bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of Intense Magnetic Fields
Authors: Montgomery D. Bruce
Published: April 2005

The advent of high-field superconducting magnets has made magnetic fields above 30 kG available to the entire scientific community. Small diameter coils to 60 kG cost considerably less than conventional 12-in. iron magnet systems. Fields to 80 kG, and in a few recent instances to 100 kG, even in multicentimeter bores, are now economically within the reach of most research budgets. The current and future status of superconducting magnets, their economic advantages and associated problems are presented. Other methods of generating fields, such as water-cooled continuous magnets, millisecond pulse magnets, and long-pulse cryogenic magnets, will find their principal use in reaching even higher fields, supplementing superconducting magnets, or in circumventing problems which preclude the use of superconductors. Pulse magnets are presented as a relatively simple and inexpensive method of producing millisecond fields up to 500 kG and long pulses to 250 kG. Relationships between energy, time, and volume are given for pulse magnets. The current and future status, and the problems associated with conventional continuous field magnets in the 100 to 250 kG range are given and the availability of such magnets at the National Magnet Laboratory discussed. New critical current—critical field data for niobium—tin materials measured in continuous fields up to 180 kG is presented.
Dilute Ferromagnetic Alloys
Authors: Crangle J. , Scott W. R.
Published: April 2005

Long-range ferromagnetic coupling occurs in several dilute solid-solution alloys of the ferromagnetic transition elements in Pd or Pt. New measurements of magnetic moments and Curie temperatures of PdFe, PtFe, PtCo, and PdNi alloys are reported, and previous work on these and some of the more general properties of these alloys are briefly reviewed. Also, ferromagnetism occurs in dilute PdGd solid solutions.

Dilute solutions of iron in gold are ferromagnetic, although below about 10% of Fe there seems to be no homogeneous bulk ferromagnetism.
Ferromagnetic Dilute Alloys
Authors: Kanamori Junjiro
Published: April 2005

In the first part an approximate method to treat the problem of one impurity atom in an otherwise pure metal is developed on the basis of tight-binding approximation. The method is capable of taking into account the degeneracy of the 3d bands and the mixing of the 3d bands with the 4s band. It is shown that one can treat each 3d atomic orbital of the impurity atom separately.

In the second part, dilute Ni alloys with other 3d transition metals are discussed on a simple model. The calculation substantiates Friedel's theory of these alloys. The negative magnetic moments of Cr and V in Fe are also discussed.
Inequivalent Magnetic Ions in Dihydrated Formates of Fe+ + and Ni+ +
Authors: Hoy G. R. , De S. Barros S. , De S. Barros F. , Friedberg S. A.
Published: April 2005

Several dihydrated formates including Ni(HCOO)2·2H2O and Fe(HCOO)2·2H2O crystallize in a monoclinic structure whose unit cell contains two each of two inequivalent types of metal ions. The temperature variation of the powder susceptibility, χp, of the Ni+ + salt suggests that those ions on one type of site become cooperatively ordered near 15.7°K while the rest remain essentially independent even at 1.3°K. χp for the Fe+ + salt exhibits a huge peak at 3.68°K associated apparently with the long-range ordering of moments on sites of both types. Mössbauer experiments at 300°K on the Fe+ + salt clearly distinguish ions on the two sites, the ratio of the effective electric field gradients being ∼5 to 1. The smaller field gradient is assumed to characterize the site (type 1) approximately octahedrally coordinated by oxygens from six formate groups. The Mössbauer spectrum near the transition point differs from those measured at 300°, 77°, 20°, and 4°K. The results show that the internal magnetic field is larger at the type 1 sites. Preliminary calculations using the observed nuclear hyperfine structure indicate that the ratio of magnetic fields at the two sites is about four to one.
Néel Temperatures of Chromium-Vanadium Alloys from NMR Measurements
Authors: Barnes R. G. , Graham T. P.
Published: April 2005

The antiferromagnetic transition temperature of chromium-rich V-Cr alloys has been investigated by means of the extinction of the 51V and 53Cr NMR signals at the transition temperature in these alloys. Measurements on both natural and isotopically enriched 53Cr chromium yield TN=39.0±0.5°C, in excellent agreement with neutron diffraction results. TN decreases roughly linearly with V content, falling below 4.2°K at 3.4% V. In all cases, the resonance intensity follows the empirical behavior, I=I0 tanh K(1-TN/T), where K ≈ 15. At temperatures well above TN, the linewidth and second moment of the 53Cr resonance are appreciably larger than the calculated values based solely on nuclear dipolar broadening. These results might be attributed to the persistence of a very small electronic moment in the paramagnetic state.
Nuclear Magnetic Resonance Study of Hyperfine Interactions in Sn3RE Intermetallic Compounds
Authors: Barnes R. G. , Borsa F. , Peterson D.
Published: April 2005

Measurements of the 119Sn isotropic and anisotropic Knight shifts, Kiso and Kax, have been made in a series of Sn3RE intermetallic compounds (RE=La, Ce, Pr, Nd, Sm, Eu, and Yb). In particular, PrSn3 and NdSn3 have large positive, temperature-dependent shifts which are proportional to the magnetic susceptibility χM. It is proposed that the mechanism relating Kax to χM in these cases is a coupling of the 119Sn spin to the RE localized moment via the conduction electrons in a manner analogous to the pseudo-dipolar interaction between nuclear spins in heavy metals. Similarly, Kiso may be regarded as arising from an isotropic indirect coupling between f-electron spins and nuclear spins. Reasonable values of the interaction strengths are obtained.
Coupling Effect Between the Magnetizations of Two Thin Layers Separated by a Thin Nonmagnetic Metallic Layer
Authors: Bruyère J. C. , Clerc G. , Massenet O. , Montmory R. , Néel L. , Paccard D. , Yelon A.
Published: April 2005

