bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear reflection of bulk acoustic waves at an interface
Authors: Zhou S. , Shui Y.
Published: July 2002

A theory as the basis for solving nonlinear boundary value problems is described. A new analysis is presented for nonlinear reflection, which reveals that there is a two-dimensional spatial increase of the second-harmonic wave. The accretion along the propagation direction is the result of the self-interaction of the primary wave; the one in the wave front is due to the boundary restriction.
Ion radiation induced diffusion of Xe implanted into a polymer film
Authors: Kaschny J. R. , Amaral L. , Behar M. , Fink D.
Published: July 2002

In the present work, we have studied the most important parameters which can influence the radiation induced diffusion mechanism of Xe ions implanted into a photoresist film. With this aim, we have Ar post-bombarded the Xe implanted samples at a fixed Ar ion energy, covering a wide range of fluences. In addition, the implantation fluences, as well as the ion species used in the bombardment, were changed. The results show that the radiation induced diffusion process undergoes a trapping-detrapping mechanism. The trapping probability is proportional to the implanted fluence, and the detrapping one depends on the kind of ion used in the bombarding experiment. Finally, it is shown that the nuclear energy transfer plays an important role in the radiation induced diffusion mechanism.
Influence of the molecular structure on the refractive index of semiconducting di-β-alkylated sexithiophenes
Authors: Yassar Abderrahim , Bennouna Amin , Khaïdar M. , Ameziane E. L. , Horowitz Gilles , Delabouglise Didier , Hmyene Mohamed , Garnier Francis
Published: July 2002

The optical absorption of thin solid films of dialkylated sexithiophene derivatives (2A6T) has been measured at incident energies below the fundamental absorption edge, where these semiconducting organic materials are transparent. The absorption spectra present interference patterns that have been used for determining their refractive index n. A value of 1.904 was measured on unsubstituted sexithiophene. Alkyl substitution leads to a decrease of n, which is more pronounced as the alkyl chain length increases. This behavior is attributed to the corresponding decrease of the density of the material. Our data are compared to other experimental determinations of the optical parameters of thiophene oligomers and polymers published to date.
Effects of oxygen on electroluminescent characteristics of ZnS:TbOF and ZnS:TmOF devices
Authors: Sohn S. H. , Hyun D. G. , Noma M. , Hosomi S. , Hamakawa Y.
Published: July 2002

ZnS:TbOF and ZnS:TmOF active layers for thin-film electroluminescent devices were deposited in oxygen atmosphere by an electron-beam evaporation method and the effects of oxygen in active layers on electroluminescent (EL) characteristics were studied. With increasing oxygen deposition pressures, the luminance and the luminescent decay time increased and the threshold voltage shifted to lower values in ZnS:TbOF devices, while they showed no notable variations in ZnS:TmOF devices. X-ray-diffraction studies for ZnS thin-films showed that by the deposition in oxygen atmosphere the film orientation of (111) plane, the film uniformity, and the grain size are improved. By an analysis based on the Auger electron spectroscopy spectra for ZnS thin films and EL emission spectra, it was confirmed that a small amount of oxygen is incorporated into films and suppresses the recombination related to zinc and sulfur vacancies. It was found that contrary to ZnS:TmOF devices, ZnS:TbOF devices show a change in the peak intensity of EL spectra by oxygen doping. From the experimental results, it is suggested that in ZnS:TbOF devices oxygen doping could give rise to the increase of the luminance due to a suppression of the nonradiative energy transfer via grain boundaries and/or vacancies, whereas in ZnS:TmOF devices it plays no role in such a mechanism. The effect of oxygen doping on interfaces is also discussed.
Cross correlation of optical properties of thin films under thermal radiation
Authors: Wong Peter Y. , Trefethen Lloyd M. , Miaoulis Ioannis N.
Published: July 2002

Optical property and temperature distributions of a multilayer thin- (∼1 μm) film structure exposed to thermal radiation (1 μm≤λ≤8 μm) are dependent on film thicknesses, geometry, and material properties. Film thickness variation, simulated numerically, resulted in local minima and maxima in reflectivity and temperature distribution of these structures. We attribute this to a cross correlation phenomenon that occurs when the optical thickness of any two films in the structure is equal over a broad radiation spectrum.
X-ray photoelectron spectroscopic studies of chemical vapor deposition with TaF5 precursor on polyimide surfaces
Authors: Ugolini D. , Kowalczyk S. P. , McFeely F. R.
Published: July 2002

Chemical vapor deposition of Ta on the polyimide pyromellitic dianhydride oxydianiline was attempted using TaF5 as the precursor. The deposition temperature was 350 °C. Photoelectron spectroscopy measurements show that Ta is bound in a high oxidation state. Our data show strong evidence that initially the ternary compound TaOF3 is formed on polyimide in a first step. The carbonyl group is the main reactive site upon TaF5 exposure. It has to be noted that no passivation of the surface takes place and that there is no limit for film thickness. At very high doses, however, the film concentration at the surface is suggestive for the stable compound TaO2F. This observation is explained in terms of the formation of a metastable TaOF3 compound in the first stages of film growth and a phase transformation to TaO2F at larger thicknesses. Annealing experiments to 500 °C suggest the transformation to the oxide Ta2O5 that is strongly related to the almost complete loss of fluorine from the film upon heating.
Density and defects in thin metal films using x-ray reflectivity and variable-energy positrons
Authors: Heald S. M. , Nielsen B.
Published: July 2002

