Giant magnetoresistance (GMR) and ferromagnetic properties of DC and pulse electrodeposited Cu–Co alloys

Cu–Co ferromagnetic alloys occurring as granular films and exhibiting giant magnetoresistance (GMR) property have been synthesized using both DC and pulse electrodeposition techniques. The growth process of these electrodeposits comprising multiple granules of disparate morphology, magnetic features exhibits critical dependence on electrodeposition conditions. Using ferromagnetic resonance and magnetic hysteresis data, we have attempted a correlation between evolution of these electrodeposits and their ferromagnetic properties with special emphasis on GMR property.     

Characterization of electrochemically deposited polyaniline–polypyrrole blend coatings on carbon fibers

Macroscopically homogeneous and uniform coatings of polyaniline, polypyrrole and their blend were successfully deposited on carbon fibers by aqueous electropolymerization technique. Electrochemical polymerization of aniline and pyrrole blend with p-toluene sulfonic acid as the electrolyte was carried out by cyclic voltammetry in the potential range of -0.2 V to 1.0 V vs. SCE. The electrochemical polymerization parameters such as the molar feed ratio of monomers and number of cycles were systematically varied. Gravimetric analysis showed that the amount of blend coatings on carbon fibers was dependant on the electrochemical deposition parameters. As the pyrrole concentration in the feed increases, the deposition rate increases. Analysis of the blend coating on the carbon fibers by infrared spectrophotometry (IR) showed that both polyaniline and polypyrrole are present in the coating. The morphology of composite coating varied from smooth to rough and globular structure during deposition.     

Performance of 2 μm Tm:YAP pulse laser based on a carbon nanotube absorber

We demonstrated the first use of carbon nanotube as a saturable absorber in the Q-switched and Q-switched mode-locking of a diode pumped Tm:YAP operating at 2 μm. At the incident pump power of 8.64 W, the minimum Q-switched pulse width of 255.1 ns, and the maximum peak power 53.1 W can be obtained with the corresponding repetition rate of 21.76 kHz. The performance of a diode-pumped passively Q-switched mode-locked Tm:YAP laser with high repetition rate formed with a folded cavity. As high as 780 mW average output power was produced in QML laser. The repetition rate of the mode-locked pulse inside the Q-switched envelope was 244.1 MHz. The dependence of the operational parameters on the pump power was also investigated experimentally.     

Influence of Cd addition on the phase transformations of β Cu–Al alloys

Cu–Al alloys in the hyper- and hypoeutectoid region with addition of Cd are studied. The phase transformation sequence during continuous heating and cooling has been followed by resistometry, calorimetry, and optical microscopy.     

TiO2–carbon nanotube composites for visible photocatalysts – Influence of TiO2 crystal structure

We investigated the influence of the crystal structure of TiO₂ and the use of different TiO₂ precursors on the properties and photocatalytic activity of carbon nanotube (CNTs)–titania composites. We found that the crystal structure and properties of starting TiO₂ nanomaterial significantly affected the effect of CNTs incorporation on the photocatalytic activity under simulated solar and visible light illumination (simulated solar illumination with UV-blocking filter). In case of significant photocatalytic activity under visible light illumination (anatase TiO₂), likely due to the presence of native defects, composites exhibited lower activity under visible illumination only, but higher activity under simulated solar illumination. The opposite trends were observed for P25 (anatase + rutile) and rutile TiO₂, where incorporation of CNTs resulted in a significant increase of photocatalytic activity under visible illumination. Thus, control over crystal structure and native defects is essential for the development of efficient visible light activated photocatalysts.     

Influence of Co–Zr substitution on coercivity in Ba ferrites

Polycrystalline BaCo_xZr_xFe_11.5−2xO_18.25 samples with 0?x?0.6$0?x?0.6$ ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:11.5. The cationic site preferences of Co²⁺ and Zr⁴⁺ in Co–Zr substituted Ba ferrite were investigated by magnetic measurements and X-ray diffractometer (XRD) analysis. The coercivity H_c was decreasing with increasing Co–Zr substitution. The datum showed that the max coercive force (H_c) was obtained when substitution of 0.2, while the best saturation magnetizations (M_s) was obtained when substitution of 0.4.     