The coupling between films of NiFe and another ferromagnetic material separated by a thin layer of a nonferromagnetic metal has been investigated for the cases of Au, Ag, Cr, and Pd intermediates. It is found that for Pd an alloy formation takes place during evaporation, and that for Cr, a porosity effect is important. It appears unlikely that either of these effects can be important for Au and Ag, and in these cases the possibility of indirect exchange must be considered seriously.
Wall Transitions in Coupled Films
Authors: Friedlaender F. J. , Silva L. F.
Published: April 2005

Néel walls have been generally observed in Permalloy films below a certain thickness whereas thicker films seem to support Bloch walls or cross-tie walls. Two coupled Permalloy films of 81% Ni-19% Fe composition separated by a layer of silicon monoxide were used to study domain wall interactions. Néel walls with no Bloch lines were observed in 900-Å coupled film segments with 300-Å film separation. In a single layer of Permalloy of this thickness, Bloch walls predominate. Since the separating layer is an insulator and nonferromagnetic, the interaction is thought to be magnetostatic. The films were prepared in a step fashion on a single substrate so that uncoupled and coupled portions of a film, prepared in the same evaporation, could be observed simultaneously using Bitter powder pattern technique. Multiple-step coupled structures of varying film thickness with constant separation and varying separation with constant film thickness were prepared with thicknesses chosen in the region of Néel-Bloch transition. The coercive force of the coupled film segments is lower than that of similar uncoupled film segments. The coercive force starts to decrease at film separations of approximately 1100 Å.
Relaxation and Nonlinear Effects in Ferromagnetic Thin Films
Authors: Berteaud André-Jean , Pascard Hubert
Published: April 2005

In the first part, the authors give curves of ΔH versus the thickness d of the films magnetized normal and parallel to the film plane. One can see that ΔH⊥ (normal case) does not vary with d whereas ΔH∥ (parallel case) increases with d. Using the classical dispersion curves of degenerate spin waves, the authors conclude that internal imperfections are not responsible of the variations of ΔH∥ but it seems that the main source of scattering may be due to the edges of the films.

In the second part, the preliminary results of the behavior of thin films with high microwave power are given. The bulk sample theory of Suhl predicts that no subsidiary absorption is present. In the measurement of our films (f=9.3 GHz and 4πM = 104 Oe), the experimental curves exhibit a subsidiary absorption and a saturation of the uniform resonance mode, similar results being obtained with other samples. Finally, the authors give the variations of χ″/χ0″ with P/Pc and conclude that these curves can be used to obtain some information concerning the internal or surface imperfections of the films.
Hard Magnetic Films of Iron, Cobalt, and Nickel
Authors: Speliotis D. E. , Bate G. , Alstad J. K. , Morrison J. R.
Published: April 2005

Thin films of Fe, Co, and Ni were prepared by vacuum deposition. The angle of incidence was varied from 0° to 80° for the explicit purpose of changing the anisotropy and producing very high coercivities. The film thicknesses, determined interferometrically, were in the range from 100 to 4000 Å. X-ray and electron diffraction examination revealed a highly faulted cubic structure for Fe and Ni, and a mixture of cubic and hexagonal phases for Co, with crystallite size ranging from 20 to 1000 Å. Increasing the angle of deposition from the substrate normal had a pronounced effect on the magnetic properties of the films. The maximum effect was observed in Fe, where easy-axis coercivity exceeded 1100 Oe at angles approaching 90°, while at normal incidence it was only 20 Oe. Next was Co with maximum coercivity of 1000 Oe and Ni with maximum coercivity of 350 Oe. This order is what would be expected on the basis of shape anisotropy of elongated particles formed on account of the oblique incidence of the vapor flux. Magnetization reversal was studied by Bitter patterns and Lorentz electron microscopy.
Magnetostriction of Polycrystalline Aggregates
Authors: Callen Herbert B. , Goldberg Norman
Published: April 2005

The magnetostriction constant of the polycrystal λs can be written as a linear combination of the constants of the cubic crystallites; λs = αλ100 + (1-α)λ111. The almost universally used approximation α = ⅖ is a poor one. It is based on the assumption of uniform stress through the aggregate (analogous to the Reuss approximation for the polycrystalline shear modulus). The alternative approximation of uniform strain (analogous to the Voigt approximation of the shear modulus) gives α = 2/(2+3c), where c = 2c44/(c11-c12) is a measure of the elastic anisotropy of the microcrystals. However, both approximations lie outside upper and lower bounds which have been derived by Hashin and Shtrikman for the elastic case (although the magnetostrictive analogs have not been calculated). A physically reasonable approximation (the analog of Kroner's spherical stress approximation which lies between the Hashin and Shtrikman bounds in the elastic case) was given in a little known paper by Vladimirsky. Here the local stress is approximated by that in a spherical microcrystal surrounded by a homogeneous material with the isotropic properties of the polycrystalline aggregate. We show that for physically interesting elastic constants the rather complicated Vladimirsky result can be represented simply by α = ⅖ − (lnc)/8. The available experimental data are compared with these various approximations; they favor the latter very strongly over the more commonly used α = ⅖.
Magnetic Structure of Rare-Earth-Cobalt (RCo2) Intermetallic Compounds
Authors: Moon R. M. , Koehler W. C. , Farrell John
Published: April 2005

