bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic susceptibility and antiferromagnetism of dilute chromium-osmium alloys
Authors: Hedman L. , Moyer C. A. , Kelly J. R. , Arajs Sigurds , Kote G. , Garbe K.
Published: February 2003

The magnetic susceptibility χ of Cr–Os alloys containing 0.3, 0.6, 1.1, and 2.0 at.% Os has been measured as a function of temperature T between 4.2 and 600 K. The χ vs T curves exhibit a well defined knee at the Néel temperature TN. TN increases with Os content, in agreement with earlier determinations from electrical resistivity data. at the Néel temperature TN. TN increases with Os content, in agreenment with earlier determinations from electrical resistivity data. The rise of TN is consistent with expectations based on the rigid band model for these alloys. The measured susceptibility in the antiferromagnetic regime below TN is compared with that calculated using the two-band model for chromium. Variation in the size of the electron jack and hole octahedron upon alloying is taken into account within the rigid band approximation. The impurity and phonon-scattering contributions to the susceptibility have been included. Agreement between theory and experiment is good over most of the temperature range, although discrepancies are apparent at low temperatures.
Paramagnetic and antiferromagnetic susceptibilities of the Kimball model of antiferromagnetic chromium
Authors: Pattnaik P. C. , Fry J. L. , Brener N. E.
Published: February 2003

Historically the nesting vector obtained from a paramagnetic Fermi surface or from the maximum of the paramagnetic susceptibility, χ(q), has been used to determine the wave vector of the spin density in antiferromagnetic chromium and various transition metal alloys. The only self consistent calculation of the wave vector is the Kimball model for antiferromagnetic chromium (1). In the present paper χ(q) is computed in both the paramagnetic and antiferromagnetic versions of the model to examine the effect of the spin density wave on the susceptibility. The analytic behavior of χ(q) which is produced by antiferromagnetic gaps of the Fermi surface is investigated to explain changes in the peak structure of χ(q).
ac susceptibility and electrical resistivity of some dilute Pd Mn alloys
Authors: Ho S. C. , Maartense I. , Williams Gwyn
Published: February 2003

The ac susceptibility and electrical resistivity of several dilute Pd Mn alloys containing between 0.5 and 2.5 at. % Mn have been measured. The ac susceptibility, taken in various collinear biasing fields, exhibits a peak close to, but above, the Curie temperature Tc. If it is assumed that the behaviour of the magnetization in the critical region close to Tc is governed by the scaling law equation of state, then the occurrence of such peaks follows directly. Such an approach also predicts a temperature and field dependent variation for such peaks which we have attempted to verify. The latter then lead us to estimates for the critical indices δ and γ for this system.
Magnetic behavior of dilute Fe impurites in the Mo-Nb alloy system by Mössbauer effect
Authors: Maley M. P. , Taylor R. D. , Erickson D. J.
Published: February 2003

We have measured the magnetic hyperfine field Hi at the Fe57 nucleus in a series of MoxNb1−x alloys in which x varies from 0.85 to 1.0. The measurements were taken over a temperature range 0.5⩽T⩽4.0 K and in magnetic fields up to 6.0 T. We fit each spectrum with a four-site model with relative strengths fixed by the statistical probabilities of the nearest-neighbor (n.n.) configurations. The results of this analysis indicate the Fe sites with eight Mo n.n. have a moment similar to that of Fe in Mo, but that the Kondo temperature TK increases with the Nb content in the alloy. Fe sites with seven Mo n.n. exhibit a temperature independent Hi about equal to the applied field over 0.5⩽T⩽4 K, indicative of a magnetic site with TK≳4 K. These results support the basic premise of the local environment model, first proposed by Jaccarino and Walker, but indicate a more continuous dependence of magnetic bahavior on n.n. configuration.
Magnetization and susceptibility of isoelectronic CoGa alloys with mixed V/Mn substitution for Ga
Authors: Booth J. G. , Prince J. G.
Published: February 2003

The bulk magnetic properties of Co(Ga/T) alloys with T = V or Mn have recently been correlated with an electron concentration parameter. We report here structural, magnetisation and susceptibility measurements on a series of mixed V/Mn compounds in which the number of Mn atoms is varied although the electron concentration remains constant. These form the series Co50(Ga50−x−yVxMny) with the values of x and y chosen to give an electron concentration corresponding to a Curie temperature of ∼250 K. The four alloys, having concentrations of 2.5, 4.375, 5.0, and 6.25% Mn show almost identical ferromagnetic behaviour but susceptibility measuremenets show a gradually increasing Peff with Mn concentration. X-ray and neutron diffraction measurements show the alloys to be structurally similar and neutron scattering measurements show with increasing Mn content a transition from normal ferromagnetic behaviour to one in which ferro and superparamagnetism co-exist. The results provide support for the premise that the superparamagnetic clusters are associated with moment bearing Mn atoms.
’’Exact’’ calculations for finite Ising spin glass lattices (invited)
Authors: Morgenstern I. , Binder K.
Published: February 2003

