bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of the fourth-order elastic moduli by acoustic harmonic generation in stressed crystals
Authors: Gerlich D. , Breazeale M. A.
Published: July 2002

The feasibility of determining the fourth-order elastic moduli by means of measurements of the acoustic second-harmonic generation in stressed crystals is explored. It is shown that the changes to be expected under hydrostatic pressure in the ratio of the second-harmonic amplitude squared to the fundamental amplitude A2/A21 are of the order of 20%–30% per GPa, which should be easily measurable.
Operation of a bidirectional voltage-dividing bremsstrahlung diode
Authors: Harper-Slaboszewicz V. J. , Lee J. R. , Hedemann M. A. , Baldwin G. T. , Poukey J. W. , Lorence L. J. , Carlson G. A. , Fowler W. E. , Faucett D. L. , Landron C. O.
Published: July 2002

Operation of a new type of high-power electron diode, the bidirectional voltage-dividing (BVD) diode, has been demonstrated on a 1-MV, 2.5-MA, 20-ns accelerator. This diode consists of a forward- and an inverse-triaxial diode in series. The diode impedance and electron flow pattern agreed reasonably well with particle-in-cell code calculations. The radiation spectrum was measured using two different diagnostics, a differential absorption spectrometer and the time-projection Compton spectrometer. Operating at a voltage of 850–1000 kV, the BVD diode produced a bremsstrahlung spectrum similar to that produced by a standard diode operating at 350–500 kV.
Optical properties of submicrometer-size silver spheroids formed on a graphite substrate
Authors: Goudonnet J. P. , Bijeon J. L. , Warmack R. J.
Published: July 2002

Oblate spheroidal particles of silver have been fabricated on graphite substrates with an additional silicon dioxide separation of the particle film from the substrate. The particles exhibit well-resolved resonances in absorption spectra. These resonances are affected by the variation of the thickness of the SiO2 separation. Calculations based upon a nonretarded, dielectric interaction for this configuration are found to be in agreement with experimental observations.
Transport properties and infrared spectra of CuCl thin films
Authors: Martin Madhavi Z. , Shuh David K. , Williams R. Stanley , Ostrom Robert M.
Published: July 2002

The current-voltage (I-V) characteristics, dc conductivity, and infrared spectra of cuprous chloride (CuCl) thin films of different thicknesses have been experimentally investigated. The absorption peak energy in the infrared spectra and the activation energy obtained from resistivity measurements were found to be the same. This may be attributed to the existence of an indirect gap EΓX =0.41 eV. It was also observed that as the thickness of the samples decreased the absorption peaks shifted toward higher energies. This is thought to be due to the creation of strain within the lattice when the samples are prepared by molecular-beam epitaxy and has been explained on the basis of quantum size effects.
Pore-size distributions from nuclear magnetic resonance spin-lattice relaxation measurements of fluid-saturated porous solids. II. Applications to reservoir core samples
Authors: Davies S. , Kalam M. Z. , Packer K. J. , Zelaya F. O.
Published: July 2002

The application of an improved model for the estimation of pore-size distributions in reservoir core samples is presented. The technique has been applied to a series of nine samples of hydrocarbon reservoir rocks. Excellent agreement with the experimental nuclear magnetic resonance data was obtained. Of particular interest is the fact that, in two cases, broadly similar distributions were obtained for two different samples taken from the same source. This may be of significance in the prediction of the bulk petrophysical properties of the reservoirs.
The influence of growth conditions on the growth rate and composition of GaAs and GaInAs alloys grown by chemical beam epitaxy
Authors: Andrews D. A. , Davies G. J.
Published: July 2002

We have studied the effect of source species, substrate temperature, substrate orientation, and group-V overpressure on the growth rate and composition of GaAs and InGaAs alloys grown by chemical beam epitaxy. Our results for GaAs growth rate versus substrate temperature show a significant effect of group-V overpressure on the details of this dependence. The incorporation of gallium from triethylgallium into GaInAs alloys is found to be strongly dependent on temperature and alloy indium concentration, but independent of the source of indium. It is also significantly dependent on group-V overpressure. We could find no effect on growth rate or composition dependence between growth on nominally (100) GaAs and InP substrates, and those cut 2° or 3° off axis.
Lateral-mode discrimination in broad-area semiconductor lasers with a smooth spatially filtering output facet
Authors: McCarthy Nathalie , Champagne Yves
Published: July 2002

We present numerical simulations of broad-area semiconductor lasers with smooth spatial filtering at the output facet. The beam-propagation and Prony methods are used to calculate the beam characteristics and discrimination against higher-order lateral modes of the laser devices. With an output facet having a Gaussian reflectivity profile, the fundamental lateral mode is favored. Discrimination between the two lowest-order modes increases significantly with narrow reflectivity profiles.
Electrical transport properties of Au-doped polycrystalline silicon: Hole trapping effect
Authors: Fujita Y. , Masuda-Jindo K.
Published: July 2002

The electrical transport properties of Au-doped p-type polycrystalline silicon have been investigated by using the electrical resistivity and Hall mobility measurements. It has been found that the specific resistivity increases with decreasing annealing temperature and Hall mobility decreases with decreasing the effective carrier (hole) concentration, in contrast to the normal result for the single-crystal specimen. A simple physical interpretation of these results is also given.
On the origin of the carrier leakage in GaInAsP/InP double-heterojunction lasers
Authors: Chik K. D. , Richardson B. A.
Published: July 2002

