bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic Properties of Some Compounds with Pyrite Structure
Authors: Adachi K. , Sato K. , Takeda M.
Published: February 2004

The magnetic properties of the dichalcogenide compounds with pyrite structure, CoS2, CoSe2, NiS2, NiSe2, and Co(SxSe1−x)2 were studied by means of magnetic measurements, neutron diffraction, NMR, and electrical resistivity in order to discuss their physical properties. Results obtained are as follows: CoS2 is a ferromagnetic with TC=124°K, θp=220°K, peff=2.13 μB, n=0.84 μB (at 0°K), and the exchange interaction J was estimated to be 24 cm−1 from the analysis of the low-temperature thermomagnetic curve. The internal magnetic field was observed to be 52 kOe at 80°K by NMR measurement. CoSe2 is an antiferromagnetic with TN=93°K, θp=−160°K, peff=2.20 μB; MnSe2 type antiferromagnetic spin ordering was determined by neutron diffraction at 53°K. NiS2 has an antiferromagnetic susceptibility with θp≃ −740°K and peff≃3.0 μB, but no magnetic ordering was observed by neutron diffraction at 53°K. NiSe2 exhibits weak constant paramagnetism, χM≈2×10−4 emu/mole. Co(SxSe1−x)2 forms a complete solid solution (0≤x≤1) with cubic pyrite structure and without ordering of S and Se. The magnetic phase diagram was determined, and the ferromagnetic region was found to exist up to 12% of Se at 0°K. The magnetic parameters of this system were determined and they show the so-called ``low spin state'' of cobaltous ion with one Bohr magneton. Electrical resistivities for the above compounds were semiconductive except for NiSe2 (metallic).

The theoretical and the experimental values of kTC/J for CoS2 (fcc, S=½) were compared. The experimental value was found to be 3.6. According to the result of the series-expansion method for the Heisenberg model, kTC/J was found to be 4.170 (kTC/J=6.00 for the Weiss approximation). It is concluded that the main origin of the discrepancy between theory and experiment is the influence of the more distant neighbor antiferromagnetic exchange interactions. The narrow ferromagnetic region in the Co(SxSe1−x)2 is explained by a statistical theory.
Multiplet Structure in the Absorption Spectrum of Eu2+
Authors: Freiser M. J. , Methfessel S. , Holtzberg F.
Published: February 2004

The Eu2+ ion in alkaline earth fluorides produces two broad absorption bands arising from 4f−5d transitions. The band at 3 eV has a structure with six resolved peaks. This structure is independent of Eu concentration. This band is attributed to transitions from the 4f7(8S) ground state to 4f6(7FJ) 5eg, the peaks being associated with the different J values in f6(7F). The higher energy band in the fluorides and the absorption band in the europous chalcognides are correspondingly attributed to 4f6(7FJ) 5t2g states. With this model, with 7FJ intervals obtained from the resolved structure in the EuF2 data, and from the experimental oscillator strengths of the observed absorption bands, the 4f−5d radial integral is calculated and a consistent set of values of 0.23±0.01 Å obtained. The Faraday and Voigt magneto-optic effects are calculated for EuF2 at 4330 Å. The room-temperature Verdet constant is −7.1 min/Oe·cm as compared with the experimental value of −6.6 min/Oe·cm. The Voigt birefringence at 15°K and 20 kOe is n∥−-n⊥=−2.0×10−4 while experiment gives −1.7×10−4.
Sublattice Rotations in Ferrimagnets: The Case of Pyrrhotite
Authors: Besnus M. J. , Munschy G. , Meyer A. J. P.
Published: February 2004

The molecular field model is used to analyze the sublattice rotations in a uniaxial two sublattice ferrimagnet, towards absolute saturation. In the particular case K, K′ <0 and (2K/M) + (2K′/M′) < −n (M1/2−M′1/2)2 with the field applied along the crystal axis, the two sublattices rotate directly towards absolute saturation with χ≃1/n as susceptibility. This model applies to pyrrhotite, Fe7S8, and explains its paramagnetic behavior along the hard axis, along with the simultaneous existence of a small spontaneous magnetization in the easy plane.
Magnetic Properties of Uranium Compounds with NaCl Structure
Authors: Grunzweig J. , Kuznietz M.
Published: February 2004

A model is proposed to account for the properties of uranium compounds UX, where X is either an element of the VA group (N, P, As, Sb; UV compounds) or of the VIA group (S, Se, Te; Uvi). Uv compounds are antiferromagnetic, while Uvi are ferromagnetic. All have high transition temperatures (50–220) °K and low electrical resistivities. It is assumed that uranium is in the U4+ state (3H4 configuration) both in Uv and Uvi compounds and the 5f electrons are strongly localized. The X anions are triply ionized in Uv compounds, and doubly in Uvi. The surplus electrons form a conduction band. The U ions are treated by the methods of ``crystal field'' theory. The coupling between them is via the RKKY mechanism. The coupling constant is calculated to be in the range of 12 to 22 eV Å3. In the octahedral field present the 3H4 multiplet splits, so that the ground state is a singlet. The observed saturation moment depends on the relative strength of the crystal field and the exchange interaction. The crystal-field splittings derived are in the range 500–1200 cm−1. The model accounts for the observed types of magnetic ordering. The assumptions used are justified briefly.
Magnetic Aftereffects in Ferrimagnetic Oxidic Spinels
Authors: Krupička S. , Závěta K.
Published: February 2004

