Intermediate valence behavior in CeCo9Si4

The novel ternary compound CeCo$_9$Si$_4$ has been studied by means of specific heat, magnetisation, and transport measurements. Single crystal X-ray Rietveld refinements reveal a fully ordered distribution of Ce, Co and Si atoms with the tetragonal space group I4/mcm isostructural with other RCo9Si4. The smaller lattice constants of CeCo9Si4 in comparison with the trend established by other RCo9Si4 is indicative for intermediate valence of cerium. While RCo9Si4 with R= Pr, .. Tb, and Y show ferromagnetism and LaCo9Si4 is nearly ferromagnetic, CeCo9Si4 remains paramagnetic even in external fields as large as 40 T, though its electronic specific heat coefficient (g~190 mJ/molK^2) is of similar magnitude as that of metamagnetic LaCo9Si4 and weakly ferromagnetic YCo9Si4.Comment: 2 pages, 3 figures, submitted to SCES 0

Structural and Optical Properties of Znse1−Xtex Nanocrystalline Thin Films in Terms of Optical Spectroscopic Ellipsometry

Polycrystalline thin films of ZnSe1−xTex (0.0 ≤ x ≤ 1.0) were deposited on glass substrate using electron beam deposition technique. The structure of the prepared films was examined using X-ray diffraction technique and revealed that the deposited films have polycrystalline zinc blend structure. The optical constants and film thicknesses of nanocrystalline ZnSe1−xTex films were obtained by fitting the spectroscopic ellipsometric data (ψ, Δ) using a three-layer model system in the wavelength range from 400 to 1100 nm. The refractive index was observed to increase with increasing Te concentration. This increase in the refractive index with increasing Te content may be attributed to the increase in the polarizability due to the large ionic radius of Te compared to the ionic radius of Zn. The optical studies of the polycrystalline ZnSe1−xTex films showed that the refractive index increases, and fundamental band gap opt g E decreases from 2.58 to 2.21 eV as the tellurium concentration increases from 0 to 1. Furthermore, it was also found that the variation of optical band gap with composition shows quadratic behavior

Structural and Optical Properties of Znse1−Xtex Nanocrystalline Thin Films in Terms of Optical Spectroscopic Ellipsometry

Polycrystalline thin films of ZnSe1−xTex (0.0 ≤ x ≤ 1.0) were deposited on glass substrate using electron beam deposition technique. The structure of the prepared films was examined using X-ray diffraction technique and revealed that the deposited films have polycrystalline zinc blend structure. The optical constants and film thicknesses of nanocrystalline ZnSe1−xTex films were obtained by fitting the spectroscopic ellipsometric data (ψ, Δ) using a three-layer model system in the wavelength range from 400 to 1100 nm. The refractive index was observed to increase with increasing Te concentration. This increase in the refractive index with increasing Te content may be attributed to the increase in the polarizability due tothe large ionic radius of Te compared to the ionic radius of Zn. The optical studies of the polycrystalline ZnSe1−xTex films showed that the refractive index increases and fundamental band gap opt g E decreases from 2.58 to 2.21 eV as the tellurium concentration increases from 0 to 1. Furthermore, it was also found that the variation of optical band gap with compositionshows quadratic behavior.Keywords: ZnSe1−xTex thin film, nanocrystalline, Spectroscopic ellipsometry, bandgap

Specific Heat Study of the Magnetic Superconductor HoNi2B2C

The complex magnetic transitions and superconductivity of HoNi2B2C were studied via the dependence of the heat capacity on temperature and in-plane field angle. We provide an extended, comprehensive magnetic phase diagram for B // [100] and B // [110] based on the thermodynamic measurements. Three magnetic transitions and the superconducting transition were clearly observed. The 5.2 K transition (T_{N}) shows a hysteresis with temperature, indicating the first order nature of the transition at B=0 T. The 6 K transition (T_{M}), namely the onset of the long-range ordering, displays a dramatic in-plane anisotropy: T_{M} increases with increasing magnetic field for B // [100] while it decreases with increasing field for B // [110]. The anomalous anisotropy in T_{M} indicates that the transition is related to the a-axis spiral structure. The 5.5 K transition (T^{*}) shows similar behavior to the 5.2 K transition, i.e., a small in-plane anisotropy and scaling with Ising model. This last transition is ascribed to the change from a^{*} dominant phase to c^{*} dominant phase.Comment: 9 pages, 11 figure

