bluuebunny/crossref_metadata_2025 huggingface dataset:
Thick films of Bi-Sr-Ca-Cu-O and Tl-Ba-Ca-Cu-O by solution processes
Authors: Barboux P. , Tarascon J. M. , Shokoohi F. , Wilkens B. J. , Schwartz C. L.
Published: July 2002

We have prepared superconducting thick films of the Bi-based and the Tl-based cuprates via the decomposition of aqueous-glycerol solutions containing the salts of the elements. Preliminary results are presented in this work. The substrates are coated prior to heat treating, either by dipping or by spraying on various substrates heated at 200 °C. Short firing times are required in order to minimize the loss of the constituent Bi (Tl). We find that nitrates of the constituents dissolved in a water-glycerol solution increase the reaction rate in comparison to pure nitrate aqueous solutions. They also help to produce the correct superconducting phase before some reaction with the substrate occurs or too much of the constituent Bi (Tl) is lost during heating to form the superconducting phase. However, the thallium phases cannot be obtained if the films are not fired in the presence of a high pressure of thallium in a sealed capsule. The films are composed of platelets, a few microns large, that are on average oriented parallel to the substrate with their c axis normal. The Bi films show an onset temperature at 85 K and zero resistance at 75 K while the Tl films show an onset temperature of 105 K and zero resistance at 95 K. The critical currents obtained to date are quite low (∼50 A/cm2 at 77 K for the thallium phase).
Effect of material constants on the orientation structure of ferroelectric liquid crystal cells
Authors: Chieu T. C.
Published: July 2002

The orientation structure of ferroelectric liquid-crystal cells in layer-normal geometry was studied based on a one-dimensional elastic continuum model which included three nonequal elastic constants. By minimizing the distortion energy and the surface energies, the critical cell thickness for the uniform, splayed, and helical states has been obtained as functions of the cone angle, the helical pitch, the elastic constants, and the surface interaction coefficients. By a proper choice of the handedness of the liquid crystal helicoid and the material constants, the critical cell thickness for the uniform state can be made very large, and the constraint on small polar surface-interaction coefficient for the stabilization of uniform state can be relaxed to a great extent. It is also shown that bistable states can only be stabilized in cells with no polarity difference between the substrate surfaces.
The iodine donor in ZnSxSe1−x alloys
Authors: Fornell J.-O. , Grimmeiss H. G. , Mach R. , Müller G.
Published: July 2002

The energy position of an iodine-related donor has been tracked through the alloyed system ZnSx Se1−x, where 0.60<x<1.00. Both optical and thermal energies have been measured with junction space-charge techniques. The results suggest that the optical threshold energies and lattice-relaxation effects are almost independent of x, although the activation energy of the thermal emission rate increases considerably with increasing x. Detailed measurements of the temperature dependence of the capture cross section for electrons show that the enthalpy of the iodine-related center is fairly constant for higher values of x.
The use of time space Green’s functions in the computation of transient eddy current fields
Authors: Davey Kent , Turner Larry
Published: July 2002

The utility of integral equations to solve eddy current problems has been borne out by numerous computations in the past few years, principally in sinusoidal steady-state problems. This paper attempts to examine the applicability of the integral approaches in both time and space for the more generic transient problem. The basic formulation for the time space Green’s function approach is laid out. A technique employing Gauss-Laguerre integration is employed to realize the temporal solution, while Gauss–Legendre integration is used to resolve the spatial field character. The technique is then applied to the fusion electromagnetic induction experiments (FELIX) cylinder experiments in both two and three dimensions. It is found that quite accurate solutions can be obtained using rather coarse time steps and very few unknowns; the three-dimensional field solution worked out in this context used basically only four unknowns. The solution appears to be somewhat sensitive to the choice of time step, a consequence of a numerical instability imbedded in the Green’s function near the origin.
Response characteristics of an oscillatory vane for flow-speed measurements
Authors: Jonsson H. H.
Published: July 2002

A differential equation describing the behavior of an oscillatory vane for flow-speed measurements is obtained. It differs from the classical equation for an ordinary flow-direction vane in that it contains a positive feedback term representing the flipovers of the fin. No analytical solution to the equation exists, but an oscillatory vane’s response may be determined to a good approximation by simple calculation of second-order parameters and by use of a relevant coefficient whose value has been obtained from a numerical solution and is provided here in a table for a variety of vanes. In agreement with experiments, the vane’s oscillation frequency is shown to be directly proportional to flow speed, and furthermore, to have a square-root dependence on the density of the flowing medium, the physical dimensions of the vane, and the reciprocal of its moment of inertia.
An electromagnetic induction-type digitizer using amorphous wire
Authors: Murakami A. , Hosaka K. , Fukushima M. , Tsuya N.
Published: July 2002

A digitizer was developed based on the operating principle of electromagnetic induction phenomenon and using high permeability amorphous wires as magnetic cores. The cordless advantage was realized by using a permanent magnet in the stylus pen. A high working height and high resolution of the stylus pen were achieved.
Characteristics of a multilayer eddy-current-type ac magnetic coil with a cooling system
Authors: Bessho K. , Yamada S. , Kooto M. , Masahashi M. , Nakano M.
Published: July 2002

