bluuebunny/crossref_metadata_2025 huggingface dataset:
The near-edge x-ray absorption spectroscopy of RT2Si2 and RT2Ge2 compounds
Authors: Ansari P. H. , Qi B. , Liang G. , Perez I. , Lu F. , Croft M.
Published: July 2002

X-ray absorption near-edge spectroscopy (XANES) measurements on 1:2:2 compounds of the form RT2X2 with R=Ce and Eu, T=a transition metal, and X=Si or Ge are presented. XANES measurements on each of the three sublattices are used to elucidate elements of the electronic structure of these compounds. In particular, the evidence for the strongly bonded T-X planes, the coupling of the Ce valence-state stability to the T-X planes, and the response of the X-p orbitals to varying transition-metal components are discussed.
The Ising model between one and two dimensions
Authors: Novotny M. A.
Published: July 2002

A method which continuously interpolates between one and two dimensions for any magnetic model on a square lattice is introduced. This interpolation scheme, which preserves the translational invariance of the lattice, can be performed for any Hamiltonian with pairwise interactions. The Potts model interpolated between one and two dimensions is studied using finite-size scaling of data obtained with a Monte Carlo method.
Temperature hysteresis and relaxation effects in amorphous Fe-Ni-Zr alloys (abstract)
Authors: Violet C. E. , Borg R. J. , Rao K. V. , Noques J. , Taylor R. D. , Batra A. P.
Published: July 2002

Amorphous Fe-Ni-Zr alloys in the ‘‘as quenched’’ and irradiated state have been studied with 57Fe Mössbauer spectroscopy and ac and dc susceptibility. Samples were irradiated by 14-MeV neutrons at room temperature to fluences of ≊1017 ns/cm2 corresponding to a dpa of 3×10−4 at the Lawrence Livermore National Laboratory RTNS-II facility. Two samples (Fe89.7Ni0.3Zr10 and Fe70Ni20Zr10) ‘‘as quenched’’ and irradiated, have been studied between room temperature and ≊4 K. ac susceptibility shows reentrant magnetic behavior for both alloys. Temperature hysteresis (no applied fields) is observed initially in the Mössbauer spectra for both alloys, ‘‘as quenched’’ and irradiated. It decreases and virtually disappears after a few thermal cycles between 20 K and room temperature. Relaxation effects are present in the magnetic hyperfine spectra of both alloys, ‘‘as quenched’’ and irradiated. The usually assumed proportionality between the magnetic hyperfine splitting and the magnetization is probably not valid for these alloys.
Head saturation in magnetic recording
Authors: Peng J. P. , Varner J. R.
Published: July 2002

In this paper, we present two new head-modeling methods and discuss their use to study head-saturation effects. One is a nonlinear multiple-subdomain finite-element method, and the other augments the first by the use of a boundary-integral method to calculate the magnetic field’s density and gradient in the medium from potentials at the head-medium interface. These two methods allow us to calculate efficiently and accurately (less than 5% errors) the head fields and gradients resulting for various models of head saturation. A modified Williams–Comstock model for thick, longitudinally oriented media is used to estimate relative signal output for three example tapes of different magnetic properties. If ferrite gap faces are assumed contaminated or damaged during head construction such that 4πMs drops to around 3750 G, then saturation losses of about 8 dB result. This agrees with Jeffers’s measurements [Proc. IEEE 74, 1540 (1986)] comparing Sendust-tipped and ferrite heads with gap lengths of 0.3 μm.
Reassessment of matrix solvers in repeated solution (abstract)
Authors: Anandaraj A. W. , Hoole S. Ratnajeevan H.
Published: July 2002

In recent years, the ICCG algorithm has been shown to be economic for large matrices.1 Moreover, it is held that the ICCG algorithm is to be preferred when repeated solutions are required2—such as in the three areas of nonlinear magnetics, adaptive mesh generation and shape optimization, of relevance to computational magnetics. In this paper it is shown, theoretically and experimentally, that the ICCG algorithm does not exploit the existence of an approximate solution. That is, since the new solution varies from its previous approximation by a small but arbitrary vector, the usual number of steps are required to identify this solution. In the light of this result, matrix solvers for repeated solution are reassessed. It is shown that only the truly iterative schemes like SOR can exploit knowledge of the previous solution and that the use of the SOR scheme3 is competitive with the Cholesky factorization and ICCG schemes only for extremely large matrices to be of practical value in many applications.
Magnetic properties of Co-B-C amorphous alloys melt-quenched beyond the eutectic regime (abstract)
Authors: Pont Montse , Rao K. V. , Inoue A. , Masumoto T.
Published: July 2002