The typical aftereffect spectra of ferrites and related oxides could usually be classified as due to either ionic (and vacancy) or electron processes. The present status of the study of these phenomena is outlined especially from the point of view of the underlying microscopic mechanisms. As an illustration, the results obtained with Mn–Fe and Mn–Cu–Fe oxidic spinels are presented. The magnetic-loss spectra were studied in a broad temperature range from 2° to 360°K and some additional measurements of induced anisotropy and permeability disaccommodation were performed. The role played in magnetic aftereffect by various valency states of the ions present is compared with electrical conductivity measurements. Three distinct relaxation bands of basically electronic origin were found in Mn–Fe spinels. The corresponding tanδ maxima for 105 Hz frequency range were situated at ≲2°K, 10°−50°K, and 90°−350°K, respectively, the exact temperature and related activation energies depending on the composition. These relaxation processes were ascribed successively with descending temperature to reorientations of Jahn-Teller distortions induced by Mn3+ ions stabilized by means of trapped electrons, to ordering of Fe-ion valencies by means of electron transfer, and to reorientation of unstabilized Jahn-Teller distortions of Mn3+ occupied octahedra.
Low-Temperature Electrical Resistivity of Pd and Pd–Ni Alloys
Authors: Schindler A. I. , Coles B. R.
Published: February 2004

Persistent spin fluctuations in strongly paramagnetic metals like Pd have been shown to give rise to electron-mass renormalization and concomitant enhancement of the electronic specific-heat coefficient. In addition, recent calculations of s-electron-spin-fluctuation interactions predict a term in the low-temperature electrical resistivity which should vary as A T2, where A is predicted to be proportional to the square of the paramagnetic spin-susceptibility enhancement. To test this theory, electrical-resistivity measurements were performed from 2° to 35°K on samples of Pd containing 0, 0.5, 1.0, and 1.66 at.%Ni. All of the samples are paramagnetic with susceptibilities which increase rapidly with the Ni content. A T2 dependence in the low-temperature electrical resistivity of all samples was observed; A was found to be 26, 114, 241, and 513×10−6 μΩ·cm/deg2 for the four samples, respectively. However, in contrast to theoretical predictions, A was observed to vary less rapidly than as the square of the magnetic susceptibility.
Influence of Spin Fluctuations on the Low-Temperature Electrical-Transport Properties of Pd and Pd–Ni Alloys
Authors: Rice M. J.
Published: February 2004

The electrical and thermal resistivities arising from s-electron scattering from itinerant d-band spin density fluctuations in nearly ferromagnetic transition metal systems like Pd and dilute Pd–Ni are investigated theoretically on a simple model for the spectral density function for the spin fluctuations.
Magnetic-Field Dependence of the Hyperfine Field at Fe in Dilute Fe–Pd Alloys
Authors: Blum N. A. , Frankel R. B.
Published: February 2004

The effect of external magnetic fields up to 130 kOe on the Fe hyperfine interaction in dilute Fe in Pd alloys has been studied using the Mössbauer effect in 57Fe. The samples were prepared by diffusing 57Co into Pd foil with and Fe impurity concentration of about 0.05% determined by mass spectrographic analysis. In two samples for which TC≈5°K and less than 1.2°K, the magnitude of the induced hyperfine field was observed to increase linearly from 300 to 308 kOe as the external field was increased from 20 to 130 kOe with the samples at 1.2°K. The data for these alloys are compared with the Mössbauer-effect observations of Craig et al.1 and Maley et al.2 as well as with the susceptibility measurements at high magnetic fields.3 The results are discussed in terms of recent models suggested by theoretical work involving Knight shift, exchange enhancement, and structure in the density of states. We have attempted to fit our data to a model proposed by Doniach and Murani,4 in which they take account of interaction effects between the Fe atoms leading to departures from the isolated ion Brillouin function dependence at low H0/T in the ``knee region'' of the curve, and in which they also suggest that there may be a Knight shift contribution of the order of 20%. Our low H0/T data are inconclusive in that they do not uniquely fit any proposed model, perhaps because there are too many adjustable parameters and still too large probable uncertainties. At large values of H0/T, however, we have clear evidence of the Knight shift. The slope, ΔHinduced/ΔHapplied, of the linear least-squared fit to the data in the saturation region (i.e., for H0/T>10 kOe/deg) is 0.07±0.005. Further details will be published elsewhere.
Low-Temperature Magnetization in Very Dilute Palladium-Iron Alloys
Authors: McDougald M. , Manuel A. J.
Published: February 2004

The magnetization curves of alloys containing 0.15, 0.10, 0.07, 0.05, and 0.01 at. % iron and two specimens of palladium of different purity have been measured in the temperature range 1.2° to 4.2°K in homogeneous fields up to 18.5 kG. The curves have been analyzed and expressed by an equation of the form σ= χH′+σL= χH′+σ0f(H′/T),where H′=H+Dσ is the sum of the applied field H and Dσ an internal field. The values of χ required are of the order of that for pure palladium and the values of D range from 6×103 to 8×103. The f(H′/T) corresponds closely to Brillouin functions with values of gJ ranging from 9 for the most dilute alloy to 20 for the most concentrated. A possible reason for this behavior is suggested. Curie temperatures have also been estimated for the alloys using the method described by Arrott (1957) restricted to values of σL for which the expansion in σL/σ0 is converging fairly rapidly. The Curie temperature found for the 0.15 at. % iron alloy is 2.12°K, agreeing well with the indications of resistivity and specific-heat measurements.
Local-Moment Saturation in a Dilute Giant-Moment Alloy
Authors: Graham L. D. , Schreiber D. S.
Published: February 2004

