bluuebunny/crossref_metadata_2025 huggingface dataset:
Slow Surface Relaxation of Germanium
Authors: Pilkuhn M. H.
Published: April 2005

The influence of temperature, ambient atmosphere, and light on the slow surface conductance relaxation of germanium was investigated. The effect of water was found to be very significant, and was studied in detail.

The experimental results are discussed in terms of a model that uses ion migration in the oxide layer as the cause for slow surface phenomena.
Impulse Streamer Branching from Lichtenberg Figure Studies
Authors: Nasser Essam , Loeb Leonard B.
Published: April 2005

The Lichtenberg figure technique for the study of the streamer mechanism in the spark transition in positive point to negative plane geometry has been extended to longer gaps. In this extension the phenomena were investigated over a wide range of variables, some of the results of which, including the nature of the figures, the potential of the streamer tips, and properties of negative streamers, are being published elsewhere. This study is confined to the observation of the growth and attenuation of branching in relation to the appearance of the commonly observed solitary spark channel. Featured in longer gaps is the very extensive branching before midgap with decline as the cathode is approached. The luminous primary-secondary streamer sequence observed by the two-photomultiplier technique is an instrumentally conditioned phenomenon resulting from branching. There is no such sequence otherwise indicated by these observations. The same instrumental effect deriving from the branching accounts for discrepancies in the earlier reported values of streamer tip velocities.
Work Hardening and Dislocation Arrangement of fcc Single Crystals. II. Electron Microscope Transmission Studies of Ni–Co Single Crystals and Relation to Work-Hardening Theory
Authors: Mader Siegfried , Seeger Alfred , Thieringer Hans-Martin
Published: April 2005

The dislocation arrangement in the primary glide plane of deformed Ni–Co crystals of different compositions and stacking fault energies was investigated by the transmission electron microscope technique. The thin foils were found to contain mainly dislocations of the primary glide system close to the edge orientation. Very few screw dislocations were observed; they were presumably lost during the preparation. Straight dislocations in 〈110〉 directions, presumably Lomer-Cottrell dislocations, were found in particular at intermediate and low stacking fault energies. The dislocation density shows local variations so that ``dislocation braids'' can be discerned from the background. For Ni+40% Co, the dislocation densities and arrangements are compared with slip line results obtained from the same crystals. These results are found to be compatible with the so-called glide-zone model and the geometrical interpretation of the slip-line pattern based on it.

The final section deals with the dynamic aspect of plastic deformation and with the theory of work hardening by long-range stresses. It is shown that the experimental observations fit this theory. Some objections that have been raised against the theory are discussed and met.
Ratio of Interstitial to Substitutional Zinc in GaAs and its Relation to Zinc Diffusion
Authors: Weiser K.
Published: April 2005

An order-of-magnitude estimate of the ratio of singly charged interstitial to substitutional zinc in GaAs is made by combining experimental data for copper in GaAs with theories of solubility and diffusion of interstitial impurities. Calculations of the diffusion constant on the basis of a substitutional-interstitial mechanism yield values which agree to within one or two orders of magnitude with experimental values in the temperature range 750° to 1000°C.
X-Ray Investigation of the Perfection of Silicon
Authors: Carruthers J. R. , Hoffman R. B. , Ashner J. D.
Published: April 2005

The integrated reflections of silicon crystals with dislocation densities from 102 to 7×104 cm−2 have been measured on a double crystal x-ray spectrometer using AgKα1 radiation and the (333) reflection. The relevancy of dislocation distribution, residual (growing) deformation strains, and solute strains to the accuracy of the correlation between the rocking curve parameters and dislocation density is discussed. Lastly, the relative contribution of the 3λ component of radiation from the continuous spectrum to the integrated intensity was found to be a sensitive function of dislocation density in these low dislocation crystals, thus providing the most reliable means for evaluating crystalline perfection by this technique.
Fatigue Deformation of Magnesium Oxide
Authors: Subramanian K. N. , Washburn Jack
Published: April 2005

Etch pit and transmission electron microscope observations were made on magnesium oxide crystals subjected to fatigue deformation. The growth of slip bands in crystals that were clamped at one end and displaced alternately in opposite directions at the other end was studied for increasing numbers of cycles up to about 106. The results were consistent with the hypothesis that there are few sites along a slip band interface at which dislocations can move far enough into the undeformed crystal to nucleate widening of the band. They also suggested that the external surface that is parallel to the Burgers vector may play an important role in slip band widening.
Stacking Fault Probabilities of Some Internoble Metal Alloys
Authors: Vassamillet L. F. , Massalski T. B.
Published: April 2005

The deformation stacking fault probability has been measured by means of x-ray diffraction in the six internoble metal alloys (Cu-Ag, Cu-Au, Ag-Cu, Ag-Au, Au-Cu, and Au-Ag) containing 1, 2, 3.5, and 5 at.% of solute. The peak shifts were obtained by use of the centroid method. Addition of the first 1% of solute produces a marked change in faulting probability of copper and gold, but not that of silver. Further increases in solute content result in much smaller increases in faulting probability for all alloy systems. The possible reasons for these changes are discussed briefly.
Thermoelectric and Thermomagnetic Heat Pumps
Authors: Varga B. , Reich A. D. , Madigan J. R.
Published: April 2005

