bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extension of Coincidence Limiting Frequency Range in Ferrimagnets
Authors: Comstock R. L. , Dean W. A. 
Published: April 2005

Power limiting using the first-order spin-wave instability has been observed in a ferrimagnetically coupled filter-limiter at higher frequencies than had previously been believed possible. For example, a filter-limiter, using orthogonal strip-line resonators coupled by the dipolar fields of a YIG sphere, was constructed at 4000 Mc. Output power was limited with the sharp break at the threshold and flat limiting curve characteristic of coincidence limiters. This result is in contrast with the operation of similar limiters at this frequency which use the second-order spin-wave instability in which the limiting characteristic has a much more gradual slope transition above the threshold. Coincidence limiters have previously been believed to have a maximum operating frequency ωc=2ωMNT (3.27 kMc for a YIG sphere) since, with an isolated sample, coincidence of the uniform precession resonance and the subsidiary absorption occurs only for ω&lt;ωc.
These results are observed for a coupled mode resonance in these ferrimagnetically coupled circuits which occurs for dc magnetic field values in the subsidiary absorption region below the uncoupled uniform precession value (ω/γ). It is found that a minimum value of the circuit-sample coupling is required to observe this extension of coincidence type limiting. Limiting thresholds as low as −10 dBm have been observed with the strip-line circuit and lower levels are believed to be possible. Wide low-level bandwidths (&gt;10%) are also obtained with these circuits, but with an increase in the limiting threshold.
The above results are explained by computing the normal modes of the microwave-ferrimagnetic resonator circuit. It is found for tight enough coupling that one of the branches of the normal mode spectrum is in coincidence with the subsidiary absorption at a higher frequency than the uniform precession resonance. The usual coincidence limiter operation (ω&lt;ωc) is thus the small coupling case of the more general type of operation.
Longitudinal Pumping of Magnetoelastic Waves in Ferrimagnetic Ellipsoids
Authors: Morgenthaler Frederic R. 
Published: April 2005

The instability threshold of parametrically excited magnetoelastic waves is derived, as a function of the dc magnetic field strength, for that region of field where the phonon and magnon spectra intersect. The case considered involves the longitudinal pumping (with an rf magnetic field of constant frequency 2ω), of a small ferrimagnetic single crystal having cubic symmetry. The crystal is ellipsoidal in shape and is magnetized along a [100] direction. (The analysis is also applicable to a uniaxial crystal magnetized along its principal axis.) In this instance, the unstable magnetoelastic waves are a mixture of transverse phonons (polarized in the longitudinal direction) and magnons (spin waves) which propagate at (or very near) right angles to the dc field.
If, as is usual, the two branches of the magnetoelastic wave spectrum are split by a frequency large compared to the phonon relaxation frequency, an approximate, and greatly simplified expression may be deduced from the general solution. In this case, it is found that the line shape of the phonon contribution to the threshold is asymmetric, and that the peak of the curve occurs for a smaller value of dc field than is generally believed. This shift in field is ∼b2(2ΔHk)Q (where b is the magnetoelastic energy coefficient, 2ΔHk is the appropriate spin-wave linewidth, and Q is the appropriate phonon Q) and must be taken into account for an accurate determination of the exchange constant (particularly at the lower microwave frequencies). The peak of the phonon contribution to the threshold curve is independent of this shift and also of b; it is ∼λω2Q−1, where ω is the frequency of the magnetoelastic wave and λ is the exchange constant. The width of the peak at half-height is essentially independent of Q (except at very low frequencies) and is ∼|b|M2ωλ½, where M is the value of the saturation magnetization.
Magnetic Annealing and Directional Ordering
Authors: Neurath Peter W. 
Published: April 2005