Itinerant electron metamagnetism in LaCo9_9Si4_4

The strongly exchange enhanced Pauli paramagnet LaCo$_9$Si$_4$ is found to exhibit an itinerant metamagnetic phase transition with indications for metamagnetic quantum criticality. Our investigation comprises magnetic, specific heat, and NMR measurements as well as ab-initio electronic structure calculations. The critical field is about 3.5 T for $H||c$ and 6 T for $H\bot c$, which is the lowest value ever found for rare earth intermetallic compounds. In the ferromagnetic state there appears a moment of about 0.2 $\mu_B$/Co at the $16k$ Co-sites, but sigificantly smaller moments at the 4d and $16l$ Co-sites.Comment: 11 pages, 5 figures, PRB Rapid Communication, in prin

Phonon-mediated anisotropic superconductivity in the Y and Lu nickel borocarbides

We present scanning tunneling spectroscopy and microscopy measurements at low temperatures in the borocarbide materials RNi2B2C (R=Y, Lu). The characteristic strong coupling structure due to the pairing interaction is unambiguously resolved in the superconducting density of states. It is located at the superconducting gap plus the energy corresponding to a phonon mode identified in previous neutron scattering experiments. These measurements also show that this mode is coupled to the electrons through a highly anisotropic electron-phonon interaction originated by a nesting feature of the Fermi surface. Our experiments, from which we can extract a large electron-phonon coupling parameter lambda (between 0.5 and 0.8), demonstrate that this anisotropic electron-phonon coupling has an essential contribution to the pairing interaction. The tunneling spectra show an anisotropic s-wave superconducting gap function.Comment: 5 pages, 3 figure

Thermodynamic and magnetic analysis of

Thermodynamic and magnetic measurements of ternary compounds RCo9Si4 with R = Pr, Nd, and Sm were analyzed in order to estimate the magnetic entropy, specific heat jump and effective magnetic moments. The samples show a ferromagnetic behaviour at low temperature with TC varying from 10 to 35 K. The saturation magnetisation Ms at 2 K with 6 T is found to be about 23.20, 24.94 and 10.70 emu/g for R = Pr, Nd, and Sm, respectively. The total effective magnetic moments μeff of RCo9Si4 for R = Pr , Nd, and Sm as obtained from the Curie constant C are estimated to be 4.94 μB, 5.26 μB, and 3.90 μB, respectively. The magnetic specific heat jump ΔCp at TC is found to be 12, 3.6, and 10.5 J/mol K for RCo9Si4 with R = Pr, Nd, and Sm, respectively. Magnetic entropy SM associated with the magnetic ordering in RCo9Si4 (R = Pr, Nd and Sm) were estimated to vary from 19.15 J/mol K and 14.90 J/mol K

Photocatalytic and optical properties of nanocomposite TiO

Nanocomposite TiO2-ZnO thin films, with different ZnO content, were deposited by electron-beam evaporation on glass and Si(1 0 0) substrates. The resulting films were annealed in air for 1 h at 450 °C. X-ray diffraction revealed the presence of monoclinic β-TiO2 and hexagonal ZnO for the films prepared with ZnO content of 0 at.% and 100 at.%, respectively. Mixed monoclinic β-TiO2 and hexagonal ZnO phases were observed at higher ZnO content between 50 at.% and 85 at.%. Spectroscopic ellipsometry (SE) was employed to determine the film thickness and optical constants. A two-layer model was used to describe the experimental ellipsometric data. At any wavelength longer than 390 nm, the refractive index decreases gradually with increasing ZnO content in the composite films. The optical band gap increased with increasing ZnO content. The photocatalytic behavior of TiO2-ZnO thin films was mainly evaluated by measuring the decomposition of methylene blue. The nanocomposite film with ZnO content of 8 at.% has the best photocatalytic activities