The dynamical equations which govern the simultaneous flows of heat and electricity in crystals express the electric and heat current densities as linear combinations of the gradients of the electrochemical potential and the temperature. When a magnetic field is applied, the coefficients in these equations become functions of the applied field. Magnetic field effects are included by expanding the coefficients in powers of the magnetic field. For isotropic media, expansion of the electrical and thermal conductivities and the Seebeck coefficient to the first order in the magnetic field gives the Hall, Righi-Leduc, and Nernst coefficients, respectively. The resulting dynamical equations have been solved assuming (a) ρ,κ,S are not functions of position or temperature, H≠0, current density J is either parallel or perpendicular to the temperature gradient ▿T and to the heat current density Q; (b) ρ and κ not functions of position or temperature, H=0, J∥▿T.
Effect of Surface Polishing on the Linewidth and High-Power Properties of Single-Crystal Spheres of ZnY
Authors: Dixon Samuel
Published: April 2005

Single-crystal (ZnY) (Ba2Zn2Fe12O22) was used in an investigation of the effects of surface finish on the linewidth and high-power properties. Measurements indicate that by polishing rough-ground spheres with successively finer grit abrasives, the linewidth can be reduced from 50 to 13.8 Oe. From the measured threshold field, the spin-wave linewidth (ΔHK) of 6.6 Oe has been calculated, in good agreement with that obtained by Green and Healy who used the parallel pump technique. Experiments indicate a threshold field an order-of-magnitude lower than for yttrium iron garnet with a comparable linewidth.
A Low-Density Plasma for Molecular Ion Dissociation
Authors: Stirling W. L. , Matlock O. D. , Hoy H. C. , Meece V. J.
Published: April 2005

A hydrogen arc has been developed which produces a low-density plasma column. The electrodes of the arc discharge are geometrically arranged such that the plasma drifts through a hole in the arc anode along a flux tube of the confining magnetic field.

A differentially-pumped vacuum system was constructed which achieved a base pressure of 2.5×10−10 Torr in the inner liner region while at liquid-nitrogen temperature. A density of about 1010 particles cm−3 can be achieved in the plasma column contained in the inner liner region, down field from the arc chamber, with a gas flow of 2 cm3 min−1 into the arc chamber. At this flow, the pressure in the inner liner rises to 3×10−9 Torr. The ion-to-neutral density ratio under these conditions is about 30 to 1 in the inner liner region.
A Numerical Method for the Determination of an Electric Field about a Complicated Boundary
Authors: Cruise D. R.
Published: April 2005

A numerical method to solve Poisson's equation with an empirical set of boundary values gives potentials about complicated configurations such as occur in the lenses of electron microscopes. It involves solving an auxilliary induction problem and then solving the integral form of Poisson's equation numerically. The case for cylindrical symmetry has been coded on the IBM 7090 computer and a program developed that evaluates the electron optical properties of lenses possessing this symmetry.
Thermal Velocity Effects in Axially Symmetric Solid Beams
Authors: Kirstein P. T.
Published: April 2005

The effect of a Maxwellian distribution of emission velocities on the longitudinal current density variation in axially symmetric solid beams is investigated to the paraxial approximation. The effects of both longitudinal and transverse initial emission velocities are included. The treatment permits variable magnetic fields and apertures which intercept some of the beam. Some particles may be turned back because all their energy is forced into the transverse motion; the reduction of the transmitted current density is evaluated. A simple illustrative example is given.
Charged Particle Orbits in a Logarithmic Potential
Authors: Hooverman R. H.
Published: April 2005

The equations of motion of a nonrelativistic particle in an attractive 1/r central force are developed, and integrated by a digital computer. The results are presented graphically, and representative orbits are sketched.
Superconducting Niobium Films by Vacuum Deposition
Authors: Fowler Peter
Published: April 2005

Niobium films 300 to 150 000 Å thick were formed by vacuum deposition using electron bombardment techniques. The films were superconducting at 4.2°K in magnetic fields as high as 30 kOe. Critical current density at 4.2°K is in the order of 106 A/cm2. The superconducting transition temperature, 9.3°K for a 2300-Å thick film, is less for thinner films. Aging effects were noted for the high-field current-carrying capacity.
Properties of Superconducting Niobium Films Made by Asymmetric ac Sputtering
Authors: Frerichs R. , Kircher C. J.
Published: April 2005

Superconducting films of niobium can be made by asymmetrical ac sputtering. This modification of the conventional sputtering process uses a reverse sputtering current to bombard the film as it deposits, thus dislodging gaseous impurities to obtain pure films. The deposition conditions to yield the purest films have been established using cylindrical geometry, that is, Vycor tubing substrates which are heated internally and surrounded by a large niobium cathode. At substrate temperatures of 500°C and with a sputtering to reverse sputtering current density ratio of 4:1, films with β=R300°K/R10°K as large as 4.7 have been obtained from bulk material of β=14. Films so made have critical temperatures between 8.9° and 9.2°K; the bulk material critical temperature is 9.25°K. The critical temperature of the films is a strong function of β, falling below 4.2°K for β<1.25.
Transient Thermal Diffusivity Technique for Refractory Solids
Authors: Cape J. A. , Lehman G. W. , Nakata M. M.
Published: April 2005