This paper deals with the performance characteristics of a new ac high magnetic field generator based on the effect of eddy currents. We have proposed a new ac high magnetic field generator and have obtained magnetic fields up to 15 T at 60 Hz. The proposed structure consists of layers of exciting coils and conductors built in concentric circles. The eddy currents in the conductor flow close to the hole in the conductor. The magnetic flux induced by the eddy currents is concentrated within the hole, and an ac high magnetic field is produced. A procedure for estimating the optimum shape and number of layers required to increase the concentration effect, together with a design of the colling system necessary for continuous operation, is presented.
Anomalous Barkhausen noise produced by the magnetic aftereffect in ferromagnetic amorphous ribbons
Authors: Celasco M. , Mazzetti P. , Stepanescu A. , Masoero A.
Published: July 2002

It has been shown that the presence of a magnetic aftereffect in amorphous ferromagnets is the origin of an anomalous Barkhausen (B.) noise. Experiments on commercial Metglas 2605 SC and 2605 CO alloys have evidenced an increment of the power spectrum of the noise of up to two orders of magnitude. This fact has been interpreted as due to the competitive effect between the onset of a viscosity field and the growth of the driving field acting on a wall after its arrest at the end of a large B. discontinuity. In the present paper experiments on the anomalous B. noise are extended to higher temperatures and the excess noise generated by the magnetic aftereffect evaluated on the basis of viscosity field measurements done on the same specimens. This allows us to check and improve a theoretical model presented in a previous paper.
The lattice Anderson model on a finite cluster
Authors: Callaway J. , Chen D. P.
Published: July 2002

The lattice Anderson model is considered with two nondegenerate orbitals per site (c and f ). The Hamiltonian matrix is constructed in a localized representation on a four site, tetrahedral cluster. All the eigenvalues are obtained for any occupancy by explicit diagonalization, using symmetry to reduce the problem to manageable size. Thermodynamic functions are calculated. Emphasis in this work is placed on the strong interaction–weak hybridization sector of the model. The behavior of the model is quite complex, with five different regions delineated.
A permanent-magnet structure for a helical free-electron laser
Authors: Leupold H. A. , Potenziani II E.
Published: July 2002

A permanent-magnet structure (twister) has been designed and built to replace the bifilar electrical coil presently used in a helical free-electron laser microwave source (ubitron). The magnet elements are thin rectangular slabs perforated by circular holes at their centers and magnetized in the direction of their long axes. Each magnet is embedded in a brass disk for protection and support. Holes drilled near the peripheries of the disks serve to position the magnets for the desired twist rates. The structure provides transverse helical fields of 1.15 and 2.30 kOe for twist periods of 2.5 and 5.0 cm, respectively. These values are double those presently generated by a much bulkier coil with considerable expenditure of electrical energy. The massive power supply is also eliminated by the permanent-magnet structures. Since the power output of ubitrons varies with the mean square of the transverse field, power output of the permanent-magnet twister should be four times that provided with the bifilar coil. The device is intended to be a radiation source/amplifier in the 10-GHz region.
Spin-dependent elastic and inelastic electron scattering from magnetic surfaces (invited)
Authors: Hopster H. , Abraham D. L. , Pappas D. P.
Published: July 2002

Results from scattering experiments, using a polarized electron beam combined with polarization analysis, are presented and discussed. There is no evidence of depolarization in quasielastic scattering for the systems studied [Ni(110), Ni(110)O(2×1), paramagnetic Ni(110), Pt(111), graphite]. In inelastic scattering from graphite for small energy losses the depolarization is found to be weak, whereas for ferromagnetic Fe and Ni surfaces large spin-flip contributions have been reported for small energy losses.
Ground-state energy of spin-1/2 and spin-1 antiferromagnetic chains: X
Y model
Authors: Pan C. Y. , Lin H. Q.
Published: July 2002

The ground-state energy of the XY antiferromagnetic chains with spin-1/2 and spin-1 are obtained by a real space renormalization group method. For S=1/2 a large spin cluster is used in the mapping to improve the accuracy and a boundary theory is applied to extrapolate to the result which is in excellent agreement with the exact Bethe Ansatz result. For S=1 the ground-state energy of the model is obtained by using the renormalization group method and a finite chain calculation for lattices up to 16 sites. The two results are in very good agreement.
Implantable transformer for an artificial heart utilizing amorphous magnetic fibers
Authors: Matsuki H. , Yamaguchi M. , Watanabe T. , Murakami K. , Nadehara K. , Yamamoto T.
Published: July 2002

It is a very serious problem for an implantable artificial heart to receive energy from outside the body. A new implantable transformer with a plain weave structure was proposed by using amorphous magnetic fibers. The transformer has the following features: (i) a thin, planar shape; (ii) high flexibility; and (iii) low waste heat in the range of several tens kHz. Appropriate conditions for the size of the transformer were shown experimentally. The transformer (70×30×1 mm3) of a trial design can supply a power of 6 W. The temperature rise of the transformer based on iron loss is considered to be negligibly small.
Computation of hyperthermia-SAR distributions in three dimensions (abstract)
Authors: Hoole S. Ratnajeevan H.
Published: July 2002