The measured 950-nm emissions induced by carrier leakage are compared with theoretically calculated Auger-recombination-induced carrier leakage in GaInAsP/InP double-heterojunction lasers. The agreement obtained between measured and calculated results provides strong evidence that carrier leakage in these devices is related to the Auger-recombination processes.
Phase transition dependence on composition in ferroelectric–ferroelastic K3−x Fe5F15 for 0≤x≤0.20
Authors: Ravez J. , Abrahams S. C. , Mercier A. M. , Rabardel L. , de Pape R.
Published: July 2002

Five compositions of K6−2x[FeII2 (FeII4−2xFeIII4+2x)]F30 with 0≤x≤0.20 have been investigated. The Curie temperature Tc decreases from 490 K for x=0 to 230 K for x=0.20. The spontaneous strain es=45×10−4 for x=0 at 300 K, and decreases with increasing x to es=0 for x≥0.075. The entropy change at the transition from the ferroelectric–ferroelastic to the paraelectric–paraelastic phase is 5.5 J mol−1 K−1 for x=0, decreasing to 1.5 J mol−1 K−1 for x=0.20. Calorimetric and dielectric measurements show that the phase transition broadens as x increases. The composition dependence of the phase transition is a function of the Fe2+/Fe3+ distribution. The presence of one Fe3+ ion on the Fe2+ sites of ten unit cells reduces Tc by 150 K. The entropy change at Tc for x≂0.2 corresponds to significant remaining displacements, from the tetragonal unit-cell positions, being associated only with two of the three independent Fe atoms and with not more than two of the eight independent F atoms in each unit cell. UFAIPXR
Characterization of donorlike interface states which play a dominant role in the surface potential pinning in AlN/GaAs interfaces
Authors: Mochizuki Y. , Mizuta M. , Fujieda S. , Matsumoto Y.
Published: July 2002

The interface states at the AlN/GaAs interface, which play a dominant role in pinning the surface potential, are studied by means of quasi-static and high-frequency capacitance transient methods. Their charge transfer processes are found to be well described based on the simple deep-level picture. The observation of both behavior as electron traps as well as hole traps has provided evidence that the ionization of these states, not the surface inversion, is the surface potential pinning mechanism in the present insulator-semiconductor system. The time-variant field effect on the electron emission process is observed and reveals the donor nature of the relevant interface states. It is also argued that a defect-related origin is favored rather than a continuously distributed scheme for the interface states examined in the study.
Interfacial reaction between a Ni/Ge bilayer and silicon (100)
Authors: Li Jian , Hong Q. Z. , Mayer J. W. , Rathbun Lynn
Published: July 2002

The sequential formation and dissociation of compounds in the Ni/Ge/Si(100) system have been studied by using Rutherford backscattering spectroscopy, Auger depth profiling, x-ray diffraction, and cross-sectional transmission electron microscopy. Ni2Ge phase is formed first on the Si substrate at 250 °C. A layered structure of NiGe/NiSi/Si(100) is formed after thermal annealing at 350 °C. Upon annealing from 350 to 425 °C, the NiGe phase dissociates, inducing further growth of NiSi phase at the nickel germanide/Si(100) interface. The NiSi phase grows with a (time)1/2 dependence and with an activation energy of 2.1 eV. Marker experiment shows that Ni is a dominant moving species. The dissociation of NiGe lead to an extensive redistribution of Ge and Ni with a configuration of Ge66Si17Ni17/NiSi/Si(100) and this layered structure remains stable until 680 °C. Cross-sectional transmission electron microscopy results show that there are polycrystalline Ge plus a ternary NiSiGe phase on the top layer. High-temperature annealing (>680 °C) induces the inward diffusion of Ge to form a Ge-rich layer on the Si substrate.
Characteristics of YBa2Cu3O7 high-T
c superconductor with KCl
Authors: Yoon Ki Hyun , Chang Sung Sik
Published: July 2002

The lattice parameters, microstructural change, transition temperature, and electrical properties of the YBa2−xKxCu3O7 high-Tc superconductor in the range from x=0 to x=0.25 have been investigated. The high-Tc orthorhombic phase increases with increasing KCl up to x=0.20, above which it decreases. The lattice parameters decrease with increasing KCl up to x=0.10, and then become nearly uniform. The grain size increases with increasing KCl up to x=0.20 due to its role as sintering agent. The specimens with x=0.2 have transition temperatures of 96 K and high magnetic susceptibility due to the contraction of lattice parameters a and b and the increase of orthorhombic distortion.
Effects of bandwidth-limiting tuning elements in synchronously pumped mode-locked lasers
Authors: Zandi Bahram , Casperson Lee W. , MacFarlane D. L.
Published: July 2002

A description of bandwidth-limiting tuning filters is introduced into a semiclassical model for synchronously pumped mode-locked dye lasers. The finite phase memory of the molecular wave functions is included as are the isotropic molecular distribution and the finite vibrational relaxation times. The new set of equations has been solved numerically using the best available values for the various parameters. The results have been compared with experimental data obtained using a rhodamine 6G dye laser, which is synchronously pumped using an acousto-optically mode-locked argon laser. Tuning element effects have been studied using two- and three-plate birefringent filters and a tuning wedge, and the experimental results agree with the numerical solutions.
Investigations of evaporated silicon p-n junctions and their application to junction field-effect transistors
Authors: Tirén J. , Grelsson Ö. , Söderbärg A. , Magnusson U. , Norde H. , Svensson B. G. , Mohadjeri B. , Berg S.
Published: July 2002

