bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetotransport in type-III Hg1−xZnxTe-CdTe superlattices
Authors: Rafol S. B. , Chu X. , Faurie J. P.
Published: July 2002

Magnetotransport experiments on several n-type Hg1−xZnxTe-CdTe superlattices reveal the existence of two species of charge carriers which dominate in low and in high magnetic fields. These superlattices exhibit low-magnetic-field Shubnikov–de Haas oscillations and Hall plateaus in one superlattice. They also exhibit a metal-insulator transition due to an energy gap induced by the high magnetic fields. The induced energy gap is estimated using a simplified parallel-conduction model. When most of the electrons in the superlattices have been magnetically frozen out, a second species of charge carriers starts dominating the charge transport. The second species of charge carriers shows large amplitude Shubnikov–de Haas oscillations and Hall plateaus. The standard determination of effective masses, mobilities, and carrier densities from the Shubnikov–de Haas oscillations in low and in high magnetic fields also confirms the presence of two species of charge carriers of different origin. It is proposed that the high-magnetic-field Shubnikov–de Haas oscillations are due to electrons residing at the buffer-superlattice interface on the superlattice side.
Maxwell displacement current across monolayer polyimide Langmuir–Blodgett films with azobenzene by photoirradiation
Authors: Iwamoto Mitsumasa , Kanai Yuichiro , Naruse Haruhiko
Published: July 2002

We investigated the Maxwell displacement current generated across one-layer polyimide (PI) Langmuir–Blodgett (LB) films with azobenzene by photoirradiation. Transient displacement-current pulses were found to be produced in precursor films of PI (AZBPAA), because successive isomerizations were induced in the films by irradiation with ultraviolet and visible light. In contrast, the displacement current was not generated in PI LB films containing azobenzene (AZBPI) by the photoirradiation, because the photoisomerization was not initiated in AZBPI LB films and the displacement current generation due to the transportation of photoexcited electrons in the films was negligibly small. The displacement current due to the photoexcited electron transfer between AZBPAA single monolayers and electrodes was found to be created only in the initial photoirradiation with visible light, and the photoexcited electron transfer was found to be eliminated by introducing a polyisobutyl-methacrylate LB film between AZBPAA single monolayers and electrodes. Finally, we concluded that motion of charged particles can be purposefully controlled and be detected by the displacement current measurement.
Molecular-beam-epitaxial growth and optical analysis of InAs/AlSb strained-layer superlattices
Authors: Yano Mitsuaki , Okuizumi Masaru , Iwai Yoshio , Inoue Masataka
Published: July 2002

Structural and optical properties of InAs/AlSb strained-layer superlattices (SLSs) grown by molecular-beam epitaxy (MBE) are described. Either an interface bond of InSb or AlAs was selectively made in the SLSs by controlling the beam supply sequence during growth. Characterization of the SLSs was performed using Raman scattering and photoluminescence (PL) spectroscopy in addition to the in situ analysis of reflection high-energy electron-diffraction signals. The Raman signals consisted of three different types of lattice vibrations: InSb- or AlAs-like phonons localized at the interface bonds, InAs- and AlSb-like optic phonons confined in the respective layers, and zone-folded acoustic phonons extending through the constituent layers. The energy shift of the optic phonons was used to determine the strain in SLSs. This analysis revealed a considerable dependence of the SLS structure on the interface bond. The Raman analysis was also supported by the PL data. These optical properties are discussed in relation to the MBE-growth conditions of SLSs.
Effects of elastic strain on the band offset and effective mass of strained InGaSb epilayers
Authors: Chen S. M. , Su Y. K. , Lu Y. T.
Published: July 2002

The effects of elastic strain induced by lattice mismatch on the effective mass and band offset at Γ point are studied in this article. We found that the effective masses (electron, light- and heavy-hole) become anisotropic in a strained layer. The theoretical calculations were made using a method of linear combination of atomic orbitals, and the overlapping integrals are adjusted in accordance with the change of atomic distance. In the kz direction, the effective mass ratios (strain: unstrain) of the electron of InxGa1−xSb/GaSb structure were found to vary from 1 to 3.38 for 0≤x≤1, the corresponding ratios of the light- and heavy-hole are 1 to 3.38 and 1 to 0.99, respectively. In the kx and ky direction, the ratios of the light- and heavy-hole are 1 to 1.02 and 1 to 1.13, respectively. For unstrained and strained interfaces, the band offset ratios of 90:10 and 57:43 (conduction band: valence band) are obtained, respectively. Experimental studies were also performed on the InxGa1−xSb/GaSb strained-layer superlattice sample. It was found that the theoretical calculations agree well with experimental results in this study.
Effects of substrate temperature and ion incident energy on silicon surface cleaning using a hydrogen plasma excited by electron cyclotron resonance
Authors: Nakashima Kenji , Ishii Masahiko , Hayakawa Tetsuo , Tajima Ichiro , Yamamoto Minoru
Published: July 2002

