Structural Properties Of Co Research Articles

Dielectric, magnetic and structural properties of Co doped CeO2 powders

Bulk samples of Ce1-xCoxO2 (x = 0.00 to 0.05) are prepared using solid state reaction technique. X-ray diffraction (XRD) results show a continuous decrease in the unit cell volume of Co doped CeO2 samples which indicates the substitutional doping of Co into the CeO2 lattice up to the doping concentration of x = 0.05. Field emission scanning electron microscopy (FESEM) images depict the formation of close packed particles of unusual morphology of size of 1–3 μm. X-ray absorption spectroscopy (XAS) at Ce M5,4 edge and Co L3,2 edge confirm the presence of Ce4+ and Co2+ ions, respectively. O K edge XAS conveys modification in electronic structure properties via formation of oxygen ion vacancies upon Co doping concentrations. Our results show that the observed large dielectric constants (ε′and ε'') and room temperature ferromagnetism are the intrinsic properties of the Co doped CeO2, which may offer this material in dielectric and magnetic devices applications.

Molecular Dynamics Simulation of Transport and Structural Properties of CO2–Alkanes

Carbone dioxide emissions have imposed serious threats on the environment and health. As such, industrially viable CO2 storage and utilization technologies are of high demand. This study by perform...

A combined synchrotron diffraction and first-principles investigation on structural properties of Co(OH)2under pressure up to 7 GPa

An H–H repulsion induced structural anomaly in Co(OH)2 at pressure around 2.5 GPa is reported using systematic synchrotron X-ray powder diffraction and density functional theory (DFT) based first-principles calculations. The diffraction pattern evidences anomalous pressure dependence of Bragg peaks (003) and (013) compared to others indicating a much stronger change in the hydrogen sublattice with pressure. Analysis of the lattice parameters reveals a subtle but clear change in the trend of the out-of-plane to in-plane lattice constants' ratio above 2.5 GPa. Two independent pressure runs using two different pressure transmitting media yielded similar results, thus proving the observations to be independent of the minor variations in the quasi-hydrostatic conditions during the pressure run. DFT calculations were performed on an extended unit cell of Co(OH)2 which enables the description of hydrogen in either ordered or disordered state. Calculations showed that only the hydrogen disordered structure is energetically favourable at high pressures. We attribute the anomalous behaviour of the (003) and (013) Bragg peaks above 2.5 GPa to the charge delocalization along hydrogen sublattice coming due to the hydrogen ordered-disordered transition, in agreement with DFT results showing the H disordered state to be energetically more favourable at higher pressure. A second-order Brich-Murnaghan equation of state (EoS) can well describe the low- and high-pressure regime separately with a 20% higher bulk modulus of the latter, further supporting the subtle transition around 2.5 GPa. Present results also complement the previous Raman spectroscopic study on Co(OH)2 which reported anomalous behaviour in the (2) mode around 2.5 GPa.

Effect of Synthesis Method on Particle Size and Magnetic and Structural Properties of Co–Ni Ferrites

Mossbauer spectroscopy, as well as magnetic measurements and transmission electron microscopy, was employed to investigate the particle size and magnetic and structural properties of Co–Ni spinel ferrites synthesized via a succession of chemical co-precipitation, hydrothermal treatment, and etching in hydrochloric acid (HCl). A maximum coercive force of 519 kA/m and saturation magnetization of $60.4~\text {A}\cdot \text {m}^{2}$ /kg were obtained after etching in HCl with a concentration of 4 mol/L. At room temperature, the samples obtained after co-precipitation showed partially paramagnetic behavior; however, this effect disappeared in the Mossbauer spectra at liquid He temperature. The area ratio of the Fe ions at A-sites and B-sites changed as particle size was increased, indicating that the cation distribution is changed as a result of the size and synthesis method. After the final stage of synthesis, i.e., etching, the degree of inversion was found to be 1, indicating that the structure is a completely inverse spinel. It is expected that the cation distribution, especially the increase of Co2+ in the octahedral site, produces a higher magnetocrystalline anisotropy and thus higher coercivity.

