202 research outputs found
Microstructure formation in electrodeposited Co-Cu/Cu multilayers with GMR effect: influence of current density during the magnetic layer deposition
The influence of the current density applied during the deposition of the magnetic layers on the microstructure formation in electrodeposited Co-Cu/Cu multilayers and on their giant magnetoresistance (GMR) was investigated using a combination of magnetoresistance measurements, wide-angle and small-angle X-ray scattering, high-resolution transmission electron microscopy, atomic force microscopy and chemical analysis. The magnetoresistance measurements revealed that a reduction of the current density stimulates a transition from the formation of the magnetic layers with predominantly ferromagnetic character to the formation of superparamagnetic regions. As based on electrochemical considerations, it was supposed that such a change in the magnetic properties can be caused by an increased amount of Cu codeposited with Co at low current densities. It turned out from the structural studies that a pronounced segregation of Co and Cu occurs at low current densities. In accordance with their very low mutual solubility at room temperature, no atomic scale intermixing of Co and Cu could be detected. The segregation of Cu and Co was related to the fragmentation of the magnetic layers, to the enhancement of the local lattice strains, to the increase of the interface corrugations, to the partial loss of the multilayer periodicity and finally to the formation of Co precipitates in the Cu matrix
Magnetoresistance and surface roughness study of the initial growth of electrodeposited Co/Cu multilayers
The giant magnetoresistance (GMR) effect has been widely investigated on electrodeposited ferromagnetic/non-magnetic (FM/NM) multilayers generally containing a large number of bilayers. In most applications of the GMR effect, layered structures consisting of a relatively small number of consecutive FM and NM layers are used. It is of great interest, therefore, to investigate the initial stages of GMR multilayer film growth by electrodeposition. In the present work we have extended our previous studies on ED GMR multilayers to layered structures with a total thickness ranging from a few nanometers up to 70 nm. The evolution of the surface roughness and electrical transport properties of such ultrathin ED Co/Cu layered structures was investigated. Various layer combinations were produced including both Co and Cu either as starting or top layers in order (i) to see differences in the nucleation of the first layer and (ii) to trace out the effect of the so called exchange reaction. Special attention was paid to measure the field dependence of the magnetoresistance, MR(H) in order to derive information for the appearance of superparamagnetic regions in the magnetic layers. This proved to be helpful for monitoring the evolution of the layer microstructure at each step of the deposition sequence
Promotion of East-West Computer Communication in IIASA's International Environment and the Hungarian Case Study
This paper describes the functions of the "IIASA Gateway" as seen by a "typical user", IIASA's Hungarian National Member Organization
Simultaneous biohydrogen production and purification in a double-membrane bioreactor system
Anomalous codeposition of cobalt and ruthenium from chloride-sulfate baths
Codeposition of Ru and Co was studied at room temperature and at 50oC with various Ru3+ and Co2+ concentrations in the electrolyte. The codeposition of Co and Ru proved to be anomalous since no pure Ru could be obtained in the presence of Co2+ in the electrolyte, but a significant Co incorporation into the deposit was detected at potentials where the deposition of pure Co was not possible. The composition of the deposits varied monotonously with the change of the concentration ratio of Co2+ and Ru3+. The deposition of Ru was much hindered and the current efficiency was a few percent only when the molar fraction of Co in the deposit was low. Continuous deposits could be obtained only when the molar fraction of Co in the deposit was at least 40 at.%. The deposit morphology was related to the molar fraction of Co in the deposit. The X-ray diffractograms are in conformity with a hexagonal close-packed alloy and indicate the formation of nanocrystalline deposits. Two-pulse plating did not lead to a multilayer but to a Co-rich alloy. Magnetoresistance of the samples decreased with increasing Ru content
Simultaneous biohydrogen production and purification in a double-membrane bioreactor system
In this work the establishment of a double-membrane bioreactor was aimed. Initially, a continuous hydrogen fermenter was coupled with a commercial Kubota® microfiltration membrane module and the production performance of the cell-retentive design was evaluated under various hydraulic retention times. As a result, it has been observed that altering HRT influenced the rejection feature of the microfiltration module while had an inverse effect on hydrogen productivity and yield, since shortened HRTs were accompanied by gradually decreasing H2 yields (HY) and progressively increasing volumetric H2 production rates (HPR). The highest HY and HPR were achieved as 1.13 mol H2/mol glucose and 0.24 mol H2/L-d, respectively. Furthermore, a Permselect® (PDMS) gas separation membrane was installed to the anaerobic membrane bioreactor and its ability to separate hydrogen from the raw fermentation gaseous mixture was assessed. The highest purity hydrogen obtained in one-step purification by the PDMS module was 67.3 vol.%, which exceeds 30% enrichment efficiency considering 51.3 vol.% H2 in the feed gas. Hence, it could be concluded that the poly(dimethyl siloxane) membrane has potential to attractively concentrate biohydrogen from fermenter off-gas and may be used for in-situ product recovery
High-Field Magnetoresistance of Microcrystalline and Nanocrystalline Ni Metal at 3 K and 300 K
The magnetoresistance (MR) and the magnetization isotherms were studied up to
high magnetic fields at T = 3 K and 300 K for a microcrystalline (c) Ni
foil corresponding to bulk Ni and for a nanocrystalline (nc) Ni foil. At T = 3
K, for the c-Ni sample with a residual resistivity ratio (RRR) of 331, the
field dependence of the resistivity was similar to what was reported previously
for high-purity ferromagnets whereas the MR(H) behavior for the nc-Ni sample
with RRR = 9 resembled that what was observed at low temperatures for Ni-based
alloys with low impurity concentration. In the magnetically saturated state,
the resistivity increased with magnetic field for both samples at T = 3 K and
the field dependence was dominated by the ordinary MR due to the Lorentz force
acting on the electron trajectories. However, the MR(H) curves were found to be
saturating for c-Ni and non-saturating for nc-Ni, the difference arising
from their very different electron mean free paths. At T = 300 K, the MR(H)
curves of both Ni samples were very similar to those known for bulk Ni. After
magnetic saturation, the resistivity decreased nearly linearly with magnetic
field which behavior is due to the suppression of thermally-induced magnetic
disorder with increasing magnetic field. The MR(H) data were analyzed at both
temperatures with the help of Kohler plots from which the resistivity
anisotropy splitting () and the anisotropic magnetoresistance
(AMR) ratio were derived. It was demonstrated that at T = 300 K,
due to the negligible contribution
of the ordinary MR. The data for the two Ni samples at 3 K and 300 K were found
to indicate an approximately linear scaling of with the
zero-field resistivity. This implies that the AMR ratio does not vary
significantly with temperature in either microstructural state of Ni.Comment: 57 pages, 19 figure
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