A new technique for the measurement of the thermal diffusivity at high temperatures is described. The diffusivity is determined from the time interval separating two radial isotherms in a cylindrical specimen. The observations are made during the transient heating (or cooling) period. Measurements are reported on Ta, ZrC, and TiC in the temperature range 1300° to 1650°C. The data are in good agreement with diffusivities calculated from specific heat and steady-state thermal conductivity measurements.
Influence of Milling upon the Magnetic Properties of the Intermetallic Compound MnAlGe
Authors: Velge W. A. J. J. , De Vos K. J.
Published: April 2005

The influence of milling upon some magnetic properties of the intermetallic compound MnAlGe has been studied. The Curie temperature of the material seems to be independent of particle size and is constant at 245°C. The saturation magnetization σs, which is 55 erg/Oe·g in the annealed state, decreases as the grinding time increases. The anisotropy field HA (∼43 000 Oe) was found to be more or less independent of the grinding time. Particles obtained by milling in a vibration mill can possess a coercivity IHC of about 3000 Oe, which can be enhanced by annealing to a value of 6400 Oe. The saturation magnetization and the coercivity decrease appreciably after mechanical loading which does not involve a reduction in particle size. This indicates that structural imperfections, rather than changes in particle size, play an important role in the observed phenomena.
Magnetic Aging of Spinodal Alloys
Authors: Cahn John W.
Published: April 2005

The effect of a uniform magnetic field on the mechanism, kinetics, and resulting morphology of a spinodally decomposing alloy is investigated. It is shown that the magnetic field is most effective in forming uniformly spaced rods parallel to the magnetization if the aging is carried out just below the intersection (on the phase diagram) of the Curie temperature and the temperature where the spinodal instability sets in. This condition limits the effective magnetic aging alloys to the composition range near this intersection.
Radiation Effects in GaAs
Authors: Aukerman L. W. , Davis P. W. , Graft R. D. , Shilliday T. S.
Published: April 2005

Comparison of the annealing properties of radiation-induced conductivity changes in GaAs indicates that about 10% of the damage created by reactor irradiations anneals in a manner quite similar to but not identical with that created by 1-MeV electrons. The remaining neutron damage requires much higher annealing temperatures and is presumed to result from complicated damage structures characteristic of highly energetic knock-on atoms (e.g., disordered regions). Heavy neutron irradiation of either p- or n-type GaAs results in very high resistivities which appear to be influenced by the presence of slow surface states. Energy levels resulting from neutron irradiation are estimated to lie at approximately 0.1 and 0.5 eV below the conduction band and at 0.6 eV above the valence band. Moderate irradiation of GaAs by fast neutrons gives rise to a continuous optical absorption spectrum for wavelengths beyond the fundamental absorption edge, with the absorption increasing as the inverse square of the wavelength. Similar behavior occurs in CdTe and CdS after neutron irradiation. Although this effect is not well understood, it is suspected of being associated with defect structures characteristic of fast neutron bombardment, since heavy bombardment with electrons does not produce the same behavior.
Calcium Tungstate. II. Observation of Dislocations
Authors: Levinstein H. J. , Loiacono G. M. , Nassau K.
Published: April 2005

An etch-pitting technique is described for revealing the points of intersection of dislocations with the (100) and (001) surfaces of calcium tungstate single crystals; each etch pit represents one dislocation. The dislocation configuration that is responsible for the residual strain in as-grown ``a'' axis crystals and the mechanism of its growth from the melt are discussed. Preliminary results concerning the distribution of impurities in doped calcium tungstate crystals and the effect of doping on dislocation density and distribution are described. The solution behavior of calcium tungstate in various solvents and a chemical polishing procedure for calcium tungstate are presented.
Influence of Alkali-Vapor Atmospheres on Pyrometrically Determined Temperatures: Cesium and Potassium
Authors: Lapp M. , Harris L. P.
Published: April 2005

The conventional pyrometric measurement of wall, electrode, and probe temperatures through an alkali-vapor atmosphere (which is, in part, cooler than the surface) has been found to lead to significant under-estimation of the temperature. The error arises from optical absorption of the alkali-vapor dimers in the region of the pyrometer passband. As an example, the observation through 6 cm of saturated potassium vapor of a surface whose brightness temperature is 2500°K results in an error of from 50° to 500°K as the vapor temperature varies from 300° to 370°C. Thus, substantial errors may be introduced into the determination of properties such as electrical conductivities and reaction rates, which are exponentially dependent upon temperature. The reciprocal-temperature error was found to be roughly proportional to the dimer optical depth, and agreed with theoretical predictions utilizing dimer optical absorption coefficients measured during these experiments.
Nernst Effect in n-Type GaSb
Authors: Silverman S. J. , Carlson R. O. , Ehrenreich H.
Published: April 2005

The Nernst coefficient, the Hall coefficient, the electrical resistivity, and the Seebeck coefficient have been measured on Te- and Se-doped GaSb between 60° and 800°K. The two minima conduction band model, as applied to the present group of measurements, provides a qualitative description of conditions under which certain scattering mechanisms will dominate the transport phenomena.
Power and Efficiency Considerations in Continuous Laser Operation
Authors: Frankl D. R.
Published: April 2005

