bluuebunny/crossref_metadata_2025 huggingface dataset:
Cycloidal Spin Configuration of Orthorhombic MnSO4
Authors: Will G. , Frazer B. C. , Shirane G. , Cox D. E. , Brown P. J.
Published: April 2005

The crystal and magnetic structures of antiferromagnetic MnSO4 (a=5.260 Å, b=8.042 Å, c=6.847 Å, space group Cmcm) have been determined from x-ray and neutron diffraction data collected from polycrystalline samples at 300° and at 77° and 4.2°K, respectively. The neutron diffraction pattern at 4°K exhibits additional peaks of magnetic origin which are slightly displaced from the positions expected on the basis of the original unit cell, or any simple multiple cell. In addition, the observed extinction rules cannot be satisfied by any combination of simple collinear magnetic structures. Complete indexing of the magnetic peaks can be achieved only on the basis of a cone spiral arrangement related to a simple antiferromagnetic structure of CrVO4 type,1 in which ferromagnetic (001) sheets are coupled antiparallel to adjacent sheets. The propagation vector of the spiral is along the a axis with a periodicity of 30 Å (almost 6a). The spin plane of the spiral component is the a-b plane. It is believed that this is the first case in which a spiral has been observed in an orthorhombic compound, and it is of particular interest that the spiral is cycloidal.

Good agreement of observed and calculated magnetic intensities is obtained with a fundamental spin component of 1.7 μB directed along the c axis, and a spiral component of 4.5 μB in the a-b plane. The resultant moment of each Mn2+ ion is therefore 4.8 μB, and the cone half-angle is about 78°. The temperature dependence of the satellite peaks indicates a Néel point of about 10°K.
Magnetic Structure versus Electron Number for Some Rare-Earth Intermetallic Compounds
Authors: Cable J. W. , Koehler W. C. , Child H. R.
Published: April 2005

Neutron diffraction measurements were made on a series of rare-earth compounds in the Tb(Pd, Ag) and Tb(Ag, In) systems. Most of these compounds exhibit the CsCl type of crystal structure and, for these, magnetic structure determinations were made in order to relate the type of magnetic structure to the number of valence electrons. Two types of antiferromagnetic structures were observed; the (ππ0) type consisting of an antiparallel array of ferromagnetic (110) planes of moments, and the (00π) type with ferromagnetic (001) planes of moments alternating in direction. On the basis of 0, 1, 3, and 3 valence electrons for Pd, Ag, In, and Tb, respectively, the (ππ0) structure is found in the region of 3.5 to 4 valence electrons per unit cell and the (00π) structure in the region of 5 valence electrons per unit cell.
Spin-Density Distribution of the Dzyaloshinsky Moment in MnCO3
Authors: Forsyth J. B. , Nathans R. , Brown P. Jane
Published: April 2005

The spin density distribution of the Dzyaloshinsky moment in MnCO3 has been determined by polarized neutron diffraction. We find the spin density is not confined solely to manganese atoms, appreciable density being located in the vicinity of the carbonate group; moreover, that part of the distribution centered on the manganese atoms is not spherically symmetric. Manganese carbonate has the NaNO3 structure with space group R3̄c; at temperatures below 32°K the spins lie in the basal plane, adjacent planes of manganese atoms perpendicular to the axis being coupled antiferromagnically. The ferromagnetic moment which lies in the same plane, corresponds to 0.034 μB per manganese atom. At 10 kOe there is an additional aligned moment of 0.075 μB per manganese atom arising from the usual antiferromagnetic susceptibility which shows a spacial dependence closer to a 3d-like distribution. These more detailed measurements confirm the conclusions of Pickart, Nathans, and Alperin1 on α-Fe2O3 that the Dzyaloshinsky moment is not merely a simple canting of the antiferromagnet spins.
Smooth Controlled Wall Motion in Thin Ni/Fe/Co Films
Authors: Spain Robert J. , Jauvtis Harvey I.
Published: April 2005

Smooth, controlled motion of domain walls in thin Ni/Fe/Co films, without spontaneous nucleation of extraneous domains, has been obtained in a planar thin-film geometry in which the easy anisotropy axis is parallel to the narrow film dimension and displacement of the walls is produced in a perpendicular direction. It is this case for which the stray field from the film edges presents the greatest difficulty to achieving the desired wall motion properties. The film edges are shown to have a pronounced effect upon the shape of a domain wall put into motion by an applied field as a result of the stray field from the edges and an increase in coercive force within the tapered regions. Tapered film edges, in producing a local ``pinning'' of the wall, are shown to provide means for monitoring the presence or location of a domain wall without causing the wall to undergo any net displacement.
Magneto-Optical Variable Memory Based Upon the Properties of a Transparent Ferrimagnetic Garnet at Its Compensation Temperature
Authors: Chang J. T. , Dillon J. F. , Gianola U. F.
Published: April 2005

