bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical properties of a new amorphous molybdenum-selenium semiconducting compound produced by the annealing of ultrathin multilayer composites
Authors: Park Wansoo , Fister Loreli , Johnson David C. , Cohen J. David
Published: July 2002

An amorphous material with semiconducting properties has been produced by the annealing of a multilayer composite consisting of alternating layers—6 Å of molybdenum and 16 Å of selenium—deposited in high vacuum. Measurements of the coplanar and perpendicular conductivities before and after a 300 °C anneal, together with x-ray diffraction data, indicate that these composite films approach an amorphous phase with a stoichiometry close to MoSe2 and with electrical properties indicative of a narrow gap semiconductor (Eg≊0.1 eV). Rectifying behavior has also been observed in conjunction with palladium contacts.
Analysis of transients in semiconductor/semi-insulator junctions
Authors: Maimon S. , Schacham S. E.
Published: July 2002

A junction between an epitaxial semiconductor and a semi-insulating substrate serves as a tool for analyzing transient behavior in semi-insulators (SI). At equilibrium a narrow region which is fully depleted from electrons exists in the SI. The application of a reverse bias results in an additional partially depleted region, initially depleted just from free carriers, adjacent to the fully depleted one. As the transient progresses electrons are released from the deep traps in the SI. The partially depleted region collapses into a wider fully depleted region. This process is manifested by a substantial current transient through the SI. The charges emitted recombine in the epitaxial layer leading to a decrease in its conductance due to a narrowing conducting path. Thus it is possible to characterize this process by measuring the (large) current through the epilayer rather than the (small) current through the SI. These transients are a function of the emission coefficient. Their analysis provides data also on the energy gap of the traps, their capture coefficient, and the electron lifetime. The long decays can be accelerated by illuminating with photons of energy below the band gap but larger than the energy spacing between the deep traps and the conduction band.
Position-dependent electronic properties of hydrogenated amorphous silicon p-i-n diodes
Authors: Lampert M. D. , Krühler W. , Schwarz R.
Published: July 2002

A new theoretical insight in the dynamics of position-dependent deep trapping within the p/i-interface region of a-Si:H p-i-n diodes is presented. The positive space charge in this region relates internal electric field and deep trapping electron lifetime profiles with each other. A hyperbolic field dependence and a position-independent capture constant can explain well the experimental delayed field time of flight results.
Transitions between Γ and X states of short-period superlattices driven by antisymmetric interface phonons
Authors: Stroscio Michael A. , Dutta Mitra , Zhang Xiao-qiang
Published: July 2002

Relative transition probability amplitudes for antisymmetric-interface-phonon-assisted Γ-X transitions in selected short-period superlattices are estimated by using the dielectric continuum model for antisymmetric interface optical phonons in conjunction with a Kronig–Penney model of the superlattice electronic properties.
Possibility of detecting Davydov solitons using transient reflectivity measurements
Authors: Rozgonyi T. , Lörincz A.
Published: July 2002

The transient reflectivity (TR) technique is considered as a means of investigating vibration solitons (called Davydov solitons) in long α-helical polymer protein molecules. It is shown that TR may provide direct proof for the existence of Davydov solitons.
A two-dimensional theory and propagation of beam fanning in photorefractive crystals
Authors: Xie Ping , Dai Jian-Hua , Wang Peng-Ye , Zhang Hong-Jun
Published: July 2002

A general two-dimensional model to describe beam fanning, which takes into consideration the finite width of the input beam and the interaction between different directions of the fanning beam, is presented. By numerical calculation of the coupled equations, the well-known curved path of a propagating beam inside photorefractive crystals is explained, and the propagation properties of the fanning beam inside the crystals are studied and discussed.
Effect of scattering on the resonant-tunneling current in double-barrier structures
Authors: Zou Nanzhi , Chen Q. , Willander M.
Published: July 2002

The scattering effect on resonant tunneling current for double-barrier resonant tunneling diode is investigated. It is clearly shown that while the elastic scattering effect is negligible, the inelastic scattering will suppress the resonant tunneling current by breaking the phase coherence. An expression for the current suppression is obtained. The inelastic scattering effect is also dominant for the temperature dependence of peak current. The numerical result is in good agreement with the experiment result.
Dependence of the light-induced degradation kinetics of photoconductivity and ambipolar diffusion length as a function of doping level in a-Si:H
Authors: Sauvain E. , Pipoz P. , Shah A. , Hubin J.
Published: July 2002

Variation of both photoconductivity σph and ambipolar diffusion length Lamb have been measured during exposure to light on a series of lightly p- and n-doped a-Si:H samples. The observed decay of the photoconductivity with time of exposure has been fitted by a power-law function. The power-law exponent observed strongly depends on doping. On the other hand, ambipolar diffusion length generally remains constant during the observed part of the degradation process, except for a slightly boron-doped sample with the Fermi-level near midgap. In the latter, Lamb decreases in accordance with σph. The experimental observations can be qualitatively explained taking into account dangling bonds with their three charge states (D+,D0,D−) as main recombination centers.
Enhancement and quenching of Berreman polaritons in SiO2/TiO2 and Al2O3/Pt superlattices
Authors: Wold E. , Bremer J. , Hunderi O. , Frigerio J. M. , Parjadis G. , Rivory J.
Published: July 2002

