bluuebunny/crossref_metadata_2025 huggingface dataset:
Transmission electron microscopy of interfaces utilizing mean inner potential differences between materials
Authors: Tafto J. , Jones R. H. , Heald S. M.
Published: July 2002

An electron beam propagating nearly parallel to the interface between two materials of different mean inner Coulomb potential (V0) is deflected towards the material with the largest ‖V0‖. It is experimentally demonstrated that this effect can be used to determine which of the two materials at an interface has the largest V0 and to image interfaces. Examples are presented from the SiO2/Si (111) interface and from a thin sandwich comprising the Al/Cu/Cr/SiO2/Si(100) interface system. Electron energy-loss spectroscopy of electrons deflected at the Si(111)/vacuum interface shows a strong surface plasmon peak, and with some instrumental improvements this may be a useful spectroscopic technique on buried interfaces.
Comment on ‘‘Crystallization characteristics of late transition metal-Zr glasses around the composition M9Zr1’’ [J. Appl. Phys. 5
9, 2364 (1986)]
Authors: Khan Y. , Sostarich M.
Published: July 2002

The phase Fe2Zr of MgCu2 type does belong to the final products after the crystallization of the amorphous Fe90Zr10 alloy. The alleged confusion between the x-ray diffraction patterns of Fe2Zr and Fe3O4 is refuted.
Quenching of NF singlet states in a hybrid chemical-laser system
Authors: Benard D. J. , Chowdhury M. A. , Pritt A. T.
Published: July 2002

Quenching of NF (a1Δ) and NF (b1Σ) was studied in a subscale upconversion gain medium that was based on energy transfer from NF (b1Σ) to IF. Quenching of NF (b1Σ) by IF was found to occur at gas-kinetic rates that were large compared to the energy-transfer rate, indicating low efficiency for the laser. Significant quenching of NF (a1Δ) by IF was also found to occur at a slower rate than was evident for the NF (b1Σ) state.
Direct observation of the current oscillation in a dc SQUID
Authors: Nakajima K. , Fujimaki A. , Sawada Y.
Published: July 2002

The current waveforms of the self-resetting oscillation in a dc superconducting quantum interference device (SQUID) are observed by means of a Josephson sampling system. The frequency of the oscillation is around 60 GHz. The time period of the self-resetting oscillation is experimentally measured as a function of the bias current to the SQUID. Theoretical and numerical analyses are presented for the self-resetting oscillation in the dc SQUID.
Heteroepitaxy of semiconductor-on-insulator structures: Si and Ge on CaF2/Si(111)
Authors: Fathauer R. W. , Lewis N. , Hall E. L. , Schowalter L. J.
Published: July 2002

Si and Ge layers have been grown on CaF2/Si(111) by molecular-beam epitaxy. Both Ge and Si grow as islands, and both the island size and the spacing between nucleation sites are considerably larger for Ge (∼300 nm) than for Si (∼100 nm). In addition, Ge and Si layers are found to be a mixture of type-A (aligned with the underlying CaF2) and type-B (rotated 180° about the surface normal with respect to the underlying CaF2) regions. The crystalline quality and surface morphology of the Ge layers are much better than those of the Si layers. This is thought to be due to the larger island size of the Ge deposits and to a greater ease of movement of the boundaries between type-A and type-B regions in Ge. Hall measurements show electron mobilities of up to 664 cm2/V s in Si layers and hole mobilities of 234 cm2/V s for Ge layers. Finally, the use of a GexSi1−x-Si superlattice, when grown on a GexSi1−x buffer layer which is lattice matched to the CaF2 at the growth temperature, is shown to improve Si heteroepitaxy.
Acousto-optic interaction efficiency in Ti:LiNbO3 waveguide collinear Bragg diffraction cell
Authors: Palma F. , Schirone L.
Published: July 2002

High diffracted power and bandwidth in acousto-optic guided wave Bragg cell are critically dependent on the interaction efficiency between the surface optic and acoustic waves. Through the overlapping integral, diffraction efficiency depends dramatically on the acoustic and optic field shapes in the crystal, and the surface acoustic wave penetration depth is strongly dependent on the frequency; thus, either the interaction efficiency and the acousto-optic bandwidth are strictly related to the guide geometry. For these reasons the technological process to build an optical slab guide plays a critical role in fulfilling the desired characteristics of the Bragg cell; it determines the optical field shape in the crystal and, thus, the overall limitation of the cell. In the present work, a method to analyze the technological process role for the lithium niobate Ti diffused guide is presented for a collinear guided wave Bragg cell.
Fabrication and transmission properties of electrically deposited germanium-coated waveguides for infrared radiation
Authors: Miyagi Mitsunobu , Shimada Youichi , Hongo Akihito , Sakamoto Kenji , Nishida Shigeo
Published: July 2002

Dielectric-coated metallic waveguides with diameters of 4–8 mm and a length of 1 m have been efficiently fabricated with small transmission losses by using a method of electrodeposition of germanium.
Polarized anisotropic photoluminescence of laser-related transitions in YAlO3:Nd and YAlO3:Er and line broadening by resonant lattice phonons
Authors: Dischler B. , Ennen H.
Published: July 2002

