bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electronic structure of crystalline uranium nitride: LCAO DFT calculations
Authors: Evarestov R. A. , Losev M. V. , Panin A. I. , Mosyagin N. S. , Titov A. V. 
Published: October 2007

AbstractThe results of the first LCAO DFT calculations of cohesive energy, band structure and charge distribution in uranium nitride (UN) crystal are presented and discussed. The calculations are made with the uranium atom relativistic effective core potentials, including 60, 78 and 81 electrons in the core. It is demonstrated that the chemical bonding in UN crystal has a metallic–covalent nature. Three 5f‐electrons are localized on the U atom and occupy the states near the Fermi level. The metallic nature of the crystal is due to the f‐character of both the valence‐band top and the conduction‐band bottom. The covalent bonds are formed by the interaction of 7s‐ and 6d‐states of the uranium atom with the 2p‐states of the nitrogen atom. It is shown that the inclusion of 5f‐electrons in the atomic core introduces small changes in the calculated cohesive energy of UN crystal and electron charge distribution. However, the inclusion of 5s‐, 5p‐, 5d‐electrons in the valence shell allows the better agreement with the calculated and experimental cohesive‐energy value. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic behaviour of superconductor/ferromagnet metallic and perovskite based superlattices
Authors: Guimpel J. , Monton C. , Haberkorn N. , de la Cruz F. 
Published: October 2007

AbstractWe present a study of the magnetic behaviour of superconducting/ferromagnetic superlattices, both for metallic and perovskite based systems. In the first case we find that the response is determined by the ferromagnetic layer regime. If these layers are very thin, no ferromagnetism is observed, but the superconducting layers are decoupled, and the superlattice behaves as a stack of independent superconducting films. For thicker ferromagnetic films, ferromagnetism is established and the effective field resulting from the superposition of stray and applied fields dominates the superconducting response of the superlattice. For the perovskite based superlattices, the physical properties are more affected by interface disorder. In this case we have found that the behaviour can be interpeted as charge carrier transfer between both materials, inducing a change in the magnetic character of the manganite. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Detailed magnetic and structural properties of exchange‐biased La1‐xCaxMnO3
Authors: Gómez M. E. , Campillo G. , Ramirez J.‐G. , Hoffmann A. , Guimpel J. 
Published: October 2007

AbstractWe measured structural, magnetic and, magneto‐transport properties of heterostructures consisting of La1–x Cax MnO3 ferromagnetic (FM) layers (x = 0.33) and antiferromagnetic (AF) layers (x = 0.67). We grew FM/AF superlattices via a high‐pressure sputtering technique on (001) oriented SrTiO3 substrates. We systematically varied the thickness of the ferromagnetic layers, while maintaining a fixed thickness of the antiferromagnetic layers. Alternatively, we also varied the thickness of the antiferromagnetic layers, keeping a fixed ferromagnetic layer thickness. The total superlattice thickness was kept approximately constant. XRD analysis confirms the existence of the superlattice structure by the observation of multiple satellite peaks around the (00l) manganite Bragg reflections. We extracted the average lattice parameter of the superlattice and its dependence on the thicknesses of the ferro‐ and antiferromagnetic layers. We conducted field cooling (FC) and zero field cooling (ZFC), magneto‐thermal, and magneto‐resistance measurements. The existence of an exchange bias effect at temperatures below the Néel temperature of the AF layer was revealed by magnetization loops measured after FC. We studied the dependence of magnetic parameters on the thicknesses of the ferro‐ and antiferromagnetic layers. We found that the structural, magnetization, and magneto transport properties as functions of F‐layer thickness are all correlated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Oxidation‐induced high‐Curie‐temperature ferromagnetism in CoAl(100)
Authors: Rose V. , Brüggemann K. , David R. , Franchy R. 
Published: October 2007

AbstractIn conventional magnetic materials, oxidation is a disagreeable effect that often lowers or destroys the magnetic capabilities of those materials. By contrast, we report on the decisive paramagnetic‐ferromagnetic phase transition in CoAl(100) at room temperature, utilizing oxidation of stoichiometric CoAl. We also discuss the control and drastic increase of the coercive field by subsequent annealing of the oxidized sample. The alumina film grown by selective oxidation protects the alloy from oxidation of Co, despite the accumulation of Al vacancies and the resulting enrichment in Co of the metallic phase underneath the oxide film. As a result, a ferromagnetic thin Co‐rich phase is formed at the interface between the insulating aluminum oxide and the paramagnetic Co50Al50 bulk. The creation via simple oxidation of a ferromagnetic thin film underneath a surface insulator demonstrates a novel path to building the majority of a magnetic tunnel junction. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanosynthesis of LaMnO3 from different manganese oxides
Authors: Cortés Escobedo C. A. , Sánchez de Jesús F. , Bolarín Miró A. M. , Muñoz‐Saldaña J. 
Published: October 2007

