bluuebunny/crossref_metadata_2025 huggingface dataset:
Cubic-Magnetic and Optical Behavior of Orthorhombic RbFeF3
Authors: Gyorgy E. M. , Levinstein H. J. , Dillon J. F. , Guggenheim H. J.
Published: February 2004

On cooling through 87°K, RbFeF3 undergoes a first-order transition from a tetragonal antiferromagnetic phase to an orthorhombic ferromagnetic phase where c/a>1.003. In this magnetic phase the magnetic energy obtained from torque and magnetization measurements is describable by a cubic-anisotropy expression. The easy axes are 〈100〉 (referred to the high-temperature cubic phase) and the effective anisotropy field is greater than 105 Oe. Strain-gauge measurements at 77°K indicate that the crystal structure does not deform such that the c axis always follows the magnetization. The measured magnetostriction Δl/l∼ 50×50−6. Optically the crystal appears uniaxial with the optic axis along the magnetization vector 〈100〉. This is just the behavior expected of a cubic crystal distorted by magnetostriction. At 40°K the crystal undergoes another phase transition. The magnetic behavior is still cubic; the easy axes merely changing from 〈100〉 to 〈110〉. To our knowledge this is the first example of a material whose low symmetry as determined by x rays is not reflected in its magnetic and optical properties.
Magnetic and Optical Properties of Ferrimagnets in the RbMgF3–RbCoF3 System
Authors: Shafer M. W.
Published: February 2004

Previously reported ABF3-type ferrimagnets with the hexagonal BaTiO3 structure all contain Ni++ as the predominate magnetic ion. This paper reports the discovery of new ferrimagnetic compositions in the RbMgF3–RbCoF3 system where Co++ is the only magnetic ion. Phase studies on this system show that at high temperatures the hexagonal phase is stable to about 70% RbCoF3. Single crystals were grown over this compositional range and their magnetic and optical properties studied. Compositions containing in excess of about 35% RbCoF3 are ferrimagnetic and their magnetic moments (as high as 22 emu/g) and Curie temperatures (up to 36°K) vary with Co++ concentration. The magnetization data are consistent with a model of a ⅓–⅔ ferrimagnetic spin arrangement. The B-B interaction, which is the resultant of the 90° Co++–F–Co++ and the direct Co++–Co+ interactions, appears to be strongly positive. Optical absorption data were used to determine the magnitude of the crystal field parameter Dq (870–880 cm−1) and the spin orbit interaction constant λ (190 cm−1). These data further indicate the strength of the crystalline field acting on the Co++ ion in the hexagonal structure, where ⅔ of the CoF6 octahedra share faces, is similar to that in ``cubic'' KCoF3 and RbCoF3 where they share corners.
High-Pressure Forms of CsNiF3
Authors: Longo J. M. , Kafalas J. A.
Published: February 2004

The atmospheric pressure form of CsNiF3 consists of hcp layers of CsF3 with F6 octahedra face-shared to form infinite chains along the c axis. CsNiF3 transforms at ∼5 kbars to a 9-layer stacking sequence with ⅔ of the layers hcp and ⅓ of the layers ccp while at ∼50 kbars it transforms to a 6-layer stacking sequence with ⅓ of the layers hcp and ⅔ of the layers ccp. Once formed, these phases are stable at atmospheric pressure to several hundred degrees C. The 9-layer phase is paramagnetic above 80°K with μeff=3.2 μB and Θp=−75°K. Trace amounts of a ferromagnetic material prevented further analysis below 80°K. The light-yellow 6-layer phase shows a ferrimagnetic Tc=111°K and a dTc/dp=0.53°K/kbar. The magnetic and optical properties are very similar to the isostructural RbNiF3.
Role of Magnetism in Technology
Authors: Jacobs I. S.
Published: February 2004

Magnetism applications permeate our whole modern society in its basics of electric power, communications, and information storage. Although the general public is mostly unaware of its role, magnetism has an economic impact of over 1% of the Gross National Product. The annual direct magnetic materials market is currently estimated at 650 million dollars, with dollar leadership shared by electrical steels and recording tape, followed by soft ferrites, magnetic disk packs and drums, permanent magnets, and nickel-iron alloys. The magnetism market is also described with reference to the role of research leading to quality improvement and to a growing list of new applications. It is estimated that the cost of basic and applied research (U.S.) is about 5% of the direct magnetics market. The world output of publications on magnetics has increased sixfold over the past decade after a plateau during the 1950's. During this same period magnetism has become more popular relative to a total science publication base and its scope has broadened in research, in discovery, and in application.
Magnetics in Memory
Authors: Pohm A. V.
Published: February 2004

Magnetic memory cells meet the essential logical and economic requirements1,2 of a memory cell and presently play a dominant role in electronically and mechanically accessed computer memories.3,4 Electronically addressed magnetic memories typically are arranged in 3D, 2D, or 2½D organizations.5–9 Progress in electronically addressed magnetic memories has resulted from a number of basic discoveries and developments in the threshold and switching properties of ferrite cores,10–12 planar thin films,13–15 and plated wires.16 As recently summarized,17,18 mechanically accessed memories such as tapes, drums, disks and data cells have had continual improvements in magnetic materials and in cell density. Present magnetic cells typically do not approach the limits set by thermal noise,19,9 and, as a consequence, a substantial increase in density is possible. The number of magnetic memory cells produced each year is increasing by more than 30% per year3 and continued growth can be anticipated.
Magnetism in Microwave Devices
Authors: Ridrigue G. P.
Published: February 2004

