bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron Paramagnetic Resonance of Trivalent Gadolinium in the Yttrium Gallium and Yttrium Aluminum Garnets
Authors: Rimai L. , deMars G. A.
Published: April 2005

The spin Hamiltonian parameters for Gd+++ when substituted for Y+++ in two diamagnetic garnets, YAlG and YaG, have been determined by electron paramagnetic resonance techniques. From these results the contribution of the independent Gd+++ ions to the anisotropy of gadolinium iron garnets may be estimated. The fourth-order constants in the spin Hamiltonian are very similar in YAlG and YGaG and their contribution to the anisotropy constant in GdIG shows good agreement with the experimental data. The contribution of the second-order constants falls short of the values needed to fit experimental data by an order of magnitude. These constants, however, differ markedly in the two garnets and thus their use to predict anisotropy in GdIG is not justified. The present results, therefore, are not in disagreement with a model that ascribes the origin of the crystalline anisotropy in magnetic garnets to the anisotropy energy of the individual ions in the presence of the crystalline electrostatic field.
Magnetodynamic Mode Ferrite Amplifier
Authors: Roberts Roy W. , Auld Bert A. , Schell Robert R.
Published: April 2005

A longitudinally pumped ferrite amplifier has been operated using two magnetodynamic modes for the signal and idler resonant circuits. This is in contrast to the more usual electromagnetic cavity-type resonance or the ferrite magnetostatic modes. These magnetodynamic modes result from the coupling of a cavity-type resonance with a magnetostatic resonance. The coupling or mixing is strongest when the two unperturbed resonant frequencies are the same.

For the amplifier described in this paper a single crystal yttrium-iron garnet sphere was used. The magnetic bias field applied was 17 kMc/γ oe. The resulting magnetodynamic modes were resonant at 21 and 14 kMc, respectively, for the two branches of the mode tuning curve.

Advantages of these modes for ferrite amplification are ease of coupling and lack of interference from other resonant modes.
Millimeter Wave Parametric Amplification with Antiferromagnetic Materials
Authors: Moore R. A.
Published: April 2005

The use of material with natural magnetic resonances in the millimeter and submillimeter wave bands makes possible electromagnetic interaction without an extremely large applied magnetic field. Antiferromagnetic materials most suitable for microwave application Cr2O3 and MnFe2 display resonances at approximately 160 and 250 kMc.

In the presence of a magnetic field applied parallel to the sublattice magnetizations, the uniform precessional mode resonates at different frequencies for oppositely directed circularly polarized excitation. A perturbation analysis has been conducted to determine the parametric response of the oppositely directed uniform precessional modes to longitudinal pumping. For materials with a sufficiently narrow linewidth, very close coupling between the uniform precessional mode on an external coaxial, stripline, or waveguide signal circuit is possible. Calculations have been conducted on the response of an antiferromagnetic medium in a silver cavity resonant to the pump frequency. The pump power absorbed by the cavity at the threshold of amplification for Cr2O3 would be 2(10)4 w. Narrower linewidth materials are needed for efficient antiferromagnetic millimeter and submillimeter amplification.

A more efficient utilization of the pump power and a simplified structure for millimeter wave application results when the pump fields are supported by a dielectric rod mode resonance. If the rod is placed across the narrow dimention of rectangular waveguide, the broad metallic wall forms the conducting end plates of the H11 mode. The signal TE01 waveguide mode couples to the appropriately directed circularly polarized uniform precessional resonance of the antiferromagnetic material on the rod.
A Microwave Magnetic Microscope
Authors: Soohoo R. F.
Published: April 2005

A microwave magnetic probe capable of measuring the spatial variation of the magnetic properties of materials has been developed. In contrast to other forms of microscopes, this instrument measures the spatial variation of the important magnetic properties of a sample directly by a selective microwave resonance technique. To date, we have observed clear resonances in portions of Permalloy films (∼1000 A thick) with a cross-sectional diameter of 0.010 in. By using a cavity made of superconducting material, it is anticipated that resonances in spots as small as 200 A in cross-sectional diameter may be observed. Some representative experimental results using this microscope are given to indicate its utility.
Microwave Resonance Linewidth in Single Crystals of Cobalt-Substituted Manganese Ferrite
Authors: Teale R. W.
Published: April 2005

Measurements of the microwave resonance linewidth ΔH are reported for small spherical single crystal specimens of nominal composition CoxMn1−xFe2O4 where, x=0, 0.02, 0.04, 0.08, 0.10. Accurate chemical analyses have been published. ΔH varies rapidly and linearly with x. At 294°K and 16.9 Gcps the gradients of ΔH against x observed are 4.0×103 and 3.0×103 oe per cobalt ion for the [100] and [111] directions, respectively. At 9.6 Gcps the corresponding gradients are 2.7×103 and 2.1×103. Measurements on disk samples for x=0.08 gave results similar to those for a sphere. At 16.9 Gcps ΔH is plotted against temperature between 150° and 500°K for x=0, 0.04, and 0.08. Above 250°K ΔH varies only slowly with temperature. Below 150°K ΔH increases and becomes anisotropic rapidly; this is associated with anomalies in the field for resonance. The results suggest that magnon-magnon scattering by the cobalt does not make a significant contribution to ΔH. The behavior observed bears a qualitative resemblance to that of yttrium iron garnet doped with certain rare-earth ions, but the fast relaxing ion model, successful for some of these, does not fit the present measurements.
On the Possibility of Obtaining Large Amplitude Resonance in Very Thin Ferrimagnetic Disks
Authors: Morgenthaler F. R.
Published: April 2005

A theoretical prediction is made that the uniform resonance and the spinwaves in a very thin ferrimagnetic disk can be made nondegenerate. If this condition can be achieved experimentally, the usual second order spinwave instabilities will be forbidden and cannot limit the component of the magnetization occurring at the resonance frequency (ω0). The precession cone angle (θ) should then increase, in response to the usual rf driving field, until limited by third order instabilities involving spinwaves with frequencies equal to 32 ω0.