By a recursive method numerically exact free energies and correlation functions are calculated for finite two- and three-dimensional Ising lattices with bonds chosen randomly either ±J or from a gaussian distribution. While (dynamic) Monte Carlo simulations of precisely the same systems show the onset of Edwards-Anderson ordering at rather sharply defined nonzero freezing temperature Tf, the exact static calculations imply that there is no static order parameter qEA = [<Si≳2T]av at nonzero temperature. The correlation length, which would become infinite when qEA would start to become nonzero, is found at Tf to be of the order of a few lattice spacings only. As a result, the freezing-in of these models is identified as a dynamic phenomenon, and not a phase transition associated with static Edwards-Anderson order. The specific heat of the gaussian spin glass is found to vary nearly linear with temperature. On the other hand, in two-dimensional Ising systems with random fields a nonzero (Mattis-like) spin glass order is found.
Origin of magnetic anistropy in transition metal spin-glass alloys
Authors: Levy P. M. , Fert A.
Published: February 2003

In order to interpret the magnetic anisotropy of spin-glass alloys, we calculate the anisotropic terms arising in the RKKY interaction between transition metal impurities when spin-orbit coupling is taken into account. We find pseudo-dipole and single ion anisotropy terms in the pair interaction and Dzyaloshinsky-Moriya terms when triangles of impurities are considered. Applying our results to AuFe alloys we find that, although the pseudo-dipole interactions are 40 times stronger than the magnetic dipole-dipole, the Dzyaloshinsky-Moriya interactions are even stronger and are sufficient to explain the magnetic anisotropy observed in AuFe spin-glass alloys.
A study of the temperature dependence of spin-wave excitations in FexCr1−x
Authors: Shapiro S. M. , Fincher C. R. , Palumbo A. C. , Parks R. D.
Published: February 2003

Certain alloys of FexCr1−x (0.18<x<0.30) have been reported to undergo a transition from a ferromagnetic state to one exhibiting mictomagnetic or spin-glass behavior at temperatures below the Curie temperature, Tc. Studies of the critical scattering on polycrystalline samples show a peak at Tc for all x’s and a monotonically decreasing intensity for T<Tc for x≳0.30. For those x’s exhibiting spin-glass behavior, there is an increase in intensity at low temperatures. The dynamical studies reveal well-defined spin waves within the ferromagnetic regime but as T approaches the spin-glass phase, the magnetic stiffness decreases dramatically.
Small-angle neutron scattering from magnetic correlations in Fe0.7Al0.3
Authors: Child H. R.
Published: February 2003

Ordered Fe0.7Al0.3 becomes ferromagnetic below 400 K but paramagnetic on cooling below 170 K and then is mictomagnetic below 92 K. A previous neutron study of this material showed magnetic diffuse scattering over this entire temperature range and we present here an extension of this study to very small angles (6×10−3?κ?30×10−3 Å−1). We find that the scattering measured at constant K shows a hump at Tc as a function of temperature but also peaks near the inverse Curie temperature and these peaks occur at different temperatures for different κ. This result is reminiscent of spin glass behavior. No significant change occurs in the scattering at the mictomagnetic transition at 92 K. The κ dependence of the scattering can be described by both a Lorentzian (Ornstein-Zernike type) and by the square of a Lorentzian (Debye type) but a more reasonable fit is found for the latter form. The application of a field of a few kilogauss eliminates the small angle scattering at all temperatures, and for scattering directions not only parallel, but also perpendicular to the applied field direction.
Ferromagnetic vs. spin glass behavior in amorphous Fe-Ni based alloys
Authors: Bhagat S. M. , Geohegan J. A. , Spano M. L. , Chen H. S.
Published: February 2003

Our recent measurements on amorphous (FexNi1−x)75P16B6Al3 alloys yielded the magnetic phase diagram (T vs. x). For x<xc (xc≲0.17) paramagnet (PM) to spin glass (SG) transitions occur and for 0.4≳x≳xc, cooling produces a PM to ferromagnet transition followed, at lower T, by a FM-SG transition. We report low field ac susceptibility measurements on alloys for x in the neighborhood of xc. Application of a constant magnetic field (Ba) produces two peaks in χac(T) which mark the PM-FM and FM-SG transition temperatures. We obtain phase diagrams in the T vs. Ba plane, compare them to our numerical calculations based on recent theory, and infer the presence of large magnetic clusters for x≃xc.
Mössbauer studies of an amorphous Fe-Mn alloy with competing exchange interactions
Authors: Keller H. , Rao K. V. , Debrunner P. G. , Chen H. S.
Published: February 2003

57Fe-Mössbauer spectroscopy was used to determine the distribution p(H) of effective internal fields H at the iron nuclei in the amorphous alloy (Fe0.65Mn0.35)75P16B6Al3. This alloy undergoes a paramagnetic to ferromagnetic phase transition at Tf≃100 K and a ferromagnetic to spin glass transition at Ts∼50 K. The distribution p(H) shows two resolved peaks at low temperatures; the larger, low field peak at Hp increases in height and shifts to lower fields with increasing temperature. We find empirically that the deviation between the average field, H̄, and Hp can be represented as the sum of the two terms, ΔH = H̄−Hp = ΔHf+ΔHs, each of which follows a power law, ΔHi = ΔHoi (1−T/Ti)βi, i = f,s. The critical parameters βf = 0.42±0.14, Tf = (100±2) K, βs = 0.52±0.19, Ts = (50.2±1.4) K, are consistent with results from standard magnetic measurements.
Neutron scattering experiments on the magnetism in Cu-Mn single crystals
Authors: Werner S. A. , Cable J. W.
Published: February 2003