Hyperthermia, the heating of tumors to greater than 42 °C, has been demonstrated to be an effective adjuvant to radiation therapy in treating cancer.1 Heating techniques using electromagnetic energy are largely employed in the clinic, at present, to produce therapeutic temperatures in the tumor. The critical parameters influencing the induced temperature distribution in the tissue are the electromagnetic power absorption rate (SAR or specific absorption rate in W/kg) and the blood perfusion rate. It is important to ensure that the SAR is high in the target volume and not harmful to healthy tissue. To this end, the general Maxwell equations have to be solved in the human body2 at a given frequency (anywhere from low to high) for an electric field applied tangential to the body (usually near the waist).3 This paper reviews the state of the methods of field computation employed today and describes the beginnings of a treatment planning system being constructed. The planning system needs to be able to construct the model of the body, solve for the fields, and show the SAR distribution. A major difficulty is encountered with the more conventional vector potential formulation. It is traditionally assumed that in the splitting of the electric field E into −jωA and −∇φ, the latter term is from externally applied power sources. While this is true in two dimensions, in three dimensions, so assuming would make E=jωA continuous across interfaces. At the same time, solving directly for E makes it difficult to impose the divergence and curl equations together because of the trial function restrictions. It is shown that the boundary-element method, where an analytical Green’s function solution is used (without the restrictions of the finite-element trial functions), will give us the best accuracy.
Heat capacity of Gd0.06Er0.94Al2 in magnetic fields
Authors: Johanson W. R. , Pierce G. , Zimm C. B. , Barclay J. A.
Published: July 2002

We have measured the specific heat of an arc-melted specimen of Gd0.06Er0.94Al2 in applied magnetic fields of 1, 3, 5, and 8 T from 4.5 to 40 K, and in zero field from 1.4 to 98 K. Inspection of entropy versus temperature with the lattice included shows that the maximum adiabatic cooling is 13 K and occurs from 30 K at 8 T to 17 K at zero field. With our previous magnetization measurements on Gd0.5Er0.5Al2, our data indicate that substitution of Gd for Er in this crystalline environment does not significantly increase the magnetocrystalline anisotropy. The solid solution is magnetically soft and most of the magnetic entropy changes occur below 30 K.
Superconducting behaviors in (Y1−xLax)Ba2Cu3Oy (0≤x≤1)
Authors: Okada M. , Matsuoka D. , Zou H. , Homma M.
Published: July 2002

The superconducting behavior of (Y1−xLax)Ba2Cu3Oy compounds for 0≤x≤1 was studied. It was found that Tc decreased with increasing La content. (Y1−xLax)Ba2Cu3Oy for 0≤x≤0.4, fired at 1050 °C in air, shows onset temperatures above 90 K. Annealing (Y1−xLax)Ba2Cu3Oy at 300 °C in O2 enhanced the onset temperature above 70 K for all studied compositions (x=0–1), and altered the crystal structure from tetragonal to orthorhombic.
Syntheses of Y(Ba1−xSrx)2Cu3O7−δ superconducting films by alternate sputtering (abstract)
Authors: Yamamoto H. , Okukawa H. , Tanaka M.
Published: July 2002

Recently, high-Tc oxide superconductors have been extensively studied because these materials can be applied to various electronic devices, especially highly sensitive magnetic sensors or high-speed switching elements. For such the applications, thin films with superior superconductivity and very smooth surfaces are needed. The purpose of this work is to develop an as-grown technique of Y-Ba-Sr-Cu-O films on comparatively low-temperature substrates by adopting a newly devised alternative sputtering. The sputtering apparatus was constructed by three targets and a substrate holder which was intermittently rotated and stopped facing the desired target. The targets were Y2O, BaO+SrO, and Cu or CuO. The thickness of the oxide layer alternately deposited was adjusted to the thickness of the each metal-oxide monolayer. The substrate used was a (100) plane of a single-crystal MgO. The substrate temperature Ts was changed from 450 to 600 °C. The deposition rate of the each layer was affected by Ts. Especially, the deposition of the CuO layer was very sensitive to conditions of the film growing surface: Ts and/or degree of oxidation. The film composition was adjusted by changing the deposition time of the each layer. The crystal with an oxygen-defective perovskite nucleated even at a Ts of about 500 °C. In the case of sintered bulks, a tetragonal phase was obtained when the content of Sr was comparatively large. In contrast, an orthorhombic phase was stabilized in the sputtered films. As-grown films showed a poor superconductivity. After a post-annealing in 1-atom O2 at a low temperature of about 450 °C, a sharp superconducting transition was observed above 77 K. As we increase the content of Sr, the resistivity of the film became large and semiconductive.
Ferrite thin films for microwave applications
Authors: Zaquine I. , Benazizi H. , Mage J. C.
Published: July 2002

Production of ferrite thin films is the key to integration of microwave ferrite devices (circulators for phased array antennas, for instance). The interesting materials are the usual microwave ferrites: garnets, lithium ferrites, barium hexaferrites. The required thicknesses are a few tens of micrometers, and it will be important to achieve high deposition rates. Different substrates can be used: silicon and alumina both with and without metallization. The films were deposited by rf sputtering from a single target. The as-deposited films are amorphous and therefore require careful annealing in oxygen atmosphere. The sputtered films are a few micrometers thick on 4 in. substrates. The optimum annealing temperature was found by trying to obtain the highest possible magnetization for each ferrite. The precision on the value of magnetization is limited by the precision on the thickness of the film. We obtain magnetization values slightly lower than the target’s. The ferromagnetic resonance linewidth was measured on toroids from 5 to 18 GHz.
Magnetic loss in the nickel-zinc-iron oxide system
Authors: Hahn H. T. , Cahill R. W. , Musal H. M.
Published: July 2002

