bluuebunny/crossref_metadata_2025 huggingface dataset:
Spinwave and Uniform Precession Linewidths in Rare-Earth Substituted Yttrium Iron Garnet
Authors: Seiden P. E.
Published: April 2005

The temperature dependence of the spinwave and uniform precession linewidths of yttrium iron garnet substituted with the order of one atomic percent of holmium, erbium, and europium was measured from 4.2° to 300°K. The data are compared to the theory of de Gennes, Kittel, and Portis which attributes the linewidth to the rapidly relaxing rare-earth ions. Although the theory qualitatively predicts the temperature dependence of the linewidth, the detailed behavior varies considerably in these materials and remains to be accounted for. A new technique is briefly described that is used for obtaining ΔHk from the main resonance nonlinear behavior of the susceptibility which avoids the detailed point measurements previously necessary.
High Temperature Susceptibility of Garnets: Exchange Interactions in YIG and LuIG
Authors: Wojtowicz Peter J.
Published: April 2005

Power series expansions of the high temperature susceptibility and its inverse in ascending powers of the reciprocal temperature have been obtained through the use of an extension of the method of Rushbrooke and Wood. The Heisenberg form of exchange is adopted and interactions between neighboring spins from different sublattices (a-d exchange) only are included. The coefficients in the series are derived for arbitrary spins on the two sublattices. The calculations have been carried out to terms including the fifth power of the exchange divided by the temperature; the molecular field theory by contrast is rigorously valid only to the first power term of its expansion. The inverse susceptibility series have been used to determine the magnitude of the a-d exchange interactions in the ferrimagnetic garnets, YIG and LuIG. The intra-sublattice interactions are assumed to be zero, in keeping with the increasing suspicion on the part of numerous investigators that these interactions have been seriously overestimated by molecular field considerations. The data of Aléonard was analyzed by a least-squaring method, and the following values for the a-d exchange were obtained: J/k=−35.0°K for YIG, and J/k=−34.5°K for LuIG. The deviation of theory from experiment is about 1%. In addition, the value for YIG is in satisfactory agreement with the Landau-Lifschitz constant determined from the heat capacity and spin-wave spectrum. It is concluded that these results support the hypothesis of relatively weak intrasublattice exchange in the garnets.
Coaxial Ferrite Phase Shifter for High Power Applications
Authors: Boxer A. S. , McCarter R. S.
Published: April 2005

The low- and high-power behavior of a coaxial ferrite-loaded transmission line has been studied experimentally at microwave frequencies. Longitudinal magnetic biasing fields both above and below the cutoff range (ω/γ−4πMs≤Hdc≤ω/γ) were explored, the two regions yielding devices with markedly different characteristics. The mechanical structure consisted of a rigid ⅞-in. coaxial line fully loaded with Trans-Tech 1–103 ferrite together with appropriate quarter-wave dielectric transformers.

(1) Operation below cutoff (0≤Hdc<ω/γ−4πMs), f=3080 Mc: These parameters permit construction of a compact, light-weight phase shifter producing 360° of phase shift in 10 in. of active length upon application of only 100 oe. Approximate values for hcrit are determined from the measured threshold powers and plotted versus applied field.

(2) Operation above resonance (Hdc>ω/γ), f=1350 Mc: With these parameters, a device can be built that is capable of handling at least several hundred kilowatts of rf peak power while maintaining a figure of merit of 1000 or more. The loaded coaxial line provides 360° of phase shift in 24 in. of active length when biased from 950 to 1350 oe. The high-power and loss characteristics of the latter device permit application to electronic steering of the transmitter beam in a linear array antenna where relatively few phase shifters suffice. The low-field device is suited for beam control in a planar array where large numbers of relatively small phase shifters of medium peak-power capability are needed.
Slow-Wave uhf Ferrite Phase Shifters
Authors: Sakiotis N. G. , Allen D. E.
Published: April 2005

A brief general discussion of the loss mechanisms of ferrites and garnets is given. An idealized representation of the absorption loss as a function of frequency and the applied magnetic field is utilized to define five distinct regions within which devices using ferrimagnetic materials may be operated with low absorption loss.

Slow-wave transmission lines for uhf frequencies are discussed, and the observed phase shifts per unit length for these and a conventional transmission line are given.

It is concluded that through the use of slow-wave transmission lines phase shifters can be designed at uhf frequencies which require as little as one-fourth the length required by a conventional transmission line.
Efficient Frequency Doubling from Ferrites at the 100-Watt Level
Authors: Risley A. S. , Kaufman I.
Published: April 2005

A ferrite frequency doubler in the microwave range with a conversion efficiency of 5% to an external second harmonic load, for an input power of 300 w, is described. The design of this 8.5 to 17 Gc converter is based upon theoretical and experimental work reported earlier. A design diagram was drawn from the equation determining efficiency as a function of χ0″ and hω and experimental curves of χ0″ vs hω for various materials. From this diagram, the optimum material for a given input power was determined. In the case treated, single crystal manganese ferrite was optimum.
Sampling Magnetometer Based on the Hall Effect
Authors: Wieder H. H.
Published: April 2005