Magnetic and structural properties of Co doped ZnO nanowires prepared by heat treatment of electrospun PVA nanofibers containing Zn and Co acetates

We report the synthesis of inter-twined ZnO nanowires doped with Co by electrospinning polyvinyl alcohol along with metal oxide precursors followed by heat treatment in air at 550 °C for 90 min. This heat treatment removed PVA from the samples and ensured crystallization of 1-dimensional metal oxide nanostructure. X-ray diffraction (XRD) patterns also confirmed single phase wurtzite-type ZnO structure in samples with 3 wt% Co. Traces of Co3O4 could be observed in XRD patterns of samples with 5 wt% Co. However, micro-Raman spectra clearly indicate the presence of Co3O4 in samples with Co content more than 2 wt% which is also supported by electron paramagnetic resonance studies. UV–Vis absorption studies showed an increase in band gap energy with substitution of Co in ZnO structure. Field dependent magnetization curves recorded at room temperature revealed weak room temperature ferromagnetism with considerable paramagnetic component. The results are used to understand the origin of magnetism in this alloy and the extent of possible doping of Co in ZnO nanofibers.

Formation of Cobalt Doped Zinc Oxide Photocatalyst for Methyl Orange Degradation

The formation of cobalt (Co) doped zinc oxide (ZnO) as photocatalyst for photodegradation of methyl orange dye was investigated. The ZnO photocatalyst was produced with different concentration of Co by using sol gel method. The hexagonal wurtzite and zincite structure were successfully formed through this method. The morphological observation of nanorod and nanodisk structure formed was done by Field Emission Scanning Electron Microscope (FESEM). While, the structural properties of Co doped ZnO were identified by X-ray Diffraction (XRD) and Raman spectroscopy. The degradation performance of methyl orange was assessed and performance of photocatalytic activity was correlated to the amount of dopant level and oxygen vacancy of photocatalyst. There is an optimum amount of Co that can be doped into ZnO nanostructure in order to provide better degradation of methyl orange.

Effect of Gas Adsorption on Graphene Nanoribbons: A Density Functional Theory

Using first principal calculations we have investigated the change in electronic and structural properties of CO, NO, CO2, and NO2 adsorbed on the ultra thin graphene nanoribbons (GNRs) with armchair and zigzag edges. Gas molecules interacts weakly with GNRs with adsorption energy of -0.07eV, -0.13eV, -0.56eV and -0.32eV for CO, NO, CO2, and NO2 respectively. The charge transfer take place from GNR to CO, CO2 and NO2 molecules while NO act as donor to GNR. Results show that armchair GNR is more sensitive to adsorption of NO2 as compare to CO, NO and CO2.

Structural, magnetic and electronic structure properties of Co doped ZnO nanoparticles

We reported structural, magnetic and electronic structure studies of Co doped ZnO nanoparticles. Doping of Co ions in ZnO host matrix has been studied and confirmed using various methods; such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersed X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, magnetic hysteresis loop measurements and X-ray magnetic circular dichroism (XMCD). From the XRD and HR-TEM results, it is observed that Co doped ZnO nanoparticles have single phase nature with wurtzite structure and exclude the possibility of secondary phase formation. FE-SEM and TEM micrographs show that pure and Co doped nanoparticles are nearly spherical in shape. O K edge NEXAFS spectra indicate that O vacancies increase with Co doping. The Co L3,2 edge NEXAFS spectra revealed that Co ions are in 2+ valence state. DC magnetization hysteresis loops and XMCD results clearly showed the intrinsic origin of temperature ferromagnetism in Co doped ZnO nanoparticles.

Magnetic and structural properties of Co2FeAl thin films grown on Si substrate

The correlation between magnetic and structural properties of Co_{2} FeAl (CFA) thin films of different thickness (10 nm<d< 100 nm) grown at room temperature on MgO-buffered Si/SiO2 substrates and annealed at 600\lyxmathsym{\textdegree}C has been studied. XRD measurements revealed an (011) out-of-plane texture growth of the films. The deduced lattice parameter increases with the film thickness. Moreover, pole figures showed no in-plane preferential growth orientation. The magneto-optical Kerr effect hysteresis loops showed the presence of a weak in-plane uniaxial anisotropy with a random easy axis direction. The coercive field measured with an applied field along the easy axis direction and the uniaxial anisotropy field increase linearly with the inverse of the CFA thickness. The microstrip line ferromagnetic resonance measurements for in-plane and perpendicular applied magnetic fields revealed that the effective magnetization and the uniaxial in-palne anisotropy field follow a linear variation versus the inverse CFA thickness. This allows deriving a perpendicular surface anisotropy coefficient of -1.86 erg/cm2

Effect of the annealing temperature on dynamic and structural properties of Co2FeAl thin films

10 nm and 50 nm thick Co 2 FeAl (CFA) thin films have been deposited on thermally oxidized Si(001) substrates by magnetron sputtering using a Tantalum cap layer and were then ex-situ annealed at 415°C, 515°C and 615°C during 15 minutes in vacuum. X-rays diffraction indicates that films CFA are polycrystalline and exhibit an in-plane isotropy growth. Ferromagnetic resonance measurements, using a microstrip line (MS-FMR), reveal a huge interfacial perpendicular magnetic anisotropy and small in-plane uniaxial anisotropy both annealing temperature-dependent. The MS-FMR data also allow concluding that the gyromagnetic factor remains constant and that the exchange stiffness constant increases with annealing temperature. Finally, the FMR linewidth decreases with increasing annealing temperature due to the enhancement of the chemical order, and allow deriving a very low intrinsic damping parameter (1.3×10 −3 at 615°C).

