Annealing effect on the structural, magnetic and transport properties in the CoxCu1-x granular alloys with 0.20 ≤ x ≤ 0.25 prepared by the ion-beam sputtering technique

We have studied the transport and magnetic properties of a metallic granular CoxCu1-x system, with 0.2≤x≤0.25, prepared by using an ion-beam sputtering technique. Giant magnetoresistance (GMR) has been observed for the all studied concentration with the average amplitude around 2%. at 300K. The maximum value has been observed for Co21Cu79 granular alloy after annealing at 450°C for 2h. Above this concentration the MR decreases which is attributed to the percolation effect, which causes a concurrent reduction in magnetic coercivity. The variation of magnetic and transport properties with the concentration and annealing time is discussed.We have studied the transport and magnetic properties of a metallic granular CoxCu1-x system, with 0.2≤x≤0.25, prepared by using an ion-beam sputtering technique. Giant magnetoresistance (GMR) has been observed for the all studied concentration with the average amplitude around 2%. at 300K. The maximum value has been observed for Co21Cu79 granular alloy after annealing at 450°C for 2h. Above this concentration the MR decreases which is attributed to the percolation effect, which causes a concurrent reduction in magnetic coercivity. The variation of magnetic and transport properties with the concentration and annealing time is discussed

Stuctural And Magnetic Characterization Of CoxZn1-x/Cu Multilayers Obtained by Electrodeposition

We present the experimental results of (CoxZn1-x/Cu)n multilayers (3<x<10) grown using the electrochemical dual bath method. The X-ray diffraction patterns have shown that the CoZn structural lattice parameters are close to those of the monoclinic CoZn13 compound. We have developed an analytical model in the X-ray kinematical theory adapted to the electrodeposited (CoxZn1-x/Cu) multilayers. We have shown that the model can give interesting structural information about the multilayer components, and reproduces the position of the satellite peaks around the main diffraction peak. Thus we have deduced the multilayer period and performed comparison between experimental results and the analytical model. The magnetic properties at room temperature reveal both superparamagnetic and ferromagnetic features. The inclusion of Zn into the magnetic layer and the existence of CoZnCu based alloy at the interfacial regions explain the magnetic properties. The magnetoresistance (MR) loop displays a broad , rounded maximum and the saturation is not observed even at high applied fields. The MR(H) behaviour and its small ratio can be attributed to interfacial effects.We present the experimental results of (CoxZn1-x/Cu)n multilayers (3<x<10) grown using the electrochemical dual bath method. The X-ray diffraction patterns have shown that the CoZn structural lattice parameters are close to those of the monoclinic CoZn13 compound. We have developed an analytical model in the X-ray kinematical theory adapted to the electrodeposited (CoxZn1-x/Cu) multilayers. We have shown that the model can give interesting structural information about the multilayer components, and reproduces the position of the satellite peaks around the main diffraction peak. Thus we have deduced the multilayer period and performed comparison between experimental results and the analytical model. The magnetic properties at room temperature reveal both superparamagnetic and ferromagnetic features. The inclusion of Zn into the magnetic layer and the existence of CoZnCu based alloy at the interfacial regions explain the magnetic properties. The magnetoresistance (MR) loop displays a broad , rounded maximum and the saturation is not observed even at high applied fields. The MR(H) behaviour and its small ratio can be attributed to interfacial effects

Fluorine-doped ZnO thin films deposited by spray pyrolysis technique

Fluorine doped ZnO thin films (FZO) are prepared onto glass substrates at 350 degrees C by the chemical spray pyrolysis technique. X-ray diffraction spectra show a polycrystalline of ZnO (wurtzite structure) where the amount of fluorine doping affects to preferential orientation (002 plane along c-axis) and does not vary the lattice parameters. Therefore, F introduction in lattice is by the substitution of O(-2) ions by F(-1) ions. Any variation is observed in transmittance and reflectance measurements in 400-2000 nm wavelength range when samples present F dopant; they have transmittance around 80% in the near infrared and visible zones. The FZO films are degenerate and exhibit n-type electrical conductivity. The best resistivity and mobility are 7.6 x 10(-3) Omega cm and 3.77 cm(2) V(-1) s(-1) respectively. The calculated values of the mean free path are very small compared to the grain sizes calculated using XRD measurements. Therefore, we suggest that ionized impurity and/or neutral impurity scattering are the dominant scattering mechanisms in these films