The state of nondegeneracy is to be achieved in the following manner: A thin disk, magnetized in a direction perpendicular to the plane, is excited by two transverse positive-circularly-polarized pulsed rf magnetic fields of specified amplitude. One of these fields has a frequency equal to ω0, the other a frequency detuned from ω0 by an amount comparable to the width of resonance. As θ increases from zero during the ensuing transient, there will occur a point at which the familar second order coupled spinwaves become unstable (the state of nondegeneracy has not yet been reached). Since there is a time lag before these modes can effect the uniform precession, the cone angle will continue to increase. When some larger value of θ has been attained the degeneracy between the spin waves and the resonance is removed; the previously unstable spin waves are then decoupled from the uniform resonance.

The degeneracy is removed because, as the author has already shown theoretically, the resonance frequency of the thin disk should lie below the main spinwave band (volume band) provided θ> (2Nt)½, where Nt (the transverse demagnetizing factor) is by assumption very small. This level of excitation would create the desired state of nondegeneracy, if it were not for the fact that a range of degenerate spinwaves (separate from the main band) still exists. These degenerate modes may be destroyed, however, by introducing the additional transverse rf field.

Large amplitude resonance would clearly be desirable for a variety of reasons. Optical modulation experiments, to give only one example, would be of great interest. The necessity for using thin disks or films is, in this case, a fortuitous circumstance. It also follows that any nonlinear device involving harmonic generation, frequency mixing, etc. would become more efficient.
dc Effects in Ferromagnetic Resonance in Thin Ferrite Films
Authors: Heinz W. , Silber L.
Published: April 2005

The dc voltage which accompanies ferromagnetic resonance has been observed in thin films of magnetite. The dependence of this voltage on microwave power and static magnetic field is in qualitative agreement with theory, but larger by a factor of 3.
Failure of the Local-Field Concept for Hysteresis Calculations
Authors: Brown William Fuller
Published: April 2005

The ``local field'' is the electric or magnetic field of external sources and of all molecules or particles except the one under examination, at the position of that one. The concept is useful in the molecular theory of dielectrics, where the basic relations are linear. It has also been applied, however, to magnetically interacting single-domain particles in a ferromagnetic powder; here the relations not only are nonlinear but involve discontinuous irreversible jumps, for which instability conditions are decisive. The local-field concept is then unreliable. In a two-particle system, for example, the local-field method examines the stability of one moment with respect to rotation in a fixed field due to the other moment and to external sources; this procedure imposes a constraint, for in the actual system the two moments may rotate simulatneously and independently. The incorrectness of the local-field method is demonstrated here by calculations for two-and three-particle chains of spheres and for two- and three-part composite cylinders. The concept of an interaction field that merely displaces the hysteresis loops of the particles without changing their widths, as in a common interpretation of the Preisach model, is thus erroneous.
The Preisach Diagram and Interaction Fields for Assemblies of γ-Fe2O3 Particles
Authors: Bate G.
Published: April 2005

The Preisach diagram calculated for an assembly of γ-Fe2O3 particles at a packing density of 20% by volume has been used to obtain a distribution function of the particle remanence-coercivities in the absence of interaction fields. This function, which has a peak at 275 oe, is then compared with the function obtained by differentiating the remanence hysteresis loop, i.e., with the distribution function in the presence of interaction fields. It is found that the latter function is broader than the former; this can be qualitatively explained in terms of a two-particle model for the interacting particles. The magnitude of the interaction fields can be estimated from the Preisach diagram and is found to have a maximum value of roughly 300 oe.
Saturation Magnetization of Swaged Mn–Al
Authors: Bohlmann M. A.
Published: April 2005

Two years ago remarkable properties were reported for a new alloy based on manganese and aluminum. The value for saturation magnetization in Mn=Al had been extrapolated to infinite magnetizing field and was given as 6200 gauss. Our measurements indicate that the extrapolated figure is too low. Magnetization values of over 7100 gauss have been measured at 13 000 oe. Extrapolations of these values to infinite fields are not made because of anomalies in the magnetization curves at 7500 oe and 12 000 oe. The material having the high magnetization had an energy product of 4.0×106 gauss oe.

To reach the high values, it was necessary to adhere to processes and procedures having narrow limits. Saturation magnetization depended directly on composition, homogenizing, quenching rate, annealing, and deformation. The latter was most critical because a preferred axis of orientation is developed by this process. Mn–Al is very brittle, but the brittleness problem was circumvented by swaging the material in suitable jackets.