Various factors entering into the continuous operation of optically pumped solid-state lasers are summarized. Numerical estimates for ruby and for Nd+++- activated materials in two types of optical systems suggest that several watts of output power should, ideally, be obtainable when pumping with a 1-kW Hg arc lamp.
A Circularly Polarized Maser Oscillator
Authors: Ogawa Toru
Published: April 2005

The frequency stability of a circularly polarized solid-state paramagnetic maser oscillator has been observed with the objective of obtaining the information needed to construct a frequency standard with a broad microwave spectral line. The beat frequency between two such masers by using ruby can be made almost free from the variation of the static magnetic field and of the angle between the crystalline axes and the static magnetic field. The stability of the 1.5-Mc beat frequency is approximately 10−6 for short time intervals, and is approximately 10−5 for long time intervals. The short-time stability is limited mainly by the fluctuation of the cavity resonant frequency in the liquid helium. The long-time stability is determined by the drift of the pump frequency, although the reason for this interrelation is not thoroughly understood. The effect of reflections from the load on frequency is considerably reduced by the unidirectional structure used here, as compared with that to be expected with a reflection type of maser. We also show that the unidirectional maser amplifier can be built with reduced cross section by utilizing dielectric-loaded circular waveguide.
Gaseous Optical Maser with External Mirrors
Authors: Polanyi Thomas G. , Watson William R.
Published: April 2005

Radiation patterns obtained with He–Ne masers employing mirrors external to the discharge region are described. Operation was obtained with discharge tubes having Brewster angle windows, windows perpendicular to the optical axis, two spherical, one flat and one spherical, and two flat mirrors. Mode selection by using obstacles interposed in the cavity is described. It is shown that the radiation pattern is established within a very small region of the cavity. Comparisons of lasers operating with external and internal mirrors show that the lack of azimuthal symmetry of the radiation patterns is intrinsic to the spherical mirror geometry and not to the Brewster angle windows.
Optical Properties of Powders. Part I. Optical Absorption Coefficients and the Absolute Value of the Diffuse Reflectance. Part II. Properties of Luminescent Powders
Authors: Melamed N. T.
Published: April 2005

The optical properties of powders are determined for the case of particles, large compared with the wave-length of light. The solution for the diffusion of light in a quasi-infinitely thick powder is applied to relate certain measurements obtained on powders with the corresponding properties of the bulk material.

In Part I, the diffuse reflectance R of a powder is first derived in general form in terms of the parameters of the individual particle, taking into account both internal and external scattering. Parameters are then obtained for a model for randomly shaped particles, and used to relate the diffuse reflectance to the optical absorption coefficient, the index of refraction, and the particle diameter. The relationship is compared with measurements on materials of different refractive indices.

Part II deals with applications to luminescent powders, the calculation of the characteristics of emission in the presence of optical absorption, and the calculation of cascade transfer yields.
Dislocations and Etch Figures in High Purity Zinc
Authors: Brandt R. C. , Adams K. H. , Vreeland T.
Published: April 2005

A method of etching high purity zinc single crystals to reveal various etch figures on {101̄0} planes is presented in the preceding paper. The procedure involves the introduction of mercury to the crystal surface prior to a chemical polish with dichromic acid. The mercury was found to be concentrated at the etch figures. This paper presents the results of several experiments which support the conclusion that there exists a one-to-one correspondence between etch figures and dislocations. Some observations of slip on (0001) basal planes and {12̄12} pyramidal planes, and of twinning in zinc are also presented.
Symmetry Limitations to Polarization of Polycrystalline Ferroelectrics
Authors: Redin R. Daniel , Marks Graham W. , Antoniak Charles E.
Published: April 2005

The general integral for the determination of the average resultant polarization P̄ in the direction of the applied polarizing electric field is evaluated under the assumption that the spontaneous polarization vector of each crystallite is limited to a highly symmetric set of directions. With the further assumption that a ferroelectric crystal has a structure which is a slight distortion of a nonpolar structure, expressions for P̄ are given which may be applied to any set of allowed polarization directions which is likely to occur; each of the 22 nonpolar crystal classes yields one such expression. The special cases of interest for each of the 10 polar classes are evaluated. A general expression for P̄ as a function of electric field strength is obtained and used to determine hysteresis curves for several commonly occurring special cases. The angular distribution of polarization vectors after complete polarization is also discussed for these special cases.
Electronic Conduction in Glass
Authors: Nelson R. C.
Published: April 2005

When a beam of electrons from a gun is used to inject carriers into glass, two regimes of conduction can be distinguished: one in which the current in the glass is proportional to the beam current; and another, at higher beam currents, in which the current in the glass remains constant as the beam current increases. In the proportional regime an electron beam retardation experiment can be carried out, indicating a surface electron affinity of approximately 4.5 eV. The photoemission of electrons from a glass surface has a threshold at about the same energy. The electronic conductivity of glass is interpreted as being due to carriers injected from the electrodes moving by a thermally activated conduction process. These results are consistent with the author's explanation of the dye-sensitized photoconduction in glass.
Numerical Determination of Ion Paths in Nonhomogeneous Magnetic Fields
Authors: Lilly A. C. , Weismann T. J. , Lowitz D. A.
Published: April 2005