The formation of cubic inverted spinel structures in the nickel-zinc-iron oxide system produces ferrites with high initial magnetic permeability. However, the electrical conductivity of nickel-zinc ferrites, when prepared under oxidizing conditions, is extremely low. Consequently, the imaginary part of the dielectric constant is correspondingly low, and the resultant rf electric loss is small. Most loss is, therefore, associated with the imaginary part of the magnetic permeability, which declines inversely with frequency in the VHF-UHF frequency regime. In this work, dielectric constant and magnetic permeability were measured for a series of nickel oxide-zinc oxide-ferric oxide compositions in order to identify the region of the ternary diagram associated with higher values of magnetic loss. Ferrites were prepared under identical conditions by a reactive sintering process at 1200 °C. Compositions corresponded to stoichiometric spinels (NixZn1−xFe2O4), or to spinels with the presence of excess or insufficient ferric oxide. Toroids were machined for coaxial analysis. Variation of the imaginary part of permeability with ferric oxide concentration indicated that larger values of magnetic loss were obtained when a relatively large excess of Fe2O3 was absent. When values of the imaginary part of magnetic permeability were plotted versus the nickel-zinc atom ratio, the sensitivity was relatively weak near and above unity. Below a ratio of 0.75, magnetic loss decreased rapidly, disappearing below the ratio Ni/Zn≂0.2. Reasons for this behavior are discussed. The largest μ″ obtained with the stoichiometric iron oxide series was at Ni0.5Zn0.5Fe2O4.
Effect of the addition of a third element in a high silicon-iron alloy
Authors: Nakamura H. , Tsuya N. , Saito Y. , Katsumata Y. , Harada Y.
Published: July 2002

Concerning the decrease of the wall motion resistive magnetic properties such as magnetocrystalline anisotropy of an electric sheet, we reported that quick quenching from 1100 °C suppressed the formation of a B2 superlattice which is roughly proportional to the anisotropy. Using iron single crystals containing 5.5 wt. % silicon with the addition of a small amount of a third element such as Mo to suppress the formation of the superlattice, we describe the quenching temperature dependence of the anisotropy and saturation magnetization. A remarkable decrease of room-temperature anisotropy was found in crystals with the additional element compared to those without the element.
Calculation of crystal field parameters in Nd2Fe14B using realistic energy-band results
Authors: Zhong Xue-Fu , Ching W. Y.
Published: July 2002

There have been several attempts to estimate the crystal field parameters of the rare-earth-iron-boron permanent magnets because of its pivotal role in understanding the energy anisotropy, spin reorientation, etc. Usually, a simple point charge model (PCM) was employed which depends on some arbitrary parameters such as the values of ionic charge and screening factors. The crystal field parameters obtained from the PCM generally have correct signs but are too large in magnitude. We report a more accurate preliminary calculation of the crystal field parameters in Nd2Fe14B based on the results of realistic energy-band calculation. Three levels of calculations are carried out: (1) The PCM calculation which essentially reproduces the published values of other workers; (2) use of effective charges on each ion from the band calculation instead of fully ionic values, which reduces the magnitude of parameters but have signs of some parameters reversed; (3) use of charge distribution calculated from the Bloch wave functions of Nd2 Fe14 B gives crystal field parameters in much better agreement with experiment. The results of these calculations and its implication are discussed.
Magnetic field dependence of 11B and 57Fe NMR in a Nd2Fe14B compound (abstract)
Authors: Zhang Y. D. , Budnick J. I. , Yang D. P. , Potenziani II E. , Pedziwiatr A. T. , Wallace W. E. , Sagawa M.
Published: July 2002

The 10B, 11B, and 57Fe spin-echo nuclear magnetic resonance (NMR) and magnetization experiments have been performed for naturally abundant and 10B-enriched Nd2Fe14B at 1.3 and 4.2 K for frequencies from 10 to 80 MHz. It was found from a comparison of NMR spectra in zero field and in an external field of 6.0 kOe that the hyperfine fields at the domain edges and at the domain-wall centers are nearly the same. This implies that the Fe hyperfine field anisotropy is small in this system. The presence of spin canting was verified by the result that the 11B NMR frequency shift due to the applied external magnetic field does not exactly follow γ(11B)ΔH. The NMR technique proves to be sensitive in detecting the trace of Fe precipitate in the Nd-Fe-B permanent magnets.
Magnetism in nonequilibrium phases of transition metals
Authors: Brener N. E. , Callaway J. , Fuster G. , Tripathi G. S. , Jani A. R.
Published: July 2002

Local spin-density theory and the linear combination of Gaussian orbitals method are employed to compute the band structure and ferromagnetic moment of nonequilibrium phases of several transition metals. The calculations are used to investigate possible magnetic order in these nonequilibrium phases, which include bcc and fcc Mn in a wide range of lattice constant, and bcc Nb and fcc Rh in regions of expanded lattice constant. The ferromagnetic moment calculations reveal transitions from nonmagnetic to ferromagnetic states and/or transitions from low-spin to high-spin ferromagnetic states as the lattice constant increases. In the case of bcc Mn, fcc Mn, and bcc Nb, large ferromagnetic moments are found in the expanded lattice constant region.
Scaling of the magnetoresistance of UBe13 under pressure
Authors: Willis J. O. , McElfresh M. W. , Thompson J. D. , Smith J. L. , Fisk Z.
Published: July 2002