The requirements to be met by a changeable memory medium for flying spot variable memory system are discussed. Although simple reversible photochromic materials satisfy most of these requirements, their lack of a writing threshold limits their applicability. The application of a transparent ferrimagnetic garnet near its compensation temperature is discussed. At the compensation temperature the net magnetization of the garnet is zero so that the remanent magnetization of the sublattices normal to the surface of a thin crystal is not subject to demagnetization fields. The magnetization of the iron sublattice of the garnet produces a large magneto-optical rotation of the polarization of a transmitted light beam in opposite senses for the two directions of the remanent magnetization, which can, therefore, be interrogated non-destructively. In passing through the compensation temperature, the coercive field for a magnetization reversal passes through a sharp maximum. Thus, the direction of remanent magnetization can be changed by applying a magnetic field in coincidence with a high-intensity pulsed light beam which produces a transient temperature excursion of ∼3°C from the compensation temperature. This provides a writing-threshold making it possible to change the remanent magnetization of a selected crystal in an array without disturbing the magnetization of the remainder. Practical aspects of this approach are discussed.
Investigation of Eddy-Current-Induced Nondestructive Readout in Thin-Film Memories
Authors: Maltz M. S.
Published: April 2005

When a magnetic thin-film bit is switched, eddy currents arise, creating fields which tend to remagnetize the bit in its original direction. A structure in which these fields are strong enough to produce NDRO was given a preliminary investigation. The bits were nickel-iron 17–83 Permalloy, 50×50 mil by 500 Å, evaporated onto a glass substrate. The structure layers were: bit line, word line, planar sense line, bit, glass, and word line. If the word drive pulse was 100 nsec long or less, the structure with the most unfavorable geometry gave stable NDRO at drive currents up to 10 times as large as the normal DRO value. Scale factors are displayed and applied to show that NDRO is possible with structures much smaller than the one tested. The eddy fields could even remagnetize partially demagnetized bits.

When the eddy field was measured as a function of time and geometry, the time constant and magnitude of the decay was a sensitive function of the word linewidth and separation, varying between 76 and 191 nsec. Experimental and theoretical evidence was found for a rapid transient decay mode which precedes the slower decay mode observed in the experiments.
Curie Constants in Concentrated Magnetic Materials
Authors: Wolf W. P. , Heintz J. F.
Published: April 2005

A theoretical expression is derived for the first-order contribution to the Curie constant arising from cross terms between the off-diagonal parts of the magnetic moments and the interactions between the magnetic moments. In certain simple cases the contribution ΔC1 is equal to 2αθ, where α is the temperature-independent part of the susceptibility and θ is the Weiss constant. Estimates of ΔC1 show that in many cases its contribution to the Curie constant may be appreciable. A discussion is given of the danger of deducing Curie constants from susceptibility measurements over a limited temperature range, even under apparently favorable conditions, and illustrated by an analysis of some new measurements on ErCl3.
Ferromagnetic Transitions and the One-Third-Power Law
Authors: Callen Earl , Callen Herbert
Published: April 2005

Experiments have shown that the reduced magnetization of insulating ferromagnets varies as m(T) = D(1-T/Tc)f for T>0.9Tc, and that f=⅓. We report calculations of the magnetization of the Heisenberg model which give, over a wide temperature range, both the observed exponent f=⅓ and the observed co-efficient D, within 2% of the experimental value. This result is obtained for a two-spin cluster theory; similar but slightly less satisfactory agreement is demonstrated by two forms of Green function theory. Because these theories are not satisfactory in the immediate vicinity of the phase transition, and because the experimental ⅓-power law extends far from the transition [in terms of m(T)], we suggest that the ⅓-power law may be a property of the stable ferromagnetic phase rather than a reflection of the phase transition in the sense of the Landau theory.
Band Structure of Gadolinium Metal
Authors: Dimmock J. O. , Freeman A. J. , Watson R. E.
Published: April 2005

The heavy rare-earth metals have been viewed traditionally as consisting of trivalent atomic cores plus three conduction electrons per atom. Previous theoretical work1-3 has attempted to explain the available experimental data by assuming that the three conduction electrons occupy essentially free electron-like bands. We have obtained approximate nonrelativistic energy bands for Gd metal using the augmented plane wave method.4 The calculated bands differ markedly from the free electron model due to the fact that the bands originating from atomic 5d and 6s states overlap and are strongly mixed. The bands, in fact, show a close resemblance to those of the transition metals. This resemblance also appears in the calculated density-of-states curve. The density of states at the Fermi energy is large, about three times that of the free electron model. This density of states is about one half that given for Sc, Y, and La by specific heat measurements.

A detailed version of this paper will be submitted to the Physical Review.5
Low-Temperature Antiferromagnetic Resonance in αFe2O3
Authors: Foner S. , Williamson S. J.
Published: April 2005

Antiferromagnetic resonance (AFMR) at 35, 70, and 121 Gc/sec in single-crystal synthetic and natural αFe2O3 from 4.2° to 280°K has been observed. The usual low-field AFMR as well as the spin-flop resonance mode are observed with pulsed magnetic fields applied parallel to the c axis. The data extend from well below the spin reorientation transition temperature TM (about −10°C) to well above TM. The spin-flop mode joins smoothly with the canted high-frequency mode above TM. The usual AFMR terminates abruptly at TM. The three modes observed here for the first time in αFe2O3 require either high fields or high frequencies or both for observation. The effects of the Dzyaloshinsky-Moriya field HDM on the spin-flop resonance, the usual AFMR, as well as possible effects of spontaneous sublattice magnetizations are discussed.
Crystal Growth and Magnetic Susceptibilities of Samarium and Europium Gallium Garnets
Authors: Schieber M. , Holmes L.
Published: April 2005