Modification of magnetic and structural properties of Co and Co–Ag electrodeposits by sulphur incorporation

The influence of sulphur incorporation during electrodeposition on the structural and magnetic properties of both Co and Co–Ag thin films from aqueous thiosulphate solutions has been investigated. Co–Ag deposits containing sulphur showed granular morphology and varying cobalt and sulphur contents as a function of the applied potential. Nanocrystalline soft-magnetic deposits whose coercivity decreased as sulphur incorporation increased were obtained. More influence of the sulphur presence on the cobalt thin film magnetic properties was observed due to the significant structural changes induced by sulphur incorporation into the crystalline lattice. When high amounts of S were present, soft-magnetic amorphous cobalt coatings were obtained. On the other hand, stronger hard-magnetic behaviour was detected on those crystalline thin films where S content was lesser.

Adsorption of CO and NO molecules on carbon doped boron nitride nanotubes

Using first principles calculations, we have investigated the electronic and structural properties of CO and NO molecules adsorbed on boron nitride nanotubes (BNNTs) and carbon doped BNNTs. Our results indicate that for non defective nanotubes, small binding energies (around 150 meV) are obtained. When a carbon substitution impurity is present in the BNNT the binding energies are substantially increased and a chemical adsorption is observed. The calculated band structures show that the defect electronic levels inside the band gap are sensitive to the presence of the adsorbed molecules. This increasing of the functionalization capacity of the tubes due to carbon doping is an important mechanism to open up new possibilities for nanodevices applications.

A combined spectroscopic and theoretical approach to investigate structural properties of Co(ii)/Co(iii) tris-cysteinato complexes in aqueous medium

Physiological and toxicological effects of metallic ions depend on their speciation and on the structure of their associated bioligand complexes. In the field of chemical and/or nuclear toxicological studies, we are investigating cobalt complexes with biorelevant ligands such as amino acids or peptides. The aqueous reaction of cobalt dichloride with an excess of cysteine (Cys, C3H5NSO22−) in a basic medium under an anaerobic atmosphere and subsequent oxidation by O2, afforded the mononuclear complexes Co(II):3Cys and Co(III):3Cys, respectively. A combination of X-ray absorption spectroscopy (XAS) measurements and Car-Parrinello molecular dynamics (CPMD) simulations allowed us to assess structural features of the already explored Co(III):3Cys complex. Inclusion of the temperature effects in the CPMD calculations gives an implicit access to disorder effects in the extended X-ray absorption fine structure (EXAFS) equation. The very good agreement between the measured and the simulated data showed the accuracy of these models provided by CPMD. The present investigation is completed by new UV-visible, X-ray absorption near edge structure (XANES) and electron paramagnetic resonance (EPR) data of Co(II):3Cys. These data are consistent with a Co(II) high-spin d7 complex in a distorted octahedral geometry. This work contributes to the knowledge of topics such as metal–bioligand interaction which is of major interest in the field of bioinorganic chemistry.

Structural Properties of Co and CoFe Electrodes Forming a Magnetic Tunnel Junction

The M1/MgO/M2 trilayer tunnel magnetoresistance systems are studied by means of X-ray diffraction, NMR, and transmission electron microscopy techniques. As M1 and M2 electrodes we used Co, Fe, and CoFe layers. The growth mechanism and structural quality of both electrodes and of the epitaxial MgO barrier forming the magnetic tunnel junctions are experimentally examined. It is shown that the crystallographic coherence of magnetic tunnel junctions across the MgO barrier is significantly disturbed by imperfect crystal structure of magnetic electrodes. The NMR results indicate a difference in short-range order between bottom and top electrodes.

