Local structure investigation of Co-Fe-Si-B ribbons by extended X-ray absorption fine-structure spectroscopy

In the present work, extended X-ray absorption fine-structure (EXAFS) investigations of Co₆₉Fe_xSi_21-xB₁₀ (x = 3, 5, 7) glassy ribbons were performed at the Co K-edge. The magnitude of the first peak of the Fourier transforms of the EXAFS signals is found to increase monotonically with increasing Si concentrations indicating the formation of the localized ordered structure at the atomic scale. The Co-Si coordination number (CN) increases at the expense of the CN of Co/Fe. Smaller interatomic distances are observed in the glassy phase compared with that in the crystalline phase which promotes the stability of the glassy phase. Calculations of the thermodynamic parameter (P_HSS), cohesive energy (E_C) and the atomic radius difference (δ) parameter show that the alloy composition Co₆₉Fe₃Si₁₈B₁₀ has a good glass-forming ability (GFA) with the highest CN of Si compared with other compositions. A linear correlation of CN with that of the GFA parameter (P_HSS) exists and the CN also plays a crucial role in the GFA of the glassy alloys. This parameter should be considered in developing different GFA criteria.

Magnetic and humidity-sensing properties of nanostructured CuxCo(1-x)Fe2O4 synthesized via autocombustion

The magnetic nanomaterials of CuxCo(1-x)Fe2O4 (x = 0.0, 0.5, and 1.0) were synthesized via autocombustion. The crystallite sizes of these materials were calculated from their X-ray diffraction peaks and were found to be within the range of 23-43 nm. The band near 575 cm(-1) that was observed in the Fourier transform infrared spectrum of these samples confirmed the presence of the ferrite phase. The conductivity versus temperature graph shows thermal hysteresis and exhibits the knee points at 475, 525, and 500 degrees C for copper ferrite, cobalt ferrite, and copper-cobalt ferrite, respectively. The M-H loops for these materials were traced using a vibrating sample magnetometer, and they indicated a significant increase in intrinsic coercivity due to the addition of Co2+ ions in the copper ferrite, while the remanence and saturation magnetization decreased. The ferrite materials that were used in this study exhibited good humidity sensitivity, but copper ferrite showed higher sensitivity compared to the other two materials.

Electronic structure studies of nanoferrite Cu(x)Co(1-x)Fe2O4 by X-ray absorption spectroscopy

Pure and mixed cobalt copper ferrites are of great interest due to their widespread application in electronics and medicine. We report on the electronic structure of a nanoferrite Cu(x)Co(1-x)Fe2O4 (0.0 < or = x < or = 1.0) system studied by X-ray absorption spectroscopy. These magnetic nanoferrites (average crystallite size approximately 31-43 nm) were synthesized by an auto combustion method and are characterized by high resolution X-ray diffraction and near edge X-ray absorption fine structure measurements at the O K and Co, Cu, and Fe L-edges. The O K-edge spectra suggest that there is a strong hybridization between O 2p and 3d electrons of Co, Cu and Fe cations and Fe L3,2-edge spectra indicate that Fe ions coexist in mixed valence states (Fe3+ and Fe2+) at tetrahedral and octahedral sites of the spinel structure. Copper and cobalt ions are distributed in the divalent state in octahedral sites of the spinel structure. The origin of high saturation magnetization and coercivity in cobalt-copper ferrites are explained in light of these results.

Electronic structure and magnetic properties of the Ni0.2Cd0.3Fe(2.5-x)A1(x)O4 (0 < or = x < or = 0.4) ferrite nanoparticles

The structural, magnetic, and electronic structural properties of Ni0.2Cd0.3Fe(2.5-x)Al(x)O4 ferrite nanoparticles were studied via X-ray diffraction (XRD), transmission electron microscopy (TEM), DC magnetization, and near-edge X-ray absorption fine-structure spectroscopy (NEXAFS) measurements. Nanoparticles of Ni0.2Cd0.3Fe(2.5x)Al(x)O4 (0 < or = x < or = 0.4) ferrite were synthesized using the sol-gel method. The XRD and TEM measurements showed that all the samples had a single-phase nature with a cubic structure, and had nanocrystalline behavior. From the XRD and TEM analysis, it was found that the particle size increases with Al doping. The DC magnetization measurements revealed that the blocking temperature increases with increased Al doping. It was observed that the magnetic moment decreases with Al doping, which may be due to the dilution of the sublattice by the doping of the Al ions. The NEXAFS measurements performed at room temperature indicated that Fe exists in a mixed-valence state.

Bi-substitution-induced magnetic moment distribution in spinel Bi(x)Co(2-x)MnO(4) multiferroic

We report the near-edge x-ray absorption spectroscopy (NEXAFS) at the Co/Mn L(3,2) edge and oxygen K edge of the well-characterized Bi-substituted Co(2)MnO(4) multiferroic samples. The evolution of peak features in NEXAFS spectra of the Co/Mn L(3,2) edge and O K edge show the Bi-induced redistribution of magnetic cations (Co/Mn). The variation in valence states of Co and Mn in all the substituted compositions is consistent with the observed ferrimagnetic behaviour of the samples. Magnetization data show the decrease in molecular field complementing the ferrimagnetism. The role of Bi in the enhancement of magnetic interactions as well as the appearance of ferroelectricity in Bi(x)Co(2-x)MnO(4) (0≤x≤0.3) is discussed.