It is very difficult to prepare a homogeneous amorphous phase of transition-metal carbon alloys by rapid quenching. However, an additional element like Cr, Mo, or W remarkably enhances the glass formation in the ternary system. Similarly with B as additional element amorphous ductile alloys containing as much as 70% metalloids (B+C) have been recently shown to be obtainable by melt quenching to produce materials with remarkable mechanical and electronic properties. The possibility that amorphous alloys with such a large concentration of metalloids which extends to beyond the eutectic regime can be obtained by melt-spinning requires modification of previous general concepts of glass forming tendency as well as amorphous structure. In this paper we present thermal, magnetic and electronic property studies of yet another system, i.e., Co-B-C containing metalloids in the range 28–44 at. %. Boron is thought to have a rather strong attractive interaction against C which results in the formation of an amorphous phase over an extended regime. We have studied systematically both the series Co76−xB24Cx as well as Co88−yByC12 to determine the composition range for the most stable amorphous range. B and C are found to enhance considerably the glass formation. The electrical resistivity is found to increase with boron concentration and reaches values close to 450 μΩ cm and yet have a positive temperature coefficient (∼0.2×10−4 Ω mK−1 for metalloid content as high as 44 at. %) indicating a metallic behavior. No indication of electron-electron correlation effects are observed at low temperatures. From the temperature dependence of Hall effect and thermomagnetic data all the alloys studied are found to be ferromagnetic. We obtain a preliminary magnetic phase diagram from which it is found that the concentration dependence of Tc obeys a (x−x0)1/2 behavior in both the series with x0=54 at. % Co at which ferromagnetism disappears. Such a concentration dependence cannot be explained on the basis of simple dilution phenomenon. Detailed studies on the effect of B and C on magnetic properties will also be presented.
Magnetoreflectivity study of excitons in Zn1−xFexSe epilayers (abstract)
Authors: Liu X. , Petrou A. , Prinz G. A. , Jonker B. T. , Krebs J. J. , Warnock J.
Published: July 2002

We have performed a magnetoreflectivity study of excitons in epilayers of the diluted magnetic semiconductor Zn1−xFexSe. The samples were grown by molecular-beam epitaxy on GaAs (100) substrates to a typical thickness of 1 μm. Using both Faraday and Voigt geometries and magnetic spin splittings of the conduction and valence bands. The band splitting was found to be linear in magnetic field B and B<6 T. We measure effective g factors of 33.4 and 28.3 for the conduction and valence bands, respectively. For fields B>6 T, deviations were observed. The band spin splitting was also studied as a function of temperature at constant fields. At low temperatures, the spin splitting is independent of temperature. These data are in agreement with previous magnetization studies1 which showed that ZnFeSe, unlike Mn-based diluted magnetic semiconductors, exhibits Van Vleck paramagnetism. The temperature study of the band splitting allowed a determination of the crystal field splitting.
Finite element optimization of field configuration for the eddy current testing of roller bearing rib rings
Authors: Palanisamy R. , Varonis O. J.
Published: July 2002

Eddy current probes are being used widely in manufacturing industries for the nondestructive testing (NDT) of electrically conductive materials and products. Although significant progress has been made in recent years in modeling of electromagnetic fields and NDT phenomena, little attention has been given to the optimization of probe field configuration for maximum sensitivity. As a result, the design of eddy current sensors still remains empirical. This paper describes the application of the finite element numerical method to the design of a special purpose eddy current probe used in the nondestructive evaluation (NDE) of rib rings to ensure adequate case depth (rib rings provide seating for rollers in single row unitized tapered roller bearings). Presented in this paper are (a) the geometry of the developed probe with dual primary, (b) results of finite element model analyses, (c) comparison of test data with predicted outputs, and (d) the performance of this new probe in production testing.
Finite element modeling of electromagnetic resonators and absorbers
Authors: Brauer J. R. , Vander Heiden R. H. , Bruno A. B.
Published: July 2002

High-frequency coupled electromagnetic field problems are analyzed using the magnetic vector potential finite element method. The two- and three-dimensional computer programs used here are extensions of previously developed static and eddy current programs. Boundary conditions are presented that enable analysis of reflected electromagnetic waves and absorbed electromagnetic waves. Calculated resonant frequencies are shown to agree closely with classical theory for reflected waves. The absorbing finite elements are shown to give low reflections.
Scattering from an infinite, finitely conducting cylinder by finite element analysis
Authors: Bruno A. B. , Brauer J. R.
Published: July 2002

The scattering of plane electromagnetic waves from an infinite, finitely conducting cylinder is evaluated by the finite element method. The conducting cylinder is embedded in a homogeneous lossy space and is electrically small, i.e., ‖ka‖<1.0. The computer program uses three-dimensional finite elements and is based on the magnetic vector potential formulation of the wave equation. Because the medium is lossy, the boundary conditions on the vector potential at the model edge are set to zero. The results of the finite element calculation are shown to agree closely with classical results. Results will be discussed for TM polarization of the incident field.
Magnetic properties of amorphous Fe-Si compositionally modulated thin films
Authors: Martinez B. , Moreu M. A. , Labarta A. , Obradors X. , Tejada J.
Published: July 2002

The present paper reports on a magnetometric study of Fe-Si compositionally modulated thin films. The low-temperature dependence of the magnetization exhibit Bloch’s T3/2 dependence with a minor T5/2 correction term. The spin-wave stiffness constant deduced from the temperature coefficient depends on the characteristic modulation length and its values are much lower that in glassy alloys.
Ellipsometric and magneto-optic properties of sputtered dysprosium-iron multilayers
Authors: Tiwald Thomas E. , Woollam John A. , Sellmyer D. J.
Published: July 2002

Ellipsometric and magneto-optical properties of Dy (3.5 Å thick) and Fe (2.5–12.5 Å thick) multilayers were investigated over the spectral range from 3000 to 8000 Å in magnetic fields to 0.21 T. In this range of layer thickness the magnetic anisotropy is vertical. Kerr rotations, were found to be weakly spectrally dependent, and as large as 0.06°. The magnetically driven change of ellipticity of reflected light was as large as 0.13, depending on sample and wavelength. Ellipsometric analysis of layer thickness was performed assuming a multilayer geometry. In addition, the optical constants were determined assuming the multilayer was a homogeneous layer with ‘‘effective’’ properties.
Hyperfine field measurements of Co-Cr multilayered films (abstract)
Authors: Stearns M. B. , Zhang Y. D. , Budnick J. I.
Published: July 2002