We report magnetoresistance measurements of the heavy electron compound UBe13 above the superconducting transition temperature Tc and below 4 K for pressures P up to 19 kbar and for magnetic fields H up to 9 T. We observe strong negative magnetoresistance at all pressures and temperatures. The resistivity ρ is quadratic in temperature T from Tc up to a maximum temperature of 1 K at 1 bar increasing to 2 K at 19 kbar. The slope of the T2 term decreases with both H and with P. We find that δ(H)≡−[ρ(H)−ρ(0)]/ρ(0) for a given pressure scales as a function of H/T and exhibits power-law behavior over one decade with an exponent of 1.7. In addition, δ(H) at high pressure shows this same power law over a more limited H/T range.
Microscopic theory of magnetic excitations in ferromagnets with random anisotropy axes
Authors: Huber D. L. , Ching W. Y.
Published: July 2002

We present a microscopic theory of the harmonic magnetic excitations in ferromagnets with random anisotropy axes. The theory is analogous to the theory of excitations in spin glasses developed by Walker and Walstedt, with the difference that the disorder arises from the anisotropy rather than the exchange interaction. We report the results of numerical calculations of magnon density of states and the ferromagnetic resonance frequency for a model system where the spins occupy sites on a fcc lattice. The exchange interaction is between nearest neighbors, and the anisotropy axis varies randomly from site to site with no correlation between different sites. Data are obtained with a range of values of the ratio of the anisotropy to the exchange interaction in both the zero-field and high-field limits.
Melt-spun Nd-Fe-B magnets and the Nd1+εFe4B4 phase
Authors: Mishra Raja K.
Published: July 2002

The microstructure of Nd-Fe-B magnets made from melt-spun ribbons differs significantly from that of the sintered magnets. An ideal two-phase microstructure of small Nd2Fe14B grains surrounded by a Nd-rich intergranular phase is easily achieved in the melt-spun magnets while sintered magnets invariably contain the boron-rich Nd1.1Fe4B4 phase. This phase can form in the melt-spun alloys only when the cooling rates are slow and excess Nd and B are added deliberately. In those cases, this new phase appears as randomly distributed and randomly oriented grains of the same size as the Nd2Fe14B grains. The Nd1.1Fe4B4 grains are highly faulted in the Fe sublattice with their fault planes parallel to the (110) plane. Energy dispersive x-ray analysis and diffraction shows that this phase forms with varying Nd:Fe ratios in different grains. We have also found that the faults form in pure bulk samples of Nd1.1Fe4B4 but not in pure NdCo4B4 samples. Possible antiphase boundaries arising from modulated Fe sublattice are seen. The faulted microstructure is believed to result from (a) sluggish kinetics of formation of this phase, (b) incommensurate crystal structure, and (c) weak bonding between the Nd chains and chains of Fe-B tetrahedra that make up the structure. Lorentz microscopy shows this phase to act as a weak barrier to domain wall motion.
Forced magnetostriction in amorphous Gd-Fe films
Authors: Iwanaga Ken-ichi , Itoh Akiyoshi , Seiki Masahiro , Kawanishi Kenji
Published: July 2002

Composition and temperature dependence of forced magnetostriction have been measured for rf-sputtered Gd-Fe films using the cantilever capacitance method. Forced magnetostriction varies remarkably with film composition and temperature, and also depends on the substrate bias voltages applied during sputtering. It has been found that the change of forced magnetostriction coincides well with the change of the parameter δ, where δ is amount of fluctuation in the exchange constant between sublattice moment, and it has been evaluated by using Handrich’s modified molecular field theory. Therefore, we conclude that forced magnetostriction of sputtered Gd-Fe films is strongly related to δ.
The microstructure of permanent magnetic material Nd15.8(Fe1−xAlx)78.2B6 (abstract)
Authors: Gui Rongli , Zhu JinHan
Published: July 2002

The research of magnetic properties and domain structure have been carried out on a series of permanent magnetic materials Nd15.8(Fe1−xAlx)78.2B6, x=0, 0.02, 0.04, 0.06. The Mössbauer spectra have been also analyzed for these alloys. It has been found that the coercive force increased directly with the aluminum content of these compounds in the range of x=0–0.04, while the magnetic energy product was not sensitive to the increase of aluminum content; the values of (BH)m have only been kept in an original level in various compositions. In order to discover the deformation of the microstructure caused by the aluminum added, the domain structure of various specimens has been studied with Kerr effect. The surface of the specimen in research is normal to the C axis of the samples. We have found that the crystal grains have been shattered, the defects of grain boundary have been increased, and the width of the domain were smaller in the specimen containing aluminum. Moreover, it is obviously minimized during tempering. The 57Fe Mössbauer spectra of Nd15.8(Fe0.6Al0.4)78.2B6 and Nd15.8Fe78.2B6 in room temperature have been fitted with the Teillet program and compared with each other. Every spectra consisted of six subspectra which corresponded to the six types of atoms in the tetragonal structure. During the addition of aluminum, all of the subspectra have been changed, but bigger changes happened in the subspectrum which is obtained from the Fe atom occupying the 16 K2 crystal sites.
Perpendicular anisotropy of bias modulated ErCo sputtered films
Authors: Nawate M. , Tsunashima S. , Uchiyama S.
Published: July 2002

