bluuebunny/crossref_metadata_2025_split huggingface dataset:
Energy Transfer between Eu2+ and Ho3+ Ions in CaF2
Authors: Ewanizky T. F. 
Published: January 2005

CaF2:Ho3+ has been reported as a visible laser at 5512 Å. Operation is at a relatively high threshold power due, principally, to weak and narrow absorption lines.
Preliminary experiments, using Eu2+ as a sensitizer, have indicated that an order of magnitude increase in Ho3+, 5512-Å emission intensity may readily be achieved through transfer of energy from Eu2+ to Ho3+ ions. Dopant concentrations, for each constituent, were nominally &lt;1 mole%.
Dynamics of Laser-Induced Breakdown in Gases
Authors: Young M. , Hercher M. 
Published: January 2005

The breakdown of gases under the influence of a laser beam is analyzed. Classical diffusion theory is taken as a model, with electrons accelerated by inverse bremsstrahlung until they have sufficient energy to ionize neutral gas atoms. Both diffusion and recombination are included as losses.
For the rare gases in the range below atmospheric pressure it is found that the relation between the laser pulse duration and the plasma growth time is the primary factor which determines the breakdown threshold. The losses play roles of varying importance depending on gas, pressure, and geometry. The initial electrons are generally assumed to have come from multiphoton ionization of impurities, although multiphoton ionization of the gas itself becomes a factor at sufficiently low pressures (high photon fluxes).
A number of experimental results is presented. These are used to justify some of the theoretical assumptions and to corroborate the results of the theory. The agreement is good.
Noise Calculations in Continuous-Parameter Systems
Authors: Blue James L. 
Published: January 2005

Noise in a Markoffian, stationary, quasilinear system may be computed by an elegant and very general procedure developed by Lax. When this procedure is applied to problems described by continuous Markoff variables, and when analytic solutions are not possible, the amount of numerical calculation required for solution may become excessively large. The present paper recasts Lax's procedure into a form which is suitable for computer evaluation, provided that the system meets two additional requirements: (1) the fluctuations in only a small number of linear combinations of the variables are of interest; (2) the diffusion matrix, or noise source term, is diagonal.
The calculation of avalanche noise in an avalanche transit-time diode is presented as an illustration.
Orientation Inversions in Polycrystalline CdS Bulk Crystals and Thin Films
Authors: Rozgonyi G. A. , Foster N. F. 
Published: January 2005

A study of the crystallographic orientation of the single-crystal grains of large (8.5-cm-diam) polycrystals of CdS and of thin films of CdS has been made. Chemical and sputter-etching observations, x-ray crystallographic techniques, and piezoelectric polarity measurements have been used to classify the growth habits of the thin films as a whole and of the individual grains of the bulk crystals.
Three types of grains have been identified in the bulk CdS polycrystals. These are type I: c axis normal to a Cd-rich growth face; type II: c axis greater than 15° from the normal to an S-rich growth face; and inverted type II: c axis greater than 15° from the normal to a Cd-rich growth face. Type I and inverted type II grains exhibit negative compression piezovoltages, while type II grains are positive. Type I grains are identical to the type I single crystals previously discussed by Reynolds, and type II grains are similar to the 14° misoriented type II single crystals of Reynolds.
Similar results were obtained from the evaporated CdS thin films which could be classified as type I and type II, with the normal to the type II films about 20° off the c axis, indicating a close parallelism between the processes occurring in evaporated thin films and in bulk crystal growth. Sputtered CdS films were always type I. It is suggested that the variable efficiencies that have been observed in piezoelectric thin-film transducers with similar crystallographic orientations are related to orientation inversions in the films.
Effects of an External Magnetic Field on Landau Damping in Maxwellian Plasmas
Authors: Babler Gary M. , Willett Joseph E. 
Published: January 2005