The hyperfine field distributions of equal layer thickness multilayered films (MLS) having nominal Co layer thicknesses of 21, 28, and 54 Å and total thickness of about 3000 Å have been measured by NMR spin-echo experiments. We have determined the actual thicknesses of the Co layers using saturation magnetization measurements and modelling the interface shape. Defining the Co layer thickness as where the magnetization drops to one-half of that of pure Co, we find that these thicknesses are 14±2, 17±3, and 38±4 Å, respectively, for the 21-, 28-, and 54-Å MLS. These thicknesses are quite insensitive to whether the interfacial shape of the composition profile is assumed to be trapezoidal, sinusoidal (Hanning function) or Gaussian. Co atoms in the magnetic portion of the film having one or more nearest-neighbor Cr atoms would be expected to have hyperfine fields that were so different and spread out from that of Co atoms with all near-neighbor Co atoms that they could contribute negligible intensity to the spectra. Thus it was anticipated that the hyperfine field spectra would mainly arise from Co atoms having all Co nearest neighbors and therefore the spectra of all the MLS would be similar. Indeed the spectra obtained for all these MLS, as well as for a pure Co film, are very similar. They have two broad peaks of slightly lower values than those of pure powdered Co (224±1 vs 228 MHz for the wall center resonance and 218±1 MHz vs 220 MHz for the wall edge resonance). The slight decrease of the resonance frequency is reasonable in these thin film MLS.
Exchange coupling between a soft and a hard ferromagnetic thin film
Authors: Ounadjela K. , Suran G.
Published: July 2002

An investigation of exchange coupling mechanism in a double film formed of the amorphous Co1−xTix and polycrystalline Co1−x−yPtxTiy layer is reported. The thin films were prepared by rf diode sputtering. The amorphous layer presents the characteristics of a soft ferromagnet (Hc<1Oe) and an in-plane induced uniaxial anisotropy Hk. The CoPtTi hard layer exhibits a large Hc. The exchange mechanism was characterized by the shift Hs of the in-plane hysteresis loop, and by ferromagnetic resonance measurements. The effect of interface contamination by oxygen upon the interfacial exchange constant is pointed out.
Kerr rotation spectra of Bi-substituted polycrystalline YCaVIn iron garnets
Authors: Egamov Shoukhrat , Wang Guiqin , Zhang Shiyuan , Wang Hao , Zhai Hongru
Published: July 2002

The Kerr rotation spectra of polycrystalline garnets BixY2−xCa1.0V0.5In0.7Fe3.8O12 (x=0–1.6) were measured in the range 1.8–3.4 eV to study the effect on Bi on the magneto-optical effect of polycrystalline YCaVIn garnets with a narrow linewidth of ferromagnetic resonance at 9 GHz (ΔH=1.6 Oe). Negative peaks appear on the Kerr rotation spectra of the samples containing Bi. The absolute value of the peak increases with the concentration of Bi, while the saturation magnetization at room temperature does not vary much and the Curie temperature increases. The Kerr rotation of the sample without Bi is much smaller, with its spectrum similar to that of yttrium iron garnet as reported in the literature. The reflectivity spectra for all samples are similar, showing a transition at about 2.8 eV, but the transition frequency shifts with Bi incorporation.
Examination of the cluster variational method for the Ising model and some possible corrections (abstract)
Authors: Leidecker H. , Harnden J. , Condon J.
Published: July 2002

The cluster variational method for approximating the Helmholtz free energy is known to give spurious results under some circumstances; for example, when applied in third order to the Ising model, it calculates a complex-valued Curie temperature. We show that truncating the entropy expansion at the low orders results in impossible values for the entropy for apparently allowed regions of the variation space. These distort the free energy, precluding it from having any real-valued minimum at the third order; hence, a complex value is found. Modifying the entropy series using numerical techniques reduces the distortion enough so that physically meaningful results are found.
Spin-polarized relativistic LMTO method
Authors: Ebert H. , Strange P. , Gyorffy B. L.
Published: July 2002

A very simple and efficient version of the linear muffin tin orbital (LMTO) method of band-structure calculation is presented. It treats spin-polarization and relativistic effects on equal footing. As a result, it can be used to investigate the spin dependence of the electronic structure of magnetic materials containing heavy elements. The method is illustrated by explicit calculations on ferromagnetic Ni.
The role of hybridization in U(Ru,Rh)Al
Authors: Veenhuizen P. A. , Klaasse J. C. P. , de Boer F. R. , Sechovsky V. , Havela L.
Published: July 2002

Magnetic susceptibility, magnetization, and specific heat on the pseudoternary series U(Ru,Rh)Al are presented. The development of magnetism, occurring in compounds with Rh concentrations larger than 20%, can be attributed mainly to a varying strength of the hybridization of the U 5f orbitals with the transition-metal d orbitals.
First-order phase transition induced by quantum fluctuations in Heisenberg helimagnets
Authors: Harris A. B. , Rastelli E.
Published: July 2002