Single crystals of EuGaG and SmGaG were grown by the flux method and the magnetic susceptibilities measured between 2° and 300°K. The magnetic susceptibility of Eu3+ in EuGaG follows Van Vleck's formula for the free ion to a first approximation, due to the fact that any splitting δ of the J=1 levels produces an increase in the susceptibility of Eu3+ at low temperatures which is only second order in δ/hv(1; 0). In the case of SmGaG, the magnetic susceptibility at 4.2°K is reduced to ∼0.3 of the free ion value, indicating a strongly rhombic crystalline field.
Spin-Flopping Relaxation Time in CuCl2·2H2O
Authors: Naiman Charles S. , Lawrence Thomas R.
Published: April 2005

The relaxation time associated with the spin-flopping transition in CuCl2·2H2O has been measured and found to be (0.70±0.15)×10−7 sec at 2.4°K. Our measurements also yield the susceptibility and temperature dependence of the critical field Hc. The rf susceptibility was measured with the applied rf and dc fields parallel to the easy axis (a axis) at Hc. The inductive and resistive components of the critical field susceptibility as a function of frequency, fit dispersion, and dissipation curves with a relaxation parameter of tsf=0.7×10−7 sec. at 2.4°K. Some otherwise strange observations have been explained by a temperature rise due to the dissipation of energy in the crystal through the resistive component of χc. For instance, in the measurement of the change of inductance as a function of H in the vicinity of Hc, the curve is found to display asymmetry about the peak and hysteresis. These effects become more pronounced with increasing power, which is consistent with their being of thermal origin.
The Constitution of CuFe5O8
Authors: Jefferson C. F.
Published: April 2005

The physical properties of the system CuFe2O4–Fe3O4 point to the existence of the compound CuFe5O8. The activation energies Ea of quenched specimens exhibit an anomaly at the composition CuFe5O8. The log of the resistivities plotted as a function of composition changes slope, the Curie temperatures Tc display a minimum, and the lattice constants A0 show a maximum at or near this composition.

As the iron concentration increases, the Seebeck coefficients θ change from positive to negative at the composition Cu0.55(CuFe)0.225Fe2O4. This is interpreted as being due to the introduction of some ferrous iron at this composition. The equilibrium Cu+1+Fe+3↔Cu+2+Fe+2 lies to the left at least up to this composition. Since the changes in ρ, Ea, A0, and Tc occur at or near the composition CuFe5O8, it is concluded that only a little ferrous iron exists even in the region of n-type conductivity, and that the copper within parentheses is predominantly monovalent in the series Cu1−2x+2(Cu+1Fe+3)xFe2O4.
Flux-Jumping Behavior of Some Niobium-Tin Solenoids
Authors: Rosner C. H.
Published: April 2005

Oscillographic and X-Y recorder observations have been made of the flux-jumping pattern in several superconducting Nb3Sn solenoids at magnetic fields ranging from 15 to above 100 kG at 4.2°K. It is noted that flux jumping is much more frequent in these solenoids than is observed in Nb–Zr solenoids. The flux-jump pattern extends throughout the high-field region. It can be modified, however, by gross rate changes in current increase, as well as by application and removal of external fields which change the induced magnetization.

Frequent quenching of the Nb3Sn superconducting solenoids does not seem to alter the flux-jump behavior appreciably. The relationship of a superconductive transition to flux jumps occurring just prior to the transition is discussed.

It is suggested that the more frequent but often lower-amplitude flux jumps in these niobium-tin solenoids contribute to the smaller coil degradation effect noticed as compared to niobium-zirconium solenoids. To eliminate, or at least minimize this effect, further exploration of magnetic instabilities and influence of material parameters is required.
Techniques to Achieve Texture in Permanent Magnet Alloy Systems
Authors: Makino Noboru , Kimura Yasuo
Published: April 2005

The formation of columnar crystals in the anisotropic Alnico alloys has been known to enhance the magnetic properties, particularly the energy product. The requirements for columnar crystal growth are fairly steep temperature gradients in the liquid metal, coupled with low solidification rates. The first method is based on casting in a hot multicavity mold having a bottom chill plate so that directional solidification occurs. The mold has a great number of cavities with the thickness of walls between cavities less than 2 mm. It must be preheated to a temperature not lower than 1000°C before pouring. The second method is based on zone melting plus rapid directional cooling. This method is convenient to produce columnar crystals in magnets smaller than 20 mm in diam. The best magnetic properties of magnets 10 mm in diam can be obtained by lowering the fusion zone at the rate of about 25 mm/min. The magnetic energy product obtainable from both methods is almost the same in value, that is, 7.0–8.0 MGOe in commercial production. Addition of silicon and sulphur to Alnico alloys helps to produce columnar crystals, but titanium is unfavorable. Addition of sulphur helps to promote columnar crystals in Alnico alloys containing titanium. The oxide and nitride in the molten metal decrease with addition of sulphur and production of columnar crystals becomes easier. Recently, it was reported that large crystals had been produced by secondary recrystallization in some experiments in a laboratory. However, it is difficult to control the orientation of enlarged grains. The texture of rolled Alnico 8 alloy was found to contain three orientation components; (100) [011], (112) [11̄0], and (111) [112̄].
NMR Measurements of the Magnetic Flux Distribution in Type II Superconductors
Authors: Gossard A. C. , Jaccarino V. , Wernick J. H. , Pincus P.
Published: April 2005