Rockwell tests indicate that hardness is directly related to 4πM.
Studies of High Coercivity Cobalt-Phosphorous Electrodeposits
Authors: Sallo J. S. , Carr J. M.
Published: April 2005

Electrodeposited Co–P films have been prepared having coercivities of 1000 to 1300 oe in the plane of the film. The material has been studied by means of x-ray diffraction, electron microscopy, and the Craik technique. It is concluded that the material has a rod-like structure and that shape anisotropy is at least partially responsible for the observed coercivity. The magnetic properties of this material are compared with those of previously reported platelet materials. An attempt is made to explain the properties of both rod and platelet materials on the basis of single domain particle theory.
Remanent Torque Studies in Polycrystalline BaFe12O19
Authors: Flanders P. J. , Shtrikman S.
Published: April 2005

Measurements of the anisotropy distribution in BaFe12O19 were carried out using the remanent torque technique. Two randomly oriented powder samples with coercive forces of 1500 and 4000 oe were tested. The remanent torque curves for both samples were essentially identical indicating an anisotropy distribution with an average of 2.1±0.2×106 ergs/cm3 compared with a value of 3.3×106 ergs/cm3 for single crystal BaFe12O19. The origin of this disagreement is unclear but it seems to be associated with splitting into domains.
The Effect of Angular Variations in Field on Fine-Particle Remanence
Authors: Daniel Eric D. , Noble R.
Published: April 2005

The Stoner-Wohlfarth model is used to calculate the remanence of a randomly-oriented assembly of singledomain particles when the applied field changes in direction. The cases considered are (1) fields applied successively in directions differing by multiples of ½π and (2) fields rotated through multiples of ½π. Some consideration is also given to the anhysteretic remanence when the unidirectional and alternating fields are orthogonal. Experimental results obtained on disks of γFe2O3 recording tape are found to be in reasonably good qualitative agreement with the calculations.
Possibility of Domain Wall Nucleation by Thermal Agitation
Authors: Aharoni Amikam
Published: April 2005

Very fine particles reverse their magnetization spontaneously, passing the energy barrier by means of thermal activation. In the same way one could argue that small portions of larger particles could be spontaneously reversed, thereby serving as nucleii for reversed domains. These can then grow, because it is known that the energy favors subdivision into domains. In treating such a possibility, however, one should take into account the additional barrier for forming a wall around the ``nucleus,'' which is usually left out in standard domain theory calculations when the wall energy is used. This energy is rather small but the barrier for formation of the wall is large.

The model studied is a small sphere, centrally located inside a spherical particle, the magnetization in which starts to rotate gradually from the z direction in which the rest of the particle is magnetized. The angle between magnetization and the z axis is assumed to vary linearily in the radial coordinate, from zero on the surface of the inner sphere, to its maximum value in the center. This value eventually reaches π, thus completing a wall around a reversed domain of radius zero, which should then start to grow by further supply of energy.

Studying the energy barrier for such a process, it is seen that the main contribution is from the exchange energy, which practically forbids the process. The probability for a domain wall to nucleate at room temperature is thus shown to be negligibly small, which justifies the neglection of temperature affects in Brown's equations.
Alloys of the First Transition Series with Pd and Pt
Authors: Pickart S. J. , Nathans R.
Published: April 2005

Neutron diffraction measurements on the ordered fcc alloys FePd3, MnPt3, and Cr0.3Pt0.7 support the existence of localized magnetic moments on the Pd and Pt atoms. The individual moments were determined by combining the difference in moment, based on reasonable assumptions about the magnetic form factors, with the total moment as determined from magnetization measurements. The results for FePd3 are consistent with suggestions based on magnetization measurements; at 300°K Fe has a moment of 2.73±0.13 μB and Pd of 0.51±0.05 μB. In MnPt3 at 77°K a small moment on the Pt is observed (0.17±0.04 μB), with most of the moment residing on the Mn (3.60±0.09 μB). At room temperature the magnetic ordering in Cr0.3Pt0.7 is ferrimagnetic, with a Cr moment (if assumed equal on both Cr and Pt sites) of 2.56±0.10 μB and a Pt moment of 0.47±0.05 oppositely aligned.
Neutron Diffraction Investigations of Ferromagnetic Palladium and Iron Group Alloys
Authors: Cable J. W. , Wollan E. O. , Koehler W. C. , Wilkinson M. K.
Published: April 2005

In order to account for the magnetic properties of alloys it becomes important to determine the individual magnetic moments of the constituent atoms. This determination can be accomplished by the combination of neutron diffraction and magnetic induction measurements. Such measurements were made on the following ferromagnetic alloys: Pd3Fe, PdFe, Pd3Co, PdCo, Ni3Co, and NiCo. The average moment values were obtained from magnetic induction measurements while the differences in the atomic moments were determined from either the ferromagnetic diffuse scattering of the disordered alloys or the superlattice reflections of the ordered alloys.
Age-Hardened Gold Permalloy and Gold Perminvar
Authors: Nesbitt E. A. , Gyorgy E. M.
Published: April 2005