X-ray reflectivity has been used to determine the absolute metal density for both metals in bilayers of Al on top of Co, Cr, Cu, Mn, Ni, and Pd. A large variation in density is found with an observed range of 0.87–1.0 of bulk values. The results can be correlated with changes in the defect character as determined by variable-energy positron measurements. The size of the open volume defects systematically increases as the metal density decreases. A distinct densification of the Co layer was observed after annealing, and was accompanied by a corresponding reduction in the average size of the defects. There seems to be at least a partial correlation of the density with the melting point of the metals, although other factors such as the crystal structure are likely important. These results also demonstrate the application of x-ray reflectivity and variable-energy positrons to studies of thin metal films, and a discussion of their potential utility is included.
Study of charge trapping instabilities in a silicon-nitride/indium-phosphide metal-insulator-semiconductor structure by the constant-capacitance method
Authors: Kim C. H. , Choe B. D. , Lim H. , Han I. K. , Lee J. I. , Kang K. N.
Published: July 2002

The applicability of the constant-capacitance method to the characterization of the charge trapping mechanisms in the insulator of a metal-insulator semiconductor (MIS) is demonstrated. It is simple, time saving, and particularly useful in a III-V compound semiconductor MIS where the density of fast interface states may be high. Under constant capacitance, the measured diode current is directly related to the average distance that the injected charges travel before being trapped within the insulator. This method was applied to Al/silicon-nitride/InP MIS capacitors where silicon nitride films were formed by plasma-enhanced chemical-vapor deposition (PECVD). From the measurements, it was found that charge trapping by direct tunneling is dominant near the silicon-nitride/InP interface under a low insulator field, and the injection of electrons to the bulk of the silicon nitride assisted by the electric field occurs at a higher insulator field. It is also confirmed that the trap density near the silicon-nitride/InP interface is higher than that of the silicon-nitride bulk due to the initial transient phenomena of the PECVD process.
Studies of high field conduction in diamond for electron beam controlled switching
Authors: Joshi R. P. , Kennedy M. K. , Schoenbach K. H. , Hofer W. W.
Published: July 2002

Experimental studies on a vertical metal-diamond-silicon switch structure have been conducted for potential pulsed power applications. Both the dc current-voltage characteristics and the transient switching response have been measured for a range of voltages. With a 1 μm diamond film, the switch has been seen to withstand electric fields up to 1.8 MV/cm. Our results show a polarity dependence which can be associated with current injection at the asymmetric contacts. Polarity effects were also observed in the presence of e-beam excitation, and arise due to nonuniform carrier generation near the diamond-silicon interface. Our switching transients were seen to follow the shape of the e-beam for a negative bias at the silicon substrate. For positive voltage values exceeding about 80 V however, the switch is seen to go into a persistent-photocurrent mode. This effect is a result of free carrier trapping within diamond and is enhanced by the double injection process.
Optical absorption spectroscopic diagnostics during sputter deposition of Y-Ba-Cu-oxide
Authors: Blair A. J. , Metzger G. , Fleddermann C. B.
Published: July 2002

Optical absorption spectroscopy has been used in situ as a diagnostic for studying the sputter deposition of high-temperature superconductors. Both atomic and molecular species were monitored using hollow-cathode lamps as line sources and a quartz tungsten-halogen lamp as a broadband source. Measurements were made of the relative atomic and molecular species concentrations in front of the target during sputtering of Y-Ba-Cu-oxide targets using a Kaufman ion gun. The absorption measurements showed that the fluxes of ground state Ba, Cu, BaO, and CuO ejected from a composite target during argon- and oxygen-ion bombardment varied greatly with sputtering parameters. Absorptions due to Y and YO were too weak to be reliably measured. Various studies of the effects of changes in ion-beam energy, ion flux to the target, target temperature, oxygen content of the beam, and incident ion angle were performed. Stoichiometry of deposited films was also measured and correlated to the absorption results. Absorption measurements during argon- and oxygen-ion sputtering of a pure copper target were made for comparison with the results from the superconducting target. These measurements show that the relative density of species ejected from the target is highly dependent on the sputtering conditions, and indicate that careful control of beam parameters is essential for repeatable stoichiometry in deposited films.
Depth profiling and ion-induced mixing of AlAs monolayers in GaAs
Authors: Vajo John J. , Cirlin Eun-Hee , Wilson R. G. , Hasenberg T. C.
Published: July 2002

Monolayers of AlAs, in a matrix of GaAs grown by molecular beam epitaxy, were characterized using 1.0 keV O2+ secondary ion mass spectrometry (SIMS) employing sample rotation to reduce uneven sputtering and improve depth resolution. Under optimal conditions, a full width at half maximum resolution of 2.6 nm was obtained. This resolution is discussed in terms of surface roughening, the cascade mixing model, and preferential sputtering. Cascade mixing predicts well the mixing estimated from experimental measurements. In addition, using this SIMS characterization procedure, mixing from 280 keV Ar+ bombardment was studied as a function of depth. The mixing with depth varied as dictated by cascade mixing. However, quantitative estimates of the mixing were only ∼0.2 of the observed values.
Three-dimensional quasistationary approach to Cherenkov-type optical harmonic generation using a unidirectional-radiation model
Authors: Hayata K. , Matsumura H. , Koshiba M.
Published: July 2002