Effect of annealing on magnetotransport and structural properties of Co∕Cu multilayers with Ta buffer layer

The main aim of this study is to investigate the effect of annealing on magnetotransport and on structural properties of Co∕Cu multilayer with Ta buffer layer, prepared by dc magnetron sputtering. The heat treatment of the sample at 250°C up to 20h induced a prominent change in giant magnetoresistance, which correlates with the corresponding changes in remanent magnetization. In order to investigate the origin of the changes in the magnetotransport properties, the microstructure of the samples has been studied by x-ray diffraction. The structural modifications were elucidated by comparing x-ray spectra calculated using a nonideal step model with measured spectra and they are related to the changes in magnetotransport properties. A correlation between the changes in remanence and interlayer exchange coupling has been established using a modified Stoner-Wohlfarth [Philos. Trans. R. Soc. London, Ser. A 240, 599 (1948)] model.

FMR study of ultrahigh vacuum e-beam evaporated Co23Cu77nanogranular films: Magnetotransport properties

The magnetic, magnetotransport and structural properties of Co 23 Cu 77 granular thin films (7-43 nm) have been investigated using ferromagnetic resonance (FMR) and high-resolution XRD techniques. Co particles possess a crystalline fcc structure in the investigated films. A correlation between the GMR effect and the anisotropy field has been found, which increases with increasing film thickness. Temperature-dependent FMR measurements revealed a blocking effect, which results from the competition of long range dipole-dipole interaction and anisotropy fields of Co particles.

Magnetic and structural properties of Co ion-implanted GaN

A GaN epilayer was grown on Al/sub 2/O/sub 3/ substrate by metal-organic chemical vapor deposition, and Co/sup -/ ions with a dose of 3/spl times/10/sup 16/ cm/sup -2/ were implanted into GaN at 350/spl deg/C. The implanted samples were postannealed at 700/spl deg/C-900/spl deg/C to recrystallize the samples and to remove implantation damage. We have investigated the magnetic and structural properties of Co ion-implanted GaN by using X-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometer, and X-ray photoelectron spectroscopy (XPS). XRD results did not show any peaks associated with the second phase formation, and only the diffraction from the GaN layer and substrate structure were observed. The temperature dependence of magnetization taken in zero-field-cooling and field-cooling conditions showed the features of superparamagnetic system in films annealed at 700/spl deg/C-900/spl deg/C. The magnetization curves at 5 K for samples annealed at 700/spl deg/C-900/spl deg/C exhibits ferromagnetic hysteresis loops, and the highest residual magnetization (M/sub R/) and coercivity (H/sub c/) of M/sub R/=1.5/spl times/10/sup -4/ emu/g and H/sub c/=107 Oe were found in the 800/spl deg/C annealed sample. XPS measurement showed the metallic Co 2p core levels and the metallic valence band spectra for as-implanted and 700/spl deg/C-900/spl deg/C annealed samples. From these, it could be explained that the magnetic property of our films originated from Co and CoGa magnetic clusters.

Atomic-scale structural analyses of epitaxial Co∕Re superlattices

High-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM) have been used to investigate atomic-scale structural properties of Co∕Re trilayers and superlattices grown via magnetron sputtering. The sample growth was epitaxial with the (101¯0) plane of Co and Re parallel to the (112¯0) plane of Al2O3, and the [001] direction of Re and Co coinciding with that of the Al2O3. Both low-angle and high-angle Z-contrast STEM images show a very uniform layer thickness. However, the interface roughness between the Re and Co layers monotonically increases with interface distance from the substrate. These results strongly imply that, in the epitaxial Re∕Co superlattice system, interface roughness plays a more important role in the giant magnetoresistance effect than thickness fluctuations of the spacer layer. Previous anisotropic magnetoresistance measurements can be explained in terms of the observed atomic-scale structure.

Magnetic and structural properties of Co–Pt perpendicular recording media with large magnetic anisotropy

A Co–Pt film with large magnetic anisotropy at room temperature deposition was studied in terms of magnetic and structural properties. A high Ar gas pressure deposition of the Co–Pt film with a high crystal orientation could realize excellent magnetic properties such as a high perpendicular coercivity and a large magnetic anisotropy. This deposition technique of the Co–Pt film could form physically isolated and magnetically weak coupled grains. Magnetization reversal mechanism of the Co–Pt film deposited at a high Ar gas pressure was revealed to be a rotational mode, while the Co–Pt film deposited at low gas pressure seemed to be a magnetic domain wall motion.

Structural Properties of Co(III), Hg(II) and Pb(II) N-Ethyl-N-Phenyl-Dithiocarbamates and their Application in the Rubber Industry

Structural Properties of Co(III), Hg(II) and Pb(II) N-Ethyl-N-Phenyl-Dithiocarbamates and their Application in the Rubber Industry