This work is an extension of previous work which showed that the addition of gold to Permalloy caused the precipitation of a gold-rich phase and thereby permitted the control of the coercive force by heat treatment. This addition of a second phase to Permalloy greatly improved the switching speed of the alloy. Some compositions of gold Permalloy had switching speeds four times faster than that of the standard composition. In the present work, some of the details of the precipitation process were studied. It was found that for some specimens annealed at 650°C, the precipitation of the gold-rich phase depended strongly upon cold working. When some alloys containing gold were quenched from the solution temperature and annealed at 650°C for 2 hr, there was little increase in coercivity and the electron micrographs showed practically no precipitation of particles of 1000-A diameter or larger. However, when the material was quenched from the solution temperature, drastically cold rolled and annealed at 650°C, the coercivity was increased substantially and the electron micrographs revealed the presence of many particles having a diameter of 1000 A. Seven percent gold was also added to the Perminvar composition of 43% Ni-34% Fe-23% Co. The alloy behaved in a manner somewhat similar to the gold-Permalloy compositions. Age-hardening appeared in the vicinity of 600°C and square hysteresis loops were obtained. However, the threshold for rapid rotational flux reversal was substantially higher than the coercive force. Consequently, these alloys appeared less desirable for switching applications than Permalloy.
Paramagnetic Behavior of Iron-Rich Iron-Vanadium Alloys
Authors: Arajs Sigurds , Colvin R. V. , Chessin Henry , Peck J. M.
Published: April 2005

Magnetic susceptibilities of 14 iron-vanadium alloys (to 26 at.% V) have been studied between their Curie temperatures and 1500°K. These alloys exhibit unusual paramagnetic behavior. Plots of the magnetic susceptibility vs vanadium concentration have a maximum which decreases with increasing temperatures. The curve of the paramagnetic Curie temperature vs at.% V also exhibits a maximum at about 10 at.% V. The paramagnetic moment per iron atom decreases gradually with the amount of vanadium in iron.
Magnetic Structures of Mn2As and Mn2Sb0.7As0.3
Authors: Austin A. E. , Adelson E. , Cloud W. H.
Published: April 2005

Neutron diffraction has been performed on powder specimens of Mn2As and Mn2Sb0.7As0.3. Mn2As has the antiferromagnetic structure found in Mn1.9Cr0.1Sb below the exchange inversion temperature. The atomic moments are 3.7 and 3.5 Bohr magnetons for Mn(I) and Mn(II), respectively. The moments lie perpendicular to the tetragonal axis. The magnetic structure of Mn2Sb0.7As0.3, which undergoes exchange inversion over the 35° to 115°C temperature range, is the same as that of Mn2As at room temperature and is the same as that of ferrimagnetic Mn2Sb at 150°C. The atomic moments at room temperature (antiferromagnetic) are 2.3 and 2.8 Bohr magnetons, respectively, for Mn(I) and Mn(II). The moments are perpendicular to the tetragonal axis at room temperature and parallel to it at 150°C.
Hexagonal Ferrites for Use at X- to V-Band Frequencies
Authors: Rodrigue G. P. , Pippin J. E. , Wallace M. E.
Published: April 2005

A series of uniaxial materials has been prepared and studied in which the effective anisotropy field can be controlled and varied over the range of 0 to 12 700 oe. The materials are solid solutions of the NiW and CoW compounds and have the chemical formula BaO·2[Ni1−xCoxO]·7.8Fe2O3 with x varying from zero, where the anisotropy field is 12 700 oe, to 0.5 where the anisotropy field is vanishingly small. The temperature dependence of the net resultant anisotropy field, linewidth, and g factor of these materials is discussed. By using oriented polycrystalline samples of these materials, the effective internal anisotropy field can be used to augument external applied fields. Different materials of this series have been used to construct resonance isolators at V- and K-band frequencies with bandwidths of the order of 20% and peak isolation ratios of greater than 30 to 1.
Plasma Potential Measurements Using an Ion Beam Probe
Authors: Haste G. R. , Barnett C. F.
Published: April 2005

The space potential of the plasma contained in the DCX-1 has been investigated using a beam of lithium ions. The ions were accelerated through a variable potential from a thermionic source and directed toward the plasma. The beam energy at which the transmission became significant was defined as the plasma space potential. The potentials obtained in this way have shown an increase with plasma density but have only a weak dependence on the background gas pressure.
Influence of Tensor Conductivity on End Currents in Crossed Field MHD Channels with Skewed Electrodes
Authors: Podolsky Boris , Sherman A.
Published: April 2005

An investigation has been carried out of the current and electric field distributions in the end region of a crossed field MHD device (accelerator or generator), with skewed electrodes, for the case in which the plasma exhibits the Hall effect. In order to simplify the situation enough to permit analytic solutions, a two-dimensional problem was considered wherein the plasma velocity and properties, and magnetic field intensity were taken to be constant and uniform. Solutions were obtained for several values of ωτ (ω=electron cyclotron frequency, τ=electron mean free time); they show that current flows a considerable distance upstream of the beginning of the electrodes, that some current concentration exists at one of the electrode corners, and that displacing this electrode upstream reduces this current concentration somewhat.
Sinusoidal Shear Generator for Study of Viscoelasticity
Authors: Miles D. O.
Published: April 2005

An apparatus is described in which a pure dynamic shear strain is produced in a small sample of liquid or other material, and the resulting shear stress is measured in the frequency range between 20 and 1000 cps. The shear stress is decomposed into its real and imaginary parts, which yield the shear rigidity and the shear viscosity. Design and working equations are derived. Two liquids are investigated and the data shown. The effect of impurity molecules is discussed, and a possible application to lubrication theory is suggested.
Kossel Line Studies of Irradiated Nickel Crystals
Authors: Hanneman R. E. , Ogilvie R. E. , Modrzejewski A.
Published: April 2005

Irradiation damage of nickel single crystals bombarded with 3 Mev electrons has been studied by Kossel line techniques. Changes of lattice parameter and x-ray line breadth were determined for crystals bombarded with integrated dosages of 1016, 1017, and 1018 electrons/cm2 at liquid nitrogen temperature. It is concluded that the formation of Frenkel defects in the lattice due to the electron bombardment is consistent with the data obtained. Subsequent annealing studies support this conclusion.