Landau damping of longitudinal electron oscillations in a boundless, Maxwellian, collisionless magneto-plasma is studied in an approximation which neglects the coupling to transverse oscillations. The longitudinal component of the electric field is explicitly developed as a superposition of exponentially damped sinusoidal oscillations for an initial perturbation sinusoidal in space and Maxwellian in velocity. A formula is derived for the minimum time for Landau damping, i.e., the time which must elapse before only the lowest frequency oscillation is significant.
An analysis is presented for the strong magnetic field case in which ωc≫2π |sinθ| (λ/λD)ωp, where ωc is the cyclotron frequency, θ is the angle between the propagation vector and the external magnetic, λD is the Debye length, λ is the wavelength, and ωp is the plasma frequency. For this case the Laundau zeros move continuously along rays from their location in the absence of a magnetic field when the angleθ is zero to the origin as this angle approaches 90 deg. With this same variation of angle the minimum time increases from the null field value to infinity. These results are independent of the cyclotron frequency, provided that the above inequality is satisfied. For no external magnetic field the minimum time is found to increase with increasing wavelength and decreasing thermal spread of the initial perturbation when the spread is less than that of the unperturbed distribution.
Thermal Expansion and Elastic Constants of β′-AgMg. II. Single-Crystal Elastic Constants from 77° to 750°K
Authors: Chang Y. A. , Himmel L. , Neumann J. P. 
Published: January 2005

The single-crystal adiabatic elastic constants of stoichiometric β′-AgMg have been determined from 77° to 750°K using the ultrasonic pulse-echo technique. The values obtained at 300°K are: c11=0.8380, c12=0.5635, c44=0.4755 (all in units of 1012 dyn/cm2).
A relationship between the elastic constants and the lattice parameters of the two β′-structures AgMg and CuZn was found. A similarity of the temperature dependence of the elastic constants was also observed. From the extrapolated values of the elastic constants at 0°K, a Debye temperature of 287°K was obtained. Finally, using the elastic constant data, specific heat of β′-AgMg at constant volume was calculated and found to compare favorably with the classical value 3R at high temperature.
Porosity Effects on the Oxidation of Tungsten
Authors: Berman David 
Published: January 2005

The rate of formation of tungsten oxide, from the internal porous area of a heated tungsten sample, has been calculated. The porosity effect has been found to increase the oxidation rate by an order of magnitude over an equivalent solid sample.
The effusion rate of WO3 from the sample is obtained by establishing the O2 and WO3 molecular distributions within the sample. The boundary conditions of the distributions are set by the partial pressure of oxygen at the surface. The rate of WO3 effusion (from the porous interior into the surroundings) is determined by the molecular concentration gradient at the boundary, times the appropriate diffusion coefficient.
The parameters used in the study correspond to vacuum-system operation of a cesium surface-contact ionizer (temperature=1400°K; pressure=10−6 Torr). Simple slab geometry is considered for the porous tungsten sample; only one side is exposed to oxygen.
Neglecting Diffusion in Space-Charge-Limited Currents
Authors: Schilling Ronald B. , Schachter Harry 
Published: January 2005

In most work dealing with space-charge-limited currents, the diffusive contribution to the current is neglected. The classic steady-state problem was handled by Mott and Gurney. For their problem of the perfect insulator it is well known that diffusion dominates near the injecting contact but, after some critical distance, drift dominates, and it is consistent to neglect diffusion.
For the case of transient SCLC the mathematical validity of neglecting diffusion has not been shown. The purpose of this work is to show that for times greater than a critical time and distances greater than a critical distance the diffusive term can consistently be neglected. The solutions found by Mark and Helfrich and by Many and Rakavy for injection of electrons into an insulator under an applied voltage pulse have been shown to be correct under the above conditions. The interesting result is that the critical parameters are related to geometrical parameters by the ratio of the thermal voltage kT/q to the applied voltage. We therefore find that for signals large compared to kT/q, the neglect of diffusion is valid over most of the range of time and distance associated with the problem.
Effect of Impurities on the Optical Properties of Yttrium Iron Garnet
Authors: Wood D. L. , Remeika J. P. 
Published: January 2005

