bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Consistent Field Analysis of Multireflector Optical Resonators
Authors: Clark Peter O.
Published: April 2005

The self-consistent field approach is used to obtain integral equations for the modes in symmetric and nonsymmetric resonators with arbitrary numbers of mirrors. The resonator fields are considered as TEM clockwise and counterclockwise traveling waves which for passive resonators are uncoupled and which independently satisfy the necessary boundary conditions on reflection from the resonator mirrors. An arbitrarily polarized field is resolved into two linearly polarized components which can be treated separately and identically. The component perpendicular to the plane of the resonator is considered and integral equations are obtained for the spatial distribution of resonator modes just after reflection from any mirror in both the symmetric and nonsymmetric resonators. The integral equation for the symmetric N-mirror resonator is investigated in detail. Because of the astigmatic focusing of the reflectors there is no situation corresponding to the confocal resonator, however, a ``pseudoconfocal'' resonator with nonspherical mirrors is discussed. The integral equation for the resonator with arbitrary mirror spacing is solved in the limit of infinite Fresnel numbers and the resonator field is described in terms of Hermite-Gaussian functions. The mirror spacing must satisfy the condition 0≤l/bcosα≤2. A general resonance condition is obtained and the results of numerical computations of diffraction losses are presented for three- and four-mirror resonators. For minimum diffraction loss the ratio of mirror spacing to mirror curvature is not constant but varies from mode to mode and the amount of variation differs with the number of mirrors.
High-Temperature Specific Heats of Ge, Si, and Ge-Si Alloys
Authors: Gerlich D. , Abeles B. , Miller R. E.
Published: April 2005

The specific heats of Ge, Si, and Ge-Si alloys were determined in the temperature range 300° to 1000°K, by a novel temperature-modulation technique. The specific heat at constant pressure cp exceeds appreciably the Dulong-Petit value cDP at high temperature. Above the Debye temperature θD the divergence can be represented by cp/cDP=0.95+αT/θD where T is the absolute temperature and α=0.081 is a coefficient independent of alloy composition. This result is in disagreement with the current theory of the anharmonic contribution to the specific heat at high temperatures, which predicts α=0.016 for Ge, and α=0.030 for Si.
Effect of Carrier Trapping on the Weinreich Relation in Acoustic Amplification
Authors: Southgate P. D. , Spector H. N.
Published: April 2005

The Weinreich relation between the acoustic absorption coefficient and the acoustoelectric field in semi-conductors is found to be modified by carrier trapping. In the presence of dc fields, the acoustoelectric field and the absorption coefficient pass through zero at different values of drift field. The effects of the trapping are particularly important when the trapping time is of the same order as the acoustic-wave period. The experimental evidence indicates that the above explanation for the effect of trapping is valid, with the dominant traps having a trapping time of about 10−9 sec. Some anomalies in the absorption were found which can be explained by the generation of a shear mode which does not interact with the carriers. Nonlinear interactions with this shear mode are found to occur at much lower power levels than those associated with second-order effects in the theory of Hutson and White.
Second-Harmonic Generation in Large g-Factor Ferrimagnets
Authors: Auld B. A. , LeCraw R. C.
Published: April 2005

Harmonic generation in a ferrimagnet is enhanced by an increase in the g factor. The physical reasons for this are examined for the case of second-harmonic generation in sphere and disk samples. Theoretical performance characteristics for a new, narrow-linewidth, large g-factor material are compared with those for conventional ferrites.
General Relationship for the Thermal Oxidation of Silicon
Authors: Deal B. E. , Grove A. S.
Published: April 2005

The thermal-oxidation kinetics of silicon are examined in detail. Based on a simple model of oxidation which takes into account the reactions occurring at the two boundaries of the oxide layer as well as the diffusion process, the general relationship x02+Ax0=B(t+τ) is derived. This relationship is shown to be in excellent agreement with oxidation data obtained over a wide range of temperature (700°–1300°C), partial pressure (0.1–1.0 atm) and oxide thickness (300–20 000 Å) for both oxygen and water oxidants. The parameters A, B, and τ are shown to be related to the physico-chemical constants of the oxidation reaction in the predicted manner. Such detailed analysis also leads to further information regarding the nature of the transported species as well as space-charge effects on the initial phase of oxidation.
Growth and Dislocation Structure of Single-Crystal Ga (As1−xPx)
Authors: Wolfe C. M. , Nuese C. J. , Holonyak N.
Published: April 2005

The preparation of single-crystal GaAsP by halide vapor transport is described. That dislocation free GaAsP can be achieved was verified experimentally for whiskers grown by the vapor-liquid-solid method. In the growth of monocrystalline ingots for device purposes, growth mechanics and the resulting crystal habit are strongly influenced by degenerate Zn, Te, and Se doping. Since n-type crystals require higher supersaturations, single-crystal growth is easier to obtain with Zn doping.