The penetration of magnetic fields in type II superconductors indicated by magnetization measurements in the superconducting state can be studied more fully using nuclear magnetic resonance (NMR) techniques. NMR measurements on finely divided superconducting V3Si (Tc=15.8°K) and V3Ga (Tc=14.6°K) have been made and yield the mean magnetic field and the spatial distribution of the field within the super-conductor. The mean field was reduced by less than 0.1% of the applied field while the root-mean-square deviation of the field was of the order of 0.2% of the applied field, all at 14 kOe and 1.8°K. Such a spatial variation in the flux penetrating a hard superconductor would be expected from either the filamentary1 or laminar2 models of type II superconductivity. A calculation of the expected magnetic field distributions for the two models has been made. The magnitude predicted from the filamentary model is in better agreement with the experimental results than that from the laminar model.
Parallel-Pumped Instabilities in Magnetic Metal Films
Authors: Comly J. B. , Jones R. V.
Published: April 2005

Parallel-pumped instability (PPI) susceptibility measurements on several Permalloy magnetic metal films demonstrate a variety of microwave power and dc field-dependent effects. In the low-field spin-wave range, thick films may show either of two distinct kinds of behavior, or a combination of both. A qualitative explanation of these behaviors based on varying drive-field coupling to two different sets of modes with wave vectors perpendicular or parallel to the film plane and similar thresholds is suggested. Very thin films have a different characteristic behavior due to severe mode distortion caused by sample shape demagnetization. Lack of correlation between spin-wave relaxation rates and resonance linewidths suggests that inhomogeneous broadening is an important linewidth mechanism.
Spin-Wave Spectra in Thin Magnetic Films
Authors: Rossing Thomas D. , Thern Royal , Larson Daniel , Heppner Richard
Published: April 2005

Spin-wave spectra have been studied in Permalloy films of varying thickness. In many of the films, the low-lying spin peaks exhibit the uniform spacing and slowly decreasing intensities associated with a parabolic variation in magnetization through the film, whereas the higher modes show the quadratic spacing and rapidly decreasing intensities associated with an abrupt change in magnetization or spin-pinning near the surface. The transition between these two regions depends upon the amplitude of the variation in magnetization and the film thickness, or in other words, the depth and width of the parabolic ``well.'' When the angle of the applied field is changed with respect to the film, the lowest modes are virtually unchanged, but the linear-quadratic transition moves to a lower mode number. This is probably because the parabolic well appears shallower as the field approaches the ``critical'' angle at which the resonance frequency is independent of the magnetization. One series of films shows line spacings which are virtually independent of the film thickness.
Magnetic Resonance in Dysprosium Metal
Authors: Rossol F. C. , Cooper B. R. , Jones R. V.
Published: April 2005

Magnetic resonance has been observed at 37.7 Gc/sec in a hexagonal platelet of dysprosium metal at temperatures in the range where the spin arrangement is spiral. The resonance behavior is in many respects similar to that observed near the spin-flop field in ordinary antiferromagnets. The temperature dependence of the field for resonance generally follows the temperature dependence of the critical field for the transition from spiral to ferromagnetic spin arrangement. Widths on the order of 1 kOe were observed for the dc field applied along both easy and hard axes of the planar anisotropy. A secondary absorption peak is resolved at a field about 400 Oe higher than the field for the main resonance for temperatures below 106°K with the dc field along an easy axis and below 120°K with the dc field along a hard direction. The planar anisotropy becomes insignificant above the latter temperature. The detailed interpretation of line shapes is complicated by changes in the conductivity occurring at the critical field.
Rolling-Induced Magnetic Anisotropy in a Co—10% Fe Alloy
Authors: Von Neida A. R. , Chin G. Y.
Published: April 2005

The development of magnetic anisotropy induced by cold rolling of an alloy containing 90% Co—10% Fe was studied with the aid of torque curves and x-ray texture data. In the annealed condition the texture is (31̄1̄) [112], and the torque dependence of the magnetization shows an easy direction both parallel and transverse to the rolling direction. As rolling proceeds to 98% reduction, the torque curves develop a sin2θ dependence with the easy direction of magnetization transverse to the rolling direction. The torque maximum associated with the transverse direction, which is a measure of the stability of the rolling-induced easy axis, develops linearly with true strain. The intensity of the x-ray reflection from {110} planes lying in the plane of the sheet, which is a measure of the development of the rolled testure, also increases in a linear manner with true strain. At 98% or greater reduction, the texture becomes (11̄0) [335]. Theoretical torque curves computed on the basis of texture and the magnetocrystalline anisotropy energy give values for the first anisotropy constant K1, which compare favorably with the measured single-crystal K1 values, showing that the rolling-induced anisotropy in this alloy is due principally to magnetocrystalline anisotropy energy.
Electronically Variable Delay of Microwave Pulses in Single-Crystal YIG Rods
Authors: Kaufman I. , Robinson W. A.
Published: April 2005

Experiments on electronically variable time delay of microwave pulses by transmission through single-crystal YIG rods are discussed. One type of delay, recently discussed by Olson and Buchmiller and by Kaufman and Soohoo and attributed to magnetostatic waves, occurs with unpolished ends, has rapidly increasing delay with increasing Hdc, and has severe pulse dispersion. The second, found here, requires parallel and polished ends, has a slowly decreasing delay with increasing Hdc, and usually has at least two pulses spaced by less than the round-trip time through the rod. Characteristics are similar to those described by Strauss, except that his experiments were of pulse reflection.