A three-dimensional calculation of Cherenkov-type frequency doubling in an optical channel waveguide is implemented by slicing the lateral profile of the interacting fields into a number of small segments. In each segment, lateral field variations of the harmonic signal are neglected. This method is more simple and requires less computational effort in comparison with a direct three-dimensional beam simulation. With the unidirectional-radiation model one can predict an optimum configuration and the conversion efficiency of miniaturized frequency doublers that utilize guided–to–radiation-mode interactions in nonlinear channel waveguides. Typical results are shown for blue-light generation through frequency doubling in a proton-exchanged MgO-doped lithium niobate channel waveguide. Analyses of green-light generation in organic channel waveguides are reported as well.
Electron microscopic study of partial dislocations in textured Y-Ba-Cu-O superconductors
Authors: Zheng Jian-guo , Li Qi , Feng Duan , Ding Shi-yin , Yu Shi-dong , Shen Guang-jun , Liu Feng-sheng , Zhou Lian , Mou Hui-lin
Published: July 2002

Electron microscopy shows that textured Y-Ba-Cu-O superconductors contain many partial dislocations associated with stacking faults in a-b planes. Two types of partial dislocations parallel to the [100] and [010] direction have been identified with Burgers vectors [a/2, 0, c/6] and [0, −b/2, c/6], respectively, which are the same as the displacement vectors of the associated stacking faults.
Si delta-doped In0.15Ga0.85As/GaAs strained quantum well by atmospheric pressure metalorganic chemical vapor deposition
Authors: Pan N. , Carter J. , Hendriks H. , Kim M. H.
Published: July 2002

Si delta-doped In0.15Ga0.85As/GaAs strained quantum wells are demonstrated by atmospheric pressure metalorganic chemical vapor deposition. The samples were characterized by variable temperature Hall effect, high magnetic field magnetoresistance, quantum Hall effect, capacitance-voltage measurements (C-V), and secondary-ion mass spectroscopy. The C-V profile showed a full width at half maximum as narrow as 15 Å. Two-dimensional electron gas transport was verified by observing step-like structures in the quantum Hall effect in samples containing sheet densities less than 5×1012 cm−2. Sheet densities as high as 1.0×1013 cm−2 were achieved. C and O contamination were not observed during the Si delta-doping process.
Tm+3 decay in chromium-thulium-holmium-doped yttrium aluminum garnet at liquid helium temperatures
Authors: Rotman S. R. , Kalisky Y. , Brenier A. , Pedrini C. , Boulon G. , Hartmann F. X.
Published: July 2002

The standard expression for the excited-state acceptor concentration in codoped solid-state materials is modified to include the possibility of nonradiative acceptor deexcitation. The chromium and thulium time-dependent emission in yttrium aluminum garnet (YAG) is then studied; evidence is given for the identification of the tendency for localized correlated chromium-thulium pairs in the crystalline material.
Energy distribution and formation mechanism of fast atoms in a fast atom beam
Authors: Shimokawa Fusao , Kuwano Hiroki
Published: July 2002

The energy distribution of fast atoms produced by modifying a McIlraith-type fast atom beam (FAB) source is measured using a retarding-field energy analyzer coupled with an ionization chamber. The energy distribution mainly depends on the gas pressure of the FAB source. When the gas pressure is low, the main energy distribution peak coincides with the discharge voltage, so the acceleration energy of the ions is retained when they become fast atoms. When the gas pressure is high, the peak energy appears at about 25% of the discharge voltage and has a broader spectrum. The energy distribution is almost completely independent of the discharge voltage, discharge current, and the geometry of the source anode. The fast atoms are mainly produced by resonant charge-transfer collisions inside the source. These collisions are dominant over electron-ion recombinations for FAB formation.
Spectroscopic analysis of Tm3+:NaLa(MoO4)2
Authors: Merkle Larry D. , Gruber John B. , Seltzer Michael D. , Stevens Sally B. , Allik Toomas H.
Published: July 2002

Absorption spectra of trivalent thulium (Tm3+, 4f12) doped double molybdate NaLa(MoO4)2 (NLM) are reported between 370 and 2000 nm at approximately 16 K. Laser-excited fluorescence spectra obtained at 4.2 K from multiplet manifolds 1G4 and 3H4 to manifolds 3F4 and the ground state 3H6 are also reported. The observed spectra are broad in this disordered host as compared with the spectra observed for Tm3+:YAG (yttrium aluminum garnet). The observed crystal field splitting of the multiplet manifolds in Tm3+:NLM is in reasonable agreement with the calculated splitting based on smoothed crystal field parameters obtained from an analysis of Nd3+:NLM and Er3+:NLM. The smaller crystal field splitting in Tm3+:NLM as compared with Tm3+:YAG may discourage cross-relaxation from the 3H4 to the 3F4 manifold in this host. This in turn may favor laser operation on the 3H4→3F4 transitions over the 3F4→3H6 transitions.
Dielectric response functions of heavily doped zincblende semiconductors with finite particle lifetime
Authors: Kaneto T. , Kim K. W. , Littlejohn M. A.
Published: July 2002