Effects of the substrate temperature and ion incident energy on silicon surface cleaning and hydrogen penetration caused by irradiation with a hydrogen plasma have been investigated using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. A silicon native oxide and a hydrocarbon-contaminated layer were removed only on the condition that the silicon substrate was struck with hydrogen ions having proper kinetic energies of less than 40 eV at temperatures from room temperature to 400 °C. However, the silicon oxide grew either at temperatures below room temperature or at no ion incidence onto the substrate. This oxidation phenomenon was attributed to residual H2O in the vacuum system. On the other hand, hydrogen penetration occurred only on the condition of hydrogen ion bombardment. The amount of penetrated hydrogen increased with substrate temperature and ion incident energy. The amount of penetrated hydrogen was found to be drastically reduced under the condition of ion incident energy of less than 5 eV and a substrate temperature of about room temperature. It is concluded that an oxideless clean surface without hydrogen penetration into silicon bulk is obtained by means of irradiation with a hydrogen plasma having a low ion incident energy (≤5 eV) at room temperature.
Multiplication performance self-stabilization in blocked impurity band photodetectors
Authors: Shadrin V. D. , Coon V. T. , Blokhin I. K.
Published: July 2002

Dependence of the electron multiplication factor on the bias voltage was considered for the blocked impurity band (BIB) detector. We found that in high gain BIB detectors multiplication factor self-stabilization can be achieved. When bias voltage VB increases, the multiplication factor curve flattens, starting at a certain value VB. This can be explained by the presence of an electric field and electron current in the neutral region of the BIB detector infrared-active layer. The influence of this behavior on the performance characteristics of BIB detectors is briefly discussed.
Optimization of superconducting tunnel junction based x-ray detectors
Authors: Foden C. L. , Rando N. , Peacock A. , van Dordrecht A.
Published: July 2002

Current research into x-ray detection using superconducting tunnel junctions indicates that the poor spectral resolution obtained so far, in comparison with theoretical expectations, is partly due to the excellent acoustic coupling of the junction and substrate. The substrate acts both as a source of noise and as a heat sink for the nonequilibrium junction, thus masking the intrinsic response of the superconducting electrodes to photoexcitation. A new design for a superconducting tunnel junction based on an x-ray detector is presented. The design effectively decouples the substrate and junction and should therefore eliminate many causes of spectral degradation, bringing resolution closer to that predicted theoretically, and thus allowing experimental investigation of the intrinsic superconducting film response to x-ray photoexcitation. An outline of the way in which the design can be optimized geometrically to achieve the decoupling is given. Further optimization of the intrinsic film response to x-ray photons is achieved through the introduction of specific absorbing and trapping regions to improve both the quantum efficiency and charge output of the new design. The use of ‘‘pairing potential barriers’’ within the electrode leads will also improve the intrinsic resolution of this device.
The use of an Al sacrificial layer to improve retention during high dose Pt ion implantation into Ni
Authors: Clapham Lynann , Whitton J. L. , Pascual R. , Ridgway M. C. , Hauser N.
Published: July 2002

Our previous work [Clapham, Whitton, Ridgway, Hauser, and Petrovic, J. Appl. Phys. 72, 4014 (1992) and Clapham, Whitton, and Ruck, Nucl. Instrum. Methods B 80/81, 501 (1993)] has shown that the sputtering limitation often associated with high-dose, heavy ion implantation into metals can be overcome by using a thin (∼1000 Å) C sacrificial layer. This layer, which is deposited on the surface prior to implantation, sputters slowly during bombardment, thus protecting the underlying target. The present study further investigates the potential of the sacrificial layer technique, using Al as a sacrificial layer on a Ni target implanted with high doses (to 7×1017 ions/cm2) of 5 MeV Pt ions. The Al layer was found to be very effective in enhancing retention of the implanted Pt, with 100% retention and a maximum concentration of 19 at. % Pt achieved for the highest dose. This compares with a saturation concentration of ∼10 at. % Pt when no sacrificial layer was used. The mixing behavior of Al into Ni was consistent with other studies conducted at lower ion energies. The temperature region of radiation-enhanced diffusion was established, and the phase Ni3Al was found to be present in the Al/Ni mixed region after Pt bombardment.
Study of dangling bonds in nanometer-sized granulet silicon nitride by electron-spin resonance
Authors: Wang Tao , Zhang Lide , Fan Xiaojun , Hu Jitong , Mo Jimei
Published: July 2002