A practical numerical method for the determination of ion trajectories in the midplane of nonhomogeneous magnetic fields utilizing a computer program is discussed. The method of determining the field profiles and a comparison of the computed and experimental focusing properties of the field in the design of a double focusing mass spectrometer are treated.
Diffraction of Light by Domain Structure in Ferromagnetic CrBr3
Authors: Dillon J. F. , Remeika J. P.
Published: April 2005

Thin sections of the ionic ferromagnet CrBr3 are transparent to visible light. Below the Curie point, in the demagnetized condition, these sections possess a fine-grained domain structure in which the characteristic distance is comparable to the wavelength of visible light. We find that near 5000 Å the optical properties of this material are closely associated with the magnetic properties, and the modulation in magnetization direction which constitutes the domain structure has an associated modulation in the optical properties. This modulation constitutes a grating which gives rise to readily observed diffraction rings. Such a large fraction of the green light is diffracted that meaningful absorption measurements can only be made if the domains are removed by saturation. Spacings deduced from the size of the diffraction rings may be compared with domain theory, as well as used in the detailed interpretation of nuclear magnetic resonance results. The study of these rings constitutes a new technique for the investigation of domain structure.
Voltage-Annealing of Radiation Damage in Tunnel Diodes
Authors: Roth H. , Bernard W. , Zeldes P. , Schmid A. P.
Published: April 2005

A unique radiation-damage annealing process has been observed at 78°K in tunnel diodes bombarded with high energy electrons. Approximately one half of the radiation-induced excess current in germanium tunnel diodes can be permanently removed by application of forward bias voltages. This ``voltage-annealing'' effect arises from the enhanced migration of charged lattice defects under the influence of the high electric fields present in degenerate semiconductor junctions. A tentative model, based on known deep-lying radiation damage levels, is proposed. Under suitable conditions of forward bias, a charged interstitial can be dissociated from its adjacent paired vacancy, allowing the now isolated interstitial to be swept from the junction region with an estimated activation energy of 0.25 eV.
Hyperfine Interactions in Rare-Earth Metals
Authors: Bleaney B.
Published: April 2005

Estimates of the hyperfine interaction constants for the rare-earth metals are compiled from electron spin resonance and electron-nuclear double resonance data on salts, and atomic beam measurements on free atoms. Correction terms for second-order effects of the hyperfine structure are considered and shown generally to be small. Comparison with the experimental data (mostly from specific heat measurements below 1°K) shows close agreement in all cases except praseodymium, which is known not to have a co-operative phase. The temperature independent susceptibility of this metal below 4°K can be explained using a ferromagnetic exchange interaction of reasonable size, and the source of the observed hyperfine specific heat is discussed. In neodymium and samarium it is likely that crystal field effects are more important than exchange in determining the ground state in the co-operative phase.
Antiferromagnetism in NiTiO3
Authors: Heller Gerald S. , Stickler John J. , Kern Sanford , Wold Aaron
Published: April 2005

The effective internal field in NiTiO3 as a function of temperature has been determined from zero-field resonance absorption in a powder sample at millimeter wavelengths. Assuming a g value of 2, the resonant frequency (187 kMc) leads to an effective field at 4.2°K of approximately 67 kG. The temperature dependence fits within experimental error a Brillouin function for S = 1, with a Néel temperature of 22°K. From dc susceptibility data, a Néel temperature of 23°K is obtained and an exchange field of approximately 270 kG is computed. These data yield an out-of-plane anisotropy of about 8.3 kG.
Dynamic Effects of the Suhl-Nakamura Interaction in Magnetic Materials
Authors: Pincus P. , De Gennes P. G. , Hartmann-Boutron F. , Winter J. M.
Published: April 2005

In a magnetic material, the nuclear spins are coupled via the exchange of virtual spin waves (Suhl-Nakamura interaction). This long range interaction is known to contribute to the nuclear transverse relaxation time. It also gives rise to a depression of the nuclear resonance frequency and in fact to a complete nuclear spin-wave spectrum. This spectrum is well defined even when the nuclear spins are far from saturation. In materials of sufficiently high concentrations of nuclear spins and at sufficiently low temperatures (helium range) nonlinear effects may occur in the nuclear resonance signal, as have been observed by Heeger, Portis, and Witt in KMnF3.
Antiferromagnetic Resonance in Hydrated Copper Salts
Authors: Date Muneyuki , Nagata Kazukiyo
Published: April 2005

The antiferromagnetic resonance in CuCl22H2O and LiCuCl32H2O were investigated experimentally using centimeter and millimeter microwaves at liquid helium temperature. Detailed study of a single crystal of CuCl22H2O shows a small deviation from the Nagamiya—Yosida theory and is explained by introducing an anisotropic exchange interaction. Similar results are presented for CoCl26H2O. Hysteresis of spin flopping at Hc was observed and a possible mechanism is discussed. Main feature of the antiferromagnetic resonance LiCuCl32H2O can be explained by the present theory as well as in CuCl22H2O.
Hyperfine Fields and Magnetic Moments in the Fe–Rh System
Authors: Shirane G. , Chen C. W. , Flinn P. A. , Nathans R.
Published: April 2005