A pulsed sampling magnetometer is described, based on the Hall effect in vacuum evaporated films of InSb. Pulsed operation of thin film Hall effect detectors provides an increase in sensitivity over cw operation of conventional Hall devices. This is due, in part, to the improved thermal dissipation of the fim, the reduction in joule heating, and the greatly improved noise discrimination because of stroboscopic sampling. A sensitivity of better than 10−4 v/gauss, over a frequency range between 100 cps to 5 Mc and an angular orientation sensitivity of 10−5 v/degree have been obtained in devices built to date.
Waveform of the Time Rate of Change of Total Flux for Minimum Core Loss
Authors: Schenk H. L. , Young F. J.
Published: April 2005

In testing magnetic materials core losses are measured when the time rate of change of total flux dφ/dt in the core varies sinusoidally. Although it may seem intuitive that the core loss for a given flux density is a minimum when dφ/dt is sinusoidal, measurements and a simple analysis indicate otherwise. It is shown that the core loss is smaller if the time rate of change of total flux in the core follows a square wave than it would be if the time rate of change of total flux followed a sine wave, with the peak induction being the same in both cases. By a variational method the ratio of square-wave to sine-wave eddy current losses for a given value of peak flux density is found to be 8/π2.

The ratio of square-wave to sine-wave core losses is measured as a function of induction for a fixed frequency and as a function of frequency for a fixed induction using a Hipersil specimen (cube-on-edge orientation). A feedback circuit is used to prevent distortion in the waveform. When the measurement is made at 60 cps the ratio is about 0.90 for flux densities below 12.5 kgauss and rises with increasing flux density to about 0.96 at 17.5 kgauss. For an induction of 5 kgauss the ratio decreases from about 0.92 at 30 cps to 0.87 at 120 cps.
Low-Frequency Losses and Domain Boundary Movements in Silicon Iron
Authors: Wycklendt Daniel A.
Published: April 2005

Earlier observations of very low-frequency losses in (110) [001] textured silicon iron have been extended to include losses produced by excitation with a sinusoidal field intensity. Excitation frequencies of 0.005 to 10 cps and flux density amplitudes of 10, 15, and 17 kgauss were used in these measurements. The downward concavity of the loss-frequency curve near zero frequency, previously reported for sinusoidal induction, is greatly exaggerated by imposition of a sinusoidal field intensity.

To further investigate these low frequency loss anomalies, low-amplitude, high-frequency fields were impressed on the material during cyclic magnetization at low frequencies. The superposed field, most often of 320- or 1000-cps frequency, had an amplitude considerably smaller than the coercive force of the material. Waveforms of the gross, low-frequency magnetization and the incremental, high-frequency magnetization were accurately controlled by high-gain, direct-coupled, feedback amplifiers. The ratio of the Ḃ amplitude to the H amplitude for the high-frequency components varied greatly within a cycle of magnetization. |Ḃh|/|Hh| was also found to vary with the peak value and waveform of the gross induction. Most significantly, the ratio increased greatly with frequency of the gross magnetization at very low frequencies. These changes can be attributed to an increase in the number of domain walls in simultaneous motion when the speed of gross magnetization is increased.
Iron Losses in Elliptically Rotating Fields
Authors: Strattan R. D. , Young F. J.
Published: April 2005

Power frequency losses in silicon iron alloys due to an elliptically rotating magnetic field have been measured by a calorimetric technique and predicted approximately using a simple model. Previously reported experiments for measuring these losses fail to approach saturation and have doubtful field unformities. A thin disk-shaped specimen is placed in the elliptically rotating field of a set of two phase air-cored rectangular Helmholtz-type coils. The 60-cps rotational loss is calculated from the initial rate of specimen temperature rise sensed by a copper-Constantan thermocouple attached to the disk. The thermocouple output is amplified and recorded with an accuracy of 10−3°C. The field coil system produces fields uniform to 2% in a 1.0-in.-diam. region and of strengths up to 250 oe, which is sufficient to approach saturation in 0.005-in. thick by 0.875-in.-diam disks. The losses have been measured for grain oriented and single-crystal materials with all materials showing a decrease in loss for an increase in flux density for large, nearly circular fields. The losses for elliptical magnetization may be approximated with a simple model composed of a mixture of lossless domain rotation, eddy current loss, and alternating hysteresis loss proportional to an alternating flux. This model is intended only for the calculation of rotational hysteresis losses and not to explain the origin of these losses. The calculated and experimental losses agree for all amplitudes and eccentricities of magnetization to within 40% for rotation in the (100) plane with the worst discrepancy for circularly rotating magnetization.
Magnetic Susceptibility and Magnetostriction of CoO, MnO, and NiO
Authors: McGuire T. R. , Crapo W. A.
Published: April 2005

The experimentally observed increase in the magnetic susceptibility and the accompanying change in length of antiferromagnetic MnO and NiO single crystals were used to evaluate critical fields and anisotropy of these materials. For CoO the susceptibility varied over too small a range to be of significance in this work.
Ferromagnetic Resonance Loss in Lithium Ferrite as a Function of Temperature
Authors: Denton R. T. , Spencer E. G.
Published: April 2005

