bluuebunny/crossref_metadata_2025 huggingface dataset:
A Stability Function for Explicit Evaluation of the Mullins-Sekerka Interface Stability Criterion
Authors: Sekerka R. F.
Published: April 2005

A stability function 𝒮 for explicit evaluation of the Mullins-Sekerka interface stability criterion is introduced and tabulated. Their criterion is then written in terms of 𝒮 and compared with the constitutional supercooling criterion for interface stability. From these results, experimental data can be analyzed and a conclusive test of the stability theory can be made.
Performance of the He–Ne Gas Laser as an Interferometer for Measuring Plasma Density
Authors: Ashby D. E. T. F. , Jephcott D. F. , Malein A. , Raynor F. A.
Published: April 2005

The characteristics of the He–Ne gas laser used in a new simple interferometric technique have been studied experimentally and theoretically. The interferometer has two novel features: first, the intensity of the laser itself is used to detect the fringes and second, because the intensities of the 0.63-μ (red) and 3.39-μ (infrared) laser beams are coupled, interference in the infrared can be detected by a simple photomultiplier monitoring the red beam.

The system does not respond instantaneously to changes in the optical path length; experimental measurements show that when the red beam is used to follow interference in the infrared, the maximum detectable response is limited to about 3×106 fringes per second. Discussion of the frequency response and the cross-coupling between the two wavelengths leads to the conclusion that the frequency response is limited by the red channel only.

Experimental details of the interferometer are described, including the application of a multipass system which, with some loss in spatial resolution, increases the sensitivity of the interferometer by at least a factor of 20.
Growth of Seeded Copper Crystals of Perfection Comparable to Unseeded Crystals
Authors: Dyer Lawrence D.
Published: April 2005

A graphite mold of a new design was made for growing better seeded crystals from the melt. The main features were (1) a narrow seed constriction, (2) a split mold, (3) high density graphite, (4) equal cross sections of seed and crystal, and (5) high ratio of sample to mass crucible mass.

The resulting crystals were compared by two complementary techniques with those grown in a conventional mold. An improvement of at least a factor of ten was obtained. The best crystals thus far have 1−2×104 etch-pit sites/cm2 intersecting the {100} surfaces, and are free from subboundaries. This brings the level of perfection of as-grown seeded crystals up to that of unseeded ones thereby making them useful in dislocation etch-pit studies.
Observations on the Morphological Changes in Thin Copper Deposits during Annealing and Oxidation
Authors: Bachmann Luis , Sawyer David L. , Siegel Benjamin M.
Published: April 2005

Thin copper films were deposited in an ultrahigh vacuum on carbon and silicon monoxide substrates at room temperature. Their morphological changes after annealing and oxidation were investigated by electron microscopy and electron diffraction. The changes during annealing of very thin deposits (<50 Å mean thickness) are strongly influenced by the substrate. The copper on carbon substrates grows into large crystallites during heat treatment at 500°C whereas on silicon monoxide substrates very little recrystallization occurs. During the annealing of thicker deposits of copper, self-diffusion of the metal can take place and the change in structure of the heat-treated film is independent of the substrate. The structures of the cuprous oxide particles formed during exposure to different pressures of oxygen at 150° to 200°C indicate that different transport mechanisms are involved in the oxidation process at very low oxygen pressures from those at pressures above 10−2 Torr.
Thermal Decomposition of Gallium Arsenide
Authors: Millea M. F. , Kyser D. F.
Published: April 2005

Single crystals of GaAs containing Ga{111}, As{111}, and {110} faces decomposed at rates between 4×10−2 and 1×10−3 times the free evaporation rates were examined microscopically. At these high values, the decomposition rate is observed to be orientation dependent in the order As{111}>Ga{111}, as previously reported. The {110} face decomposes at a rate intermediate between the As{111} and the Ga{111} faces. At our high decomposition rates, the As{111} faces are completely corroded in a noncrystallographic manner, while crystallographic decomposition pits are produced on the Ga{111} face. At low decomposition rates, the degree of decomposition on all three faces appears equal and decomposition pits made up of {111} faces are formed. Surface kinks produced by mechanical damage and chemical etch pitting act as nucleation sites for decomposition pits. Dislocations do not serve as nucleation sites for decomposition pits. A model that accounts for the experimental observation is presented.
Long-Transient Effects in Lasers with Inserted Liquid Samples
Authors: Gordon J. P. , Leite R. C. C. , Moore R. S. , Porto S. P. S. , Whinnery J. R.
Published: April 2005

Buildup and decay transients were observed when polar or nonpolar liquid cells were placed within the resonator of a helium—neon laser operating in the red at 6328 Å. Similar but smaller effects were also observed with two solids. Time constants were the order of a few seconds for all materials, which suggests a thermal phenomenon, but general heating effects were ruled out by the strong localization of the phenomenon. Transverse motion of the cell by about one beam width caused new transients similar to the initial ones.

It is believed that the effects are caused by absorption of the red light in the material, producing a local heating in the vicinity of the beam and a lens effect arising from the transverse gradient of refractive index. Absorptions of 10−3 to 10−4 parts per centimeter are sufficient to produce the effects, and are believed to be reasonable values for the materials studied. One of the most important applications may in fact be for the measurement of small absorbancies.