Polarized anisotropic photoluminescence spectra are presented for the 4F−43/2 I11/2 transitions of YA1O3:Nd3+ and for the 4S3/2–4I9/2 transitions of YAlO3:Er3+. It is shown that differences in the individual linewidth are caused by different degrees of resonance between lattice phonons and sublevel spacings. This model is also successfully applied to Y3Al5O12:Nd.
Electrode material release into a vacuum gap and mechanisms of electrical breakdown
Authors: Nevrovskii V. A. , Rakhovskii V. I.
Published: July 2002

Two types of instabilities of electrodes of vacuum gaps, leading to the electrical breakdown, are analyzed in connection with newly published experimental results on the electrode material release into a gap. It is noted that the cathode material release, in correlation with short time delays of the breakdown, is in agreement with the widely accepted model of explosive emission of electrons, whereas the anode material release and long time delays cannot be expanded by the model of clump detachment of the anode material as it was supposed in the experimental study. An alternative explanation is proposed on the basis of the thermal anode instability.
Atomic resolution study of displacement cascades in ion-irradiated platinum
Authors: Pramanik Dipankar , Seidman David N.
Published: July 2002

The field-ion microscope technique has been employed to study, on an atomic scale, the vacancy structure of individual depleted zones (DZs) in platinum specimens which had been created by 20-keV Kr+ ions. DZs are the final quiescent state of collision cascades. The irradiations were performed in situ at 60 K and the specimens were examined at this temperature by the pulse field-evaporation technique. The following experimental quantities were determined for each DZ: (a) the absolute number of vacancies (ν); (b) the average diameter; (c) the average vacancy concentration based on ν and the actual volume filled by the vacancies; (d) the radial distribution function of the vacancies out to the ninth nearest-neighbor; (e) the fraction of first-nearest-neighbor vacancies in clusters of size n; (f) the average depth (L) from the irradiated surface, measured along a direction parallel to the incident ion beam, at which each DZ was detected and its direction of elongation; and (g) the sputtering yield based on the number of vacancies detected in the near-surface region (<5 Å thick). All of the measured quantities are compared with corresponding quantities extracted from either an analytical model or a Monte Carlo computer code (Transport of Ions in Matter—trim) of radiation damage. We demonstrate that it is possible to transform a microscopic spatial distribution of vacancies to a continuous radiation damage profile with atomic resolution.
Application of the boundary matching method to elliptic conductors
Authors: Hussein A. M. , Biringer P. P.
Published: July 2002

A boundary matching method for the calculation of current density distribution in a long conductor with arbitrary cross section is presented in another paper. An example is given here treating an elliptical cross section. Explicit expressions for the current density distribution and conductor internal impedance are obtained. The current density and impedance are evaluated for elliptic conductors with different ellipticity. Experimental and published data confirm the analysis.
A study of the aftereffect of the magnetic permeability in Co-rich amorphous ferromagnetic alloys
Authors: Allia P. , Beatrice C. , Vinai F. , de Rezende Absair T. , Turtelli R. Sato
Published: July 2002

Room-temperature measurements of saturation magnetization, saturation magnetostriction, and aftereffect of the magnetic permeability have been performed on a set of Co-based amorphous ferromagnetic alloys with magnetostriction values in the range −4×10−6 ≲λs≲+1×10−6. The theoretical relation between aftereffect and λs has been verified to hold also in Co-rich amorphous alloys. The fraction of atoms participating in the ordering processes giving rise to the aftereffect is calculated to be of the order 10−4. The aftereffect is shown to be related, even in these alloys, to a damping of 180° Bloch walls, whose thickness increases with decreasing λs. The influence of the alloy’s stability on the permeability aftereffect is discussed in detail.
Origin of persistent photoconductivity in n-InP/GaInAs two-dimensional electron gas
Authors: Tsubaki Kotaro , Fukui Takashi , Saito Hisao
Published: July 2002

The time response of the photoconductivity of n-InP/GaInAs has been studied in detail to clarify the mechanism of persistent photoconductivity. The photoconductivity was found to be dependent upon the structure of n-InP/GaInAs which is closely related to the electronic properties of the two-dimensional electron gas. It can be concluded that the persistent photoconductivity in n-InP/GaInAs two-dimensional electron gas only originates due to the electron-hole separation and that the main recombination process is a radiative process involving an electron transition from the conduction band to the acceptor level. The calculated lifetime value of persistent photoconductivity is 5 h. This is large enough to explain the experimental results. The persistent photoconductivity in n-InP/GaInAs two-dimensional electron gas can be suppressed by reducing electron-hole separation.
Calculation of phonon-assisted tunneling between two quantum wells
Authors: Weil T. , Vinter B.
Published: July 2002

We have calculated the longitudinal optical phonon scattering between two subbands of a system of two coupled quantum wells. Our model takes the delocalization of the wave function over the whole structure into account, thus avoiding the shortcomings of earlier computations for thin barriers. The dependence on the various parameters (width of the wells and of the barrier, band offset, voltage drop between the wells, temperature, and effective mass of carriers) is discussed and illustrated.
Modeling a voltage-locked Josephson junction array amplifier: Gain, input impedance, and bandwidth
Authors: McDonald D. G.
Published: July 2002