The dangling bonds in pellets made by compacting nanometer-sized silicon nitride (NASN) grains are studied by electron-spin resonance (ESR). The ESR results of NASN show that the number of dangling bonds in NASN is about three orders of magnitude higher than that of coarse-grained silicon nitride. It is also observed that compaction pressure and thermal treatment temperature affect the type and the number of dangling bonds. An explanation is presented for the changes in the dangling bonds caused by the processes of compaction and thermal treatment.
Influence of surface anchoring and viscosity upon the switching behavior of twisted nematic cells
Authors: Stelzer J. , Hirning R. , Trebin H.-R.
Published: July 2002

Numerical calculations are presented on the dynamics of twisted chiral nematic cells. We are emphasizing the influence of surface effects on the optical switching behavior. Apart from the anchoring strength we have taken into account viscous effects at the surface by constructing a surface dissipation function. The dynamical light transmission curve has been determined for different strengths of the surface anchoring and various viscosity parameters by computer simulation.
In0.49Ga0.51P/GaAs heterostructures grown by low-pressure metalorganic chemical vapor deposition
Authors: Feng M. S. , Lin K. C. , Wu C. C. , Chen H. D. , Shang Y. C.
Published: July 2002

We have successfully grown In0.49Ga0.51P/GaAs heterostructures and made InGaP-based high electron mobility transistors (HEMTs) by low-pressure metalorganic chemical vapor deposition. We have found the epitaxial layer of InGaP with a Hall mobility of 4073 cm2/V s (300 K) and the photoluminescence full width at half-maximum of 1 meV (4.2 K) for GaAs, 12 meV (4.2 K) for In0.49Ga0.51P. Zinc-induced disordering phenomenon was examined by transmission electron microscope. By Shubnikov-de Haas measurement, we demonstrated the existence of a two-dimensional electron gas in InGaP/GaAs heterojunctions. The sheet carrier concentration of 2DEG is around 8.8×1011 cm−2 at 1.5 K. A HEMT device with 1 μm×40 μm gate (pattern) shows an extrinsic transconductance of 65.5 mS/mm and an intrinsic transconductance of 266 mS/mm at 300 K.
On the possibility of a mode selector and its application to quantum devices
Authors: Xu Guangzhao , Jiang Ping
Published: July 2002

A mode selector is proposed to realize single modedness in the waveguidelike quantum devices. The mode selecting function is theoretically demonstrated by the principle of resonant tunneling effect. Its applications to quantum field-effect directional couplers and three-port devices are also theoretically studied. The result shows that the mode selector can considerably improve device function by suppressing the mode correlation in the device.
GaInAsP/InP 1.35 μm double heterostructure laser grown on silicon substrate by metalorganic chemical vapor deposition
Authors: Mobarhan K. , Jelen C. , Kolev E. , Razeghi M.
Published: July 2002

A 1.35 μm GaInAsP/InP double heterostructure laser has been grown on a Si substrate using low-pressure metalorganic chemical vapor deposition. This was done without the use of a superlattice layer or a very thick InP buffer layer, which are used to prevent the dislocations from spreading into the active layer. Pulsed operation with output power of over 200 mW per facet was achieved at room temperature for broad area lasers with 20 μm width and 170 μm cavity length. The threshold current density of a 350 μm cavity length device was 9.8 kA/cm2. The characteristic temperature was 66 K.
High gain recombination O VIII x-ray laser
Authors: Zhang Jie , Key Michael H.
Published: July 2002