The ferromagnetic resonance linewidth as measured in ferrites is often dominated by loss due to ferrous ions. However, theoretical investigations of the scattering mechanisms in disordered magnetic materials such as ferrites have shown that volumetric disorder scattering should also play a significant role in determining the total linewidth of these materials. Lithium ferrite, Li0.5 Fe2.5O4, is one of the ferrites which in stoichiometric proportions would have all of the iron ions in the ferric state and which can have either an ordered or a disordered crystal structure at room temperature. It should thus be possible to reduce the contribution of ferrous ions so that the effects of disorder scattering can be observed by comparing the linewidths of ordered and disordered crystals. The data of this paper were taken on samples of lithium ferrite in which the linewidths are of the order of oersteds so that parallel pumping techniques can be used. The advantage of these measurements is that the role of surface scattering mechanisms is minimized and the resulting linewidth is the intrinsic linewidth for long-wavelength spin waves. Data are presented of intrinsic linewidth at microwave frequencies as a function of temperature from 290°K through a low-temperature maximum at 25°K. The value of the linewidth maximum in the disordered crystal proves to be quite anisotropic. Ordering the crystal increases the low-temperature maximum and alters the linewidth anisotropy. The effects of disorder scattering can be obtained from the linewidths above the low-temperature maximum and are shown to agree qualitatively with the predictions of theory.
Antiferromagnetic Resonance in MnTiO3
Authors: Stickler J. J. , Heller G. S.
Published: April 2005

The effective internal field (2HEHA)½ as well as its temperature dependence has been found from antiferromagnetic resonance experiments for two different single crystals of MnTiO3, and from absorption edge data for a pure powder sample. The data are consistent with a uniaxial collinear two sublattice model as predicted from dc susceptibility and neutron diffraction measurements. The data for one crystal yielded results in good agreement with the powder material with a g value of 2.1 and effective internal field of 52 kgauss at 4.2°K. All samples followed a Brillouin function for spin 52 fairly well but with different Néel temperatures higher than that previously reported for this material.
Antiferromagnetic and Paramagnetic Resonance in CuF2·2H2O
Authors: Peter M. , Moriya T.
Published: April 2005

Antiferromagnetic and paramagnetic resonance absorption has been measured in CuF2·2H2O. At 1.4°K, the antiferromagnetic resonances in zero field occur at 95.84±0.05 kMc and 95.91±0.05 kMc. The easy direction of magnetization occurs at an angle of 3.5° with the c axis. This orientation is in agreement with neutron diffraction and single-crystal susceptibility measurements. Due to strong exchange narrowing, narrow paramagnetic resonance lines were observed. The g values are gξ=2.07, gη=2.08, and gζ=2.42. The principal axes are nearly coinciding with the ligand directions. From the g values, the energy levels and wave functions of the Cu++ ions are determined. A discussion of the anisotropy is given. The dipolar part is calculated numerically, and the anisotropic exchange of pseudodipolar type is determined, using the fact that ω1∼ω2 and the known easy magnetization direction. From the total anisotropy determined in this way, and the perpendicular susceptibility measured by Williams, the antiferromagnetic resonance frequency is predicted to occur at 130 kMc. The agreement with experiment is not unreasonable in view of the reduction of this frequency by the zero-point oscillations of the spin waves. A brief discussion of the superexchange interaction in this crystal is given.
Permanent Magnetic Properties of Iron-Cobalt-Phosphides
Authors: De Vos K. J. , Velge W. A. J. J. , Van Der Steeg M. G. , Zijlstra H.
Published: April 2005

An investigation of the phase relations of the section Fe2P–Co2P in the system Fe–Co–P showed that at high temperature all (Fe, Co)2P alloys, including the final components Fe2P and Co2P, probably form a continuous range of solid solutions having the hexagonal Fe2P structure. At low temperatures Fe2P and Co2P form an almost complete range of solid solutions with the orthorhombic Co2P lattice. The Curie temperature of the hexagonal phase increases from about room temperature for Fe2P to a value of nearly 190°C for (Fe, Co)2P with an Fe:Co ratio of 70:30. The anisotropy field HA appeared to be a function of the Fe:Co ratio and possesses a maximum value of about 19 000 oe near an Fe:Co ratio of 90:10. Particles obtained by lixiviating an Fe–Co–Cu–P melt can possess a coercivity IHC up to 2000 oe. This value can be substantially increased by annealing. The temperature coefficient of IHC appears to be relatively large and seems to be linked to the change of K with temperature. The coercivity decreases appreciably after mechanical loading, e.g. pressing, but can be restored by annealing; the anisotropy field HA as well as the saturation magnetization σ∞ changes in the same sense. Anisotropic permanent magnets have been made with a BHmax value of about 2×106 gauss oe.
Magnetic Properties of Cr5S6 in Chromium Sulfides
Authors: Dwight K. , Germann R. W. , Menyuk N. , Wold A.
Published: April 2005

Several samples of CrSx with 1.145<x<1.200 were carefully prepared and chemically analyzed. The expected crystal structures were verified by x-ray analysis, which failed to indicate the presence of any impurities. Conductivity measurements indicated the existence of metallic conductivity in these samples between 77° and 300°K. Magnetic measurements supported the suggestion that the ferrimagnetism of CrSx materials arises from the presence of the Cr5S6 phase.