Optical properties of SiO2/TiO2 and Al2O3/Pt superlattice films have been studied by infrared ellipsometry with emphasis on the reststrahlen bands of the silicon and aluminum oxides. The SiO2 and TiO2 thicknesses were 5.0 and 3.2 nm, respectively, while the Al2O3 and Pt layer thicknesses were 10.0 and 2.5 nm. The presence of TiO2 layers created a pronounced spectral feature just above the SiO2 LO frequency. The results were analyzed by means of transfer matrices. It was found that a superlattice film is capable of introducing sharp spectral features at wavelengths where the refractive index of the substrate is close to unity and the absorption coefficient is small. The validity of effective permittivity calculations is investigated for insulator/insulator and insulator/metal superlattices, and the influence of Berreman polaritons is discussed. We also address the question of how the strength of these polaritons may be suppressed in certain configurations.
Thermal parameters affecting low temperature zone-melting recrystallization of films
Authors: Robinson Richard D. , Miaoulis Ioannis N.
Published: July 2002

An experimental study and numerical simulation of low temperature (m.p.<800 °C) zone-melting recrystallization (ZMR) were conducted to identify the critical thermal processing parameters. Results were compared to previous studies of high temperature ZMR of silicon. The critical thermal processing parameters for low temperature ZMR were found to be the conductive heat flux from the strip heater through the gas and to the film, the radiative heat transfer from the strip heater, the susceptor temperature, the effects of phase change on material properties, the scanning speed, and the material’s latent heat of fusion. Thermal effects of these parameters are studied and discussed. In contrast to high temperature ZMR, in which the thermal radiation is the main mode of heat transfer, low temperature ZMR processing relies heavily on the conductive heat flux from the line heater. The dominance of the conductive heat flux makes melting ‘‘explosive.’’
External bias voltage and incident light intensity dependent effects of quantum-confined excitonic transitions on bulk background photocurrent spectra
Authors: Tokuda Yasunori , Abe Yuji , Tsukada Noriaki
Published: July 2002

An experimental investigation of the unique photocurrent spectra of p-i-n photodiode with a GaAs/AlAs/AlGaAs quantum well and bulk GaAs absorption regions at 77 K is presented. The results showed that the excitonic absorption transitions in the quantum wells create sharp dips in the featureless bulk background spectra for low reverse bias voltages, while the spectra at high reverse biases show normally expected features with sharp quantum-confined excitonic absorption peaks superimposed on the background absorption. Furthermore, we found that the spectral features are very sensitive to the incident light intensity. These remarkable results are explained in terms of competition between the carrier escape rate from the quantum well region and the carrier generation rate in the bulk GaAs region, as well as by partial screening induced by carriers accumulated in the quantum well region.
On the correlation among photodegradation, charged dangling bonds and microstructure in hydrogenated amorphous silicon
Authors: Irrera Fernanda
Published: July 2002

We propose that in hydrogenated amorphous silicon the mechanism of conversion from charged to neutral dangling bonds adds to the weak Si—Si bond breaking during light soaking. Our model is developed from an equilibrium picture of the density of states as given by the defect pool theory [K. Winer, Phys. Rev. B 41, 150 (1990)] and predicts an increase rate of the neutral dangling bonds density (D0) proportional to (1/D0)2, which is related either to the charged defect conversion probability and to the bond-breaking probability. This model explains photoconductivity experiments and, in particular, the short-time features: it shows that the photodegradation is enhanced in clustered hydrogen-rich samples provided the density of charged dangling bonds is correlated with the clustered hydrogen present in the amorphous network.
Low-temperature irradiation effects in natural crystalline quartz
Authors: Bahadur Harish
Published: July 2002

Near-infrared absorption results have been used to discuss low-temperature irradiation effects before and after 300 K irradiation on good quality alkali- and H-swept natural quartz crystals. Samples used had similar aluminum but widely different alkali and H levels. Using the irradiation cycle and defect dynamics consideration, a quantitative estimation of deep and shallow alkali and proton traps, Al–Li+, Al–OH, and Al–hole defect centers has been presented. Comparisons on high-H and low-H natural quartz samples have been made. The results can be directly applied to understanding the radiation response of several impurity-related groups of near-infrared bands and possibly to developing better growth procedures for production of radiation-resistant cultured quartz for aerospace applications.
Temperature dependent electron-beam-induced-current investigation of electronic damages in silicon due to reactive ion etching
Authors: Jäger-Waldau G. , Habermeier H.-U. , Zwicker G. , Bucher E.
Published: July 2002

The damage introduced by reactive ion etching in silicon was investigated by the planar-electron-beam-induced-current (PEBIC) method. A reduction of the EBIC signal in the etched areas is detected and studied of temperature dependency in the range of 5 K<T<300 K. The EBIC contrast between etched and unetched areas increases with decreasing temperature. Our results are interpreted by a reduction of the net acceptor dopant impurity near the etched surface.
Epitaxial CoAl/AlAs/GaAs metal semiconductor heterostructures: Growth, structure, and electrical properties
Authors: Tanaka M. , Nishinaga T. , Ikarashi N. , Shimada H.
Published: July 2002