The experiments are described, and analysis of the lens effect from absorption is given. Alternate explanations which were considered are stated briefly.
Stability of Arcs in Gases
Authors: Farrall George A. , Cobine James D.
Published: April 2005

A study has been made to determine the average duration of dc arcs in various gases at slightly higher than atmospheric pressure. These arcs were drawn between ¾-in. copper contacts with power being supplied from a 125-V dc generator. The experimental vessel, which contained about 1 liter volume, was provided with two liquid-nitrogen traps through which gas was admitted and withdrawn. The gases studied were hydrogen, helium, argon, nitrogen, oxygen, and sulfur hexafluoride. It was found that in the current range studied (about 1 to 45 A) arc duration was always statistical and finite. This behavior is similar to that observed earlier for metal vapor (vacuum) arcs. For a given current, average arc duration increased for those gases in the order listed above. In the case of the latter two (O2, SF6), arc stability is believed to have been strongly affected by arc reaction products. It was concluded that for each of the gases studied, arc duration was greater than that found for a copper vapor arc at the same current, using the same generator source. It is believed that the gases blanket the cathode surface during the arc and reduce the loss of metal vapor from cathode emission sites below that occurring in the vacuum arc. There has been strong evidence in earlier work that abundant metal vapor at the arc cathode enhances arc stability.
Magnetic Hysteresis in Superconducting Thin Films
Authors: Caswell Hollis L.
Published: April 2005

Tin films were deposited from the vapor at various substrate temperatures and their superconducting properties determined as a function of film structure. Magnetic hysteresis in the superconducting state to normal state phase transition of these films increased with increasing grain size. Hysteresis could be attributed solely to supercooling only in the smaller-grained films deposited at low substrate temperatures. For the larger-grained films, superheating was also observed. The hysteresis observed experimentally was in agreement with the predictions of the Ginzburg-Landau theory of superconductivity.
Effect of Cesium Fluoride on a Cesium Vapor Diode
Authors: Skeen C. H.
Published: April 2005

A cesium vapor diode was operated both before and after cesium fluoride was introduced into the interelectrode space. The electrodes were plane parallel, had a cross-sectional area of 2 cm2, and were made of molybdenum having a polycrystalline surface. The interelectrode spacing was varied from 0.01 to 10 mm. The cesium fluoride vapor additive caused an increase in the optimized output power density. For a given emitter temperature this enhancement increased with spacing until the spacing reached about 0.89 mm, after which it became uniform. The enhancement decreased with an increase in emitter temperature. The increase averaged about 20% for a combination of these cases. When all parameters were held constant except the cesium fluoride reservoir temperature, an increase in the additive vapor pressure caused the enhancement to decrease. The optimum collector temperatures decreased up to 2% after the cesium fluoride addition. The optimum cesium vapor pressures were decreased by about 15°K after the CsF addition.
Magnetic and Crystallographic Studies of Substituted Gadolinium Iron Garnets
Authors: Geller S. , Williams H. J. , Sherwood R. C. , Espinosa G. P.
Published: April 2005

Magnetic data from measurements at moderate to high magnetic fields in the temperature range 1.4° to 300°K, lattice constants, and preparative data are reported for the systems {Gd3}[ScxFe2−x](Fe3)O12, {Gd2Y}[ScxFe2−x](Fe3)O12, {Gd3−xCax}[Fe2] (Fe3−xSix)O12, {Gd3−xCax} Fe5−xGexO12, {Gd3}Fe5−xAlxO12, {Gd3}[MgxFe2−x] (Fe3−xSix)O12, and for the three garnets {Gd2Ca}[ZrFe](Fe3)O12, {Gd0.6Y2.4}[ScFe](Fe3)O12, and {GdCa2}[Zr2](Fe3)O12.

The following model for the general features of the 0°K magnetic structures of the substituted gadolinium iron garnets is proposed. At 0°K, gadolinium iron garnet itself is an ideal Néel ferrimagnet. The moments of the octahedral Fe3+ ions and of the dodecahedral Gd3+ ions are strictly antiparallel to the moments of the tetrahedral Fe3+ ions. Replacement of some of the octahedral Fe3+ ions by nonmagnetic ions such as Sc3+ ions as in {Gd3}[ScxFe2−x](Fe3)O12 causes random canting of the tetrahedral Fe3+ ions. Because the strong interactions of the Gd3+ ion moments are with those of the tetrahedral Fe3+ ion moments, this leads also to random canting of the Gd3+ ion moments thereby reducing the contribution of the dodecahedral sublattice to the net spontaneous moment of the garnet. Replacement of the tetrahedral Fe3+ by nonmagnetic ions as in {Gd3−xCax}[Fe2] (Fe3−xSix)O12 causes random canting of the octahedral Fe3+ ion moments, but this is not expected to affect the alignment of the Gd3+ ion moments. Such substitution appears to have the effect of removing from contribution to the net moment, those Gd3+ ions which are not linked through oxygen atoms to at least one tetrahedral Fe3+ ion.