AbstractWe report on the synthesis of lanthanum manganese oxide (LaMnO3) by solid state reaction using high energy reactive ball milling from manganese oxides (MnO, Mn2O3, MnO2) mixed with lanthanum oxide in stoichiometric ratios. Morphology and particle size of powders were investigated by SEM and laser diffraction at different milling times. A prolonged milling time (>630 min) produces an important reduction in particle size but also powder agglomeration. Structural characterization as a function of milling time was carried out by XRD as well as by TEM for specific samples. Lanthanum manganites were successfully obtained by the simplest possible process, a single step milling at room temperature showing however different transformation kinetics respective to the manganese oxide precursors. Complete reaction of LaMnO3 using Mn2O3 and MnO2 was achieved only after 210 and 270 min of milling, respectively obtaining a mixture of rhombohedral, cubic and orthorhombic phases. From MnO, mainly rhombohedral LaMnO3 could only be obtained after a calcination process. In order to avoid iron contamination, precursor mixtures were milled in nylamid vials with zirconia balls at 360 min for Mn2O3 and MnO2 as precursors. The crystalline structure of the manganites prepared using zirconia/nylamid milling system was mainly cubic. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wear and corrosion behavior of W/WC bilayers deposited by magnetron sputtering
Authors: de Sánchez N. A. , Jaramillo H. E. , Bejarano G. , Villamil B. E. , Teran G. 
Published: October 2007

AbstractWC/W coatings were deposited by reactive magnetron sputtering using 40%, 60% and 80% methane CH4 in the gas mixture. The bilayers were grown on to AISI 420 stainless‐steel substrates in order to study the wear and corrosion behavior. Before growing the bilayers, one Ti monolayer was grown to improve the adherence of the coatings to the substrate. The wear resistance and the friction coefficient of the coatings were determined using a pin‐on‐disk tribometer. All coatings had a friction coefficient of about 0.5. The measured weight lost of the bilayers from each probe allowed the qualitative analysis of wear behavior all coatings. The bilayers grown with 80% methane showed the best abrasive wear resistance and adhesion without failure through the coating in the wear track for dry pin‐on‐disk sliding. Electrochemical corrosion test showed that the bilayers grown with 80% methane were more resistant to corrosion than the ones uncoated. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Effect of boron on the microstructure of hydrogenated microcrystalline silicon thin films
Authors: Dussan A. , Koropecki R. R. 
Published: October 2007

AbstractIn this work, a series of boron doped microcrystalline silicon films (μc‐Si:H (B)) were deposited by plasma‐enhanced chemical vapor deposition (PECVD), using silane (SiH4) diluted in hydrogen, and diborane (B2H6) as a dopant gas. The concentration of B2H6 was varied in the range of 0–100 ppm. The microstructure and morphology of samples were analyzed by atomic force microscopy (AFM), X‐ray diffraction (XRD), and Raman spectroscopy. A trend towards increasing crystalline volume fraction and grain size were observed as boron concentration in the samples increased; while the XRD spectra show that the peak intensity at 2θ ≈ 47° decreases and becomes gradually amorphous with the increasing degree of doping. The doped microcrystalline silicon films presented a crystallographic preferential orientation in the plane (220). Correlations between structural and electric properties were also studied. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Mechanical and chemical behavior of sintered 6061 powder aluminium alloy reinforced with CuAl2 particles
Authors: Vanegas O. , Castro I. J. , Barona W. , Sanchez Sthepa H. 
Published: October 2007