Using an electron microbeam probe to obtain the Kossel patterns, the absolute precision of the lattice parameter obtained is better than 1 part per 100 000 or ±0.00003 A. The limit of relative precision of change in lattice parameter of a given crystal is 3 parts per 1 000 000 or 0.00001 A. Basic principles of the formation of Kossel lines, experimental arrangements, various errors, and related models are presented.
Lattice Parameter Studies of Annealed, of Aged, and of Cold-Worked Alpha Brass
Authors: Otte Henry M.
Published: April 2005

On aging at 120°C two annealed alpha brasses containing 30 and 35% Zn, respectively, a small (about 0.0003 to 0.0006 A) reduction in the lattice parameter occurs. In the present work all diffraction lines in the spectrum were measured using monochromated CuKαi radiation, and all indicated the same change. Cold work induced by filing produced a measurable amount of stacking faults as detected by the shifts in the diffraction lines and in addition caused an apparent increase in lattice parameter of about 0.0008 A. On aging these cold-worked alloys for over 1000 hr at 120°C, the lattice parameter decreased. For the Cu-35Zn the decrease was 0.0037 A and was accompanied by the precipitation of a small but measurable amount of beta phase. Thereby the solubility limit of the alpha phase was placed between 33 and 34% Zn. The Cu-30Zn alloy also showed a decrease in the lattice parameter of 0.0029 A but, as expected, no beta phase. In neither case was there any observable change in the stacking fault density. These data are interpreted in terms of solute clustering, possibly to stacking faults, as considered by Suzuki. It is suggested that solute clustering may also be the cause of the decrease in lattice parameter for the annealed and aged alloys, rather than short-range ordering.
Twinning in Permalloy Films as Observed by Electron Diffraction and Electron Microscopy
Authors: Schoening F. R. L. , Baltz A.
Published: April 2005

Permalloy films (83 wt.% Ni-17 wt.% Fe) epitaxially grown on NaCl, were annealed by electron bombardment in an electron microscope. Perfect single-crystal diffraction patterns indicated the presence of the [100] parent crystal and [122] twin crystals. Fringe patterns observed on electron micrographs were identified by dark field microscopy and electron diffraction as being caused by platelets of twins, 100–400 A thick, lying parallel to {111} planes of the parent crystal. The nonintegral reflections, commonly observed in conjunction with twin reflections, were shown to be caused by double diffraction.
Electron Space-Charge-Limited Operation of Cesium Thermionic Converters
Authors: Carabateas E. N.
Published: April 2005

Recent experimental results from a cesium thermionic converter reported by Houston and Gibbons show that at low emitter temperatures and high cesium pressures the output current approaches an asymptotic value as the emitter is made more and more negative with respect to the collector. With further decrease in voltage the current jumps to much higher values. The assumption was made by Houston and Gibbons that the operation of the converter under these conditions is electron space-charge-limited and that in the high current mode, collision ionization is present. In the present communication a quantitative analysis of this electron space-charge-limited operation is presented. On the basis of this assumption an expression for the limiting value of the output current is obtained. A method is outlined by means of which the difference in emitter and collector work functions can be found from an experimental current-voltage characteristic and conversely such a characteristic can be plotted if sufficient information is given. This method is applied to experimental I–V curves obtained from a parallel plate converter with a tantalum emitter. From these curves the emitter work function and the true saturation current have been estimated. These values of work function are approximately 0.5 v less than extrapolated values obtained from other experiments reported in the literature for cesium on tantalum. With the assumption that ions are introduced in the interelectrode spacing only by surface ionization, the magnitudes of the emitter and collector sheaths are computed at different points of the I–V curve.
Measurements of Dielectric Constant of Rutile (TiO2) at Microwave Frequencies between 4.2° and 300°K
Authors: Sabisky Edward S. , Gerritsen Hendrik J.
Published: April 2005

The microwave dielectric constant k′ and loss tangent (tanδ) of rutile have been measured as a function of temperature from 4.2° to 300°K. At low temperatures, k′ approaches the limiting value of 256 in the c direction and 131 in the a direction. The loss tangent at 4.2°K is 2.5×10−6 for pure rutile and increases by an order of magnitude for both 0.12% chromium and 0.2% iron-doped rutile.
Multiple Ribbons of Partial Dislocations in Chromium Chloride
Authors: Amelinckx S. , Delavignette P.
Published: April 2005

In chromium chloride the basal dislocations consist of ribbons containing either four or six partials. It is possible to explain this behavior in detail on the basis of the crystal structure.
Observation of Fission Fragment Damage in Thin Films of Metals
Authors: Kelsch J. J. , Kammerer O. F. , Goland A. N. , Buhl P. A.
Published: April 2005

Direct observation of the effects of fission events has been made in thin films of Al and Pt by transmission electron microscopy.

