bluuebunny/crossref_metadata_2025_split huggingface dataset:
Uniaxial Anisotropy due to Magnetoelastic Energy in Constrained Polycrystalline Films
Authors: West Forrest G. 
Published: April 2005

A possible mechanism for uniaxial anisotropy in ferromagnetic films is the magnetoelastic energy Wλ which results from the constraint imposed on the film by the substrate. Below some temperature T′ at which the mobility of the film atoms on the substrate is sufficiently low, the constraint prevents the film from deforming in magnetostriction. An increase in the magnetoelastic energy, therefore, occurs when the film is magnetized in a direction other than that in which the film was deposited.
This paper examines this constraint energy in detail and shows that earlier calculations which have been based on the average polycrystalline magnetostriction are not correct in principle, since the correct calculation requires averaging the magnetoelastic energy over a polycrystalline aggregate. For the maximum value of Wλ at room temperature the correct calculation gives 4.2, 1.8, and 42 (103 erg cm−3) in nickel, iron, and cobalt, respectively. The value for iron is an order of magnitude larger than that given by earlier calculations. These values are found to be consistent with the experimental results of several groups of workers for films of nickel, iron, and cobalt deposited on amorphous substrates in vacua of less than about 10−5 Torr and for electrodeposited films of nickel and cobalt. The particular case of the temperature dependence of Wλ in nickel films is found to be in agreement with the reported experimental behavior when annealing of the constraint is allowed for. The annealing kinetics are discussed qualitatively in the light of observations by Benjamin and Weaver on film-substrate adhesion. This discussion predicts, in agreement with experiment, the possibility of room-temperature magnetic annealing in films deposited on unheated glass substrates in good vacua.
Evidence is also presented for the presence of constraint energy in evaporated films of the nickel-iron alloys, particularly near the 50% Ni composition. The calculations for the maximum room-temperature values of Wλ give a maximum of 3×103 erg cm−3 at 50% Ni and a minimum of about 20 erg cm−3 at 82% Ni.
Pressure Theory of the Thermoelectric and Photovoltaic Effects
Authors: Green Milton 
Published: April 2005

The theory is based upon the hypothesis that free charge carriers—electrons and holes—and phonons exert pressures inside a solid. Gradients of such pressures exert motive forces on the carriers. On this basis, the hole current density Ip, in the absence of a magnetic field, is assumed to be Ip=σpE−μpgrad Pp−μp[open phi]gradP[open phi],where σp, μp, and Pp are, respectively, the conductivity, mobility, and pressure of holes; μpφ is the interaction mobility between holes and phonons; Pφ is phonon pressure; and E is the electrostatic field. A similar expression is obtained for electrons by exchanging the subscript p for n. (The two mobilities associated with electrons, however, are negative.)
The theory is applied to the nondegenerate semiconductor, with the assumption that the equation of the ideal gas law applies. (Thus, Pp=pkT, Pn=nkT, where k is the Boltzmann constant, T is temperature Kelvin, and p and n are concentrations of holes and electrons, respectively.) It is also assumed— for small currents—that deviation from the equilibrium pressures can be neglected.
Assumptions concerning the phonon effect are quite general; the contribution from this source to the hole current density Ip is given by Ip[open phi]=−σp(kT/e)δp grad ln T,where e is magnitude of electronic charge. The dimensionless quantity δp, the phonon-dragging coefficient for holes (a temperature- and material-dependent parameter), is not amenable to calculation by the theory, in its present form, and must be determined experimentally. Again, a similar expression exists for electrons.
Energy Dependence of Proton Irradiation Damage in Silicon
Authors: Rosenzweig W. , Smits F. M. , Brown W. L. 
Published: April 2005

The energy dependence of radiation damage in silicon for proton energies in the range 1.35 to 130 MeV has been measured by observing the degradation of the bulk minority carrier diffusion length in silicon solar cells. Variability in proton flux determination at four different accelerators was minimized by employing prebombarded solar cells with known minority carrier diffusion lengths as calibrated solid-state ionization chambers. Where beam intensity measurement comparisons with Faraday cups could be made, agreement to better than 5% was obtained.
The quantity characterizing the damage rate is the rate of change of the inverse square diffusion length with flux K≡d(1/L2)/dΦ. The 1-Ω-cm p-type silicon degraded, on the average at a rate six times less rapid than 1-Ω-cm n type, independent of energy. Room temperature annealing gave 30% to 50% decrease in K whenever the diffusion length was measured during and after irradiation. The energy variation of K agrees with the variation predicted by Rutherford scattering below 8 MeV, but decreases less rapidly at higher energies.
The measured diffusion lengths increased with excess carrier density n from 2% per decade at n=109cm−3 to 20% per decade at n=1014cm−3. The reported results, obtained at low excess carrier density, can be used to predict solar cell degradation under conditions of outer space illumination if the appropriate excess carrier density is used. Failure to take into account the diffusion length variation will result in an underestimate of the solar cell output of less than 7%.
Microstrain Yield Stress in Neutron-Irradiated Copper Single Crystals
Authors: Koppenaal T. J. 
Published: April 2005