The as-grown dislocation structure of ingots with low-index natural facets is examined by decoration and etching. Typical densities are 5×103 to 106/cm2. From their simple crystallographic orientations different dislocations are identified. 〈211〉, {111} and 〈100〉, {110} edge dislocations are observed in {110} polygonization walls. Values of mobility and carrier density are evaluated from a device point of view. Laser diodes with threshold currents as low as 3000 A/cm2 at 33.3% GaP have been obtained from this material.
Optical Thickness Measurement of Thin Transparent Films on Silicon
Authors: Reizman F.
Published: April 2005

The thickness of thin transparent films on reflecting substrates is determined by an interference technique using a spectrophotometer. The method is rapid, routine, nondestructive, and precise to ±100 Å for layers over 1000 Å thick. An empirical calibration is presented for the case of oxide layers on silicon, avoiding errors due to the dispersion of the oxide.
Lattice Parameters, Thermal Expansion Coefficients, Phase Width, and Perfection of the Structure of GaSb and InSb
Authors: Straumanis M. E. , Kim C. D.
Published: April 2005

The lattice parameters of GaSb and InSb, prepared from 99.999% pure elements, were redetermined: a25° of GaSb was 6.09593±0.00004 Å and a25° of InSb was 6.47937±0.00003 Å (with the refraction correction included). Any width of the GaSb and InSb phases could not be detected. The expansion coefficients of the two compounds between 10° and 70°C were (7.75±0.50)×10−6 and (5.37±0.50)×10−6 °C−1, respectively. The experimental density d25 of GaSb was 5.6137±0.0004 and that of InSb 5.7747±0.0004 g·cm−3. In both cases, the actual number of molecules n′ per unit cell was very close to 4.0000 (within the limits of error), indicating that the structure of both compounds is sound or perfect.
Surface Layers on Ferroelectric BaTiO3 Crystals
Authors: Bhide V. G. , Gondhalekar R. T. , Shringi S. N.
Published: April 2005

The rf-induced electroluminescence emitted from a BaTiO3 crystal surface is studied in detail as a function of temperature, voltage, frequency of the rf field, electrode material, etc. It is shown that electroluminescence is essentially produced in the surface layer which exists on BaTiO3 crystals and is not associated with dipole reversal or domain rearrangement, although the dielectric properties of the bulk alter the light output considerably. The characteristics of the surface layer, which is shown to be a space-charge layer, have been determined and the mechanism of electroluminescence elucidated.
Double Pitch Windings on Cylindrical Metal Block Thermostats
Authors: Babb Stanley E.
Published: April 2005

Mathematical expressions are developed for the mean temperature and the amplitude of control variations within a cylindrical metal block thermostat equipped with windings of double pitch. These expressions are compared with experiment, with good agreement. Formulas for calculating the frequencies of control for both on-off and proportional types of control are developed for the case of the infinite solid cylinder. It is shown that control can be best for a certain value of the fine control voltage.
Electron-Hole Pair Creation in Gallium Phosphide by α Particles
Authors: Goldstein Bernard
Published: April 2005

The energy required to form one hole-electron pair in gallium phosphide has been measured to be 7.8±0.8 eV/pair. The experimental method consisted of determining the charge produced and collected when α particles of known energy bombarded a surface barrier which had been formed by evaporating a thin layer of gold onto an etched surface of the gallium phosphide. When high-resistivity gallium phosphide (produced by copper diffusion) was used, the α-particle detection efficiency dropped very sharply but could be restored to almost unity efficiency by illumination. This effect is attributed to the action of traps on the charge collection process.
Effects of Single Neutron-Induced Displacement Clusters in Special Silicon Diodes
Authors: Gereth R. , Haitz R. H. , Smits F. M.
Published: April 2005

Radiation damage in uniform silicon avalanche diodes having an active volume of 10−11 cm3 has been investigated. Radiation-induced centers contribute to the carrier generation within the diode breakdown region, causing a corresponding increase in the avalanche pulse rate of the diode.

The high sensitivity and the small volume of the diodes allow the study of permanent radiation damage resulting from single primary neutron collisions. By measuring the distribution function of the pulse rate on a statistical lot of diodes, a relationship between the pulse rate and the energy dissipated in atomic processes is derived. A superlinear increase of pulse rate with energy is observed. In general the higher pulse rates have a temperature dependence characterized by a lower activation energy than is the case for the lower pulse rates.

For comparison, the effect of 2-MeV electron irradiation has been studied. The pulse rate is found to increase linearly with integrated flux. At low fluxes the pulse rate is dominated by generation centers only, while in heavily irradiated diodes trapping effects become observable. Also at low fluxes the observed activation energy for carrier generation is 0.66 eV, while at higher fluxes this activation energy is lower by as much as 0.3 eV.

The dependence of the observed activation energy on the flux in the electron case and the generally lower activation energies for the higher pulse rates in the neutron case is attributed to a tunneling interaction between individual defects. The defects in the larger neutron displacement damage clusters will have a wider spread in energy levels than those in the smaller clusters. This, in connection with the interaction between the individual defects, results in a reduced activation energy and an increased pulse rate.
Orientation-Dependent Dissolution of Iron Whiskers
Authors: Shemenski R. M. , Beck F. H. , Fontana M. G.
Published: April 2005