Evidence in support of the view that magnetic annealing is due to directional ordering in substitutional alloys has been obtained in experiments on a 3% Si-Fe alloy. In addition to the theoretical interest of this result, the improvement in properties of practical importance, such as the 60 cycle watt losses and the magnetostriction have been demonstrated.
3×28×0.03 cm strips of (110) [011] oriented 3% Si-Fe material were isothermally annealed in fields of the order of 10 Oe parallel to their long axis, and at temperatures from below 350°C to above the Curie point. It was found that the temperature dependence of the magnetic annealing expressed as a ratio of the maximum obtainable effect was linear when plotted against 1/T and could be interpreted as due to an activation energy of 46 000 cal per mol, which is in excellent agreement with the activation energy for diffusion of Si in ferrite. From the practical point of view, it was demonstrated that a 5-min magnetic anneal at only 510°C was very effective in reducing losses and particularly in lowering the magnetostriction in the [011] direction. The absence of any effects in pure iron samples, compared to similarly oriented Si-Fe samples, showed that the effect was really due to the diffusion of silicon only.
New Method to Measure Directly the 180° Bloch Wall Energy
Authors: Aléonard Roland , Brissonneau Pierre , Néel Louis 
Published: April 2005

Using the Bitter technique, the traces of a single 180° Bloch wall are observed by a device composed of two microscopes, one on each side of the sample. The wall is twisted by an inhomogeneous magnetic field. The measured displacements of the wall traces are related to the surface energy γ0 of the Bloch wall which in turn is related to the Heisenberg exchange constant A.
In an iron-silicon alloy with 3% Si we find γ0=1.48 ergs/cm2 and A=1.48×10−6 ergs/cm at room temperature, in fair agreement with the value A∼1.7×10−6 ergs/cm derived from Bloch's law and spin-wave theory at 0°K.
Magnetic Characteristics of Praseodymium, Neodymium, and Samarium Hydrides
Authors: Kubota Yoshio , Wallace W. E. 
Published: April 2005

Magnetization-temperature data are presented for the hydrides PrH2.02 to PrH2.71, NdH2.02 to NdH2.75, and SmH1.99 to SmH2.88 and for the three parent metals from 4.2° to 300°K. Of the twelve hydrides examined only NdH2.02 and NdH2.03 exhibited magnetic ordering. These hydrides exhibited a Curie point at 9.5°K and the saturation moment measured at 4.2°K was 1.36 μB per Nd atom. Assuming the applicability of a Brillouin function with J=9/2 the moment extrapolated to 0°K is 1.51 μB. These values are considerably lower than the value for the free tripositive ion (3.27 μB) or the moment observed in the paramagnetic region (3.40 μB) but are in reasonably good agreement with the theoretical value (1.58 μB) computed for 4.2°K taking into account crystal field effects.
The susceptibility behavior of the four Sm hydrides studied is generally similar. The trend with temperature is in reasonably good agreement with theory which treats Sm as a free tripositive ion. Susceptibility of the Nd hydrides follow the Curie-Weiss law above about 100°K with the expected slope but deviate negatively from it at lower temperatures. The deviations are attributed to either incipient ferromagnetic ordering or crystal field effects or a combination of the two.
The susceptibility behavior of the Pr hydrides is very unusual. The highest hydrides exhibit Curie-Weiss behavior above about 80°K but show positive deviations from linearity in 1/χ vs T at lower temperatures. That the deviations may be due to crystal field effects is considered possible but unlikely. PrH2.03 and PrH2.04 exhibit essentially identical susceptibility behavior and do not follow the Curie-Weiss law. Their susceptibilities are anomalously high near room temperature, exceeding the values for the element and the saturated hydride by a factor of about five.
Magnetic Structures of TbD2 and HoD2
Authors: Cox D. E. , Shirane G. , Takei W. J. , Wallace W. E. 
Published: April 2005

TbD2 and HoD2 have the calcium fluoride type of structure and become antiferromagnetic below 40° and 8°K, respectively. A powder neutron diffraction study of TbD2 at 4°K revealed a sinusoidal modulation of basic magnetic ordering of the first kind, in which ferromagnetic (001) layers are coupled antiparallel to the two adjacent layers. Both the magnetic moment and the wave vector are directed along the [001] axis, with a periodicity of about 24 Å. The moment associated with the Tb ion is 7.9 μB.
The diffraction pattern observed for HoD2 was quite complicated and attempts to index the magnetic reflections either with multiple cell dimensions or with simple modulation of a few basic antiferromagnetic structures have proved unsuccessful.
High-Field Study of a Hall-Effect Microwave Converter
Authors: Chang K. K. N. , Hughes R. D. 
Published: April 2005