p-n junctions formed by vacuum evaporation of silicon on crystalline silicon have been investigated. The junctions were formed by ion implantation of 49BF+2 in the evaporated silicon films. Subsequently, an isochronal heat treatment in the range of 600–850 °C was performed and its influence on the doping distributions and corresponding diode behavior was studied. Secondary-ion mass spectrometry was used to investigate the resulting boron distributions. A sharp decrease in the boron concentration was found at the interface for the sample annealed at 850 °C.The fabricated p-n junctions were evaluated by measuring the current-voltage characteristics. Comparisons were made to ordinary diffused p-n junctions in bulk silicon. Using the current-voltage measurements, the leakage current and the ideality factor of the diodes were extracted. The reverse currents were also measured and show a nonsaturating behavior. The resistivity of the films were investigated as a function of anneal temperature, and it was found that the boron in the films is effectively activated for heat treatments >700 °C. An estimation of the hole mobility in the films was made from the measured resistivity and doping distributions. The annealed structure was investigated with transmission electron microscopy. The heat treated films were found to be polycrystalline with very small grains (<250 Å). To demonstrate the usefulness of this technology, a junction field-effect transistor with evaporated gate diode was fabricated. The performance of this transistor is also demonstrated.
Characterization of polycrystalline silicon contacts by photoconductance measurements
Authors: Jalali Bahram , Yang Edward S. , Mei Ping
Published: July 2002

The confinement of minority carriers by polycrystalline silicon (polysilicon) contacts has been studied using the photoconductivity technique. Steady-state and transient optical measurements show a dramatic increase of stored carriers by these contacts. From a thermionic-diffusion model, a barrier height of 130 meV for the polysilicon/silicon contact has been extracted.
Tunneling current spectroscopy of electron subbands in n-type δ-doped silicon structures grown by molecular beam epitaxy
Authors: Li Hui-Min , Berggren Karl-Fredrik , Ni Wei-Xin , Sernelius Bo E. , Willander Magnus , Hansson Göran V.
Published: July 2002

Tunneling current measurements on n-type δ-doped Si(100) structures were carried out, with sheet doping concentrations ranging from ∼4×1012 to 2.0×1013 cm−2 at 4 K. All samples have been grown by using a low-energy ion source for antimony doping in a silicon molecular beam epitaxy system. From analysis of dI/dVg and (dI/dVg)/ (I/Vg) spectra, tunneling associated with quantized electron subbands is identified. The subband energy positions relative to the equilibrium Fermi level EF0 under zero bias were determined from the tunneling current measurements as a function of the sheet doping concentration. Self-consistent theoretical calculations of the electronic structure of δ layers have been performed, and good agreement between theory and experiment is obtained for most structures in the tunneling spectra.
Line shape of the intersubband optical absorption in a cylindrical quantum well
Authors: Huang F. Y.
Published: July 2002

The line shape of the intersubband optical absorption is calculated with the density-functional formulation in a cylindrical quantum well. The resonance energy shifts due to the excitonlike effect and the depolarization effect are considered. Dynamical electric conductivity in this system is found to be of the similar form obtained by Ando [Z. Phys. B 24, 33 (1976), and Phys. Rev. B 13, 3468 (1976)] in a surface space-charge layer.
Numerical simulation of collective ion acceleration in an intense electron beam–localized gas cloud system
Authors: Yao R. L. , Striffler C. D.
Published: July 2002

In experiments in which an intense relativistic electron beam is injected into an evacuated drift tube with a localized gas cloud located near the anode, ions with energies several times the electron beam energy have been observed. These experiments have been simulated using a particle-in-cell code which realistically models ionization of the gas. It was found that when the injected electron beam current exceeds the space-charge limiting current, ions are accelerated to energies several times the electron beam energy by coherent motion of the ions and the intense virtual cathode electric fields. The dependence of the peak ion energy on the system parameters as observed in the simulations is also discussed. For the parameter regimes investigated with beam energies up to 3 MV, beam currents up to 35 kA, gas pressures up to 600 mTorr, and gas cloud widths up to 6 cm, peak ion energies of 5–6 times the electron beam energy have been observed.
A surface charging technique in photoemission spectroscopic studies of dielectric-semiconductor structures
Authors: Lau W. M.
Published: July 2002

A surface charging technique used in conjunction with x-ray photoelectron spectroscopy (XPS) has been applied as an in situ surface analytical tool for the studies of the fabrication of dielectric-semiconductor structures. It was found that the measurements of surface composition and Fermi level position by XPS gives useful information on the effects of in situ surface modification prior to the deposition of the dielectric film and on the properties of the dielectric-semiconductor structure. When the thin dielectric film thickness is within 10 nm, XPS yields information on both the dielectric film and the semiconductor at the interface, and thereby allows the monitoring of the initial growth of the dielectric film. In addition to this conventional approach, surface charging of the thin dielectric film during XPS analysis, either by photoemission or by flooding the surface with low-energy electrons, provides additional information on Fermi level stabilization of the semiconductor at the insulator-semiconductor interface. Furthermore, the charging potential associated with a local impurity in the sample structure can be used to estimate the depth location of the impurity. The measurement of the degree of charging also gives information on the electrical properties of the dielectric.
Interphase-reaction controlled growth and its application to the massive transformation in Fe-Ni alloys
Authors: Jönsson Björn
Published: July 2002