The magnetization curves for x=1.194 demonstrated the following salient properties of the Cr5S6 phase: a ferrimagnetic Curie point of 305°K, a peak magnetization of 6.9 emu/gm in an external field of 8500 oe, a ferrimagnetic-antiferromagnetic transition over a 5° temperature interval, a transition temperature in the neighborhood of 158°K which is subject both to thermal hysteresis and to shifting by an external magnetic field, and an antiferromagnetic susceptibility below this transition. The transition temperature, as well as the peak magnetization, decreases with increasing chromium content. A simple model is tentatively proposed, and appears to be consistent with the observed behavior.
New Modified Mn2Sb Compositions Showing Exchange Inversion
Authors: Bither T. A. , Walter P. H. L. , Cloud W. H. , Swoboda T. J. , Bierstedt P. E.
Published: April 2005

Transformations from ferrimagnetic to antiferromagnetic ordering with decreasing temperature have now been observed in manganese antimonides modified with V, Co, Cu, Zn, Ge, and As as well as with Cr. The magnetic structure change is accompanied by a first-order change in the volume of the unit cell as well as a change in electrical resistivity. Crystallographic data for these materials in the exchange inversion region and at room temperature are presented as a function of the concentration of modifying element.
Magnetic Characteristics of Hydrogenated Holmium
Authors: Kubota Y. , Wallace W. E.
Published: April 2005

Various physical and chemical properties of the lanthanide hydrides suggest that they are saline in nature, the hydrogen existing as a negatively charged ion. These properties further suggest that the anionic charge is obtained from the conduction band of the lanthanide and that in the fully hydrogenated metal the conduction band is completely depopulated. Since coupling of the lanthanides occurs via the conduction electrons, this should lead to very considerable suppression of the interactions in the hydrides compared to the element, but an unchanged effective atomic moment. To determine whether this is the case susceptibility measurements have been made on a series of nine Ho–H alloys. These show for the dihydride, which still contains some conduction electrons, a Néel point at around 8°K (instead of 135°K for the element), whereas for the trihydride, which lacks conduction electrons, no Néel point is observed down to 4°K. Susceptibilities of the hydrides above about 15°K obey the Curie-Weiss law with a much smaller Weiss constant than that for elemental holmium. The atomic moment is found, however, to be virtually unaffected by hydrogenation.
Magnetic Moment of Co–Cu Solid Solutions with 40 to 85% Cu
Authors: Kneller E.
Published: April 2005

Metastable Co–Cu solid solutions in the concentration range between 12% and 95% Cu were obtained by simultaneous evaporation of Co and Cu on a cold substrate. The spin moment of the as-deposited alloys is equal to that of Fe–Ni, Co–Ni, Ni–Cu solid solutions with the same average number of electrons per atom. During annealing at 700°C for a suitable time the spin moment increases to the value calculated for the two-phase equilibrium state of the alloys. For an alloy with 65% Cu the Curie temperature is 580°K. All alloys have fcc structure before and after annealing.
Investigations of Spin-Wave Interactions by the Parallel Pumping Technique
Authors: Green J. J. , Schlömann E.
Published: April 2005

The imaginary part of the parallel pump susceptibility has been measured over a wide range of power levels and applied dc fields. Some of the structure present in the susceptibility curves is explained by a confluence process between two parametrically excited spin waves. The square of the frequency of the relaxation oscillations, which are frequently present in parallel pump excitation, has been found to increase linearly with the square of the magnetic field.
Resonance Properties of Single-Crystal Hexagonal Ferrites
Authors: Buffler C. R.
Published: April 2005

Ferromagnetic resonance measurements have been performed on single-crystal samples of the hexagonal ferrites BaFe12O19, Zn2Y, and Co2Y. Values of linewidth, g value, and anisotropy field are given as a function of temperature from 77°K to 600°K at various frequencies between 8 and 75 kMc. Zn2Y is singularly interesting because it exhibits an extremely narrow room temperature linewidth at X band. Values as low as 16 oe, with anisotropy fields of 9000 oe are reported. The theory of the resonance behavoir is developed and compared to the experimental results.
Growth of Yttrium Iron Garnet on a Seed from a Molten Salt Solution
Authors: Laudise R. A. , Linares R. C. , Dearborn E. F.
Published: April 2005

Yttrium iron garnet has been crystallized on a seed crystal from molten BaO−xB2O3, where x is 0.61. Two methods were used: (1) slow cooling of a melt in which a rapidly rotating seed was suspended, and (2) growth in a temperature gradient where excess yttrium iron garnet was maintained in a hotter part of the system, and a rapidly rotating seed was suspended in a cooler region. The geometry of the furnace, crucible, baffle, stirrer, and circulator system required to produce controlled growth in each of these systems is described, and the nature of the rate limiting step in each of the systems is discussed. The dependence of growth rate in the [110] direction on stirring rate, cooling rate, and solvent weight is presented. Good quality growth with rates as high as 50–75 mil/day was achieved in favorable cases.
Cobalt Ferrite Crystal Growth from the Ternary Flux System Na2O–CoO–Fe2O3
Authors: Kunnmann W. , Wold A. , Banks E.
Published: April 2005