A very thin layer (10 to 20 A thick) of UO2 was incorporated between evaporated metal films. The samples were exposed to a total thermal neutron flux of 2.8×1015 n/cm2. The fission fragments produced tracks in the matrix, the characteristic appearance of which is strongly influenced by the thickness and the atomic number of the matrix.

The mechanism of track formation is discussed from the viewpoint of dissipation of energy by the thermal spike mechanism.
Mechanics of Deformation and Acoustic Propagation in Porous Media
Authors: Biot M. A.
Published: April 2005

A unified treatment of the mechanics of deformation and acoustic propagation in porous media is presented, and some new results and generalizations are derived. The writer's earlier theory of deformation of porous media derived from general principles of nonequilibrium thermodynamics is applied. The fluid-solid medium is treated as a complex physical-chemical system with resultant relaxation and viscoelastic properties of a very general nature. Specific relaxation models are discussed, and the general applicability of a correspondence principle is further emphasized. The theory of acoustic propagation is extended to include anisotropic media, solid dissipation, and other relaxation effects. Some typical examples of sources of dissipation other than fluid viscosity are considered.
Saturation of Ferrimagnetic Resonance with Parallel Pumping
Authors: Gottlieb P. , Suhl H.
Published: April 2005

The microwave susceptibility for subsidiary ferrimagnetic resonance with parallel pumping is calculated from the saturation amplitude of the unstable spin waves. The limiting of these runaway magnons is caused by three, four, and higher number magnon interactions. These interactions can lead to a nonlinear (as well as the usual linear) relaxation rate, which can be evaluated using certain approximations. The main features of the results agree with experiment.
X-Ray Observations of Partial Dislocations in Epitaxial Silicon Films
Authors: Schwuttke G. H.
Published: April 2005

Crystal perfection of epitaxial silicon films has been studied by x-ray diffraction microscopy. X-ray observations indicate the presence of defects in {111} planes with 〈112〉 Burgers vectors. The x-ray image associated with these defects is interpreted as due to stacking faults bounded by partial dislocations. Large stacking faults, the faulted area between the partials as wide as 10 μ, have been found to be the principal imperfections in epitaxially grown silicon films.
Photoeffect in Au-CdS and Cu-CdS Photovoltaic Cells
Authors: Fabricius E. D.
Published: April 2005

A study has been made of the photovoltaic effect in Au-CdS and Cu-CdS photocells in an attempt to determine the origin of the conducting electrons. Evidence is presented to show that, for evaporated films of gold and copper on copper-doped CdS, the entire photovoltaic current is due to electronic excitation in the depletion region of the CdS crystals.
Na(Nb1−xVx)O3 System and ``Ferrielectricity''
Authors: Miller Robert C. , Wood Elizabeth A. , Remeika Joseph P. , Savage Albert
Published: April 2005

Following a report of ferroelectricity at room temperature in Na(Nb1−xVx)O3, crystals of pure NaNbO3 and Na(Nb1−xVx)O3 have been investigated electrically, optically, and by x-ray diffraction. Attempts to introduce amounts of vanadium larger than x≈0.005 into the crystals were unsuccessful. The room temperature phase of pure NaNbO3 has been reported to be antiferroelectric, that of NaVO3 nonferroelectric but perhaps also antiferroelectric. The vanadium-doped crystals appear to be antiferroelectric in the room temperature as grown state. A transition to a ferroelectric phase can be induced in both the vanadium-doped and the pure crystals by a sufficiently high field (of the order of 50 kv/cm), called the transition field, applied normal to the orthorhombic b axis. In one type of crystal plate, when the field-induced transition into the ferroelectric phase occurs, a crystallographic reorientation is also observed. Some crystals revert to the nonferroelectric phase when the transition field is removed.

All of the crystals investigated while in the ferroelectric phase were found to have the length of the b axis twice the length of the simple perovskite cube, whereas in the antiferroelectric phase, the length of the b axis is four times that of the simple perovskite cube.

In so far as the phenomena studied in the present investigation are concerned, it can be stated that the vanadium-doped crystals behave in most respects like pure NaNbO3 crystals. In particular, no evidence was found for an unbalanced antidipole configuration, i.e., ``ferrielectric'' structure, proposed by another investigator in an earlier paper. Further differences between the content of that paper and the present results are pointed out.
Fast Moving Edge Dislocations on the (111) Plane in Anisotropic Face-Centered-Cubic Crystals
Authors: Weertman J.
Published: April 2005

The elastic displacement field around a uniformly moving edge dislocation has been obtained for the case where the dislocation glides on a (111) plane in a 〈110〉 direction in an anisotropic face-centered-cubic crystal. An equation is obtained for the velocity (the Rayleigh wave velocity) at which the shear stress on the slip plane of a moving dislocation is zero. Dislocations of like sign moving at velocities faster than this velocity attract rather than repel each other. It is concluded that when anisotropy is small and the elastic constant c11 is smaller than c12+2c44 (the more commonly occurring relationship between the elastic constants) the Rayleigh wave velocity is increased above its value in an isotropic crystal and therefore, the extent of the velocity region where dislocations exhibit an anomalous behavior is decreased. For slightly anisotropic crystals the limiting velocity of dislocation motion is the slower of the two shear velocities in the 〈110〉 direction.
Reversible Flux as a Source of Irreversible Noise in Multipath Cores
Authors: Baldwin J. A.
Published: April 2005