Molecular beam epitaxial (MBE) growth, structural, and electrical properties of novel epitaxial metal/semiconductor heterostructures (MSHs), consisting of monocrystalline CoAl, an intermetallic compound, and AlAs/GaAs III-V semiconductors have been studied. The CoAl with stoichiometric composition has a CsCl-type crystal structure whose lattice constant is very close to half the lattice constant of GaAs and AlAs, hence, it is a good candidate as a constituent metal in epitaxial monocrystalline metal/semiconductor heterostructures. MBE growth of CoAl thin films on AlAs/GaAs, and also semiconductor overgrowth on ultrathin CoAl films, together with structural characterizations by in situ reflection high energy electron diffractions, ex situ x-ray diffractions and cross sectional transmission electron microscopy have been explored. By optimizing the growth parameters and procedures, high quality monocrystalline CoAl/AlAs/GaAs heterostructures with atomically abrupt interfaces have been successfully grown. Furthermore, the electrical properties of such novel heterostructures as Schottky barrier heights of CoAl/AlAs/GaAs MSHs and transport properties in ultrathin buried CoAl films are described.
Contactless electromodulation of excitons measured by photoluminescence
Authors: Gal M. , Chtanov A. , Eyland P.
Published: July 2002

An optical modulation technique has been used to observe the electromodulation of photoluminescence in single and multiple quantum wells. It is shown that this photomodulated photoluminescence technique can yield similar information to that obtained from electroabsorption and photoabsorption experiments but, because it does not require special sample geometry or sample preparation, it is easier to implement, especially in the case of samples grown on nontransparent substrates.
Steady-state Nyquist theorem for multi-terminal nondegenerate semiconductor devices
Authors: Lee J. B. , Min H. S. , Park Y. J.
Published: July 2002

Formulas for the spectral intensities of the short-circuit thermal noise currents in arbitrarily shaped multi-terminal semiconductor devices under dc bias are derived by solving the Langevin-type Boltzmann transport equations. The derived formulas are valid when the carrier distributions are not far from the local equilibrium distributions. Measurement data on short-circuit thermal noise currents are obtained for a three-terminal silicon bulk device. A comparison between the calculated and experimental results is made and thereby the validity of our theory is confirmed.
Optical control of polarity in short electrical pulses generated from coplanar waveguide metal-semiconductor-metal photodetectors
Authors: Shu C. , Choy H. S. , She T. C.
Published: July 2002

We have demonstrated a simple technique to control the polarity of electrical pulses generated from metal-semiconductor-metal photodetectors. By applying the optical beam to different regions of a coplanar waveguide structure incorporating the photodetector, a change in sign of the electrical signal was observed. The signal had an amplitude of 8.5 mV and a full width at half maximum about 150 ps. The results are explained based on voltage induced on the detector electrode.
Compositional variations in Ti-W films sputtered over topographical features
Authors: Liu D. , Dew S. K. , Brett M. J. , Smy T. , Tsai W.
Published: July 2002

To study compositional variations in Ti-W films sputtered from Ti-W alloy targets and deposited over topographical features, the sticking coefficients and angular distributions of sputtered flux arriving at the substrate for titanium (Ti) and tungsten (W) atoms have been investigated by an overhang structure, pinhole experiment, and simulation package. The simulation involves the combination of a vapor transport model which is able to model the angular distributions for the respective materials, and a film growth model which is able to predict the compositional variation of the deposited Ti-W films over topographical features. Experimentally, it was found that the sticking coefficients of Ti and W are both very close to unity for the conditions considered. However, the angular distributions of these two materials are quite different due to their different transport properties through the sputter gas. For the Ti-W films, the compositional variations calculated using the simulated angular distributions agreed well with the ones measured experimentally. This result clearly demonstrates that the differences between the angular distributions of Ti and W atoms cause the compositional variations in the films. In the case of Ti-W films deposited over vias or trenches, the films on the sidewalls are Ti enriched, but on the bottom are Ti deficient. The good agreement between the simulation and experimental results indicates that the model will be very useful for predicting and optimizing the properties of films deposited by alloy targets.
589 nm light generation by intracavity mixing in a Nd:YAG laser
Authors: Danailov M. B. , Apai P.
Published: July 2002

A new approach of all-solid-state generation of yellow radiation which matches the sodium D2 transition wavelength is proposed in this article. We study the possibility of producing 589 nm light by an intracavity sum-frequency generation in Nd:YAG laser, operated simultaneously at two lines: 1064 and 1319 nm. This technique combines the advantages of better efficiency due to the higher intracavity power and the simplicity of the single oscillator design. We present preliminary experimental results which confirm the possibility of stable two wavelength operation with a simultaneous frequency mixing at 589 or 592 nm.
Bicrystal junctions and superconducting quantum interference devices in YBa2Cu3O7 thin films
Authors: Nilsson P. Å. , Ivanov Z. G. , Olsson H. K. , Winkler D. , Claeson T. , Stepantsov E. A. , Tzalenchuk A. Ya.
Published: July 2002