The dissolution kinetics of iron filamentary single crystals in dilute acidic environments were shown to obey the topographical theorems proposed by Frank to describe etch-rate anisotropy. Successive dissolution profiles of iron whiskers were observed in situ. by using time-lapse motion picture photomicroscopy. Reluctance diagrams constructed from these dissolution shapes agreed very favorably with experimentally measured dissolution rates and in this way demonstrated the validity of Frank's theory to metallic substrates. A three-dimensional reluctance surface for iron whiskers having 〈111〉 growth axes inferred from the experimental data was consistent with known relative magnitudes of anisotropic dissolution rates; in fact, the reluctance plots constructed according to the kinematic theory were seen to be two-dimensional sections of this surface.
Removal of Thin (20 Å) Layers of Metals, Metal Oxides, and Ceramics by Mechanical Polishing
Authors: Whitton J. L.
Published: April 2005

The method of vibratory polishing has been applied to the reproducible removal of thin layers from metals, oxides, and ceramics. The rate of removal depends on the hardness of the material being polished, and for the materials tested, i.e., W, Ta, Si, Zr, Au, UO2, Ta2O5, and ZrO2, is in the range of a few atom layers (20 to 50 Å) per minute of polishing time. Experimental details are described and the results obtained are shown.

Studies have been made of the surfaces of these materials by x-ray diffraction, reflection e lectron diffraction, and electron microscopy to determine the effect of the polishing on crystal structure and surface topography. The results show that all the materials except gold have surfaces smooth to within 50 Å, that W and Ta single crystals have disturbed or deformed layers of less than 250 Å and that single-crystal Si is not deformed at all.
Kink and String Models of Dislocation Motion
Authors: Brailsford A. D.
Published: April 2005

The formal equivalence of the string model and kink models of dislocation motion is demonstrated for dislocations not lying along the same close-packed row. The only modifications of the older formulation of the string model arise from the hypothesis of lateral kink displacement as the mechanism of dislocation displacement.
Laser Amplifiers
Authors: Steele Earl L. , Davis Walter C.
Published: April 2005

The performance of a ruby laser amplifier is described and compared with a theoretical model. The ruby laser amplifier was driven by a Q-switched laser oscillator with a stable output, whose properties are due, in part, to a newly developed output coupler and a spinning roof-top prism for Q-spoiling. From the theoretical amplifier model, a relation between the population inversion and the energy stored in the system supplying the xenon flash lamps is derived and fitted to the particular laser configuration by a single parameter established by the laser threshold. Experimentally, the gain of the 15-cm (6-in.) ruby amplifier saturates at values between 5 and 7, apparently caused by complete pumping of the system rather than limited by the energy input to the flashlamp pump.
Penetration of an Ion Through a Monolayer of Similar Ions Adsorbed on a Metal
Authors: Gadzuk J. W. , Carabateas E. N.
Published: April 2005

A fractional monolayer film of ions is formed by the adsorption of a gas onto a metal substrate. These ions form a discrete dipole layer, the potential across it being the change in electron work function of the surface. As additional ions are brought to the surface, they penetrate only a fraction f of the potential across the dipole layer.

In this work the penetration coefficient f valid for the entire range of coverages is derived for two limiting types of films, immobile and mobile. By considering thermal effects, a penetration coefficient for partially mobile films is also derived. The values obtained for the penetration coefficient are applicable to any substrate-adsorbate system.

The theoretical expressions for the penetration coefficient are evaluated for cesium on tungsten and compared with the data of Taylor and Langmuir.
Constricted Discharges in the Rare Gases. II. Analysis of the Macroscopic Properties of the Discharge
Authors: Massey J. T.
Published: April 2005

The macroscopic properties of the rare gas constricted discharges are discussed. For the rf excited discharge an equivalent circuit for the electrode coupling has been found, comprising a capacitor with the electrode and plasma forming the plates and the discharge tube wall the dielectric. An explanation for the observed striations is advanced, based upon the existence of voltage standing waves at the plasma resonance frequency. A numerical analysis based on an energy balance indicates that these discharges should have a finite radius, in this case smaller than the discharge tube radius. It is necessary to require that the electron energy distribution be Maxwellian near the center of the discharge and that deviation from this energy distribution causes the sharp boundary observed for the heavier rare gases. For the microwave discharge it is pointed out that it is necessary to include the electromagnetic field equations in the analysis and that this requirement naturally leads to a maximum radius for a single discharge channel which is much smaller than for the rf-excited case. This, in turn leads to an explanation of the multicolumn effect observed.
Internal Modulation in Multimode Laser Oscillators
Authors: Yariv Amnon
Published: April 2005

Multimode laser oscillation in the presence of internal resonator modulation is discussed. Modulation of the dielectric constant (ε) is shown to lead to frequency modulation of the laser light while modulation of the losses (or gain) leads to amplitude modulation. The results are discussed with particular reference to recent experiments and proposals involving modulation inside laser resonators. The mathematical formalism is that of normal-mode parametric interactions.
Power-Dependent Frequency Shifts in Ruby Lasers at 77°K
Authors: Birnbaum M. , Stocker T. L.
Published: April 2005