Absolute reaction rate theory is applied to derive expressions for two kinetic parameters appearing in a model recently presented by Ågren. It is a model capable of treating simultaneously the effects of the surface tension, the finite interface kinetics, and the so-called solute drag upon diffusion-controlled phase transformations. The kinetic parameters are estimated and are applied to the massive growth of α in Fe-Ni alloys. Reasons for deviations of calculated and experimental values are discussed.
Valence-band electronic structure of Zn3P2 as a function of annealing as studied by synchrotron radiation photoemission
Authors: Nelson Art J. , Kazmerski L. L. , Engelhardt Mike , Hochst Hartmut
Published: July 2002

Ultraviolet photoemission (UPS) utilizing synchrotron radiation has been used to characterize changes in the valence-band electronic structure of crystalline Zn3P2 as a function of annealing temperature. The Zn3P2 crystal was etched in bromine-methanol prior to analysis and annealing was performed in vacuum at 300 and 350 °C after sputter cleaning. The UPS spectra for the virgin material are qualitatively similar to the photoemission results for various II-VI Zn compound semiconductors and a comparison of the Zn 3d binding energies with respect to the valence band maximum is presented. The results for the virgin material and the 300 °C anneal are further compared with the theoretically predicted band structure of Zn3P2 as determined by a pseudopotential energy band calculation. Loss of phosphorus from the surface and the presence of elemental zinc on the surface after the 350 °C anneal is evident.
The phase angle method for electrical resistivity applied to the hollow circular cylinder geometry
Authors: Ramos Maria José , Jardim Renato Figueiredo , Laks Bernardo
Published: July 2002

The phase-angle method to measure electrical resistivity in nonmagnetic metals is calculated for samples presenting the hollow circular geometry. The phase angle versus the operating frequency for a general hollow circular cylinder geometry shows a similar qualitative behavior when compared with the massive cylinder geometry. A discussion of a procedure for a desirable experimental condition related to the geometrical parameters and exciting signal is presented. UFaipxr
Photoacoustic investigation of the specific heat of high T
c superconductors
Authors: Song Yang Sup , Chung Nak Sam
Published: July 2002

Photoacoustic measurements for the polycrystalline samples of orthorhombic GdBa2Cu3O7−x and DyBa2Cu3O7−x have been carried out in the temperature region around the superconducting transition. The relative values of the specific heat for the superconducting samples are obtained from the photoacoustic signal by using the thermal conductivity data measured by the longitudinal heat flow method and show a good agreement with the specific heat data measured using a calorimetric method by others. The usefulness of the photoacoustic technique for the specific heat measurement is confirmed by the photoacoustic measurement of KDP(KH2PO4) sample near the phase transition.
Novel method of determining conduction-band discontinuities by using monolayer energy splitting in quantum-well structures
Authors: Uomi Kazuhisa , Sasaki Shinji , Tsuchiya Tomonobu , Chinone Naoki
Published: July 2002

We propose a novel method of determining conduction-band discontinuities ΔEc by using the relationship between the splitting energy ΔE due to monolayer fluctuation and quantum energy shift Eq in single-quantum-well (SQW) structures. This evaluation method is described by differentiating the eigenvalue equation for a finite square quantum well. The obtained formula indicates that ΔE is approximately proportional to E3/2q and that this evaluation technique is independent of ambiguity in estimation of well thickness. We apply this method to an InGaAs/InP SQW system. 4.2-K photoluminescence spectra of InGaAs/InP SQWs grown by low-pressure metalorganic chemical vapor deposition show clearly resolved doublets and in some cases triplets caused by monolayer fluctuations. As a result, we found that ΔEc =(0.25–0.30)ΔEg gave the best fit for the InGaAs/InP heterointerface.
Slowly decaying electromagnetic pulse beams
Authors: Wang Xueming , Ruan Chengli
Published: July 2002

It has been shown that the variation of energy flux of a transient electromagnetic field with distances, under some conditions, may obey a slowly decaying way instead of the usual inverse-square law. In this communication we present that the pulse beams whose spectra are depicted with the Gaussian beam theory may have slowly decreasing energy flux in the paraxial region. This result contributes new signficance to both the slowly decaying wave theory and the Gaussian beam theory.
Crystallographic structure and superconductive properties of Nb-Ti films with an artificially layered structure
Authors: Sato Noboru
Published: July 2002

Artificially layered niobium-titanium (Nb-Ti) films with various thickness ratios (3/1–1/3) and periodicities (2–100 Å) are made in an argon or in a mixed argon/nitrogen atmosphere by a dc magnetron sputtering method. Films with small periodicities (less than 30 Å) have an artificial superlattice structure (ASL) with crystallographic coherence between constituent layers, where Nb and Ti grow epitaxially on the closest planes. The crystallographic structures of films are bcc with the (110) plane parallel to the film for films with the same or a thicker Nb layer than a Ti layer, and hcp with the (001) plane parallel to the film for films with a thinner Nb layer than a Ti layer. Films with large periodicities have an artificial superstructure (ASS) with only periodic stacking of constituent layers. Films deposited in the Ar/N atmosphere also have the artificially layered structures of ASL or ASS. The artificially layered structure is thermally stable at temperatures up to 500 °C. The superconducting properties of the films depend strongly on the periodicity and thickness ratio of Nb and Ti layers. The dependence of the transition temperature on the periodicity and thickness ratio is qualitatively explained by a proximity effect with a three-region model. Films with periodicities less than 20 Å, composed of the same or a thicker Nb layer than a Ti layer, show high transition temperatures (above 9.3 K). The highest Tc of about 13.6 K is obtained in the film composed of monatomic layers of constituents deposited in an Ar atmosphere including 30 vol % N.
The effect of Fe in Fe-doped YBa2Cu3O7 superconductors
Authors: Qiu Z. Q. , Du Y. W. , Tang H. , Walker J. C.
Published: July 2002