We have performed an investigation of the conduction-electron polarization in the paramagnetic state of dilute alloys of Co and Fe in a host matrix of platinum. This has been done by observing the nuclear magnetic resonance of the platinum host. Our measurements of Knight shift, linewidth, and relaxation time have been made as functions of impurity concentration (0.005–0.1 at. %), temperature (1.4°–300°K), and magnetic field (4–22 kG). We find that for small values of H/T the strength of the interaction between the conduction electrons and the local moments increases linearly with H/T. For higher values of H/T, but before saturation of the Brillouin function is expected to set in, we see a saturation of the linewidth with increasing 1/T, but not as a function of increasing H. We find the net shift of the center of gravity of the line is zero with respect to the Knight shift of pure platinum metal, and that the linewidth increases linearly with impurity concentration. These results provide evidence for interpretation in terms of a Ruderman-Kittel-Kasuya-Yosida interaction and a non-Brillouin-function saturation of the local moment.
Fe Hyperfine Fields in Dilute Pd–Fe Alloys
Authors: Skalski S. , Budnick J. I. , Lechaton J.
Published: February 2004

We have studied the 57Fe hyperfine field distribution in an alloy of 0.5 at. % Fe in Pd by NMR spin-echo spectroscopy at temperatures between 1.3° and 4.2°K. The Fe spectrum at 4.2°K is asymmetric. The asymmetry decreases and the frequency of the maximum increases as the temperature is lowered so that at the lowest temperature the Fe line is essentially symmetric about a value corresponding to a field of −299.7 kOe. The interpretation of this data in terms of an enhanced RKKY spin polarization model is presented. The temperature dependence of the maximum is fitted to a T3/2 law and a value of 34°K Å2 for the acoustic spin-wave stiffness constant in this alloy is obtained.
Alternating Antiferromagnetic Heisenberg Linear Chains
Authors: Duffy W. , Barr K.
Published: February 2004

Calculations are reported of the eigenvalue spectrum and thermodynamic properties of the spin Hamiltonian H=2 | J | ∑ i=1N/2(S2i·S2i−1+aS2i·S2i+1)+gβH ∑ i=1NSiz,where SN=SN+1, for the case of spin ½. Exact eigenvalues were obtained corresponding to N=4, 6, 8, and 10 and alternation parameter a=0.2, 0.4, 0.6, and 0.8. Ground-state energies, energy gaps, and absolute-zero magnetizations are discussed as a function of N and a. Infinite chain behavior as a function of a is inferred, and compared with various approximate calculations including perturbation theory results for small a and the Hartree-Fock calculation of Bulaevskiǐ.1

The zero-field internal energy, entropy, specific heat, magnetic susceptibility, and short-range order at absolute zero are calculated and compared with the well-known results for uncoupled pairs (a=0) and the regular chain (a=1) calculations of Griffiths2 and Bonner and Fisher.3

Experimental data on solid organic free radicals are compared with these theoretical results.

An expanded version of this paper will be published elsewhere.
Low-Lying Energy Levels and Magnetic Susceptibility of Thulium in the Garnets
Authors: Pearson J. J. , Herrmann G. F. , Buchanan R. A.
Published: February 2004

Susceptibility measurements on TmGaG, when analyzed in terms of a cubic crystal-field model, predict that there should be no excited energy levels lower than 104 cm−1 above the ground state.

Measurement and analysis of the spectrum of thulium in three different hosts, however, reveal the presence of levels lying well below 104 cm−1 and very sensitive to the detailed surroundings of the ion. A calculation of the energy levels of Tm3+ in the known crystal field for Yb3+ in the gallium garnet shows that a low-lying Λ5 triplet is split by the noncubic field to an extent which drastically affects the susceptibility. One is led to conclude that cubic models are insufficient for prediction of macroscopic magnetic properties in ions having degenerate cubic levels very near the ground state.
Effect of Dislocation Distribution on the Coercivity of Nickel Single Crystals
Authors: Geiss R. H. , Silcox J.
Published: February 2004

Single crystals of nickel have been deformed in tension into the three stages of the stress-strain curve. Thin wafers were cut with an acid saw on planes parallel and perpendicular to the primary slip plane for use in thin-foil electron microscopy and magnetic measurements. The Burgers vectors and densities of the dislocations have been determined in the electron microscope studies, while the dependence of the coercivity on the orientation of the magnetic field has been determined with a modified Foner magnetometer. Domain configurations at remanence have also been determined by Bitter techniques. The results show an anisotropy in the coercivity which is related to the dislocation structures observed in the electron microscope. In samples deformed into stage I and early stage II, a uniaxial magnetocrystalline anisotropy dominates the anisotropy in the coercivity. Later in stage II and in stage III the anisotropy in the coercivity is attributed to domain wall dislocation interactions.
Domains in Imperfect Crystals
Authors: Clark John R. , Leibovich Harry A.
Published: February 2004