Broad spectral pulse operation of 2 μm Tm:YAP laser based on reflection-type carbon nanotube absorber

We demonstrated the first use of reflection-type single-walled carbon nanotube (RSWCNT) as a saturable absorber in the Q-switched mode-locking (QML) of a diode pumped Tm:YAP operating at 2 μm. The spectrum of the QML laser is centered at 1.97 μm with a broad spectral region of 36 nm. At the incident pump power of 10.33 W, as high as 432 mW average output power was produced in QML laser. The repetition rate of the mode-locked pulse inside the Q-switched envelope was 158 MHz. The dependence of the operational parameters on the pump power was also investigated experimentally.     

Influence of ageing on the low cycle fatigue behaviour of an Al–Mg–Si alloy

Abstract

The low cycle fatigue (LCF) performance of AA6063 Al–Mg–Si alloy at under-aged (UA), peak-aged (PA) and over-aged (OA) conditions has been examined to understand the micromechanism of fatigue and the associated dynamic structural changes in this alloy. The LCF behaviour of the differently aged AA6063 alloys has been studied at strain amplitudes ranging between 0.2 and 1.0% under strain control mode. The UA state exhibits pronounced cyclic hardening unlike the PA and the OA states at strain amplitudes greater than 0.4%. The PA and the OA states show hardening only for a few cycles followed by prolonged softening. Characterisations of the micro- and the sub-structural alterations due to LCF establish that the phenomenon of dynamic precipitation results in cyclic hardening the UA alloy. The softening of PA alloy occurs due to shearing of precipitates and that in the OA alloy takes place owing to reversibility of slip by the formation and annihilation of the Orowan loops around the β (Mg₂Si) precipitates. Analyses of the hysteresis loops reveal Masing, nearly-Masing and non-Masing behaviour in the UA, OA and PA states, respectively. Analyses of the asymmetry factor of the hysteresis loops assist to infer that the Masing behaviour in the UA alloy is due to dislocation–dislocation interactions, whereas the nearly-Masing behaviour in the OA alloy and the non-Masing behaviour in the PA alloy are the consequence of varying degrees of dislocation–precipitate interactions associated with inhomogeneous deformation.     

Influence of Co:Cu ratio on properties of Co–Cu films deposited at different conditions

A series of Co–Cu films with different Co:Cu ratio was electrodeposited at different electrolyte pH, deposition potential and film thickness, and their morphology, crystal structure and magnetic properties were investigated. Compositional analysis by energy dispersive x-ray spectroscopy disclosed that the Co and Cu content were 75 and 25 wt%, respectively, at high pH (3.2) level, while for films at low pH (2.5) level the compositions are 61 Co and 39 wt% Cu, and further decrease of Co:Cu ratio occurred as the film thicknesses increased. The surface morphology of the films changed from an initial dendritic stage to expanded dendrites with increasing Cu content by the electrolyte pH. The dendrites became more obvious at 3 μm and the dendritic structures increased with further increase of film thickness as the Co:Cu ratio decreased. Hence, the increase of the Cu content is thought to be the cause of the increase of dentritic structure. Structural characterizations by x-ray diffraction (XRD) showed that all films have face-centered cubic structure. In the XRD patterns, the peak intensity of Co (111) is lower for the films grown at low pH compared to that of high pH, and the (111) peaks of Co and Cu slightly separated at 3 μm and then the intensity of the Cu (111) increased with increasing film thickness from 4 to 5 μm, so that the Co:Cu ratio changed at all deposition parameters. Magnetic measurements displayed that the saturation magnetization decreased and the coercivity increased as the Co:Cu ratio decreased with all deposition parameters. Also, the magnetic easy axis was found to be in the film plane for all films. It was seen that the variations in the properties of the films might be attributed to the change of Co:Cu ratio caused by the deposition parameters.     

Influence of Cobalt on the Adhesion Strength of Polycrystalline Diamond Coatings on WC–Co Hard Alloys

The influence of cobalt on the phase composition and adhesion strength of polycrystalline diamond coatings has been studied using scanning electron microscopy, Raman spectroscopy, and X-ray microanalysis. The coatings have been deposited on WC–Co hard alloy substrates in glow discharge plasma. It has been found that the catalytic amorphization of carbon only takes place during the direct synthesis of the diamond coating, when the cobalt vapor pressure over the substrate is high and the cobalt-related degradation of the synthesized diamond is absent.     