The two aspects of magnetostatic wave pulse delay to be discussed are: (1) Additional experimental verification of Schlömann's theory of wave excitation by nonuniform demagnetizing fields, by grinding a rod into ellipsoidal shape, and by measure coupling. (2) A nonreciprocal microwave time delay has been constructed utilizing magnetostatic waves in a YIG rod to couple two rectangular waveguides. The coupling is between the positions in the waveguide where the magnetic field is circularly polarized. The directionality of the coupling was found to be greater than 15 dB with delays of 4 μsec at 2500 Mc/sec.
Dielectric Permittivity Tensor of ErFeO3 for Radiation in the Visible Spectrum
Authors: Jung Wun
Published: April 2005

As part of an effort to understand the nature of the transition responsible for the very strong absorption band edge and the large magneto-optical effects in ferric ion containing ferro- and ferrimagnets, the optical and magneto-optical properties of erbium orthoferrites (ErFeO3, ΘN = 620°K for Fe+3 spins) have been examined by reflection techniques. Ellipsometer and Kerr rotation measurements were made on growth surfaces (c plane) at room temperature over the visible spectrum. The real and imaginary parts of the dielectric constant show two bands at 22 000 and 26 000 cm−1, with oscillator strengths of 0.03 and 0.4, respectively. The normal incidence polar Kerr rotation has a sharp peak of 11.5 min at 23 500 cm−1. There are several weaker structures between 15 000 and 22 000 cm−1 which are believed to be due to low-lying branches of the crystal-field spectrum of the Fe+3 ion. By combining the Kerr rotation and dielectric constant data, the off-diagonal element of the dielectric permittivity tensor was calculated. The results suggest that the main 26 000 cm−1 band and the unresolved 23 500 cm−1 band represent the σ and π processes of the electron transfer transition. They further suggest that the π process component of the off-diagonal element has opposite sign relative to that for the σ process and the first allowed internal transition.
Transversely Pumped Magnetoelastic Instabilities
Authors: Auld B. A.
Published: April 2005

A detailed theory is developed for first-order transverse pumping mechanisms arising from terms in the magnetocrystalline energy which are linear in strain. A physical description of these mechanisms is given in terms of direct and indirect interactions among the particle displacement and magnetization variables, and the instabilities of the medium are classified as direct or indirect according to the mechanisms involved. Numerical values of the thresholds are calculated as a function of propagation angle for longitudinal magnetoelastic instabilities in YIG pumped at 1000 Mc/sec. It is shown that two magnetoelastic instabilities have thresholds which are substantially lower than the second-order spin-wave instability threshold. The implications of this result relative to the parametric amplification of elastic waves and the interpretation of certain anomalous saturation effects in ferrites are discussed.
X-Ray Yield and Line/Background Ratios for Electron Excitation
Authors: Birks L. S. , Seebold R. E. , Grant B. K. , Grosso J. S.
Published: April 2005

X-ray yield in photons/sr/electron was measured for the Kα lines of Ti, Cr, Mn, Fe, Cu, Zn, Ge, Zr, and the Lα lines of Ta and Au. Incident electron energy was varied from 11 to 38 keV, and for some elements the take-off angle for emerging x rays was varied from 6 to 45 deg. Theoretical yield values calculated after the method of Metchnik and Tomlin showed an average deviation of about 30% from the measured values, a very satisfactory agreement.

Line/background ratios were also measured for the same elements and conditions. Normalization to the natural x-ray line breadths gave ratios between 100/1 and 26 000/1 depending on the element and experimental conditions. Line/background ratios are consistently larger at low take-off angles indicating that the characteristic radiation must be generated relatively closer to the surface than the continuum of the same wavelength.
Stabilization of the He–Ne Maser on the Atomic Line Center
Authors: Shimoda Koichi , Javan Ali
Published: April 2005

Application of an automatic feedback control for long-term frequency stabilization of a He–Ne optical maser at the center frequency of the atomic resonance is described. The length of the Fabry-Perot resonator is modulated at a low frequency with small amplitude. The fundamental, second harmonic, and third harmonic components of this modulation frequency in the light output of the maser are used to control the tilt angles of the mirrors, the radio-frequency excitation power input, and the separation of the mirrors, respectively. The frequency stability is determined by observing the photobeat between the outputs of two independently stabilized masers. Isotopically enriched samples of Ne are used in the two masers with one of them enriched in 20Ne and the other in 22Ne. The optical output of a maser stabilized in this manner is frequency modulated and the center frequency has been found to be stable to several parts in 1010 over very long periods.
Multiple Quantum Transition and Raman Action in Three-Level Systems
Authors: Margolis Jack S. , Birnbaum George
Published: April 2005

A theory is presented of induced Raman emission in a three-level system whose parameters are appropriate for microwave to optical frequencies. Solutions of the time-dependent Schrödinger equation are obtained for arbitrary intensity of the pump and signal radiations, which are assumed to be not too many line-widths off resonance. It is shown how the quantum-mechanical aspects of the problem may be separated from the statistical-mechanical aspects, in contrast to the density matrix techniques. The frequency dependence of the Raman emission on the frequency and intensity of the pumping radiation obtained by this method is presented and compared with the results we have obtained by other methods. The intensity and line shape of the Raman emission when the pump frequency is far off resonance are also obtained. The case of three interacting fields is also considered.
Mechanism for the Shock Polarization of Dielectrics
Authors: Harris Paul
Published: April 2005