A comparison of the results on the systems {Gd3}[ScxFe2−x](Fe3)O12 and {Gd2Y}[ScxFe2−x](Fe3)O12 indicates that at or very near 0°K, the interaction in the dodecahedral sublattice appears to have a ferromagnetic component. Also the garnet {GdCa2}[Zr2](Fe3)O12 appears to be a weak ferromagnet.
Noise Transformation and Cyclotron Waves in Crossed Fields
Authors: Rowe J. E. , Wadhwa R. P.
Published: April 2005

A transmission-line analog is developed for crossed-field space-charge flows from the simultaneous solution of Maxwell's equations, the Lorentz force equation, and the continuity equation. A thin one-dimensional injected beam is assumed. The resulting fifth-degree secular equation is solved for several values of ωc/ωp. The five system waves consist of a pair of hybrid waves, a pair of near-cyclotron waves and a near-synchronous wave. The results indicate that noise transformers may be based on an equivalent piecewise uniform transmission line.
Effect of Holes on the Elastic Constant C′ of Degenerate p-Type Si
Authors: Csavinszky P.
Published: April 2005

A generalized theory of the dependence of the elastic constant C′ of heavily doped p-type Si on hole concentration is presented. The strain dependence of the valence subband shifts is assumed to be an admixture of terms linear and quadratic in the strain. The theory accounts for the measured values of δC′=C′doped −C′pure and it is consistent with a constant value of the shear deformation potential constant Ξs′. This is an improvement over previous results, based on purely linear subband shifts in strain, where the interpretation of the experimental data required the assumption of a hole-concentration-dependent deformation-potential constant.
Basic Equations and Conservation Theorems for the Electrostriction Phonon Maser
Authors: Haus H. A. , Penfield Paul
Published: April 2005

Brillouin scattering of light by phonons and the phonon maser are usually described in terms of an approximate set of linearized equations. Here we give a more exact set of equations for a lossless polarizable fluid; only relativistic effects are disregarded. When these equations are linearized and higher order terms in the ratio of sound speed to light speed are disregarded, they reduce to the customary set of equations. The more exact equations permit the derivation of the law of conservation of energy with a simple physical interpretation. From these equations the Manley-Rowe relations and other conservation laws also follow relatively easily.
Absolute Determination of Refractive Indices of Gases at 47.7 Gigahertz
Authors: Newell A. C. , Baird R. C.
Published: April 2005

The refractive index of a gas is determined to high accuracy by measuring the change in the resonant frequency when the gas is admitted to a previously evacuated microwave cavity. This measurement was made at a frequency of 47.736 GHz, and is the first such measurement in this frequency range.

The resonant frequency of the cavity is detected by means of a hybrid tee bridge circuit. When the cavity is matched to the waveguide the null at resonance is very sharp, and the frequency can be set to ±5 parts in 108.

Two types of resonant structures were used in this measurement, a conventional cylindrical cavity and a Fabry-Perot resonator using one plane and one spherical mirror. Measurements were made with both structures on each of the gases, and the agreement between the two was within the limits of experimental error. Because the Fabry-Perot resonator has no side walls, air could be passed through it much more easily, and it is therefore preferred for use with moist air.

The values of (n−1)×106 for the gases at 0°C and 760 Torr are as follows: Dry CO2 free air288.13±0.05,Argon277.48±0.05,Carbon dioxide495.16±0.08,Helium34.51±0.05,Hydrogen135.77±0.05,Nitrogen293.81±0.07,Oxygen266.95±0.05.

The primary values of these results lies in their increased accuracy over previous measurements and their confirmation of existing accurate data on these gases. In addition the use of the Fabry-Perot resonator as a refractometer is demonstrated and its advantages under certain conditions discussed.
Measurement of Brine Droplet Migration in Ice
Authors: Harrison J. D.
Published: April 2005

Migration of NaCl, KF, and KI droplets through ice was measured in the temperature interval from −6° to 0°C in the presence of a 15°C/cm thermal gradient. Normally the droplets increased in velocity and size as they approached the ice-water interface. A 30-μ-diam droplet migrating at 0.3 μ/sec at −5°C would be 65 μ in diam and migrating at 1.2 μ/sec at −½°C. Special phenomena observed were droplet elongation, diagonal migration, and constant-velocity migration.
Effect of Hydrostatic Pressure on the Curie Points of Several Ferrites
Authors: Foiles C. L. , Tomizuka C. T.
Published: April 2005

The effect of hydrostatic pressure on the Curie temperature Tc was measured for four members of a Ni–Zn ferrite series (30%, 50%, 80%, and 100% NiO) and for two members of a gadolinium-iron-garnet series (Gd3AlFe4O12 and Gd1.5Y1.5Al0.5Fe4.5O12). A transformer technique was used for the measurements with the maximum pressure available being 8 kbar. The Curie temperature showed a linear increase with pressure and the slopes ranged from 0.58±0.05 to 1.16±0.07°C/kbar. The approximate Curie points varied from 153°C (Gd3AlFe4O12) to 616°C (100% NiO ferrite). The samples with Tc less than 400°C were measured in a liquid-pressure system and the others were measured in a gas-pressure system.
Effect of Tensile Stress on the Transition Temperature and Current-Carrying Capacity of Nb3Sn
Authors: Buehler E. , Levinstein H. J.
Published: April 2005

