe precipitates and Fe-Cu alloy clusters of sizes up to 60 Fe atoms embedded in the Cu matrix are calculated and the influence of the local environment on these properties is discussed.

Influence of calcination temperature on the morphology and magnetic properties of Ni-Zn ferrite applied as an electromagnetic energy absorber

An evaluation was made of the influence of calcination temperatures on the structure, morphology and eletromagnetic properties of Ni-Zn ferrite powders. To this end, Ni(0.5)Zn(0.5)Fe(2)O(4) ferrite powders were prepared by combustion reaction and calcined at temperatures of 800, 1000 and 1200 degrees C/2 h. The resulting powders were characterized by XRD, SEM and reflectivity measurements in the frequency bands of 8-12 GHz. The results demonstrated that raising the calcination temperature increased the particle sizes of the powders of all the systems in question, improving the reflectivity of the materials. (C) 2008 Elsevier B.V. All rights reserved.

Structural and magnetic properties of chromium-doped ferrite nanopowders

This paper reports on a study of Cr(3+)-doped nanosized Ni-Zn ferrites produced by combustion reaction, and evaluates their morphological and magnetic properties. The powders were characterized by X-ray diffraction (XRD) and SEM and magnetic properties. All the compositions showed the formation of the inverse spinel phase of Ni-Zn ferrite. The average crystallite size ranged from 21 to 26 nm. The saturation magnetization was found to be in the range of 53-43 emu/g. The increase in Cr(3+) concentration in the Ni-Zn ferrite caused a reduction in hysteresis losses and a slight reduction in the saturation magnetization. (C) 2008 Elsevier B.V. All rights reserved.

Structural and magnetic properties and hyperfine interaction in La(3.5)Ru(4)O(13) compound

Structural, magnetic and hyperfine interaction measurements have been carried out on the novel compound La(3.5)Ru(4)O(13) prepared under two different atmospheres (air and oxygen flow). This compound is formed in the orthorhombic structure (space group Pmmm, # 47). The coexistence of the triple-layered perovskite-type planes (quasi-2D structure) and the rutile-like slabs (1D structure) leads to interesting magnetic and electronic properties in this compound. The magnetic susceptibility of this system shows a peak at T similar to 47 K associated with antiferromagnetic interactions. The Curie-Weiss behaviour of the susceptibility provides an effective magnetic moment consistent with Ru ions in low-spin state. Perturbed angular correlation measurements carried out with (111)Cd probe in the temperature range 10-60 K reveal only quadrupole interactions and indicate the occurrence of structural distortions for T<40K. (C) 2009 Elsevier B.V. All rights reserved.

Thermoluminescence, structural and magnetic properties of a Li(2)O-B(2)O(3)-Al(2)O(3) glass system doped with LiF and TiO(2)

A Li(2)O-B(2)O(3)-Al(2)O(3) glass system, un-doped and doped with LiF, and/or TiO(2) was synthesized by the fusion method and its physical properties were investigated by thermoluminescence (TL), X-ray diffraction (XRD), electron paramagnetic resonance (EPR), atomic force microscopy (AFM) and differential thermal analysis (DTA). The samples were subjected to gamma-rays from a colbalt-60 ((60)Co) source. These techniques provided evidence of LiF and LiF doped with Ti crystal formation in the glass system. A TL glow peak at about 433 K was sensitive to (60)Co gamma-rays and showed good linearity with doses and consequently could be used to quantify radiation doses. Crown Copyright (C) 2011 Published by Elsevier B.V. All rights reserved.

Magnetic and structural properties of NiFe(2)O(4) ferrite nanopowder doped with Zn(2+)

This work involved an investigation to ascertain how the substitution of nickel ions for zinc ions affects the structural, morphological and magnetic properties of NiFe(2)O(4) ferrite samples. Ni(1-x)Zn(x)Fe(2)O(4) (x = 0.0, 0.3 0.5, 0.7) powders were prepared by combustion reaction and characterized structurally by X-ray diffraction. The specific surface area of the powders was determined by the nitrogen adsorption method (BET). Magnetization measurements were taken using an alternative gradient magnetometer (AGM), which revealed that the powders prepared by combustion reaction resulted in nanosized particles with a particle size of 18-27 nm. The crystallite size and lattice parameter increased as the concentration of Zn increased. Moreover, augmenting the Zn content in the NiFe(2)O(4) ferrite increased the saturation magnetization and coercive field. (C) 2008 Elsevier B.V. All rights reserved.