Hyperfine fields and isomer shifts of Fe57 in the Fe–Rh system have been measured by the Mössbauer technique in the composition range between 0 and 52 at. % Rh. When the Rh concentration exceeds 25%, chemical ordering of CsCl type develops and two distinct hyperfine fields are observed, corresponding to Fe on Fe sites (Fe I) and Fe on Rh sites (Fe II). For example, Hi(I) = 277 kOe and Hi(II) = 384 kOe in an alloy containing 48% Rh. Neutron diffraction study of this alloy gives μFeI = 3.2 μB and μRh = 0.9 μB. It is suggested that Fe II, which is surrounded by 8 Fe nearest neighbors, may have a smaller magnetic moment than Fe I despite its higher hyperfine field. These results are consistent with a model in which the polarization of conduction electrons is negative and its magnitude is reduced when rhodium replaces iron as nearest neighbors.
Internal Magnetic Fields and the Saturation Magnetization of Iron—Aluminum Alloys
Authors: Friedman E. A. , Nicholson W. J.
Published: April 2005

Internal magnetic fields in several iron—aluminum alloys ranging in composition from 19 to 28 at. % aluminum have been measured in a Mössbauer absorption experiment. In the composition range 22% to 26% aluminum three distinct internal magnetic fields were observed. At 300°K the magnitudes of these fields are in the ratio 1.00:0.88:0.72. In a 19% alloy only the two larger fields were observed, while in a 28% alloy only the largest and smallest fields were seen. The largest and smallest fields are the previously observed internal magnetic fields at iron atoms having, respectively, 8 and 4 iron nearest neighbors in an Fe3Al structure. The 0.88 field is attributed to iron atoms surrounded by 5 iron nearest neighbors in an Fe13Al3 structure. Using the known relation between the internal magnetic field and the atomic moment and the supposition that an iron atom with 3 iron nearest neighbors has no aligned moment, saturation magnetization curves of the iron—aluminum system have been calculated on a statistical basis under various known ordering conditions. In the case of annealed alloys, this calculation yields a saturation magnetization curve which agrees with measurements within experimental accuracy. The measured differences between the saturation magnetization of quenched and annealed alloys are also reproduced in these calculations. In the case of cold-worked alloys, good agreement with experiment is similarly obtained.
Increasing the Kerr Magneto-Optic Effect in Thin Films
Authors: Kolk A. J. , Orlovic M.
Published: April 2005

The magneto-optic rotation of light reflected from thin ferromagnetic films has been found to depend on the optical properties of the substrate as well as the optical properties of the ferromagnetic material. Rotations greater than the thick film longitudinal Kerr rotation were observed at certain thicknesses of ferromagnetic films deposited on silver surfaces.
Checkerboard Domain Patterns on Epitaxially Grown Single-Crystal Thin Films of Iron, Nickel, and Cobalt
Authors: Sato H. , Toth R. S. , Astrue R. W.
Published: April 2005

Domain structures of epitaxially grown single-crystal thin films of iron, nickel, and cobalt are investigated by the Bitter pattern technique. In the case of iron and cobalt films of (001) orientation, checkerboard patterns are observed, from which the sign of the anisotropy constant can be determined. In the case of nickel, however, no such regular patterns were observed. On Ni films with (110) orientation, however, one can observe an elongated domain in the [110] direction. This seems to indicate that a [100] wall has a higher energy than a [110] wall. The 180° walls in thin films are unstable and tend to have fine structures.
Wall-Wall Interaction between Thin Magnetic Films
Authors: Fuller Harrison W. , Lakin Lynda R.
Published: April 2005

Interactions between parallel Néel walls in sandwich-type films were measured by transmission electron microscopy. A lower limit for the true interaction field was measured to be 3 Oe for two 100-Å films of 80–17–3 Ni–Fe–Co separated by a 100-Å layer of carbon. This experiment was limited by the coercive force of the two films. A locked-in wall and domain configuration is described which prevented destruction of interacting walls. Escape fields in excess of 33 Oe (upper limit of the experimental apparatus) were measured for this type of structure. Based on the pair of linear dipoles model, the calculated escape field is 425 Oe. Other models, based on the interaction between linear dipoles and a uniformly distributed sheet-of-charge dipole, give similarly high escape fields. It is shown that the maximum interaction energy approaches the wall energy in magnitude, so that the effect on individual wall energies and widths resulting from the interaction of two walls should be included, although the effect of the interaction on the walls is shown to have a minor effect on calculated escape fields.
90° Magnetization Curling in Thin Films
Authors: Hornreich Richard M.
Published: April 2005

A 90° curling of the magnetization is found in magnetic films of 550 Å and less. This rotation takes place in a distance of the order of tens of microns. It provides a basis for the explanation of at least three distinct phenomena, the absence of closure domains at the film edge, the ending of domain walls before the film edge is reached, and the structure of 360° walls. Other experiments dealing with the motion of domain walls can also be explained on the basis of magnetization curling. Experimental curling distances at film edges are compared with those found from a theoretical model. The qualitative and quantitative experimental evidence is in reasonable agreement with theoretical predictions.
Hard Magnetic Films of Co–Ni–P
Authors: Bate G. , Speliotis D. E.
Published: April 2005