The functions of ferrite components in advanced microwave systems are briefly outlined, and the principal requirements described. The successful development of these sophisticated devices is the cumulative result of contributions from many areas of basic research and technology. As an example of the dependence of device performance on diverse efforts, the status and evolution of ferromagnetic digital phasers are reviewed. In this instance, materials research, ceramic technology, methods of numerical analysis, and the understanding of basic damping mechanisms have all contributed to the realization of practical devices. The application of ferrite devices to microwave integrated circuits is also outlined and some recent experimental results given. Other new trends in the field of microwave ferrite devices are briefly mentioned, as are areas most in need of further research.
Potentially Useful Properties of Magnetic Materials
Authors: Jarrett H. S.
Published: February 2004

Magnetism has played a vital role in the development of basic concepts of solid-state physics. Early research in magnetism was concerned largely with the reaction of the magnetization on external applied static and electro-magnetic fields. Indeed, technological developments in magnetism have utilized such behavior highly successfully. Today's trend in basic magnetics research emphasizes the interrelation of magnetism with other physical properties of solids. For example, magneto-electronic, -optical, and -electric properties of materials, the magnitude of the interaction, and how external fields coupled to the magnetization influence other properties is the subject of many of the basic papers in this Conference. This paper reviews current magnetics research with emphasis on the experimental observations. These effects provide a wealth of new material on which to base future technological applications.
History of the Geomagnetic Field
Authors: Doell Richard R.
Published: February 2004

Direct measurements of the direction and strength of the earth's magnetic field have provided a knowledge of the field's form and behavior during the last few hundreds of years. For older times, however, it has been necessary to measure the magnetism of certain rocks to learn what the geomagnetic field was like. For example, when a lava flow solidifies (at temperatures near 1000°C) and cools through the Curie point of the magnetic minerals contained in it (around 500°C) it acquires a remanent magnetism that is (1) very weak, (2) very stablel, (3) paralle to the direction of the ambient geomagnetic field, and (4) proportional in intensity to the ambient field. Separating, by various analytical means, this magnetization from other ``unwanted'' magnetizations has allowed paleomagnetists to study the historical and prehistorical behavior of the earth's field. It has been learned, for example, that the strength of the field was almost twice its present value 2000 years ago and that it has often completely reversed its polarity. Paleo-magnetists have also confirmed that most oceans are, geologically speaking, relatively new features, and that the continents have markedly changed their positions over the surface of the earth.
Transport Properties Near Magnetic Critical Points
Authors: Craig Paul P. , Goldburg Walter I.
Published: February 2004

In the last few years intense interest has developed in the nature of second-order phase transitions. Experimental and theoretical investigations have centered primarily on equilibrium properties. Transport or nonequilibrium properties are only now beginning to be intensively studied. Thus far there exists only very limited theoretical work in this area, and little experimental data for comparison. We review the theoretical and the experimental situation (excluding neutron diffraction) as it applies to magnetic systems. Scaling-law theory is summarized and the importance of the dynamic-scaling hypothesis is emphasized. An attempt is made to relate existing experiments to these scaling laws. We conclude that the closest contact between scaling theory and experiment at present comes in the prediction and observation of transitional behavior between the hydrodynamic regime far from the critical point, and the critical regime in which the fluctuation range becomes large compared to other characteristic lengths.
Laser-Beam Recording on a Magnetic Film
Authors: Treves D. , Hunt R. P. , Dickey B.
Published: February 2004

A method of recording digital information on a thin magnetic film is described. The change of magnetization in the film is accomplished by a coincidence of a high-power optical beam from a laser and a magnetic field. Films having coercive force ratios Hc(25°C)/Hc(150°C) of at least 3 were used as the media. Information was recorded with a 1 W Argon-Ion laser beam controlled by an electrooptic switch to provide spots down to 3.5μ diam. Photographs and electrical readout of tracks of written bits are presented.
Temperature-Sensitive Magnetic Film for a Magneto-optic Memory
Authors: Treves D. , Wolf I. W. , Ballard N.
Published: February 2004

Thin cobalt films, with low phosphorous content, electroplated on suitable substrates, at a pH of 6–6.5, have useful properties for thermomagnetic recording. They have a room-temperature coercivity, Hc(25°C) in excess of 200 Oe, Hc(25°C)/Hc(150°C) in excess of 3, and good working margins.
Development of a Closed-Flux Magnetic Memory Element
Authors: Carter W. S. , Greene F. S. , Wright J. D.
Published: February 2004

The fabrication and basic magnetic characteristics of a closed-flux memory element will be described. The element is made entirely by vacuum deposition and photoetching techniques. The element, which uses oxidized silicon as a substrate, consists of two 0.5-μ cobalt-Permalloy films deposited so that they overlap the bit line and provide flux closure in the easy direction. Partial flux closure in the hard direction is obtained by using a 1-μ ``keeper'' film. Tabs are included on the memory films to help reduce the reluctance through the SiO layer, which insulates the word lines from the bit lines. The problems involved in this development include: obtaining satisfactory insulation from the silicon, raising the Hc of the first magnetic film by a suitable undercoat, keeping the dispersion of the second magnetic layer and keeper film low by use of a smoothing coat, keeping the crystal size of the word and bit lines small during subsequent processing by using 95:5 Al–Cu alloy, and interlayer adherence, particularly the keeper layer.
Dynamic Magnetization Spread in Thin Magnetic Films
Authors: Lin Y. S.
Published: February 2004