During the drive phase of the operation of a flux-limited multipath core the flux change produced in the driven branch is the irreversible flux available to that branch plus a certain amount of reversible flux. Most of this flux will return through the shortest path in that part of the magnetic circuit of the core which constitutes the load for the driven branch. It is shown, however, that if the irreversible flux of some branch of this path saturates, the additional flux from the driven branch will produce an irreversible flux change in the next shortest path. This flux change reappears as noise during the reset phase. This fact leads to the surprising result that under some circumstances a greater flux change occurs in the longer branch of the load structure of a three-rung laddic than in the shorter. This source of noise may in many cases be circumvented by reducing the cross section of the driven branch. These ideas are applied to explain the existence of optimum hold currents in the general laddic. A modification of the geometry of the three-hole memory core which improves the signal-to-noise ratio in inhibited-flux operation is described.
Diffusion of Copper in Polycrystalline Silver Selenide
Authors: Foster K. W. , Milnes M. V.
Published: April 2005

The diffusion of copper in polycrystalline Ag2Se was determined from measurement of the rate of change of the resistivity profile of a partially copper-plated ingot of the semiconductor material. The copper concentration profile that was determined from the resistivity profile, was found to agree very satisfactorily with a theoretical concentration curve computed from a normalized complementary error function. The room temperature diffusion coefficient of copper in Ag2Se was computed from these data and was found to be 4.7×10−8 cm2 sec−1.
Magnetic Moments of Intermetallic Compounds of Transition and Rare-Earth Elements
Authors: Nesbitt E. A. , Williams H. J. , Wernick J. H. , Sherwood R. C.
Published: April 2005

The effect of adding the rare-earth elements to cobalt, iron, and nickel has been investigated. Antiferromagnetic coupling was found to exist in the cobalt and iron rare-earth compounds. The moment per formula unit of the compound Co5Y is increased when Sm, Pr, and Nd are substituted for yttrium and decreased when Tm, Gd, Tb, Er, Dy, and Ho are substituted. This is explained on the basis that although the spin moments of cobalt and rare earths are coupled antiferromagnetically in these compounds, the orbital moments add to the cobalt moment in the compounds containing Sm, Pr, and Nd, but they subtract from the cobalt moment in the compounds containing Tm, Tb, Er, Dy, and Ho. For the iron compounds investigated, the moment of the compound Fe4Y was found only to decrease when Tm, Er, Ho, and Dy were substituted for yttrium. The nickel compounds behaved entirely differently from the cobalt and iron compounds since very little or no antiferromagnetic coupling was observed in these compounds.
Scattering of a Plane Wave by an Infinite Inhomogeneous, Dielectric Cylinder—an Application of the Born Approximation
Authors: Albini F. A. , Nagelberg E. R.
Published: April 2005

The scattering and absorption of an obliquely incident, plane electromagnetic wave by an infinite, cylindrically symmetrical region characterizable by a complex dielectric ``constant'' is determined by application of the Born approximation for the case of dielectric ``constant'' near unity. Differential-scattering cross sections and absorption cross sections are derived as a function of angle of incidence, angle of polarization, and integrals over the inhomogeneous region. The expressions for the scattered fields are compared to the expansion of an exact solution for the homogeneous dielectric cylinder in the limit of dielectric constant near unity. The approximate expressions agree exactly. Of singular notability in this respect is the fact that polarization is altered in the Born approximation by the appearance of dyadic terms in the propagation equation in the region of inhomogeneity, while the exact solution requires the generation of cross-polarized waves to satisfy boundary conditions.
Growth of Refractory Oxide Single Crystals
Authors: Linares R. C.
Published: April 2005

It has been found that various refractory oxides can be crystallized from molten PbO–PbF2 and Bi2O3–BiF3 solutions. The PbO–PbF2 solvent has proved successful for the growth of high alumina compounds including aluminum garnets, rare-earth orthoaluminates, spinels, magnetoplumbite-type aluminates, aluminum oxide, and the divalent oxides BeO and MnO. The Bi2O3–BiF3 system has proven successful for the growth of the ferrite GaFeO3. The stability ranges of these various compounds is discussed in addition to problems of doping and attainment of large single crystals.
The Observation and Interpretation of Dislocation Tangles in the Easy Glide Range of Aluminum
Authors: Wilsdorf H. G. F. , Schmitz J.
Published: April 2005

Crystals of aluminum, oriented for single slip, were deformed up to 1% glide strain. Specimens for diffraction electron microscopy were prepared, and direct observations on dislocations were made. The presence of three-dimensional tangles as well as small prismatic dislocation loops was established. Considerations have been made as to how the tangles were formed. It was further concluded that dislocations move in glide zones, mainly between tangles which can act as sources for dislocations and as obstacles against their motion.
Dielectric Anomaly in Quartz for High Transient Stress and Field
Authors: Graham R. A.
Published: April 2005