Ruby lasers, when operated near threshold at 77°K with a low Q cavity (one end silvered for maximum reflectivity and the other end uncoated) oscillated at two frequencies. The frequency differences near threshold, measured with Fabry-Perot etalons, were in good agreement with the splitting of the R1 doublet, previously measured by microwave methods. As the power of the laser increased, the frequency difference between the oscillating components [2Ē → 4A2(±32, ±½)] decreased. These results are accounted for on the basis of saturation broadening of overlapping Lorentzian lines. The observed variations in the splitting are in good accord with the theory. The rise in temperature of the ruby rods produced a negligible change in the splitting of the R1 doublet. The same mechanism which produces the variation in the splitting should broaden the output spectrum of the laser.
Asymptotic Plasma and Sheath Representations for Low-Pressure Discharges
Authors: Self S. A.
Published: April 2005

The collisionless plasma-sheath equation is discussed in the limit that the ratio of Debye length to discharge dimension is vanishingly small, for the cases of planar, cylindrical, and spherical symmetric discharges. Separate representations for the plasma and sheath regions are found and numerical results given for the potential profiles, ion currents, energy distributions, and floating wall potentials for two different assumptions regarding the ion generation function in each case.
Two-Stream Cyclotron and Plasma Wave Interactions
Authors: Maxum B. J. , Trivelpiece A. W.
Published: April 2005

Cyclotron and plasma wave interactions between drifting electron streams in a steady axial magnetic field are studied for configurations of finite transverse cross section. It is shown for the case of equal and opposite drift velocities, that there exists an instability at approximately one-half the cyclotron frequency. This instability is a consequence of the coupling between the slow space-charge wave on one stream and backward cyclotron wave on the other stream. This coupling can occur whenever the streams are of finite transverse cross section.

In order to verify some of the features of this instability, experiments in which two coaxial oppositely directed electron beams were passed between two planes, were carried out for a limited range of electron drift velocity and magnetic field values. These experiments demonstrated the existence of an instability at one-half the cyclotron frequency, in agreement with the theory. It was found experimentally that at a particular stream velocity the instability could exist over a small range of magnetic field values. The upper limit of magnetic field can be explained by the assumption that nonlinearities result in a thermalization which causes the velocity spread on the electron beam to become comparable to its mean velocity. The lower limit is a consequence of the finite length of the interaction region.

Although the measured signal level was much less than that expected on the basis of converting a reasonable fraction of the beam energy to rf energy, it was found that the signals observed had a narrow frequency spread (−3 dB width was 10 kc/sec at 50 Mc/sec).
Induced emf Produced by a Ferromagnetic Wire Carrying Alternating Current in a Static Magnetic Field
Authors: Skórski Roman , Duracz Andrzej
Published: April 2005

The amplitude of the emf in Procopiu's effect has been found to be an inverse square function of the static magnetic field. This has been predicted theoretically and verified experimentally.
Remanent Domain Structures of BaFe12O19
Authors: Kojima H. , Gotō K.
Published: April 2005

In order to investigate the magnetizing process of uniaxial oxides, the remanent domain structure of a thin single crystal of BaFe12O19 was observed on the basal plane by means of Faraday effect. Three kinds of remanent domains—radial, maze, and honeycomb—were found, when the field was reduced to zero along the c axis from saturation. When the angle θ between the c axis and the magnetizing field was changed from 0° to 90°, the remanent domains lost their characteristic and altered to maze, parallel, honeycomb, and finally to a mixed structure of honeycomb and parallel domains. These changes are discussed from the magnetizing process based on the critical field diagram and it is suggested that the critical field can be determined as a field where the remanent structure changes into a saturated state. The anisotropy field 2K/Is of BaFe12O19, obtained as the critical field at θ = 90°, was 17 000 Oe and showed good agreement with the previously reported value.
High-Temperature Transference Number Determinations by Polarization Measurements
Authors: Vest R. W. , Tallan N. M.
Published: April 2005

A polarization technique for the measurement of electronic and ionic transference numbers in mixed conductors is described; also a discussion of the conditions governing its applicability. The application of this technique is demonstrated by measurements on the solid solution Zr0.85 Ca0.15 O1.85, which is shown to be intrinsically a pure oxygen ion conductor even at room temperature at an oxygen partial pressure of 10−9 atm. The electronic conductivity in this material can be increased significantly at low oxygen partial pressures by the addition of transition metal impurities.
Thermoelectric and Electrical Measurements in the La–Te System
Authors: Ramsey T. H. , Steinfink H. , Weiss E. J.
Published: April 2005

An evaluation of the electrical conductivity and Seebeck coefficient of the compounds in the La–Te system has indicated values of ρ from 0.1 Ω-cm to 20×103 Ω-cm. The bonding, based on earlier crystal-chemical studies and supported by this evaluation, indicates a variation from almost pure metallic in LaTe to metallic with a substantial ionic component in La2Te3. An evaluation of the Seebeck coefficient has further differentiated between the purely metallic and semiconducting nature of the various compounds. The evaluation was conducted on polycrystalline pressed-powders or sintered materials, and the energy-gap measurements are believed to be a measure of surface phenomena activation processes rather than an indication of true intrinsic character.
Defects in Cadmium Sulfide Crystals
Authors: Kulp B. A.
Published: April 2005