The dynamic magnetization spread in a uniaxial film sheet excited by a pulse current in a strip line has been investigated by the application of the Landau-Lifshitz equation for distributed systems. A numerical solution is obtained from two coupled nonlinear integrodifferential equations. The key mechanism responsible for the wide spread of magnetization is: Different speeds in the gyromagnetic precession of spins in regions underneath and outside the strip result in nonuniform magnetization distribution which in turn causes propagation of the magnetization change at high speed (10 μm/nsec) through magnetostatic and exchange coupling. Direct measurements on the dynamic magnetization distribution are made with a nanosecond microscopic (3 nsec rise time, 25 μm resolution) Kerr apparatus. Experimental results are in good agreement with analytical predictions.
Life Expectancy of Plated Wire Memories
Authors: Brown R. G. , Richard R. T. , Narahara Y.
Published: February 2004

The life expectancy of DRO-plated wires was studied from various aspects by using an accelerated aging technique. Theoretical predictions regarding annealing processes were made by considering a structural defect model which assumes fixed and rotatable components of anisotropy with different activation energies. The predictions were verified experimentally under various annealing conditions. An extrapolation method to estimate the lifetime at operating temperature was established by adopting the Arrhenius equation. Activation energies were determined by using the rate of decay of output voltage under a worst-case DRO memory test as a criterion. Three activation energies were evaluated: (1) 1.3 eV for the zero applied field case, (2) 2.4 eV for a 36 Oe hard-axis field applied, and (3) 0.8 eV for fringing fields off the ends of a solenoid applying the 36-Oe hard-axis fields. The shelf life was extrapolated to be 2×106 years at 40°C. The dynamic test evaluated the lifetime under environmental conditions using a 256-bit experimental plane which was exercised, sensed, and data recorded at 150°C and the memory lifetime at operating temperature was determined by extrapolating the above results using the lowest activation energy projection. Therefore, memory working lifetime in DRO mode is estimated to be >100 years at 50°C with no dropouts, and >350 years at 50°C with a 5% dropout occurrence.
Stark Effects in Rutile Antiferromagnets
Authors: Halley J. Woods
Published: February 2004

We show that, as a consequence of the fact that the Bogoliubov transformation mixes spin waves on different sublattices, the phenomenological Loudon Hamiltonian describing the two spin-wave absorption in rutile antiferromagnets also predicts a linear Stark effect on the two spin-wave line in these materials in the presence of dc electric fields. We present calculated line shapes for ir absorption in a dc field. The dc field needed to observe significant effects is of order 106 V/cm. The Stark-effect experiment could be used to measure the parameter of the Loudon Hamiltonian, which is of interest from a theoretical point of view, since some mechanisms of two spin-wave absorption predict π2=0. The Stark effect also provides the possibility in principle of producing a phase transition in these antiferromagnets by the application of a dc electric field. This is the case because the shift in the spin-wave energy produced by the dc field can be negative for some values of k. We study this possibility in a simple approximation. The required fields are too large to be realizable in rutile antiferromagnets but there is some hope of observing such transitions in other kinds of antiferromagnets.
Multiple Magnons in the Absorption Spectra of Thin Slabs of MnF2 and KMnF3
Authors: Shapiro M. M. , Stevenson Richard
Published: February 2004

The spectra of thin slabs of single-crystal MnF2 and KMnF3 at low temperatures have been measured, both in the far infrared (40–360 cm−1) and in the visible (3850–4000 Å). The far infrared spectra consist of many sharp lines superimposed on a broad phonon background. The sharp lines are caused by processes involving the simultaneous creation of as many as 8 magnons, sometimes accompanied by the creation or absorption of standing elastic waves. In the visible spectrum, exciton lines with magnon sidebands are observed, accompanied by many weak satellite lines. The satellite lines correspond to processes in which as many as 30 magnons may be created simultaneously. For both substances, the observed lines in both spectra can be fitted to within experimental accuracy using combinations of only 3 single-magnon energies.
Temperature Dependence of the Local Mode in Cobalt-Doped MnF2
Authors: Holden T. M. , Buyers W. J. L. , Stevenson R. W. H.
Published: February 2004

The temperature dependence of the localized magnetic mode associated with cobalt impurities in MnF2 has been studied by neutron inelastic scattering methods. The frequency of the localized mode, relative to its value at the lowest temperatures, falls with increasing temperature less rapidly than the sublattice magnetization and also less rapidly than the frequencies of the band modes in the doped crystal. The frequency of the local mode falls from 3.57±0.05(1012 Hz) at T/TN=0.06 to 3.12±0.13(1012 Hz) at T/TN=0.84. Results have also been obtained for the temperature dependence of the relative intensities of the neutron groups associated with the local and band modes. Molecular field calculations show that the cobalt ion produces an enhancement, at elevated temperatures, of the thermal average value of the spin on neighboring manganese ions over that in the pure material. This leads to a temperature dependence of the local modes smaller than that of the sublattice magnetization, as observed.
Localized Magnetic Mode in MnF2:Fe2+ and MnF2:Co2+
Authors: Weber R.
Published: February 2004