We have carried out neutron polarization analysis experiments, and unpolarized neutron scattering experiments, on annealed single crystal Cu-Mn samples of 5, 10, 15 and 25 atomic percent Mn. Peaks in the magnetic diffuse scattering are found at the [1, 1/2±δ, 0]-type positions in reciprocal space, where δ = 0.34, 0.29, 0.25 and 0.19 for the 5, 10, 15 and 25 percent Mn samples respectively. This magnetic scattering is symmetry-related to the diffuse nuclear scattering centered at the [1, 1/2, 0]-type positions arising from atomic short range order. The intensity of this diffuse magnetic scattering in all of the alloys decreases smoothly with temperature, approaching zero in the range 300–350 K. The spin-spin correlation range, as judged from the width of the magnetic diffuse peaks, also decreases smoothly with temperature. Neither the width nor the intensity of this magnetic scattering gives any hint of a freezing transition at lower temperature.
Anomalous paramagnetic-state μSR in spin-glass AgMn
Authors: Brown J. A. , Heffner R. H. , Kitchens T. A. , Leon M. , Olsen C. E. , Schillaci M. E. , Dodds S. A. , MacLaughlin D. E.
Published: February 2003

Muon spin rotation (μSR) experiments have been carried out in the paramagnetic state (T≳Tg) of a dilute AgMn spin glass, to probe internal field distributions during the onset of impurity-spin freezing. μ+ resonance frequencies and depolarization rates were measured in a 1.6 at.% Mn sample in transverse fields between 0.15 and 5 kOe for temperatures up to ∼3Tg. The depolarization rate Λ increased well above the value Λd expected in the absence of impurity-spin exchange coupling as Tg was approached from above. The largest relative increase of Λ was obtained for lowest fields. The average precession frequency was constant to within 0.2% down to 1.1Tg. The data scale roughly with T/Tg and H/Tg when compared to recent μSR studies of CuMn. Although a case has been made for attributing this anomamous increase in Λ to dynamic broadening (spin-lattice relaxation), evidence exists which argues that static inhomogeneity in the muon hyperfine field is the origin of Λ. If this is the case, the absence of muon environments with weak hyperfine couplings conflicts with the notion that clustering or percolative effects are involved in the spin-glass transition. The μSR results may be relevant to recent interpretations of ESR data.
Magnetization in a rare-earth spin glass
Authors: McAlister S. P.
Published: February 2003

The difference between the thermo- and isothermal remanent magnetization in a spin glass has been called the clamped magnetization. Here I show that the clamped magnetization in the spin glass Y-4 at.% Tb exists a few degrees above To. This fact supports the contention that the spin-glass temperature does not signify a true phase transition.
Spin resonance and magnetic susceptibility of amorphous GdxY0.33−xAl0.67 films showing spin-glass behavior
Authors: Malozemoff A. P. , Krusin-Elbaum L. , Taylor R. C.
Published: February 2003

The effects of dilution of Gd by Y in a series of evaporated amorphous GdxY0.33−xAl0.67 films (x from 0.33 to 0.0027) has been studied by microwave magnetic resonance and SQUID magnetometry. The SQUID measurements show a spin glass freezing temperature Tf of 13.5K for x = 0.33 and 6.5K for x = 0.16, with Tf being less than 1.6K or nonexistent for samples with x<0.04. X-band microwave measurements reveal a line broadening ΔH and an increasing g-shift as the temperature T is lowered. These low temperature effects are interpreted in terms of a theory by Salamon which permits determination of the spin-spin relaxation time τ∝xm/(T−Tf)n. Contrary to earlier experimental or theoretical indications, we find m∼−0.5 and n∼1.5.
Spatially correlated molecular field theory of phase transition in amorphous ferromagnets
Authors: Herzer G. , Fähnle M. , Egami T. , Kronmüller H.
Published: February 2003

The behavior of amorphous ferromagnets near the phase transition temperature is significantly different from that of simple crystalline ferromagnets. A non-local Landau-Ginzburg theory based upon the spatially correlated molecular field is introduced. The theory correctly describes the curvatures in the inverse susceptibility vs. temperature plot and in the Arrott plot.
A model relating local structure to Curie temperature in amorphous alloys
Authors: Kudo T.
Published: February 2003

The Curie temperature of (FexNi1−x)75B15Si10 amorphous alloys has been determined from ac susceptibility measurements for x<0.30, and analyzed using Kouvel’s model. The experimental data on Tc vs. x can be explained reasonably well by this model. The change in Tc due to annealing (5 min.) is also studied in (FexNi1−x)75B15Si10 and Fe16Ni59(B1−ySiy)25 amorphous alloys. The change in Tc after annealing appears to be due to the increased compositional short range order among the Fe and Ni atoms rather than the metalloids.
Hyperfine field distributions in ferromagnetic amorphous FexB1−x thin films
Authors: Blum N. A. , Moorjani K. , Poehler T. O. , Satkiewicz F. G.
Published: February 2003

Sputtered films of amorphous FexB1−x (0.40?x?0.50) were studied by Mössbauer spectroscopy. The films were characterized for composition and homogeneity by secondary-ion mass spectrometry (SIMS) and for lack of crystallinity by X-ray diffraction. Below the magnetic ordering temperature Tc, the hyperfine spectra consist of a large amplitude quadrupole doublet superimposed on a broad magnetic hyperfine field distribution. The spectra of these alloys are remarkably different from that of polycrystalline FeB and from those of liquid-quenched alloys which are restricted to compositions near the eutectic at x≊0.8. Comparison with the polycrystalline FeB spectrum clearly shows that for a significant fraction of the Fe atoms in the amorphous alloys, the local environment is substantially different from the Fe environment in FeB.
Temperature dependence of the anomalous FMR transmission peak at 24 GHz at Metglas Fe82B12Si6
Authors: Heinrich B. , Cochran J. F.
Published: February 2003