Influence of ternary addition of transition elements (Cr,Si and Mn) on the microstructure and magnetic properties of nano-structured CuCo alloy

The current state of studies presents the effect of ternary addition of transition elements such as Mn, Cr and Si (10 wt%) on the mechanically driven non-equilibrium solubility of 40 wt% Co containing Cu–Co alloy. X-ray powder diffraction analysis indicates that addition of Mn has been found to be the most effective in enhancing the solubility and formation of a complete solid solution between Co and Cu in a short duration (30 h) of ball milling. The microstructure of the ball milled CuCoMn alloy was found to be stable after the isothermal annealing up to a temperature of 450 °C for 1 h. The magnetic properties such as magnetic saturation, coercivity and remanence of ball milled CuCo alloy in the presence of Mn significantly altered after annealing in the temperature range 350–650 °C for 1 h. The best combination of magnetic properties of CuCoMn alloy has been found after annealing at 550 °C for 1 h.     

The microstructure and magnetic properties of electrodeposited Co–Pt thin films on Ru buffer layer

For high-density magnetic recording media, this study examined the crystal structure and the texture of electrodeposited cobalt–platinum (Co–Pt) films on Ru buffer layer. A 15-nm-thick Co–Pt film exhibited very high out-of-plane coercivity and squareness, which were 6248 Oe and 0.89, respectively. The coercivity, H_c, of Co–Pt films grown on Ru buffer layer decreased significantly with increasing thickness, possibly due to the lattice misfit of 5.4% between Co–Pt and Ru, leading to the decrease of perpendicular magnetic anisotropy (PMA) of Co–Pt films as indicated by the observed hexagonal-closed-packed (HCP) (1 1¯ 0 1) plane of Co–Pt films. According to nano beam diffraction pattern (NBDP), however, Co–Pt film grown on Ru layer of HCP exhibited mixed HCP and FCC phases. Also, cross-sectional TEM image suggests that the high PMA may result from the columnar structure of physically isolated Co–Pt grains with the c-axis perpendicular to the film plane.     

Influence of Copper(II) Ions on Radicals in DOPA–Melanin

DOPA–melanin (DOPA = 3,4-dihydroxyphenyl-alanine) complexes with Cu(II) cations were studied by electron paramagnetic resonance (EPR) spectroscopy. After the addition of metal cations to the melanin polymer, the EPR spectra parameters were measured. The axial g-factor values are g _|| = 2.20 and g _^ = 2.0 5 g_{ \bot } = 2.0 5 . Since $ g_{||} > g_{ \bot } > 2 $ g_{||} > g_{ \bot } > 2 , the ground state orbital of the unpaired electron of the Cu(II) complex is | x ²  -   y ² ñ \left| {{{x}}^{ 2} } \right. \, - \, \left. {{{y}}^{ 2} } \right\rangle . Square coordination of these cations in melanin is proposed. The influence of the Cu(II) concentration in solution used during synthesis on the concentration of melanin radicals was investigated. Cu(II) cations causes the decrease in the paramagnetic center concentration in melanin. The Cu(II) EPR spectra are not saturated within the microwave power range of 0.7–70 mW used in our experiment.     

Influence of the annealing atmosphere on the properties of LiCoPO4–graphitic carbon foams composites

The investigation on the properties of LiCoPO₄–graphitic carbon foams (LCP-GCF) composites is reported in this work. The diffraction analysis (XRD) on powders confirmed the presence of LiCoPO₄ as major crystalline phase and Li₄P₂O₇ and Co₂P as secondary phases. The morphological investigation of the composites shows a layer of crystalline spongy-like material on the surface of the GCF for t?=?0 h and of acicular crystallites with different dimensions (5–50 μm) for t?≥?0.1 h. The voltammetric curves (cyclic voltammogramms) show mean values of reduction potential above 5.0 V independently of the annealing time. The LCP-GCF composites deliver a discharge-specific capacity of 76mAh g^?1 (t?=?0 h) and of 102mAh g^?1 (t?=?0.1 h) at a discharge rate of C/10 and room temperature. The electrochemical impedance spectroscopy data reveal a decrease of the electrical resistance and the improvement of the Li-ion conductivity as a function of the annealing time.     

Effective synthesis of carbon nanotubes via catalytic decomposition of methane: Influence of calcination temperature on metal–support interaction of Co–Mo/MgO catalyst

The present work investigated the influence of calcination temperature for bimetallic Co–Mo/MgO catalyst on the synthesis of carbon nanotubes (CNTs) via catalytic chemical vapor deposition (CCVD) of methane. The experimental results showed that variation in the catalyst calcination temperature affected carbon yield, diameter distribution and quality of the CNTs. Increasing the catalyst calcination temperature enabled Co–Mo/MgO catalysts in growing CNTs at higher yield, narrower diameter distribution and better degree of graphitization, credited to the strong metal–support interaction (MSI) formed between CoO species and MgO support. We also discovered that the catalysts of weak MSI were beneficial to the nucleation and growth of CNTs, meanwhile the catalysts with strong MSI provoked the growth of CNTs with narrow diameter distribution. The catalyst calcined at 700 °C, possessing moderate MSI, was found to be the most suitable catalyst for the growth of high quality CNTs with the diameter of 7.70±0.77 nm and the carbon yield of as high as 647.4%.     