The dielectric response functions in the valence bands and in the conduction band of heavily doped zincblende semiconductors have been evaluated using the self-consistent field method and incorporating the finite lifetime of particles in the relaxation time approximation. Scattering rates of injected electrons are calculated with the Born approximation in the dielectric response function formalism at finite temperature. The finite particle lifetime introduces significant modifications to the spectral density function {Im[−1/ε(q,ω)]} at small q, where collective excitations (i.e., coupled phonon-plasmon modes) are heavily damped due to collisions. However, these modifications are small at large q. At the same time, the scattering rates of injected electrons are strongly affected by the temperature dependence of these effects, which are particularly significant for p-type semiconductors.
Role of native oxide in the activation of implanted Si in GaAs
Authors: Cho Jaeshin , Pawlowicz Leszek M. , Saha Naresh C.
Published: July 2002

We have investigated the effect of oxygen plasma treatment on GaAs surface prior to plasma enhanced chemical vapor deposition of silicon nitride cap on the activation efficiency of implanted Si in GaAs. The oxygen plasma treatment improved the activation efficiency by ∼35% over (1:10) NH4OH:H2O treatment. In addition, the oxygen plasma treated samples had uniform sheet resistance across the wafer with minimum wafer-to-wafer variations. X-ray photoelectron spectroscopy analysis of oxygen plasma treated GaAs surface indicated the formation of ∼25-Å-thick oxide layer consisting of Ga2O3, As2O3, As2O5, and elemental As. During the activation anneal, the arsenic-containing oxides react with the GaAs substrate to form Ga2O3 and elemental As which increases the probability that the implanted Si incorporates in the Ga sites over the As sites, and thereby improves the activation efficiency. This surface related mechanism suggests that the variation in activation efficiency is mostly attributed to variation in surface conditions, and may explain the wide variety of reported values of activation efficiency. The higher and uniform activation efficiency for high Si implants improved the wafer scale variation of ohmic contact resistance to n+-GaAs.
Oscillatory interlayer magnetic exchange coupling in Ni80Fe20/Cr multilayer structures
Authors: Peng Chubing , Dai Chen , Dai Daosheng
Published: July 2002

The evidence of antiferromagnetic interlayer exchange coupling in Ni80Fe20 /Cr multilayers is reported. In Ni80Fe20/Cr multilayers, both the magnitude of the interlayer magnetic exchange coupling and the saturation magnetoresistance have been found to oscillate with the Cr spacer layer thickness with a period of about 13 Å. Moreover, a weaker absorption line above main line in ferromagnetic resonance spectrum for the antiferromagnetically coupling film with Cr layer thickness of 12 Å has been observed in perpendicular geometry, and the strength of the antiferromagnetic coupling has been estimated to be about 0.017 erg/cm2 as well.
Cross-sectional observation of YBa2Cu3Oy/La0.7Ca0.3MnOz/YBa2Cu3Oy trilayered films
Authors: Ohno Toshiyuki , Kasai Masahiro , Kanke Yoko , Kozono Yuuzoo
Published: July 2002

Cross-sectional observations of YBa2Cu3Oy/La0.7Ca0.3MnOz/YBa2Cu3Oy trilayered films on MgO (100) substrates were performed using transmission electron microscopy. Each layer grows epitaxially with crystal orientations of YBa2Cu3Oy(100)∥ La0.7Ca0.3MnOz(110) ∥ YBa2Cu3Oy(100)∥ MgO(010). The Mn—O—Mn bond is parallel to the Cu—O—Cu bond. A reactant is absent at the interfaces and the La0.7Ca0.3MnOz layer is continuous until a thickness of about 7 nm.
Steady-state temperature profile for a thin-film resistor under bias
Authors: Sabeti Roya , Charlson E. M. , Charlson E. J.
Published: July 2002

A finite difference approximation is used to predict the temperature profile on an oxidized silicon substrate resulting from the biasing of a thin-film resistor fabricated on the surface of the wafer. The wafer is coated with a polymer whose deposition rate depends on the substrate temperature and the resulting thickness variation is compared to that predicted by theory, as a means of comparing the expected temperature distribution to the actual distribution.
Response of a semiconductor tunneling structure to a time-dependent perturbation
Authors: Fu Y. , Willander M.
Published: July 2002

The one-dimensional electron resonant tunneling spectrum (I-V characteristics) is calculated for a GaAs/AlGaAs double barrier resonant tunneling structure in the presence of a small time-dependent electric field, assuming a coherent tunneling mechanism and local equilibrium in the electrodes. The small time-dependent signal is applied as a probe perturbation in addition to the usual dc voltage. When the perturbation frequency is 4.6×1012 rad/s, the calculated current density at resonance is maximally decreased in response to the external ac perturbation. The current density returns to its dc value when the perturbation frequency is higher than ωmax=1.5×1013 rad/s. It is interpreted that the response time for the tunneling electrons in this structure is of the order of τ=1/ωmax=6.7×10−14 s. The comparison of this calculation result with the experiment [τ=6.5×10−14 s, T. C. L. G. Sollner, E. R. Brown, W. D. Goodhue, and H. Q. Le, Physics of Quantum Electron Devices, edited by F. Capasso (Springer, Berlin, 1990), p. 147] suggests that the speed of the electron redistribution in the time-dependent wave functions is very fast in these tunneling structures.
Photoluminescence characterization of Nd-doped GaP grown by metalorganic chemical vapor deposition
Authors: Takahei Kenichiro , Nakagome Hiroshi
Published: July 2002