The optical absorption spectrum of single-crystal YIG is dominated at the short wavelengths by electronic transitions due to iron ions. For the long wavelengths, it is dominated by lattice vibrational transitions. Between about 1 μ and 6 μ there is a region of great transparency which can be modified in several ways. The valence of the iron ions can be altered by heat-treatment of crystals in oxidizing or reducing atmospheres, or by doping with divalent or tetravalent ions. The altered valence leads to increased optical absorption, as well as increased electrical conductivity.
Foreign ions such as cobalt or the rare earths may have characteristic absorption lines in the region of transparency, and when yttrium is completely replaced by a rare earth, the short-wavelength edge absorption may be shifted appreciably due to lattice expansion or contraction.
Another anomaly in the transparent region of YIG is found in hydrothermally-grown crystals, where OH-group stretching vibrations occur.
Calculation of the Rare-Earth—Iron Superexchange Interaction in the Garnets
Authors: Pearson J. J. , Herrmann G. F. 
Published: January 2005

The exchange potential for the rare earth—iron interaction in the garnets depends on ten theoretical parameters. Since experiments provide only six splittings, the potential has been simplified in past treatments by various drastic assumptions which are highly implausible on physical grounds.
By treating directly the superexchange mechanism involved we obtain a potential whose parameters are physically well-defined exchange and transfer integrals. By invoking the ``orthogonality requirement'' the number of these parameters is greatly reduced. A preliminary calculation for ytterbium shows that a good fit can be obtained by assuming the interaction of the rare earth with its nearest iron neighbor to predominate.
Structures and Magnetic Properties of Grain-Oriented 3.2% Silicon—Iron
Authors: Littmann M. F. 
Published: January 2005

After almost 30 years of use, grain-oriented silicon—iron remains the most important soft ferromagnetic material where high permeability and low core loss are required.
In this paper we show how grain structures which the metallurgist has learned to produce affect permeability at H=10 Oe and core loss at B=15 kG. Deviations from the ideal (110) [001] and (100) [001] are compared. The effect of thickness for both textures is shown over a range of about 1 to 25 mil. Ascertainment of the true effect depends on maintaining other factors constant, such as degree of texture and grain size. The effect of grain size on core loss of Epstein test specimens is shown over a wide range from 0.03- to 20-mm diameter for a relatively constant degree of texture and chemical purity. For very small grain sizes, small grain diameter is detrimental to core loss but the effect is reversed for large grains near 10 mm diameter.
Attainment of superior magnetic properties depends on combination of a high degree of crystal texture together with a grain diameter of about 1 mm. This appears to be the case for both cube-on-edge and cubic textures.
Magnetic Properties of Ferrite Single Crystals with the Y Structure
Authors: Verweel J. 
Published: January 2005

Single crystals of BaZnFe6O11 (Zn Y) were grown by the flux technique. Chemical analysis showed the presence of some ferrous ions in most batches. A relation between the Curie temperature and the ferrous content could be established. The anisotropy in the specific resistivity was measured (20–260 Ω·cm in the basal plane, 240–1400 Ω·cm in the c direction) and was found to be a structural effect. The magnetostriction in the basal plane was measured to be 1.5×10−6.
The crystal anisotropy field in the basal plane was found to be smaller than 1 Oe at room temperature for all samples and 10–20 Oe at 77°K. Linewidths of thin disks were found to be 14–20 Oe at room temperature and 50–60 Oe at 77°K. The permeability of single-crystal toroids in the basal plane was measured at room temperatures between 0.5 and 500 MHz. Two dispersion mechanisms were found near 10 and 100 MHz, which could be ascribed to wall and spin relaxation, respectively.
The rotational permeability was found to be about 300, whereas from the anisotropy data at least 1300 would have been expected. This discrepancy could be understood from the investigation of the Bloch-wall pattern of these samples, as will be discussed in some detail.
Linear Theory of the Vertex Function in Spin Dependent s-d Scattering
Authors: Duke C. B. , Silverstein S. D. 
Published: January 2005