A series of samples of YBa2(Cu1−xFex)3O7 with x ranging from 0 to 0.13 was made and investigated by x-ray diffraction, dc SQUID magnetometry, and Mössbauer spectroscopy. In the samples made by the ordinary process, Fe mainly occupies Cu(1) sites. The orthorhombic-to-tetragonal structural transition occurs at x≂0.03, and the superconducting transition temperature is depressed to zero at x≂0.17. By annealing the samples in Ar gas at 750 °C for 24 h and then reloading the lost oxygen in O2 gas at 210 °C for 48 h, we were able to draw about 30% of the Fe from Cu(1) sites into Cu(2) sites. This was verified by the enhancement of the component in the Mössbauer spectrum corresponding to Fe in the Cu(2) sites. The structural and superconducting properties of this new series of samples were also investigated. Comparison with the ordinary Fe-doped samples was also made.
Toroid magnetometer for high-critical-temperature superconductors (abstract)
Authors: Cross R. W. , Goldfarb R. B.
Published: July 2002

An improved flux-integration magnetometer was used to measure the magnetization of a toroidal sample of sintered YBa2Cu3Ox high-critical-temperature (high-Tc) superconductor as a function of field amplitude, frequency, and temperature. The sample was wound with copper drive and sense windings, and electronic integration was used to obtain magnetic induction. Drive fields up to 144 kA/m (1800 Oe) were generated with a burst of ac current at 0.1–1000 Hz through the field coil. The integrated wave forms were digitally recorded and manipulated to yield calibrated hysteresis loops of induction B and magnetization M versus field H with no need to correct for demagnetization factor. Several interesting effects were observed in the hysteresis loops, illustrating the usefulness of this high-resolution measurement technique for the study of high-Tc materials. As a function of increasing field amplitude, hysteresis first appears at the lower critical field Hc1 of the intergranular coupling component. There is a change in the slope of the magnetization curve as the grains decouple at higher fields. Above a certain temperature, the grains are decoupled even at the lowest fields. Frequency effects were observed at temperatures just below the transition temperature.
The classical equivalent-neighbor X
X
Z model: Exact results for dynamic correlation functions
Authors: Liu Jian-Min , Müller Gerhard
Published: July 2002

The dynamics of the classical XXZ model with uniform interaction is nonlinear for N≥2 spins and nonintegrable for N≥3. However, the nonlinearities disappear in the thermodynamic limit N→∞, and the spin autocorrelation functions can be determined exactly for infinite temperature. The function 〈Szi(t)Szi〉 exhibits a Gaussian decay to a nonzero constant, and the function 〈Sxi(t)Sxi〉 decays algebraically to zero or like a Gaussian, depending on the type (easy axis or easy plane) and amount of uniaxial anisotropy.
Phenomenological unloaded Q-factor theory for magnetostatic-wave straight-edge resonators
Authors: Chen Hao , De Gasperis P. , Marcelli R.
Published: July 2002

A phenomenological unloaded Q-factor (Qu) theory has been derived for all the three kinds of magnetostatic-wave straight-edge resonators (MSW-SERs), i.e., forward volume wave (MSFVW), backward volume wave (MSBVW), and surface wave (MSSW). It turns out that the Qu values of MSW-SERs are very close to that of the uniform precession mode with the exception of MSSW-SERs and MSBVW-SERs operating at frequencies below 3 GHz. The experimental responses on MSFVW-SERs are in good agreement with those predicted by the present theory
Magneto-acoustic Bragg diffraction of magnetostatic waves (abstract)
Authors: Hanna S. M. , Murphy G. P.
Published: July 2002

This experimental investigation is concerned with the study of diffraction of magnetostatic waves (MSWs) by surface acoustic waves (SAWs) when both types of waves travel in the same yttrium iron garnet (YIG) film. The SAWs are used to set up a space and time modulation of the medium in which the MSW propagates. Because of their mostly isotropic propagation properties in the plane of the film, magnetostatic forward volume waves are employed in this investigation. In the configuration used, MSW is launched at different angles with respect to the acoustic beam. Different MSW microstrip transducers are used to detect the scattered and unscattered MSW signals. The frequency of the Bragg-diffracted MSW signal is shifted by an amount equal to the SAW frequency. The MSW microstrip transducers are 65-μm-wide and 15-μm-thick copper lines on an RT/duroid substrate of thickness of 5 mils and εr=10.5. A YIG film of 120 μm thickness is placed in contact with the microstrip structure described above. A dc magnetic field is applied normal to the film plane. The SAW is excited using bulk wave transducers (36° Y-cut lithium niobate) placed on plexiglass wedges to convert the bulk acoustic waves into SAW. Our experimental results are in good agreement with calculations based on Bragg’s diffraction. Different device applications that employ this effect for spectrum analysis1 and frequency shifting2 have been proposed recently.
Determination of surface magnetic profiles of thin Permalloy films using ferromagnetic resonance (abstract)
Authors: Ounadjela K. , Speriosu V. S. , Alexopoulos P. S.
Published: July 2002