At low temperatures certain crystals of CdS emit green light when struck a blow with a hard object. Many of these crystals show unusual electrical properties. When cooled in the dark, the conductivity goes to very low values, 10−12 (Ω-cm)−1 or less; then, upon exposure to light of wavelength less than 6900 Å, the conductivity increases irreversibly to values as high as 10−2 (Ω-cm)−1. The defect structure of these crystals has been studied by the technique of thermally stimulated currents in the temperature range 80° to 300°K. Five current peaks are observed with different intensities in different crystals. When the crystal is illuminated with light of wavelength longer than 6900 Å, the traps noted above can be filled without changing the conductivity of the crystal. The energy of the traps can be determined by the threshold wavelength of light required to fill the various levels with electrons from the level located 6900 Å (1.79 eV) below the conduction band as well as by the position of the Fermi level when the traps are being emptied.
Square-Mean-Root Approximation for Evaluating Asymmetric Tunneling Characteristics
Authors: Chow C. K.
Published: April 2005

A new method of approximating the basic tunnel integral is used to calculate the asymmetric characteristics of the tunnel effect between two dissimilar electrodes separated by a thin insulating film. The method is to approximate the true potential barrier by an equivalent rectangular barrier whose height is determined by the square-mean-root value of the true barrier. Even for barriers of trapezoidal shape, the calculation gives the polarity dependence of the J—V characteristics in the low-voltage region, as well as in the higher-voltage region. The asymmetry at low voltage for trapezoidal barriers has not been predicted in previous calculations.
Photovoltaic Effect in Photoconductors
Authors: Keating P. N.
Published: April 2005

On the basis of the assumption that the induced minority and majority carrier densities are large compared with the ``dark'' densities, a theory of the photovoltaic effect in photoconductors is presented. The theory is initially set up in general terms and then applied to specific cases: (i) abrupt homojunctions and heterojunctions between two photoconductors, (ii) abrupt homojunctions and heterojunctions between a semiconductor and a photoconductor. The existence of interfacial recombination is included in the analysis and the self-consistency of the theory is examined. The photovoltage is evaluated in terms of the photovoltaic current and the change in Fermi energy across the interface and, in addition, an expression for the short-circuit current is obtained. The results are used to discuss the suitability of some of the physical mechanisms which have been proposed to account for the photovoltaic phenomenon in photoconductors.
Nature of Long-Range Order in Cu3Au and Cu72Au28
Authors: Schwartz L. H. , Cohen J. B.
Published: April 2005

Diffuse x-ray scattering and the intensity of Bragg peaks from single crystals of Cu3Au and Cu72Au28 have been studied for various degrees of long-range order. Equations are developed for the effects of differences in atomic size of the species and zero-order temperature effects on diffraction from an alloy when long-range order is present. A peak due to differences in atomic size is predicted under the superstructure reflections as well as under the fundamentals when order is not perfect; this prediction is experimentally confirmed. If the local order is not large for coordination shells greater than the eighth or ninth, then the Warren short-range order parameters can be accurately determined from data along only two lines in reciprocal space.

The results indicate that excess Au atoms, replacing Cu in Cu3Au, distribute themselves at random when Cu72Au28 is heat-treated for maximum long-range order. Thus there is no marked tendency for the Au atoms to avoid each other. Local order develops among misplaced atoms as the long-range order decreases with increasing temperature and just below the critical temperature this local order is similar in both Cu3Au and Cu72Au28. There are about the same number of wrong first bonds just below the critical temperature Tc for both alloys, even though the degree of long-range order indicates that there are more wrongly occupied sites for the nonstoichiometric alloy than for Cu3Au. (The data for Cu3Au are in agreement with Cowley's latest thermodynamic treatment and Peierl's theory.)

The results for both ordered alloys can be explained in terms of a large number of small antiphased regions in a well-ordered matrix. These regions are essentially two dimensional except near the critical temperature for the nonstoichiometric alloy where they are three dimensional. They vary in composition from point to point in the structure. The extra Au atoms in Cu72Au28 may play a key role in forming these as the temperature is raised, as they appear in the boundaries of the domains.

The atomic volumes of Cu and Au in ordered Cu3Au and Cu72Au28 are the same as in the pure metals; their rms vibrations are similar.
Magnetic Anisotropy of an Fe-Ge Alloy
Authors: Becker J. J. , Symes E. M.
Published: April 2005

The Fe-Ge β phase extends from about 34 to 45 at. % Ge and has a modified NiAs structure. Previous investigations have established the saturation magnetization and Curie temperature, and have shown that the c axis is the hard direction of magnetization, but have not established the easy axis within the base plane. In the present experiments, an alloy of 57% Fe+43% Ge by weight (36.7 at. % Ge) was prepared, found to be a single phase, and ground into a powder consisting of individual single crystallites. These were aligned in a field and held in a binder. It was then established by x-ray diffraction that the a axis was aligned parallel to the field. A lower limit to K3 can be arrived at by ascribing the observed coercive force of further subdivided material entirely to coherent rotation in the base plane. On this basis, |K3|≥1.5×104 erg/cm3 at 77°K.
Magnetic Properties of Several Substances in Strong Pulsed Fields
Authors: Guillot Maurice , Pauthenet René
Published: April 2005

An experimental determination of the magnetization laws for the Gd+3, Dy+3, Tb+3, Ho+3, Er+3, Yb+3 ions in the garnet structure gallates is presented as well as proof for the quenching of the moment, and a calculation for the saturation magnetization and the thermal variation of spontaneous magnetization of the corresponding ferrite.