The effect of a uniaxial tensile stress on the superconducting properties of a Nb3Sn-cored wire has been measured. The critical temperatures based on the midpoint of the resistance-temperature curves, decrease with increasing applied stress for a niobium-sheathed wire, while the critical temperature first increases and then decreases for a Monel-niobium-sheathed wire. In the Monel-sheathed wire the initial increase in critical temperature is probably due to the fact that the Nb3Sn is under compression. The current-carrying capacities of both types of wire first increase, then decrease on application of stress. As much as 10% of the zero-stress critical-current value can be lost under tension and still be recovered on unloading.
Effect of Unidirectional Current on a Ferromagnetic Wire Carrying Alternating or Unipolar Current in a Static Magnetic Field
Authors: Kaufman Alvin B.
Published: April 2005

A new ferromagnetic effect is described and some connection to the Procopiu effect is indicated. The experimental arrangements and procedure are delineated. The phenomenological results are illustrated, and a tentative hypothesis is advanced.
Diffusion in an Isolated Dislocation
Authors: Stark J. P.
Published: April 2005

The mathematical analysis of diffusion from a constant source into a dislocation and into its surroundings is considered. Because the exact solution to the problem would contain too many terms to be useful, approximate solutions are found. The method of steepest descents gives a useful solution at large distances from the source of diffusing material. This method permits both the concentration and amount of mass transferred to be determined. For experimental considerations, the latter may prove the more useful.
Velocity and Potential Distribution in a Linear, Smooth Anode Magnetron (Magnetic Diode). II
Authors: Lindsay P. A. , Goodell R. S.
Published: April 2005

We present the results of numerical calculations of the potential, space-charge, and current distributions in linear magnetrons, taking into account the three-dimensional spread of the initial electron velocities. For most practical configurations, the potential distribution is nearly parabolic within the electron cloud, with a slight dip in front of the cathode and the space-charge distribution is remarkably constant and approximately equal to that predicted by the single stream flow, although the electron trajectories are now anything but linear. For other choices of the parameters, the space-charge distribution can be ``triangular'' or may resemble that associated with the so-called double-stream flow. In all such cases the potential, space charge, and current distributions cannot be predicted on the basis of a Brillouin flow and have to be calculated separately.

We have also shown that in most practical cases the systems seem to operate in what is called the magnetic-field-limited, rather than space-charge-limited regime, so that the anode current depends on the values of the external parameters only and is independent of the amount of space charge or the potential distribution between the electrodes. In ballistic terms this means that the force due to the magnetic field acting on an electron at the peak of its trajectory is greater than the corresponding force due to the electric field. Finally, we have shown that contrary to our expectations, there seems to be a great deal of agreement between the operations of systems using finite and infinite cathodes, even when the initial electron velocities are taken into account.
Charge Decay of Carnauba Wax Electrets
Authors: Perlman Martin M. , Meunier Jean-Louis
Published: April 2005

The phenomenological theory of Wiseman and Feaster, based on the two-charge theory of Gross, expresses the polarization response of an absorptive dielectric as the superposition of responses to changes in the internal field, using a time-dependent specific polarization function. This theory is extended to explain quantitatively the charge decay of unshielded dielectrics of finite resistivity. From measurements of the net surface charge on unshielded Carnauba wax electrets at 40°C and 10−5 Torr, it is concluded on the basis of this theory: (i) that the internal field is the main decay agent, governing both polarization growth and real surface decay, which together account for the decay of the net surface charge; (ii) that there is no net local charge within the volume of the dielectric; (iii) that the volume resistivity is 9.0±0.5×1017 Ω-cm, and the dielectric constant at a frequency of the order of 1 cps is 3.08±0.12.
Regenerative Rubidium Maser Oscillator
Authors: Arditi M. , Carver T. R.
Published: April 2005

Continuous self-sustained oscillations at 6834 Mc/sec were obtained with an optically pumped rubidium maser amplifier in a regenerative feedback loop. Some additional gain introduced by a parametric amplifier was required. The use of pulsed light for optical pumping permits the study of the oscillation build-up under various experimental conditions.
Propagation and Instabilities of Waves in Bounded Finite Temperature Plasmas
Authors: Lichtenberg A. J. , Jayson J. S.
Published: April 2005

The quasistatic analysis is used to examine propagation and instabilities of waves in a plasma in which the transverse bounds and the temperature are important. A dispersion equation is derived by use of a dielectric tensor, which is correct within the quasistatic assumption and the assumption of longitudinal velocity, only. The dispersion curves have a smooth transition from the zero temperature case at long wavelengths to the unbounded finite temperature case at short wavelengths. The stop-bands which appear in the zero temperature analysis become propagating regions in the more general case. Landau-type damping is calculated; the cyclotron wave is strongly damped. The effect of the boundaries and the magnetic field on a double-humped velocity distribution is examined. The transverse boundaries are stabilizing with respect to space-charge waves, but the cyclotron interactions are strengthened. The temperature always exerts a stabilizing influence which is particularly marked for the interaction between the cyclotron waves. Curves of the limiting regions of stability, with respect to various parameters, are given, illustrating these effects. By the use of an example it is demonstrated that a moderate temperature can suppress the cyclotron instability. This result is in agreement with the experimental observation that a plasma, predicted to be unstable with respect to the cyclotron-wave interaction, was actually stable.
Search for a Stokes' Shift in the R1 Lines of Ruby
Authors: Warter Peter J. , Martinelli Ramon U. , Brault James W.
Published: April 2005