Utilization of the Hall effect in the frequency conversion of microwaves with gain was investigated. A conversion gain which seemed to be feasible was found to be dependent on the control sensitivity of the conversion system. A high control sensitivity can be achieved through use of a high-mobility Hall sample, like InSb, an efficient coupling of a modulating field to the sample, and a suitable high-energy pump source.
The high-power test was performed by using a pulsed microwave pump. Conversion gains were measured as a function of the pumping power and showed some ``saturation'' effects. These effects were explored and explained, based on the behavior of carriers in the sample under high-power microwave fields. In particular, a breakdown field beyond which the saturation seemed to disappear was found.
The present S band experimental model still suffered a conversion loss of 25 to 30 dB. Results have, however, revealed the possibility of a practical microwave Hall converter with gain.
Conditions Existing at the Onset of Oscillistor Action
Authors: Larrabee R. D. 
Published: April 2005

One of the major problems in oscillistor work is connected with the stability and reproducibility of the surface conditions of the oscillistor specimen. An empirical surface treatment has been found which enables one to prepare reasonably reproducible and stable oscillistors. By utilizing this surface treatment, it has been possible to measure the conditions existing at the onset of current oscillations. The quantitative dependence of the minimal applied magnetic field required for oscillistor action has been measured as a function of applied voltage and specimen size. Some qualitative information regarding the dependence of the minimal applied magnetic field on bulk and surface properties has been inferred from the experimental data. These data reveal that there is an optimum size for oscillistor specimens that will minimize the electrical input power required for oscillations, and by using such samples, oscillistors have been fabricated that will function continuously at room temperature. An experiment designed to interact with the magnetic field produced by the helical perturbation proposed by Glicksman has disclosed a new effect that may provide a way of constructing an oscillistor amplifier.
These experiments have revealed that the conditions necessary for oscillations in the current are quantitatively different from the conditions necessary for oscillation of the components of electric field that are transverse to the applied electric field. Since no quantitative theory of the mechanism of current oscillation has appeared in the literature, no direct comparison between theory and experiment is possible. However, the applied electric and magnetic fields required for current oscillations are of the same order of magnitude as those predicted by the existing helical instability theories.
Resonance Phenomena in a Gaseous Discharge in a Strong Magnetic Field
Authors: Beeken Basil , Goldman Robert , Oster Ludwig 
Published: April 2005

The rf spectrum of a gaseous discharge in a strong magnetic field is measured with the aid of a fixed frequency receiver by sweeping the magnetic field by approximately two percent. Source of radiation and receiving equipment are described. The following results were obtained: (1) A series of emission lines around the cyclotron frequency. (2) An emission at a frequency which increases with increasing magnetic field strength and decreases with increasing external voltage. (3) A strong resonance when both frequencies coincide: the intensity increases by a factor of 100 and more.
The frequency spectrum is discussed in terms of a simple theory, which accounts for local space-charge fields. Their spatial distribution is inferred from the frequency behavior of the emission lines. Finally, a mechanism is suggested which classifies the resonance effect as an energy transfer from a longitudinal plasma mode into e.m. radiation.
Parametric Coupling of the Magnetization and Strain in a Ferrimagnet. II. Parametric Excitation of Magnetic and Elastic Plane Waves
Authors: Comstock R. L. 
Published: April 2005

The parametric coupling between traveling electromagnetic and elastic waves in a ferrimagnet supplied by magnetic pumping is theoretically investigated. The pumping threshold is calculated for steady-state wave propagation in the presence of loss for plane electromagnetic and longitudinal elastic waves in an infinite ferrite medium. This threshold is compared to the threshold for second-order spin-wave instabilities and it is found that these spin wave processes should not prevent the magnetoelastic process from occurring.
It is shown that this traveling wave system may be useful for amplifying electromagnetic or elastic waves.
Heat-Wave Methods for the Measurement of Thermal Diffusivity
Authors: Cutler M. , Cheney G. T. 
Published: April 2005