The ferro—antiferromagnetic transition of UO3CoO at 4.2°K is determined and the magnetic properties of the MnAu2 alloys are discussed.
Observation of Superparamagnetism by the Mössbauer Effect
Authors: Schuele W. J. , Shtrikman S. , Treves D.
Published: April 2005

Mossbauer spectra of 57Fe in ultrafine NiFe2O4 and CoFe2O4 powders were studied, as a function of crystallite size and temperature. The hyperfine field was found to collapse at a temperature, lower then the Curie points which decreased with particle size. This collapse of the hyperfine field is interpreted as motional narrowing due to the onset of superparamagnetism.
Particle-Size Effect in Oxidation of Natural Magnetite
Authors: Elder Tait
Published: April 2005

Significant oxidation to γFe2O3 of natural magnetite (Fe3O4) crystals ground in water to <1 μ was produced by heating in air; the proportion converted at 250°C exceeded 75% as measured by specific magnetization, chemical, and x-ray diffraction analysis. This resembles the behavior of synthetic magnetite. The same natural material ground to ≥25 μ, similarly heated and characterized, converted to αFe2O3 only, with less than 45% conversion at temperatures below 400°C. This striking effect of small particle size is attributed to the stabilizing effect of water adsorbed or hydrated on the fine-particle surface. Differential thermal analysis measurements in various atmospheres and thermogravimetric analysis tend to support this view. In a corroboratory experiment, natural magnetite was ground in dry acetone to <1 μ. Oxidation in dry oxygen produced only αFe2O3, but in an atmosphere of water vapor and oxygen oxidation proceeded exclusively toward γFe2O3. The importance of particle size and water on the oxidation of both natural and synthetic magnetite helps resolve reported differences between the two, since typical samples of natural magnetite differ from synthetic material in being of larger particle size and unhydrated.
Substitution of Divalent Cobalt in Yttrium Iron Garnet
Authors: Geller S. , Williams H. J. , Espinosa G. P. , Sherwood R. C.
Published: April 2005

Magnetic and crystallographic data are reported on the systems {Y3}CoxFe5−2xMxO12, M≡Si and Ge. When M≡Si, the maximum value of x appears to be between 1.00 and 1.25, while when M≡Ge, the maximum value of x=2.50. A distribution of the ions in these garnets is proposed that is compatible with the results and conclusions obtained on all other substituted yttrium iron garnet systems. In particular, it appears that a constant 20% of the Co2+ ions enter tetrahedral sites. When x≥1.00, some Ge4+ ions enter octahedral sites.

The garnet {Y2.7Ca0.3}CoFe2.7Ge1.3O12 has a compensation point at 236°K; it is the first garnet reported which has a compensation point resulting from a difference in the temperature behavior of only the a and d sublattice magnetizations. The other garnets having compensation points all contain magnetic rare-earth ions in the c sites.

The garnet {Y2.5Ca0.5}CoFe3V0.5Ge0.5O12 has a higher Curie temperature, 410°K, than that, 350°K, of {Y3}CoFe3GeO12. This is in accord with the expected effect of pentavalent vanadium substitution.

The full-length paper with the above title appeared elsewhere.1
Parallel Pumping in Narrow Linewidth Planar Mn–ZnY
Authors: Dixon Samuel , Tauber Arthur , Savage Robert O.
Published: April 2005

Parallel pump measurements were made on Mn-substituted single-crystal ZnY at room temperature and 17.2 kMc/sec. The experimentally determined values of 1500 Oe for Hc and 1700 Oe for Hd were found to be in good agreement with theoretical predictions. The threshold rf field at Hc is 0.65 Oe. This threshold field for spin-wave instability gives a spin-wave linewidth (ΔHK) of 1.24 Oe. The susceptibility curve rises sharply at Hd, peaks in the vicinity of Hc, and then falls off slowly at lower values of dc field.

The ferrimagnetic resonance linewidth and dc magnetization were studied as a function of increasing Mn substituent at room temperature. The resonance linewidth decreases with increasing Mn substitution. A minimum of 3.8 Oe at 9.0 kMc/sec is observed in crystals with approximately 4 to 5 wt % Mn. The magnetization decreases linearly with increasing Mn substituent.
Nuclear Magnetic Relaxation in Magnetite
Authors: Mizoguchi T. , Tomono Y.
Published: April 2005

The nuclear magnetic relaxation of 57Fe on tetrahedral sites in polycrystalline magnetite has been studied by spin-echo method with special interest in the relation to the low temperature transition and the electron diffusion among octahedral sites. Spin-lattice relaxation time T1 increases from about 0.7 msec at room temperature to 9 msec at 130°K. At the transition point (118°K) T1 decreases abruptly by the factor of about seven. It makes a minimum of 0.6 msec at about 88°K, then increases with decreasing temperature up to about 500 msec at 4.2°K.

The minimum of T1 may be interpreted by the electron diffusion among B sites. This effect is considered to be dominant from the transition temperature to liquid-nitrogen temperature. The discontinuity of the relaxation time at the transition temperature suggests that the hopping frequency increases very rapidly as the order collapses and this mechanism becomes no more effective to the nuclear magnetic relaxation.