Films of Co–Ni–P with thicknesses from 0.020 to 3 μ and showing unusual magnetic properties have been prepared by electrodeposition onto polished brass substrates. The crystallite size was very small (∼100 Å); no crystallographic orientation could be detected. The coercivity, in the range 375–600 Oe, increased steeply with thickness from 0.020 to 0.1 μ, then decreased logarithmically with increasing thickness. The remanence coercivity behaved similarly. The ratio of remanent intensity to saturation intensity was high (∼0.70–0.80), the sides of the loop were almost vertical, and yet the films were completely isotropic in the film plane. This combination of properties in films of high coercivity is difficult to explain in terms of existing theories of magnetization reversal. Torque curves were measured and showed a weak sinθ dependence at fields less than the coercivity and a weak sin2θ dependence at higher fields. Graphs of rotational hysteresis W as a function of applied field had a shape which was, in general, independent of film thickness. The peak occurred at about 600 Oe and the maximum anisotropy field was ∼6500 Oe. Calculation of the rotational hysteresis integral ∫ 0∞WIs(1H)gave values which ranged from 1.9 for the thin films to 4.8 for the thicker ones. Models for magnetization-reversal processes in these films are discussed.
Ferromagnetic Resonance in Thin Films with Perpendicular Fields at Radio Frequencies
Authors: Hasty Turner E.
Published: April 2005

Ferromagnetic resonance absorption in thin Permalloy films has been studied at frequencies from 1 to 50 Mc with the steady magnetic field applied perpendicular to the plane of the film. This technique provides a direct means of measuring the saturation magnetization since the rf resonance absorption occurs when the applied field is equal to 4πM+Hk. The main problem with this experiment is that of keeping the film oriented so that at least parts of it are exactly perpendicular to the applied field. A misorientation of 20 sec causes the precession frequency at H = 4πM+Hk to shift from zero to 90 Mc. This problem was overcome by using a cross modulation field.

The width of the absorption line at 2 Mc for a typical film was 22 Oe. The linewidth increased with frequency until a maximum width of 65 Oe was observed at 15 Mc. As the frequency was increased past this, the linewidth began to decrease and a number of subsidiary absorption peaks began to appear below the main line. This behavior is attributed to the roughness of the film surface.
Magnetic Properties and Crystal-Structure Transformation of the Ordered Alloy (MnRh)
Authors: Kouvel J. S. , Hartelius C. C. , Osika L. M.
Published: April 2005

The magnetization and electrical resistivity of the ordered alloy MnRh were measured during a complete temperature cycle between 4.2° and 700°K. At all temperatures the magnetization is proportional to field. From 700°K down to about 170°K, the susceptibility rises according to a Curie-Weiss relation, χ=C(T−θ)−1, where θ≃−260°K and C gives an average effective atomic moment of about 3.3 μB, and the resistivity decreases slowly, yielding a large spin-disorder term, about 85 μΩ-cm, when extrapolated linearly to 0°K. This classical paramagnetic behavior is identified with the ordered cubic (CsCl-type) phase of this alloy. Below 170°K the susceptibility and resistivity decrease very rapidly and then gradually level off at lower temperatures, reaching values of about 5×10−6 emu/g and 6 μΩ-cm, respectively, at 4.2°K. The subsequent return of these properties to their original values at higher temperatures reveals a large temperature hysteresis in this transition. It is discovered from x-ray diffraction measurements below room temperature that this transition corresponds to a transformation to an ordered tetragonal (CuAu-type) structure, accompanied by a density increase of over 2%. The small temperature-independent susceptibility and small residual resistivity of this low-temperature tetragonal form of MnRh suggest it is a strong antiferromagnet.
Adiabatic Magnetization of Antiferromagnets
Authors: Joenk R. J.
Published: April 2005

Spin-wave theory was used to determine the magnetic field dependence of the thermodynamic properties of cubic or uniaxial antiferromagnets at temperatures well below the Néel point. These properties were found to be exponentially increasing functions of applied field for values of H0 less than the critical spin-flopping field. This field dependence suggests that if spin wave effects are dominant an antiferromagnet can be cooled by adiabatic magnetization in contradistinction to the paramagnetic case of cooling by demagnetization. (The phenomenon of antiferromagnetic cooling by isentropic magnetization was recognized many years ago.) Both lattice and nuclear effects can alter the situation in a real material and were included in this investigation. The dependence of adiabatic magnetization cooling on the physical quantities characterizing the antiferromagnet is discussed and theoretical temperature changes for several uniaxial antiferromagnets are given.
Magnetic First-Order Phase Transition and Anisotropy in Single-Crystal MnAs
Authors: De Blois R. W. , Rodbell D. S.
Published: April 2005

The experimental and theoretical effects of magnetocrystalline anisotropy upon the magnetic first-order phase transition in the compound MnAs are here described. A 3°C orientation-dependent difference in the transition temperature is observed near 20 kOe for a single-crystal specimen. Anisotropy measurements using Shenker's method give anisotropy sums, ΣnnKn, varying from −11.9×106 ergs/cm3 at 77°K to −5.6× 106 ergs/cm3 at 314°K, where Kn are the anisotropy terms in the energy representation, EK=ΣnKn sin2nθ, that is appropriate for this hexagonal material. A separate method gives an anisotropy field of 18.3 kOe at 35°C. Data analysis indicates that three constants, K1, K2, and K3, are needed to describe the anisotropy. Their values at 35°C are −5.75, +1.5, and −1.15×106 ergs/cm3, respectively. Theoretical checks using the magnetic form of the Clausius-Clapeyron equation are in close accord with the experimental data and the determined constants.
Thermal Properties of Dysprosium Aluminum Garnet near the Néel Temperature
Authors: Ball M. , Leask M. J. M. , Wolf W. P. , Wyatt A. F. G.
Published: April 2005