The ground-state energy of a spin-density wave of wave vector Q in a Heisenberg ferromagnet with competing interactions is calculated for small Q as EG (Q)=EG (0)+A1Q2 +A2Q4+ . . . . The coefficients A1 and A2 are calculated exactly at zero temperature in the limit as the ferromagnet to helix transition is approached. For some ranges of parameters we find that quantum zero point motion causes A2 to become negative thus leading to a first-order transition not present in the classical system.
Magnetic state of Mn in Fe40−xNi40MnxB12Si8 before and after crystallization
Authors: Krishnan R. , Le Dang K. , Veillet P.
Published: July 2002

We have prepared amorphous Fe40−xNi40Mnx B12Si8 ribbons by melt spinning and investigated them using magnetometry and spin echo spectrometry. The magnetization increases with the addition of Mn, by 17% for x=0.5. Such an increase is not observed for Ni concentration in less than 40. The NMR frequency of 55Mn at 4 K for x=0.5 is 380 MHz (μMn=3.3μB) and it decreases to 340 MHz for x=5.5. The Mn moments are found to be aligned ferromagnetically to that of the alloy. The presence of Mn also leads to an increase in the magnetic moment of Fe+Ni. After crystallization, one observes in the alloy with x=5.5, two 55Mn impurities in two different compounds. The former should be a canted antiferromagnet and the latter a normal ferromagnet. The temperature-dependence results are also discussed.
Singularity and corner effects in a boundary element model for a short, linearly magnetic conducting cylinder
Authors: Ahmed M. R. , Burke P. E. , Lavers J. D.
Published: July 2002

An impedance boundary condition, boundary integral equation formulation is presented for the eddy currents induced in a magnetically linear conducting body having rotational symmetry. The treatment of kernel singularities and the representations of sharp edges are examined. A numerical treatment based on Chiba’s method is outlined. This method can be used to estimate correct values for the singular terms that can occur in the boundary integral equations. Two different representations of sharp edges are compared. The recommended representation is one in which well-defined normal directions are obtained everywhere on the conductor boundary. Numerical results are presented for the case of a short, conducting disk in a uniform, axially directed, time harmonic source field. It is shown that when the sharp edge is inadequately handled, the computed current density and power loss can be significantly in error.
Direct determination of physical properties from continuous orientation distributions
Authors: Wenk H. R. , Johnson G. C. , Matthies S.
Published: July 2002

Traditionally, the orientation distribution function (ODF) of textured materials has been derived by a deconvolution of pole figures using the harmonic method. Recently, other methods of ODF calculation have been proposed which require a modification of procedures. We describe here a combined method for deriving harmonic coefficients from any ODF, using as an example the WIMV method [S. Matthies and G. W. Vinel, Phys. Status Solidi B 112, K111 (1982)] applied to calcite with orthorhombic specimen and trigonal crystal symmetries. The results demonstrate that elastic properties derived from the harmonic and WIMV results are indistinguishable. Furthermore, we document that the ODF contribution which is not implicit in pole figures (odd coefficients) can be obtained by WIMV with fair accuracy for a complex simulated texture.
Studies on coercivity in Co-Cr thin films by means of a multilayer technique
Authors: Nakagawa Shigeki , Sumide Makoto , Kitamoto Yoshitaka , Niimura Yoshiro , Naoe Masahiko
Published: July 2002

It is known that there is a significant dependence of perpendicular coercivity Hc⊥ of Co-Cr sputtered thin films on thickness δ even if substrate temperature Tsub is constant during film deposition. Such a δ dependence of Hc⊥ suggests the nonuniformity of magnetic properties normal to the film plane. In order to prepare Co-Cr thin films with satisfactory magnetic homogeneity, multilayered films composed of many Co-Cr thin layers were fabricated by the facing targets sputtering (FTS) system. The experimental results indicated that these multilayered films may be magnetically and crystallographically homogeneous. For example, films deposited at Tsub of 150 °C with thicknesses above 1000 Å have Hc⊥ about 1.5 kOe, however, Hc⊥ of the multilayered films piled up with 300-Å-thick Co-Cr layers which are deposited even at Tsub of 150 °C indicate almost the same value as that of the 300-Å-thick unit layer. Those are about 500 Oe regardless of the total thickness of multilayers. Hc⊥ of the multilayered film depends not only on Tsub but also the thickness of the unit layer.
Subharmonic responses of ion-implanted arrays reflecting magnetostatic forward volume waves
Authors: Hartemann P.
Published: July 2002

A subharmonic response at twice a fundamental wavelength was observed by reflection of magnetostatic forward volume waves on 45° oblique incidence ion-implanted arrays. The waves were reflected by two nonperiodic arrays and traveled along a U-shaped path. Each array made of 25 bars with an average fundamental wavelength of 69 μm was implanted with 3×1015 11 B+ ions per cm2 at 150 keV. For such a dose the damaged propagation material was nonferrimagnetic and the subharmonic reflection is attributed to an energy storage consequence of the magnetic field distortion introduced by the crystalline-nonferrimagnetic material-interface corrugation. It vanished after an annealing at 620 °C without great degradation of the fundamental wavelength reflection level.
Investigation of ionic transport mechanisms during plasma anodization of Si and Si through ZrO2
Authors: Pelloie B. , Perrière J. , Siejka J. , Debenest P. , Straboni A. , Vuillermoz B.
Published: July 2002