We have observed a magnetic dipole-active localized mode in MnF2, doped with 0.04 mol% FeF2 at 94.8 cm−1 at 1.2°K, using an ir lamellar interferometer. To our knowledge, this is the first direct spectroscopic evidence using far ir techniques for a magnetic dipole-active impurity mode in an otherwise magnetically ordered system. The line has the following features: the half-width is 0.4 cm−1 and the absorption strength ∫αdv∼1 cm−2. With increasing temperature, the line shifts to lower frequencies and finally disappears at about 25°K. Magnetic fields up to 45 kG have been applied parallel to the c axis of the sample, yielding a linear splitting of the line. A g factor of 2.3 is derived from the data. The experimental results at 1.2°K can be understood satisfactorily both with a simple molecular field picture and, also, with the help of a simple spin-wave calculation. In the molecular field approximation, the line is correlated to a transition of the ground spin state to the first excited state of the orbital ground state of Fe2+. The observed value for the frequency is fitted by a Fe2+–Mn2+ exchange coupling constant J=1.9 cm−1 in both models. Preliminary results on a localized mode in MnF2:Co2+ are also reported.
Magnon-Optic Phonon Interaction in Antiferromagnetic CoF2
Authors: Allen S. J. , Guggenheim H. J.
Published: February 2004

Far infrared absorption experiments in the antiferromagnet CoF2 reveal a sharp, transverse magnetic-dipole absorption in the vicinity of 250 cm−1. The resonance is interpreted as the excitation of an Eg optic phonon. Normally inactive, this phonon may derive intensity from the strong spin-phonon coupling. The more interesting experimental results show that the linewidth narrows by more than a factor of 2 as the temperature is raised from 4.2°K to TN. The intensity drops abruptly at the Néel point but does not vanish at temperatures as high as 4.5TN. A theory of the temperature dependence of the transfer of magnetic dipole intensity to the Eg phonon has been derived. One contribution monitors the infinite-range longitudinal-spin correlation where as a second contribution is insensitive to ground-state correlations. Comparison between experiment and theory indicates that in CoF2 the correlation sensitive contribution is absent. The temperature variation of the intensity is caused solely by the change in magnetic excitation energies and the thermal population of these states.
Magnon-Phonon Interaction Observed in Far Infrared Studies of FeCl2·2H2O and CoCl2·2H2O
Authors: Hay K. A. , Torrance J. B.
Published: February 2004

A study has been made of spin waves in the antiferro-, ferri-, and ferromagnetic phases of FeCl2·2H2O. These levels are found to interact strongly with a field independent level at 31.5 cm−1. A similar interaction is found in CoCl2·2H2O near 29.3 cm−1. This field independent level has been tentatively identified as a k=0, low-lying optical phonon. This phonon appears to be infrared active only because of its coupling with nearby magnon levels. The experimental data for both materials is well described by a phenomenological magnon-phonon interaction.
Acoustoelastic Effect in Vitreous Silica, Pyrex, and T-40 Glass
Authors: Meitzler A. H. , Fitch A. H.
Published: February 2004

The phase velocities of acoustic shear-wave motions in isotropic solids such as glasses can be influenced by residual or applied stresses that make the material acoustically birefringent (the acoustoelastic effect) in much the same way as residual or applied stresses make a transparent material optically birefringent (the photoelastic effect). When a uniaxial stress is applied to an isotropic solid, the acoustoelastic effect depends upon μ, the shear modulus, and ν3, one of the three third-order elastic constants describing an isotropic solid. A method based on an analysis by Toupin and Bernstein is used to determine values of ν3 for four glasses: fused quartz and fused silica (two types of vitrous silica), Pyrex, and Bausch and Lomb T-40 glass. The values of ν3 obtained for vitreous silica and Pyrex are compared with previously reported values. Although the paper includes results for Pyrex and T-40 glass, the principal emphasis is on the results for vitreous silica and the significance of the findings regarding the acoustoelastic effect in vitreous silica for applications of this material in high-frequency ultrasonic devices.
Prediction of X-Ray Production and Electron Scattering in Electron-Probe Analysis Using a Transport Equation
Authors: Brown D. B. , Wittry D. B. , Kyser D. F.
Published: February 2004

The solution of a Boltzmann equation for electron transport is discussed with emphasis on its application to x-ray production and electron scattering in electron-probe microanalysis. Particular attention is given to the assumptions involved in associating an energy, a cross section for scattering, and a cross section for ionization with each position along the electron path. The Spencer-Fano theory of electron stopping power is applied. The treatment of electron scattering of Brown and Ogilvie is refined using (1) a single scattering equation for short path lengths, (2) a transport equation for intermediate path lengths, and (3) a diffusion equation for long path lengths. The predictions of this Transport Equation Program are compared with experimental data for (1) the energy distribution of backscattered electrons, (2) the depth distribution of x-ray production, and (3) x-ray intensity ratio as a function of alloy composition. The x-ray intensity ratios are corrected for fluorescence due to the continuum, and it is indicated that this correction may be significant.
Electron-Probe Microanalysis of Alkali Metals in Glasses
Authors: Vassamillet L. F. , Caldwell V. E.
Published: February 2004