A new type of electromechanical coupling is postulated to explain the polarization signals resulting from the shock loading of nonpiezoelectric materials. The driving force is viewed as being proportional to the gradient of the stress. The electromechanical coupling constant is found for an ionic solid by deriving the effect for a linear ionic chain. A stress gradient of 1011 dyn/cm3 is found to give rise to a voltage gradient of 10 V/cm.
Resistivity of Xenon Plasma
Authors: Goncz John H.
Published: April 2005

By measuring voltage drop in xenon flashtubes the resistivity of intense xenon plasmas is found to bear an inverse square root relation to the current density. A weak dependence on pressure is discussed.
Transient Motion of Space Charge through a Neutral Gas
Authors: Demetriades Anthony , Hill Jack H.
Published: April 2005

The history of motion of charge carriers generated in a gap by ionizing radiation is investigated. The study is limited to cases where the field-induced motion of these carriers overcomes their inertia and diffusion; the motion is thus completely collision-dominated. The severity of the space-charge effect is described by a single nondimensional parameter γ. When γ is not much smaller than unity, usual linearization procedures are inapplicable. The nonlinear problem is solved for two limiting cases. In the first, the electric current is carried by the free electrons and ions as originally created. In the second, the electric current is carried by positive and negative ions, the latter formed by electron attachment. The method of characteristics is employed to solve the equations of motion and exact analytical and numerical solutions are presented. It is shown that if γ>2 the nonlinear effects of the induced charges are important and depart appreciably from calculations based on linear approximations.
Modes of the Screw Instability in a Positive Column with Longitudinal Magnetic Field
Authors: Itoh Satoshi , Kawaguchi Motoichi , Yamamoto Kenzo
Published: April 2005

The modes of screw instability in a positive column of a nitrogen gas discharge have been studied. Under a certain condition, the critical magnetic field for the m=2 mode has been found to be smaller than that for the m=1 mode. In addition, the regular oscillations have been observed at the magnetic field larger than the critical one. These phenomena can not be described by the results of Kadomtsev and Nedospasov which are calculated from the small-amplitude theory. In this paper a theoretical explanation for these phenomena is proposed based on the conception that only the instability which has the maximum growth rate can grow while other instabilities are masked.
Determination of Third-Order Elastic Coefficients in Crystals
Authors: Brugger K.
Published: April 2005

Third-order elastic coefficients can be derived from sound speed measurements in statically stressed crystals. The necessary relations between experimental data and elastic coefficients are here presented for orthorhombic, tetragonal, cubic, rhombohedral, and hexagonal crystal classes. For each symmetry a sufficient number of wave modes and stress systems is selected to determine all third-order coefficients and to allow experimental cross checks. All the modes considered are pure longitudinal or transverse. They are selected so as to minimize the number of specimen orientations required, and following experimental procedures for uniaxial static stress, only wave modes propagating at right angles to the stress direction are considered.
Elastic Constants of Cubic Lead Fluoride at Room Temperature
Authors: Wasilik J. H. , Wheat M. L.
Published: April 2005

Using an ultrasonic pulse echo technique operating at frequencies ∼10 Mc/sec, we have obtained the following elastic constants for cubic PbF2: C11=8.88×1011 dyn/cm2, C12=4.72×1011 dyn/cm2, C44=2.454×1011 dyn/cm2 at 27°C. From these data a Debye θ of 221.2°K was calculated.
Twist and Axial Imperfections in Filamentary Crystals of Aluminum Nitride. II
Authors: Drum C. M.
Published: April 2005

Simultaneous and independent measurements have been made of the magnitude and direction of the lattice twist and of the direction of the Burgers vector of the axial dislocations in filamentary crystals of AlN, using electron microscopy and electron diffraction. The twist was revealed by extinction contours from reflecting planes with normals perpendicular to the filament axis, and measurements of the widths and separations of these contours were used to calculate the twist.

Good agreement with theory was found in the case of crystals containing the simple axial dislocation, but crystals with a complicated extended axial imperfection were found not to be twisted. It is believed that the extended axial imperfection was a fault which met the surface of the crystal and which originated from an axial dislocation; the lack of twist was then due to one or more partial dislocations having left the crystal.
Static Atomic Displacements Resulting from Vacancies in Defect Structures TiNx□1—x
Authors: Houska C. R.
Published: April 2005

Both static atomic displacements (resulting from vacancies) and vibration amplitudes, were measured in specimens having the compositions TiN0.59, TiN0.78, and TiN0.95. The static displacements for titanium (and nitrogen) in the first two specimens were about 5.5% of the first neighbor distance and were comparable to the dynamic displacements at 250°C. Static displacements were not observed for TiN0.95. The specimen of intermediate nitrogen concentrations, TiN0.78, had smaller dynamic displacements and thermal expansions than the other two specimens, indicating the existence of a minimum in these thermal properties.
Behavior of the Thermal Expansion of NaCl at Elevated Temperatures
Authors: Enck Frank D. , Dommel J. Gerald
Published: April 2005