Neilson and Benedick have reported an anomalous piezoelectric behavior for negatively-oriented synthetic alpha-quartz crystals when subjected to transient stress of about 65 kbar. This paper describes the piezoelectric behavior of negatively-oriented quartz in the stress region of from 5 to 50 kbar. The first indication of anomalous behavior occurs at 8 kbar. Between 8 and 24 kbar the negative x-current waveforms show evidence of partial electric breakdown in the quartz. Between 25 and 34 kbar disruptive breakdown occurs. Above 34 kbar disruptive breakdown is followed by gross conduction with positive currents being observed for stress greater than about 50 kbar. The fields associated with the piezoelectric behavior are lower than the field for steady-state electric breakdown at atmospheric pressure. It is proposed that the anomaly is triggered by stress-induced dislocation motion resulting in liberated electrons which are accelerated into the stressed region of the specimen by the high negative electric field.
Concerning ``Anomalous'' Solution and Etching Phenomena
Authors: Westwood A. R. C. , Opperhauser H. , Goldheim D. L.
Published: April 2005

On the basis of observations on the etching and dissolution behavior of LiF crystals in aqueous solutions of fatty acids, it is suggested that certain solution phenomena previously considered anomalous are no longer so, once the significant role of lattice defects and step-poisons in the dissolution process is appreciated.
Threshold Energies in Mechanical Collision Theories of Cathode Sputtering
Authors: Henschke Erich B.
Published: April 2005

It is shown that the very low threshold energies for sputtering, measured with highly sensitive methods (surface ionization, radioactive deposits, spectroscopic method), immediately after applying a ``clean-up'' sputtering with higher ion energy, are due to the fact that the applied intermediate sputtering produces on the target upper-most surface atoms with reduced binding energies ranging from a maximum to a minimum number of bonds. The lowest ion energy, at which a yield can be measured in the described manner, is just sufficient to remove the latter atoms and is defined as the ``minimum-bond'' threshold. The thresholds, formerly determined for polycrystalline targets at normal ion incidence without intermediate sputtering for many metal-ion combinations by ``detection of deposits'', correspond to the ``full-plane'' thresholds, necessary for sputtering of atoms, having the maximum number of bonds, and represent the lowest ion energies at which continuous, i.e., plane by plane, sputtering of the target surface is feasible. The ratios of the ``full-plane'' thresholds to the ``minimum-bond'' thresholds, the latter measured at exclusively normal ion incidence with a sensitive method, after intermediate sputtering with a higher ion energy, are assumed to be the same (about 2:1) as calculated for a polycrystalline surface from the ratio of the binding energies of an atom in a full plane to the binding energies of an atom on top of a full-plane area. The larger ratios (about 3:1) of the formerly measured ``full-plane'' thresholds to the very low thresholds, as measured with highly sensitive methods, are shown to be probably due to boubly-charged ions and to oblique ion incidence, which are exclusively active at the lowest ion energies.
Growth of Cubic ZnS Single Crystals by a Chemical Transport Process
Authors: Samelson Harold
Published: April 2005

A chemical transport process for the growth of zinc sulfide single crystals is described. The reaction employed is ZnCl2(g)+H2S(g)=2HCl(g)+ZnS(s).

The rate of transport of ZnS is discussed, and details of the thermodynamics of the system and the conditions for the growth of single crystals with a pure cubic structure are given. Crystals having this structure and as high a chemical purity have been difficult to obtain heretofore. The chemical analysis and some of the luminescent properties of these crystals are described briefly.
Electron Streams in an Oscillating Electric Field
Authors: Sackinger W.
Published: April 2005

A general theoretical expression is derived for an electron trajectory in an oscillating electric field. This result is extended to an electron stream, and the current and velocity are found exactly, in the absence of space charge, for any plane within the region of the oscillating field. The limits on the validity of the analysis are established, and application is made to the parallel-plane diode or klystron gridded gap. Within the restriction that the normalized gap voltage be less than the normalized gap lenth, exact results for current and velocity are obtained.
Application of a Ferroelectric Material in an Energy Conversion Device
Authors: Childress J. D.
Published: April 2005

The thermodielectric converter, a device employing a ferroelectric material as the active element in converting thermal to electrical energy, is analyzed. The efficiency and power-handling capacity are calculated for operation of a ferroelectric material in the induced-ferroelectric region on the basis of an idealization of the polarization (P-E) characteristics. The idealization includes the induced-ferroelectric transition but excludes hysteresis and other nonlinear effects. For a barium titanate-like material, the following values are obtained: A maximum theoretical efficiency of about 0.5% in an ideal temperature cycle of Carnot efficiency 7.1%; and a power-handling capacity of roughly 32 w/lb per temperature cycle per sec.
Internal Friction and Young's Modulus in Irradiated Tungsten
Authors: Muss D. R. , Townsend J. R.
Published: April 2005

Measurements of internal friction and Young's modulus as a function of temperature and 13.7-Mev deuteron bombardment flux are reported for polycrystalline tungsten. A dislocation-relaxation peak in the internal friction as a function of temperature is observed. The peak height is found to be reduced by irradiation. The background internal friction decreases and the modulus increases with bombarding flux. The experimental results for modulus change with bombardment is shown to fit a simple dislocation pinning model reasonably well. The effect of immobile radiation induced vacancies on Young's modulus in tungsten is observed to be −0.44% per atomic percent of vacancies compared with Dienes' prediction of −1.0%.