Previously published experimental results are used to deduce an equivalent circuit for this amplifier, based on the shunted junction model. It is found that the very small inductances of the junction shunt resistors play an important role in determining the shape of the current-voltage curves in the voltage-locked region. Once the circuit is determined using the shunted junction model a combination of an approximation method (the method of slowly varying amplitudes) and the shunted junction model is used to approximately maximize the power gain of the circuit. The maximum gain achieved in these simulations of the two-junction amplifier is 11.3. This gain occurred with a negative resistance imput impedance of −0.41R and a signal source impedance of 0.167R, where R is the junction shunt resistance. It is estimated that the bandwidth of this amplifier is about 1 GHz.
Growth of periodic structures in pyrolytic laser-deposited SiC
Authors: Shaapur F. , Allen S. D.
Published: July 2002

Nonmelting surface interference ripples have been conclusively observed for the first time in thermally driven deposition of SiC from SiH4 and CH4. One set of ripples with a spatial frequency close to the primary beam wavelength (9.27 μm) is formed normal to the E field of the incident beam. An additional set of small-amplitude ripples of 1 μm or less in spacing and oriented parallel to the E field is also observed. These structural features are more pronounced in samples with higher melting points and completely disappear as the irradiated surface melts.
Infrared spectrum of oxygen in silicon
Authors: Oates A. S. , Stavola Michael
Published: July 2002

Weak absorption bands appear at 1720, 1227, and 1013 cm−1 in the infrared spectrum of Czochralski silicon. A study of the stress-induced dichroism of these features has been performed to confirm assignment of these bands to combination and overtone modes of interstitial oxygen vibrations. We show that the 1720- and 1227-cm−1 bands involve the antisymmetric stretching mode of vibration which also gives rise to the well-known interstitial oxygen band at 1106 cm−1 (the 9-μm band). Our results are inconclusive for the 1013-cm−1 line.
The distortion of the interface-state spectrum due to nonequilibrium occupancy of the interface states at the metal-semiconductor interface
Authors: Tseng Hsun-Hua , Wu Ching-Yuan
Published: July 2002

Using the Shockley–Read–Hall statistics and considering the charge exchanges between metal and interface states, the effects of nonequilibrium occupancy on the interface-state spectrum measured from a forward-biased Schottky barrier diode have been studied, both theoretically and experimentally. It is shown that due to the rapid interaction between the interface states and the minority-carrier reservoirs at the interface, the energy density of the interface states experimentally measured can exceed that of the actual one when the constant-temperature Schottky capacitance spectroscopy and current-voltage methods are used. Moreover, taking the applied voltage drop across the interfacial (dipole) layer into consideration, the apparent interface-state spectra in the vicinity of the thermal equilibrium Fermi level for various metal- and metal-silicide-Si Schottky barrier contacts can be well interpreted by a simplified interface state occupation function model, which is physically consistent with the nonideal current transport characteristics of the Schottky barrier diodes.
The emissivity of etched Cu-Nb i
n s
i
t
u alloys
Authors: Downing H. L. , Verhoeven J. D. , Gibson E. D.
Published: July 2002

Cu-Nb in-situ alloys possess high strenght plus thermal conductivity properties and are therefore of interest in heat transfer applications. Etching the surfaces of these alloys to preferentially remove Cu places the Nb filaments in relief. Experiments demonstrate that the emissivity of such etched surfaces can be increased from around 0.08 to values greater thana 0.9.
Photoionization cross-section studies of the platinum-donor center in silicon
Authors: Mayo Santos , Lowney Jeremiah R.
Published: July 2002

The relative photoionization cross section of the platinum donor center in silicon was measured over the wavelength range of 2.4 to 3.9 μm by electrical deep-level optical spectroscopy on an n+p junction at 80 K. The data were analyzed in terms of the lattice-coupling model proposed by Ridley and Amato which was modified for valence-band nonparabolicity. Good agreement was obtained between the experimental results and the model calculations of the cross section with the energy level of the donor at 0.320±0.005 eV above the valence-band edge and a Huang–Rhys factor S of approximately 1.4. This S value corresponds to a Franck–Condon energy shift of 70 meV with a phonon energy of 50 meV. Previously reported photoionization data of the gold donor were also fit by the same model, yielding S≂0.4, a surprisingly small value. Estimates were made of the majority-carrier capture cross section for these two levels and for the platinum acceptor center in silicon, which was measured previously. These estimates, based on Ridley’s quantum-defect model and our measured S values, are several orders of magnitude smaller than the corresponding measured values, indicative of the complex nature of these 5d-transition elements in silicon. More detailed models, perhaps including anharmonicity of the defect vibrations, are required to understand these large capture cross sections.
Stochastic structures observed on laser-evaporated V2O5, Bi, and Pb surfaces
Authors: Nánai L. , Hevesi I. , Bunkin F. V. , Luk’yanchuk B. S. , Morozova E. A.
Published: July 2002

The thermal instability effects caused by laser light on the surfaces of several solids have been investigated experimentally. At sufficiently high-radiation intensities, the evaporation front was found to be unstable and different kinds of periodic structures appeared on the laser-damaged surfaces. The features of irradiated surfaces are connected with developing instabilities of melting and evaporation formed from plasma, and with excitation of surface electromagnetic waves.
Effects of pressure on Cd1−xZnxTe alloys (0≤x<0.5)
Authors: Webb A. W. , Qadri S. B. , Carpenter E. R. , Skelton E. F. , Kennedy J.
Published: July 2002