A scheme is presented for producing a high gain recombination x-ray laser in hydrogen like oxygen by irradiating 7-μm-diam fiber targets with picosecond high-power laser pulses. The lasing gain coefficient for the O viii Balmer α transition at 10.2 nm is predicted to be over 100 cm−1. The optimized electron density and temperature are 8.8×1019 cm−3 and 22 eV, respectively, at the time when the lasing gain reaches its maximum. Significant improvement in gain performance of recombination x-ray lasers is indicated for picosecond pulse drivers, which might be a route towards saturated recombination x-ray layers.
Spherical center for nucleation by curling in a bulk ferromagnet
Authors: Aharoni Amikam , Baltensperger W.
Published: July 2002

The process of nucleation of magnetization reversal in bulk materials by the magnetization curling mode is investigated by a numerical integration of an approximate differential equation. This computation shows that limiting the curling to a spherical shell does not lead to a saddle point, and that the energy which has to be overcome for reversing the magnetization by the curling mode is larger than that required for the previous, tilting mode. Therefore, the latter is left as the only practical nucleation center in bulk materials.
Solving the one-dimensional quantum mechanics problems using the matter wave multireflection
Authors: Polak Wiesl/aw
Published: July 2002

This article presents a simple, yet general and exact analytic-numerical method of solving one-dimensional quantum mechanics problems. It is based on the concept of dividing an arbitrary potential into convenient segments and analyzing the multiple reflection of a plane matter wave between neighboring potential walls. Amplitude reflection and transmission coefficients of each segment are the basis for the analysis. A simple iterative technique for calculating them by a square barrier approximation is given. This method is applicable to various potential barriers, wells, and periodic structures including continuous variations of potential energy and particle effective mass.
Compressive and tensile strain effects on hole tunneling in an InGaAs/AlInAs asymmetrical coupled quantum well
Authors: Chen P. A. , Chang C. Y. , Juang C.
Published: July 2002

Hole tunneling dynamics are investigated in a strained asymmetrical coupled quantum well (ACQW). The tunneling probabilities between heavy-hole states are calculated at different internal strains on the basis of the time-dependent Schrödinger equation analysis with the Luttinger–Kohn and an additional strain Hamiltonians. In a certain range of strain, a higher oscillation frequency (but a smaller oscillation amplitude) of hole tunneling at resonance is obtained in a biaxial tensile strain ACQW at in-plane wave vector k∥=0. The biaxial compressive strain is observed to lower the oscillation frequency. With a nonzero wave vector (k∥≠0), the oscillation frequency is found to be dominated by mixing effects and less dependent on the internal strain. The oscillation frequency remains roughly constant; however, the biaxial compressive strain ACQWs would still have a larger oscillation amplitude than biaxial tensile strain ACQWs.
Measurement of ion induced damage-profiles in GaAs
Authors: Shwe C. , Kraisingdecha P. , Gal M. , Varley B. , Gross M.
Published: July 2002

In this study, with the use of a sensitive optical technique, we demonstrate the possibility of measuring the depth distribution of damage in GaAs that is generated by various ion-assisted processes such as ion implantation and ion assisted plasma etching. We have used this technique to measure the depth distribution of damage in both He and Ar implanted GaAs and in inert gas and reactive ion etched GaAs. The sensitivity of the technique allowed us to measure damage profiles over a large range of ion energies and ion doses. We have also confirmed previously published results indicating that damage created by sputter etching is inversely proportional to the mass of the ions used in the etching process.
Chemical modification of magneto-optic garnet film properties
Authors: Belt Roger F. , Ings John B. , Whitlock Jonathan B.
Published: July 2002

Single-crystal magneto-optic garnet films of composition (BiTm)3(FeGa)5O12 have applications to spatial light modulators, optical isolators, and magnetic-field sensors. These as-grown films have a coercivity under 1 Oe and can support cm-size stable domains. It has been found that chemical treatments with oxidizing or reducing gases can reversibly modify the magnetic properties. Treatments are performed at 400–700 °C for fixed times. Reducing treatments dilate the x-ray lattice constant up to 0.1%, introduce Fe2+ monitored by increased optical absorption at 1.00–1.06 μm and decrease Faraday rotation about 5% over the visible spectrum. Oxidation can partially or totally reverse these parameters. Magnetic measurements on the bulk film show that coercivity can be finely controlled, square hysteresis loops attained, and domain-wall mobility changed. At the same time the initial perpendicular anisotropy Hk of 8–12 kOe is decreased while the saturation magnetization (4πMs) of 100–150 G is affected to a minor degree. For magneto-optic imaging of defects, the resolution, contrast, and device operation are assisted favorably. Magnetic measurements are presented as a function of specific chemical treatment. The data suggest that an oxygen vacancy mechanism is operative at the film surface layers.
Micromagnetic study of narrow track orthogonal giant magnetoresistive heads
Authors: Guo Yimin , Zhu Jian-Gang
Published: July 2002