Saturation magnetization and neutron diffraction measurements have been performed on cubic Laves phase compounds RCo2 in which R is Nd, Tb, Ho, and Er. Neutron powder patterns obtained at room temperature and at 15°K allowed the determination of the magnetic structures. The low-temperature patterns are of the ferromagnetic or ferrimagnetic type, with large magnetic intensities superimposed on the nuclear peaks. For the compounds of Tb, Ho, and Er, the rare-earth atoms show nearly the full moment expected for the free tripositive ion and the cobalt moment is about one Bohr magneton. The rare-earth moments are coupled parallel to each other, but antiparallel to all the cobalt moments. For NdCo2, the observed Nd moment of 2.6±0.2 Bohr magnetons is smaller than the free ion value of 3.27 Bohr magnetons, and it is coupled parallel to the cobalt moment of 0.8±0.2 Bohr magnetons. In the Nd ion, the spin is opposite to the moment (J = L−S), while for the heavier rare earths the spin is parallel to the total moment (J = L+S). Thus, in all cases there is antiparallel coupling between the spins of the rare-earth and cobalt atoms. The values for the total moment per molecule based on the neutron diffraction results are in satisfactory agreement with the magnetization measurements.
Exchange Anisotropy and Long-Range Magnetic Order in the Mixed Intermetallic Compounds, (Mn, Fe)3Sn
Authors: Kouvel J. S.
Published: April 2005

Magnetization and neutron diffraction results are reported for hexagonal (DO19) pseudo-binary compounds of compositions intermediate between antiferromagnetic Mn3Sn and ferromagnetic Fe3Sn. Both Mn2.5Fe0.5Sn and Mn2FeSn exhibit a complex magnetization-field-temperature behavior that is suggestive of a finely mixed ferro-antiferromagnetic state of the type previously proposed for Cu–Mn and other disordered alloys. This exchange anisotropy state is further demonstrated by displaced hysteresis loops produced by cooling to low temperatures in a magnetic field; unidirectional anisotropies of about 106 erg/g are computed from these loops. However, unlike Cu–Mn, these compounds also give neutron diffraction evidence for some long-range periodic magnetic order. The magnetic structure for Mn2.5Fe0.5Sn is basically that for Mn2Sn, in which three equivalent sublattice moments add vectorially to zero by describing a closed equilateral triangle, whereas Mn2FeSn probably has a ferrimagnetic variant of this structure.
Theory of Magnetoelastic Effects in Ferromagnetism
Authors: Brown William Fuller
Published: April 2005

Standard magnetostriction theory constructs a free energy from three terms: the energy of a rigid magnetized body, the energy of a nonmagnetic elastic body, and the volume integral of an interaction energy-density linear in the strains. This procedure is open to three criticisms. First, strains invalidate the magnetic calculation; in particular, the magnetostatic self-energy is strain-dependent. Second, magnetization invalidates the elastic calculation; the stresses (whose definition is somewhat arbitrary) need not be symmetric or even constitute a tensor. Third, small-strain formulas, valid only to the first order of small quantities, are being used in energy terms that must be correct to the second order and that are linear in the strains. Previous studies make possible a rigorous treatment, by finite-strain theory, and a small-strain approximation with assumptions explicitly stated. The mechanical equilibrium equations contain the usual terms plus others; the ``form effect'' is a special case. The theory is easily related to microscopic models and is suited to nucleation-field calculations.
Frequency Dependence of the Anomalous Skin Effect in High-Purity Copper
Authors: Johnson Eric W. , Johnson H. H.
Published: April 2005

A new technique for anomalous skin-effect studies is described. At low temperatures (∼4°K) it measures both surface reactance and surface resistance over a wide band of frequencies extending to below 100 cps. For the transition region from classical to anomalous behavior, experimental results on high-purity copper show excellent agreement with theory, assuming diffuse scattering of electrons at the metallic surface. A new numerical table of theoretical values is included.
Fields Produced by a Current Source in a Partly Ionized Gas
Authors: Tanenbaum B. Samuel
Published: April 2005

A technique is developed for treating each of the waves generated by an arbitrary current source in a partly ionized gas with no steady magnetic field. Starting with Maxwell's equations and three sets of coupled hydrodynamic equations (for the electrons, ions, and neutral molecules), it is shown that one can obtain a separate inhomogeneous wave equation for each type of wave in the plasma, with the source term for the transverse and longitudinal waves dependent, respectively, on the curl and divergence of the current source.
Electrical Breakdown in Vacuum: New Experimental Observations
Authors: Rabinowitz M. , Donaldson E. E.
Published: April 2005

Electrode geometry effects neglected by previous investigators are shown to be significant for electrical breakdown in vacuum for gap lengths 0 to 1 mm exhibiting breakdown at 0 to 60 kV for Al, Cu, and stainless steel electrodes. In particular, data demonstrating curvature, area, and polarity effects are reported. The effects of material transfer, particle inertia, protrusion formation, erosion, and patterned deposits are also reported.
Complete Solutions to the Rate Equations Describing Q-Spoiled and PTM Laser Operation
Authors: Kay R. B. , Waldman G. S.
Published: April 2005