Improvement of the photocatalytic degradation property of atomic layer deposited ZnO thin films: the interplay between film properties and functional performances:

In this work, we have evidenced the impact of stoichiometry on the photocatalytic properties of ZnO nanofilms grown by atomic layer deposition (ALD). We point out the importance of hydrogen incorporation and propose here a model explaining the presence of Zn-OH impurities in the form of a ZnOxHy amorphous matrix hosting ZnO crystallites. We evidence that this phase prevails in films grown at low temperatures and prevents the photoluminescence and photocatalytic activity of ZnO films. We also point out that high temperature ALD processes promote the preferential growth of ZnO films in the (002) orientation, leading to a significant increase of the film wettability and so their photocatalytic degradation performances

Photoluminescence properties of rare earth (Nd, Yb, Sm, Pr)-doped CeO2 pellets prepared by solid-state reaction

Several structural and optical properties of ceria (band gap, refractive index and lattice parameter) make this material very promising for applications in optoelectronics and photovoltaics. In this paper, we show that CeO2 can be efficiently functionalized by doping with trivalent rare earth ions to give rise to photon management properties. The trivalent ions can be successfully inserted by solid-state reaction of the elementary oxide powders. By combining the information obtained from the absorbance spectra with that of the PL excitation spectra, we demonstrate the presence of the trivalent ions in CeO2 and provide insight in the electronic level structure and transfer mechanism. In particular, we prove that both the complex absorption spectra and the energy transfer mechanisms cannot be fully explained without considering the presence of isolated Ce3+ ions in CeO2

Photoluminescence of Nd-doped SnO2 thin films

Structural, optical, and electrical properties of Nd-doped SnOx thin films are reported. The atomic structure was characterized by x-ray diffraction and infrared absorption spectrometry. Investigation of the photoluminescence properties revealed Nd-related bands at 920 and 1100 nm for samples annealed at 700 degrees C, which present the tetragonal structure of the SnO2 rutile phase. Nd3+ ions can be indirectly excited and no concentration quenching was observed up to 3 at. %. It is concluded that Nd3+ ions are efficient optically active dopants in addition to be responsible of the observed electric conductivity improvement. These materials are then interesting for solar cell applications

Structural, optical, and electrical properties of Yb-doped ZnO thin films prepared by spray pyrolysis method

Yb-doped ZnO thin films were prepared on glass substrates by spray pyrolysis technique in order to investigate the insertion of Yb ions in the ZnO matrix and the related optical properties of the films. The molar ratio of Yb in the spray solution was varied in the range of 0-5 at. %. X-ray diffraction patterns showed that the undoped and Yb-doped ZnO films exhibit the hexagonal wurtzite crystal structure with a preferential orientation along [002] direction. No secondary phase is observed in Yb-doped ZnO films. All films exhibit a transmittance between 75 and 90% in the visible range with a sharp absorption onset about 375 nm corresponding to the fundamental absorption edge at 3.3 eV. The photoluminescence measurements show a clear luminescence band at 980 nm that is characteristic of Yb(3+) transition between the electronic levels (2)F(5/2) and (2)F(7/2). This is an experimental evidence for an efficient energy transfer from ZnO matrix to Yb(3+). Hall effect measurements showed low resistivities and high carrier mobilities which makes these films of interest to photovoltaic devices.This work is supported by the program interdisciplinaire énergie du CNRS Grant No. PE10-2.1.2-2