A simple method for measuring thermal diffusivity is considered. It consists in suddenly heating one end of a sample and measuring the time it takes for a heat wave to arrive at the other end. This paper considers the application of this method for two kinds of boundary conditions relating to the heat input. These conditions correspond to step-function heating (a) by radiation and (b) by a good contact to a constant-temperature heat source, such as liquid metal.
In addition to consideration of the effects on the analytic solution due to radiation heat loss, other factors which affect the accuracy and sensitivity of the technique are discussed. The heat-wave method is related to many other techniques for measuring thermal diffusivity, ranging from Angstrom's original method to several pulse heating techniques which have been described recently. The interrelationships between these different techniques are discussed.
Surface Lines on Soda-Lime Glass Slides
Authors: Stilwell G. R. , Dove D. B. 
Published: April 2005

It has been found that a remarkable line structure may be developed on the surface of soda-lime glass slides by treatment in a hot detergent solution (2% Alconox). The lines are produced by an etching process which exposes ridges or cords of less soluble material that have been introduced into the surface layer by the manufacturing procedure of drawing the glass through an orifice (Fourcault process). Details are given of etch rates, size and distribution of the ridges, and of the effect of annealing treatments.
The possibility of the inadvertent production of an anisotropic surface structure is of some importance since soda-lime microscope slides are frequently used as substrates for vapor deposition processes. Preliminary experiments to examine the effect of the line structure on vapor deposited Permalloy films are discussed.
Gain Saturation and Output Power of Optical Masers
Authors: Rigrod W. W. 
Published: April 2005

The nonlinear gain characteristics of optical maser amplifiers at high beam intensities, and the optimum cavity coupling of maser oscillators for maximum output power, are computed for maser media with homogeneous and inhomogeneous line broadening. An approximate expression is derived for the power output of a gas maser oscillating simultaneously at many longitudinal cavity resonances, based on the assumption that the gain saturates independently at each frequency. In each case, the decrease of maser gain with radiation intensity involves an empiric constant, or saturation parameter, which is characteristic of the active medium.
Power and gain measurements at 1.15 μ on three He–Ne maser tubes of different diameter, in a cavity 1.75 m long, are found to satisfy the derived multifrequency power expression, and permit evaluation of the gain—saturation parameter for this gas mixture. The power expression, derived for a single transverse mode, is unexpectedly found to hold for multimode oscillations as well, within the range of measurements. From the measured saturation parameter and the derived expressions, the performance of amplifiers and other oscillators with the same active medium can be predicted.
Crystal Growth of GaAs from Ga by a Traveling Solvent Method
Authors: Mlavsky A. I. , Weinstein Martin 
Published: April 2005

The temperature gradient zone-melting technique described by Pfann has been extended to the growth of semiconducting compounds from solution. In particular, single crystals of GaAs have been grown at temperatures much below the congruent melting point, using a thin zone of Ga as the solvent. The parameters influencing zone movement have been studied, including zone thickness, average temperature, temperature gradient, and seed orientation. For the case of the GaAs–Ga system, the rate of zone movement has been shown to be liquid diffusion limited. The passage of a pure Ga zone brings about considerable purification, as evidenced by the electrical properties of the grown crystals. Conversely, the passage of a suitably doped Ga zone can bring about the formation of abrupt p-n junctions. The electrical characteristics of such junctions are described.
Preliminary work has shown that the method is widely applicable to the growth of various classes of crystals and to the formation of various junction structures in semiconducting compounds.
Alloyed, Thin-Base Diode Capacitors for Parametric Amplification
Authors: Mortenson K. E. 
Published: April 2005