The solutions of the rate equations describing the Q-spoiled and pulsed-transmission-mode (PTM) operation of a three-level laser are given. These solutions were carried out in two time regions: (1) the delay time followed by (2) the pulse time. Region (1) was tractable with approximate analytic methods, while in region (2) the equations were solved by analog computer. The effect of the duration of the Q switch on the delay time and on the PTM operation is investigated. It is found that Q-switch times as long as 20 nsec give satisfactory PTM operation.
Change of Elastic Constants through the Ferroelectric to Antiferroelectric Phase Transition in a Pb(Ti,Zr,Sn)O3 Ceramic
Authors: Burlage S. R.
Published: April 2005

Ultrasonic pulse-echo measurements are used to determine the changes in c11E, c33D, c44D, c44E, and c12E through the reversible ferroelectric—antiferroelectric phase transition in a Pb(Ti, Zr, Sn)O3 ceramic. The results indicate that after the transition is enforced by hydrostatic pressure the material loses both electrical and mechanical orientation and becomes elastically isotropic.
Electrical Properties of Inert Gas Plasmas Generated in Thermionic Cold-Cathode Diodes by Radiation in a Nuclear Reactor
Authors: Forman R.
Published: April 2005

The electrical properties of inert gas (Xe, Kr, Ar) plasmas have been studied in a nuclear reactor environment at gamma radiation dose rates up to 6×108 rad/h. The measurements are made by inserting a gas-filled thermionic diode into the core of a 5-MW nuclear reactor. The space-charge neutralization effects caused by the ion-electron pairs generated in the gas are measured and interpreted in terms of plasma properties of the gas. The electrical conductivity of the plasma, at a constant radiation level, goes through a maximum as a function of pressure in the range of 1–300 Torr. If the radiation dosage is varied, keeping all other factors the same, one finds the electrical conductivity monotonically increases with dose rate in the range of 106−6×108 rad/h.

Experiments are described which indicate that electrons can be removed from a low work function ``cold'' electrode into the plasma by a mechanism different from either thermionic or field emission. A physical model is proposed to explain this phenomenon.
Magnetic Susceptibility, Electric Resistivity, and Lattice Parameters of Iron-Rich Iron—Tin Alloys
Authors: Arajs Sigurds , Chessin Henry , Dunmyre G. R.
Published: April 2005

Magnetic susceptibility of iron—tin alloys containing 0.45, 0.82, 1.33, 1.83, and 2.14 at.% tin have been studied as a function of temperature up to 1500°K. Tin influences the magnetic properties of iron in an unusual way. The mass magnetic susceptibility of γ iron is increased by about 1% due to 0.45 at.% tin. The paramagnetic moments of the bcc phase, determined from the susceptibility data between 1300° and 1500°K, show a small increase with increasing tin content. These results are, in principle, consistent with the ferromagnetic properties studied by Fallot (1936) indicating that tin does not act as simple diluent in regard to the magnetic behavior of iron. Electrical resistivities of iron—tin alloys, determined at 4.2°, 77.2°, and 297.0°K, show that tin increases the resistivity of iron very considerably, i.e., about 8 μΩ cm per 1 at.% at 4.2°K. Lattice parameters of iron—tin solid solutions up to 5 at.% tin (quenched from 1013°K) have been measured at 298°K. None of the present theories are capable of explaining satisfactorily the observed behavior.
Surface-Energy Determinations by Cleavage
Authors: Gillis Peter P.
Published: April 2005

An analysis is made of the strain-energy distribution in a slotted double-cantilever cleavage specimen. In this type of specimen the crack is medially constrained by a pair of longitudinal slots, so that surface energies can be determined in nonmonocrystalline samples.

The analysis treats the arms of the crack as end-loaded cantilever beams, and the post crack-tip region as a pair of elastically supported beams. The web produced by slotting is assumed to act as an elastic foundation for the remaining beam-like portions of the post crack-tip region. An expression for the specific surface energy of the material is then derived from conservation of energy at the instant the crack begins to propagate. Linear elastic behavior of the material is assumed and shearing strains are neglected.

Extension of the analysis to conventional (unslotted) specimens in which medial constraint of the crack is obtained through a preferred direction of cleavage, is discussed semiquantitatively in terms of an effective foundation modulus.
Transition between Bloch and Néel Walls
Authors: Torok E. J. , Olson A. L. , Oredson H. N.
Published: April 2005

The transition between Néel and Bloch walls is shown to be gradual rather than abrupt, resulting in a wall with Néel and Bloch components superposed. For films thick enough so that such a transition can occur, the wall is a pure Néel wall if φf, the acute angle between the wall normal in the plane of the film and the magnetization at the edge of the wall (half the angle between the magnetization vectors in the two domains separated by the wall) is less than a critical value. For φf larger than that critical value but less than π/2, the wall contains both Néel and Bloch components. When φf is π/2, i.e., a 180° wall, the wall is of the pure Bloch type; however, this situation is often unstable, resulting in a transition wall with the Néel component reversing periodically in distance along the wall in a crosstie-like structure. These conclusions are supported by Lorentz micrographs.
Supersonic Domain Wall Motion in Triglycine Sulfate
Authors: Binggeli B. , Fatuzzo E.
Published: April 2005