The mechanism of alkali ion movement in glasses during electron-probe analysis must include a dependence on the temperature of the volume irradiated. Experimental results of the composition changes of binary oxide glasses of Na2O and K2O with SiO2 during electron bombardment indicate that there is a critical temperature for alkali ions in the diffusion process. Dependence of the critical temperature on composition and a comparison of these temperatures to the equilibrium temperature that can be produced from heat flow consideration indicates that for small beam diameters the actual temperature may be lower than that predicted. The rate of change of temperature may be more important to a probe operator than the equilibrium temperature.
Etching and X-Ray Topography of Flux-Grown Magnetic Garnets
Authors: Belt Roger F.
Published: February 2004

Internal growth defects of high-quality garnet crystals were studied by selective etchants and Lang x-ray transmission topography. Terminal growth sections contained the fewest defects and dislocation densities were 102−104/cm2. Internal sections revealed both randomly dispersed etch pits and linear arrays. The latter were frequently found in the form of parallel grids. Results indicated that {100}, {111}, {411}, and {105} were the defective planes. X-ray topographs verified that parallel linear faults are present in crystals on these same planes. The faults are not dislocation lines but tubular structural deviations caused by flux precipitation or other compositional changes. The origin and arrangement of the internal faults are related to fluctuations of the crystal growth rate. The rate changes can be initiated by small thermal gradients in the solution.
Morphology of Unstable Ice Cylinders
Authors: Coriell S. R. , Hardy S. C.
Published: February 2004

The wavelengths of sinusoidal perturbations in the shape of single-crystal ice cylinders growing in supercooled water have been measured as a function of the experimental variables, primarily bath supercooling. The experimental results are in good agreement with theory.
Electron Microscope Studies of the Deviation of a Stress-Annealed Pyrolytic Graphite Matrix from a Single Crystal
Authors: Roscoe C. , Baker J.
Published: February 2004

By means of a preferential etch technique in conjunction with transmission electron microscopy, a stress-annealed pyrolytic graphite has been shown to be a compact of crystallites with La values typically lying in the range 1–40 μ. The boundaries defining these crystallites varied from the low-angle tilt boundaries θ∼1′, found in Ticonderoga crystals, to high-angle boundaries denoting misorientations of up to 30°. In contrast to the low over-all boron concentration of the material, 1–2 ppm wt/wt, the concentration of this element residing in the intercrystallite boundaries was calculated at ∼103 ppm wt/wt. This provides confirmation of the premise that the lattice disorder existing across a boundary trace supports a vacancy concentration far in excess of that pertaining to more perfect regions of the graphite. It is postulated that at temperatures >2100°C this enhanced vacancy concentration will allow a dynamic interchange mechanism for crystallite growth, having an activation energy given by E* = ½(Efv + Efi) + Emai. Nonbasal screws have a deleterious effect on the rate of graphitization for two principal reasons. First, the nonbasal screws residing in intercrystallite boundaries effectively stabilize the excessive vacancy concentration at the latter sites. Second, if the distance of closest approach of these dislocations becomes less than some critical value, they may be responsible for creating new boundaries. As it appears unlikely that many formal boundaries, which can be described in terms of lattice defects, will exist between neighboring crystallites in pyrolytic graphite, the initial stages of graphitization must occur by an alternative mechanism. The recent work of Murty would seem to imply that the latter is in fact an interstitial mechanism, having an activation energy of 9.8±0.7 eV as compared to the value of 8.3±0.3 eV predicted for the dynamic interchange mechanism.
Spontaneous Polarization Measurements in Several Ferroelectric Oxides Using a Pulsed-Field Method
Authors: Camlibel I.
Published: February 2004

The room-temperature spontaneous polarizations in LiNbO3, LiTaO3, Ba2NaNb5O15, Sr0.5Ba0.5Nb2O6, Ba1.1Sr0.9NaNb5O15, and Sr2KNb5O15 have been measured directly by a pulsed field method using an aqueous solution of LiCl as the electrode material. The experimental results are: P8 (LiNbO3) = 0.71±0.02 C/m2, P8 (LiTaO3) = 0.50±0.01 C/m2, P8 (Ba2NaNb5O15) = 0.40±0.01 C/m2, P8 (Ba1.1Sr0.9NaNb5O15) = 0.36±0.01 C/m2, P8 (Sr2KNb5O15) = 0.25±0.01 C/m2, and P8 (Sr0.5Ba0.5Nb2O6) = 0.25±0.01 C/m2. Experimental techniques are presented, and the advantages of the pulsed-field method over hysteresis-loop methods are discussed.
Temperature Variation of the Piezoelectric Constant of Quartz
Authors: Mullen Anthony J.
Published: February 2004

The variation of the piezoelectric constant d11 of quartz has been measured from 22°C to near the transition temperature 573.3°C (highest recorded measurement, 565°C). The quartz was mounted on a metal anvil and its piezoelectric response was excited by dropping a steel ball onto the center of the quartz disk. At room temperature, a value of d11 was found to be −2.16×10−12 C/N with a standard deviation of 0.11×10−12. From 20°–200°C, the magnitude of d11 decreases linearly at −4.5% per hundred degrees, in close agreement with the behavior observed by Langevin. Above 200°C, the value decreases sharply, following a smooth curve and reaching zero in the near vicinity of 573.3°C.
Lateral Diffusion in Ag–Te Thin-Film Couples
Authors: Johnson D. B. , Brown L. C.
Published: February 2004