Virtually simultaneous measurements of the emission and absorption profiles of the ruby R1 line show that no significant Stokes' shift is present. Observations were made on rubies of 0.0055% and 0.0186% Cr by weight with both crystallographic orientations and both polarizations in the temperature range from 77° to 153°K. The position of the peaks in the absorption line matched those of the emission line to within 0.002 cm−1. Shifts of this size or smaller cause no significant change in the operating characteristics of a laser.
Thermal Conductivity of GaAs and GaAs1−xPx Laser Semiconductors
Authors: Carlson R. O. , Slack G. A. , Silverman S. J.
Published: April 2005

Measurements of thermal conductivity for the range 3° to 300°K are reported for both pure and heavily doped n- and p-type GaAs single crystals, and n-type heavily doped polycrystalline GaAs1−xPx crystals with six compositions between x=0 and x=0.5. The alloy ingots have much lower K values due to alloy scattering, with a composition of 35% phosphide content (near the limit of laser operation) having a K less than 1/20 that of pure GaAs at 77°K. Hence heat dissipation is a serious obstacle to continuous operation of alloy lasers.
Crystal Growth and Thermal Etching of Argon
Authors: Pollack Gerald L. , Farabaugh E. N.
Published: April 2005

Thermal etching and grain size of argon polycrystals grown from the melt and the vapor near the triple-point temperature and below have been investigated. Average grain area and its observed dependence on canonical crystal growth parameters such as: temperature gradient, supersaturation, chamber geometry, coolant temperature, initial nucleation conditions, and especially growth rate, is described and compared with the same problems in high-temperature crystal growth. For a growth rate of 1.0 cm/h average grain area was about 0.1 cm2 with the largest grain observed measuring 1.0×1.0×0.7 cm. The grain area decreased with increasing growth rate, asymptotically approaching zero. Surface ``rosettes'' and a method for crystal orientation, depending on occurrence of slip lines on the crystal surfaces, are described.
Pressure Dependence of the emf of Thermocouples to 1300°C and 50 kbar
Authors: Hanneman R. E. , Strong H. M.
Published: April 2005

The relative and absolute effects of pressure on the emf of commonly used thermocouples were measured to 1300°C and 50 kbar. The relative temperature corrections due to the effect of pressure are presented for Pt/Pt10Rh, Pt/Pt13Rh, Chromel-Alumel, and iron-constantan thermocouples as a function of temperature and pressure. The accuracy of these relative temperature corrections is approximately ±1°C and their magnitudes can exceed 40°C in some cases. The absolute corrections of these thermocouples are approximately determined by: (1) correlating experimental and theoretical results on the boundary conditions for the diamond ⇄ graphite equilibrium, (2) relating experimental and calculated results for the effects of pressure on other single-component phase transformations, and (3) evaluating theoretical and experimental results for diffusion at high pressures and high temperatures.

The absolute temperature corrections for all of the thermocouples investigated are proportional to the pressure at a given temperature. The magnitude of the absolute correction ΔT can exceed 50°C, as in the case of Pt/Pt10Rh at 50 kbar and T>1300°C.
Phonon Emission in Piezoelectric Solids
Authors: Ashley J. C.
Published: April 2005

The spontaneous ``Čerenkov-like'' emission of phonons is calculated for a charged particle moving in an arbitrary direction with a supersonic velocity through a solid. The coupling of the particle to the lattice is through the electric fields of piezoelectric origin; first-order perturbation theory is used to calculate the rate of energy loss by the particle to the phonon field. A special case is considered for particle motion along the axis of hexagonal symmetry for a class 26 crystal (such as CdS) using a quasi-isotropic model to describe the tensor properties of the solid. Comparison of the induced emission and absorption of phonons with the spontaneous emission indicates that the ``Čerenkov-like'' emission is negligible under most conditions.
Diagram and Nondiagram Lines in K Spectra of Aluminum and Oxygen from Metallic and Anodized Aluminum
Authors: Fischer David W. , Baun William L.
Published: April 2005

Wavelength and intensities are reported for the Al K series using primary excitation. Included in the tabulation are the diagram lines α1α2 and β1, and the nondiagram lines α′, α3, α4, α5, α6, β′, β″, and β″′. Spectra are shown and line positions and intensities are detailed using both aluminum metal and aluminum oxide as the target materials. Significant differences are seen between metal and oxide spectra, especially in wavelength and shape of the Kβ1 band, and large changes are noted in the intensity of some satellite lines. The oxygen K band at 23.60 Å from an anodized film is shown. The band is only slightly asymmetrical and no satellites are detected on the band contour. The application of x-ray spectroscopy to the study of elements in anodic oxide pores is discussed with reference to quantitative changes and coordination determination.
X-Ray Diffraction and Absorption Topography of Synthetic Diamonds
Authors: Kamiya Y. , Lang A. R.
Published: April 2005

Detailed observations were made on two selected GE synthetic diamonds; one was representative of the more perfect specimens, the other of less perfect but more common specimens. Diffraction topography of the more perfect crystal revealed lattice defects interpreted as dislocation bundles radiating from a central region, individual dislocations apparently resolvable locally, and a severely strained surface layer. Dislocations were not resolved in the less perfect specimen. Absorption topography using monochromatic Cu Kα and Cu Kβ radiations showed a nickel-rich surface film on the more perfect specimen, but few internal Ni-rich particles. The less perfect specimen contained many Ni-rich globules 2 to 15 μ in diameter, sheets of submicron-size Ni-impurity occluded under certain crystal edges and some Ni-rich surface film. The face-centered cubic ``satellite'' diffraction pattern of the less perfect specimen showed the presence of large crystallites misoriented up to 6° from the diamond matrix and fine crystallites closely parallel to the matrix. An explanation is put forward for the development of cube faces on synthetic diamonds.
Interpretation of the Temperature Autostabilization of a Ferroelectric Crystal
Authors: Fousek Jan
Published: April 2005