By applying high electric fields to triglycine sulfate at temperatures close to the Curie point, switching times of the order of nanoseconds were observed. It was assumed, from previous studies, that at these high fields all domain nuclei form almost at the same time and grow together through the thickness of the specimen. In this case the transit time for the domain nuclei is almost equal to the switching time and the experimental results show that the domain velocities observed in the faster switching times were supersonic. A sudden increase in wall mobility occurred at the transition from subsonic to supersonic velocities. Both the supersonic and the subsonic mobilities are thickness-dependent. Models to explain these effects in a qualitative way are provided.
Influence of Crystal Face on Surface-Induced Electrical Properties of Silver Bromide Photographic Grains
Authors: Brady L. E. , Hamilton J. F.
Published: April 2005

Measurements of ionic conductance and electron lifetimes have been made on the grains of two AgBr photographic emulsions, one composed of regular octahedral grains bounded by (111) planes and the other composed of regular cubical grains having (100) faces. The field decays more slowly in the cubical grains, indicating that crystal habit affects ionic conductivity. Electron lifetimes were observed to be approximately equal to the field decay in the octahedral grains and shorter than the field decay in the cubical grains, in contrast to the tabular grains measured previously, in which the electron lifetime was longer than the field-decay time. An explanation for this is proposed, based on the assumption that the interstitial silver ions are inhomogeneously distributed in the volume of the grains.
Light Scattering from Diffusion-Controlled Phase Separations in Glass
Authors: Hammel Joseph J. , Ohlberg Stanley M.
Published: April 2005

Light-scattering measurements were made on a number of phase-separated glasses in which the number and size of the particles of the new phase were varied. Plots of scattering intensities versus scattering angles showed two unique features: (1) higher scattering intensities were found in the back angles and (2) in some cases sharp maxima in intensities were found. In the first case the experimental data were in excellent quantitative agreement with Goldstein's theory for scattering from systems in which the growth of the new phase is diffusion controlled. In the second case the data were explained using Rayleigh-Gans theory of light scattering for spheres and Frank's theory for diffusion-controlled growth. The results confirmed the existence as well as the extent of the composition gradient around the growing particles as predicted by diffusion-controlled growth theory.
Elastic Constants of Rhenium Single Crystals in the Temperature Range 4.2°–298°K
Authors: Shepard M. L. , Smith J. F.
Published: April 2005

The five independent elastic constants of single crystals of hexagonal close-packed rhenium have been determined by the ultrasonic pulse-echo technique over the temperature range 4.2°–298°K. The values at 298°K in units of 1011 dyn/cm2 are C11=61.25, C33=68.27, C44=16.25, C12=27.0, and C13=20.6. The bulk modulus derived from these constants shows a temperature variation somewhat analogous to that which has been reported for other 4d–5d transition metals. The Debye temperature calculated from the elastic constants at 4.2°K is 416.2°K.
The g Factor of Polycrystalline Magnetite at Low Temperatures
Authors: Sharma Virendra Nath
Published: April 2005

The g factor of polycrystalline magnetite was measured at liquid-nitrogen temperatures and at K-band frequencies. A high value of 4.06 for the g factor was obtained for the stoichiometric composition. The g factor gradually changed to 2.29 as the oxygen concentration of the sample was increased above the stoichiometric composition.
Gamma Irradiation of Silicon. III. Levels in p-Type Material
Authors: Sonder E. , Templeton L. C.
Published: April 2005

60Co gamma irradiation of p-type silicon produces donors in the lower half of the forbidden gap. From the temperature dependence of the electrical properties, a level 0.35 eV above the valence band was located for the case of silicon pulled from silica crucibles. For the case of float-zone silicon, two levels 0.21 and 0.28 eV above the valence band were found. The 0.35-eV level is introduced at the rate of 10−4 net donors/cm3 per photons/cm2. The introduction rate for the 0.21-eV level is lower than that for the 0.35 level, and that for the 0.27-eV level is so low that it was difficult to measure.
Morphological Changes of a Surface of Revolution due to Capillarity-Induced Surface Diffusion
Authors: Nichols F. A. , Mullins W. W.
Published: April 2005

The partial differential equation describing morphological changes of a surface of revolution due to capillarity-induced surface diffusion has been derived under the assumption of isotropy of surface tension and surface self-diffusion coefficient. A stable, convergent finite-difference method has been developed for the general case of an arbitrary surface of revolution and solutions have been obtained for the specific problems of the blunting of field-emission tips and the sintering of spheres. Spheroidization of cylindrical rods, as well as field-emission tips with taper below a certain critical value, is predicted; for tapers above the critical value, steady-state shapes are predicted and equations describing the blunting and recession of the tips are presented. If the sintering results for spheres are represented by a plot of log x/a vs log t, it is found that the inverse slope varies from approximately 5.5 to approximately 6.5 for the range 0.05≤x/a≤0.3, in contrast with the constant value of 7 found by Kuczynski from an order-of-magnitude analysis. At higher values of x/a, n increases steadily and without bound.
Sublattice Magnetizations of Yttrium Iron Garnet as a Function of Temperature
Authors: Prince E.
Published: April 2005