Spin-spin relaxation time T2 is equal to T1 above about 60°K and becomes smaller than T1 below that temperature. T2 (=10 msec) at 4.2°K may be attributed to Suhl's interaction.
Magnetic Ordering and Fluorescence in Manganese Salts
Authors: Prohofsky E. W. , Holloway W. W. , Kestigian M.
Published: April 2005

The effect of antiferromagnetic ordering on the fluorescence of several manganese salts has been observed. The fluorescence undergoes a shift in frequency, intensity, and lifetime at the Néel temperature. At temperatures below the Néel temperature, the fluorescence shifts to higher frequencies. The salts investigated were MnF2, RbMnF3, NaMnF3, and CsMnF3. The effects are illustrated by data representing RbMnF3. In addition to the change in fluorescence at the Néel temperature, a similar change was observed in each material at roughly one-half the Néel temperature. Again the fluorescent frequency increased at lower temperatures. The magnitude of the changes occurring at the lower temperature was larger than that observed at the Néel temperature. All the salts investigated show Stokes shifts in their fluorescence spectra. It is believed that the magnetic ordering alters the Stokes shift through the magnetoelastic effect, causing the fluorescent changes observed. The low-temperature changes are believed to be caused by the same mechanism when the excited Mn2+ ion becomes ordered with respect to the surrounding lattice. The temperature at which this occurs is a measure of the exchange energy for the excited-ion electron configuration.
Exchange Effects in the Electronic Absorption Spectrum of Mn(II) in Perovskite Fluorides
Authors: Ferguson J. , Guggenheim H. J. , Tanabe Y.
Published: April 2005

The electronic absorption spectrum of Mn in cubic perovskite fluorides is strongly modified by exchange interaction. This has been shown from the temperature dependence and concentration dependence of the spectrum of Mn in KZnF3 and the temperature dependence of the spectrum of KMnF3. The electronic transitions of particular interest are the ones near 4000 and 3300 Å which have narrow line structure. This structure has been analyzed and the contribution to the intensity from single ions and pairs of ions (Mn–F–Mn) evaluated. Studies of the temperature dependence of the pair lines give a ground state J (JSa·Sb) interaction) of between +3.0° and +3.5°K and it is about twice as large in the excited state. The absorption lines correspond to pure electronic transitions and the selection rule is ΔS=0. The anomalously intense bands in the spectrum of KMnF3 are interpreted on the basis of pure electronic transitions involving more than one ion and the temperature shifts of the bands have been correlated with known magnetic and structural changes.
Lorentz Microscopy of Small Ferromagnetic Particles
Authors: Cohen M. S.
Published: April 2005

Theoretical considerations show that uniaxially anisotropic ferromagnetic particles of sufficiently small size will not exhibit complex multidomain states, but simple magnetization configurations. Special methods have permitted the preparation of two-dimensional analogs of such particles, i.e., islands of NiFe film on a nonmagnetic substrate. Lorentz microscopy of these specimens gave direct evidence for the predicted configurations: (a) a circular magnetization configuration, (b) a two-domain state, (c) a single-domain state. Islands in the single-domain state reversed by creation and breakup of a ``locked'' magnetization configuration.
Ferromagnetic Domains in Thin Single-Crystal Nickel Platelets
Authors: De Blois R. W.
Published: April 2005

Ferromagnetic domain observations have been made on single-crystal nickel platelets, ranging from 900 Å to over 10 μ in thickness, that have been grown nonepitaxially by the hydrogen reduction of the bromide. The platelets are generally rectangles or right triangles with (001) faces, 〈100〉 sides or legs, and edges from several microns up to 3 mm in length. Because their perfection is close to that of metal whiskers, the intrinsic coercive force for domain wall motion is minute (<0.01 Oe). Thus the domain configurations, observed by Lorentz microscopy and the Bitter technique, are in stable or metastable equilibrium. For platelets less than 1.0 μ thick, the magnetization lies in the plane along 〈110〉 directions, these being the projections of the 〈111〉 directions of minimum anisotropy energy. Echelons form the common closure structure near the edges. Some 180° walls appear to be of a combined Néel-Bloch type. At a thickness of 1.0 μ a striped powder pattern appears within the planar domains, with a 0.7 μ spacing between stripes. Near 2 μ the pattern changes to a coarser one in which the stripes are not parallel to the planar magnetization. Above about 7 μ the surface pattern is essentially that for the bulk crystal. Near 1100 Å, Néel walls and spotted transition walls are observed. Cross-tie walls and individual cross-tie spots appear with unusual clarity in single-crystal nickel-cobalt platelets (7% Co). Their creation and transformation are readily observable. Striped and planar domain patterns similar to those for nickel appear on fcc cobalt platelets.
Dynamic Pulse Hysteresis of Magnetic Devices
Authors: Sie C. H.
Published: April 2005