The motivation for this study arose from experimental evidence of oxidation phenomena of Permalloy films, which causes large variation in their magnetic properties as a function of film thicknesses.1 We report a numerical determination of surface magnetic profiles for films of different thicknesses and explain the modification of these profiles in terms of their oxidation. Magnetic profiles of Permalloy films can be obtained from ferromagnetic resonance (FMR) experiments. Approximate calculated profiles of saturation magnetization, exchange constant, and induced anisotropies can be determined using perpendicular resonance alone. For maximum information and accuracy, both perpendicular and parallel resonance spectra are necessary, giving the most probable magnetic profile of the films. To quantify the magnetic profiles of 50–1000-Å-thick NiFe films, we calculated the ferromagnetic resonance of a model structure using a graded saturation magnetization and exchange constant at the interface. This resonance calculation involves, in its simplest form, one second-order differential equation for perpendicular and two coupled differential equations for parallel polarization.2 The results of these calculations are matched to experimental spin-wave resonance spectra obtained at 9.5 and 34.1 GHz in perpendicular and parallel polarization, respectively. Finally, this FMR numerical solution allows us to solve the ambiguity in the source of the pinning of the magnetic moment in these films. It is due to the graded saturation magnetization at the interface and not to any significant surface anisotropy.
Numerical studies of the quantum spin chain (abstract)
Authors: Lin H. Q. , Pan C. Y.
Published: July 2002

We report the results of recent numerical studies of the antiferromagnetic Heisenberg chain with S=1/2, 1, 3/2, and 2. The ground-state energy and the energy gap between the ground state and the first excited state are obtained by using exact diagonalization method on various finite lattices and an improved real-space renormalization method. We discuss our numerical methods and results. Some of our results on the S=1 biquadratic antiferromagnetic model will also be discussed.
Chaos in magnetostatic modes in an yttrium iron garnet film between 2 and 4 GHz
Authors: Carroll T. L. , Pecora L. M. , Rachford F. J.
Published: July 2002

We have studied chaos in spin waves in an yttrium iron garnet film between 2 and 4 GHz. We have used dimension and Lyapunov exponents to differentiate the chaos resulting from driving a volume magnetostatic mode or a surface magnetostatic mode.
Mechanism of quasilinear temperature dependence of the surface magnetization in a semi-infinite ferromagnet (abstract)
Authors: Rado George T.
Published: July 2002

A semiclassical method involving surface spin waves is used to calculate the spontaneous magnetization M near the surface of a semi-infinite ferromagnet. It is assumed as before1 that the magnitude of the surface anisotropy constant Ks introduced by Néel is negligible compared to the surface anisotropy constant Kss introduced by the present author. We now generalize our calculations in two respects. First, we include dipolar interactions to keep the calculated M from diverging even when the value of Kss is relatively large. We find, as in our previous work,1 that under the above conditions any positive value of Kss causes the dependence of M on the temperature T to be quasilinear rather than proportional to T3/2 and the dependence of M on position to be exponential. Alternative predictions2 of a quasilinear T dependence of M apply only to T values near the Curie temperature. Second, we explore the consequences of assuming that the exchange stiffness constant A is weakened at the surface. We show that such a weakening is equivalent to the use of a spatially uniform value of A and an increased value of Kss. This mechanism provides a possible interpretation of recent experimental results3 on MnF2-covered Fe(110) which require a relatively large value of Kss. The full text of the present paper recently appeared4 in Physical Review B.
Synchrotron x-ray scattering studies of magnetic materials (invited) (abstract)
Authors: Gibbs Doon
Published: July 2002

With the recent development of resonant techniques,1–3 interest in x-ray magnetic scattering as a probe of magnetic and electronic structure has been steadily increasing. Significant efforts now exist at most of the x-ray storage rings around the world. These have led to proposals for dedicated beamlines at the Advanced Photon Source and at the European Synchrotron Radiation Facility planned for Argonne and Grenoble, respectively. In this talk we describe recent results of polarization and resonance studies of rare-earth and actinide materials using synchrotron radiation. For incident x-ray energies far above an absoption edge, we measure the degree of linear polarization of the scattered beam and identify the orbital and spin contributions to the magnetic cross section.1 When the incident x-ray energy is tuned near the M and L absorption edges, large resonant enhancements of the magnetic cross section, and resonant harmonics, are observed.1–3 This behavior may be understood on the basis of electric multipole transitions to unoccupied magnetic states in the conduction band.2 These techniques provide new directions to x-ray magnetic scattering studies using synchrotron radiation, including possible applications to multilayer and surface magnetic structures, and to the spectroscopy of magnetic states in the rare-earth and actinide series.
Variational wave function for nonuniform, noncollinear S=1/2 quantum antiferromagnets
Authors: Henley C. L. , Larson B. E.
Published: July 2002

The ‘‘Marshall–Huse–Elser’’ variational wave functions describe ordered planar (possibly noncollinear) ground states of s=1/2 Heisenberg spin-exchange Hamiltonians. We show how to generalize these wave functions to allow nonuniform states, arising from interactions which may be random and/or frustrated. In the Szi basis, the amplitude is exp[1/2H̃({Szi})] where the pseudo-Hamiltonian is given by H̃=−∑i2iθiSzi −(1/2)!∑ijKijSziSzj −(1/3!)∑ijkiLijkSzi SzjSzk. Here the classical ground-state directions {θi} (=0 or π in the Néel state) are found by minimizing an effective classical energy F=∑ij[Aij cos(θi−θj) +Bij cos2(θi−θj)], where (Aij,Jij) are functions of nearby Jij’s. Next, Kij and Lijk are taken to be functions of the values {Jij} and the angles {θi−θj}. The functions for Aij, Bij, Kij, and Lijk depend parametrically on a small set of variational parameters. Thus the dimension of parameter space does not grow with system size. We estimate the parameter values analytically, using the spin-wave approximation in a uniformly twisted square-lattice antiferromagnet. Also, the general form of the three-spin coefficient Lijk is roughly a sum of contributions ∝Jij sin(θi−θj), and j and k are both neighbors of spin i.
The magnetic state and its macroscopic anisotropy in amorphous rare-earth alloys (invited)
Authors: O’Shea M. J. , Lee K. M. , Fert A.
Published: July 2002