The intensity of the 220 neutron reflection of a single crystal of yttrium iron garnet has been measured as a function of temperature from 4.2° up to 598°K. The information from this, when combined with measurements of the saturation magnetization, yields values for the sublattice magnetizations Ma(T) and Md(T) individually. As was found previously with lithium ferrite, the sublattice magnetizations are significantly higher at temperatures between 0.5 Tc and 0.9 Tc, where Tc is the Curie temperature, than those predicted by molecular field theory. It has been shown that the effect of a biquadratic term in the exchange interaction can be approximated by distorting the temperature scale such that T/Tc = (T′/Tc)[1+βS2Ma (T′)Md(T′)/Ma (0)Md(0)], where Ma(T′) and Md(T′) are the sublattice magnetizations calculated at temperature T′ by molecular field methods, S is the spin of the magnetic ions, and β is an adjustable parameter. If the a-a and d-d interactions are neglected but the biquadratic correction is introduced with β = 0.04, the same value as in lithium ferrite, the fit with the experimental data is greatly improved. A maximum discrepancy of 5% between the observed and calculated magnetizations corresponds to a discrepancy of 1% in the sublattice magnetizations. This might be accounted for either by an improved approximation or by small values for the a-a and d-d interactions.
A Heat-Flow Problem in Electron-Beam Microprobe Analysis
Authors: Almasi G. S. , Blair J. , Ogilvie R. E. , Schwartz R. J.
Published: April 2005

In low melting point or low decomposition temperature materials with low thermal conductivity the local heating generated by the electron beam of an electron microprobe induces permanent damage to the sample and thus makes the technique unreliable. An aluminum layer of 1-μ thickness helps to dissipate the heat and lowers the temperature to tolerable levels. This paper analyzes the heat-flow problem of the two-layer target, consisting of the sample and the deposited aluminum layer, by the method of images and presents results for various thicknesses of aluminum. Experimental evidence is presented from HgTe and a Bi-Sb-Te-Se alloy on the usefulness of the method.
Low-Temperature Heat Capacity of Vitreous Germania
Authors: Antoniou A. A. , Morrison J. A.
Published: April 2005

The heat capacity of a specimen of pure vitreous germania has been measured between 2.3° and 23°K. An ``excess'' heat capacity is found which is qualitatively similar to that of vitreous silica which has been widely discussed. However, in contrast to the example of vitreous silica, the heat capacity of vitreous germania at the lowest experimental temperatures is very close to that corresponding to the elastic constants.

In the region just above T = 0°K, the ``excess'' heat capacities of both vitreous silica and germania can be accounted for within about the experimental error by the occurrence of small peaks in the low-frequency part of the vibrational distribution. The ratio of the frequencies of the lowest peaks is about 3, which is very close to the ratio of the temperatures at which acoustic attenuation is observed in the two glasses. Nevertheless, a direct correlation between attenuation and ``excess'' heat capacity does not seem possible. The integrated relaxation strengths of the ultrasonic attenuation are nearly the same in the glasses but the numbers of low frequencies required to explain the initial ``excess'' heat capacities differ by a factor of about 50.
Intensities of L X-Ray Spectra of the Lighter Elements
Authors: Wyckoff Ralph W. G. , Davidson Franklin D.
Published: April 2005

Relative intensities, as recorded with a flow proportional counter, have been measured for the L spectral lines of antimony (n = 51) through chlorine (n = 17).
Electron Emission, Electroluminescence, and Voltage-Controlled Negative Resistance in Al–Al2O3–Au Diodes
Authors: Hickmott T. W.
Published: April 2005

The temperature dependence of the conductivity of Al–Al2O3–Au diodes that exhibit voltage-controlled negative resistance (VCNR) in their current-voltage (I-V) characteristics, as well as electron emission and electroluminescence from such diodes, have been studied. Electron emission into vacuum and electroluminescence are both characterized by a steep increase in intensity for diode voltages greater than 1.8 V. Electron emission exhibits a second rise when the diode voltage exceeds the work function of the metal facing vacuum; electroluminescence, in contrast, is quenched when the diode voltage exceeds about 4V. The resistance of Al–Al2O3–Au diodes is independent of temperature down to 3°K if Vm, the voltage for maximum current in the I-V characteristic, is not exceeded. If the full I-V characteristic is traced out as temperature is decreased, diode resistance increases, VCNR in the I-V characteristic disappears, and electron emission into vacuum from the diode disappears. The attenuation length for electrons emitted into vacuum through the gold films of Al–Al2O3–Au diodes is ∼200 Å, independent of diode voltage; the attenuation length in the oxide is greater than 200 Å. Retarding potential measurements of the normal energy component of emitted electrons, and electroluminescence of diodes, show that some electrons gain energies in the oxide film that are higher than the applied voltage. The maximum excess energy gained is 4.1 V. Electroluminescence occurs from spots on Al–Al2O3–Au diodes. The spectrum covers the visible range with peaks of higher intensity at 1.8, 2.3, and 4.0 V. The experimental data are used to derive values of the parameters of a proposed model of VCNR in metal-insulator-metal diodes.
Relationship between Preferred Orientation, Thermal Expansion, and Radiation-Induced Length Changes in Graphite
Authors: Price R. J. , Bokros J. C.
Published: April 2005