Nd-doped GaP is grown by metalorganic chemical vapor deposition and characterized by photoluminescence measurements. The liquid-helium-temperature luminescence spectra due to Nd intra-4f-shell transitions depend on the growth conditions of the crystals. Some crystals show only a small number of luminescence lines, while some other crystals show many luminescence lines, indicating the presence of many kinds of Nd light emitting centers. Intensities of some luminescence lines begin to decrease at about 50 K and they are below the detection limit at 100 K. However, thermal quenching of some other luminescence lines begins at higher temperatures and their luminescence can be observed up to room temperature. A study on photoexcitation with above- and below-band gap energy photons reveals that some Nd centers can be excited even by below-band gap energy photons, indicating the role of mid-gap levels, in the excitation mechanism, related to the Nd centers. A further comparative study of luminescence characteristics on GaP and GaAs doped with Nd shows that the experimental evidence is consistent with the excitation mechanism proposed for intra-4f-shell luminescence of Yb in InP, where the rare earth 4f shells are excited by way of electron-hole recombination at rare-earth-related trap levels with successive energy transfer.
A novel approach to a transport model for ultra-small-scale compound semiconductor devices
Authors: Cheng Ming-C. , Huang Lin
Published: July 2002

The concepts of the previously developed macrokinetic distribution function and the ensemble average are used to develop a transport model that can account for effects of intervalley transfer, anisotropic scattering, and nonequilibrium dynamics of electrons in compound semiconductors. The developed transport model is rather simple and can be used for modeling of ultra-small-scale transport behavior of electrons in compound semiconductor devices. The developed model is applied to various multivalley semiconductor models. The study shows that the energy-dependent macroscopic effective mass of electrons in nonparabolic bandstructure, that is usually assumed for modeling of devices, is inadequate in situations where strong anisotropic scattering is involved and velocity overshoot is pronounced. It is found that the momentum dependence of the macroscopic effective mass is also significant during the interval of pronounced velocity overshoot.
Temporal response of photodiodes with GaAs/AlxGa1−xAs (0.1≤x≤0.3) multiquantum well absorption regions
Authors: Goswami S. , Davis L. , Bhattacharya P. K.
Published: July 2002

We have measured and analyzed the temporal response characteristics of high-speed photodiodes having GaAs/AlxGa1−xAs (0.1≤x≤0.3) multiquantum well absorption/transit regions. It is seen that the response time of devices with Al0.1Ga0.9As barriers is fairly insensitive to the applied reverse bias and a 30-μm-diam mesa-etched device exhibits a 30 ps response time. The response time of devices with barriers having x≥0.1 is sensitive to the applied bias, which changes the mode of carrier escape from the wells for collections.
Anharmonic betatron motion in linearly polarized undulators
Authors: Dattoli G. , Galli M. , Ottaviani P. L.
Published: July 2002

In this article we discuss the betatron equations of motion for an e-beam propagating in a linearly polarized undulator. We include the magnetic field multipolar contributions and go beyond the usual harmonic approximation. The equations of motion are derived with the inclusion of anharmonic and transverse motion coupling terms. The single particle motion as well as the beam dynamics are carefully examined.
Two-dimensional equations for guided electromagnetic waves in dielectric plates surrounded by free space
Authors: Lee P. C. Y. , Yang J. S.
Published: July 2002

Two-dimensional governing equations of successively higher-order approximations for guided electromagnetic (EM) waves in an isotropic dielectric plate surrounded by free space are deduced from the three-dimensional Maxwell’s equations by expanding the EM vector potential in a series of trigonometric functions of a thickness coordinate in the plate and in exponentially decaying functions of a thickness coordinate in the upper and lower halves of free space. By further satisfying the continuity conditions of the EM field at the interfaces between the plate and free space, a single system of two-dimensional governing equations is obtained. Solutions and dispersion relations are obtained from the two-dimensional approximate equations. Dispersion curves are computed and compared with the corresponding ones obtained from the solutions of the three-dimensional Maxwell’s equations for the transverse electric (TE) and transverse magnetic (TM) waves of the first four modes and for values of the refractive index n̂=1.5, 5, 15. It is shown that the agreement between the approximate and exact dispersion curves is very close for various order of TE and TM waves and for a broad range of the values of n̂. For bounded plates with edges in contact with free space, a uniqueness theorem for the solutions of the system of two-dimensional equations is derived from which the specification of continuity conditions on the components of the two-dimensional H and E fields at the edges are established.
Comparison of the diode, switch, and overshoot modes of magnetic-spiker excimer laser excitation
Authors: Delaporte Philippe , Taylor Rod S. , Leopold Kurt E.
Published: July 2002

As part of a program to develop a repetition rate (10–20 Hz) long optical pulse (500 ns) XeCl excimer laser, a parametric study of three different modes of magnetic-spiker circuits has been made: the switch mode, the diode mode, and the overshoot mode. A 500-ns-duration laser pulse was achieved using the overshoot mode and the possibility of developing a 20 Hz long-pulse XeCl laser is discussed.
119Sn Mössbauer and magnetization studies of Co2ScSn
Authors: Chen Z. W. , Lin C. L. , Mihalisin T. , Bykovetz N.
Published: July 2002