The dielectric heating of a ferroelectric crystal in an alternating electric field is discussed from the point of view of the properties of the polarization reversal process. On the basis of a simplified description of a P(E) hysteresis loop the complex permittivity of a ferroelectric crystal in strong fields is calculated as a function of the crystal temperature T and field amplitude. The amount of heat developed in the crystal is found and from the condition of thermal equilibrium of the crystal with the surroundings, T is calculated as a function of the ambient temperature Ta and the field amplitude. It is shown that the decreasing temperature dependences of the spontaneous polarization and the coercive field are responsible for the existence of states of temperature autostabilization (STA), defined by ∂T/∂Ta < 1, which were found experimentally by Glanc et al. There are three possible ways of bringing the crystal to STA which are realized at different frequencies of the applied field or at different rates of conduction of heat into the surroundings. At a high enough frequency the dependence of the temperature of the crystal on the amplitude of the field is discontinuous and the crystal is heated to the neighborhood of the Curie temperature in one step. The coefficient S = ∂T/∂Ta, the dielectric properties of the crystal in STA (called TANDEL—the temperature autostabilized nonlinear dielectric element) and the hysteresis property of a TANDEL are calculated, and compared with the experimentally determined properties of a TANDEL of triglycine sulphate. It follows from theory that the states of temperature autostabilization are attainable in ferroelectrics with transition both of the first and second kind. The possibility of realization of STA above the Curie point is discussed.
Diffusion Mechanism for the Nickel-Activated Sintering of Molybdenum
Authors: Smith J. T.
Published: April 2005

The sintering kinetics of cold-pressed molybdenum powder and molybdenum powder with nickel additions of 0.50–0.75 wt% have been investigated in the temperature range from 1100° to 1400°C. Diffusion coefficients calculated from the sintering kinetics indicate that molybdenum densifies by a grain boundary diffusion process in the range 1100° to 1400°C. The activation energy for the process is about 38 kcal/mole. The nickel additions, present on particle surfaces, enhanced the sintering rate such that it was possible to achieve densities in excess of 90% of theoretical after sintering for only 60 min. It is suggested that the mechanism for the nickel-activated sintering of molybdenum is the increased diffusion rate of molybdenum through the grain boundary layer of nickel. An activation energy of 21 kcal/mole was determined for this process.
Pressure—Temperature Phase Diagram of Iron to 200 kbar, 900°C
Authors: Bundy F. P.
Published: April 2005

The resistance changes in iron during the transitions between the α(bcc), γ(fcc), and ε(hcp) phases have been studied quantitatively in the high-compression belt apparatus. The samples were monitored by thermocouples and voltage probes. The P,T locations of the (α,γ) (α,ε), and (ε,γ) phase lines, and the (α,γ,ε) triple point were determined. The latter is placed at 110 ±3 kbar and 490 ±10°C. The changes of molar volume at the triple point are deduced to be −0.275, +0.135, and +0.140 cc/mole for the (α,ε), (ε,γ), and (γ,α) transitions, respectively. The resistivity of the α phase follows a quadratic relationship with temperature, whereas the γ and ε forms vary linearly with temperature.
Investigation of the Magnetic Structure of ErMn2, TmMn2, TbNi2 by Neutron Diffraction
Authors: Felcher G. P. , Corliss L. M. , Hastings J. M.
Published: April 2005

Magnetic measurements by H. J. Williams (ErMn2 and TmMn2), and W. E. Wallace (TbNi2) have shown that these compounds are magnetically ordered at low temperature with a net moment per formula unit lower than that of the free rare-earth ion. Neutron diffraction powder patterns have been used to determine the actual magnetic structure. ErMn2 and TmMn2 crystallize with the hexagonal Laves phase structure (C-14 type). ErMn2 is ferromagnetic, with a moment of 7.72 μB/Er atom at 4.2°K aligned along the c axis. No detectable moment on Mn is observed. TmMn2 is almost completely ferromagnetic, with a moment of 4.95 μB/TM atom at 2.1°K aligned along the c axis, and essentially zero moment for Mn. A faint additional line at low angle seems to indicate a weak antiferromagnetic contribution. TbNi2 crystallizes with the cubic Laves phase structure (C-15 type). At 4.2°K, ferromagnetic lines as well as additional peaks appear in the diffraction pattern, but the magnetic scattering is rather sensitive to sample preparation.
Coercive Force of Single-Crystal GdIG as a Function of Temperature
Authors: Hanton J. P. , Morrish A. H.
Published: April 2005

Intrinsic coercive force data for both single-crystal and polycrystalline gadolinium iron garnet (GdIG) are presented. Measurements near the magnetization compensation temperature (TCM) are stressed, and an explanation for the single peak in the intrinsic coercive force based on magnetization reversal by domain rotation rather than wall motion is proposed.
Single-Crystal Magnetization Data for Anisotropic Rare-Earth Iron Garnets at Low Temperatures
Authors: Harrison F. W. , Thompson J. F. A. , Lang G. K.
Published: April 2005