Studies of the oxygen ion and cation transport processes during plasma anodization of bare Si and Si through thin ZrO2 films have been carried out using a combination of transport number measurements of cations t+ (ratio of the cationic current to the overall ionic current), isotopic tracing, and nuclear microanalysis. t+ in SiO2 grown through ZrO2 was found to be ∼0.25, which means that cations and oxygen ions take part in oxide growth. As t+=0 in ZrO2 in similar conditions, the transport number is not preserved through the whole oxide thickness, indicating modification of the nature of transport events in the oxide films. Isotopic tracing experiments by the use of 30Si enriched layers on 28Si substrates show that the order of cations is preserved during plasma anodization of Si and Si through ZrO2. The consequences in terms of the microscopic mechanism of ionic transport are presented and show that processes based on point defect migration cannot explain the results; other mechanisms have to be postulated.
Microhardness and plastically deformed regions in CdS single crystals
Authors: Goto Fumiaki , Kudo Shigeo
Published: July 2002

A microindentation test of CdS single crystals is performed on the {001}, {101̄0}, and {12̄10} surfaces using the sublimation method. The plastically deformed region around the indentation mark is measured by using the chemical etching technique and the optical microscope. The typical dimension of etch-pit array r μm caused by indentation is assumed as a radius of the plastically deformed region. The main results obtained are as follows: (1) The swell h from the crystal surface is 2–3 μm on the {101̄0} surfaces when the load of identer W is 2.94 N. (2) The microhardness Hv on the (0001) surfaces revealed the asteroid pattern and the rosette pattern are distributed 100 to 140 and 95 to 130, respectively. (3) The functional relation between the load of indenter W N and the r μm is r=53.3 (W−0.127)1/2 for the asteroid pattern and r=99.9 (W−0.145)1/2 for the rosette pattern of the etch pits on the (0001) surfaces.
Turn-on delay time fluctuations in gain-switched AlGaAs/GaAs multiple-quantum-well lasers
Authors: Böttcher E. H. , Ketterer K. , Bimberg D.
Published: July 2002

The turn-on delay time jitter in unbiased gain-switched AlGaAs/GaAs multiple-quantum-well lasers is determined by measuring the transient fluctuations of the total emitted power with the use of a fixed-time sampling technique with a picosecond temporal resolution. The turn-on jitter is found to decrease significantly with increasing pumping rate, particularly when the lasers are operated at an excitation level at which only the first relaxation oscillation is emitted. The root-mean-square jitter of the emitted optical pulses decreases from about 20 ps just above the laser threshold to a value of 14 ps at the threshold for the appearance of the second relaxation oscillation. These results demonstrate that an accurate adjustment of the pumping rate is essential for a low-jitter single-pulse operation of the gain-switched lasers.
dc and rf magnetron sputter deposition of NbN films with simultaneous control of the nitrogen consumption
Authors: Hedbabny H.-J. , Rogalla H.
Published: July 2002

To obtain high-quality NbN films with reproducible properties standard dc and rf magnetron sputter-deposition techniques were applied. As a sputtering gas a mixture of nitrogen and argon was used. The actual amount of nitrogen in the chamber is monitored by a differentially pumped mass spectrometer. The dependence of the nitrogen partial pressure on the amount of nitrogen injected into the chamber and the electrical power yields information about the target reaction with the nitrogen. In order to find the best preparation parameters, the interdependence between electrical sputtering power, nitrogen flow, nitrogen consumption, and the superconducting properties of the NbN films was investigated.
Two-impurity Kondo problem: Relevance to heavy fermions (invited) (abstract)
Authors: Jones B. A.
Published: July 2002

We have applied the numerical renormalization group to the problem of two Kondo impurities in an electron gas.1 This approach allows an analysis of the physics at all temperature scales as a function of the initial (high-temperature) exchange coupling and of the initial RKKY interaction. A new symmetry of the Kondo and Anderson models, which we call the axial charge, provides further details of the important physical states involved in the evolution to the low-temperature (strong-coupling) fixed point. At high temperatures, we calculate the change of the coupling interactions as the temperature is lowered from the free-local-moment fixed point. We identify the relevant lower temperature fixed points, and provide scaling results for the flows in the crossover regions. We evaluate both the range of validity of thermodynamic scaling2 at high temperatures and the strong influence of the initial interimpurity interaction on the scaling of the effective RKKY interaction. At the strong-coupling fixed point we construct a Fermi-liquid model and calculate the low-temperature specific heat, susceptibility, and staggered susceptibility; and discuss the nonuniversality of the Sommerfeld ratio. In particular, antiferromagnetic correlations produce an increased tendency to Cooper-type pairing, and we discuss these interactions in light of the new axial charge symmetry. Extensions of these pair interactions to the Fermi liquid for a lattice provide a possible description of correlations in heavy fermions.
Magnetostatic resonance of holes
Authors: Peuzin J. C. , Gay J. C.
Published: July 2002

Existence of a simple magnetostatic mode localized around a hole drilled in an infinite ferromagnetic medium was recently verified by the present authors. In this experiment, the conditions of an infinitely long hole were reproduced by placing a drilled ferromagnetic plate (an yttrium iron garnet crystal) between two silver coated soft iron blocks which acted as ‘‘magnetic mirrors.’’ In the present work, using similar arrangements, we report further results on hole magnetostatic resonance: By measuring the unloaded linewidth as a function for frequency on various samples, we show that for hole aspect ratio near unity the dominant loss of the resonator still comes from the ferromagnetic material and not from the mirrors. We also report observation of hole resonance in low-loss ceramic samples, and as a tentative illustration we briefly demonstrate application of hole resonance to single-pole transmission filters.
Aging of Schottky diodes formed on air-exposed and atomically clean GaAs surfaces: An electrical study
Authors: Miret A. , Newman N. , Weber E. R. , Liliental-Weber Z. , Washburn J. , Spicer W. E.
Published: July 2002