The coefficient of linear thermal expansion (α) for NaCl has been determined from 50°C to near the melting point (800°C) with an automatic recording dilatometer. The results confirmed the authors' suspicions that the values of α reported by Eucken and Dannöhl are systematically high above 450°C. The experimental data are not satisfactorily represented by polynomial curves from the first through the eighth order as there is a decided increase in the thermal expansion above 600°C. Consequently, two second-order polynomials are employed to adequately fit the data. The difference (Δα) at constant temperature between the high-temperature polynomial and the extrapolation of the low-temperature polynomial behaves logarithmically with respect to 1/T at high temperatures. The slope of this curve corresponds to a formation energy of 1.916 eV, which compares favorably with the energy required to form a pair of isolated positive and negative ion vacancies within the crystal (a Schottky defect).
Etch Pits and Dislocations in SnO2 Crystals
Authors: Koffyberg F. P.
Published: April 2005

Dislocation etchants have been developed for SnO2 single crystals grown from the vapor phase. The correlation between etch pits and dislocations was established by an analysis of the pit patterns formed on matched cleavage surfaces, and on as-grown faces after plastic deformation and annealing. The slip systems were found to be {110}/〈001〉 and {101}/〈101̄〉, and arguments for the existence of partial dislocations on the latter slip plane are given. The shapes of pits produced by boiling HI on {110} faces are analyzed for a correlation with the following dislocation characteristics: angle of incidence of the dislocation line, the presence of segregated impurities on the dislocation, and the direction of the Burgers vector. A simple technique for decorating dislocations is described. Finally, it is shown that dislocations in as-grown crystals arise from two processes, both occurring during cooling after growth: (1) the differential thermal expansion of the growth substrate and adhering crystals, and (2) the diffusion of oxygen into the material resulting in a stoichiometry gradient.
Spin Waves and Neutron Scattering
Authors: Lowde R. D.
Published: April 2005

A review is given of the problems in this field, and of the possibilities opened up by the fact that neutron scattering gives access to the time-dependent spin-correlation function in magnets over virtually the whole range of q, t, and T. New experimental results are given in connection with magnon energy linewidth and renormalization, and some data are presented for the spin-wave stiffness of bcc 3d transition-metal alloys as a function of electron concentration, showing effects explained by the electronic density-of-states curve. It is pointed out that the ground-state fluctuations of magnets give rise to effects in the formulas for neutron scattering.
Angular Momentum Compensation in Narrow Linewidth Ferrimagnets
Authors: LeCraw R. C. , Remeika J. P. , Matthews H.
Published: April 2005

Studies are described of the ferrimagnetic garnet system Eu3Fe5—xGaxO12. It is shown that a compensation point of the net angular momentum occurs at x≅1.2, at which the resonance linewidth remains narrow. In all previously observed ferrimagnetic systems with angular momentum compensation points, e.g. GdIG, strong line broadening occurs. The reasons for this are discussed together with the relaxation processes involved. Application of the resulting large g factors to millimeter wave harmonic generation is considered.
55Mn Nuclear Magnetic Resonance in MnO
Authors: Jones E. D.
Published: April 2005

The 55Mn NMR has been observed in the paramagnetic state of the antiferromagnet MnO. The separation between the absorption derivative extrema of the 55Mn NMR is 55(δH)≃340 Oe, in satisfactory agreement with the predictions of exchange narrowing of hyperfine broadened nuclear magnetic resonances in paramagnetic media. The 55Mn NMR frequency shift 55a=(δv/v) is found to be temperature dependent, varying from about −11.75% to −9.3% in the range 130° to 350°K. From the observed linear dependence of 55a on the magnetic susceptibility, the hyperfine coupling constant is determined to be 55A=−(81.5±1.6)×10−4 cm−1. Combining the 17O NMR data of O'Reilly and Tsang with the 55Mn NMR data yields a value for the 17O transferred hyperfine coupling constant of 17A=(2.46±0.04)×10−4 cm−1.
Nonlinear Shielding in Rare-Earth Crystal Field Interactions
Authors: Freeman A. J. , Watson R. E.
Published: April 2005

A number of the magnetic properties of rare-earth ions, which depend strongly on their interaction with the crystalline environment, are inferred by studying their electronic spectra. Basic to current methods for analyzing these spectra is the assumption of a static crystalline field Vc which acts on the open 4f shell. Generally, one takes Vc=Σn,mAnmrnn Ynm(θ, φ). In fitting observed spectra, matrix elements of Vc over the 4f electrons alone are considered and one is left with the quantities Vnm=Anm 〈rn〉 (where 〈rn〉 is the integral of rn over the 4f radial density) which are taken to be empirical parameters which somehow absorb all environmental effects not included in Vc. These empirical parameters have been used ``successfully'' to interpret other rare-earth properties. However, if one considers multi-electron Coulomb and exchange contributions arising from the closed shells, it may be shown1 that, in addition to the occurrence of substantial linear shielding effects1,2 (which reduce the magnitude of the Vnm parameters), there may be significant nonlinear shielding contributions which change the ordering and spacing of the electronic energy levels. When these latter terms are significant, the standard parameterization scheme breaks down.