Effect of Ti-C and Cr Additions on Magnetic Properties of Nanocrystalline (Pr,Nd)-Fe-B Alloys

The addition of both Ti-C and Cr as grain refiners in Nd-Fe-B nanocomposites substantially increases the coercive field Hc. This motived our investigation of the effect of Ti-C and Cr on Pr-Fe-B nanocomposites. Melt-spun ribbons of composition (Pr(9.5)Fe(84.5)B(6))(0.97-x)Cr(x)(TiC)(0.03)(x = 0; 0.25; 0.5; 0.75; 1) and (Nd(9.5)Fe(84.5)B(6))(0.97-x)Cr(x)(TiC)(0.03)(x = 0.5 and 1) were produced for study. For a Pr nanocomposite with 1% Cr, Hc = 12.5 kOe. However, the energy product was limited to 13.6 MGOe by the remanence value. Rietveld analysis of X-ray spectra showed the ribbons to consist of predominantly hard (similar to 70 wt%) R(2)Fe(14)B, the soft phase being (similar to 30 wt%) alpha-Fe. Mossbauer measurements at 300 K are consistent with a reduced hyperfine field for the hard magnetic phase due to the Cr addition. Analysis of transmission electron microscopy images showed the Pr nanocomposite with 1% Cr to have an increased average grain size.

Particle acceleration and magnetic field structure in PKS 2155-304: optical polarimetric observations

In this paper, we present multiband optical polarimetric observations of the very-high energy blazar PKS 2155-304 made simultaneously with a HESS/Fermi high-energy campaign in 2008, when the source was found to be in a low state. The intense daily coverage of the data set allowed us to study in detail the temporal evolution of the emission, and we found that the particle acceleration time-scales are decoupled from the changes in the polarimetric properties of the source. We present a model in which the optical polarimetric emission originates at the polarized mm-wave core and propose an explanation for the lack of correlation between the photometric and polarimetric fluxes. The optical emission is consistent with an inhomogeneous synchrotron source in which the large-scale field is locally organized by a shock in which particle acceleration takes place. Finally, we use these optical polarimetric observations of PKS 2155-304 at a low state to propose an origin for the quiescent gamma-ray flux of the object, in an attempt to provide clues for the source of its recently established persistent TeV emission.

Programs to compute magnetization to density ratio and the magnetization inclination from 3-D gravity and magnetic anomalies

Vector field formulation based on the Poisson theorem allows an automatic determination of rock physical properties (magnetization to density ratio-MDR-and the magnetization inclination-MI) from combined processing of gravity and magnetic geophysical data. The basic assumptions (i.e., Poisson conditions) are: that gravity and magnetic fields share common sources, and that these sources have a uniform magnetization direction and MDR. In addition, the previously existing formulation was restricted to profile data, and assumed sufficiently elongated (2-D) sources. For sources that violate Poisson conditions or have a 3-D geometry, the apparent values of MDR and MI that are generated in this way have an unclear relationship to the actual properties in the subsurface. We present Fortran programs that estimate MDR and MI values for 3-D sources through processing of gridded gravity and magnetic data. Tests with simple geophysical models indicate that magnetization polarity can be successfully recovered by MDR-MI processing, even in cases where juxtaposed bodies cannot be clearly distinguished on the basis of anomaly data. These results may be useful in crustal studies, especially in mapping magnetization polarity from marine-based gravity and magnetic data. (c) 2007 Elsevier Ltd. All rights reserved.

Ac and dc magnetotransport properties of the phase-separated La(0.6)Y(0.1)Ca(0.3)MnO(3) manganite

The physical properties of the La(0.6)Y(0.1)Ca(0.3)MnO(3) compound have been investigated, focusing on the magnetoresistance phenomenon studied by both dc and ac electrical transport measurements. X-ray diffraction and scanning electron microscopy analysis of ceramic samples prepared by the sol-gel method revealed that specimens are single phase and have average grain size of similar to 0.5 mu m. Magnetization and 4-probe dc electrical resistivity rho(T,H) experiments showed that a ferromagnetic transition at T(C) similar to 170 K is closely related to a metal-insulator (MI) transition occurring at essentially the same temperature T(MI). The magnetoresistance effect was found to be more pronounced at low applied fields (H <= 2.5 T) and temperatures close to the MI transition. The ac electrical transport was investigated by impedance spectroscopy Z(f,T,H) under applied magnetic field H up to 1 T. The Z(f,T,H) data exhibited two well-defined relaxation processes that exhibit different behaviors depending on the temperature and applied magnetic field. Pronounced effects were observed close to T (C) and were associated with the coexistence of clusters with different electronic and magnetic properties. In addition, the appreciable decrease of the electrical permittivity epsilon`(T,H) is consistent with changes in the concentration of e(g) mobile holes, a feature much more pronounced close to T (C).

Electrical transport in disordered and ordered magnetic domains under pressures and magnetic fields

Magnetic M( T, H, P) and electrical transport.( T, H, P) measurements in a strong spin-lattice-charge coupled La(0.7)Ca(0.3)MnO(3) system have been conducted. The application of H and P leads to the formation of different magnetic domain structures in the vicinity and below the polaronic-to-ferromagnetic transition temperature. The charge mobility is more sensitive to the variation of the spatial wave function overlap between Mn(3+) eg and O(2-) 2p orbitals due to the applied compacting pressure rather than the relative spin orientation between neighbouring Mn ions when the magnetic field is applied. In spite of the presence of different magnetic domain structures due to the sample history, the effect of magnetic field and pressure is less pronounced at lower temperatures on electrical transport properties.