A transmission peak at FMR has been observed at 24 GHz in an iron rich Metglas. The temperature dependence of this anomalous transmission signal has been measured over the range 300 to 600 K. The experimental results have been compared with a calculation which includes magnetoelastic coupling between the lattice and the magnetization. The results are described very well by the theory using a phonon mean free path of 2.7 μm.
Transport at low temperature in amorphous magnetic metals (invited)
Authors: Imry Y.
Published: February 2003

The scaling theory of conduction for a noninteracting electron gas in a disordered system at T = 0 is reviewed and the conductivity at various length scales obtained. The concepts of the mean free time between inelastic collisions and the corresponding inelastic length ℓin, are introduced. The conductivity for a dirty metal is obtained as a function of temperature at low temperatures in terms of ℓin(T). For the case of a disordered magnetic metal the effect of the temperature-dependent magnetic disorder is introduced and several possible typical situations schematically analyzed. The effect of electron-electron interactions is briefly discussed, as determining the effective inelastic length and a simple qualitative picture of conduction as a function of temperature suggested. Some cautionary remarks about the testing of these ideas by experiments are made.
Pressure effect on the magnetic and electric properties of Fe-Zr amorphous alloys
Authors: Kaneko T. , Shirakawa K. , Ohnuma S. , Nose M. , Fujimori H. , Masumoto T.
Published: February 2003

The pressure effects on magnetic and electric properties were studied for amorphous Fe1−xZrx alloys. The pressure effect on the Curie point was measured by applying hydrostatic pressure. The initial pressure coefficient of the Curie point was −1.0, −1.4 and −1.8×10−2 kbar−1 for Fe0.8Zr0.2, Fe0.85Zr0.15 and Fe0.9Zr0.1 alloys, respectively. It was found that the alloys with x<0.15 have strong pressure dependence of permeability. These occurred an anomalous decrease of electrical resistance with pressure in amorphous Fe0.85Zr0.15, which was considered to be due to a kind of electronic transition by applying pressure.
dc electrical conduction in carbon black filled c
i
s-polybutadiene
Authors: Cashell E. M. , Coey J. M. D. , Wardell G. E. , McBrierty V. J. , Douglass D. C.
Published: February 2003

dc electrical conductivity measurements on carbon black filled cis-polybutadiene are reported. A temperature reversible peak is found in the resistance (defined as V/I) versus temperature curves which separates regions of positive and negative temperature coefficients. The temperature of the peak depends critically upon the type of black and the voltage used for the measurement. The data have been analyzed in terms of two contributions to the conductivity: (i) an intrinsic Ohmic process, described by an activation energy DE = 0.6 eV, and identified with ionic conduction in the rubber matrix, and (ii) a non-Ohmic mechanism which dominates at high filler loadings, high fields, and low temperatures. This process obeys an expression of the form I = AVeBV. NMR measurements on the samples show that there is no gross irreversible morphological rearrangement over the temperature range studied.
True three-dimensional nuclear magnetic resonance imaging by Fourier reconstruction zeugmatography
Authors: Lai Ching-Ming
Published: February 2003

A new method of obtaining three-dimensional nuclear magnetic resonance images is introduced. This imaging method, Fourier reconstruction zeugmatography, reconstructs true three-dimensional images directly from transient NMR signals by a Fourier transform technique. A theoretical analysis and experimental results are presented. The method is simple in operation and provides a safe, efficient, and versatile alternative to other methods for medical diagnostic imaging.
Photoacoustic study of layered samples
Authors: Helander Per , Lundström Ingemar , McQueen Douglas
Published: February 2003

The application of photoacoustic spectroscopy to the spectroscopy of layered samples with thicknesses of tens of microns is demonstrated both theoretically and experimentally. Theoretical expressions for the signal damping and phase delay are developed in terms of the thermal diffusion length, which is determined by the chopper frequency and the thermal properties of the sample. The theory is supported by measurements of both amplitude and phase on a color photographic film containing three light absorbing layers. The application of the method is further illustrated by a simple study of fading leaves.
Confinement of ions created externally in a radio-frequency ion trap
Authors: O Chun-Sing , Schuessler Hans A.
Published: February 2003

The various aspects of injecting ions into a three-dimensional radio-frequency quadrupole trap and their trapping for considerable periods of time are investigated by a numerical method. It is shown that for suitably chosen experimental parameters sufficiently long trapping times can be achieved to make this method attractive for on-line high-resolution spectroscopy of short-lived isotopes and of highly charged stable ions. The narrow range of the phase of the driving voltage during which trapping of injected ions occurs is determined. Injection through an end cap electrode is more favorable than ring electrode injection. It is also shown that in the absence of collisions injection through the gaps between the electrodes of the quadrupole ion trap is not feasible. The process of moderating high-energy ions by a thin foil before trapping and the various mechanisms of energy reduction after trapping are discussed.
Transient fields of a vertical electric dipole over a two-layer nondispersive dielectric
Authors: Ezzeddine A. , Kong J. A. , Tsang L.
Published: February 2003