Josephson junctions and superconducting quantum interference devices (SQUIDs) were made by depositing thin films of YBa2Cu3O7 on bicrystal substrates of Y-ZrO2 and SrTiO3. The critical current density of the junctions at 77 K could be adjusted from 100 to 106 A/cm2 by selecting bicrystals with misorientation angles θ from 45° to 0°. Current-voltage curves from junctions with θ≳22° followed the resistively shunted junction model with noise rounding close to the transition temperature. The response of the critical current to magnetic fields was Fraunhofer-like and the width (w) dependence was 1/w2 due to flux focusing effects. Shapiro steps under microwave radiation were observed. SQUIDs based on these junctions had energy resolutions at 77 K down to 8.6×10−30 J/Hz and a 10 Hz flux noise level down to 1.5×10−9 Φ20/Hz at 85 K. A SQUID of the Ketchen design with a flux focusing washer had a magnetic field sensitivity of 15 pT/√Hz at 77 K. The temperature dependence of the voltage modulation depth close to TC was examined and found to be in agreement with theory [K. Enpuku, Y. Shimomura, and T. Kisu, J. Appl. Phys. 73, 7929 (1993)].
Effect of anisotropy on the excess stress and critical thickness of capped Si1−xGex strained layers
Authors: Shintani K. , Fujita K.
Published: July 2002

By using the anisotropic image force theorem of Barnett and Lothe, single- and double-kink models for capped (buried) Si1−xGex strained layers are extended so as to take into account cubic anisotropy. The crystallographic configuration considered is such that the free surface is a (001) plane, misfit dislocation segments in the [11̄0] direction and threading dislocations in the [011] direction lie within a (1̄1̄1) glide plane, and the Burgers vector is 1/2[101]. The results show that the effect of cubic anisotropy is significant and that it tends to decrease the excess stress and to increase the critical layer thickness in both of the single- and double-kink models.
Role of dynamical cooperativity for an enhanced isotope effect during transport
Authors: Rendell R. W.
Published: July 2002

The effect of particle-lattice interactions on the hopping of particles over a barrier in a double-well system is studied within a simple microscopic model. The probability of escape becomes modified by the slow dynamics of the lattice and results in nonexponential relaxation. The macroscopic relaxation time is related to the local hopping time by a type of scaling relation which has been experimentally observed in a wide range of relaxation phenomena. In particular, the scaling relation is consistent with an enhanced isotope effect recently observed in comparing hydrogen and deuterium dispersive transport in irradiated metal-oxide-semiconductor devices. In these systems, the hydrogen locally deforms the oxide lattice as it hops and the evidence for a connection with the type of mechanism studied is discussed. The existence of a scaled relaxation time in the present model is demonstrated from numerical solutions and this is supported by the analytic properties of the kinetic equations for this class of systems.
Vibrations of AT-cut quartz strips of narrow width and finite length
Authors: Lee P. C. Y. , Wang Ji
Published: July 2002

A system of one-dimensional equations of motion for AT-cut quartz strip resonators with narrow width and for frequencies up to and including the fundamental thickness shear is deduced from the two-dimensional, first-order equations for piezoelectric crystal plates by Lee, Syngellakis, and Hou [J. Appl. Phys. 61, 1249 (1987)] by expanding the mechanical displacements and electric potentials in a series of trigonometric functions of the width coordinate. By neglecting the piezoelectric coupling and the weak mechanical coupling through c56, four groups of coupled equations of motion are obtained. For the equations of each group, closed form solutions are obtained and the traction-free conditions at four edges are accommodated. Dispersion curves and frequency spectrum are computed for quartz strips. The predicted frequency as a function of the length-to-thickness ratio and as a function of the width-to-thickness ratio of the quartz strips is compared with experimental data with good agreement.
Synchrotron radiation topography studies of twinning in NdP5O14 crystals
Authors: Huang X. R. , Hu Z. W. , Jiang S. S. , Jiang J. H. , Tian Y. L. , Han Y. , Wang J. Y.
Published: July 2002

An investigation of twin structures in NdP5O14 single crystals has been undertaken using white-beam synchrotron x-ray topography. The so-called a-type twins along the a axis are clearly revealed in the topographs. The displacements of the images that arise from the twins are directly measured in different topographs. With the measured values, the monoclinic distortion angle δ(δ=β−90°) is calculated, which is in good agreement with the unit cell parameters. A fine-beam Laue diffraction pattern of the twin has also been taken which is well consistent with its simulation. From these results, the twin structures of NdP5O14 are discussed.
Characterization of stress generated in polycrystalline silicon during thermal oxidation by laser Raman spectroscopy
Authors: Kawata Masato , Katoda Takashi
Published: July 2002

The generation and relaxation of stress in polycrystalline silicon (poly-Si) by oxidation were studied based on laser Raman spectra. The rapid generation of compressive stress and saturation of its value with oxidation period were observed at temperatures between 650 and 850 °C. The saturated value of the stress was independent of the oxidation temperature. The generation and saturation of stress during oxidation at 850 °C can be explained by taking into account preferential oxidation at the grain boundary, expansion of volume at grain boundaries, and retardation of oxidation rate due to stress. The relaxation of compressive stress during oxidation at 900 °C was also found. The relaxation can be explained by taking into account the viscous flow of silicon oxide at grain boundaries.
Low noise Josephson dc parametric amplifier
Authors: Jeffery Mark , Goto Eiichi
Published: July 2002