Single-crystal magnetization measurements using a force method and fields up to 17 000 Oe applied in the principal crystal directions are presented for TbIG, DyIG, HoIG, ErIG, and SmIG in the range 20°–300°K. In the region below 100°K, where these garnets have high anisotropies, the results differ from the original measurements of Pauthenet on polycrystalline samples by as much as 6 μB, though the compensation temperatures found are close to those of Pauthenet. Residual anisotropies in the magnetization <1 μB are apparent for ErIG and TbIG below 80°K.
New Acoustic and Magnetic Properties of YIG and YAG with Small Mn and Ni Additions
Authors: Fraser D. B. , Gyorgy E. M. , LeCraw R. C. , Remeika J. P. , Schnettler F. J. , Van Uitert L. G.
Published: April 2005

The resonant frequency and Q of the acoustic modes of YIG and YAG have been investigated as a function of temperature at approximately 1 Mc/sec. The samples studied have either Mn or Ni additions in the range from 0 to 1% of the total weight. For the samples with Mn or Ni additions, the resonant frequency of the shear modes has a maximum as a function of temperature. This maximum does not exist with pure YIG and YAG. The Mn or Ni additions also lead to a large increase in the low-temperature acoustic loss. Similar results have been obtained with Mn additions in the corundum and spinel structures. We tentatively attribute the observed effects to the static and dynamic Jahn—Teller distortions arising from the Mn and Ni additions.
Thermogravimetric Investigation of Fe2+ in Ferrites Containing Excess Iron
Authors: Macklen Eric D.
Published: April 2005

The weight changes occuring in manganese-zinc ferrites containing 2–15 wt % ferrous iron have been followed by TGA up to 1420°C. Those changes which result from the valency change Fe3+→Fe2+ have been more closely studied as a function of temperature between 1100° and 1350°C and of atmosphere for oxygen contents between 0.025% and 21%. From the equilibrium partial pressures of oxygen over MnZn ferrites having ferrous contents up to 10 wt %, a composition-temperature-atmosphere diagram has been constructed. Ferrites containing more than 10 wt % of Fe2+ showed marked deviations from this diagram.
Graphical Correlation of the Néel Temperatures of Chlorides, Bromides, and Iodides of Divalent 3d Transition Metal Ions
Authors: Van Uitert L. G. , Williams H. J. , Sherwood R. C. , Rubin J. J.
Published: April 2005

Indirect exchange in isostructural compounds of divalent Mn, Fe, Co, and Ni increases with the electron affinities of the cations and the polarizabilities of the anions. Spin-orbital coupling can increase TN (for Fe) in a strong trigonal field, and decrease TN in a cubic field. Exchange interactions in the chlorides, bromides, and iodides take place via double layers of anions. As a result, a higher threshold cation electron affinity is required to effect spin alignment than for single anion intermediaries. A graphical comparison of the TN values of the chlorides, bromides, and iodides as a function of the ionization potentials of the cations demonstrates the consistency of these data with those of cubic oxides and fluorides and with simple principles.
Studies on Orthoferrites at the Weizmann Institute of Science
Authors: Treves D.
Published: April 2005

The Curie point, lattice constants, sublattice magnetization, spontaneous magnetic moment, susceptibility, and the nonlinear susceptibility have been measured on the compounds RFeO3 with R yttrium or a rare earth. The main conclusions from these measurements are: (1) The rare-earth ions contribution to the magnetic properties of these materials at relatively high temperature is mainly through the geometrical effect of ionic radii. (2) The ratio of iron sublattice to the weak ferromagnetic moment shows that the canting angle is temperature independent. (3) Between liquid-air temperature and the Curie point, the rare-earth ions behave like a paramagnet in an effective magnetic field of the iron ions. This field is of the order of a few thousand gauss of either sign. (4) From measurements of the spontaneous moment, the susceptibility and the nonlinear dependence of the magnetization on applied fields it appears that the antisymmetric exchange interaction is responsible for the weak ferromagnetism of these materials. (5) It is found that near the Curie temperature there exists an appreciable deviation of the iron sublattice magnetization from the theoretical S = 52 curve.
Interpretation of the Magnetic Properties of LaCoO3
Authors: Naiman C. S. , Gilmore R. , DiBartolo B. , Linz A. , Santoro R.
Published: April 2005

Susceptibility measurements have been carried out on single-crystal LaCoO3 in the temperature range of 4.2° to 300°K. We find an effective magnetic moment squared that agrees with Heikes et al. at 300°K, but which falls more rapidly with decreasing temperature. Paramagnetic resonance measurements at 4.2°, 77°, and 300°K have ruled out the presence of modest quantities of paramagnetic cobalt, leaving only the possibilities of diamagnetic or highly concentrated paramagnetic Co+3. (Large concentrations of other cobalt valencies are ruled out for chemical reasons.) Using a model found successful by Goodenough, we assume that Co+3 is near the crossover point, with the 1A1 state lowest. A calculation including spin-orbit effects, but assuming cubic symmetry for the 300° to 4.2°K range, gives essentially a linear variation for the energy difference between the 1A1 and the center of gravity of the 5T2 states, opposite to that expected for a cubic variation. This effect can be explained by including a lower symmetry distortion (probably trigonal) which increases with decreasing temperature, similar to that found in LaAlO3:Cr.
The Sign of the Trigonal Field Splitting of B-Site Ions in Spinel
Authors: Berger S. B.
Published: April 2005