τ0, the stress necessary to produce a plastic strain of 2×10−6, has been measured with the use of electrical resistance strain gauges in neutron-irradiated copper single crystals as a function of neutron dose (∼1016 to 1020 neutrons/cm2) and testing temperature (77° and 300°K). τ0 increases from about 0.3 kg/mm2 for ∼1016 neutrons/cm2 to over 5 kg/mm2 for ∼1020 neutrons/cm2; in annealed copper crystals, τ0 is ∼0.02 kg/mm2 (previously determined by other researchers). At all neutron doses, τ0 is about 75% of the macroscopic flow stress. τ0 is observed to increase with the cube root of the neutron dose; the macroscopic flow stress shows the same dose dependence.
The results are explained on the basis of dislocation generation and obstacle cutting mechanisms controlling the yielding. These mechanisms are thought to be simultaneously operative.
An Analysis of Direct Energy Converters by the Methods of Irreversible Thermodynamics
Authors: Robinson Lawrence Baylor , Beaty Robert Carroll 
Published: April 2005

Methods of thermodynamics of irreversible processes are presented within the framework of the Burgers-Pipkin solution of the Boltzmann transport equation. The thermionic energy converter is treated as a thermocouple and analyzed by the nonequilibrium thermodynamic methods which are developed.
Following a general treatment, the cesium diode is treated as a specific example. Detailed calculations are made of the thermal conductivity and the electrical conductivity, as well as the ratio. In making the calculations, contributions from the electrons, positive ions, and neutral particles, are considered as well as interactions among the various types of particles. Binary interactions between the neutral particles, collective (Coulomb) interactions among charged particles, and (quantum-mechanical) collisions between electrons and neutral particles are taken into account. Each type of interaction has its appropriate effect on the thermal and electrical conductivities.
A brief discussion of the results and implications of the analysis is given, along with a reiteration of the assumptions and the limitations of the calculation.
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.
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.
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.
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.
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.
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&gt;1300°C.
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.
Neutron Diffraction Studies of Pd, Ni, FeMn, and Cu(Mn) Single Crystals
Authors: Arrott Anthony 
Published: April 2005

The possibility of antiferromagnetism in Pd at 4.2°K was investigated by using neutron diffraction to survey along lines in reciprocal lattice space from the origin through the (002), (111), and (220) positions and along lines from the (111) position to the (002), (001), and (110) positions. The sensitivity (except near nuclear peaks or near the origin) was sufficient to detect a magnetic induction wave of amplitude equal to 200 G (depending on form factor and distance from the origin a 200 G amplitude corresponds to from 0.02 to 0.03 μB). Despite several strange ``peaks'' in the patterns, no evidence of antiferromagnetism was inferred from the data.
The possibility that Ni possesses a helical component to its ferromagnetism (similar to the familiar conical spin arrangement in holmium) was investigated by neutron diffraction with a field applied along the (111) direction of a Ni crystal at 4.2°K. The line from the origin of reciprocal space through the (111) nuclear peak was surveyed with the same sensitivity as the Pd experiment and with the same qualifications one could conclude that any such conical spin arrangement must have a cone angle of less than three degrees.
The same survey as made for Pd was carried out in Cu(5%Mn) and the results were similarly negative as far as demonstrating antiferromagnetism. Cu(15%Mn) shows very broad peaks which could be indexed as (1½0) and (½10) and these vectors added or subtracted with respect to any primitive reciprocal lattice vector. The temperature independence of these reflections from 4.2° to 420°K points to the likelihood that they arise from an atomic ordering rather than from a magnetic ordering. This ordering is just detectable in the Cu(5%Mn) specimen.
The antiferromagnetism of FeMn was investigated as this material appears (from resistivity and susceptibility data) not to possess ``localized moments'' above its Néel temperature. The temperature dependence of the spontaneous magnetization mode (a longitudinally polarized wave with (π00) wave vector) does not show a sharp break at the Néel temperature. This is due to the excitation of sizeable fluctuations in the magnetization modes. The fluctuating modes for a wide range of wave vectors are observed over a wide temperature range above and below the Néel temperature.
Low-Temperature Magnetic Susceptibilities of the Hydrated Nickel Nitrates
Authors: Berger L. , Friedberg S. A. 
Published: April 2005

The zero-field magnetic susceptibilities of Ni(NO3)22H2O, Ni(NO3)24H2O, and Ni(NO3)26H2O have been measured in the liquid-hydrogen and liquid-helium ranges. The dihydrate is obtained by evaporation of a solution at 105°C.1 Its powder susceptibility has a large, sharp, peak at 4.20°K, where it reaches 0.74 cgs/mole, then drops down to 0.2 cgs/mole below 2°K. When measured along the a axis, the susceptibility of monoclinic single crystals of the dihydrate shows a similar peak. It reaches 1.5 cgs/mole, but drops to vanishing values at lower temperatures. The susceptibility in the bc plane reaches only 0.3 cgs/mole, and is nearly isotropic. It drops little below 4.20°K. This behavior is similar2-5 to that of FeCl2 or FeCO3, and suggests the existence of two magnetic sublattices, with strong ferromagnetic interactions within each sublattice, and weaker antiferromagnetic interactions between one sublattice and the other (metamagnetism). Direct evidence for such a layer structure is also provided by a recent x-ray structural work.6 A spin Hamiltonian with S=1 and uniaxial one-ion anisotropy gives results in fair agreement with the experimental data if the exchange interactions are described in the molecular field approximation. The best fit corresponds to g=2.25, D/k=−6.50°K, n1=+0.32 mole/cgs, n2=−2.12 mole/cgs, where n1 and n2 are, respectively, the antiferromagnetic and the ferromagnetic molecular field constants. In the case of the tetrahydrate1 and of the hexahydrate, the powder susceptibility approaches a constant value of 0.35 cgs/mole below 2°K; the data can be fitted to the spin Hamiltonian7 for a nickel ion in a rhombic field, without exchange, with E/k=−2.66°K, D/k=−8.67°K, and g=2.25.
A detailed account of this work has been published elsewhere.8