It is shown that the simple ferrite spinels (M2+Fe2O4) crystallize readily from the ternary flux system MO–Na2O–Fe2O3. The liquidus-solidus phase diagrams for the pseudobinary of Na2Fe2O4–CoFe2O4 and the ternary Na2O–CoO–Fe2O3 are presented. A general discussion of flux growth of ferrite crystals of both the simple spinel type and the more complex layered structures (BaFe12O19) is given. Crystals of CoFe2O4 were grown from a mixture of 1.5 moles of CoFe2O4 and 1 mole of Na2Fe2O4 by utilizing a platinum wire cold finger.
High-Power Characteristics of Single-Crystal Ferrites with Planar Anisotropy
Authors: Dixon Samuel
Published: April 2005

Single crystal (ZnY) (Ba2Zn2Fe12O22) was used in an investigation of the variation of the magnetic susceptibility with microwave magnetic field. The large anisotropy field in these materials makes them attractive for applications in microwave devices. Measurements were made in the frequency range of 8.6 to 37.7 kMc. The microwave magnetic field in the cavities extended up to 35 oe. Measurements taken at a constant frequency indicate that there is an appreciable shift in the field required for resonance as a function of power. This shift in the resonance field is superimposed on the usual decline of the main resonance. Measurements indicate that the shift effect of the resonance field decreases as the linewidth and frequency are increased. In the frequency range of 8.6 to 16.6 kMc, the critical field increases with frequency. Above this frequency, the critical field tends to decrease. At X-band frequencies, the critical field compares favorably with that of YIG material.
Subsidiary Absorption Effects in Ferrimagnetics
Authors: Saunders J. H. , Green J. J.
Published: April 2005

Subsidiary absorption measurements on polycrystalline yttrium aluminum iron garnet and nickel aluminum ferrite yield values of ΔHk which are the order of several oersteds. These spin wave linewidths appear to be independent of aluminum content. At power levels several db in excess of the power level for the onset of subsidiary absorption, a power dependent zero field loss has been found.
Temperature Stable Microwave Hybrid Garnets
Authors: Harrison Gordon R. , Hodges L. R.
Published: April 2005

Temperature stability of the magnetization of microwave garnet materials is very desirable provided in obtaining this stability the linewidth, g factor, and Curie temperature of the material are still suitable for microwave applications. Most rare-earth garnets possess compensation points in their magnetization vs temperature characteristics. These compensation points when suitably controlled by ionic substitutions can be used to produce microwave garnet materials whose magnetizations are quite temperature independent. The microwave properties of the following compositions have been investigated: 3[(1−X−Z)Y2O3·XGd2O3·ZDy2O3]·5[(1−W)Fe2O3·WAl2O3], for X=0 to 1.00, Z=0 to 0.1, and W=0 to 0.1. The magnetizations of these compositions have been studied from −195°C to the Curie temperatures. The compensation points of the magnetization are controlled by varying the rare-earth and aluminum content of the material. The result is a series of materials possessing magnetizations in the region of 1200 to 300 gauss which vary no more than ±10% over the temperature range of −25° to +125°C. The other associated properties of these compositions are very suitable for microwave applications. The thresholds for nonlinear effects in these materials are relatively high particularly for those compositions containing dysprosium. Many temperature stable microwave components have been developed for high-power applications using these materials.
Effect of Mechanical, Thermal, and Chemical Treatment of the Ferrimagnetic Resonance Linewidth on Lithium Ferrite Crystals
Authors: Nielsen J. W. , Lepore D. A. , Zneimer J. , Townsend G. B.
Published: April 2005

Ferrimagnetic resonance linewidths as low as 2.6 oe can be obtained in lithium ferrite spheres at room temperature and 5 kMc by a series of treatments including polishing, heat treatment at 800°C, addition of lithium, and ordering. There exist optimum times of processing for each crystal. Freshly grown crystals show unusual variations in linewidth with processing, and this behavior is tentatively explained on the basis of strains in the crystal and nonuniformity of lithium content within the spherical sample.
Magnetic Studies of Some Intermetallic Compounds between Cobalt and the Lanthanide Elements
Authors: Cherry L. V. , Wallace W. E.
Published: April 2005

Thermomagnetic studies of intermetallic compounds having the stoichiometry ACo5, in which A represents yttrium or a lanthanide element, have been extended to liquid helium temperatures. At applied magnetic fields of 2600 and 7200 oe, anomalies not appearing at high fields have been observed in the behavior of PrCo5 and NdCo5. These anomalies are an apparent second (low-temperature) Curie point at about 126°K in PrCo5 and a maximum in the thermomagnetic curve of NdCo5 in the vicinity of 270°K. The data obtained for other ACo5 compounds are consistent with those reported recently by Nesbitt et al. Results for PrCo5 and NdCo5 indicate ferromagnetic coupling of the cobalt moments on cooling below 910° and 925°K, respectively, while in each case at low fields, the lanthanide moments remain disordered. With PrCo5 the data indicate ferromagnetic coupling of the Pr and Co moments below 126°K. Data for NdCo5 suggest that on cooling, a similar type of coupling develops at about 270°K, but this is almost immediately superseded by antiferromagnetic coupling of the Nd moments with one another at lower temperatures.
Volume Conductivity of Borosilicate Glass
Authors: Muray Julius J.
Published: April 2005