The magnetic state and anisotropy of amorphous rare-earth transition-metal systems with a microscopic random uniaxial anisotropy are discussed. Both sputtered Tb-Fe and rapidly quenched Gd65−xRxCo35 alloys (R is a rare earth) were studied. The low-temperature magnetic state of these alloys depends on the anisotropy, exchange, and applied field strength. For the case of weak anisotropy (alloys with small concentrations of anisotropic rare earth) the low-field results can be explained in terms of a correlated spin-glass state and the higher-field magnetization curves by a ferromagnet with wandering axis state. It is also shown that a weak anisotropy such as that found in Gd65−xErxCo35 (x<8) can lead to double-transition behavior as a function of temperature. The microscopic anisotropy in Gd-Tb-Co, Gd-Er-Co, and Tb-Fe alloys leads to a large macroscopic anisotropy and hysteresis is observed in the torque at 2 K. The macroscopic anisotropy strength depends on the particular rare-earth component present in the alloy and shows a strong temperature dependence. None of the alloys of this work show a significant perpendicular anisotropy. In alloys where the macroscopic anisotropy is weak (Gd65Co35) a fixed in-plane anisotropy is found which is ascribed to anisotropic structural ordering in the plane of the sample. Finally, possible explanations for the movable macroscopic anisotropy found in some Tb-Fe alloys are discussed.
Long range order in random anisotropy magnets
Authors: Fisch R. , Harris A. B.
Published: July 2002

High temperature series for the magnetic susceptibility, χ, of random anisotropy axis models in the limit of infinite anisotropy are presented, for two choices of the number of spin components, m. For m=2, we find Tc=1.78 J on the simple cubic lattice, and on the face-centered cubic lattice we find Tc=4.29 J. There is no divergence of χ at finite temperature for m=3 on either lattice. For the four-dimensional hypercubic lattice, we find finite temperature divergences of χ for both m=2 and m=3.
Generalized Slater–Pauling curve and the role of metalloids in Fe-based amorphous alloys
Authors: Sostarich M.
Published: July 2002

A modification of the generalized Slater–Pauling curve so as to consider the concentration dependence of the number of majority-spin sp electrons per average atom is proposed for amorphous iron-metalloid alloys. In this way an improved matching of the measured magnetic moment dependence on composition is achieved for Fe alloys with B and/or P as metalloids. Comparison of theory with experiment shows that amorphous Fe-P alloys tend to be magnetically rather strong, whereas their Fe-B counterparts are weak itinerant ferromagnets in almost the entire range of compositions.
Amorphous oxides with ferromagnetic exchange coupling and optical transparency
Authors: Inomata K. , Hashimoto S. , Okuno S. , Matsubara E. , Waseda Y.
Published: July 2002

0.5La1−xSrxMnO3⋅0.5B2O3 (0.2≤x≤1.0) oxides were melt quenched using a twin-roll technique. The resultant ribbons were amorphous for thicknesses below 30 μm, which was confirmed by x-ray diffraction, anomalous x-ray scattering, and transmission electron microscopy. They were characterized by high crystallization temperatures above 920 K and optical transparency. Their Curie temperatures are higher than 380 K over a wide range of Sr concentrations (0.3≤x≤1.0), thus differing from crystalline La1−xSrxMnO3 perovskites. Magnetic susceptibility above the Curie temperature follows the Curie–Weiss law with a positive paramagnetic Curie temperature, suggesting ferromagnetic spin coupling in the present amorphous oxides. The ferromagnetic behavior of the amorphous state may be explained by positive double-exchange interactions of Mn3+ and Mn4+ ions.
Magnetic field computation in a transformer core with an automatic adaptive mesh generator
Authors: Raizer A. , Dedulle J. M. , Meunier G.
Published: July 2002

This paper presents an automatic adaptive mesh generator in two and three dimensions for the study of a three-phase, three-limbed transformer core. The transformer core is laminated with grain-oriented steel sheets. A homogenization model for the iron-air lamination is investigated for the three-dimensional analysis and an elliptic model is applied to represent the crystals’ anisotropy in two and three dimensions. A scalar potential analysis for nonlinear anisotropic problems has been performed. Because of the geometry of the transformer and its mesh, numerical difficulties may appear, and a poor convergence of the solution could be obtained. In order to improve the solution, an adaptive mesh refinement procedure is used.
A formulation of the inverse problems in magnetostatic fields and its application to a source position searching of the human eye fields
Authors: Saito Y. , Itagaki E. , Hayano S.
Published: July 2002

In order to exploit an inverse problem solver in the magnetostatic fields, a new formulation of the inverse problems is proposed in this paper. As a result, it is shown that all of the inverse problems in magnetostatic fields can be reduced to find the position and magnitude of field source. By combining this new formulation, the finite-element method, and the artificial intelligence technique, we work out a general purpose inverse problem solver in the magnetostatic fields. Intensive tests of this solver suggest that the ability of this solver is depending greatly on the available data base. This solver is now applied to find a source position of the human eye fields. As a result, a plausible source position of the human eye fields can be estimated.
Magnetic ordering in Ho(CF3SO3)3⋅9H2O and Ho(C2H5SO4)3⋅9H2O
Authors: Bellesis G. H. , Simizu Satoru , Friedberg S. A.
Published: July 2002