Expressions may be derived for the thermal expansion coefficient of polycrystalline graphite in terms of the single-crystal coefficients and the preferred orientation of the sample. Thermal expansion and preferred orientation measurements were performed on pyrolytic, molded, hot-worked, extruded-rod, and extruded-tube graphites in order to test the validity of this model. They showed that such expressions adequately represent the behavior of several different graphites over a range of temperatures, provided that the ``accommodation'' of a part of the c-direction crystallite expansion by microcracks is taken into account. The amount of c-direction accommodation is a function of preferred orientation and the direction of measurement. It is small for the principal c direction in a highly oriented body and large for a random aggregate of crystallites and is probably controlled by the number of microcracks which form on cooling from the graphitization temperature. A model similar to that used for thermal expansion may be used to express the irradiation-induced dimensional changes in polycrystalline graphite in terms of the preferred orientation of the sample, a contraction in the crystallite a direction, and an expansion in the crystallite c direction which is partially accommodated by microcracks. The model was found to be in reasonable agreement with published irradiation data for a number of graphites.
Peierls-Barrier Minima
Authors: Hobart R.
Published: April 2005

Several authors predict minima in the Peierls energy barrier to the motion of a dislocation when the barrier is considered as a function of the elastic or force-law parameters of a crystal. The present paper reports a numerical calculation of the Peierls barrier in the Frenkel—Kontorova dislocation model modified to include the second harmonic of the force substrate. For the elastic constants of polycrystalline copper, the model predicts Peierls-barrier minima, at stacking-fault energies of 660, 530, 360, 210, 120, 62, 32,…erg/cm2, which range approximately from 10−5 to 10−2 times the intervening barrier maxima of about 2.5×10−9 erg/cm. This prediction is more accessible to experimental test since the stacking-fault energy of copper can be modified by alloying with silicon. The Peierls barrier can be determined according to the Seeger interpretation of the Bordoni experiment.
Effect of Thin Carbonaceous Films on 500-keV Helium Ion Sputtering of Copper
Authors: Smith Harold P. , DeMichele D. W. , Khan J. M.
Published: April 2005

A radioactive tracer technique capable of measuring less than 10−10 g of copper has been developed. A 500-keV magnetically analyzed beam of helium ions is used to observe the sputtering yield as a function of carbonaceous film thickness over a copper target. It is shown that an amorphous film of the order of 2×1017 atoms/cm2 reduces the sputtering yield of copper by a factor of 100. A first collision model of sputtered atom penetration of the film is in good agreement with the data and yields a copper—carbon cross section of 3×10−17 cm2. A clean surface sputtering yield of 2×10−2 atoms/ion is obtained by extrapolation of the data and is consistent with the yield of 800-keV D+ sputtering of copper reported by Kaminsky [Phys. Rev. 126, 1267 (1962)]. It is postulated that ordering of the amorphous film occurs for areal densities greater than 2×10+17 atoms/cm2 on the basis that the rate of reduction of copper yield with increasing film thickness undergoes a sharp decrease at that point.
Electrodes for Ceramic Barium Titanate Type Semiconductors
Authors: Landis Harry M.
Published: April 2005

A variety of commonly used methods for making electrical connections to ceramic semiconductors were compared, with indium amalgam, electroless nickel, and ultrasonic soldering having the lowest resulting resistances. It is suggested that, because of its ease of application, ultrasonic soldering may be the best over-all choice.
X-Ray Pinhole Photographic Evidence of Multiple Field-Emission Sources
Authors: Singer Barry , Doolittle H. D.
Published: April 2005

An investigation was carried out to exhibit the existence of localized field-emitting areas on nickel electrode surfaces. To this end, a system consisting of concentric cylindrical electrodes, whose radial electrode spacing and inner radius were 7.75 and 16 mm, respectively, and which had an effective length of 12 cm and a cathode area of 130 sq cm, was used as a source to expose x-ray films through a pinhole setup. The resultant images clearly show the existence of discrete electron beams bombarding the anode. There were an average of 3.5 spots per square centimeter at a gross field of 157 kV/cm. A number of Fowler-Nordheim plots were taken, and the usual result was a straight line. The x-ray sources from the anode were also found to be smaller than 0.1 mm.
Velocity Dependence during the Stick-Slip Process in the Surface Friction of Fibrous Polymers
Authors: Lyons W. James , Scheier Stanley C.
Published: April 2005

Examination of chart tracings representing frictional force during the slip phase of the stick-slip process, in fibers of two polymer types, revealed that these tracings do not have the sinusoidal character associated with a constant coefficient of kinetic friction. Considerations of the dynamics of the system of fiber surface and measuring instrument led to the suggestion that a velocity-dependent term be introduced into the equation of motion of the slider. The new force represented by this term was assumed to be directly proportional to the velocity of the slider. Curves for the displacement of the slider as a function of time, based on solutions of the modified equation of motion, for both the underdamped and overdamped cases, were found to be in excellent agreement with typical examples of the experimentally observed curves for the two fiber types. An expression is obtained for the coefficient of friction, which predicts the well-known experimental fact that, for most materials, the kinetic coefficient is less than the static.
Description of Crystallite Orientation in Polycrystalline Materials. III. General Solution to Pole Figure Inversion
Authors: Roe Ryong-Joon
Published: April 2005