The double-integral expression for the time response of the vertical magnetic field due to a vertical electric dipole placed on a two-layer dielectric medium has been reduced to a series of single integrals by asymptotic methods and explicit inversion approaches. The summation of the infinite series represents contributions arised from the multiple images due to the presence of the two interfaces. Causality of the solutions is shown to be preserved.
Depolarization of the scattered light on internal reflection from surface acoustic waves on fused quartz. II. Experiment
Authors: Lee J. , Singh M. P. , Zucker J.
Published: February 2003

The intensity of light scattered by surface acoustic waves (SAW’s) on internal reflection for fused quartz medium was measured for the geometry where the incident light is perpendicular to the SAW propagation direction. ZnO thin-film interdigital transducers are used for generating SAW on fused quartz substrates. Measurements of the scattered light intensity give excellent agreement with theory. Either s- or p-polarized incident light is scattered by the SAW into s- and p-polarization states. The scattered light is left (right) elliptically polarized if the incident light is s(p)-polarized.
Compressibility effects in shaped charge jet penetration
Authors: Haugstad B. S.
Published: February 2003

Among other hypotheses, the classical theory of high-speed penetration assumes the incompressibility of both the projectile and target. Employing a simple Murnaghan equation of state, we show here that direct compressibility effects (pv-work) on penetration depth are at most on the order of 10–15% for projectile speeds as high as 104 ms−1. Our results agree closely with similar results by Coombs (private communication, Royal Air Force Research Establishment, 1978), who used a more complex five-parameter equation of state. This indicates that rather simple equations of state may adequately represent essential thermodynamic features of high-speed penetration phenomena. The equation of state employed here furthermore allows approximate analytical results to be derived for both small and large projectile velocities.
Dopant incorporation during liquid phase epitaxy
Authors: Mazuruk K. , Bryśkiewicz T.
Published: February 2003

A quantitative treatment of nonequilibrium dopant incorporation during the growth by conventional liquid phase epitaxy (LPE) as well as by electroepitaxy has been put forward. Analytical expression for the stationary distribution of dopant concentration and potential in the solid near the liquid metal-semiconductor interface is derived. On this basis the effect of the Schottky barrier height, supplied voltage, diffusion coefficient in the solid, and growth rate on the incorporation of the donor impurities is calculated. The experimental verification of the proposed model can be easily carried out as all the dependences are plotted versus normalized variables.
Epitaxial growth of amorphous Ge films deposited on single-crystal Ge
Authors: Grimaldi M. G. , Mäenpää M. , Paine B. M. , Nicolet M-A. , Lau S. S. , Tseng W. F.
Published: February 2003

The epitaxial growth of amorphous Ge films deposited onto 〈110〉 Ge substrate is demonstrated. Substrate cleaning prior to deposition involves only conventional chemical procedures. The growth appears to be a strong function of the interface cleanliness. Two different growth mechanisms are observed: (a) a direct transition from amorphous to single-crystalline layer and (b) the growth involving the transition of amorphous to polycrystals to single crystal.
Optical and structural properties of black molybdenum photothermal converter layers deposited by the pyrolysis of Mo(CO)6
Authors: Chain E. E. , Seshan K. , Seraphin B. O.
Published: February 2003

Black molybdenum thin films, combining high infrared reflectance with significant solar absorptance, have been prepared by pyrolyzing Mo(CO)6 under oxidizing conditions and subsequent annealing under a hydrogen atmosphere. X-ray and electron diffraction, electron microprobe, and Auger analysis show that the films, as deposited, are fine grained (300 A), stress-free, monoclinic MoO2 with [010] preferred orientation. As the annealing progresses the reflectance in the infrared rises faster than in the visible. Consequently, the spectral selectivity can be optimized in a partially annealed state characterized by a complex mixture of Mo and MoO2. Like black chrome, black molybdenum is a composite material, consisting of metal particles suspended in an oxide matrix. However, black molybdenum is capable of prolonged operation at temperatures in excess of the decomposition temperature of black chrome. After passivation with Si3N4, very simple photothermal solar converter coatings with a respectable spectral selectivity and significant temperature durability at 500 C in vacuum are obtained.
Effect of Cr impurity on the dc resistivity of Mn-Zn ferrites
Authors: Rao K. H. , Raju S. B. , Aggarwal K. , Mendiratta R. G.
Published: February 2003

The effects of composition, temperature, applied field, and duration of the applied field on the dc resistivity of chromium-doped manganese-zinc ferrites have been studied. From the observed temperature variation of resistivity, activation energy of each sample is calculated. The overall results are discussed in light of the existing understanding of these systems.
Determination of the drift mobility in high-conductivity amorphous silicon
Authors: Crandall Richard S.
Published: February 2003

A new technique for measuring the drift mobility in semiconductors is proposed. This method consists in measuring the current transient in a Schottky-barrier device during a reverse bias voltage pulse. Measurements on a-Si:H doped with 0.2% phosphorous show a temperature activated mobility. The activation energy is 0.13 eV and the drift mobility is about 6.5×10−2 cm2/V sec at room temperature. This technique is particularly applicable to material in which the dielectric relaxation time is shorter than the carrier transit time, precluding time-of-flight measurements.
Bulk and surface states analysis in a-Si:H by Schottky and MIS tunnel diodes capacitance and conductance measurements
Authors: Viktorovitch P.
Published: February 2003