We describe a new Josephson Inductive Kinetic Amplifier (IKA) designed to measure weak dc magnetic fields with low noise. The IKA operates by frequency shifting dc input to a high frequency range and then parametrically amplifying. The IKA does not require dc offset and by frequency shifting dc input 1/f noise may be reduced. We define the circuit Lagrangian and derive the system equations. An analytical expression for the IKA transfer function is derived and the frequency response, optimal parameters, and stability are all obtained from the analytic theory. We also calculate the temperature at which the internal Nyquist noise should equal the quantum sensitivity limit. Our analysis suggests that the IKA could be more sensitive than the conventional dc Superconducting Quantum Interference Device.
Determination of leakage resistance of Schottky contacts by photovoltage measurements
Authors: Chen T. P. , Lee T. C. , Fung S. , Beling C. D.
Published: July 2002

The leakage resistance of Schottky contacts has been determined from photovoltage measurements, thus allowing the contribution of the leakage current to the current transport in the Schottky contacts to be easily evaluated. It is found that under identical conditions of sample fabrication, different Schottky contacts have nearly the same leakage resistance. A comparison between a theoretical calculation and experimental data for the photocurrent-photovoltage relationship shows that the leakage current becomes dominant at low temperatures and small photocurrents. In these regimes, the current transport is dominated by the leakage current, and as a result, a linear relation (the Ohmic rule) between the photocurrent and the photovoltage is observed.
One-dimensional transport of warm electrons in In0.53Ga0.47As quantum well wires at low temperatures
Authors: Chattopadhyay D. , Ghosh P. K.
Published: July 2002

The ohmic mobility μ0 and the warm electron coefficient β of the electrons moving one-dimensionally in a quantum well wire (QWW) of In0.53Ga0.47As are investigated for lattice temperatures in the range of 4–10 K. Deformation potential acoustic, piezoelectric, ionized-impurity, and alloy scatterings are included considering the nonequipartition of phonons. β values are calculated by two models: one using a heated Fermi–Dirac distribution function, and the other using a more general moment method. Momentum relaxation is found to be controlled predominantly by alloy scattering. μ0 is larger for a QWW of greater cross section and decreases slowly with the increase of the lattice temperature. In both models used here, β is negative; its magnitude falls with increasing lattice temperature and is greater for larger cross sections of the QWW. However, ‖β‖ is larger in the heated Fermi–Dirac distribution function model.
Spin-glass structures in biological systems (abstract)
Authors: Tsapin Alexandre I. , Blumenfeld L. A.
Published: July 2002

We have discovered spin-glass structures in different biological systems like animal and plant tissues, cells, chloroplasts, mitochondria, etc. These structures were detected by the ESR method. This work has been done using a synchronous culture of yeasts, saccharomyces cer. To detect spin-glass structures in a biological system, the sample must be cooled in the presence of a strong magnetic field, from 77 to 10 K. After such cooling, we recorded the ESR signal at g factor about 3.0 caused by spin-glass structures. The rotation of the sample at 10 K relative to the permanent magnetic field (always present in ESR experiments) leads to the significant change in the intensity of the ESR signal as well as in its shape. The curve of the dependence of the ESR signal intensity on the magnetic field in which the sample was cooled is S-shaped. The cooling of the same sample in zero magnetic field resulted in the absence of the ESR signal at g=3,0. It had been shown that the maximum ESR signal at g factor about 3,0 was reached 15 min before the beginning of mitosis. The study of the properties of the ESR signal at g=3,0 allowed us to make the conclusion that the paramagnetic centers responsible for this signal have been formed by Fe(II) ions localized at the chromosomes. Formed during mitosis, spin-glass structures which play a significant role in cell biology, can be detected only by the ESR method in field cooling experiments.
Database of magnetochemistry in solutions (abstract)
Authors: Tarasov O. Ju. , Vinogradov A. G.
Published: July 2002

The database (DB) of magnetochemistry in solutions was created to systematize and to critically review data of the magnetic susceptibility of liquids, solutions, and substances in solutions. The database ‘‘MagChemSol 1.0’’ was made on a mfoxplus base and may be supported by dbaseiii plus or higher. Search fields include substances, solvent, condition and method of investigation, critical magnetochemistry characteristics, and references to literature. All material is printable and the database can change and expand itself. System requirements include IBM PC or compatible with 640 Kb of RAM, 5 in. and 3 in. diskette drive or hard-disk, and dos 3.30 or higher; printers are Epson or compatible. The DB ‘‘MagChemSol 1.0’’ version includes about 1000 data entries according to the magnetochemical properties, the majority solvents in general use some diamagnetic and paramagnetic salts, and also the complex compounds of d and f elements in the solutions.
The magnetodynamic filters in monitoring the contaminants from polluted water systems (abstract)
Authors: Swarup R. , Singh Bharat
Published: July 2002

The magnetic interaction seems to influence the ‘‘structural memory’’ of water systems which is quenched in ideally pure water. The sedentary lifetime of each water molecule is extremely short (10−10 s) and its molecular structures may be influenced by some physical effect like magnetic field treatment, it’s space time gradients, water velocity, pressure drop, etc. in the interpolar space, so as to yield a noticeable temporal magnetopotential development characterizing the properties of homogeneous and heterogeneous water systems. This principle is also extended to prevailing water systems which always contain various impurities, gas, molecules, ions, microscopic particles in random order. Still the existence of structural memory may be verified by reliable experimental data. The magnetopotential curves of different water systems depict the design and develop–software package for constructing the magnetodynamic-filters superior to the existing techniques on pollution studies like remote sensing, muon spin resonance, laser spectroscopy, nuclear techniques, the gamma ray peak efficiency method, trace elemental characterization due to NBS, neutron activation analysis, and graphite furnance atomic absorption spectrometer. The physiochemical characteristics of water calibrated in terms of magnetopotential curves change with the removal of dissolved gasses, impurities, thermal activation, etc. and the algae, bacteria, phosphates, etc. have been removed at a rapid rate. The magnetodynamic study of ganga water proves it to be an extremely pure and highly resourced fluid.
Influence of spreading neuronal electric sources on spatio-temporal neuromagnetic fields
Authors: Iramina K. , Ueno K. , Ueno S.
Published: July 2002