In this report we show that the application of a large voltage and current stress can significantly change the barrier height of a given metal (Ag,Al,Au,Pd,Cr)/GaAs(110) contact. These changes of barrier height depend on the metal used, the method of fabrication of the diode (air exposed or UHV cleaved), and the intensity and direction of the potential and current during the electrical aging. In particular, the air-exposed Ag diodes exhibit the largest change in the barrier height (∼85 meV) upon aging, while the UHV-cleaved Ag diodes do not exhibit a significant change. In the case of Au, both UHV-cleaved and air-exposed diodes show a small change (∼20 meV). The barrier heights of Pd, Al, and Cr air-exposed diodes do not exhibit an appreciable change upon aging (i.e., <10 meV). The changes in barrier height are found to have a very consistent and characteristic logarithmic dependence upon time. Once the electrical aging is stopped, the barrier height is found to recover to near the unaged value. The long time constant of the aging process, the ability of the barrier height to recover after aging, the long time constant of the recovery process, and the acceleration of the recovery process by illumination suggest that the changes in the barrier height which occur upon electrical aging are due to the creation and/or annihilation of deep level traps near the interface. We also report a systematic study of a comparison of barrier height determinations for Ag, Al, Au, Cr, and Pd diodes formed on air-exposed and UHV-cleaved GaAs(110) surfaces.
Bonding and electrical properties of boron-doped microcrystalline SiNx:H films
Authors: Hasegawa S. , Segawa M. , Kurata Y.
Published: July 2002

Microcrystalline (μc-) SiNx:H films have been prepared by rf glow discharge of SiH4-B2H6-N2-H2 mixtures as a function of the substrate temperature Ts, N2 gas ratio RN, and B2H6 gas ratio RB. The bonding, electrical, and optical properties have been investigated. Crystallization is observed at Ts below 350 °C and above 700 °C, at RN below 0.04, and at RB below 5×10−3. The ratio of the volume fraction ρ of the crystalline phase to the crystallite size δ is roughly constant. The Si-N bond density agrees well with the Si-H bond density, indicating enhanced formation of N-SiH bonds. For the films with larger ρ or δ, N and H atoms are segregated in a part of the amorphouslike boundary region between crystallites, but those for the films with lower ρ or δ are uniformly distributed in the boundary region. The optical gap is mainly characterized by the N and H contents. As the film is deposited at a preparation condition giving transformation from μc to amorphous structure, the dark conductivity and photoconductivity abruptly decrease, and the slope K in the Tauc equation for optical absorption is a maximum. Furthermore, at this condition, we obtained B-doped μc-SiNx:H films with both wide gap (∼1.9 eV) and high conductivity (10−1–10−2 Ω−1 cm−1).
Infrared absorption study of neutron-transmutation-doped germanium
Authors: Park I. S. , Haller E. E.
Published: July 2002

Using high-resolution far-infrared Fourier transform absorption spectroscopy and Hall effect measurements we have studied the evolution of the shallow acceptor and donor impurity levels in germanium during and after the neutron transmutation doping process. Our results show unambiguously that the gallium acceptor level concentration equals the concentration of transmutated 70 Ge atoms during the whole process indicating that neither recoil during transmutation nor gallium-defect complex formation play significant roles. The arsenic donor levels appear at full concentration only after annealing for 1 h at 450 °C. We show that this is due to donor-radiation-defect complex formation. Again recoil does not play a significant role.
Influence of broad Ga1/2Al1/2As interfaces on the dispersion of the interface modes in binary GaAs/AlAs superlattices
Authors: Gridin V. V. , Ning Y. B. , Datars W. R.
Published: July 2002

We developed a model for the calculation of the dispersion curves of the interface optic phonons in a superlattice with a unit cell composed of a four-layer sequence, ABCD. Allowing the B,D layers to represent the mixed Ga1/2Al1/2As broad interfaces imposed between the binary A(GaAs) and C(AlAs) layers with a reduced thickness, we applied the model to study the influence of the thickness of the B,D layers on the dispersion relation of the interface modes in this type of a superlattice. An application of this model is to estimate the influence of significant thermal annealing on the dispersion of the interface modes in GaAs/AlAs superlattices.
Magnetic field effects in a photoconductive switch
Authors: Parikh Chetan D. , Lindholm Fredrik A.
Published: July 2002

This paper analyzes a photoconductive switch design utilizing a static magnetic field to displace the optically generated electron-hole plasma to surfaces having high recombination velocities. It is demonstrated that this mechanism markedly speeds up the turnoff transient of the switch without affecting its conductance in the illuminated steady state.
Electron transport mechanism in Al/Al2O3/n-InTe/Bi thin-film structures
Authors: Rousina Roughieh , Shivakumar G. K.
Published: July 2002

Thin-film metal-insulator-semiconductor structures have been prepared by deposition of n-type indium telluride films on partially oxidized aluminum layers. An analysis of the current-voltage characteristics indicates the current transfer mechanism in these structures to be of the Schottky thermionic emission type in low field and space-charge limited at high fields. The barrier height presented to the conduction electrons in such structures has also been calculated from the temperature dependence of the I-V characteristics.
Growth and characterization of epitaxial silicon on heteroepitaxial CaF2/Si(111) structures
Authors: Sinharoy S. , Greggi J. , Schmidt D. N.
Published: July 2002