Through use of circuitry of variable RC time constants it has been shown that the slow exponential rise and decline of the charging current of the glass condenser between metal plates that do not exchange ions with the glass, in the past assumed to be characteristic of the glass, is an instrumental RC-conditioned time constant. The previously unexplained linear decline, sometimes called the ``anomalous'' charging current, in consequence represents the migration of the mobile alkali ions to create a cathode potential fall establishing the steady-state conduction current. While temperature variation of resistance follows the previously assumed pattern, the steady-state current is limited by the rate of recombination of the alkali ions in the space-charge sheath close to the cathode with O− ions created by electrons from the metal electrode. Near the anode, loss of alkali ions through accumulation of O− ion space-charge fields provides the electron current to the anode. From the alkali atom density, measurement of the time constant of the linear decline, measurement of the steady-state current density, and measurement of the activation energy, one can estimate the dissociation energy, the depth of the ionic potential well, the alkali-ion density, and the ionic mobility. The mobility is in fortuitously good agreement with that calculated from logically assumed basic constants. The data yield an ``effective'' ion-electron surface recombination coefficient responsible for steady-state current flow. The theory of the linear current indicates limits to the superposition principle. Current passage, at room temperatures at high current density, on the order of hundreds of hours reduces the alkali-ion concentration near the anode and changes the resistance. Thus, there is achieved a unified self-consistent theory for the bulk conductivity, the constants of which are directly determinable from the measurements, with minimum assumptions of arbitrary nature.
Surface Conductivity of Borosilicate Glass
Authors: Muray Julius J.
Published: April 2005

An electron beam projected onto a clean glass surface in vacuum is blown up by deceleration caused by the high surface charge accumulated, thus spreading the beam on a very short time scale before arrival on the surface. Arriving at the surface, electrons are rapidly bound to lattice imperfections (not adsorbed gas atoms) presumably creating O− ions. Thereupon, spread of the charge along and through the surface, progresses by movement of labile alkali ions which combine with the surface O− ions, leaving their initial negative O− partners behind in the glass. The rapid transfer of the negative charge from the surface to the interior of the glass, where it encounters dielectric screening, causes a temporary positive displacement current which masks the displacement current due to the discharge movement to the grounded electrode. It has a maximum value immediately following the electron beam cutoff, and declines approximately exponentially with a time constant τ, of about 0.1 sec for the range of electron surface charge densities, computed from beam cross sections ranging from 1010−3×1011 electrons/cm2. Thereafter, the charge leaks off as a volume conduction current on a time scale of tens of minutes. There is no surface conduction by free electrons, and surface conductivity of clean glass is low and comparable with volume conductivity. High apparent plasma induced surface conductivity lies in the plasma, and not in the glass.
X-Ray Observations of Diffusion-Induced Dislocations in Silicon
Authors: Schwuttke G. H. , Queisser H. J.
Published: April 2005

Diffusion-induced dislocations in silicon have been studied by x-ray diffraction microscopy. Lines lying in a (001) diffusion plane forming rectangular arrays have been identified as edge dislocations in [11̄0] and [110] directions with Burgers vectors ½ [110] and ½ [11̄0] and (001) glide plane.
Deformation of Dislocation-Free Platelets of Nickel Bromide
Authors: Price P. B. , Nadeau J. S.
Published: April 2005

Nearly perfect platelets of nickel bromide, a compound which normally has the CdCl2 structure, were deformed on a straining stage inside the electron microscope and observed in transmission. Widely extended ribbon dislocations were produced at the platelet edges and moved entirely on the layer planes. Interactions between sets of ribbon dislocations with Burgers vectors at 120° resulted in the formation of networks which, because of the low stacking fault energy in this material, consisted of a triangular mosaic pattern of stacking faults extending over large areas of the crystal. Two types of stacking fault, having energies in the ratio ∼1:2, were enclosed by the ribbon dislocations. The fault with the lower energy (γ/μ∼5×10−12 cm), which occurred most frequently, corresponds to a layer of CdI2 stacking and accounts for the presence in the x-ray powder pattern of lines characteristic of the CdI2 structure. It results from translation between adjacent bromine sheets. The higher energy fault (γ/μ∼10−11cm)probably results from translation between a bromine and a nickel sheet and contains a layer in the molybdenite (MoS2) stacking.
Theory of a Plasma Negative Resistance Amplifier
Authors: Wada J. Y. , Kaprielian Z. A.
Published: April 2005

The purpose of this paper is to present the theory of a plasma negative resistance amplifier based on an approximate quasi-electrostatic model of a modified quadrupole cavity containing a plasma column and hyperbolic quadrupole electrodes with side resonators. The theory is extended to plasmas with finite collision frequencies in a finite magnetic field. By use of a nonlinear equation of the electron motion obtained by expanding the time varying applied electric field in Taylor's series, it is shown that the electrons in a plasma column behave as a nonlinear reactance and that a net signal amplification can be realized when sufficient pump-power is properly applied. It is also shown that the effective noise contributed from the plasma can be reduced by decreasing the plasma electron collision frequency or the plasma density. A preliminary experimental result which indicates the presence of a nonlinear plasma interaction is described.
Secondary Emission of Thin Self-Supported Films of MgO
Authors: Arntz Floyd O. , Van Vliet K. M.
Published: April 2005