Structural, magnetic and electronic structure studies of NdFe(1-x)Ni(x)O(3) (0 ≤ x ≤ 0.3)

We present here the structural, electronic structure, magnetic and Mössbauer studies of NdFe(1-x)Ni(x)O(3) (0≤x≤0.3) samples. All the samples exhibit a single-phase orthorhombic structure with space group Pbnm. The near-edge x-ray absorption fine structure (NEXAFS) studies reveal that, with the Ni substitution at Fe sites, a new spectral feature about 1.5 eV lower than the pre-edge structure of NdFeO(3) in the O K edge is observed due to the 3d contraction effect and is growing monotonically with the increase of Ni concentration. The Fe L(3,2), Ni L(3,2) and Nd M(5,4) edges confirm the trivalent state of Fe, Ni and Nd ions. The Mössbauer spectra fitted with two Zeeman sextets confirm the different surroundings of Ni around Fe ions. With the increase in Ni concentration, the sextets are broadened. The increase of quadrupole splitting and the decrease of the hyperfine field suggest the change in the ordered regime of the system. The magnetic behaviour at low temperatures is explained in the context of competition among moments of rare earth (Nd) and transition metal ions (Fe/Ni). The strong paramagnetic contribution of the Nd magnetic sublattice and spin flip phenomenon is observed from the temperature dependence of zero-field-cooled and field-cooled magnetization where spin crossover is observed. The isothermal hysteresis loops show a decrease of magnetization and increase of coercivity with the increase in temperature and complements magnetization versus temperature. The results are explained on the basis of the spin reorientation phenomenon.

NEXAFS and XMCD studies of single-phase Co doped ZnO thin films

A study of the electronic structure and magnetic properties of Co doped ZnO thin films synthesized by ion implantation followed by swift heavy ion irradiation is presented using near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) measurements. The spectral features of NEXAFS at the Co L(3,2)-edge show entirely different features than that of metallic Co clusters and other Co oxide phases. The atomic multiplet calculations are performed to determine the valence state, symmetry and the crystal field splitting, which show that in the present system Co is in the 2+ state and substituted at the Zn site in tetrahedral symmetry with 10Dq = -0.6 eV. The ferromagnetic character of these materials is confirmed through XMCD spectra. To rule out the possibilities of defect induced magnetism, the results are compared with Ar annealed and Ar-ion implanted pure ZnO thin films. The presented results confirm the substitution of Co at the Zn site in the ZnO matrix, which is responsible for room temperature ferromagnetism.

Structural determination of the low-coverage phase of Al on Si(001) surface

The atomic structure of Al layer on Si(001)-(2 x 1) surface has been studied by coaxial impact collision ion scattering spectroscopy. When 0.5 monolayer (ML) of Al atoms are adsorbed on Si(001) at room temperature, it is found that Al adatoms are dimerized and Al ad-dimers are oriented parallel to the underlying Si dimers at the position of centering T3 site with a height of 1.02 Angstroms from the first layer of Si(001). The bond length of the Al dimer is 2.67 Angstroms. With increasing Al coverage up to one ML, Al ad-dimers still occupied near T3 site and the next favorable site is near HH site.

Structural analysis of the reconstructed Si(001)-C surface

The atomic structure of reconstructed Si(001)c(4 x 4)-C surface has been studied by coaxial impact collision ion scattering spectroscopy. When the 100L of ethylene (C(2)H(4)) molecules have been exposed on Si(001)-(2 x 1) surface at 700 degrees C, it is found that C atoms cause the ordering of missing Si dimer defects and occupy the fourth layer of Si(001) directly below the bridge site. Our results provide the support for the previous model in which a missing dimer structure is accompanied by C incorporation into the subsurface.

Constraints on cosmological parameters from the analysis of the cosmic lens all sky survey radio-selected gravitational lens statistics

We derive constraints on cosmological parameters and the properties of the lensing galaxies from gravitational lens statistics based on the final Cosmic Lens All Sky Survey data. For a flat universe with a classical cosmological constant, we find that the present matter fraction of the critical density is Omega(m)=0.31(+0.27)(-0.14) (68%)+0.12-0.10 (syst). For a flat universe with a constant equation of state for dark energy w=p(x)(pressure)/rho(x)(energy density), we find w<-0.55(+0.18)(-0.11) (68%).

Development of a new photoinitiation system for dental light-cure composite resins

OBJECTIVES

The purpose of this study is to explore the synergistic effect of combining camphorquinone (CQ) with 1-phenyl-1,2-propanedione (PPD) as a new photoinitiator.

METHODS

A BisGMA, UDMA, TEGDMA monomer mixture was made light-curing with CQ and/or PPD plus 0.2 wt.% N,N-cyanoethyl-methylaniline (CEMA). Seventeen groups, three specimens each, were tested in which the concentrations of PPD and CQ were varied. The effect of photosensitizer type (CQ or PPD) and ratio (PPD/CQ) on degree of conversion (DC) was investigated using FTIR spectrophotometry. The results were analyzed by ANOVA and Student-Newman-Keuls' multiple range comparison. The absorption spectra of PPD and CQ were recorded by UV-Vis spectrophotometry. A blind color comparison of specimens containing combinations of the two photosensitizers was also undertaken.

RESULTS

Alone, PPD induces a DC which is not significantly different from that of CQ alone. In combination, CQ + PPD produces a DC that generally exceeds that produced by the same concentration of either used alone. The maximum DC occurs between PPD/CQ = 1:1 and 1:4. At total photosensitizer concentrations above 1.8 wt.%, DC is increased by PPD but depressed by CQ, which is evidence that different mechanisms are involved. PPD (lambda max approximately 410 nm) and CQ (lambda max approximately 468 nm) have different wavelength absorption ranges, resulting in a perceptibly lighter shade of yellow for PPD.

SIGNIFICANCE

1-phenyl-1,2-propanedione is a photosensitizer of potential value in reducing color problems associated with visible light cured dental resins. In combination with camphorquinone, it acts synergistically to produce a more efficient photoinitiation reaction.