An experimental and theoretical study of both the capacitance and the conductance of Schottky and MIS tunnel diodes made on undoped a-SI:H, versus frequency, temperature, and voltage is presented in this paper. It is based on a general model using an equivalent electrical circuit of the devices, which permits an unambiguous distinction to be made between the contributions of bulk surface states, to determine their respective densities and to analyze their kinetic properties, It is shown that the bulk density of states (DOS) can be determined from capacitance and conductance measurements versus temperature and frequency on both Schottky and MIS devices, provided the modulation frequency is high enough to prevent any contribution from surface states. It is demonstrated that capacitance-voltage characteristics of Schottky diodes cannot provide reliable information about either bulk or surface as the diffusion theory and not the thermionic theory is appropriate to describe the transport of electrons across the junction. It is shown theoretically and experimentally that a MIS device is required to measure surface states, the insulator preventing the screening of their contribution by the metal. The measured surface DOS, derived by three different and independent methods, is very high (5×1012−2×1013 cm−2 eV−1) and essentially the same for all the investigated samples whose bulk DOS around the Fermi level ranges between 5×1015 and 4×1017 cm−3 eV−1. From conductance measurements, it is shown that the kinetics of the occupancy of both bulk and surface states is controlled by free electron transport in the conduction band and not by the states’ interaction kinetics with these electrons. The very high derived lower limit of the effective capture cross section sn of electrons by states around the Fermi level EF(sn ≳5×10{13 cm2) implies either that the interaction between states around EF and free electrons takes place via intermediate states of that the actual distance between the bulk Fermi level and the conduction level is smaller than the activation energy Es of the conductivity.
Influence of electrode resistance on tunnel junction conductance
Authors: Will T. , Escudero R.
Published: February 2003

The tunneling conductance of thin-film M-O-M junctions is distorted by electrode resistance, which can be significant if one of the electrodes is, for example, a semimetal. We present a model relating the tunneling conductance of junctions in which such resistance is appreciable with that of junctions in which it is negligible and comparison is made with experimental results in Al-oxide-Bi junctions. We conclude that much of the apparent variation in characteristics of such junctions is due to the distortion produced by the semimetal film.
Lateral spreads of energy dissipation profiles of 20-kV electrons in polymethylmethacrylate: Functional representation and its application to proximity effect
Authors: Shimizu Ryuichi , Everhart T. E.
Published: February 2003

Monte Carlo calculations have been used extensively to study the energy dissipation of electrons penetrating into solid materials both in the direction of the initial electron trajectory and lateral to it. Knowing the lateral energy dissipation is important for the prediction of proximity effects in electron-beam lithography and limiting resolution in scanning electron microscopy. The Weibull probability density functions are shown to approximate the lateral energy dissipation profiles determined by Monte Carlo calculations of 20-keV electrons in polymethylmethacrylate (PMMA), and their application to simple line and square patterns of electron-beam exposure are also discussed.
A molecular dynamics simulation study of the influence of the ion-atom potential function upon sputtering
Authors: Harrison Don E.
Published: February 2003

A molecular dynamics simulation has been used to investigate the ion-atom potential function dependence of single-crystal sputtering. Atom yields from the (111) and (001) crystal orientations have been calculated at 5.0 keV for the Cu/Ar+ system for 28 Born-Mayer and Moliere potential functions. The multimer yield ratios, layer yield ratios, ejected atom energy distribution, and angular distribution of ejected atoms are essentially independent of the potential parameters chosen in a Born-Mayer function. The atom yields from a target orientation can be ordered, or estimated, from a knowledge of the magnitude of the potential function in a sensitive range of separations near the maximum of the impact parameter distribution function for that surface. This property of the potential functions has been reproduced at 600 eV. The Moliere function yields and other properties fall exactly into the positions predicted from a knowledge of magnitude of the potential function in the sensitive range. With the exception of the atom yields, yield ratios, and the atoms per single ion distribution the properties of the sputtered atom distribution can be computed from any of a large number of potential functions.
The characterization of x-ray photocathodes in the 0.1–10-keV photon energy region
Authors: Henke B .L. , Knauer J. P. , Premaratne K.
Published: February 2003

A method and an instrument are described for the measurement of the absolute quantum yield for front-surface and transmission photocathodes in the 0.1–10-keV photon energy region. The total and the secondary electron photoemission yields have been measured for the Al, Au, CuI, and CsI photocathodes as required for the absolute calibration of the x-ray diode detectors and for the x-ray streak cameras. The relative secondary electron yields have also been measured for the same photocathodes by high resolution electron spectroscopy of the secondary electron energy distributions, which are in good agreement with the absolute yield measurements. The secondary electron yield of CsI is ten to one-hundred times higher than that for Au in the 0.1–10-keV region and with a secondary energy distribution that is appreciably sharper. For these reasons, CsI should be an effective photocathode for sensitive, time-resolved spectroscopy into the picosecond region. It is verified experimentally that the secondary electron quantum yield varies approximately as Em(E), with E as the photon energy and m(E) as the photoionization cross section, and that the primary (fast) electron quantum yield is a small fraction of the total yield and varies approximately as E2m(E). A simple model for x-ray photoemission is described which leads to semiempirical equations for front- and back-surface secondary electron photoemission as based upon an escape depth parameter that may be obtained from yield-versus-photocathode thickness data. The model predictions are in good agreement with experiment.
Positive-ion emission from a-Agl films
Authors: Pong W. , Lam W. , Tong A. , Brandt D.
Published: February 2003