This article contains experimental reflection and transmission secondary emission yield curves obtained from a 475 Å unbacked MgO film. The film has a transmission yield maximum of 2.6 at a primary energy of 3 kev. An analysis, employing experimental transmission retarding potential characteristics also obtained in this study, proves a lack of proportionality between the production of secondaries and the energy dissipated by the primary beam in MgO. The extreme range of a 3600-ev primary in MgO is found to be 475 Å.
Electrical Breakdown of Argon in Glass Cells with External Electrodes at Constant and at 60-Cycle Alternating Potential
Authors: El-Bakkal Jafar M. , Loeb Leonard B.
Published: April 2005

The electrical breakdown in borosilicate glass cells of plane parallel plate geometry with external electrodes was studied under static and 60-cycle alternating potential using Linde spectroscopically pure grade Ar gas introduced under Alpert vacuum conditions at 7, 15, and 35 mm. Oscilloscopic studies at fast and slow sweep as well as measurement of charge, wall potential and of apparent leakage charge through the glass using a large series condenser with Keithly electrometer and recorder were made. Three differing modes of breakdown appear as potential increases. These are associated with space-charge distribution and density. The two modes at lower potentials are Townsend discharges operating by photoelectric processes at the cathode. The third mode has streamer-like characteristics and a rise time equal to one avalanche crossing time. All breakdowns terminate through counter potentials from charge accumulation on the glass electrodes. The fairly complete data lead to a clear understanding of the observed breakdown patterns with 60-cycle alternating potential. The electrical properties of the glass involved are discussed in terms of recent findings.
An Analysis of the Maser Oscillator Equations
Authors: Sinnett D. M.
Published: April 2005

This paper analyses the maser oscillator equations which describe the interaction between the resonant cavity and the inverted population of the electron spin system of the paramagnetic substance. It is shown that these equations will not allow periodic solutions thus refuting the theory, based on computer solutions, that this interaction is responsible for the pulsed mode of operation of the oscillator.

Characteristics of solutions of these equations are determined analytically, and the ambiguity of computer solutions is discussed with the aid of examples. Numerical solutions are presented which show that periodic solutions may be induced by supplementing the spin system equation with an additional term.
Fast Moving Edge Dislocations in Various Face-Centered-Cubic Metals
Authors: Van Hull A. , Weertman J.
Published: April 2005

Calculations have been made of the shear stress produced by an edge dislocation moving on its slip plane in aluminum, copper, silver, gold, lead, and nickel. It is found that, except in the case of aluminum, the anomalous velocity range in which dislocations of like sign attract one another is very small. It is concluded that the effect of anisotropy in decreasing the extent of the anomalous velocity range is much greater in face-centered-cubic than in body-centered-cubic metals.
Sound Waves in Water Containing Vapor Bubbles
Authors: Trammell G. T.
Published: April 2005

The rapid evaporation or condensation of a vapor bubble when out of equilibrium compared to the slow dissolving or growth of an air bubble results in quite different propagation properties of sound waves through water containing one or the other types of bubbles. Adapting a method developed by Foldy in his treatment of the air bubble case, we derive an expression for the propagation number for sound waves in a ``vapor bubbly'' medium. As an application of the theory it is shown that as few as 10/cm3 vapor bubbles of radius about 10−3 cm will (for ambient pressure about one atmosphere) attenuate an ultrasonic (f=̇3·104 cps) sound wave by a factor of 10 in 10 cm. Suggestions are made concerning the use of these waves for the early detection of shut-down bubbles following a power burst in a reactor.
Secondary Electron Production from Fission Fragments Emerging from Thin Layers of Uranium Dioxide
Authors: Anno James N.
Published: April 2005

Measurements of the currents leaving thin films of uranium dioxide undergoing a known rate of fission have determined the secondary electron yield due to fission fragments emerging from the films. This yield was found to vary from about 570 to 300 electrons per fragment over a film thickness from 0.1 to 3 microns. The ratio of charge carried by the secondary electrons emitted from the surface to the charge carried by fission fragments was also determined. This ratio varies slowly with film thickness, from 28 for a 0.1-micron coating to about 21 for a 3-micron coating. The behavior of the charge ratio and secondary electron yield with coating thickness is in qualitative agreement with theory.
Ferroelectric and Pyroelectric Properties of Mineral and Synthetic Colemanite
Authors: Wieder H. H. , Clawson A. R. , Parkerson C. R.
Published: April 2005

The ferroelectric and pyroelectric properties of mineral and synthetic colemanite were investigated. It is shown that the synthetic compound, prepared by the controlled dehydration of higher order calcium borates, has a much lower Curie temperature than mineral colemanite. The substitutional impurity concentration of strontium for calcium in natural colemanite is proposed to be primarily responsible for its higher Curie temperature. The occurrence of a double dielectric anomaly in some specimens of mineral colemanite is described and it is shown that the temperature at which the lower anomaly occurs is consistent with the ferroelectric transition observed in the synthetic compound while the upper anomaly is characteristic of the more common calcium-strontium-borate pentahydrates.
Fracture Processes in Polymeric Materials. III. Topography of Fracture Surfaces of Poly(methyl Methacrylate)
Authors: Berry J. P.
Published: April 2005