Electrical resistance measurements have been performed on samples of Cd1−xZnxTe (0≤x<0.50) as a function of pressure up to 7.0 GPa. Based on a multidecade decrease in the resistance, the transition pressure of the B3 to B1 phase change is observed to increase from 3.3 to 6.7 GPa as x increases from 0 to 0.49. An anomalous drop in the resistance is observed to precede this transition; the magnitude of this drop increases with increasing x up to x=0.45, where it takes the form of a local minimum in the resistivity. The origin of this anomaly is not understood, but it is presumed to be similar to the local resistance minimum previously reported in ZnTe.
Electro-optical effects of uniform layer-tilted state in ferroelectric liquid crystals
Authors: Yang K. H.
Published: July 2002

Experimental results on the electro-optical behavior of uniform layer-tilted ferroelectric liquid crystals (FLCs) are reported for the first time. The special arrangement of the uniform layer-tilted state, with the spontaneous polarization parallel to the cell substrates, responds equally to either polarity of the electric field without a storage effect. Due to the presence of a small pretilt angle of the director of the FLC caused by rubbing alignment, the saturated light transmission through such a FLC cell between crossed polarizers shows a characteristic asymmetry with respect to different polarities of the field. The saturated light transmission and the angular position to null the asymmetry have been used to determine the cone angle and the pretilt angle of the FLC director, respectively. The switch-on time at 15 V is less than 23 μs for both polarities of the field. Field induced switch-off time is 34 μs.
An empirical theory of isc and voc in the ZnzCd1−zS/Cu2S solar cell
Authors: Mojumder M. A.
Published: July 2002

A simple empirical theory has been given for the short-circuit current (isc ) and the open-circuit voltage (voc ) of the ZnzCd1−zS/CU2S solar cell. The heterojunction band lineup at the interface is assumed to be determined by the pinning of the Fermi level at the collector surface by the copper impurity/cation vacancy level. Since the impurity level remains fixed with respect to the collector valence-band edge and the collector band gap goes up with z, such a pinning produces a potential barrier (‘‘spike’’) at the junction. The height of the spike increases with z. An estimate is made of the Cd impurity level in the emitter. This level is believed to act as the recombination center for electrons diffusing back to the emitter from the collector conduction band. These electrons would normally face a strong opposing field but because of an expected incipient Zener breadkdown of the potential barrier in the narrow highest field region they would face a substantially smaller opposing field. Zener breakdown field for CdS is known and for the mixed sulfide we have considered this field as a parameter obtained by fitting the voc values. The parameter, thus

obtained, varies with z smoothly in a logarithmic scale and is within an order of magnitude of the Zener breakdown field for CdS. We have given some physical arguments to show that the Zener breakdown and consequent reduction of the field does not necessarily mean a widening of the depletion layer. While for CdS the known Zener breakdown field gives a value of voc in good agreement with the experiment, it is a measure of the expected correctness of the fitted values of this field that, in conjunction with the heights of the conduction-band spike, they give reasonable isc values. The generally consistent values of the parameters of the cell measured in different specimens are ascribed to the self-doping and self-compensating properties of the collector material. An explanation of the crossover of dark and light current-voltage characteristics for different types of cells has been given. Since it is futile to aim at any numerical accuracy in view of the uncertainties in some of the material parameters, the main emphasis has been on the explanation of the trends of the variation of the parameters with z. This explanation has been given in terms of a few physically reasonable assumptions. Although at least one experimental result tends to confirm the position of the recombination level, a few specific experiments have been suggested which would hopefully sustain the assumptions of the theory.
UV-Cu II-laser with helical hollow cathodes
Authors: Eichler H. J. , Hamisch J. , Macdonald R. , Sollinger M. , Chen Yuging
Published: July 2002

UV lasing was obtained with helical copper hollow cathodes. The output powers have been measured multiline (248–270 nm) for some helix geometries as a function of different discharge currents, Ne pressures, and mirror reflectivities. A maximum laser power of 580 mW has been obtained in a segmented discharge tube with a total active length of 1.2 m. Laser action was also observed at 780 nm with a power of 1.3 W. The discharge stability is superior to other arrangements.
Preparation of Hg1−xCdxTe with a semiclosed rotational liquid-phase-epitaxy system
Authors: Lan H. , Cheng K. Y. , Shiue C. C. , Pang Y. M. , Yang S. J.
Published: July 2002

Hg1−xCdxTe epitaxial layers were grown on CdTe substrates by the liquid-phase-epitaxy method in a horizontal open system. A semiclosed rotational boat was developed to prevent Hg loss from the Te-rich growth melt during growth processes. The solid composition of HgTe-rich Hg1−xCdxTe layers can be reproducibly controlled. Through the rotation mechanism, the melt entrapment on the as-grown surface can be avoided. With a small amount of excess Hg added into the growth melt and in situ annealing at 300 °C right after the growth, an n-type epilayer can be obtained. The electron concentration of 3×1015 cm−3 and the electron mobility of 7.5×104 cm2/V s were obtained.
A local measurement of Ba+ density temporal evolution
Authors: Chen Guoxong , Nee Tsu-Jye A.
Published: July 2002