The lateral diffusion of Ag along a thin evaporated Te film has been studied by optical and electron microscopy. Diffusion occurred only when the Ag was at least 1.0 times the Te thickness, corresponding to the presence of sufficient Ag to form Ag2Te in the diffusion zone. Electron microscopy of the diffusion zone showed considerable grain-boundary diffusion and this was in agreement with the observation that the growth rate had a maximum at a Te film thickness of about 80 Å when the Te structure had an optimum number of grain-boundary paths. The activation energy for the diffusion process was found to be 10.0 kcal/mole.
Enhancement of Photon-Bunching Effects
Authors: Aldridge Melvin D.
Published: February 2004

An analysis is presented which shows that photon-bunching effects in a spatially coherent noise field can be enhanced by the superposition of a monochromatic coherent ``signal'' and/or by shaping the spectrum of the incident noise. For a Lorentz spectral shape, the addition of ``signal'' to noise is shown to increase bunching effects by a factor no greater than 4. By changing the noise spectrum from a Lorentz to a rectangular shape, bunching effects are shown to increase by a factor of 2 despite the fact that total incident noise power decreases. In all cases, the ratio of bunching noise to shot noise is proportional to the average number of detected noise photons per cycle of noise bandwidth. For the specific problem analyzed, the maximum value of the ratio of bunching noise to shot noise is determined. In the absence of ``signal,'' the results are found to agree with the exact distribution of Bèdard.
Numerically Calculated Properties of a Wall-Stabilized Electric Arc
Authors: Hodnett P. F.
Published: February 2004

Some properties of a static electric arc in a circular cylindrical tube are calculated numerically. The radiative influence in the problem is accounted for in a simplified way, and the assumed variations with temperature of the radiated power density, electrical conductivity, and thermal conductivity represent an attempt to cover the whole range of conditions from a weakly ionized gas to a fully ionized gas. With these theoretical expressions for the gas transport properties (i.e., thermal conductivity, etc.), it is possible to calculate the temperature distribution in the arc and, hence, the voltage gradient-current characteristic of the arc and to compare the results with experimental results. The distinct disagreement between these theoretically produced results and experimental results seems to indicate a fundamental discord between the theoretical expressions for the gas-transport properties, and their experimental values, that merits further investigation. The calculations also indicate that the arc is heat-conduction dominated at very high currents (as well as at very low currents).
Marginal Stability in Inhomogeneous Porous Media
Authors: Green Theodore , Freehill Robert L.
Published: February 2004

Marginal stability is examined in a saturated porous layer of thickness h heated from below, in which the permeability k and the thermometric conductivity K* vary markedly in the vertical direction. A straightforward perturbation treatment, with numerical solutions provided by a digital computer, shows that the over-all temperature gradient [T(0) − T(h)]/h necessary for marginal stability is independent of the directions of increase of k and K*, and decreases noticeably with increasing changes of k and K* over the layer. The horizontal wavelength of the first unstable mode is found to decrease somewhat less rapidly with increasing changes in k and K*.
Dynamics of a Gas Bubble Moving in an Inviscid Liquid Subjected to a Sudden Pressure Change
Authors: Yeh Hsu-Chieh , Yang Wen-Jei
Published: February 2004

A gas bubble moves with constant translatory velocity in a quiescent liquid. Its shape deviates from sphericity due to asymmetrical forces exerted upon its surface. Then the liquid pressure undergoes a step change. It is the purpose of the study to analytically predict the time history of the bubble size, translatory velocity, and deformation. The mechanisms involved in the acceleration of the translatory motion and in the growth or collapse rate of the bubble are discussed.
Pressure and Temperature Dependence of the Acoustic Velocities in Polymethylmethacrylate
Authors: Asay James R. , Lamberson Donald L. , Guenther Arthur H.
Published: February 2004

The acoustic velocities in polymethylmethacrylate have been measured with an ultrasonic pulse-echo technique as functions of frequency, temperature, and pressure. At atmospheric pressure, data on the velocities and attenuation coefficients were obtained for the temperature range of 22°–75°C in the frequency range of 6–30 MHz. For the measurements of velocity and attenuation as a function of frequency, the complex adiabatic bulk modulus was calculated at room temperature and atmospheric pressure for the above frequencies. At temperatures of 25°, 40°, 55°, and 75°C, the pressure dependence of the longitudinal and shear velocity was determined to 150 kpsi at a frequency of 6 MHz. It was found that the measured velocities under increasing pressure conditions were generally lower than those of decreasing pressure by about 0.5% for the longitudinal measurements and about 1% for the shear measurements. However, measurements of the velocities at atmospheric pressure after the specimens had been exposed to 150 kpsi were usually within 0.1% of the initial values. A discussion is presented which compares the continuity of the present data with equation of state determinations in PMMA at elevated pressures.
Characterization of Linear Viscoelastic Materials Tested in Creep and Relaxation
Authors: Gradowczyk M. H. , Moavenzadeh F. , Soussou J. E.
Published: February 2004