Abstract A 75 μm 6061 powder Aluminum Alloy (A.A) plus 5, 10 and 15 wt% CuAl2 particles were prepared by mixing the powders in a small milling tumbler during 4 hours at 58 rpm. The samples were compacted at room temperature and at (210±5) °C by using a 38 mm diameter uniaxial floating die. A vacuumed chamber set with an Argon flux was adapted to sinter the samples at 555 °C, temperature that was determined by the exothermic peak of CuAl2 and sinter time was experimentally determined in 13/4 h. The sintered samples were tailored to perform the tension and hardness tests. The 10wt% reinforced Alloy exhibits the best properties: the fluency stress is higher in approximately 130% as compared with the plain alloy. Also the maximum stress, the stress at 0.1% strain and the Young modules are better. The Tafel polarization curves show that corrosion resistance increases as the reinforcement particles increase. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study of the magnetic and structural properties of nanostructured powders of Nd2Fe14B mechanically alloyed
Authors: Oyola Lozano D. , Zamora L. E. , Pérez Alcázar G. A. , Rojas Y. A. , Bustos H. , Greneche J. M. 
Published: October 2007

AbstractIn this work we report the magnetic and structural properties obtained by Mössbauer spectrometry, Vibrating Sample Magnetometry and X‐ray diffraction, of powder of Nd2Fe14B prepared by mechanical alloying. The mixtures were ball milled during 48 hours and submitted to heat treatments between 500 and 900 °C under an argon atmosphere. Structural parameters were derived from high statistics X‐ray patterns. The Mössbauer spectra registered at 300 K for samples without heat treatment were fitted by means of a sextet and a hyperfine field distribution, associated to a residual pure iron phase (α‐Fe) and a disordered iron‐based phase, respectively. From the spectra at 300 K the formation of the Fe3C phase is observed for samples heat treated at 900 °C. A quenching above 900 °C accelerates the formation of the Fe3C phase. The hysteresis loops allow to conclude that these samples behave as soft ferromagnets. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Study on the pozzolanic properties of silica obtained from rice husk by chemical and thermal process
Authors: Salas A. , Ospina M. A. , Delvasto S. , Mejía de Gutierrez R. 
Published: October 2007

AbstractIn this study, the effect of chemical and thermal treatment on the pozzolanic properties of rice husk ash (RHA) was investigated. The rice husks were subjected to chemical and thermal treatments. After the chemical treatment, the husks were burned under controlled conditions in order to obtain amorphous silica to be used as a pozzolanic material. Finally the ash obtained was milled in a ball mill to reduce the size of the particles. All the products obtained were characterized in terms of silica content, amorphous character, particle size distribution, and pozzolanic activity. The ash produced after an acid treatment with HCl to the husks produced a high percentage of ash with amorphous silica; high fineness, purity, and pozzolanic activity. The silica obtained was incorporated to cement pastes and concretes to evaluate the mechanical, rheological and durability properties. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Pinning energy of domain walls in MnZn ferrite films
Authors: Calle V. H. , Cuéllar F. , Calle C. , Marín O. , Roa‐Rojas J. , Arias D. , Guzmán O. , Prado J. , Gómez M. E. , Volkmann U. G. , Prieto P. , Mendoza A. 
Published: October 2007

AbstractMn Zn ferrite films deposited on (100) MgO substrates by rf sputtering technique with different thicknesses ξ in the range of 30‐450 nm were studied. AFM images show grain size increase as film thickness increases. Grains with diameters between L ∼ 70 and 700 nm were observed. The mono and multidomain regime in MnZn ferrite films and their effect on the pinning energy of domain walls are observed via Magneto‐optical Kerr Effect, MOKE. At ξ ∼ 300 nm, the coercive field, Hc, reaches a maximum value of 80 Oe. This result indicates the existence of a multidomain regime associated to a critical grain size, Lc. We used the Jiles‐Atherton model (JAM) to discuss the experimental hysteresis loops. The k pinning parameter obtained from JAM shows a maximum value of k /μo = 67 Am2 for grains with Lc ∼ 529 nm. The total energy per unit area E was correlated with k and D. We found a simple phenomenological relationship given by E α kD; where D is the magnetic domain width. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Magnetic and electrical properties of BiMnO3 thin films
Authors: Grizalez M. , Delgado E. , Gómez M. E. , Prieto P. 
Published: October 2007