Stacking faults in a crystal enable structures defined by crystallographic operations to be fitted together without filling space. If the displacement resulting from a succession of stacking faults is represented by a lattice vector or by a twinning vector the composite structure is arranged on a single lattice containing domains. Variations in domain configuration are reflected in the relative intensities in the x-ray diffraction pattern of the composite crystal. Changes in the diffracted intensities are observed when an external magnetic field is applied to a single crystal of iron.
Magnetization Curves of Fe–Ni (50–50) Single Crystals Ordered by Neutron Irradiation with an Applied Magnetic Field
Authors: Paulevé J. , Chamberod A. , Krebs K. , Bourret A.
Published: February 2004

Spherical Fe–Ni (50–50) single crystals were ordered by neutron irradiation at 295°C in the presence of a magnetic field. Magnetization curves and magnetic anisotropy energy measurements demonstrate the very important directional effect of the irradiation magnetic field on the bulk anisotropy of the single crystal. When the magnetic field is applied along a fourfold axis, the bulk magnetic anisotropy is tetragonal with a very large value for K3. When the magnetic field is applied along a three fold axis, the bulk magnetic anisotropy is cubic and the threefold axis becomes an easy axis of magnetization; the magnetization measured along the easy direction reaches saturation with a certain law of approach, while the magnetization measured along the [100] direction reaches saturation immediately. The model proposed by Néel, in which three types of quadratic ordered domains are assumed to be strongly coupled, fits well the experimental results. An electron microscopy image shows the different type of ordered domains and the superlattice spots.
The Fundamental Theorem of Fine-Ferromagnetic-Particle Theory
Authors: Brown William Fuller
Published: February 2004

The theory of fine-particle magnets is based on the theorem that the state of lowest free energy of a ferromagnetic particle is one of uniform magnetization for particles of less than a certain critical size and one of nonuniform magnetization for larger particles. The theorem is inferred from several approximate calculations and has not been proved rigorously. Rigorous statements can be made if one is content to replace equalities by inequalities and exact values of critical radii by upper and lower bounds. For a sphere of radius a with uniaxial anisotropy, it can be shown that the lowest-free-energy state is one of uniform magnetization if aac1 (for low anisotropy) or ac2 (for high anisotropy), where ac0, ac1 (>ac0), and ac2(>ac0) are determined by the exchange and anisotropy constants and the spontaneous magnetization. These bounds locate the critical radius to within about 12% at low anisotropy but only to within an order of magnitude or more at high.
Restoration of Motionally Narrowed Hyperfine Splitting in Superparamagnetic Particles by Magnetic Field
Authors: Eibschütz M. , Shtrikman S.
Published: February 2004

Mössbauer absorption spectra of 57Fe in ultrafine powders of NiFe2O4 were taken in external magnetic fields from 0 to 20 kOe at room temperature. A transition from a spectrum with no hyperfine field, Hhpf, to a Zeeman split spectrum of Hhpf=500 kOe has been observed. Comparison of the results with magnetization measurements suggest that the drastic effect of the external field is due to the polarization of the superparamagnetic particles by the field.
Ferrites as Contrast Material for Medical X-Ray Diagnosis
Authors: Frei E. H. , Gunders E. , Pajewsky M. , Alkan W. J. , Eshchar J.
Published: February 2004

The use of ferromagnetic contrast materials seem to offer advantages over barium sulfate in the x-ray diagnosis of gastrointestinal lesions. Most ferrites are inert inside living bodies. Magnesium ferrite, which has been found to be the most useful material tested so far, did not cause any adverse reactions. As a contrast medium it possesses the desirable characteristics of barium sulfate. Due to its magnetic properties, manipulation from the outside by a magnet allowed for easy control of the material during x-ray screening and satisfactory visualization of the stomach and the entire course of the small intestines in guinea pigs, dogs, and four human volunteers.
On the Theory of Charging of Aerosol Particles in an Electric Field
Authors: Liu Benjamin Y. H. , Yeh Hsu-Chi
Published: February 2004

Theories for the charging of aerosol particles by unipolar gaseous ions have been reviewed, and a new theory taking into account both the random thermal motion of the ions and the motion of ions induced by an applied electric field has been developed. The theories have been compared with the experimental data of Hewitt, and the results indicate that the new theory developed in this paper shows the best agreement with the experimental data over the entire range of conditions covered by the data, i.e., for particle size ranging from 0.09 to 0.46 μ radius, for electric field intensities ranging from 300 V/cm to 10 800 V/cm, and for the product N0t, ranging from approx 106 to 5×107, where N0 is the concentration of ions in number of ions per cc, and t is the charging time in seconds.
Exact Solution of Coil Forces for Uniform Transverse Field Magnet
Authors: Atherton David
Published: February 2004

An exact solution is obtained for the coil forces acting on the conductors of a magnet producing uniform transverse field and having crescentic cross-sectional coils. The solution is general and may be evaluated directly for any particular case without further integration or recourse to magnet tables. The solution is relevant to m.h.d. and bending magnets which approximate this shape. Examples are discussed.
Analysis of Materials by Electron-Excited Auger Electrons
Authors: Harris L. A.
Published: February 2004

The energy spectra of Auger electrons emitted from many elements and alloys have been observed. Differentiation of the secondary electron-energy distribution by perturbation and synchronous detection techniques, and suppression of the effects of low-energy secondaries, were used to obtain well-defined spectra. The Auger lines afford a sensitive indicator for light elements, though spectra for elements as heavy as gold have been obtained. Because the method examines only a superficial layer of the sample, it is useful for detecting contamination, surface migration, or segregation, and for diffusion studies. Cleaning of the surfaces is critical for useful analysis. Quantitative analysis is hindered by noise and the lack of known surface conditions for calibration.
Some Observations of Surface Segregation by Auger Electron Emission
Authors: Harris L. A.
Published: February 2004