This study focuses on the influences of spreading multiple dipoles in the human head upon surface magnetic fields. A source model of the magnetoencephalogram (MEG) activity is proposed. This source model is expressed by spreading multiple dipoles which have time-varying dipole moments. Using this source model, spatio-temporal patterns of MEGs are simulated. Effects of spreading dipoles on spatio-temporal magnetic fields are investigated. The computer simulations show that the wave forms and amplitude of magnetic fields are affected significantly by the spread of the source and the conduction velocity of traveling dipoles. The latency of the peak magnetic field generated by spreading multiple dipoles varies with the measurements points on the surface of the head.
Epitaxial Bi-content ferrite-garnet film memory (abstract)
Authors: Il’yashenko E. I. , Klin V. P. , Nickolsky A. D. , Solovjov A. G.
Published: July 2002

Memory conception in epitaxial ferrite-garnet films on a compensation wall has been developed in recent work.1 Further original solutions for memory element formation by heat treatment under Si layers have been found but this method has not been used in practice due to the difficulty of reproducing results. In this work the possibility of a memory matrix on the ferrite-garnet films by rf treatment has been investigated. In comparison with other work2 this memory element formation method arrived at by an MS decrease due to Ga redistribution from octahedral into tetrahedral positions provides the possibility to decrease significantly the device power intensity, to increase the speed of response, and to simplify the designing and technology. The work has been carried out with (YBi)3(FeGa)5O12 films doped by Lu, Tm, Gd, Pr, and grown by the LPE method on GGG and GGG+CaMgZr substrates. The treatment mode and film composition influence upon the element switching stable threshold has been studied and read-only memory formation parameters have been found. Experimental results of rf-treatment influence upon epitaxial layer magnetic and magneto-optic features and main display parameters (optical transmission, contrast, speed of response) have been provided. The possibility of element formation from 1 up to 20 μm with a space of 12 μm and over has been shown. Figure 1 shows memory file elements with 60 and 20 μm space between them.
Magnetic ordering in UCoNiSi2 and UCoCuSi2 studied by ac-susceptibility and neutron-diffraction measurements
Authors: Kuznietz Moshe , Pinto Haim , Melamud Mordechai
Published: July 2002

Polycrystalline samples of intermediate solid solutions of the UM2Si2 compounds (M=Co,Ni,Cu), namely UCoNiSi2 and UCoCuSi2, were prepared and were found to have body-centered tetragonal ThCr2Si2-type crystallographic structure. In UCoNiSi2 ac susceptibility indicates a single antiferromagnetic (AF) transition at TN=115±5 K, confirmed by neutron-diffraction observation of the AF-I structure down to 10 K (with uranium moments of 1.6±0.2μB, along the tetragonal c axis). In UCoCuSi2 ac susceptibility indicates ferromagnetic transition at TC=107±5 K, and implies an AF transition at lower temperature, confirmed by the AF-I structure, observed in neutron diffraction below T0=95±5 K down to 10 K (with uranium moments of 1.6±0.1μB, along the c axis). The magnetic properties are discussed in comparison with UM2X2 and U(M,M′)2X2 materials (X=Si,Ge).
139La nuclear quadrupole resonance and relaxation in Zn-doped La2CuO4
Authors: Corti M. , Lascialfari A. , Rigamonti A. , Tabak F. , Licci F. , Raffo L.
Published: July 2002

139La nuclear quadrupole resonance and relaxation measurements, aimed at the study of static magnetic properties and of the dynamical generalized susceptibility in La2Cu1−xZnxO4, upon substitution of Zn2+ (S=0) for Cu2+ (S=1/2) inducing a spin vacancy in the antiferromagnetic matrix, are presented. From the doublet resulting from the mixed Zeeman-quadrupolar eigenstates, it is shown how the sublattice magnetization is only slightly x dependent, while its temperature dependence changes with respect to pure La2CuO4. The relaxation rates show moderate (compared to the case of itinerant spin vacancies, as in La2−xSrxCuO4) effects, which are related to the decrease of the correlation length and to the modifications induced in the spin-wave spectrum.
Low-field ac magnetic susceptibility under pressure in GdMn2 and TbMn2 intermetallics
Authors: Ibarra M. R. , Arnold Z. , Marquina C. , García-Orza L. , del Moral A.
Published: July 2002

Low-field ac magnetic susceptibility experiments under pressure up to 10 kbar have been performed on the GdMn2 and TbMn2 compounds in the temperature range of 4–300 K. The results reveal the possible coexistence of two phases below TN, one in which the magnetic moment of Mn is stable and other in which the Mn does not present any magnetic moment.
Unusual magnetic properties and time dependent magnetization in ErCo3Ga2 (abstract)
Authors: Ali Naushad , Zhang Xianfeng
Published: July 2002