Positive-ion emission from evaporated films of AgI was observed when the films were heated to temperatures above 160 °C. A slow sublimation of AgI was also found to occur with the ion emission when the temperature was sufficiently high. The activation energy for positive-ion emission from the surface of a-AgI is estimated to be 1.7 eV.
Large grains of InP and CdTe on recrystallized CdS substrates
Authors: Krajenbrink Frans , Hoberg Peter , Montano Hank , Zanio Ken
Published: February 2003

Thin films (∼1 mm) of large-grained (∼40 mm×∼40 mm) InP were epitaxially deposited on low-cost recrystallized CdS substrates at 280 °C by planar reactive deposition. Large grains of CdTe (∼40 mm) were also deposited on similar substrates at 460 °C by physical vapor deposition. Typically, the recrystallized CdS grain size is about 40 mm. However, grains with dimensions up to 300 mm were observed.
cw laser annealing of Nb3Al and Nb3Si
Authors: Shibata T. , Gibbons J. F. , Kwo J. , Feldman R. D. , Geballe T. H.
Published: February 2003

cw laser annealing has been applied to synthesize the metastable A15 superconductors, Nb3Al and Nb3Si. Qualitative agreement with the equilibrium phase diagrams have been obtained for the Nb-Al system. Laser annealing permits the high-temperature A15 phase to be fast quenched to room temperature without decomposition. Subsequent use of multiple low-temperature laser scans raises the superconducting transition temperature, probably by improving the atomic order. For the Nb-Si system, a single-phase nonstoichiometric A15 structure is formed from the amorphous phase upon laser annealing.
Characterization of gallium arsenide phosphide light-emitting diodes by photoluminescence
Authors: Ziegs W. , Riedel W. , Preier H.
Published: February 2003

The use of spectrally and spatially revolved photoluminescence for investigation of GaAs0.6P0.4 light-emitting diodes is described. A HeCd laser focused to 8 μm was used for excitation. Photoluminescence spectra were taken at 95 and 300 K. They show distinct differences between the p-type junction area and the n-type substrate region. Devices with a different electroluminescence efficiency showed corresponding differences in their photoluminescence behavior. The p-n junction depth was found to be a critical parameter, influencing electroluminescence as well as the photoluminescence spectra. Spectrally resolved photoluminescence can be used as a tool to characterize light-emitting diode materials and devices at different production stages.
The kinetics of dissociation of Cryolite (Na3AIF6) induced by electron bombardment
Authors: Knapp A.G. , Hughes J.R.
Published: February 2003

The variation in the rate of fluorine loss from electron-bombarded Na3AlF6 films with time, beam-current density, and temperature is reported. The loss is shown to be due to the emission of F atoms; the observation of F2 emission is shown to be an experimental artifact. A kinetic model is proposed which involves movement of fluorine into the bombarded area and which provides a good quantitative fit to a range of experimental data. The value for the cross section for dissociation of Na3AlF6 under bombardment with 500-eV electrons is found to be (1.35±0.4)×10−16 cm2.
Diffraction effects in free-electron lasers
Authors: Slater J. M. , Lowenthal D. D.
Published: February 2003

The spatial photon intensity distribution is calculated for geometries pertinent to tapered-wiggler free-electron lasers. A large-radius incident photon field interacts with a small-radius e-beam gain medium, and the diffraction of extracted energy from the gain medium to larger radii is analyzed in the limit of small gain. The results are compared with a simple fill-factor approximation.
Subsurface particle growth kinetics in physical vapor deposition
Authors: Robertson David , Pundsack Arnold L.
Published: February 2003

In a well-defined range of conditions, selenium vapor deposited onto a thermoplastic substrate forms a monolayer array of spherical particles located just beneath the surface. A model for the growth of these particles has been proposed. In it, the particles grow by two mechanisms: (i)capture of selenium molecules diffusing into the substrate, and (ii)coalescence with other particles when they grow into contact. Expressions for both rates are presented and analytical solutions for the time dependence of the numbers and sizes of the particles are devived for two limiting cases—complete condensation (in which all impinging materials become incorporated into the particles) and incomplete condensation (in which re-evaporation of adsorbed species limits the kinetics). Experimental data confirm the model’s predictions.
A study of the mechanisms of ion nitriding by the application of a magnetic field
Authors: Brokman Avner , Tuler Floyd R.
Published: February 2003

A model for ion nitriding is proposed which is based on the formation and diffusion of vacancy-nitrogen ion pairs. A theoretical expression is developed for the local effective diffusion coefficient of the combined vacancy-ion pairs which explains the accelerated case hardening associated with ion nitriding as compared with conventional nitriding. Ion-nitriding experiments on AISI 304 stainless steel were performed in a magnetic field to increase the number of vacancy-ion pairs. The experiments confirmed the theory, showing that in the current density range 100 –1000 A m−2 the local effective diffusion coefficient is proportional to the current density.
Rheological behavior of progressively shear-thickening solutions
Authors: Peng Steven T. J. , Landel Robert F.
Published: February 2003