Dynamic pulse hysteresis is defined as the instantaneous hysteresis of a magnetic device during the risetime of an applied pulse field. A method of measuring the dynamic pulse hysteresis of magnetic devices has been developed. The pulse hysteresis differs from the quasistatic hysteresis in its ability to display magnetic damping phenomena. By applying sampling technique the flux sensitivity of this method is extended to 10−4 Mx. The theoretical pulse hysteresis obtained by computer solution of Gilbert's equation is compared with the measured pulse hysteresis of a 10 000-Å uniaxial Permalloy film at 7-nsec risetime. From the comparison, the intrinsic damping constant of the film is determined to be 8×108 sec−1. The measured pulse hysteresis of a ferrite core in a time-limited partial switching mode is also presented.
Kerr Effect and Bitter Pattern Measurements of Easy-Axis Distributions in Uniaxial Permalloy Films
Authors: Dove D. B. , Long T. R.
Published: April 2005

Measurements on small regions (1 mil2) of magnetic films have been made with a Kerr magneto-optic apparatus that utilizes a laser light source and employs narrow-band detection techniques. Sensitivity is adequate to allow observations on permeabilities, remanent flux, and other properties. At the same time, Bitter patterns may be obtained facilitating detailed correlation between dynamic magnetic behavior and remanent state domain patterns.

Bitter patterns have been recorded during the course of an angular distribution fall-back experiment. The pictures have been assembled sequentially as a motion picture showing the remanent domain state developed throughout the experiment. Dynamic Kerr effect observations show that significant domain wall rearrangements occur near zero transverse field. The direction of M in small regions of single domain films has been determined to 0.1° using an MH alignment technique, and hence an alternative estimate of the angular distribution of easy axes is obtained. Strong transverse magnetostatic coupling between regions is of importance in both the fall-back and MH alignment measurements. The validity of various easy axis distribution measurements is discussed in the light of present observations.
Spin-Wave Scattering of Polarized Neutrons from Nickel and Cobalt
Authors: Riste T. , Shirane G. , Alperin H. A. , Pickart S. J.
Published: April 2005

The polarized neutron technique provides a very powerful method of distinguishing ferromagnetic spin wave scattering from other elastic and inelastic intensity components. The diffraction method in which the size of the scattering surface is measured as a function of offset angle from the Bragg position has been employed to investigate the magnon scattering from nickel and cobalt single crystals. In the case of cobalt, the observed inelastic scattering proved to be entirely of magnon character for misset angles greater than 3.5°. For nickel, the constant D in the spin wave dispersion relation E=Dq2 was measured to be 360±75 meV Å2.
Magnetic Properties of Rare-Earth Metals and Alloys
Authors: Koehler W. C.
Published: April 2005

A review of neutron diffraction studies of the magnetic properties of rare-earth metals and alloys is presented. For each of the pure metals Tb, Dy, Ho, Er, and Tm there is observed a transition at a temperature TN to an oscillatory antiferromagnetic configuration (helical or linear oscillator type). At lower temperatures, further transitions to ferromagnetic, ferromagnetic spiral, or antiphase domain-type configurations are observed. For Gd, only the ferromagnetic configuration is found. The magnetic moments in the ordered configurations at low temperatures approach the values expected from the corresponding free tripositive ions. In the first half of the series only Nd has been studied by single-crystal methods, but Ce, Pr, and Eu have now been investigated with polycrystalline samples. The data for Ce are complicated by the existence of several allotropic forms, but a complex antiferromagnetic structure appears to be associated with the hexagonal form at low temperatures. For Nd and Pr, oscillatory antiferromagnetic configurations are observed at very low temperatures in which, as in Ce, the moments have magnitudes considerably smaller than the free-ion values, which result suggests a strong influence due to the crystalline field. A helical spin structure in bcc Eu has been reported in which the moment of Eu is somewhat smaller than that of Eu++. A number of alloy systems, R-Y, R-R′, and R-La, where R and R′ are among the group Tb–Tm, have been investigated and results are discussed. These results and those for the pure metals are discussed relative to the theory of the magnetism of the rare-earth metals.
Some Measurements of Exchange Energies by Paramagnetic Neutron Inelastic Scattering
Authors: Collins M. F. , Nathans R.
Published: April 2005

Neutron paramagnetic scattering techniques have been applied to the measurement of exchange constants for a series of perovskite salts, KMnF3, NaMnF3, LaCrO3, LaMnO3, and LaFeO3.
Magnetic Structure of Fe2As
Authors: Katsuraki Hisao , Suzuki Kazuo
Published: April 2005

Magnetic structure of single crystal of Fe2As, which corresponds to C38 type of crystal structure, the same as that of Mn2Sb, has been determined by neutron diffraction method. The crystal is antiferromagnetic with the Néel temperature of approximately 50°C. A series of (00l)-type reflections at room temperature reveals magnetic superstructure reflections at (001/2), (003/2), (005/2), and (007/2). These reflections disappear when the temperature of the specimen is elevated to 50°C, whereas the main reflections do not show any changes within the experimental error. One of the remarkable features of the relative intensities of the superstructure reflections is that the (003/2) reflection is considerably weak relative to (005/2). From these results it can be concluded that this crystal has such an antiferromagnetic arrangement that FeII, FeI, and FeII atoms, each on three successive layers parallel to the (001) plane, form a group in which the magnetic moments are parallel to one another, and these moments are antiparallel to those of the neighboring groups. The [001] spacing of the magnetic unit cell is two times as large as that of the chemical unit cell.