AbstractBiMnO3 thin films were deposited on single‐crystal (001)‐oriented SrTiO3 substrates by rf‐magnetron sputtering method. X‐ray diffraction was used to analyze the crystal structure of the thin films, indicating that the films were monoclinic with two dominant orientation relationships along the substrate. The first is (111) BiMnO3 ‖ (001) SrTiO3; the second is (222) BiMnO3 ‖ (002) SrTiO3; other peaks showed that the films were polycrystalline. The roughness of the films was characterized by AFM. R vs. T was measured from 390 K to 15 K using a Keithley Model 167 Programmable Electrometer. Magnetic characterization was carried out by using a quantum design™ magnetometer for magnetization versus temperature and for hysteresis loops at different temperatures. The saturation magnetic moment of 2.8μB per Mn ion (still fairly smaller than that of the bulk, 3.6μB) was observed at 5 K decreasing with increasing temperature. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Synthesis and characterization of Fe0.79Si0.09C0.12 by mechanical alloying
Authors: Barona Mercado W. , Cuevas Ochoa J. , Fajardo M. , Pérez Alcázar G. A. , Sánchez Sthepa H. 
Published: October 2007

AbstractIron silicon carbide Fe0.79Si0.09C0.12 was prepared by mechanical alloying from elemental powders, with a ball‐to‐powder weight ratio of 20:1. This synthesis was carried out in two stages: in the first stage cementite Fe3C was prepared from elemental iron and carbon powders, the mixed powders were milled for 30 hours. In the second stage Fe0.79Si0.09C0.12 was prepared from cementite Fe3C and Silicon elemental powder as precursors, the samples were milled for 1, 3, 5, 10, 15, 20, 25, 30 and 35 hours. The alloy progress for each milling time was evaluated by X‐ray diffraction (XRD) and 57Fe Mössbauer spectrometry. Nanocrystalline Fe3C powders were obtained from Fe and C, with an average grain size of 15 nm. It was possible to prepare metastable iron silicon carbide such as Fe0.79Si0.09C0.12 and Fe0.81Si0.02C0.17 and their respective hyperfine parameters are reported. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Current‐voltage characteristics of capacitor structures based on PZT thin films grown on Nb‐doped SrTiO3 substrates
Authors: Cortes A. , Lopera W. , Prieto P. 
Published: October 2007

AbstractCurrent measurements, as functions of voltage (I –V curves), at different temperatures were carried out in SrTiO3+Nb/Pb(Zr0.52Ti0.48)O3/Ag capacitor structures grown on (100) SrTiO3 Nb‐doped substrates by using a technique of high‐oxygen pressure on axis sputtering. Crystalline quality and structure were measured by X‐ray diffractometry (XRD). Surface roughness and morphology were studied by atomic force microscopy (AFM). Ferroelectric characterization was conducted by P –E hysteresis loops on different capacitors with electrode areas of 5.0×10–4 and 6.5×10–3 cm2. Conductance measurements revealed a hopping mechanism of conduction through 2 or 3 localized states in the range of temperatures between 130 K and 40 K. On the other hand, in the temperature range between 385 K and 180 K, our results fit very well with the variable range hopping (VRH) model. The measurements of current as a function of voltage on SrTiO3+Nb/PZT/Ag structures showed typical electronic tunneling behavior. The process of electronic tunneling through capacitive structures can be interpreted as a transition from hopping mechanisms via N localized states to variable range hopping, when temperature is increased. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Performance of new dispersion‐precipitation strengthened copper‐ceramic materials made by mechanical alloying
Authors: López M. , Corredor D. , Ramam K. , Jiménez J. A. , Ruano O. 
Published: October 2007

AbstractThe dispersion strengthened copper alloys obtained by mechanical alloying (MA) followed by elevated temperature treatment are attractive due to their excellent combination of thermal and electrical conductivities, strength and microstructural stability. The strengthening of pure copper is provided by mechanical milling with 0.5% of ZrB2 and 1 or 0.5 vol.% of ZrC as fine dispersants. The alloyed powders are hot consolidated by an uniaxial pressing at 923 K and rolling with a 25% of reduction at 1073 K. Microstructural characterization of consolidated samples are by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The hot consolidation process resulted in fully dense MMCs materials with an adequate tensile strength as high as 650 MPa and electrical conductivity up to 48% IACS. The effect of milling process on microstructure and mechanical properties observed has been related to the collection of iron, chromium, carbon and oxygen, with Fe‐Cr oxicarbides and cuprospinel particles of size about 5‐15 nm, which are precipitated during hot consolidation. The electron microscopy studies revealed that the strength of consolidated metal matrix composites, Copper‐Zirconium ceramics are consistent with approximations based on Orowan and Hall‐Petch strengthening mechanisms. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Electrical transport properties of MoO3 thin films prepared by laser assisted evaporation
Authors: López‐Carreño L. D. , Pardo A. , Zuluaga M. , Cortés‐Bracho O. L. , Torres J. , Alfonso J. E. 
Published: October 2007