Surface segregation of sulfur in nickel and steel, and of chromium and antimony in steel have been observed using an Auger electron method of analysis. The method provides a useful technique for studies of diffusion and segregation in solids.
Double Injection in Long Silicon p—π—n Structures
Authors: Mayer J. W. , Marsh O. J. , Baron R.
Published: February 2004

Current—voltage characteristics and electric field distributions have been measured in a series of long silicon p—π—n structures biased into the double injection regime. The I—V characteristics obey an I∝V2/L3 relation in which the magnitude of the current is predicted within a factor of two by the Lampert expression. As predicted by Baron (in the preceding paper) it is necessary to correct for diffusion effects. A first-order correction can be made by the use of an effective length Leff=L—Q(2La), where La is the ambipolar diffusion length. The field distribution approximates the Lampert region in the center (ε∝x1/2) bounded by exponential regions due to carrier diffusion from the n—π and p—π junctions. Detailed analysis indicates that the observed I∝V2 region was not due to pure high-level double injection, but rather exhibits the transition region due to both diffusion and thermal generation. Further, the measured lifetime is greater by about a factor of two than the lifetime required for an exact fit to the theoretical current—voltage characteristics and field distribution. The reason for this discrepancy might be due to the fact that high-level conditions were not reached.
Conductance Extrema in Metal—Insulator—Semiconductor Tunnel Junctions
Authors: Chang L. L.
Published: February 2004

The conductance in metal—insulator—degenerate semiconductor tunnel junctions is obtained and analyzed. Regions of various shapes of the conductance are determined by use of two reduced parameters. For relatively light degeneracy and high barrier, a conductance minimum occurs at the Fermi energy. Otherwise, a minimum may occur at a voltage equal to or smaller than the Fermi energy and an additional pair of extrema may exist, depending on the type of the semiconductor and the nature of the insulator band edges in providing the tunneling barrier.
Magnetic and Electrical Properties of Some Yb–Sb Phases
Authors: Bodnar R. E. , Steinfink H. , Narasimhan K. S. V. L.
Published: February 2004

The magnetic susceptibilities and electrical and thermoelectric behavior of YbSb2, YbSb, α-Yb5Sb4, β-Yb5Sb4, Yb4Sb3, Yb5Sb3, and Yb5Sb2 were investigated. The compounds YbSb and Yb3Sb4 have considerable trivalent ytterbium present; 0.89 and 0.26 electrons, respectively, have been removed from the 4f shell. The other phases are essentially diamagnetic and behave similarly to ytterbium metal. The resistivity of the phases containing trivalent ions is enhanced because of the possibility of s—f scattering. Yb5Sb2 is weakly paramagnetic, but has the highest resistivity because its crystal structure appears to have partially occupied ytterbium sites.
Stacking Faults in Hexagonal Gold—Cadmium Alloys
Authors: Sharan B. , Agnihotri O. P.
Published: February 2004

The x-ray powder spectra of three hexagonal gold—cadmium alloys containing 18, 19, and 20 wt% Cd show the anomalous broadening of reflections with h—k=3t±1 (l≠0) showing the presence of a large amount of stacking faults in these alloys. The analysis of line shape shows that in the 18-wt% Cd alloy, whose composition is nearest to the fcc phase boundary, has the greatest stacking-fault density. The stacking-fault probability is a decreasing function with an increasing electron-to-atom ratio.
A New Multipolar Mode in Bounded Gyrotropic Plasma
Authors: Bevc Vladislav
Published: February 2004

Multipolar modes in a cylindrical, axially magnetized, cold, collisionless plasma that propagate near the cyclotron frequency are studied quantitatively. Examination of electromagnetic field patterns shows that in addition to the well-known spectrum of cyclotron modes there exists at positive azimuthal eigenvalues (n>0 in expjnφ) a mode that is distinguished by a different type of field pattern. The electric field of this mode is predominantly solenoidal, in contrast with the cyclotron modes, where a substantial part of the electric field is lamellar. This mode may be of importance in thick-beam parametric amplifiers at microwave frequencies (X-band) and in beam—plasma interaction near cyclotron frequency.
Theory of Magnetization Ripple in Ferromagnetic Films
Authors: Harte K. J.
Published: February 2004