Orthogonal narrow track magnetoresistive heads using giant magnetoresistive multilayers have been studied by micromagnetic modeling. The modeling shows that the hysteresis arises from irreversible switching of the edge-curling wall (ECW) on the side edges of the giant magnetoresistive (GMR) sensor layers. Effects of thickness and interlayer exchange coupling on the switching of the ECW are analyzed. It is also found that if the interlayer exchange coupling is ferromagnetic, the GMR orthogonal head has significant high signal amplitude.
Dynamic domain instability and popcorn noise in thin-film heads
Authors: Liu F. H. , Kryder M. H.
Published: July 2002

The effects of dynamic domain instability on popcorn noise probabilities were studied by correlating the measured popcorn noise probabilities with the instantaneous observations of dynamic domain states of thin-film heads during and after writing. Heads with large peak popcorn noise probabilities at intermediate values of write current amplitude were observed to exhibit asymmetric domain patterns and occasional popping wall motion in the yoke structure during writing. The occurrences of dynamic domain instability were imaged by comparing many instantaneous domain patterns at 10 μs after a specific write current excitation. Delayed-relaxation Barkhausen wall jumps near the backgap closure were observed occasionally in several noisy heads. Quantitative correlation between the probabilities of popcorn noise and dynamic domain instability was also obtained in a very noisy head. Dynamic domain instabilities in the yoke are thus responsible for the peak popcorn noise probabilities in thin-film heads.
Local spin-density theory of interface and surface magnetocrystalline anisotropy: Pd/Co/Pd(001) and Cu/Co/Cu(001) sandwiches
Authors: Wang Ding-sheng , Wu Ruqian , Freeman A. J.
Published: July 2002

The interface magnetocrystalline anisotropy (MCA) of Cu/Co/Cu(001) and Pd/Co/Pd(001) sandwiches are investigated, employing our recently developed state tracking approach based on the full potential linearized augmented plane wave energy band method. The strong negative MCA energy for the Co monolayer is found to be decreased for Co/Cu, and even becomes positive for Co/Pd due to the interfacial hybridization, which reduces the spin orbit coupling (SOC) between the dxz,yz − dz2 pair at M̄.
In situ measurement of stress and surface morphology for Co/Pd multilayer films fabricated by rf sputtering
Authors: Takeshita H. , Hattori K. , Fujiwara Y. , Nakagawa K. , Itoh A.
Published: July 2002

In this paper, we report the results of in situ measurements of stress and surface morphology for Co/Pd multilayer films deposited on glass substrate by rf sputtering. For the multilayer film sputtered in low Ar gas pressure at 10 mTorr, after more than 20 periods of Co/Pd deposition, the film is subjected to compressive stress, however, during the Co layer deposition, the value of the compressive stress is decreasing. For the film sputtered in high Ar gas pressure at 40 mTorr, the film is always subjected to tensile stress, and the value of the tensile stress in the film is increasing during the deposition of the Co layer. These changes in the stress during the Co deposition can be explained qualitatively by the difference in the lattice constants of Co and Pd at the interfaces. The surface morphology of the films observed by an atomic force microscope (AFM) in air shows that the surface of both films become rougher with increasing total film thickness. The surface roughness of the films deposited at 10 mTorr is smaller than that of the films deposited at 40 mTorr.
Isoelectronic early n-d impurities in Fe: Magnetic and hyperfine field properties
Authors: de Oliveira N. A. , Gomes A. A. , Troper A.
Published: July 2002

The hyperfine fields and the local magnetic moments in a series of alloys of isoelectronic transition impurities diluted in iron are discussed. We intend to show that, even within a very simplified model, period effects for isoelectronic impurities at the beginning of an n-d series (e.g., Sc, Y, and Lu) are dominated by the charge difference effect, inducing a very strong repulsive potential. We find that the local impurity magnetic moments are very close to each other, leading to hyperfine fields, in fair agreement with experimental data. Our calculation accounts for the general trends of the local impurity moments in ferromagnetic Fe, despite quantitative deviations that do occur, due to the very simple structure of this model. We point out, however, that our calculation is a starting point for a more refined one, dealing with rare-earth impurities (such as Eu, Gd, and Tb) placed in the Fe host, where the strong charge effects are present, together with f-spin scattering.
Critical magnetic neutron scattering above T
N in Cr+0.18 at. % Re (abstract)
Authors: Noakes D. R. , Fawcett E. , Sternlieb B. J. , Shirane G. , Jankowska J.
Published: July 2002