AbstractIn the present paper the growth of MoO3 thin films on common glass substrates are described. The films were prepared by evaporation of a MoO3 target with a CO2 laser (10.6 μm), operating in the continuous wave mode. The effect of substrate temperature on the crystallographic structure and electrical properties of MoO3 thin films was studied. The chemical composition of the different species formed on the films surface was obtained by X‐ray photoelectron spectroscopy (XPS) and the crystalline structure was studied with X‐ray diffraction (XRD). The electrical conductivity of the films was determined using the standard four‐points method. Conductivity of the films varied from de 10–9 to 10–5 (Ωcm)–1 in the 300‐600 K temperature range. Arrhenius‐type plots for the electrical conductivity indicate the presence of at least two different conduction mechanisms. The I‐V characteristic curve shows an ohmic behavior only in the 4.5‐60 V range. Outside this interval the I‐V curve has a behavior described by a power law. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Low‐temperature growth of high quality AlN films on carbon face 6H‐SiC
Authors: Kim Myunghee , Ohta Jitsuo , Kobayashi Atsushi , Fujioka Hiroshi , Oshima Masaharu 
Published: October 2007

AbstractAlN films have been grown on atomically flat carbon face 6H‐SiC (000$ \bar 1 $) substrates by pulsed laser deposition and their structural properties have been investigated. In‐situ reflection high‐energy electron diffraction observations have revealed that growth of AlN at 710 °C proceeds in a Stranski–Krastanov mode, while typical layer‐by‐layer growth occurs at room temperature (RT) with atomically flat surfaces. It has been revealed that the crystalline quality of the AlN film is dramatically improved by the reduction in growth temperature down to RT and the full width at half maximum values in the X‐ray rocking curves for 0004 and 10$ \bar 1 $2 diffractions of the RT‐grown AlN film are 0.05° and 0.07°, respectively. X‐ray reciprocal space mapping has revealed that the introduction of misfit dislocations is suppressed in the case of RT growth, which is probably responsible for the improvement in crystalline quality. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Measuring metal substrate roughness with glow discharge optical emission spectrometry
Authors: Biao Xu , Meng Zhang 
Published: October 2007

AbstractAlthough there are many methods to evaluate metal surface roughness, it is difficult to detect the substrate roughness of coated samples. Depth profile analysis (DPA) is proposed as a new method for the substrate roughness measurement, and glow discharge optical emission spectrometry (GDOES) becomes a candidate in substrate roughness measuring instruments. With this method, the typical roughness parameters Ra (arithmetic mean of the absolute deviation values of the roughness profile) and Ry (maximum value of consecutive peak and valley heights of the roughness profile along the sampling length) can be easily obtained. The principle of this method is discussed and the formulasof the principle are deducted in this paper. Electrodeposited zinc coating on copper substrate specimens is used as an example to explain the measuring process. Copyright © 2007 John Wiley & Sons, Ltd.
Early loss of dopaminergic terminals in striosomes after MDMA administration to mice
Authors: Granado Noelia , Escobedo Isabel , O'Shea Esther , Colado Ma. Isabel , Moratalla Rosario 
Published: October 2007

AbstractThe amphetamine analogue 3,4‐methylenedioxymethamphetamine (MDMA or “Ecstasy”) is a popular drug of abuse which causes different neurotoxic effects in the mouse compared with the rat. In mice, MDMA produces damage to striatal dopamine terminals, having little long‐term effects on serotonin (5‐HT) containing neurons. A relevant feature of the striatum is its striosome/matrix compartmental organization; defined by different connexions, and functions. In this study we examined the long‐term effect induced by MDMA on tyrosine hydroxylase (TH) and dopamine transporter (DAT) immunoreactivity in the striosomes and matrix compartments of mouse striatum. Mice given MDMA showed significant reductions in TH and DAT immunostaining in striatum compared with control animals. Interestingly, this effect was considerably more pronounced in striosomes than in the matrix. These data provide the first evidence that striosomes and matrix compartments of the mouse striatum have differential vulnerability to MDMA and that the long‐term neurotoxicity induced by MDMA in mice is primarily associated with a loss of striosomal dopamine fibres. Synapse 62:80–84, 2008. © 2007 Wiley‐Liss, Inc.