The magnetic susceptibilities χ∥ and χ⊥, both ac (80 Hz) and static, of hexagonal crystals of the structurally similar Ho(C2H5SO4)3⋅9H2O, HoES, and Ho(CF3SO3)3⋅9H2O, HoTFMS, have been measured down to ∼0.1 K. Both order ferromagnetically along the c axis at Tc=0.23 K. Analysis of the susceptibilities above Tc shows g∥≊15.5 and g⊥≊0, ground doublet-excited singlet separation 8.4 K in HoES and 15 K in HoTFMS, and dipolar interionic interactions. Cp for both salts was also measured and found to exhibit similar sharp cooperative λ peaks at 0.23 K due to ordering of the Ho3+ moments. This peak sits atop the rounded Schottky anomaly of a system of nuclear spins in a fixed hyperfine field. The independence of the electron and nuclear contributions to Cp is associated with the Ising character of the Ho3+ ground non-Kramers doublet.
Enhancement of magneto-optic recorded domain image by mathematical morphology
Authors: Zhang X. T. , Lee Zo-Yi , Zhou M. L. , Zhu P. , Zhu Y. T. , Chen S. B.
Published: July 2002

To observe the magneto-optic (MO) recording domains precisely it is necessary to erase noise and overcome poor contrast. By applying image averaging and subtracting nonmagnetic contrast in digital image processing system, the sharp domain image can be obtained. This is the first time the domain image has been combined with morphological signal processing. By using mathematical morphology in the processing algorithms, the nonmagnetical contrast (background image) can be generated from a real image directly. Subtracting it from the real image, the target domains can be segmented and enhanced.
Exchange interactions in Fe7S8 from magnetization-pressure studies
Authors: Mulay L. N.
Published: July 2002

Per-gram magnetization (σ) is studied as a function of pressure from 0 to 16 kbar for various applied fields at room temperature (295 K). The data are combined with the pressure dependence of the Curie temperature (Tc) to obtain 1/σ0(∂σ0/∂P)H,T, 1/J(∂J/∂P)H,T, and ‖J‖, the exchange-interaction constant. The forced volume magnetostriction was found to be 1.53 Oe−1. The positive slope for (∂T/∂P)H,T and the negative one for (∂σs/∂P)H,T are discussed in terms of the exchange-striction model. ‖J‖∼104 K is estimated.
Considerations for using the attenuated total reflection technique for characterizing magneto-optical media
Authors: Zhou Y. , Ruane M.
Published: July 2002

This paper discusses theoretical and experimental aspects of applying the attenuated total reflection technique to the characterization of a multilayered structure consisting of an optically active magneto-optical medium deposited on a dielectric substrate. The dispersion relation for a uniaxial birefringent medium [ω=ω(k)] is studied through an electromagnetic surface-mode approach. The excitation of the surface plasmon in structures consisting of dielectric/magneto-optical medium/dielectric is simulated to show the angular spectra as functions of dielectric constants and thicknesses.
Infrared absorption analysis of films deposited by glow-discharge of silane/helium mixtures
Authors: Gutiérrez M. T. , Gandía J. J. , Cárabe J.
Published: July 2002

Using infrared (IR) absorption measurements, it is proposed that amorphous hydrogenated silicon films obtained from plasma-enhanced chemical vapor deposition of Silane (SiH4 ) highly diluted in helium at high rf-power densities, consist of an amorphous tissue in which a columnar microstructure is embedded. The evolution of the IR spectrum with dilution evidences a remarkable tendency to the substitution of monohydrides by dihydrides. The films show high transparency and good conductivity. These properties make them suitable to be used as window layers for thin-film solar cells when conveniently doped.
Shallow junctions by out-diffusion from Arsenic implanted polycrystalline silicon
Authors: Georgiou G. E. , Sheng T. T. , Baiocchi F. A. , Kovalchick J. , Lynch W. T. , Malm D.
Published: July 2002

We describe reverse bias diode leakage and physical analysis (secondary ion mass spectroscopy, Rutherford backscattering and transmission electron microscopy) data from shallow n+/p junctions made by implanting various doses of arsenic into polycrystalline Si and out diffusing at various temperature/time conditions, into the underlying (100) Si substrate. The polycrystalline Si is cobalt disilicided to provide the first level of metallization. The minimum process specifications giving good junction quality (reverse bias diode leakage current density ≤10 nA/cm2 at 10 V) are 7×1015 cm−2 As out diffused at 950 °C, 30 min with a junction depth 1200 Å below the polycrystalline Si. At these conditions, most of the As (≳90%) uniformly redistributes in the polycrystalline Si. There is a segregation to the polycrystalline Si/Si interface which is characterized by a porous, <50 Å thin silicon oxide interface. The polycrystalline Si/Si interface is also characterized by a laterally non-uniform large grain(∼2000 Å) or epitaxial regrowth at the 950 °C process temperature. These interface conditions may be used to explain the ∼20% high leakage population which is independent of out-diffusion condition at high As dose. Such a high sport population is not observed when P is implanted into polycrystalline Si and out diffused at 900 °C, 30 min to obtain ∼2500-Å-deep junctions below the polycrystalline Si/Si interface.