In a polycrystalline ferromagnetic film, the magnetization direction is not uniform but exhibits small wave-like fluctuations known as magnetization ripple. In this paper, a general theory of ripple is developed, extending previous treatments by the present author, Hoffmann, and others. The theory is applicable to almost any magnetic film without gross domain structure, containing randomly oriented local anisotropies arising from inhomogeneities on any scale and of any physical origin. The magnetization direction is assumed to fluctuate in the plane of the film only. In addition to local anisotropy fields, the theory includes the effects of magnetostatic and exchange interactions, and a uniform field that consists of uniform uniaxial anisotropy and external fields. Nonlinear magnetostatic and uniform fields, which in previous treatments have been either neglected or treated as small perturbations, are taken fully into account through third-order torque terms. The ripple spectrum is derived, and from it a physical picture of the ripple is obtained in terms of a coupled region which (except for very large-scale inhomogeneities) is an elongated rhombus with long axis perpendicular to the mean magnetization. The spectrum contains a nonlinear effective field, which is evaluated in several limiting cases determined by the scale of inhomogeneity, the film thickness, an exchange length, and a magnetostatic length. The magnetization dispersion (mean ripple amplitude) is also obtained for these limiting cases, but no attempt is made to calculate other measurable magnetic-film properties. The results show: a weakening of first exchange and then magnetostatic forces as the scale of inhomogeneity increases, with the consequence that the dispersion shows an increasing dependence on the uniform field; a weakened dependence of the dispersion on both the magnitude of the local anisotropy and the uniform field for large-amplitude, nonlinear ripple; and a thickness-independent ripple in the thick-film limit, where the magnetostatic field is given by its bulk value.
Thermopower in Thin-Film Copper—Constantan Couples
Authors: Chopra K. L. , Bahl S. K. , Randlett M. R.
Published: February 2004

The thickness dependence of the thermal emf of thin-film copper—constantan thermocouples at room temperature and above shows nearly bulklike behavior when the thickness of both elements comprising the thermocouple is greater than ∼1200 Å. The thermal response time of the thermocouples as measured with a pulsed laser beam heating source is less than 10-6 sec. The thickness-dependent contribution to the thermopower of copper films is deduced from the thermal emf data on thermocouples formed with a thick constantan film and compared with the size-effect theory based on the free-electron model. The marked thickness dependence observed yields anomalously high dependence (an order-of-magnitude higher) of the mean free path on the energy of electrons. This result is tentatively ascribed to the thermopower behavior of a transition layer formed by diffusion of the two components of the thermocouples.
Multipacting Discharges between Coaxial Electrodes
Authors: Woo Richard
Published: February 2004

Experimental evidence is presented to demonstrate the scaling relations of the similarity principle for multipacting as applied to coaxial electrodes with b/a (b and a are the radii of the outer and inner electrodes, respectively) varying between 2.3 and 18.26. The two field configurations considered are: (1) rf voltage applied to the electrodes and (2) rf and dc voltages applied to the electrodes. The modes of multipacting are also studied and identified.
Pressure Dependence of Barrier Heights in Ge–GaAs n—n Heterojunctions
Authors: Howard W. E. , Fowler A. B. , McLeod D.
Published: February 2004

The pressure dependence of barrier heights in Ge–GaAs n—n heterojunctions has been determined, for hydrostatic pressures up to 28 kbar, by means of electrical measurements. The results, expressed in terms of the pressure coefficient of the conduction-band discontinuity ΔEc, are d(ΔEc)/dP = (6.7±1.0) meV/kbar for junctions having both (100) and (110) orientations. This result is seen to be in approximate agreement with predictions based upon considerations of bulk band energies only. It is concluded that the pressure dependence of any dipole-layer contribution to ΔEc can be ignored. The results for d(ΔEc)/dP can then be used to obtain a value of - (6.8±1.0) eV for the dilatational deformation potential for the conduction band of GaAs.
Investigation of Fast-Neutron Radiation Damage in Nearly Perfect Copper Crystals by X-Ray Diffraction Techniques
Authors: Baldwin T. O. , Sherrill F. A. , Young F. W.
Published: February 2004

The effects of fast-neutron irradiation at about 40°C in nearly perfect copper crystals have been examined by x-ray diffraction techniques. Anomalous x-ray transmission (Borrmann) and Bragg reflection geometries were used to investigate the changes in diffracted intensities caused by defects produced by the neutron irradiation. Both Borrmann and Bragg peak intensities were reduced to values significantly below those for perfect crystals, and the reduction in the Bragg intensities was accompanied by a large increase in the diffuse scattering in the wings of the peak. It is shown that isolated point defects and the distortion associated with them would not account for the changes in x-ray intensities. Annealing studies indicated that both vacancies and interstitials were present in these crystals after irradiation, and all of the damage was removed by annealing at 500°C.
Electroluminescence from Ge-Doped GaP p—n Junctions
Authors: Shih K. K. , Pettit G. D. , Lorenz M. R.
Published: February 2004

The electroluminescence from GaP containing Ge has been studied. p—n junctions were formed by the liquid epitaxy method. The peak of the dominant emission from these diodes is near 1.96 eV at 77°K. The maximum external quantum efficiency at 77°K was 8%. The emission appears to involve Zn and Ge pairs even though these impurities were doped on opposite sides of the junction. It was not possible to ascribe any emission lines to recombination involving Te and Ge. Current, voltage, and intensity dependences of the diodes have been measured. The results indicate that radiative recombination between Zn and Ge at 77°K is predominantly in the space-charge region. At low currents, photon-assisting tunneling becomes important.
Calculations of Electron-Radiation Damage Rate as a Function of Depth in Silicon
Authors: Stevens P. R. C.
Published: February 2004

The distribution of electron-radiation damage defects with depth has been calculated from recent measurements of electron angular dispersion and energy loss in silicon combined with experimental measurements of damage rate as a function of electron energy. The results of the calculation are shown to be substantially in agreement with the experimental results of Hitchcock.
X-Ray Stress Topography of Thin Films on Germanium and Silicon
Authors: Schwuttke G. H. , Howard J. K.
Published: February 2004