On the assumption that the colors observed on the fracture surfaces of poly(methyl methacrylate) are due to interference in a thin layer of structurally modified material, the peculiar arrangement of the colors can be explained if (a) the mean fracture plane lies centrally within modified layer and (b) the fracture surface is regularly biplanar. Compliance with the first condition would be expected from the mechanical system which obtains during fracture. Interference microscopy shows that the surface topography is in accord with second condition. The occurrence of hyperbolic surface features, due to the initiation of a secondary fracture, introduces only a temporary disturbance in the general pattern. Evidence for the mechanism of formation of the hyperbolas is also found in the interference micrographs.
Correlation between Dislocation Length and Density
Authors: Schoeck G.
Published: April 2005

The relation between the dislocation density ρ in the surface of a crystal and the dislocation length per unit volume Λ is calculated assuming either isotropic distribution in space or isotropic distribution in one or several glide planes. It is found that for practically all purposes the relation Λ=2ρ can be used.
Electron Microscope Diagnostics of Thin Film Sputtering
Authors: Medved D. B. , Poppa H.
Published: April 2005

A new technique for measuring relative changes in thin film thickness is utilized as a means of monitoring sputtering yields at low energies. The apparatus consists of a Hitachi HU-10 electron microscope with an ion source attached to it which allows exposure of the specimen to ion bombardment before and after monitoring transmission current of electrons through it. Operating the microscope in the selected area diffraction mode, the electron beam current is monitored by a Faraday cup placed in the microscope at the position of the final diffraction pattern image. Relative changes in thickness as low as 4 Å for 100-Å thick films are measured. A scanning technique avoids contamination buildup during the electron transmission measurement. The specimens monitored have shown a high degree of uniformity with variations in sample thickness less than the estimated error of the measurement. The sensitivity of this method is limited only by available ion current densities rather than total current to the specimen. In principle, mass losses of 2×10−14 g are detectible by the electron beam probe of 2-μ diameter. The apparatus has been applied to measuring sputtering yields of polycrystalline silver thin films as a function of energy at normal incidence utilizing argon, krypton, and neon as the bombarding ions. The results in an energy range from 30 to 200 ev agree qualitatively with those of Koedam, particularly with regard to the mass variation. The sputtering yields for Kr+ ions on Ag is intermediate to that of Ar+ and Ne+. At 30 ev S≃2×10−4 for Kr+ on Ag.
Configurations of Superconducting Shells Required for Near Critical Uniform Magnetic Fields
Authors: Hildebrandt Alvin F. , Wahlquist Hugo , Elleman Daniel D.
Published: April 2005

The boundary value problem for a superconductor has been solved for specific axially symmetric geometries. The interior field of a right circular shell is found to be quite uniform. Also it is found that the ends of the shell can be shaped to overcome a singularity at the end. This permits a near critical and uniform field to be obtained over a very large volume of the central region. Experimentally it was found that a simple geometric shape electrolytically coated with lead would trap a field of 630 gauss with homogeneity in agreement with calculation.
Theory of the Ettingshausen Cooler
Authors: El-Saden M. R.
Published: April 2005

A cooling system referred to here as the Ettingshausen cooler, based on the Ettingshausen and Nernst-Ettingshausen effects is studied. It is shown that under dynamic conditions, these two effects are coupled and provide a mechanism for producing a cooling effect. Thermodynamic analysis is carried out and the coefficient of performance is determined. The analysis produced a dimensionless thermomagnetic figure of merit, which sets the requirements on the material's properties. For effective cooling, materials with high thermomagnetic numbers are required. A brief review of the relevent transport processes is made, which shows that intrinsic semiconductors, within certain temperature ranges, are most suitable for the Ettingshausen cooler.
Curved Growth of Ice on Surfaces
Authors: Knight Charles A.
Published: April 2005

Ice growing dendritically from supercooled water along some foreign surfaces changes its orientation as it grows, in response to asymmetrical temperature gradients. A qualitative, preliminary description and discussion of this phenomenon is presented. The only stable growth is with the c axis [0001] perpendicular to the surface. Other orientations in general curve toward this. Increased initial supercooling sharpens the curvature, and dissolved NaCl inhibits it. The curvature is discussed in terms of edge dislocations introduced during growth. The density of dislocations responsible for the curvature reaches 108 lines/cm2. Orientations of ice grown in containers is a consequence of curved growth. Direct formation of polycrystalline ice from supercooled water is reported. The method used in observing curved ice growth also allows observation of the formation of striations and related phenomena.
Beat Frequency Bridge for Large Signal Field Effect
Authors: Gerlich D.
Published: April 2005

A beat frequency bridge for large signal field effect measurements based on an ac modulation method is described. Some field effect measurements with this bridge on low resistivity germanium and gallium arsenide are reported.
Some Observations on the Structure of Polytetrafluoroethylene
Authors: Speerschneider C. J. , Li C. H.
Published: April 2005

Changes in the structure of PTFE produced by different cooling rates from the sintering temperature and following permanent mechanical deformation have been studied with the electron microscope. Slow cooling rates resulted in longer and wider striated bands (which constitute the PTFE) than fast cooling rates, however, there was no apparent change in the relative amount of crystalline material as x-ray and infrared absorption studies indicate. Permanent strain resulted in severe distortion of the band structure; the striations either slipped past one another or became kinked. The manner in which the deformation occurred indicated it was controlled by a viscous noncrystalline phase. It is proposed that the band structure itself consists of two phases, crystalline striations or platelets separated by viscous noncrystalline matrix.