The experimental creep and relaxation functions determined by a set of independent experiments may not fulfill identically the equation ∫ 0tE(τ)D(t−τ)dτ=tof linear viscoelasticity, where E(t) and D(t) are the relaxation modulus and creep compliance, respectively. The consistency of the experimental data can be improved by the introduction of appropriate error functions. Two different methods have been suggested in order to compute the error functions so that the above equation is satisfied. In Method I, the error function is a solution of a Volterra nonlinear integral equation which is solved by a numerical procedure. In Method II, the error functions are defined in the Laplace domain; the application of the convolution theorem reduces the determination of the error functions to the solution of an algebraic equation. These methods are applied to creep and relaxation tests performed on a sand-asphalt composite. The computations show the extent of the improvement achieved by making the transient functions D(t) and E(t) consistent.
Double-Shock Method for Detecting Pressure Limits of Magnetic Phase Transitions
Authors: Wong J. Y.
Published: February 2004

A double-shock method for detecting pressure limits of magnetic phase transitions in solids was developed. Its performance was found to be very satisfactory when applied to the dynamic α→(ε, γ) polymorphic transition of iron.
Color Centers and Ruby-Laser Output-Energy Degradation
Authors: Stickley C. M. , Miller H. , Hoell E. E. , Gallagher C. C. , Bradbury R. A.
Published: February 2004

The use of lasers in rangefinding and other applications requires that the laser be capable of being fired many times without its output characteristics changing substantially. A gradual reduction in ruby (Cr3+ in Al2O3) laser output energy has been observed during repeated firing of the laser. This degradation is found to occur with varying degrees of severity in all ruby rods tested. We have traced this to the formation of color centers within or on the surface of the ruby rod: defects, impurities, etc., present before exposure can be converted into color centers by the blue and ultraviolet content of the pumplight. Conversion of Cr3+ to other valence states is very small, amounting to less than 1% of the total Cr3+ density (the sensitivity of the measurement) for most samples and to 3% for one vintage of ruby. The radiation induced absorption which was found agrees well with x-ray induced color-center absorption in undoped α-Al2O3 rather than absorption by Cr2+ or Cr4+. We have shown that the subsequent pump light absorption by these color centers, which serves to deplete the pumping energy internally in the rod and to cause bulk absorption loss at 6943 Å, fully explains the degradation observed to within the limits of experimental error. A reliable indicator of color center formation is the orange-brown appearance which develops in the ruby; only a partial restoration of output energy can be achieved by heating the rods at 900°C for 24 h; the use of pyrex to filter the ultraviolet from the pump light can reduce but not eliminate the rate of energy decay. The contribution of this work is that we have determined the principal mechanisms out of several possible ones which explains the energy decay observed in U.S. grown ruby samples. The complete solution to this problem will be known when it is understood how to prevent color center formation in Al2O3 upon ultraviolet irradiation.
Optimum Stripe Width for Continuous Operation of GaAs Junction Lasers
Authors: Dyment J. C. , Ripper J. E. , Zachos T. H.
Published: February 2004

The continuous (cw) operation of 41 GaAs junction lasers bonded on identical copper heat sinks is investigated for different widths of the stripe metallic contact (S = 5.0, 12.7, 25.4, and 50.8 μ). The highest cw operating temperatures are consistently found for S = 12.7 μ. This behavior is in agreement with computer calculations which predict an ``optimum'' stripe width between 10 and 15 μ and a sharp reduction in cw operating temperature for S < 10 μ. The calculations are based on experimentally measured threshold current densities (Jth) at 77° and 297°K which show that Jth increases by factors of 2 or 3 when S is reduced from 12.7 to 5.0 μ. Intensity scans of mode patterns at the laser mirrors suggest that these increases in Jth are due to the effect of the unpumped regions along the junction plane on the laser mode.
Critical Currents and Current Distributions in Josephson Junctions
Authors: Matisoo J.
Published: February 2004

This paper discusses the dependence of IJ, the maximum zero-voltage current, on magnetic fields for a series of Josephson junctions of differing size when compared with λJ, the Josephson penetration depth. The experimental results are in excellent agreement with the calculations; in particular, for junctions with L≫λJ, the Meissner effect and overlapping vortex structure are clearly demonstrated. The current density distributions are also shown. Finally, the implications of size dependence for tunneling cryotron devices is discussed.
Electroluminescence of Diffused GaAs1 − xPx Diodes with Low Donor Concentrations
Authors: Herzog A. H. , Groves W. O. , Craford M. G.
Published: February 2004

The optical and electrical properties of electroluminescent diodes formed by Zn diffusion into vapor epitaxially grown substrates with donor concentrations in the range 1016–1017 cm−3 have been studied. This doping range, which is somewhat lower than has been previously investigated in the GaAs1−xPx alloy system, has been found to be the optimum range for the fabrication of high efficiency diodes. The spectral emission is appreciably different than has been previously observed. Throughout the alloy composition range at 300° and 77°K a high energy peak occurs within ∼20 meV of the conduction bandedge, and at 77°K a second peak ∼30 meV lower in energy is present. Donor-acceptor-pair recombination peaks similar to those observed in GaP, located ∼0.1 and ∼0.37 eV below the bandedge, are found to occur and remain the same distance below the bandedge throughout the indirect region of alloy composition. At 300°K direct recombination from the higher lying k = 0 minimum is observed to persist into the indirect gap alloy composition region. Diode fabrication techniques were found to have a strong effect on the shape of the spectral emission curves.
Absorption and Dispersion in Porous and Anisotropic Polycrystalline Ferrites at Microwave Frequencies
Authors: Vrehen Q. H. F.
Published: February 2004