The design of double alloyed, thin-base diode capacitors for parametric amplification is described which indicates that capacitors with maximum Q's well in excess of 200 at 1 kmc and capacitive swings in excess of 15 are obtainable. The high Q's resulting from the type of fabrication and the small base thickness used; the large capacitive swing resulting from the abrupt p+n junction created.
Three figures of merit are defined and evaluated: (1) an over-all device figure, FD, proportional to the product of the maximum Q and capacitance ratio evaluated in terms of material parameters, degree of base doping, and geometry factors; (2) a Q factor, FQ, proportional to just the capacitor Q; and (3) a material factor, FM, by which different materials used for fabrication can be compared. Fixing the choice of material (with germanium shown to be superior to silicon for this purpose) and achieving the best geometry, FD and FQ are examined as a function of doping. It is shown that FQ is nearly constant over the entire practical range of doping while FD, because of the capacitive swing, increases substantially with lighter doping.
Results are presented for units with all soldered connections (no pressure contacts) fabricated from double alloyed pellets with a p+nn+ structure. To date, diode capacitors with maximum Q's in excess of 200 at 1 kmc and with capacitive swings in excess of 10 have been made. It is anticipated that this fabrication process will yield Q's in excess of 500 at 1 kmc with closer alloying control.
Dislocation Sources in Crystals
Authors: Gilman J. J. 
Published: April 2005

Lithium fluoride crystals were subjected to short stress pulses (1–10 μsec in length) in order to study dislocation nucleation in them. It was found that several heterogeneities can lead to dislocation nucleation: (a) cleavage steps, (b) dislocation loops, (c) glide bands, (d) inclusions or ``dirt'' particles, (e) precipitates (as grown), and (f) radiation-induced precipitates.
Also, it was found that annealing treatments at moderate temperatures (200–600°C) followed by ``rapid'' cooling (&gt;5°C/hr) made segments of previously pinned dislocations become mobile. These mobile segments multiplied as they moved through the crystals.
Several treatments were tried that were ineffective in producing dislocation nucleation. These included: temperature changes, surface wetting, simultaneous irradiation and stressing, reflections from free surfaces, and diagonal bending.
Carefully cleaned glass spheres were pressed into contact with dislocation-free regions of a LiF crystal. In this way, shear stresses that were 100 times greater than the normal yield stress of the crystal (∼G/85) were reached without causing homogeneous dislocation nucleation.
It is concluded that small foreign heterogeneities cause most of the dislocation nucleation in real crystals. Homogeneous nucleation occurs only at high stresses (∼G/30). Relatively little dislocation multiplication results from classical Frank-Read sources (almost none in LiF). Most dislocation multiplication occurs as a prior dislocation moves through a crystal.
Theory of Rolling Friction for Spheres
Authors: Flom D. G. , Bueche A. M. 
Published: April 2005

A theory of rolling friction featuring the importance of elastic hysteresis losses is presented. A simple model of retarded elasticity is chosen to represent the physical properties of the material. A prediction resulting from the theory is that the coefficient of friction for a relatively hard sphere rolling on a softer base material should vary with speed so as to go through a maximum. This relationship resembles closely the variation of mechanical loss with frequency.
The results are not restricted to rolling but also apply to well-lubricated sliding where shearing forces have been minimized. Although the theory is developed for a material with idealized physical properties, it nevertheless affords a basis for comparing real materials and for predicting their frictional properties in cases where deformation losses are predominant.
Theoretical Approach to the Asymmetrical Magnetization Curve
Authors: Aharoni A. , Frei E. H. , Shtrikman S. 
Published: April 2005

The method previously used to calculate the magnetization curve of an infinite cylinder is applied to the new Meiklejohn and Bean material which is made of Co particles in a CoO shell. It is assumed that the interface of the ferromagnetic and antiferromagnetic materials is held parallel to the cylindrical axis and does not change its direction for any value of the applied field. The crystal anisotropy is neglected.
It is shown that the easiest nucleation mode for small radii is buckling and for large radii is curling. The transition from buckling to curling is at about RIsA−½=2, where R is the radius of the cylinder, Is is the saturation magnetization and A is the exchange constant.
Numerical solution of the nonlinear equations involved, yields two branches in the magnetization curve, which are both stable with respect to curling perturbations. The general stability is not tested.
A similar calculation is carried out for an infinite slab with the spins on the surface held at a fixed direction and with the crystal anisotropy neglected.