Magnetic critical neutron scattering from a single crystal of Cr+0.18 at. % Re was observed above its Néel transition (323 K) to an incommensurate spin density wave state. The data were analyzed in terms of the critical susceptibility model that successfully fit analogous data from single crystals of pure chromium and Cr+0.2 at. % V. An additional complication in this case is the fact that a small portion of the sample becomes commensurate antiferromagnetic at a temperature well above 323 K, which causes a commensurate magnetic Bragg peak that partially obscures the critical scattering near 323 K. The ‘‘Sato-Maki’’  form of incommensurate critical susceptibility fits the data reasonably well. The intensity of magnetic critical scattering in Cr+0.18 at. % Re is about a factor 2 stronger than in pure Cr, whereas in Cr+0.2 at. % V it is about the same factor weaker.
Magnetic order of Pr ions in related perovskite-type Pr123 compounds
Authors: Guillaume M. , Fischer P. , Roessli B. , Podlesnyak A. , Schefer J. , Furrer A.
Published: July 2002

The magnetic order of Pr ions in polycrystalline, tetragonal PrBa2Cu3O6.2 has been studied by neutron-diffraction measurements. The basic ordering consists of an antiferromagnetic arrangement with the propagation vector k=[1/2, 1/2, 1/2], but the magnetic ordering is imperfect due to finite correlation length ξc=(10±1) Å along the c axis. The Néel temperature is determined to be TN=(12±1) K, and the magnetic saturation moment of the Pr ions turns out to be (1.9±0.2) μB. The distance Pr-O(2) compared in several related perovskite-type Pr compounds correlates with the Néel temperature in accordance with the superexchange interaction.
Vortex flux creep and magnetic hysteresis in a type-II superconductor (abstract)
Authors: Hasan M. K. , Park S. J. , Kouvel J. S.
Published: July 2002

Upon reversal of the external magnetic field H during any hysteretic cycling of a type-II superconductor in its vortex state, the rate at which the magnetic flux density B varies with H is typically seen to start from zero and then change gradually. Measurements have now been made of the time dependence of B (the vortex flux creep) at many fixed-H points on several hysteresis loops of a grain-oriented YBa2Cu3O7 sample at 4.2 K (with H and B along the c axis), and it is observed that the size of the logarithmic dB/dt drops abruptly to zero, before proceeding to change in sign, whenever H is reversed. This curious similarity between the hysteretic behavior of dB/dt at fixed H and that of the nearly instantaneously measured dB/dH can be understood qualitatively in terms of the vortex pinning. As rotational magnetization measurements have recently shown,1 the unpinning and repinning of moving vortices is manifested macroscopically as a frictional process. Thus, the reversal of vortex motion involves the reversal of frictional forces, during which the vortex population in the superconducting sample (which is proportional to B) does not change with time or field.
Probing of the pairing state of HTSCs utilizing a-b plane magnetization anisotropy (abstract)
Authors: Buan J. , Israeloff N. E. , Huang C. C. , Goldman A. M. , Liu J. Z. , Shelton R. N.
Published: July 2002

We have performed measurements of the a-b plane longitudinal and transverse magnetization anisotropy on an untwinned, high quality single crystal of LuBa2Cu3O7−x in magnetic fields below Hc1 as a function of temperature, from 2 K to the transition temperature and the angle between the field and a fixed direction in the a-b plane. When the superconducting order parameter has nodes on the Fermi surface, such as the case of the spin-singlet dx2−y2 order parameter, nonlinear effects associated with low-energy quasiparticles should become important.1 It was pointed out by Yip and Sauls that these effects will be most important at low temperatures. They should be observable in a measurement of the anisotropy of the magnetization or the magnetic torque. The magnetization is predicted to develop an anisotropic component transverse to the applied field. Anisotropic transverse magnetization with dx2−y2 symmetry is not seen in the temperature regime 5 to 25 K. Our results set stringent limits on the anisotropy of the transverse magnetization in this range. Within the resolution of our experiment no evidence for d-wave pairing is observed.
Magnetic anisotropies in RFe10−xCoxMo2 compounds (R=Dy, Er)
Authors: Tucker Roy , Xu Xie , Shaheen S. A.
Published: July 2002