Magnetization measurements on the Heusler alloy Co2ScSn show that the system undergoes a transition from a paramagnetic state to a possible helimagnetic state at Tc=238 K, and exhibits spin-glass behavior below 100 K. 119Sn Mössbauer spectra of Co2ScSn are found to be influenced significantly by heat treatment. Single-dip spectra are observed above Tc as expected from the cubic symmetry at the Sn sites. The transferred hyperfine field at the Sn nuclei appears below Tc, increases with decreasing temperature, and has a value of 38 kOe at 4.2 K. The temperature dependence of the hyperfine field at the Sn nuclei shows a small break at 100 K which correlates with the onset of the spin-glass transition.
Magnetic resonance of two-dimensional Heisenberg antiferromagnets with nonmagnetic impurities
Authors: Grigereit T. E. , Drumheller John E. , Zaspel C. E.
Published: July 2002

The EPR linewidths of (C3H7NH3)2Mn1−xCdxCl4 have been measured in the paramagnetic region as a function of temperature. An Arrhenius behavior exp(b/T) is observed with b strongly dependent on Cd concentration. This behavior in the pure compound is characteristic of soliton-like (skyrmion) excitations with b related to the excitation energy. In the doped compound, gapless nonlinear excitations are possible, resulting in a much different temperature-dependent linewidth. It is concluded that skyrmions dominate the low-temperature thermodynamics of two-dimensional magnets.
Long wavelength two magnon bound states in two-dimensional lattice (abstract)
Authors: Rastelli E. , Sedazzari S. , Tassi A.
Published: July 2002

Bound states with energy below the two magnon band are proven to exist for any wave vector in the triangular ferromagnet. This statement is in contrast with early conclusions1 based on numerical calculations. On the other hand, we stress that the proof of the existence of bound states in 2D lattices is beyond any possible numerical accuracy so that analytic approaches are essential. This is due to logarithmic divergences of some integrals which assure a nonvanishing binding energy for a vanishing wave vector, but which are so weak that they escape any numerical evaluation. Consequently, we confirm that the presence of at least a two magnon bound state for any wave vector seems to be a reliable signal of absence of long range order.
Magnetic structure in Dy/Sc superlattices
Authors: Tsui F. , Flynn C. P. , Beach R. S. , Borchers J. A. , Erwin R. W. , Rhyne J. J.
Published: July 2002

We have investigated magnetic order in superlattices of Dy and Sc grown along the hcp c axis by molecular beam epitaxy (MBE) techniques. Our neutron diffraction experiments reveal that individual Dy layers order ferromagnetically below Tc∼150 K. The magnetic coherence length along the growth direction is less than the Dy-layer thickness. Previous studies of rare-earth superlattices with Y or Lu as spacer layers have shown that magnetic coherence propagates through sufficiently thin nonmagnetic interlayers. This arises from the long-range exchange interaction that originates from nesting features in the Fermi surface of the spacer material. The lack of coupling in Dy/Sc superlattices reflects the very different Fermi surface of Sc, with much weaker nesting than Y and Lu.
Magnetic circular x-ray dichroism studies of Fe/Tb multilayers
Authors: Attenkofer K. , Stähler S. , Knülle M. , Fischer P. , Schütz G. , Wiesinger G. , Scholz B.
Published: July 2002

The local magnetic structure of TbFe multilayers with various layer thicknesses of Tb (26 Å) and Fe (10, 20, 30 and 35 Å) has been investigated by circular magnetic x-ray dichroism (CMXD) studies. From the dichroic signal at the L3 edge both the local magnetic Tb moment and the anisotropic behavior of the Tb compound could be deduced. The magnetic spectra at the Tb L2 edge and the Fe K edge, which are known to be sensitive to the local chemical environment, have been used to obtain information on the binding characters of the magnetized atoms in the various TbFe compositions. Significant deviations of the CMXD spectra compared to the corresponding spectra in the pure Fe and Tb metals have been observed. This indicates significant contributions to the magnetism from an interface region, whose chemical structure resembles strongly those of the intermetallic TbFe2 compounds.
Calculations of the magnetocrystalline anisotropy of R2Fe17Nx compounds
Authors: Xu You , Ba Tu , Liu Yinglie
Published: July 2002

The calculations of the magnetocrystalline anisotropy (MCA) of the rare earth (RE) sublattice of R2Fe17Nx compounds with R=Sm, Er, Tm, and Nd based on the single ion crystal field (CF) model are presented. The MCA constants K1 and K2 and the stabilization energy of these nitrides in the temperature range 0–300 K have been obtained. The MCA behavior of these nitrides is well explained. For Sm3+ ions in Sm2Fe17Nx, the second-order CF parameter A20 is negative and large, the second-order Stevens coefficient αJ is also large. Therefore, Sm2Fe17Nx shows strong uniaxial anisotropy. It is shown that the nitrogen atoms at different interstitial sites show very different effects on the MCA. So it is thought that if the distribution of nitrogen can be controlled, the performance of Sm2Fe17Nx might be improved.
Magnetic properties and structure of sputtered Co/Pd-Ag multilayers
Authors: Bogomolov S. S. , Highmore R. J. , Shih W. C. , Greer A. L. , Somekh R. E. , Evetts J. E.
Published: July 2002

We have used magnetron sputtering to deposit Co/Pd-Ag multilayers onto unheated (111) Si substrates. The influence of Ag concentration on their structure, coercivity, and hysteresis loop squareness was studied. The best rectangular characteristics and highest coercivity were obtained for the films with 4.0 at. % Ag. These multilayers indicate considerable improvement in the magnetic properties necessary for magneto-optic recording media compared with Co/Pd films. The role of tensile stress in the system is pointed out and discussed.
Electro-optic beam deflectors for magneto-optic recording heads (abstract)
Authors: Lepore John A. , Stancil Daniel D.
Published: July 2002