Perpendicular anisotropy in bias modulated ErCo sputtered films has been investigated. A ErCo single layer film with or without substrate bias has in-plane magnetization, while a multilayered film formed by the bias modulation has perpendicular magnetization when the modulation period is in the range of 30–60 Å. The perpendicular anisotropy is thought to originate in the interface and the value of interface anisotropy Ks is estimated to be 0.01–0.02 erg/cm2.
Influence of precipitate dispersion and texture differences through the sheet thickness on selective grain growth in silicon-iron
Authors: Abbruzzese G. , Fortunati S.
Published: July 2002

Two steels having slightly different chemical compositions were transformed by a conventional two-stage cold rolling process. Different dispersions of second phase particles (grain growth inhibitors) were obtained by controlling the Mn/Cu ratio in the steels, which ultimately came to have significantly different core losses as a consequence of a different magnetic permeability and the size of the secondary recrystallized grains. After primary recrystallization and just before secondary recrystallization, the steels were analyzed for grain size distribution, texture, and particle size evolution. The size of every single grain was classified in relation to its orientation in different positions through the sheet thickness. The evolution of grain size distribution for grains near (±10°) the {110}〈001〉 was found to differ from that for grains with the other orientations. This is in agreement with the theory of grain growth in the presence of texture and special orientation relationships between classes of grain having different orientation. Magnetic properties were related to the starting conditions (frequency and dispersion around the exact Goss orientation) of grain growth after primary recrystallization. The amount of inhibitor and the effect of process parameters (like temperature of intermediate annealing, partition of cold rolling degree, etc.) were found to play a decisive role in improving the intensity of {110}〈001〉 grains and in reducing their dispersion after primary recrystallization.
Locking and chaos in magnetic resonance experiments (invited)
Authors: Warden M. , Waldner F.
Published: July 2002

Nonlinear ferromagnetic resonance in YIG and (CH2NH3)2CuCl4 has been observed by the parallel pumping technique. When pumped above the threshold power the microwave absorption displays self-oscillations. In (CH2NH3)2CuCl4 the self-oscillations have the form of relaxation oscillations with varying irregularity described by high fractal dimensions up to D=5. A typical measurement is presented and compared to the results of the classically described 2n-dimensional stroboscopic model (SM). In YIG nearly harmonic self-oscillations at 170 kHz are observed as the system has approached a limit cycle. The microwave power was modulated at variable frequencies and locked states were observed at rational ratios of self-oscillation frequency to modulation frequency. The locked states are reproduced by SM for parameter values giving a limit cycle behavior and with the addition of a time-dependent pump. Both the experiment and the SM follow the main predictions of the circle map.
Composition dependence of dynamic Young’s modulus and internal friction in Al2 O3 -3Y-ZrO2 composites
Authors: Ono Teruaki , Nurishi Yukio , Hashiba Minoru
Published: July 2002

The specific dynamic Young’s modulus E′/ρ and the internal friction Q−1 of Al2 O3 -3Y-ZrO2 composites with different 3Y-ZrO2 content were investigated. With the increase of 3Y-ZrO2 content, the E′/ρ decreased linearly showing a large inflection point at about 20% and a small one at 65%, and the Q−1 reached a peak at 17% and a trough at 40%, and increased showing a shoulder at about 70%. The specific loss modulus E″/ρ calculated from E′/ρ and Q−1 showed the peaks at 17% and 65%. The E″/ρ peaks corresponded with the E′/ρ inflection points in composition. As a result, it was estimated that they were due to the tetragonal to monoclinic transformation of ZrO2 phase, and that the increase of internal friction at above 40% was not due to the crack formation and the ZrO2 phase transformation, but due to the flexural deformation caused by shearing force.
Long-term stability of Fe-B-Nd-Dy alloys made by Dy2O3 additions
Authors: Doser M. , Keeler G.
Published: July 2002

For several years efforts have been devoted to increasing the coercivity of Fe-B-Nd alloys in an effort to increase the magnetic stability of this product. Some authors have shown that coercivity can be increased and irreversible losses reduced by alloying Dy with Fe-B-Nd. Ghandehari has shown that Dy2O3 can be added to milled Fe-B-Nd powder compositions before sintering to increase coercivity. In this paper we studied the effects of long-term aging in air on magnets at 100 and 150 °C for periods up to 1500 h for selected Fe-B-Nd-Dy alloys made by the oxide addition method and compared these to an alloy made by vacuum melting the elemental metals. Metallography and microprobe data are also presented.
Modeling photoexcitable donors in one-dimensional unipolar structures
Authors: Hurd C. M. , McAlister S. P. , Day D. J. , Sitch J.
Published: July 2002

We show how to incorporate the effects of photoexcitable deep donors into a one-dimensional calculation of the band structure of a unipolar heterostructure in steady illumination. We consider a single-interface GaAs/AlxGa1−xAs heterostructure having deep donors in both the AlxGa1−xAs supply layer and in the GaAs buffer, but our approach is applicable to other configurations. The calculation accounts for photogenerated electrons arising from DX centers in the AlxGa1−xAs layer and from optical pumping of the GaAs buffer. Using realistic parameters in a quantitative calculation applicable to the steady state, we show how illumination modulates the potential spikes in a typical high-electron mobility transistor, alters the distribution of electrons throughout the active layers, and changes the access to the conduction channels. We consider the consequences of these effects in structures with different thicknesses of active layers.
Low-noise Josephson parametric amplification and oscillations at 9 GHz
Authors: Olsson H. K. , Claeson T.
Published: July 2002