X-ray stress topography of thin films deposited on single-crystal substrates is established. This method permits a nondestructive rapid analysis of the stress environment of film-crystal interfaces. It is based on dynamical diffraction phenomena that occur at such interfaces. This technique is principally useful for the measurement of the sign of the stress in film and/or substrate. It is used to detect stress buildups and stress reversals connected with processing procedures, in particular, with those of the planar semiconductor device technology. It is also an elegant way to measure the adhesion properties of thin films deposited on single-crystal slices as large as 2 in. in diameter. Dynamical diffraction phenomena of film-crystal interfaces are discussed in terms of the Penning and Polder theory and shown to be caused through tie-point migration. Topographical x-ray contrast of film-crystal interfaces is interpreted in terms of Bragg plane curvature. Relations between lattice curvature and film stress are given.
Microwave Breakdown in High-Temperature Air
Authors: Light G. C. , Taylor E. C.
Published: February 2004

A review of investigations of microwave breakdown in high-temperature air reveals significant discrepancies between theoretical expectations and experimental observations. Experimental measurements obtained in shock-heated air are presented to confirm the temperature dependence of ionization frequency previously observed. The data are examined with regard to the nonequilibrium thermodynamic state of the gas behind the shock wave. An explanation is offered that attributes the temperature effect to the temperature dependence of the electron-molecule energy-transfer rate, and a method for modifying the conventional theory to take account of this is indicated. The relevance of these results to antenna breakdown on reentry vehicles is discussed.
Excitation of Magnetoelastic Waves in YIG Delay Lines
Authors: Auld B. A. , Collins J. H. , Webb D. C.
Published: February 2004

The excitation mechanism based on the propagation of magnetoelastic waves in axially magnetized single-crystal samples of yttrium iron garnet (YIG), of nonellipsoidal geometry, is proposed for microwave delay lines. A qualitative theory is advanced that excitation takes place by electromagnetic energy being coupled to a spin wave through magnetostatic modes, driven at the minimum value of internal dc magnetic field. The theoretical model decomposes the guided wave propagation in a ferrimagnetic slab, between metal plates, into pairs of plane waves, which essentially propagate in an inhomogeneous and anisotropic medium. This theory is supported by experiments in which a YIG rod was precisely translated along the dc field axis, with respect to the coupling antenna. These experiments demonstrate that minimum insertion loss requires that a large transverse rf magnetic field exist at the end face of the rod, that loss increases monotonically when the coupler is moved away from the end face, and that no minimum of the insertion loss occurs when a large transverse field exists in the vicinity of the theoretical turning point.
Magnetically Induced Ordering in Nickel and Magnesium Ferrous Ferrites
Authors: Michel R. E. , Chapman F. W. , Poplawsky R. P.
Published: February 2004

Microwave measurements have been made at 9.5 GHz in the temperature range of 4.2°–30°K on a series of spinel single crystals with nominal compositions (M1−xFex2+Fe23+)O4; M is nickel or magnesium and x assumes values between 0.16 and 0.61. All samples developed a noncubic contribution to the anisotropy when cooled from above 30° to 4.2°K in the presence of a saturating magnetic field, the annealing field. The dependence of the fields for resonance at 4.2°K upon the orientation of the annealing field in the (110) plane is described by an induced uniaxial anisotropy energy of the form Ea=K′Σi cos2τi cos2τ′i, where τi and τi′ are the angles between the magnetization and the three cube-edge directions at the measuring and annealing temperature, respectively. The temperature dependence of the fields for resonance as the samples are warmed from 4.2°K indicates that there is an additional temperature dependent term in the anisotropy. For the compositions investigated the temperature Ta, above which all anneal effects vanish increases with increasing ferrous iron concentration from 12° to 24°K. Also, the magnitude of the induced anisotropy increases in a nonlinear manner with increasing ferrous ion concentration. The induced anisotropy is attributed to a magnetic ordering of distortions associated with the ferrous ions. The nonlinear increase of the induced anisotropy and the increase of Ta with increasing ferrous ion concentration are interpreted in terms of an interaction between these active centers.
Shock Compression of Foamed Graphite
Authors: Boade R. R.
Published: February 2004

Conventional high-explosive techniques have been used to determine the principal Hugoniots of two graphite foams for stresses up to about 190 kbar. The initial densities of the foams were 0.55 and 0.68 gm/cm3. Hugoniot data for each foam fall into two distinct domains, depending on the amplitude of the input shock wave. Continuous free-surface velocity measurements on the foam surfaces indicate that shock waves in the lower stress domains have two-wave structures. The inherent irregularity of the surfaces of the foams, however, prevented exact measurement of the properties of these two-wave structures. Results of further experiments which were designed to study loading and unloading from shocked states in the foam are consistent with the two-wave picture in the lower stress domains and also show that single shock waves exist in the higher stress domains. Data in the higher stress domains show an increase in specific volume with increasing stress. This ``bending back'' of the Hugoniot is attributed to increases in thermal energy which occur in the compression process. Estimates of Grüneisen's parameter have been made for the higher stress domains, where voidless states are believed to exist. The values obtained for Grüneisen's parameter as well as the general behavior of the Hugoniots suggest that the graphite-to-diamond phase transition occurs at the higher stresses.
Measurement of Charge Transfer in Electrographic Processes
Authors: Brodie I. , Dahlquist J. A. , Sher A.
Published: February 2004