To make magneto-optic recording more competitive for data storage, the access times for the magneto-optic head must be reduced. By incorporating nonmechanical beam deflection into a split head architecture, fine access times can be reduced considerably and tracking robustness can be improved. Track switching times of ∼10 μs have been reported by Arimoto et al. using a surface acoustic wave beam deflector.1 In the present work, the use of electro-optic deflection techniques is discussed and demonstrated. Potential advantages of electro-optic scanners include lower power consumption and higher optical throughput. To demonstrate the use of an electro-optic beam deflector, an optical system using a commercially manufactured electro-optic deflector has been assembled to detect a signal from a magneto-optic sample. In this system, a 488 nm laser beam is sent through the deflector into a microscope which is used to focus the beam onto the medium. As the beam deflector scans a focused spot across a magnetic stripe domain on a thin film medium, the reflected beam is sent through a differential detection system which detects the change in polarization due to the Kerr effect. In this way, the presence of the domain is detected without mechanical motion. Experimental detection of 0.6 μm wide stripes has been demonstrated using this system. We believe similar beam deflectors in thin film form could significantly impact the performance of magneto-optic recording heads.
Ferromagnetic films of MnSb prepared by laser ablation deposition (abstract)
Authors: Shvets I. V. , Cugat O. , Lunney J. G. , Coey J. M. D.
Published: July 2002

MnSb films prepared by pulsed deposition from stoichiometric MnSb cold-pressed targets were characterized by x-ray diffraction, scanning electron microscopy, scanning tunnelling microscopy, vibrating sample magnetometry, and transverse magneto-optic Kerr effect measurements. Films deposited on glass or quartz below 400 °C show preferential orientation with the (110) plane parallel to the surface of the film. They show an increased lattice constant a which is likely to be due to manganese deficiency. Square in-plane hysteresis loops were observed with a coercivity of 8 mT. The reflectivity change at saturation is 1.4%.
Design for a 1 MHz soft magnetic material hysteresisgraph (abstract)
Authors: Dennison Eric
Published: July 2002

Until recently, high frequency (1 MHz) testing of magnetically soft materials has been typically limited to measurement of core loss and peak or inductive ac permeability. A high frequency hysteresisgraph allows direct examination of the hysteresis loop and calculation of values for magnetic parameters such as coercivity (Hc), peak permeability (μp), remanence (Br), core loss (Pc,Pcv,Pcm), bias drive field strength (Hbias), maximum H drive (Hmax) and maximum or saturation induction (Bmax). This paper describes the methods used to construct and calibrate a commercial high frequency magnetic hysteresisgraph which is capable of recording the primary current and secondary voltage waveforms of magnetic cores driven at up to 1 MHz. A system accuracy of 2% (for B and H parameter values) and 5% (for core loss) was achieved through careful control and calibration of signal phase shifts within the circuitry. System calibration, magnetic field calculations, and use of FFT post-processing of the acquired waveforms are discussed. The ability to accurately record the hysteresis loop of a material at 1 MHz allows high frequency core materials to be characterized not only by core loss and permeability, but by their hysteresis loop shape, coercivity, and remanence, both under pure ac and dc biased ac drive conditions. Changes in material characteristics due to dc biasing, temperature variations, defects, or mechanical stresses can be readily observed and described in terms of changes to the hysteresis curve shape.
Magnetostatic finite-element analysis on MIMD/DMMP parallel computers (invited)
Authors: Bedrosian G. , Benway R. W.
Published: July 2002

This paper examines our recent experiences and progress in porting an in-house magnetostatic finite-element analysis code, H3D, to multiple-instruction, multiple-data (MIMD) parallel computers using the distributed-memory, message-passing (DMMP) paradigm. Experiments with two different message-passing software libraries were done, one specifically for the Intel iPSC/860 Hypercube, and another called parallel virtual machine (PVM) that runs on many different systems from networks of heterogeneous workstations connected by a local area network to supercomputers with multiple closely coupled CPUs. Techniques are discussed for performing key parts of the finite-element analysis in a parallel environment, including calculation of the source field, matrix assembly, and matrix solution. In conclusion, PVM is the preferable environment for most applications, despite its lack of maturity, because it facilitates porting software to many hardware systems without extensive rewriting.
Magnetic field-based finite-element formulation for 3D transient eddy currents
Authors: Lee J. S.
Published: July 2002

A finite-element formulation for the calculation of three-dimensional (3D) transient eddy currents in nonferrous conductors is presented in this paper. In an attempt to develop a simple yet robust finite-element formulation, the magnetic field intensity H is directly chosen as the state variable. Unlike the ‘‘curl–curl’’ formulation, this formulation is based on the vector diffusion equation and the divergence free condition is enforced by the penalty method. Finite-element implementation of the formulation is described in some detail. The proposed direct field formulation is simple to implement and computationally economical. An illustrative numerical example is also presented.
Calculation of stator radial vibration for a hybrid stepping motor using 3D finite element method
Authors: So E. C. T. , Yang S. J.
Published: July 2002