We have investigated the performance of a resistive rf SQUID as a 9 GHz parametric amplifier and oscillator. It was coupled to a low impedance microstrip transformer. Stable Josephson oscillations were obtained for βLQ =2eI0ZL/hf <1.1–1.8. Oscillation linewidth (830 kHz) and output power (−74 dBm) were measured. The four-photon internally pumped amplifier produced large single sideband (ssb) noise temperatures, typically around 50 K, due to the broad flanks of the pump. The best performance was achieved in the three- and four-photon externally pumped modes. Both modes gave signal gains of about 10 dB and negligible noise power contributions. A hot/cold measurement on the four-photon amplifier yielded Gdsb =13 dB (dsb=double sideband) and Tdsb =3±4 K over a bandwidth of 310 MHz. For larger values of βLQ , subharmonics 1/2 and 1/3, as well as noninteger ‘‘excitations’’ of the Josephson oscillation, were observed. The subharmonic oscillations were not tunable in frequency with unchanged linewidth. Amplification close to an excitation also produced gain but with ssb noise temperatures of ∼20 K.
Exact analysis of a three-dimensional cylindrical model for a polycrystalline solar cell
Authors: Elnahwy S. , Adeeb N.
Published: July 2002

Analytical expressions for the short-circuit current densities and the spectral response were derived for a thin-film polycrystalline n/p junction solar cell. A three-dimensional model was used for a typical grain. It has the shape of a columnar cylinder. The spectral response and the total short-circuit current density were then evaluated for different values of grain size, grain boundary recombination velocity, and film thickness. The calculations aimed at studying some possible enhancements in the spectral response and the short-circuit current. Such enhancements can result from increasing the grain size or from reducing the grain-boundary recombination velocity. These two parameters can more or less be controlled experimentally through recrystallization and passivation of grain boundary states, respectively.
On the mode of growth of CaF2 and (Ca,Sr)F2 on GaAs and Si(111) substrates
Authors: Fontaine C. , Castagné J. , Bedel E. , Munoz-Yague A.
Published: July 2002

The early stages of molecular-beam epitaxy of (Ca,Sr)F2 and CaF2 on GaAs and Si(111) substrates have been studied by means of in situ Auger electron spectrometry and reflection high-energy electron diffraction. The results obtained show (i) that the growth proceeds in all cases via a two-dimensional mechanism that preserves the atomic flatness of the growth front and (ii) that this growth has a nonpseudomorphic character. This behavior is related to the properties of the fluorides involved. The general trends in fluoride-semiconductor heterostructure growth are discussed.
Magnetism of interfaces between Fe(110) and noble metals
Authors: Elmers H. J. , Gradmann U.
Published: July 2002

Changes of magnetic surface moment and out-of-plane surface anisotropies of Fe(110) surfaces, caused by coating with Cu, Ag, and Au, are determined by torsion oscillation magnetometry of epitaxial Fe(110) films on W(110) in UHV. Changes of magnetic moment Δm, normalized by the monolayer moment mML, are given by Δm/mML=0.00 for Cu coating, 0.01 for Ag coating, and −0.09 for Au coating, respectively.
Pseudomorphic InGaAs/GaAs/AlGaAs mirrors for optical devices in the near-infrared 0.9–1.3 μm
Authors: Gourley P. L. , Dawson L. R.
Published: July 2002

We propose using pseudomorphic multilayers of InGaAs, GaAs, and AlGaAs in optical mirrors for near-infrared devices including surface-emitting lasers, bistable optical devices, and optical modulators. We demonstrate the growth of a Fabry–Perot etalon by molecular-beam epitaxy and characterize it optically (reflectance, transmittance, photoluminescence) and structurally (scanning electron microscopy and dislocation imaging). We find the optical characteristics of the etalon as a whole and the individual quarter-wave layers indicate high structural quality for the mirrors. This is in spite of the fact that the lattice constant of the etalon structure is slightly relaxed from that of the GaAs substrate. These results indicate that pseudomorphic mirrors are useful candidates for integrated optical devices.
Instability in resistance and variation of activation energy with thickness and deposition temperature of CdSe0.6Te0.4 thin films deposited at high substrate temperatures
Authors: Sebastian P. J. , Sivaramakrishnan V.
Published: July 2002

CdSe0.6Te0.4 thin films deposited at high substrate temperatures showed a rapid increase in resistance when exposed to oxygen and atmosphere. This behavior is explained by an oxygen adsorption model. A decrease in activation energy with an increase in thickness and deposition temperature is explained by the fact that the depth of the impurity levels is reduced with an increase in thickness and deposition temperatures. The low activation energy obtained in oxygen or atmosphere heated films is accounted for by the fact that oxygen acceptor levels are very shallow from the conduction band.
Selection criteria for AlGaAs-GaAs heterostructures in view of their use as a quantum Hall resistance standard
Authors: van der Wel W. , Haanappel E. G. , Mooij J. E. , Harmans C. J. P. M. , André J. P. , Weimann G. , Ploog K. , Foxon C. T. , Harris J. J.
Published: July 2002