In polycrystalline ferrites the relaxation of ferromagnetic resonance is often considerably increased by the random variations in the orientation of the anisotropy fields in different grains and by the presence of pores. The magnitude of this relaxation has been calculated most often in terms of scattering to spin-waves, and the theories have been tested experimentally by measurements of the ferromagnetic resonance linewidth as a function of frequency or sample shape. In this paper it is discussed how an effective linewidth W and shift S of the resonance field can be derived from a measurement of the tensor susceptibility χ+, over a wide range of the applied magnetic field at a given frequency. The measuring apparatus is described and experimental results are presented for Ni0.36Zn0.64Fe2O4 with porosities from 0.2% up to 19%, and for a dense material of NiMn0.05Fe1.95O4, at a frequency of 9005 MHz, and applied magnetic fields from 1500–8000 Oe. These results are compared with the predictions of the spin-wave model. Spin-wave effects are clearly observed in anisotropy broadening as well as in porosity broadening. However, the perturbation of the spin-wave manifold itself, respectively, by the nonuniformity of the anisotropy fields and by the inhomogeniety of the static demagnetizing fields around a pore, must be taken into account. The dependence of the relaxation parameters S and W on the applied magnetic field is modified significantly by this perturbation, particularly in the case of porosity broadening.
Ferromagnetic Resonance Shift in a Ferrite Disk
Authors: Sawado E.
Published: February 2004

A theory of some general features on the shape effects in ferromagnetic resonance is presented. Calculations and measurements have been made of the shift of the ferromagnetic resonance frequency in the presence of the excited spin waves with long-wavelength limit. It is found that the consideration on the contribution from the local demagnetization fields may be of decisive importance in analyzing the shape effect in the ferromagnetic resonance phenomena.
Magnetic Structure of MnAlGe
Authors: Murthy N. S. Satya , Begum R. J. , Somanathan C. S. , Murthy M. R. L. N.
Published: February 2004

The ternary alloy MnAlGe has been studied by diffraction techniques using both neutrons and x rays. The unit cell is found to be tetragonal with a0 = 3.914±0.001 Å and c0 = 5.933±0.001 Å. The space group is D4h7-P4/nmm. The intensities in the neutron-diffraction patterns agree with a ferromagnetic spin alignment of the Mn atoms with a magnetic moment of 1.40±0.12 μB each. The magnetic field dependence of the diffracted neutron intensities reveal a high magnetic anisotropy and a high retentivity.
Scattering of Highly Focused Kilovolt Electron Beams by Solids
Authors: Nosker R. W.
Published: February 2004

A study has been made to determine the resolution limitations of electron beams interacting with thin films, due to scattering in the film and substrate. For a typical film thickness of 3000 Å, and an incoming Gaussian electron distribution with half-amplitude at 1500 Å radius, forward-scattering becomes significant for solids with atomic number Z≳20. Back-scattering from a substrate produces negligible resolution loss, and in fact heavy substrates may be used to advantage to increase electron densities in the thin film. Computer programs have been written that are capable of determining scattering data for a large range of materials and incident electron conditions.
Fluorescence Spectra of Anthracene and Naphthalene Excited by Giant-Pulse Ruby Laser
Authors: Jaseja T. S. , Parkash Ved , Dheer M. K.
Published: February 2004

The fluorescence spectra of anthracene and naphthalene in the visible region, when excited by a giant-pulse ruby laser, were recorded. The spectrum of anthracene consisted of four very broad bands extending from blue to violet. In the case of naphthalene, the spectrum consisted of comparably much sharper bands extending from blue to deep violet. Two-photon excitation from vibrationally excited levels of the ground electronic state is believed to be the process involved in producing the fluorescence in naphthalene.
Electron Density in Mixed Gas Plasmas Generated by Fission Fragments
Authors: Rees D. B. , Leffert C. B. , Rose D. J.
Published: February 2004

Studies of electron density are reported for a quiescent neon-argon gas plasma generated by fission fragments in the core of a nuclear reactor. Reaction kinetic equations for the various ionic and excited species are solved self-consistently with electron-energy balance equations to yield values of electron density and temperature. It is shown that for containers of diffusion length of about 1.6 mm or greater, there exists a maximum value of electron density at a total gas pressure p≈90 Torr and [Ar]/[Ne]≈10−4; the dominant ion in this case is the atomic Ar+ ion. At low values of neutron flux (∼1010 cm−2 sec−1) and electron density (∼1010 cm−3), the electron temperature is computed to be at or near the gas temperature, but at high values of neutron flux (∼1013 cm−2 sec−1) and electron density (∼1012 cm−3), the electron temperature is higher than the gas temperature by an important amount (∼600°K). Inpile measurements of electron density using microwave techniques are in very good agreement with the theoretical predictions.
Derivation of an Equivalent Dielectric Tensor for a Warm, Drifting, Lossy, Electron Plasma
Authors: Articolo George A.
Published: February 2004

The equivalent dielectric tensor for an unbounded, beam-electron plasma system is derived in detail. The plasma model simulates that plasma found in the positive column of low pressure, weakly ionized discharges. Electron stream drift, electron-electron thermal interactions, and velocity dependent electron-neutral collision interactions are included in the model.