This paper presents results from radial force and stator radial vibration calculations using the 3D finite element method. Because of the special construction of a hybrid stepping motor with both unipolar flux due to the rotor magnet and heteropolar fluxes due to the currents in stator poles it is treated as a 3D magnetostatics problem. The radial force in the air gap under each stator pole has been calculated by the Maxwell stress method. The variation of radial force under each pole with one rotor tooth pitch movement is analyzed by Fourier series to obtain the force frequency spectrum with magnitudes and phase angles. It is then multiplied by the corresponding measured stator mobility values to obtain the stator radial vibration. The results are compared with experimental data and have shown a reasonable agreement.
Spin-wave self-oscillations: Experimental verification of the two-mode origin (invited)
Authors: Rezende S. M. , de Aguiar F. M. , Azevedo A.
Published: July 2002

Most theoretical models used to explain self-oscillations and chaotic phenomena observed in microwave pumped spin-wave instabilities are based on the assumption that the dynamics is governed by a few interacting modes. This assumption is somewhat disturbing because it is known that in principle an extremely large number of modes can be excited when the microwave field h exceeds the Suhl instability threshold hc. In this paper we describe pulsed microwave (8.2 GHz) spin-wave pumping experiments in spheres and films of yttrium–iron–garnet which clearly demonstrate that, with increasing power, one mode is excited at h=hc, a second mode appears at h≳hc, and subsequently the self-oscillation sets in. The observations agree very well with computer results for the transient behavior of the spin-wave equations, showing that the two-mode assumption for the onset of self-oscillation is correct. We also present data for films which add evidence to the sample-size dependence of the self-oscillation frequency and support recent improvements proposed for the two-mode model.
Multistability and chaos at parametrically excited spherical modes in an yttrium iron garnet sphere
Authors: Wiese G.
Published: July 2002

The different behaviors observed in different regimes of field of recent high-power ferromagnetic resonance experiments on yttrium iron garnet spheres within the coincidence regime of the first-order Suhl instability, which showed a complex multistable behavior beneath auto-oscillations, are examined on the basis of a detailed model which utilizes the true eigenmodes of the sphere instead of plane spin waves.
Controlling chaos in a thin circular yttrium iron garnet film
Authors: Ye M. , Jones D. E. , Wigen P. E.
Published: July 2002

Ott, Grebogi, and Yorke [Phys. Rev. Lett. 64, 1196 (1990)] proposed that the chaotic oscillations of nonlinear dynamic systems could be stabilized onto periodic orbits by introducing weak perturbations upon an available parameter of the system. In the present work, stabilization and control of chaos are demonstrated for the first time in an rf-pumped magnetostatic-resonance instability experiment on a thin circular yttrium iron garnet film, using open-loop and closed-loop feedback methods to modulate the static magnetic field. Computer simulations using a standard model have yielded qualitative agreement with the experimental results.
Quantum tunneling and spin dynamics in nanometer scale magnetic systems (invited) (abstract)
Authors: Awschalom D. D. , Smyth J. F. , Grinstein G. , DiVincenzo D. P.
Published: July 2002

We report low temperature dc SQUID measurements of the magnetic noise S(ω) and magnetic susceptibility χ(ω) on the naturally occurring magnetic protein horse spleen ferritin.1 These proteins contain a 7.5-nm-diam antiferromagnetic core of crystalline Fe2O3 with ∼4000 spins, and so have a volume more than 100 times smaller than the particles previously studied.2 Owing to their biological significance, these systems have been investigated intensively and are extremely well characterized. Studies using diluted concentrations of these superparamagnetic proteins reveal a clearly defined resonance at ∼1 MHz in both S(ω) and in χ(ω) for T<100 mK. The behavior of this feature as a function of temperature, particle concentration, and applied field is markedly different than that of earlier measurements,2 showing large shifts in frequency within fields as small as 1 mG. These results are consistent with theoretical expectations for the occurrence of macroscopic quantum tunneling in small antiferromagnets.
Microwave permeability and structural properties of CoFeSiB alloys prepared by ion beam sputtering (abstract)
Authors: Vermeulen J. L. , Acher O. , Ravel F. , Peuzin J. C.
Published: July 2002

Structural properties and microwave permeability of CoFeSiB (Co content ≊87 at. %) films prepared by an ion beam deposition technique were investigated as a function of boron content and growth temperature. A microcrystalline phase is obtained for low boron content and substrate temperatures above 80 °C. X-ray rocking curve indicate that the material is textured with 〈111〉 direction perpendicular to the film plane. The dispersion of the 〈111〉 axis is below 6°. Kerr measurements show that the magnetization is oriented in the film plane and has a uniform direction over the sample. Moreover, coercive force Hc is no higher than 0.5 Oe. The gyromagnetic resonance frequency is 2.2 GHz while the initial permeability is 700 along the hard axis and zero along the easy axis. In contrast, when substrate temperature is decreased below 50 °C, the films are amorphous. Lorentz microscopy domain observations and Kerr effect reveal a local dispersion of magnetization. This is related to the higher coercive force observed in the amorphous samples. As a consequence, microwave permeability shows several resonances and is isotropic in the film plane. It cannot be described by the Bloch–Bloembergen model.
On the k-dependence of the hybridization in two-band superconductors
Authors: Japiassu G. M. , Continentino M. A. , Troper A.
Published: July 2002

We study the influence of a k-dependent hybridization on superconductivity of a two-band model, within an extended BCS picture. Considering intraband d-d pairing and using homothetic relations for the bands and for the hybridization we calculate the energies and the gap of the quasiparticles, the order parameter and the critical temperature Tc. We verify that Tc vanishes at a critical hybridization which depends on the ratio of the effective band masses. Numerical results and possible applications are also presented.