The effects of several practical properties of GaAs-AlGaAs heterostructures on the accuracy of a quantum-Hall resistance standard at a level of 1:108 are discussed. Conduction through a parallel layer, metallic current contacts, homogeneity of the electron density, sample size, and mobility are addressed. Measurements are presented concerning the influences of sample size and mobility. As regards mobility, the slope of the Hall plateau, longitudinal resistance, and critical current have been investigated. Recommendations are given on sample geometry and mobility. Feasible measurement methods are presented to check the absence of a parallel conducting layer and the quality of the contacts.
Influence of the tank circuit noise on the dc impedance of the rf-biased R-SQUID
Authors: Seppä Heikki
Published: July 2002

The tank circuit noise in an rf-biased R-SQUID noise thermometer is shown to have a small but a detectable influence on the dc impedance of the resistively shunted Josephson junction. The result supplements earlier calculations which have been used to explain some of the experimentally observed characteristics of the dc impedance.
The equilibrium charge distribution and electric field at a vacuum/dielectric interface
Authors: Enloe C. L.
Published: July 2002

The unique equilibrium electric field configuration for a planar dielectric/vacuum interface subjected to electric stress is found, based on the requirement that the local electric field be inclined to the dielectric surface at the critical angle at which the secondary electron yield of electrons impacting the dielectric surface is unity. The critical angle is independent of the magnitude of the applied field and is a function of material properties. The electric field, potential, and charge distributions are calculated for several orientations of the interface versus the applied stress field. The results show that when the surface is charged, the electric field may be enhanced near either the cathode or the anode depending on whether the angle of the interface is greater or less than the critical angle. This is in contrast to the uncharged case, for which the field is always enhanced near the narrow end of the dielectric independent of the polarity of the applied field. The equilibrium surface charge distribution is not constant over the surface and varies in sign with the orientation of the interface. The magnitude depends on both the critical angle and the relative permittivity of the dielectric. The implications of these results for researchers and designers who are investigating or using high voltage is discussed.
Influence of Hall current on the stability properties of a self-pinched intense electron beam
Authors: Choi Eun H. , Uhm Han S. , Choi Duk I. , Shin Hee M.
Published: July 2002

Influences of Hall current on the stability properties of azimuthally symmetric perturbations (e.g., sausage and hollowing modes) of a self-pinched electron or ion beam immersed in a resistive plasma are investigated. The perturbed space charge and plasma current with the Hall term are treated self-consistently for any value of the plasma conductivity. It is assumed that ν/γb ≪1, where ν is Budker’s parameter and γbmc2 is the characteristic beam electron energy. The analysis is carried out within the framework of linearized Vlasov–Maxwell equations. In the high-conductivity background plasma, the growth rates of the sausage (n=1) and hollowing (n=2) modes are significantly enhanced by the influence of Hall currents.
Ion mixing of near-noble monosilicides with Si substrates
Authors: Hong Q. Z. , Hung L. S. , Mayer J. W.
Published: July 2002

Xe ion irradiation of NiSi, PdSi, and PtSi on Si was performed at various substrate temperatures. The phase formation and mixing behavior of the three monosilicides with their Si substrates are quite different. For NiSi, NiSi2 was formed on amorphous Si substrates at 350 °C, while NiSi remained stable on crystalline Si substrates even at 400 °C. PtSi reacted with Si to form a metastable Pt4Si9 phase, which decomposed back to PtSi and Si by successive irradiation at higher temperatures. The decomposition of the metastable Pt4Si9 was easier on crystalline Si substrates than on amorphous substrates. No mixing was observed for PdSi on Si in the temperature range of 35–400 °C. The ion mixing results were compared with those from thermal annealing. The importance of demixing of a thermally stable system was explored.
Limitations of an amorphous-metal magnetometer operated by modulating the magnetostrictive strain
Authors: Pantinakis A. , Jackson D. A.
Published: July 2002

An analysis is presented of the characteristics of a magnetometer which uses an amorphous-metal ribbon as its primary sensing element and which operates by modulating the magnetostrictive strain. Magnetic fields at the second harmonic of the modulation frequency are identified as capable of significantly degrading the magnetometer performance. A second-harmonic field is measured and its contribution to the noise is estimated.
A photoemission investigation of surface processes affecting the reactive ion etching of TiSi2 in CF4
Authors: Robey S. W. , Jaso M. A. , Oehrlein G. S.
Published: July 2002

Photoemission was used to probe the surface modifications which occur while etching TiSi2 in CF4 plasmas. Fluorination of the silicide leads to the depletion of Si from the surface region and the formation of a relatively thick (∼15–20 Å) overlayer with an average stoichiometry of TiF3. An identical overlayer also forms on pure Ti. The overlayer is primarily composed of a single fluorinated species and apparently does not contain a distribution of different species as in the case of fluorinated Si. This observation strongly suggests that the limiting factor in the etching of these materials is the further reaction/sputtering of this stable, nonvolatile fluoride. Also, as in the case of Si etching in halocarbon plasmas, CFx films were found to form with increasing addition of H2. Significant differences in the quantity and composition of the films were found compared to those formed on Si substrates, with Si exhibiting a higher tendency to promote CFx film growth.