In this abstract we will present the measurements of magnetization, ac susceptibility, and the time dependent effects on the magnetization of polycrystalline samples of ErCo3Ga2 and YCo3Ga2. The field cooled (FC) and zero field cooled (ZFC) magnetization data suggest a spin glass transition in YCo3Ga2 below 160 K. The FC magnetization ErCo3Ga2 exhibits a negative minimum at 25 K and a compensation temperature at 150 K. It is suggested that ErCo3Ga2 has two magnetic phase transitions: one at 150 K (most likely a spin glass transition due to Co sublattice) and the other below 25 K (due to Er sublattice ordering). We have found an unusual time dependence of magnetization of ErCo3Ga2 at a constant temperature (below 150 K) and constant applied magnetic field. The magnetization M increases with time t and dose not attain a constant value over a period of 64 h. The time dependence of magnetization follows the relation MT,H(t)=MT,H(t0)+aT,H ln t. The slope aT,H is always positive and depends on temperature and the applied magnetic field. The field dependence of the slope shows a peak at a field Ha. The value of Ha decreases with increasing temperature. At a constant temperature the slope aT,H increases exponentially with the applied magnetic field and then decays towards zero values at high applied magnetic field. This suggests an activation energy process. Detailed experimental results on time effects will be presented.
Magnetic and magneto-optical properties of (Tb,Dy)Nd/FeCo multilayers (abstract)
Authors: Yu X. Y. , Fujiwara Y. , Watabe H. , Iwata S. , Tsunashima S. , Uchiyama S.
Published: July 2002

Nd-Co and Nd-FeCo amorphous films are known to have larger Kerr rotation θk at shorter wavelength and ultraviolet light compared with other RE-TM (rare earth-transition) amorphous films. This property is desirable for MO (magneto-optical) media for the next generation. In order to satisfy the perpendicular magnetization condition, we replaced a part of Nd by Gd to decrease the saturation magnetization Ms and applied the multilayer (ML) structure to enhance the perpendicular anisotropy Ku. Then we succeeded in getting a new ML medium of Nd0.34Gd0.66/Fe0.9Co0.1 with a bilayer period of 1 nm. However, the substitution of 66% Gd resulted in undesirable decreases of Kerr rotation and coercivity. In this experiment, a part of Nd is replaced by either Tb or Dy instead of Gd with an expectation that the amount of replacement to get the perpendicular magnetization configuration may be smaller since Tb and Dy have large one ion anisotropy compared with Gd. The magnetic and MO properties of Nd(Tb,Dy)/FeCo MLs will be reported. In the case of Tb, for example, a square Kerr hysteresis loop is obtained by the substitution of about 40%. However, θK at 400 nm is about 0.30°, which is larger than that of Tb-FeCo but smaller than NdGd/FeCo MLs.
Early embryonic development of frogs under intense magnetic fields up to 8 T
Authors: Ueno S. , Iwasaka M. , Shiokawa K.
Published: July 2002

A possible influence of intense magnetic fields on the embryonic development of frogs was studied in reference to a potential hazard in magnetic resonance imaging technology. Some of the most serious hazardous effects that could be induced by intense magnetic fields are teratogenic effects on developing embryos. In the present experiment, the possible influence of intense magnetic fields up to 8 T on the early embryonic development of Xenopus laevis was studied. Embryos were exposed to magnetic fields up to 8 T for the period from the precleavage stage to neurula in a small glass vial. Embryos were then cultured in Brown–Caston’s medium until the feeding-tadpole stage. No apparent teratogenic effects were observed when embryos were cultured for 20 h from the stage of uncleaved fertilized egg to the neurula stage under magnetic fields of 8 T. We conclude that static magnetic fields up to 8 T do not appreciably affect the rapid cleavage and the following cell multiplication and differentiation in Xenopus laevis. We have also studied the early embryonic development of Xenopus laevis in a 40 nT magnetic field, or 1/1000 of the earth’s magnetic field, and obtained negative results. Thus, again under this very low magnetic field, fertilized eggs developed normally and formed tadpoles with no appreciable abnormality.
Optical and magneto-optical constants of Pr substituted TbFeCo films
Authors: Carey R. , Newman D. M. , Snelling J. P. , Thomas B. W. J.
Published: July 2002

Optimization of tri- or quadrilayer magneto-optic recording media requires knowledge of the optical and/or magneto-optical constants for all of the individual active or passive layers that together comprise the complete disk structure. The optical (n+ik) and first-order magneto-optical (Q1+iQ2) constants for two series (i) (Tb23Fe72.5Co4.5)100−xPrx, (ii) (Tb27Fe65Co8)100−xPrx of Pr substituted TbFeCo films, for which x varies between 0 and 30, have been determined by a combination of ellipsometry and Kerr polarimetry. Ellipsometry has also been used to determine independently the optical constants of the optimized SiN passivation layers developed to protect these samples. Using constants determined experimentally on thick samples, the variation of the polar Kerr rotation and ellipticity as a function of magnetic film thickness has been calculated for light incident from both the air and substrate side of a typical trilayer magneto-optic disk structure in which material from the above series, the magnetic and thermomagnetic properties of which have been previously reported [Carey et al., J. Magn. Magn. Mater. (to be published)], forms the active storage layer. The agreement obtained with measurements demonstrates the self-consistency of the modeling process and the validity of the determined constants.
Synthesis of high-temperature superconducting thin films in microwave field
Authors: Kojuharoff Victor I.
Published: July 2002