The local temporal evolution of the Ba+ number density in a resonant laser-driven barium plasma has been measured for the first time by using near-resonance Rayleigh scattering. This local temporal evolution is quite different from other measurements, where spatially integrated absorption methods were employed.
Reduction of friction between a tape and a smooth surface by acoustic excitation
Authors: Tam A. C. , Bhushan B.
Published: July 2002

The frictional force acting on a tape moving in contact with a smooth surface leads to wear of the latter. An important example exists where the magnetic tape is wrapped around or supported on surfaces that do not have hydrostatic air bearings or hydrodynamic air bearings during start/stop in a tape-drive system; the abrasion of the bearing surface by the tape results in the generation of debris and wear. This communication describes our observation that the friction between a magnetic tape and a smooth glass surface can be significantly reduced by acoustic excitation of the tape or of the glass surface. Possible explanation of the observation in terms of a squeeze film theory is discussed.
Titanium silicide ultrafine powder: CO2 laser generation and thin-film applications
Authors: Gupta Arunava , Beeson Karl W. , Donlan Jeffrey P. , West Gary A.
Published: July 2002

A continuous wave carbon dioxide laser has been used to produce ultrafine (∼50 nm) titanium silicide powder by homogeneous nucleation from the gas phase of a mixture of titanium tetrachloride and silane. Depending on the process conditions, titanium subhalides (TiCl3, TiCl2) and silicon are also present in the powder. Thin films (1– 4 μm) have been prepared on alumina and silicon substrates by spraying a suspension of the powder on the substrate and subsequently sintering it in vacuum. Dense films can be prepared by sintering powders containing 25– 40 wt. % excess silicon at 950–1050 °C. The resistivity which has been achieved after densification of 2– 4-μm-thick films is 80–90 μΩ cm.
Acousto-optic interaction in proton-exchange 128° rotated Y-cut LiNbO3 optical waveguides
Authors: Saiga N. , Ichioka Y.
Published: July 2002

The characteristics of proton-exchanged optical waveguides using a new substrate of 128° rotated Y-cut LiNbO3 were investigated. The variation of refractive index was found to be Δn≂0.07, because the crystallographic c axis was oblique to the surface normal. As a result, the number of guided modes versus the depth of proton exchange was small compared with that in conventional substrates. Acousto-optic interaction between a guided mode and surface acoustic wave exhibited the diffraction efficiency of about 50% for the acoustic power of 18 mW at 130 MHz. This suggested that after the proton-exchange process, an apparent photoelastic coefficient was still maintained with the reduction factor of 1/ 7/8 .
Insulated dipole antennas for heating oil shale
Authors: Casey John P. , Bansal Rajeev
Published: July 2002

Insulated dipole antennas in the HF band are potentially useful in heating shale in situ to extract oil. To help evaluate the efficiency of such antennas, the spatial distribution of the power absorbed per unit volume in the shale is computed.
X-ray diffraction studies of microstructural transformations in single-crystal silicon during current filamentation
Authors: Pimpale Ashok , Choudhari S. M. , Bhide V. G.
Published: July 2002

The (111) Bragg peak of p- and n-Si single crystals is studied when a large dc current (average current density 10 A/cm2) is passing through the specimen. The integrated intensity of the peak changed drastically with time after current filamentation, showing existence of microstructural transformations. The fresh samples (type A) showed a decrease in integrated intensity by a factor of about 50, 15 min after current filamentation, with a limiting current of 330 mA passing through the sample. The intensity partially recovered when the current was switched off, and, after cooling to room temperature, the specimen behaved differently when the electric field was again applied. The specimen (type B) then showed an increase in integrated intensity a couple of minutes after current filamentation so that the diffracted intensity became comparable to the type A specimen. Thereafter, with continued high current passing through the specimen, it behaved like a fresh silicon sample. The results are interpreted by considering formation of current filaments and consequent local heating.
Comment on ‘‘Particle size distribution effects on sintering rates’’ [J. Appl. Phys. 6
0, 383 (1986)]
Authors: Harrett T.
Published: July 2002

A recent paper in the Journal of Applied Physics analyzed the dependence of sintering rate on power particle-size distribution to derive a basic relative rate constant for the process. The derivation involved rather cumbersome numerical quadratures of the lognormal functions concerned. This procedure is unnecessary, since an exact closed-form result, as given in this Comment, is easily obtained. Some fairly obvious incidental errors in the original presentation are also corrected. Several other lognormal distribution integrals, apparently unlisted in previous literature and which might prove similarly useful in connection with distribution problems, are also presented.
Transfer-matrix method applied to multiregion cylindrical induction devices with two-dimensional current excitation
Authors: Cao M. , Biringer P. P.
Published: July 2002

A theory is presented here to obtain the electromagnetic field in a multiregion cylindrical induction device with arbitrary two-dimensional current sheet excitation. This theory is based on the transfer-matrix method and provides a closed-form solution. It applies also to the case of one-dimensional excitation where it reduces to the known results presented by Freeman [Freeman, IEE Proc. 121, 1117 (1974); Greig and Freemen, IEE Proc. 114, 1681 (1967); Freeman and Blank, IEE Proc. 123, 149 (1976)]. A numerical example is shown, and it is in good agreement with published data.
Angular variation of the coercivity in anisotropic barium and strontium ferrite permanent magnets
Authors: McCurrie R. A. , Jackson S.
Published: July 2002