We report the epitaxial growth of silicon on a CaF2/Si(111) heteroepitaxial structure. The results show that contrary to previous reports, the room-temperature predeposition of a very thin layer of silicon does not significantly affect the problem of calcium migration to the top surface of the silicon film, although it appears to improve the surface morphology of the film. Planar and cross-sectional transmission electron microscope and x-ray diffraction studies have shown that the silicon film, although single crystalline, is highly defective, the main defects being twins on both the inclined {1̄11} planes and the parallel (111) planes.
Negative fluorescence in high-pressure Na/Hg arcs
Authors: Jongerius M. J. , Ras A. J. M. J.
Published: July 2002

This is the first report of the fact that absorption of a cw laser beam by a high-pressure arc may result in a fluorescence signal from the arc that has a negative sign. The laser-induced fluorescence (LIF) is detected at a number of optical sodium and mercury lines, while the wavelength of the laser is tuned in the wings of the Na-D lines. The negative fluorescence signal is found if the laser beam is chopped at frequencies below about 100 Hz. The amplitude and the sign of the fluorescence signal appear to depend strongly on the relative spatial positions of the laser beam and the arc volume from which the fluorescence is detected. At higher chopper frequencies the generally expected positive LIF is regained. The frequency region where the transition occurs depends on the total gas pressure in the arc. A model is presented which explains the negative fluorescence signal. In this model the absorbed laser power affects the electrical conductivity of the plasma. This causes a distortion of the electrical current distribution, leading to a change in the electrical heating of the gas in the arc. Based on this model, results are calculated which qualitatively agree with the experimental results. We discuss the consequences of the discovery of the negative fluorescence for the application of LIF in arc diagnostics.
dc-type voltage reset characteristics for soft magnetic cores at high frequencies
Authors: Yamaguchi M. , Tsuruta T. , Kikuchi S. , Matsuki H. , Murakami K.
Published: July 2002

dc-type voltage reset characteristics for amorphous ribbon, permalloy ribbon, sendust ribbon, and amorphous fiber were examined and compared with constant current reset characteristics (CMC) up to 500 kHz. A new instrument with square-wave driving is developed. We defined the control force by using the average value of control current when the control current flows forwardly with control voltage. An amorphous core with ribbon thickness of 5 μm exhibited highest gain among the cores. This clarified that the average value of reset magnetizing force for an amorphous core corresponds to the average speed of flux reset and that dc-type voltage reset characteristics for an amorphous ribbon are almost identical to CMC at high frequencies. These results are applicable for a detailed steady-state analysis of magnetic amplifiers.
The role of inelastic exchange scattering in spin polarization experiments (invited) (abstract)
Authors: Penn D. R. , Apell S. P. , Girvin S. M.
Published: July 2002

Inelastic exchange scattering of electrons can result in spin-dependent mean free paths (MFP) for electrons in ferromagnetic transition metals and glasses. The MFP of electrons with spin in the majority-spin direction will be greater than those with spin in the minority direction due to the larger number of empty minority-spin d states into which minority-spin electrons can scatter. This difference in MFP can explain the increase in the spin polarization of secondary electrons in transition metals and glasses that is observed at low energies. In addition, it will be shown that the ratio of the majority to minority spin MFP as a function of energy can be determined directly from measurements of the energy dependence of the secondary electron-spin polarization. A different type of experiment in which exchange is important is the production of Ni Auger electrons by the scattering of metastable He atoms from a Ni surface. The number of Auger electrons produced is found to depend on the relative spin of the He and Ni, parallel or antiparallel. The normalized difference of these two cases is found to increase with increasing energy of the Auger electrons. It is found that this effect is directly related to exchange scattering of the Ni electrons that neutralize the He atoms and that the experimental results can be accounted for by a simple model.
Magnetic studies of R-Ba-Cu-O superconductors made by rapid solidification (abstract)
Authors: Hadjipanayis G. C. , Li Y. P.
Published: July 2002

We have examined the magnetic hysteresis behavior and critical current density of R-Ba-Cu-O superconductors (R=Y, Dy, Er) made by melt spinning. The samples had a spherical shape with a diameter in the range 0.2–1.5 mm. The as-spun samples became superconducting after a heat treatment at around 900 °C. The critical temperature was measured with a SQUID magnetometer and found to be in the range 60–80 K. The critical temperature showed a strong dependence on sample size and was maximum for samples with a diameter approximately 0.6 mm. The critical current density was estimated to be 2×103 A/cm2, which is comparable to the values reported for bulk samples. Scanning electron microscope data showed a very fine grain structure with an average grain size of 2 μm. Detailed magnetic, structure, and chemical composition analyses will be reported.
Grain boundary diffusion of fast diffusing impurities: Investigation in the lead-silver system
Authors: Bernardini J. , Amenzou H. , Moya G. , Trampenau J. , Herzig Ch.
Published: July 2002

Grain boundary diffusivities of a 110Ag radioactive tracer have been measured in polycrystalline Pb specimens over a temperature range of 57–118 °C. Diffusivity parameter values are expressed by the Arrhenius relation: P(cm3 s−1)=Dgbδα=1.58×10−4 ×exp(−41120 J mol−1/RT). These values are five orders of magnitude higher than those relative to self-grain boundary (gb) diffusivity of lead. Thus, the difference between silver and lead grain boundary mass transport is almost the same as that measured for bulk diffusion. The possible explanations for such a similarity are discussed in relation with the particular bulk diffusion mechanism of silver and a possible high grain boundary segregation of this solute.
Magnetoresistivity in a NiFeCo/Ta multilayer thin film with elevated substrate temperature
Authors: Hur J. H. , Comstock C. S. , Pohm A. V. , Pearey L. A.
Published: July 2002