Electron spin resonance experiments were performed at 9.5 to 9.7 and 23.08 Gc/sec and the spin Hamiltonian parameters were determined: g∥=1.985±0.001,g⊥=1.983±0.003, and 2D=+1.83±0.004 cm−1 (+55 Gc/sec). The g values and absolute value of 2D are in close agreement with those obtained earlier. The present value of 2D was obtained from the M = ½ to 32 transition and the sign determined by the relative intensity change with temperature of the M = ½ to 32 and M = −32 to −½ transitions (high magnetic field quantum numbers used). The positive sign obtained directly in this work contradicts the previous indirect determination which yielded a negative sign.
Ferromagnetic Resonance Measurements in Ni–Fe Films from 2–100 Mc/sec
Authors: Vescial F. , Hutchings T. J. , Jacobs E. D. , Zingery W. L.
Published: April 2005

The anisotropy field dispersion in both magnitude and direction has been investigated in Ni–Fe thin films through the frequency range of 2–100 Mc/sec using rf ferromagnetic resonance (FMR). Measurements were centered around the region of field values near Hk where the theory of Smit and Beljers predicts that resonance can be seen at these frequencies. The linewidth measurements as a function of frequency follow a linear relationship which is extrapolated to zero frequency to obtain magnitude dispersion. The slope of this line yields ferromagnetic damping parameters α0 in agreement with Rossing and Nelson. Angular dispersion measurements are obtained by extrapolating a linear relationship between apparent angular dispersion and frequency to zero frequency.

Magnitude and angular dispersion measured by ferromagnetic resonance have been compared with measurements of the same quantities using a vibrating sample magnetometer (VSM), and the results are generally in agreement.

In addition, the strain dependence of the FMR linewidth has been measured at 2.5 Mc/sec for strains up to 3.4×10−4. A small increase in linewidth with strain has been noted.
Two-Peak Output Waveforms in Uniform Rotation Switching of Thin Films
Authors: Toppeto A. A. , Grimes D. M.
Published: April 2005

A theoretical model for high-drive switching of a thin-film, finite length, ferrite, cylindrical shell or toroid is developed from Gilbert's equation. The equation of uniform magnetization reversal includes terms which result from an arbitrary applied field and terms due to the axial demagnetizing field. Machine solution of the equation shows the existence of two peaks in the output waveform which are directly traced to the axial demagnetizing field. The dependence of these peaks on the applied field is also shown. Comparison with published data on a thin-walled toroid is made. A physical description of the reversal mechanism which leads to the two peaks as they result from the axial demagnetizing field is included. Principal conclusions based on the various solutions are as follows: (1) The two-peak effect is a direct result of the axial demagnetizing field. (2) The damping constant, over the range studied, results in slower switching time as α increases; however, minimum switching as a function of α exists in this model. The higher values of α tend to damp out the two-peak effect. (3) Increased intensity of the applied field decreases the appearance of the two peaks. (4) Greater values of the saturation magnetization cause the two-peak effect to be accented, but the switching constant is essentially independent of M.
Lorentz Microscopic Examinations of Polycrystalline Films with Biaxial Properties
Authors: Gondo Y. , Gran B. E. , Prosen R. J.
Published: April 2005

Polycrystalline Permalloy films with biaxial properties have been examined in detail by Lorentz microscopic techniques. The stable configuration for type I films, consisting of an array of discrete small squares, is a simple arrangement of four domains with complete flux closure and 90° walls along the diagonals. At high fields, a single domain configuration is obtained in which the spins along the edge deviate from the field direction due to the ``boundary anisotropy.'' The magnetization curling distances D along the edge are found to be proportional to MT/H, independent of the dimension of the square. The critical field HA for the flux closure structure is proportional to MT/L, where T is the film thickness. For type II films, composed of discrete thick squares superimposed on an isotropic continuous film, the conditions for flux closure are the same as for type I films. Type III continuous films with nonmagnetic square voids have also been examined, and their biaxial properties are similar to those of type II films.
Magnetic Properties of MnCr2S4
Authors: Menyuk N. , Dwight K. , Wold A.
Published: April 2005

The neutron diffraction pattern of MnCr2S4 at room temperature shows it to be a normal cubic spinel. The magnetization of this material was measured from 4.2° K through the Curie temperature. It was then determined, on the basis of a molecular field calculation, that the shape of the magnetization curve requires a large and ferromagnetic B-B interaction such that JBB/JAB∼−4. This is in general accord with Lotgering's conclusion, which was based on paramagnetic susceptibility data, and indicates that the material should have a simple Néel (collinear) spin configuration. This expectation was confirmed by a 4.2°K neutron diffraction investigation which also established the cation moments to be 3μB per chromium ion and 4.7μB per manganese ion, in agreement with the measured net magnetization of 1.3μB. Furthermore, the 4.2°K diffraction pattern clearly indicates that the reduction of the manganese moment below its spin-only value cannot be attributed to A-site canting. On the basis of the above results, we are forced unequivocally to the conclusion that the tetrahedrally coordinated Mn2+ cannot be in a pure S526 state.