This paper describes a pulse technique for measuring the properties and charge-transfer characteristics of electrographic receptors. This method has the unique capability, as compared with electrometer methods or ac bridge methods, of separately measuring the charge deposited on the surface of the dielectric layer, the displacement charge, and the charge passing through the dielectric. The technique is used to obtain a detailed analysis of the electrographic properties of a dielectric coated paper, including the relaxation of the paper substrate, the capacitances of the virtual air gap and the dielectric layer, and the threshold voltage for charge transfer.
Diffusion Instabilities in Semiconductors
Authors: Blötekjaer K. , Weissglas P.
Published: February 2004

When a strong electric field is applied to a high-conductivity, nearly intrinsic semiconductor, it has been shown that the effective diffusion coefficient may become negative and lead to an instability. The conditions for occurrence of this instability have been investigated in detail, and suitable materials for observation are suggested.
Vitreous Bi–Se Layers as Near-Infrared Photodetectors
Authors: Bowman D. L. , Schottmiller J. C.
Published: February 2004

The infrared photodetecting properties of new vitreous Bi–Se films are described. Such films are prepared by coevaporation and vapor quenching. A room-temperature D* value of 2×1011 cm/W·sec1/2 was measured at the peak sensitivity wavelength (∼1 μ) for an optimum composition film. Response times range between 0.3 and 3 msec. In addition, measurements were made of D* as a function of sample composition, incident photon flux, and temperature.
Lateral Wave on a Symmetrical Epstein Transition
Authors: Lang R. H. , Shmoys J.
Published: February 2004

A theoretical investigation is made of a lateral wave on a diffuse interface. Half of a symmetrical Epstein layer is used as the transition between a free half-space and an underdense plasma region. An electric current line source is placed in the free-space region and an exact integral expression is obtained for the reflected field. A high-frequency asymptotic approximation, uniform with respect to transition thickness, is then obtained for the reflected field. This approximation consists of two terms. The first of these terms can be interpreted as a reflected wave for arbitrary transition thickness, while the second term can be interpreted as a lateral wave contribution when the wavelength is much greater than the transition thickness, and as a reflected wave when the wavelength is much smaller than transition thickness.
Noise Suppression in a Space-Charge-Limited Gas Diode
Authors: Murray C. B. , van der Ziel A.
Published: February 2004

Noise suppression has been measured in a cylindrical gas diode under space-charge-limited current conditions and calculated for a parallel plane gas diode using the transport theories of van der Ziel and van Vliet. The shot-noise suppression theory and the older thermal-noise theories are shown not to hold in this case. The results should be directly applicable to the solid case under the conditions of a field-dependent mobility.
Flow of Polycrystalline Ice at Low Stresses and Small Strains
Authors: Bromer D. J. , Kingery W. D.
Published: February 2004

Tensile creep tests from −3° to −13°C at stresses between 2×105 and 2×106 dyn/cm2 with millimeter range grain-size polycrystalline ice showed that the strain rate was proportional to the stress, and that the viscosity was proportional to the grain size squared. The flow process had an apparent activation energy of 12 kcal/mol. Calculated diffusion coefficients were several orders of magnitude larger than directly measured diffusion coefficients for single crystals. Enhancement of the diffusion rate in a wide band adjacent to grain boundaries is believed to account for the observed behavior. Previously reported data for ice sintering are interpreted on the same model.
Negative Differential Photovoltages in ZnS Crystals
Authors: Shachar G. , Brada Y.
Published: February 2004

The intensity dependence of the anomalous photovoltaic effect was measured on ZnS crystals at room temperature and at 77°K. A decrease in photovoltage caused by an increase in illumination intensity was observed in many crystals. For all the investigated crystals, the short-circuit current was found to increase linearly with light intensity. These results are explained in terms of the general theory of photovoltaic effects. It is shown that a decrease in photovoltage caused by an increase in carrier concentrations is to be expected to occur in photovoltaic effects observed under the following conditions: (1) sample is under high-level excitation so that the thermal equilibrium carrier concentrations are negligible in comparison with the excess carrier concentrations. (2) The conditions at both contacts are identical (i.e., no contact effects). The decreases in photovoltages can be explained by the tendency of all the elementary photocells to saturate at high carrier concentrations. These considerations also furnish an explanation for a shift in the wavelength of photovoltage reversal, which was observed in many crystals. Various models for the explanation of the anomalous photovoltaic effect in ZnS crystals are discussed, with reference to the results presented.
Magnetic and Crystallographic Properties of Some Rare Earth Cobalt Compounds with CaZn5 Structure
Authors: Velge W. A. J. J. , Buschow K. H. J.
Published: February 2004

The magnetic and crystallographic properties of CaZn5-type intermetallic compounds of cobalt and rare-earth elements (including Th) have been investigated. Strong deviations from 1:5 stoichiometry are observed when the rare-earth radius becomes relatively small. Both the saturation magnetizations (4πIs=2360–12 300 G) and the crystalline anisotropies (HA=25–210 kOe) depend on the rare-earth component. The coercive forces have been studied as a function of the milling time. For SmCo5 and GdCo5IHc values larger than 13 000 Oe are observed. These high values are possibly due to small structural details in SmCo5 and GdCo5, if compared to the other compounds. First experiments for making permanent magnets by pressing fine powders of SmCo5 in a magnetic field have led to an energy product of 8.1×106 G Oe; the corresponding value for BHc is 5200 Oe.