The most widely used technique to obtain high-temperature superconducting (HTSC) thin films at present, i.e., the in situ method, has the disadvantage of heating the substrate up to 700–800 °C. This paper proposes a novel, low-temperature method for HTSC synthesis that is capable of producing new types of multilayer structures. The technique is based on the use of microwave (MW) field to treat a thin film deposited on a single-crystal substrate. The process of superconductor formation depends on the MW power, the sample volume, and the dielectric constant. The nature of the synthesis in MW field differs significantly from the ordinary high-temperature baking, since the solid-state reaction is initiated simultaneously in the entire volume and runs at a relatively high rate. Aerosol deposition proved to be the most suitable technique, especially when combined with ultrasonic aerosol homogenization. Scanning electron microscopy observations show that the film surface consists of comparatively densely ordered, almost round grains with sizes between 100 and 130 nm. X-ray diffraction analysis clearly demonstrates that no admixtures from the substrate have penetrated the layer. The resistance versus temperature characteristic is measured by four-probe technique and the critical current densities were 2×105 and 0.8×105 A/cm2 at 77 and 4.2 K, respectively.
Design of fast acting actuators for cryogenic valve applications in the ARIANE5-program (abstract)
Authors: Schiebener Peter , Pfeiffer Alfred , Smirra Karl
Published: July 2002

Presently valve developments are being carried out for the new European space launcher ARIANE5. In the case of the tank pressurization and helium supply system valve actuation times in the order of 20–50 ms, liquid hydrogen and liquid helium temperatures, pressures of up to 210 bar, and the need of a very compact volume lead to a requirement profile of the valve actuation unit which is met by directly controlled solenoid actuators with an additional permanent magnet. The modeling of the magnetic circuit comprises the elements of permanent magnets, solenoids, ferromagnetic materials, and several airgaps. The solutions of the model are gained by means of FE program the which is capable of taking into account not only the time transients of the developing current in the solenoid but also moving parts in the magnetic field, which themselves contribute to the magnetic flux change. The results of major interest being calculated are the force versus stroke curves and the current versus time curves. The mechanical and magnetic properties of the employed materials are taken either from available data sources or from critically reviewed measurement data. Additionally, subsequently needed material characterizations were performed at ambient down to T=4 K. The simulation results are compared to static and dynamic test results and show good agreement. Finally the simulation proves to be very helpful to predict and explain the behavior of the complete valve unit consisting of actuator and flow part. Even effects due to cryogenic operation, which occur in the integrated valve, may be analyzed.
Giant magnetoresistance in heterogeneous (CoFe)XAg1−x films (abstract)
Authors: Beach R. S. , Rao D. , Carey M. J. , Parker F. T. , Berkowitz A. E.
Published: July 2002

The soft magnetic properties of CoFe prompted an investigation of magnetoresistance in Co-Fe-Ag alloys. A series of (FeCo)xAg1−x (10<x<30) films were prepared by dc magnetron sputtering, followed by annealing in H2 at a variety of temperatures TA≤400 °C. The samples exhibit giant magnetoresistance (GMR) ratios which exceed 25% at a temperature of T=10 K, and 17% at T=300 K. The results of magnetization and x-ray scattering experiments indicate that FeCo alloy particles precipitate from the Ag matrix upon annealing. We note in particular that the full width at half maximum (FWHM) of the MR curves (approximately 2 kOe) is significantly less than that of Fe-Ag or Co-Ag sputtered films having comparable GMR ratios. We compare the sharp MR response of the (FeCo)xAg1−x system to that of heterogeneous (Ni80Fe20)xAg1−x films.
Relationship between ac and dc magnetic properties of a Co-based amorphous alloy
Authors: Lim S. H. , Choi Y. S. , Noh T. H. , Kang I. K.
Published: July 2002

How the ac effective permeability (μe) correlates with dc magnetic properties over a wide frequency range of 1 to 1000 kHz was studied, in an effort to understand the magnetization behavior of the Co-based amorphous alloy of Metglas 2714A subject to an ac magnetic field. In the low-frequency range up to 50 kHz, the correlations between μe and the dc initial permeability, and between μe and the coercivity are found to be good, the correlation coefficient being positive and negative, respectively. No definite correlation is observed with the dc maximum permeability. At high frequencies ranging from about 200 to 1000 kHz, the correlations between μe and the dc maximum permeability, and between μe and the coercivity are observed to be good, the correlation coefficient being negative and positive, respectively. The correlation of μe with the dc initial permeability is poor in this high-frequency range. The correlation with the remanence ratio is found to be rather different from the other three; the ac permeability exhibits a maximum at the value of remanence ratio of 0.5–0.6 at frequencies up to 200 kHz but, at frequencies higher than 500 kHz, it decreases linearly with the remanence ratio. From the correlation results it is considered that the dominant magnetization mechanism is the domain wall motion at frequencies up to 50 kHz and it is spin rotation at frequencies higher than 500 kHz.