Following the field theoretic techniques of Abrikosov,1 we have derived a linear equation for the vertex function associated with the scattering of conduction electrons from magnetic impurities. We consider the model of a general nonlocal interaction consisting of the standard spin-independent impurity potential plus an s-d exchange interaction. In addition to the development of the linear theory, we have made an exact calculation of those terms in the electron proper self-energy which are linear in the density of the impurities to fourth order in the coupling constant for the restricted model of only an s-d exchange interaction.
We show that to logarithmic accuracy (in the sense of Abrikosov1), not only Abrikosov's vertex function, but also that of Suhl2 and the one which satisfies a linear integral equation all give the same result for the proper self-energy. However, the less divergent terms in any order of perturbation theory are not correctly reproduced by any of the vertex functions, which among themselves lead to different contributions to these terms in the self-energy. Thus, the use of the various vertex functions to compute the self-energy must be considered as inequivalent interpolation procedures for obtaining a substitute for the exact perturbation-theory results. We have solved the linear equation for separable s-wave interactions using both the ordinary and s-d terms in the potential. The linear equations do not manifestly exhibit the absence of singularities in the upper half-energy plane, and for weak, long-range separable interactions such singularities occur despite the interference between the spin-flip and non-spin-flip scattering. Although the linear theory is manifestly invariant under rotations, the resulting vertex functions do not satisfy single-channel, energy-shell unitarity2 in channels labeled by the coupled angular momentum of the incident electron plus impurity. The origin of this result is the linear theory's incorporation of correlations in the wavefunction of Fermi gas for which the incident electron couples to both the impurity and a particle-hole excitation to give other states of the same total angular momentum as that of the incident electron plus ``bare'' impurity. The states associated with such correlations assume the role of additional channels for the decay of an initial state with fixed angular momentum.
Raypath Trajectories in Magnetic Delay Lines
Authors: Addison R. C. , Auld B. A. , Collins J. H. 
Published: January 2005

Behavior of the magnetoelastic waves in a magnetoelastic variable delay line has been simulated using geometrical acoustics. Assuming a magnetic field which approximates the internal field of a rod immersed in a uniform field, differential equations for the magnetoelastic rays have been obtained and solved numerically.
The rays are found to oscillate rapidly about the rod axis when they are predominantly spin waves. As they change into predominantly acoustic waves, the rays stop oscillating and propagate at a nearly constant angle with the rod axis. The final angles of the rays are quite dependent on the shape and magnitude of the magnetic field. Because of this, the final angles of the rays in the acoustic region of a delay line will vary as the delay is changed by adjusting the magnetic field. When these rays are not parallel to the rod axis, they will not retrace their paths upon reflection at the end of the rod. This phenomenon may explain oscillatory variations of insertion loss with delay which have been observed in delay line experiments. The validity of this interpretation is explored using results of the computer simulation.
Suppression of Spin-Wave Instabilities by Field Modulation
Authors: Hartwig C. P. 
Published: January 2005

Spin-wave instabilities associated with ferromagnetic resonance have been suppressed in experiments on parallel pumping as well as ``second-order'' saturation of the main resonance. A method is described in which a modulating field (∼1 Mc/sec) is applied along the dc bias field. Theoretical suppression curves have been derived and are compared with experiments on spheres of YIG at X band. An experiment is described in which the cone angle of the uniform precession is opened beyond the usual instability threshold without the generation of sidebands.
The extent of suppression is determined by the modulation index δ, which is proportional to the ratio of modulating field strength to modulating frequency. In the parallel-pumping experiment, threshold power is expected to increase 7 dB per decade increase in δ for δ&gt;0.92. Experimentally the threshold has been raised in excess of 10 dB. A mathematical model has been developed to explain deterioration of the suppression when the modulating frequency is comparable to or less than the relaxation frequency of the spin waves. Stabilization of the main resonance requires application of both transverse and longitudinal modulation. Where a ``second-order process'' is involved, only half as much suppression is possible as in the case of parallel pumping for equal δ.
Ferromagnetic Properties of Single-Crystal Nickel Platelets and Submicron Whiskers
Authors: DeBlois R. W. 
Published: January 2005