Room-temperature measurements have been made of the variation of the intrinsic coercivity Hc of anisotropic barium ferrite and strontium ferrite permanent magnets as a function of the angle θ between the direction of measurement and the preferred axis of magnetization. For the strontium ferrite specimen the angular variation Hc vs θ was also measured at 77, 130, and 230 K. All the results showed a gradual increase in Hc with increase in θ up to a maximum and thereafter a rapid decrease to Hc=0 at θ=90°. The angular variation in coercivity was also measured after saturation parallel to the direction of measurement. An attempt has been made to interpret the results.
Photoluminescence study of heat-treated InP
Authors: Kim T. S. , Lester S. D. , Streetman B. G.
Published: July 2002

Low-temperature photoluminescence is used to study optical transitions in InP which arise from moderate-temperature annealing or dielectric encapsulation. A total of seven shallow emission lines appear in annealed or encapsulated InP that are not present in unprocessed material. These transitions are easily observed in undoped substrates. They are less intense or absent in Fe-doped material, and are not seen in p-type material. It is found that dielectric capping with SiO2 enhances the formation of several transitions, while phosphosilicate glass or Si3N4 effectively suppresses their formation. Surprisingly, some of these recombination centers are found to extend many microns into the substrate after SiO2 deposition at 350 °C or after annealing at temperatures as low as ∼400 °C. These centers appear to be related to previously observed processing-induced carrier concentration changes. Possible origins of the transitions are discussed.
High-power XeCl discharge laser with a large active volume
Authors: Hasama Toshifumi , Miyazaki Kenzo , Yamada Kawakatsu , Ohuchi Kazumi , Sato Takuzo
Published: July 2002

An x-ray preionized discharge-pumped XeCl laser with a 10-cm laser-electrode separation has been developed. The laser has a pulse-transmission line in the excitation circuit to realize a high pulse-forming line voltage and a low output impedance. The maximum laser energy obtained is 44 J in an 85-ns pulse (FWHM), corresponding to the peak power of 520 MW. The highest electrical efficiency of 2.9% has been achieved with a laser energy of 16.4 J.
Effect of defects and further neighbor interactions on a two-dimensional dipolar system on a honeycomb lattice
Authors: Zimmerman George O. , Ibrahim A. K. , Wu F. Y.
Published: July 2002

A theoretical investigation of a planar dipolar system on a honeycomb lattice reveals that the ground-state energy is increased for finite systems over that of an infinite system. The infinite system has a ground-state degeneracy with respect to dipole orientations. This degeneracy is lifted for finite systems. A mean-field calculation including nearest, second, and third neighbors shows that there are three phases, an ordered phase, a paramagnetic one, and a magnetic-field-induced ferromagnetic phase. A defect in the second nearest neighbor has the effect of introducing a finite magnetization at zero field at low temperatures.
Unusual critical behavior in a bilinear-biquadratic exchange Hamiltonian
Authors: Bonner J. C. , Parkinson J. B. , Oitmaa J. , Blöte H. W. J.
Published: July 2002

We have performed a variety of numerical studies on the general bilinear-biquadratic spin-1 Hamiltonian H/J=∑Ni=1[Si⋅Si+1 −β(Si⋅Si+1)2], over the range 0≤β≤∞. The model is Bethe Ansatz integrable at the special point β=1, where the spectrum is gapless, but is otherwise believed to be nonintegrable. Affleck has predicted that an excitation gap opens up linearly in the vicinity of β=1. Our studies involving spectral excitations (dispersion spectra), scaled-gap, and finite-size scaling calculations are not consistent with the Affleck prediction. The situation appears complex, with novel crossover effects occurring in both regimes, β<1 and β>1, complicating the analysis.
Spin dynamics across the metal-insulator transition
Authors: Sachdev Subir , Bhatt R. N.
Published: July 2002

A theoretical study of the dynamics of electron spins in disordered insulators and metals is performed. Spin diffusion is found to slow down at low temperatures, making the system unusually sensitive to spin-dependent perturbations. This sensitivity shows up in an unusual frequency and temperature dependence of the linewidth and resonance field of the electron spin resonance (ESR) signal. These results are used to interpret recent ESR measurements in phosphorus doped silicon in both the insulating and metallic phases, and good agreement is obtained with experiment.
Anomalous electrical properties of MnxFe3−xO4
Authors: Brabers V. A. M. , Proykova Y. G. , Salerno N. , Whall T. E.
Published: July 2002

Two anomalies are observed in the temperature dependencies of the electrical conductivity and the thermoelectric power of ferrimagnetic manganese ferrites: a magnetic anomaly at the Néel temperature which can be explained with a model proposed previously and a second anomaly at 620 K which is due to a cation redistribution process.
Influence of magnetic field cooling on electrical properties of magnetite
Authors: Rasmussen R. J. , Aragón R. , Honig J. M.
Published: July 2002

The effect of magnetic field cooling on the dc electrical resistivity and Seebeck coefficient of single-crystalline magnetite is reported for samples in which the degree of cation nonstoichiometry determines the occurrence of either a first- or a higher-order Verwey transition.
Hall effect in heavy fermion compounds (abstract)
Authors: Levy P. M. , Fert A.
Published: July 2002