The effects of substrate temperature on magnetoresistive (MR) ratio of the NiFeCo mutilayer thin films were investigated. Films were fabricated by rf sputtering with substrate temperature elevated to 200 and 300 °C prior to deposition. MR ratios increased by an average of 5% at 200 °C and 7.7% at 300 °C, as compared with the films deposited on unheated substrate.
Photoinduced current transient spectroscopy in silicon-on-insulator films formed by oxygen implantation
Authors: Papaioannou G. , Ioannou-Sougleridis V. , Cristoloveanu S. , Jaussaud C.
Published: July 2002

The carrier trapping properties in silicon on insulator material synthesized by deep oxygen implantation (SIMOX) are investigated by photoinduced current transient spectroscopy. The method consists of filling interface states and bulk traps via photoexcitation and then monitoring the transient current in the dark which corresponds to the carrier emission process. Original experimental results and theoretical treatment are used to evaluate the energy profile of minority-carrier traps. In SIMOX material annealed at high temperature, the density of states is in the range of 1012 cm−2 at the buried Si-SiO2 interface and increases near the valence-band edge. A localized level of hole traps is hardly detected at 0.3–0.4 eV above the valence band.
Characterization of Si/CoSi2/Si(111) heterostructures using Auger plasmon losses
Authors: Schowengerdt F. D. , Lin T. L. , Fathauer R. W. , Grunthaner P. J.
Published: July 2002

The cobalt LMM Auger spectra are observed to undergo significant shape changes as a function of Si overlayer thickness and annealing temperature in Si/CoSi2 /Si heterostructures prepared by codeposition and solid phase epitaxy on Si(111) substrates. The changes are dominated by strong increases of the bulk plasmon loss intensity and shifts in the plasmon loss energy with increasing Si overlayer thickness. These effects can be used to probe the overlayers with electrons generated in the underlying layers. They are used here to measure the thickness of Si overlayers on CoSi2 . We find a linear relationship between the ratio of the plasmon loss peak associated with the Co-L23 VV Auger peak to the Auger peak itself and the known thickness of deposited Si overlayers for thicknesses up to 30 Å. Using this calibration, we monitor island formation in annealed Si/CoSi2 /Si and diffusion of Si in CoSi2 /Si. We deduce the formation of islands in the deposited Si overlayers at temperatures of 550 °C for thicknesses less than 30 Å. We observe Si diffusion in CoSi2 /Si at temperatures as low as 400 °C. We measure activation energies of 0.52–0.60 eV for the diffusion, as determined from Arhennius plots of the plasmon/Auger data, and conclude that the diffusion most likely proceeds through residual defects in the CoSi2 .
On the growth of segregated C layers on top of Fe films on pyrolytic graphite samples during high-fluence D+ irradiation at elevated temperature
Authors: Santaniello A. , Möller W. , Roth J.
Published: July 2002

On Fe films evaporated on pyrolytic graphite, thick C layers segregate during high-temperature (above about 800 K) light ion irradiation if the penetrating ions are energetic enough to reach the Fe-graphite interface. The thickness of the C segregated layer and the C depth distribution in the Fe film have been determined with 2-MeV 4He+ Rutherford backscattering. A steady-state carbon overlayer is reached at high fluences (above about 1019 particles/cm2), the thickness of which depends on the energy of the irradiating beam for a given thickness of the Fe evaporated film. The anisotropic structure of the pyrolytic graphite substrate influences the thickness of the steady-state C overlayer, thicker C layers being measured for edge-oriented C substrates. Using the Monte Carlo code trim, the production of defects in the graphite substrate has been calculated for different thicknesses of the C overlayer. The total amount of defects produced in the graphite substrate has been identified as the parameter regulating the growth and the steady-state value of the C overlayer. With the depth distributions of defect production generated by trim as source functions, the diffusion of C interstitials in graphite under the influence of recombination with vacancies has been modeled. The segregating C fluxes are identified with the fluxes of interstitials arriving at the Fe/graphite substrate interface for a suitable choice of the parameters in the diffusion equation.
Gain dynamics of Tm:Ho:YAG pumped in near infrared
Authors: Tyminski Jacek K. , Franich Douglas M. , Kokta Milan
Published: July 2002

This paper reports time-resolved spectroscopic studies of mid infrared (IR) gain in Tm:Ho:YAG. The gain was populated through an excitation of the 3H4 states of Tm3+ ions. The excitation was at 0.78 μm and was followed by the energy transport from Tm3+ ions to the 5I7 states of Ho3+. We measured the rise and the relaxation characteristics of the mid-IR gain of Ho3+. The results demonstrated Stokes energy shifts and a strongly inhomogeneous broadening of the Stark components of the Ho3+ spectrum. The gain dynamics demonstrated negligible interaction between the Stark components. The interaction between the center and the wings of inhomogeneously broadened energy levels was also weak. The studies also demonstrated a two-step excitation process (involving 3H4 states of Tm3+ and 5I7 states of Ho3+ ions) which populates the 5I7 states of Ho3+. The Stark splitting of the states, the energy level inhomogeneity, and the two-step excitation will limit the narrow-band gain extraction efficiency.