Nearly perfect nickel, nickel alloy, and iron single-crystal platelets of thin-film thickness are excellent specimens for basic ferromagnetic domain, domain-wall,1,2 and resonance3 studies. Submicron nickel whiskers that grow with the platelets are also ideal for nucleation studies.4 Individual whiskers as thin as 600 Å (2 pg) are readily observed (by Rayleigh scattering), tested, and handled. Physical buckling of the whiskers into forms of the elastica5 allows measurements of both end and infinite-rod nucleation fields. Observed fields versus whisker diameter and versus field angle follow curling theory.6 Thickness comparisons by electron microscopy and by bending yield an effective Young's modulus near 10×1111 dyn/cm2, about half the handbook value. A motion-picture film showing the physical bending and the magnetic nucleation of whiskers suspended in a thin layer of oil and viewed through a microscope by dark-field illumination was presented at the conference.
The platelets show with classic simplicity many details of domain and domain-wall structure and behavior, making them especially suitable for educational purposes, for testing theories, and for supplementing thin-film studies. Recent platelet observations include double 90° and 180° Bloch walls; a double wall apparently composed of 180° walls of mixed Néel-Bloch character; 180° Bloch walls that may press against a platelet edge without parting; 45° walls formed by magnetostrictive anisotropy; a field-induced stripe pattern in [100] Ni-Co platelets with +K1; and the transitional domain structure in a Ni-Co platelet with a linear variation in composition from +K1 to −K1.
Evidence for Domain-Wall Compressibility in Permalloy Wire
Authors: Schulz-DuBois E. O. 
Published: January 2005

This paper describes dynamic magnetization experiments in hard-drawn niobium silver Permalloy wire of the type used in domain wall shift registers. In particular, it reports evidence for the compression under the influence of an applied bucking field of the transition region separating two domains of antiparallel longitudinal magnetization. In the absence of external field, the transition region is characterized by a domain wall roughly in the shape of a paraboloid of revolution with a minimum length of about 1 cm for wire of 0.005-cm diameter. Within the transition region a longitudinal derivative of flux exists which may be conveniently referred to as magnetic pseudo charge. For a transition, the total charge is conserved and the length of the transition is inversely proportional to charge per unit length. The charge contained in about 0.1-cm length of wire was measured by a pickup coil consisting of two adjacent coils with opposite sense of winding, connected in series, and subsequent electronic integration. The charge under this coil was increased and decreased by applying a 60-Hz longitudinal field to the wire with a reversal of direction under the pickup coil. These dynamic experiments with or without an additional homogeneous field result in hysteresis loops of particularly simple and predictable shape. The identifiable individual processes within the cycle are nucleation, wall compression and expansion, and wall motion. A compression of the longitudinal dimension of the domain wall by a factor 4 is inferred from that increase in charge when the compressing field is ±17 Oe. The curved portions of the loop follow, with good accuracy, a square-law dependence. Such a shape is expected from dimensional arguments applied to the magnetostatic situation which predict the proportionality Q ∝ (HB±HW)½, where Q is the charge under the pickup coil, HB is the applied bucking field, HW is the wall motion threshold, and the choice of signs implies some hysteresis connected with the motion of parts of the wall. Loops taken without the additional homogeneous field indicate the absence of a distinct nucleation phenomenon. A process akin to pair creation is proposed which converts a wall of positive charge, for example, into a sequence of positive, negative, positive charged walls and where the outer two walls then move away by conventional wall motion.
A more complete account of this work is intended for publication elsewhere.
The Contribution of Dislocations to the Magnetocrystalline Energy and Their Effect on Rotational Hysteresis Processes
Authors: Kronmüller H. 
Published: January 2005

Internal stresses of dislocations interact in ferromagnetic crystals with the spontaneous magnetization through the magnetoelastic coupling energy. The magnetic free energy (MFE) of a straight dislocation line is calculated by means of Brown's micromagnetic equations. This energy corresponds to a magnetostrictive contribution to the magnetocrystalline energy which is superimposed on that of the ideal crystal. In a material with isotropic magnetostriction the MFE of a straight edge dislocation line possesses orthorhombic symmetry.
The theoretical results may be compared with those of an investigation of magnetization processes of plastically deformed Ni single crystals by Köster. Analysis of measurements of the magnetostriction and of the increase of magnetization as a function of the applied field has shown that in deformed Ni crystals the MFE of the dislocations may become comparable to the magnetocrystalline energy constant K1 of the ideal crystal.