As a result of a recent analysis of data on the Hall effect in heavy fermion compounds1 we evaluated the higher-order resonant scattering contributions to the skew scattering of conduction electrons. In the single-site approximation we have calculated the t matrix elements for skew scattering correct to fourth order in the Anderson mixing interaction, i.e., we have neglected pair correlation effects. By including this fourth-order correction in our calculation of the Hall resistivity we find it is positive at high temperatures which is in agreement with data on heavy fermion compounds. Prior calculations of this scattering in these compounds were limited to second order in the mixing interaction above TK, and predicted a negative Hall constant at high temperatures.2 By using a phase shift analysis of the skew scattering we have extended our calculation to the incoherent (single-site) strong coupling regime. In the temperature ranges we considered the Hall resistivity is proportional to the product of the resistivity and magnetic susceptibility. This is in agreement with data on heavy fermion compounds.
Magneto-optical analysis of domain-wall oscillations in garnet films
Authors: Valette P. , Bernstein P. , Le Gall H.
Published: July 2002

Domain-wall oscillations have been analyzed in Bi-Ga and Bi-Gd-Pr-Ga substituted garnet films by magneto-optical effects at 6328 Å wavelength and under rf magnetic excitation of up to 50 MHz. The amplitude of wall oscillations in a stripe-domain structure was determined from the change of the light intensity transmitted by the garnet film placed between polarizer and analyzer. The detected signal is proportional to the variation θeff of the Faraday rotation associated with the wall displacement d as described by θeff =4dθs/P0, where θs and P0 are the specific Faraday rotation and the stripe period. The amplitudes of θeff and d are linear functions of the excitation magnetic field H at low frequencies, but present a saturation behavior at high frequencies. When subjected to the same excitation field amplitude, the two garnet series present different frequency dependencies of the wall displacement, which can be correlated with the magnetic susceptibility of the samples. After annealing at high temperatures, the oscillating amplitude d of wall displacement shows opposite evolutions for the two garnet series. These results are discussed using both a theoretical model of wall oscillation and the change of the basic magnetic properties of the garnet films after annealing.
Dynamics of flat domains in a single layer
Authors: Labrune M. , Puchalska I.B.
Published: July 2002

Flat lozenge-type domains in a NiCoP onefold layer may propagate under the influence of a transverse magnetic field and two electric currents. Its sideway motion in the hard axis is due to the local coercivity of the domain walls and tips as well as of the shape of the currents.
Reproducibility of domain wall motion in Metglas 2826
Authors: Wadekar S. , Kramer J. J.
Published: July 2002

Domain wall motion is known to be more sporadic in amorphous ferromagnetic alloys than in crystalline material. This is displayed, in part, by the lack of reproducibility of domain wall motion from cycle to cycle. An investigation was therefore conducted to determine the effect of various treatments on the extent of wall motion reproducibility during 60-Hz magnetization of amorphous Metglas 2826, Fe40Ni40P14B6. The as-received material (Allied Corp.) was subjected to thermal annealing or various proton irradiations. Observation of the dynamic domain behavior via the Kerr magneto-optic effect indicated, as expected, significant nonreproducible wall motion in the as-received specimens at all levels of magnetization. At low levels of magnetization, the annealed specimens showed reproducible wall motion; however, the reproducibility dropped substantially when these specimens were magnetized close to saturation. In the proton irradiated specimens, wall motion reproducibility was higher than of the untreated specimens. These observations are explained in terms of the effective pinning of domain walls.
Optimum design of a magnetostatic surface wave delay line based on a multiple-layer structure
Authors: He Huahui , Su Jun , Feng Zekun , Zhou Shichang , Liao Daoxun
Published: July 2002

Selection of the thicknesses of the layers and the magnetic parameters for a given multiple-layer configuration is formulated as a constrainted optimization problem. Recursive equality constrainted quadratic programming is used to minimize the design objective from an arbitrarily initial point in the parameter space of design variables. The solutions of a few design examples at the S band are presented.
Nondispersive MSFVW propagation in an inhomogeneously magnetized YIG film (abstract)
Authors: Wey C. T. , Tuan H. S. , Parekh J. P. , Craig A. E. , Lee J. N.
Published: July 2002

The present paper reports a theoretical and experimental study of the realizability of bandwidth enhancement for nondispersive magnetostatic forward volume wave (MSFVW) propagation in a YIG film via bias-field inhomogeneity. The theory assumes that the bias field varies linearly and weakly with distance along the direction normal to the sagittal plane. In agreement with expectation, the MSFVW signal profile along this direction is channelized, i.e., the MSFVW profile corresponding to a fixed frequency exists predominantly over a confined spatial region which shifts in the direction of increasing bias field as the frequency is increased. An in-depth characterization of the channelization process, which is crucial in unraveling the MSW dispersion control capability afforded by bias-field inhomogeneity, will be presented. Interestingly, the MSFVW wave-number variation over the confinement region is such that an essentially nondispersive propagation is achieved. The theoretical prediction of significant enhancement in the bandwidth for nondispersive MSFVW propagation as a result of bias-field inhomogeneity was verified experimentally utilizing specially machined pole pieces.
Study of the optimal values of d/t for MSFVW delay lines
Authors: Hu Wenzhong , Huang Qingqing
Published: July 2002