Measurements of the specific heat of Dy3Al5O12 at temperatures between 1.2° and 4°K are described. A sharp λ anomaly was found at 2.49°K, and this is discussed in terms of an unusual type of antiferromagnetic ordering previously deduced from magnetic susceptibility and resonance experiments. Two different estimates are made of the mean interaction energy, and these show that about 70% of the total interaction is due to magnetic dipole-dipole coupling. An estimate of the entropy is in excellent agreement with the assumption that the Dy3+ ions may be described in terms of only one Kramers' doublet S′=½.
Direct Observation of Rotational Switching in Polycrystalline Ferrite Materials
Authors: Elfant Robert F.
Published: April 2005

The high-field switching mechanism of polycrystalline ferrite material is investigated. Direct experimental evidence for rotational switching is obtained by observing the charges in the longitudinal and transverse components of the magnetization, for a long (L=1.33 cm), thin-walled (o.d.=0.05 cm, i.d.=0.028 cm) ferrite tube, during the reversal process. For a 10-Oe circumferential pulse field in the presence of a 4.3-Oe longitudinal bias field, it is found that at least 30% of the total magnetization reverses by a rotational process.
Dynamic Squareness in Polycrystalline Garnets
Authors: Lovell B. W. , Epstein D. J.
Published: April 2005

Certain samples of polycrystalline yttrium iron garnet and lutetium iron garnet have previously been found to acquire a square 60-cps hysteresis loop when cooled to 78°K in a magnetic field. It is found that these are not normal square-loop materials, for at sufficiently slow excitation (ca. 0.5 cps for yttrium iron garnet, one cycle per hour for lutetium iron garnet) they revert to normal, but strongly frequency-dependent loops. At 78°K, for proper amplitude step excitation, the response of these cores is a delayed pulse. For lutetium iron garnet this delay can be several hundred μsec in duration. The behavior of these materials can be qualitatively explained by domain wall instability produced by a diffusion after-effect mechanism.
Flux Switching in Overdriven Multipath Cores
Authors: Nitzan D.
Published: April 2005

Flux-switching phenomena characteristic to multipath cores result from the dependence of switching in one leg (a physical branch between the core junctions) on switching in the others. Reversible Δφ in a leg driven far into saturation may cause appreciable irreversible Δφ in other legs. This effect is analyzed by tracing the variations of φ and F of each leg of a three-leg core under two conditions: a positive drive on an inside leg, and a negative drive on an outside leg. Due to variations in air-flux linkage, a tight winding on the driven leg minimizes this effect. Upon termination of the drive pulse, the legs are shown to be left in a ``stressed'' state; i.e., a residual H field, sustained by magnetic poles near the leg junctions, remains in each leg.
Spin-Wave Resonance in Films Magnetized Parallel to the Surface
Authors: Wolf Peter
Published: April 2005

A theoretical analysis is presented for spin-wave resonance in thin ferromagnetic films magnetized in the plane of the film by a dc field. It is shown that, at very high frequencies, a spin-wave resonance spectrum occurs if a suitable surface anisotropy is present.

The analysis is based on the Landau—Lifshitz equation and Maxwell's equations. Both surfaces of the film are assumed to possess uniaxial surface anisotropies of equal magnitude with the axes normal to the plane of the film. Magnetization precession is excited by a weak rf field applied in the plane of the film but perpendicular to the dc field and equal at both surfaces of the film.

The boundary conditions for the magnetization1 are different for the oscillating component Mn normal to the film and the component Mp in the plane of the film. The component Mn is influenced by the surface anisotropy and, therefore, more or less pinned at the surfaces. However, the surface anisotropy has no influence on the component Mp, and accordingly, the derivative of Mp with respect to the normal direction vanishes at the surfaces. To fulfil these and the electromagnetic boundary conditions, three linearly independent wave solutions of the Landau—Lifshitz equation and Maxwell's equations are required.

The amplitude of the spin-wave modes and their spacing depends not only on the surface anisotropy constant Ks but also on the frequency ω of the rf field. At frequencies ω, much smaller than 4πMγ the precessional cone is very flat with Mn<<Mp. In this case the influence of the surface anisotropy is weakened and the rf field can strongly excite only one spin-wave mode, the slightly disturbed uniform precession. The other modes are weak. At frequencies equal to or higher than 4πMγ, the cone of precession becomes nearly circular with Mn ≈ Mp, and the pinning action of the surface anisotropy increases correspondingly. At these higher frequencies, two modes are excited strongly.

Theoretical absorption curves for Permalloy films with 4πMγ ≈ 2π·30 Gc are calculated for two frequencies and a range of thicknesses. For the surface anisotropy constant a value of 1 erg/cm2 is chosen. At 10 Gc only one strongly excited mode is predicted. At 30 Gc two modes have large amplitudes. The amplitude of one mode increases with increasing film thickness, whereas the amplitude of the other mode remains approximately constant. This theoretical result is similar to the experimental findings of Chen and Morrish2 at 24 Gc which, however, the authors explained in terms of stratified layers within the film.