Previous work1 on Ce3+, using perturbation theory techniques, was seen to be inadequate for accurate estimates of nonlinear shielding. We have extended these investigations using configuration interaction methods to estimate the leading nonlinear (and linear) shielding terms in a number of ions, Ce3+, Tb3+, Er3+, Tm3+, Ho3+, Dy3+, and Yb3+. Calculations have been carried out as a function of crystalline field strength since the nonlinear shielding is dependent, of course, on the strength of the applied external field. Nonlinear shielding of V2 and V4 external fields were determined as a function of atomic number as were their effects on apparent V2, V4, and V6 crystal field parameters. From these certain conclusions may be drawn. Antishielding rather than shielding of the V4 field occurs, but only by a few percent at most, whereas the V2 field is always shielded. For the heavy rare-earth ions, the shielding effects are much smaller than for the lighter ions, with the apparent V4 and V6 shielding being very small. The most severe nonlinear effects arise when relatively strong V2 and V4 fields contribute to a relatively weak V6 field.

A full report will be submitted to the Physical Review.
Pressure Dependence of the Internal Field at the 59Co Nucleus in a 99.5% Ni-0.5% Co Alloy
Authors: Bennett Lawrence H.
Published: April 2005

The room-temperature nuclear magnetic resonance absorption of 59Co in an alloy of 0.5% Co in Ni has been measured under hydrostatic pressures of up to 7 kbars. The change in the resonance frequency with pressure is Δv/Δp=159±5 Hz/bar. This is in the same direction (increasing frequency for increasing pressure) as for 61Ni in Ni. The ratio of the resonance frequency at absolute zero to the change in frequency with pressure v0: Δv/Δp is 750 kbar for 59Co and 1200 kbar for 61Ni in Ni. The internal field at the 59Co nucleus decreases with increasing temperature more slowly than that at the 61Ni nucleus in Ni-rich Ni-Co alloys. This discrepancy in the temperature dependences remains as large, when plotted at constant volume, as it was at constant pressure.
Spin-Wave Effects in Magnetic-Film Switching
Authors: Harte K. J.
Published: April 2005

The nonlinear reaction of dispersion-induced spin waves on the uniform mode m0 has been calculated for a thin film undergoing rapid rotational magnetization reversal. It is found that if m0 rotates faster than longitudinal spin waves can relax, the magnetization goes through a transient state of high magnetostatic energy. If the pulse switching field Hp is less than a critical field Hpc, the uniform mode becomes locked at some point in the reversal process; rotational switching cannot proceed until initially longitudinal spin waves have relaxed into components propagating in the instantaneous direction of m0, a highly damped process suggestive of the intermediate-speed reversal mode observed in thin films. The dependence of Hpc on a dc bias field has been verified experimentally; the dispersion dependence should provide a crucial test of the theory.
Field-Induced Anisotropy in Fe–Co Evaporated Thin Films
Authors: Humphrey F. B. , Takahashi M.
Published: April 2005

Field-induced uniaxial magnetic anisotropy is observed in vacuum evaporated thin Fe–Co films over the entire composition range. Using an inductively heated slug, a consistently reproducible relation between slug composition and film composition was found with the maximum difference occurring near 30% Co where the film turned out to be 47% Co. A uniaxial anisotropy, with the easy axis parallel to a field during evaporation, was observed using a torque magnetometer. The observed value of Ku as a function of composition, for films made on substrates at 300°C, increased smoothly from 2×103 ergs/cm3 for Fe to a maximum of 35×103 ergs/cm3 for FeCo and then decreased to 10×103 ergs/cm3 for Co. No indication of a reduction of the anisotropy constant could be observed at the Fe2Co, FeCo or FeCo3 composition even after post-evaporative anneals up to 70 h at 300°C. The observed value of Ku for films made at room temperature was similar. For selected compositions, Ku was observed to be less for films evaporated onto hotter substrates. The FeCo composition changed least with a 10% reduction from −200° to +525°C. It is concluded that, in contrast to the situation in Fe-Ni alloys, the contribution from pair orientation to Ku must be very small. The coercive force of all films was in the 10 to 60 Oe range with considerable spread observed; the films were generally inverted. The rotational hysteresis integral scattered from 0.5 to 2.2 with no substantial trend observed.
Investigation of the Effect of O2, N2, and H2O on Nickel Thin Films
Authors: Freedman J. F.
Published: April 2005

The role of oxygen, nitrogen, and water vapor adsorbed during the evaporation process was investigated for nickel films grown on room-temperature glass substrates. A change in pressure from 10−10 to 10−7 Torr oxygen caused a marked shift in the resonance field and the perpendicular anisotropy (i.e., the anisotropy resulting from the rotation of the magnetization out of the plane of the film). This shift could be accounted for by an increase in internal stress from 5×109 dyn/cm2 at 10−10 Torr to 2×1010 dyn/cm2 at 10−7 Torr. The wall-motion coercive force also increased with increasing pressure, ranging from 50 to greater than 200 Oe. Samples made in pressures as high as 1×10−5 Torr nitrogen appeared identical (as determined by the measurements) to films made in residual vacuum of 10−10 Torr. The presence of water vapor caused a slight increase in internal stress and Hc when the pressure changed from 10−10 to 10−5 Torr. The effect appears to be related to an internal oxidation phenomenon.

These experiments clearly demonstrate the role of impurity atoms in determining the stress-sensitive magnetic properties of films and emphasises the need for controlling the partial pressures of gases during evaporation, and not just the total pressures.