Influence of spectral characteristics of the pump pulse on the transient absorption of donor–acceptor complexes in polar solvents

We derive an analytical expression for calculating the transient absorption signal measured in the pump?Cprobe experiment. The expression explicitly accounts for dynamic properties of the medium, the population decay of the photoexcited state, and the angle ?? between the directions of the reaction coordinates corresponding to the electron transitions at the pump and probe stages. We investigate numerically the influence of the carrier frequency of the pump pulse and ?? on the transient absorption signal. We study the signal dynamics and its deviation from that of the excited state population under variation of these parameters. We show that these effects are manifested in complexes including methyl-substituted benzene and tetracyanoethylene in polar solvents.     

Influence of pulse duration on the doping quality in laser chemical processing (LCP)—a simulative approach

The laser chemical processing (LCP) technique for the local doping of crystalline silicon solar cells is investigated. Here, a liquid jet containing a dopant source acts as a waveguide for pulsed laser light, which results in the melting and subsequent doping of the silicon surface. Typical LCP pulse durations are in the 15 ns range, giving satisfactory results for specific parameter settings. While great potential is assumed to exist, optimization of the pulse duration has until now not been deeply investigated, because it is hard to change this parameter in laser systems. Therefore, this paper accesses the influence of the pulse duration by a simulative approach. The model includes optics, thermodynamics, and melt dynamics induced by the liquid jet and dopant diffusion into the silicon melt. It is solved by coupling our existing finite differences Matlab-code LCPSim with the commercial fluid flow solver Ansys Fluent. Simulations of axial symmetric single pulses were performed for pulse durations ranging from 15 ns to 500 ns. Detailed results are given, which show that for longer pulse durations lateral heat conduction significantly homogenizes the inhomogeneous dopant distribution caused by the speckled intensity profile within the liquid jet cross section. The melt expulsion by the liquid jet is low enough that a sufficiently doped layer remains after full resolidification for all pulse durations. Last, temperature gradients are evaluated to give an indication on the amount of laser damage induced by thermal stress.     

Influence of Cr on microstructure and elastocaloric effect in Ni–Mn–In–Co–Cr polycrystalline alloys

Ni–Mn-based metamagnetic shape memory alloys have been proposed as potential elastocaloric refrigerants. The intrinsic brittleness of the alloys has limited their cooling application. Introducing a soft second phase is an effective way to reduce the brittleness. From the viewpoint of application, the effect of second phase on elastocaloric effect should be illustrated. In this paper, we have investigated the microstructure, martensitic transformation and elastocaloric effect of Ni₄₅Mn_37-xIn₁₃Co₅Cr_x ($x=0,1\text{ and }2$) polycrystalline alloys. Single-phase and precipitates-containing microstructures are obtained for the undoped and doped alloys, respectively. The precipitates in Cr-doped alloys enhances the fracture strength but significantly hinders the martensitic transformation. Balancing the fracture strength and martensitic transformation, the Ni₄₅Mn₃₆In₁₃Co₅Cr alloy with small amount of precipitates along grain boundaries exhibits large cooling effects of 4–6 K in the temperature range of 317–353 K.     

Influence of pelletization pressure on magnetic susceptibility samples of ceramics Bi (Pb)–Sr–Ca–Cu–O

The influence of pelletization pressing 100–500 MPa on the quality of the samples from Bi_1.7Pb_0.3Sr₂Ca_2.5Cu_3.5O_10+δ superconducting transition was investigated. Samples which were pelletized at 100, 200, 300 MPa increased weight by an uncontrollable diffusion of elements from a filling. Obviously, these elements form additive phases on borders of grains, what is possible to conclude from the dependence χ′–T. The weight of samples pressed at pressure 400 and 500 MPa practically does not change at sintering. These samples after sintering within 250 h have a rather precise superconducting transition from a magnetic susceptibility. XRD shows that the phase structure of samples differs insignificantly—after sintering time 250 h samples consist basically of a phase 2223. The powder of the same composition annealed also within 250 h without a filling by results of XRD consists of approximately equal amounts of phases 2223 and 2212.