The influences of d and d/t (d and t are the thickness of YIG film and dielectric layer, respectively) on the dispersive characteristics of magnetostatic forward volume wave (MSFVW) have been studied. The following results have been obtained: (1) when H=1300 Oe and d/t=0.9, the time bandwidth product (TB) of the linear-dispersion delay line (LDDL) of MSFVW reaches the maximum. (2) The linear dispersion operation bandwidth almost does not vary with d. The (TB)max and differential delay time increase with decreasing d. When d=5 μm, (TB)max>600 μs MHz. (3) There is an optimal value of d/t for nondispersion delay line.
Rhombohedral Heisenberg antiferromagnet: Infinite degeneracy of the ground state induced by the lattice structure. Application to β-oxygen
Authors: Rastelli E. , Tassi A.
Published: July 2002

Exchange coupling competition between different shells of neighbors is the well-known source of helimagnetism. Unexpected interesting new features were found for suitable competition: infinite degeneracy of the ground state, soft lines in the magnon energy spectrum, absence of long-range order in 3D for any T≠0, and possible algebraic decay of the correlation function. We find a similar scenario in the rhombohedral Heisenberg antiferromagnet (RAF) even if the exchange coupling range is limited to nearest neighbors. The general expectation of a 120° three-sublattice configuration in the c planes is confirmed only if the interplane coupling J′ is rigorously zero, whereas for any ‖J′‖<3‖J‖, J being the NN in-plane coupling, the ground state is a degenerate helix (DH). The RAF model is suitable to describe solid oxygen in the β phase, where O2 molecules are arranged on a rhombohedral lattice and interact via direct exchange. The evaluation of the elastic neutron scattering cross section by a polycrystalline sample of β-O provides a non-Lorentzian peak whose width is determined by the presence of infinite isoenergetic helices in the ground state. This points out that LRO could persist in β phase in spite of the current interpretation of the large peak at zero energy transfer as an evidence of absence of LRO.
Polarized neutron diffraction studies of Gd-Y synthetic superlattices
Authors: Majkrzak C. F. , Cable J. W. , Kwo J. , Hong M. , McWhan D. B. , Yafet Y. , Waszczak J. V. , Grimm H. , Vettier C.
Published: July 2002

The microscopic magnetic structures of coherent, single-crystal epitaxially grown superlattices consisting of successive bilayers of NGd basal planes of hexagonal-close-packed Gd followed by NY such atomic planes of nonmagnetic Y have been studied by polarized neutron diffraction. It has been found that for NGd=10, either a simple parallel alignment of the ferromagnetic Gd layers or an antiphase domain structure occurs, depending on the number of intervening Y planes in an oscillatory manner. These data are consistent with a RKKY coupling mechanism between Gd layers. In addition to the investigation of the interlayer interactions, measurements of the magnetization profile across the thickness of a Gd layer have been performed.
Orientation-dependent relaxation in spin glass Cu2MnAl
Authors: Ellison Michael J. , Pechan Michael J.
Published: July 2002

Electron spin resonance measurements have been performed as a function of temperature, cooling field, and sample orientation on the amorphous spin-glass system Cu2MnAl (Tg=65 K). The peak in the linewidth (Γ) does not occur until T≊25 K which is shown to result from the reduction of the transition temperature in an applied field. The linewidth for the applied field parallel to the film surface is much greater than if the applied field is perpendicular to the film surface. This anomalous orientation dependence of Γ is not well understood.
Specific heat of uniaxial spin glasses in the mK range and fields of 6 T (abstract)
Authors: Meierling H. , Wassermann E. F.
Published: July 2002

The magnetic contribution to the specific heat Cm(T) of polycrystalline Ising-like spin glasses (SG) ScEr(1.05; 2.5 at. % Er) and ZnMn (195, 270 ppm Mn) has been measured in the temperature range 0.1<T<2.5 K, using a nonadiabatic heat pulse method. Cm(T) of the x-y–like SG CdMn (488 ppm Mn) has been measured on single crystals in external fields (Bex≤6 T) with Bex either ⊥ or ∥ to the c axis. The data are compared with susceptibility measurements.1 For all samples the behavior of Cm(T) is similar to that in archetypal SG’s. There is scaling and a linear dependence Cm(T) for T→0. The high-temperature data do not follow a simple 1/T or 1/T2 law. In contrast to the results from mean-field calculations for uniaxial systems we find no peaks in Cm(T). Yet, the relatively sharp maxima in Cm(T) at Tm of ScEr and ZnMn are close to the freezing temperatures T∥g. In CdMn T⊥g from χ(T) lies well below Tm. The data for ScEr and ZnMn can be fitted within a two-level system model. For CdMn Cm is strongly

dependent on Bex and shows anisotropic behavior. For Bex⊥ c (parallel to the easy axis) Cm(T,B) is SG-like for all fields and comparable to isotropic SG’s. With increasing fields Tm shifts to higher temperatures and the slope in the linear range decreases. For Bex∥c (hard direction) the behavior is quite different. For Bex <2 T the linear slope in Cm(T) and Tm are only weakly dependent on Bex. Increasing the field leads to a remarkable reduction of Cm(T) around Tm, and Cm(T) becomes nonlinear for T→0. This can be understood in terms of new mean-field calculations on anisotropic Ising-SG’s by Usadel,2 who predicts a breakdown of the SG interactions in strong magnetic fields transverse to the easy axis.