A method is presented here by which orientation distribution of crystallites in anisotropic polycrystalline samples can be derived from a set of plane-normal distributions obtained by x-ray diffraction measurements. It is the generalization of the similar procedure proposed previously for analysis of samples having fiber texture. It thus represents a completely general solution to the problem of pole figure inversion, applicable to samples having any arbitrary symmetry elements. The plane-normal distribution function is expanded in a series of spherical harmonics, the coefficients of which, Qlmi, can be determined by numerical integration of experimental diffraction data. The crystallite distribution function is expanded in a series of generalized spherical harmonics which appear as solutions to the Schrödinger wave equation of a symmetric top. The coefficients of the crystallite distribution function, Wlmn, are then obtained as linear combinations of Qlmi. Symmetry properties of Wlmn arising from crystallographic or statistical symmetry elements existing in the sample are examined. The methods of estimating the series truncation errors and of minimizing the experimental error by a least-squares method, previously proposed in connection with fiber texture analysis, are still applicable here with appropriate generalizations. In addition it is shown that the effect of diffraction line broadening due to finite size or imperfection of crystallites can also be allowed for at least approximately.
Thermoelectric Properties of Niobium in the Temperature Range 300°–1200°K
Authors: Raag V. , Kowger H. V.
Published: April 2005

The electrical resistivity, thermal diffusivity, and Seebeck coefficient of niobium have been measured from 300°–1200°K. Using measured values of thermal diffusivity and literature values of specific heat, the thermal conductivity has been calculated for the same temperature range. The Lorenz number is 2.75 ×10−8 W-Ω-deg−2 and is independent of temperature. The absolute Seebeck coefficient is very close to zero, its largest magnitude being −2.6 μV/°K and occurring at 450°K. Data are also presented on the Seebeck coefficient of tungsten up to 1400°K.
Mechanics of Iron Inhibition during Dissolution of Lithium Fluoride Cleavages
Authors: Ives M. B. , Baskin Marjorie S.
Published: April 2005

Radiotracers of iron are used to obtain adsorption isotherms for iron adsorbed on lithium fluoride surfaces from dilute solutions of ferric chloride. The isotherms are related to the observed etch morphologies and substantiate the argument that the condition for good crystallographically defined etch features is achieved by ``monokink'' adsorption of iron on the surface. Two distinct mechanisms are proposed for the effect of iron on the morphologies. At low iron concentrations the adsorption of iron at kinks is rate controlling, but at higher concentrations diffusion control becomes increasingly dominant. It is suggested that the diffusion barriers are increased by ferric ion complexes in solution. Isotherms determined under the steady state conditions provided by solutions saturated with lithium fluoride are more reproducible and applicable to adsorption theories than those determined from etchants. β-track autoradiography and low-background counter methods are compared.
Theory of Magnetic Detection of the Heart's Electrical Activity
Authors: Baule Gerhard , McFee Richard
Published: April 2005

The currents set up in the chest by the electromotive forces of the heart produce magnetic fields at the chest surface which have a peak intensity of about one microgauss. To detect these fields, an optimized coil assembly has been constructed which yields an rms noise level of about 10−8 G in a 1- to 40-cycle band. The design of the coil assembly and the interpretation of its output are based on an analysis employing an unusual form of the reciprocity theorem. The theory shows that magnetic detection is fundamentally different from its electric counterpart and may reveal new clinical information. It also shows how immunity to magnetic interference can be achieved without resorting to bulky and expensive magnetic shields.
Nonlinear Optical Sum Generation in ADP using only Incoherent Light
Authors: McMahon D. H. , Franklin A. R.
Published: April 2005

Incoherent-incoherent nonlinear optical sum generation has been achieved in ADP using the intense infrared line spectrum from a xenon arc lamp source. The amount of sum power generated is in agreement with rough theoretical calculations.
Inelastic Scattering of Fast Electrons by Crystals. II. Phonon Scattering
Authors: Whelan M. J.
Published: April 2005

The inelastic scattering of fast electrons due to phonon excitation is examined using a simple Einstein model. The method of analytic approximation to the atomic electron scattering factor given by Smith and Burge enables analytic expressions for the Fourier coefficients of the imaginary potential due to phonon scattering to be obtained. The Fourier coefficients are computed for several elements and reflections and the temperature dependence is examined. It is concluded that phonon scattering could account for the localization of the complex potential at the atomic positions as required to explain anomalous absorption effects, in agreement with previous results of Yoshioka and Kainuma.
Shock-Induced Polarization in Plastics. I. Theory
Authors: Allison F. E.
Published: April 2005

Experiments have shown that some dielectric materials are electrically polarized by the passage of an intense shock wave. If the dielectric is contained between electrodes that are connected through a resistor, the shock-induced polarization produces an electric current, which can be detected as a voltage drop across the resistor. Equations are derived which relate the magnitude of the electric current to the shock propagation characteristics and dielectric properties of the material.
Anomalous Properties of Silicon Recrystallized Layers Containing Indium Atoms
Authors: Migitaka Masatoshi
Published: April 2005

Experimental studies have been made on junctions prepared by alloying indium into silicon wafers. The junctions made using n-type silicon, the resistivity of which ranges from 0.02 to 100 Ωcm, have good Ohmic characteristics, whereas the junctions made using p-type silicon, in the range of resistivities from 0.05 to 50 Ωcm, indicate rectifying characteristics like ordinary p-n junctions. From the measurement of thermoelectric voltages on recrystallized layers, electrical characteristics, and capacitance of the junctions, it has been concluded that the recrystallized layer containing indium atoms showed n-type electrical conductivity. The carrier concentration in these layers is estimated to be about 1017 cm−3 near the junction side and about 1019 cm−3 near the indium dot.