FM-9 (the commercial name of an ICI product) in organic solvents or poly(methacrylic acid) (PMMA) in aqueous solution exhibit strong time-dependent shear-thickening behavior. The induction time needed for the onset of the thickening depends markedly on shear rate, solvent used, concentration, and molecular weight. Slightly altering the nature of the solvent profoundly affects the behavior. The effects are similar to those obtained by changing the concentration or molecular weight. The nature of thickening behavior is not well understood. The effect will be illustrated (using FM-9 solutions) as a function of shear rate, concentration, and temperature. Defining a critical shear rate γ̇c as that at which the induction time for thickening becomes so short as to be immeasurable within the resolution of the viscometer, γ̇c for this polymer is found to be inversely proportional to the zero shear-rate viscosity of the solution for the temperature and concentrations studied.
High pressure infrared xenon laser excited by a UV preionized discharge
Authors: Collier F. , Lacour B. , Maillet M. , Michon M.
Published: February 2003

Laser action from neutral Xe transitions has been achieved in an Ar–Xe mixture at 1 atm and in a He–Xe, He–Ar–Xe mixture at 2.5 atm excited by a UV preionized short discharge (Δt?50 ns). In the best mixture, He–Ar–Xe (100–60–1), an overall conversion efficiency of 0.2% was obtained with a 10-mJ output. These nonoptimized results may be improved by decreasing the input energy density and increasing the pressure.
Longitudinal polarization of α-poly(vinylidene fluoride) by kink propagation
Authors: Clark J. D. , Taylor P. L. , Hopfinger A. J.
Published: February 2003

The α- phase chain of poly(vinylidene fluoride) has a component of dipole moment parallel to the chain axis which can be reversed by propagation of a solitary wave along the chain. Calculations of the energy required to create such a wave in a perfect chain yield larger values than are implied by experiment. This suggests that either head-to-tail defects or regions of stress at the lamellar boundary might play an important role in causing the observed dielectric behavior.
Melting temperature and periodicity
Authors: Van Uitert L. G.
Published: February 2003

The temperature of melting Tf for most metals can be related to bond distance d, the number of electrons per atom (V) in an sp, sd, or sf band, and electron interactions through a parameter K3≡Tfd2/V. The value of this parameter varies systematically with the quantum states of the elements or their positions in the periodic table.
An injector based on electric insulation for the controlled ballistic focusing of light ion beams
Authors: Phelps D. A. , Salisbury W. W. , Jorna S.
Published: February 2003

An injector design is described which uses a space-charge-limited source of alkali ions and accelerates the ions through two stages of acceleration and slight deceleration stage (to retard the neutralizing electrons) before matched phase space neutralization with an electron reflex triode source occurs. For typical conditions of a 200-ns pulse and a 1-MeV 1-10 A/cm2 lithium ion beam, computer simulation experiments demonstrate that 55% of the beam trajectories have an angular divergence less than 250 μrad (thereby meeting an order of magnitude more stringent constraint at more than an order of magnitude higher power density than any previous electrostatically focused injector design). The method of achieving the low angular divergence profile at readily attainable voltages of 200 kV, current densities of 150 mA/cm2, and vacuum stresses of 50 kV/cm is described. By simply increasing the voltage towards 1 MV, state-of-the-art advances in all the parameter areas can be made without altering the angular divergence profile. Discussions of other issues, such as source temperature, neutralization, self-magnetic fields, and electrostatic field error contributions to the angular divergence are presented. Finally, the benefits of additional stages of acceleration (needed for future MeV operation) are disclosed and justified.
The diocotron instability in annular relativistic electron beams
Authors: Jones Michael E. , Mostrom Michael A.
Published: February 2003

A dispersion relation which includes finite axial wavevectors, k, is derived in the rest frame of the beam where the instability is assumed to be electrostatic. The dispersion relation is obtained in the lab frame by a Lorentz transformation. The instability is found to have a finite k bandwidth with the most unstable mode occurring at k≠0. The growth rate for the most unstable mode is found to be reduced by approximately 1/γ2 from the nonrelativistic result while the real frequency of this mode remains virtually unchanged. The effects of finite vz shear, which are left out of the analysis, are estimated and discussed.
Very low threshold-current temperature sensitivity in constricted double-heterojunction AlGaAs lasers
Authors: Botez D. , Connolly J. C. , Gilbert D. B. , Ettenberg M.
Published: February 2003

The temperature dependence of threshold currents in constricted double-heterojunction diode lasers with strong lateral mode confinement is found to be significantly milder than for other types of lasers. The threshold-current relative variations with ambient temperature are typically two to three times less than for other devices of cw-operation capability. Over the interval 10–70 °C the threshold currents fit the empirical exponential law exp [(T2−T1)/T0] with T0 values in the 240–375 °C range in pulsed operation, and in the 200–310 °C range in cw operation. The external differential quantum efficiency and the mode far-field pattern near threshold are virtually invariant with temperature. The possible causes of high-T0 behavior are analyzed, and a new phenomenon—temperature-dependent current focusing—is presented to explain the results.
Heat regeneration in Malone-type liquid engines using a parallel-plate thermodynamic pile geometry
Authors: Allen P. C. , Fisher G. H. , Knight W. R. , Paulson D. N. , Wheatley J. C.
Published: February 2003

Liquids working in heat engines require especially effective thermal regeneration as they flow between the remote and ambient temperature regions of a machine. Using liquid Freon 114 (C2Cl2F4) as a test fluid, we have studied this process experimentally in a parallel-plate geometry for the pulsating unidirectional flow of a Malone engine. A theoretical analysis of the thermohydrodynamical process is presented whose results compare favorably with experiment. For a constant average volume rate of flow of liquid, the regenerative loss decreases as the period of the engine decreases.