The effects of Co substitution on magnetic anisotropy and spin reorientation phenomena have been investigated in the DyFe10−xCoxMo2 and ErFe10−xCoxMo2 (x=0 to 10) series in the temperature range from 4.2 to 300 K. X-ray diffraction patterns on aligned samples indicated that the easy direction of magnetization (EDM) of the DyFe10−xCoxMo2 series is along the c axis at room temperature for all values of x. The spin reorientations were observed for all samples in the DyFe10−xCoxMo2 series except for x=10, and the spin reorientation temperature, Tsr, decreases with the increase of Co content x. The magnetic phase diagram of DyFe10−xCoxMo2 has been constructed. These results, together with the results from the YFe10−xCoxMo2 series, may lead to the conclusion that the anisotropy of Dy sublattice changes from planar to axial in the DyFe10−xCoxMo2 series with the increase of Co content. The EDM in the ErFe10−xCoxMo2 series was found to be nonaxial for 2≤x≤6 for all temperatures below Tc. For x<2 and x≳6 the ErFe10−xCoxMo2 compounds exhibit an axial EDM at room temperature, and spin reorientations occur at about 210 K for x=8 and at 140 K for x=10. Since Er and Dy have opposite sign of second-order Stevens factor, the above results of two systems are consistent.
Structure and magnetic properties of Gd2Fe17−xGaxC2 compounds
Authors: Shen Bao-gen , Wang Fang-wei , Kong Lin-shu , Cao Lei , Zhang Bo , Zhao Jian-gao
Published: July 2002

The single-phase compounds of Gd2Fe17−xGaxC2 (x=0, 1, 2, 3, 4, 5, and 6) with rhombohedral Th2Zn17-type structure were prepared by melt spinning for x≤1 and arc melting for x≥2. Their formation, structure, and magnetic properties were studied. The substitution of Ga for Fe in Gd2Fe17C2 helps the formation of the 2:17-type structure. The addition of Ga results in the increase of the lattice constants and the unit-cell volumes. The Curie temperature has a small change when x≤2, and then decreases rapidly with increasing Ga concentration. An approximately linear decrease of the saturation magnetization with x is observed when the nonmagnetic Ga atom is substituted for Fe.
Magnetic and microstructural properties of CoCrPt/CoCrPtSi dual-layered magnetic recording media
Authors: Inaba N. , Matsuda Y. , Suzuki M. , Nakamura A. , Futamoto M.
Published: July 2002

The magnetic properties of CoCrPt/CoCrPtSi dual-magnetic-layered thin films are investigated in terms of the crystalline microstructures using a vibrating-sample magnometer, transmission electron microscope, and scanning electron microscope. The magnetic crystal grains of the films are aligned with forming chainlike clusters. Each stacked magnetic crystal grain is epitaxially grown on individually isolated columnar Cr crystals with a relationship of hcp (101̄1)Co-based alloy //bcc (110)Cr. The direction of magnetic easy axes of two stacked magnetic crystals are aligned in a same direction. Single-crystalline dual-magnetic-layered thin films, which are epitaxially grown on MgO(110) single-crystal substrates, are prepared to estimate the Ku of the dual-layered magnetic grains. The Ku is determined to be 4×106 erg/cm3, whose value is about 2 times as large as that of single-layered CoCrPtSi. This large anisotropy energy is presumed to lead the increase of Hc in the dual-layered magnetic films.
Noise properties and microstructure of oriented CoCrTa/Cr media
Authors: Ranjan R. , Bennett W. R. , Tarnopolsky G. J. , Yamashita T. , Nolan T. , Sinclair R.
Published: July 2002

Magnetic and noise properties of oriented CoCrTa/Cr media sputtered at temperatures from ambient to 250 °C were studied and correlated with microstructural data from HRSEM and HRTEM micrographs. Coercivity increases monotonically and loop squareness decreases with substrate temperature. Transition and uniform magnetization noise power are highest for media sputtered at 150 °C. Micrographs and noise powers show that the media sputtered at 150 °C is relatively highly exchange-coupled. Media sputtered below 150 °C shows topographic isolation, and those sputtered above 150 °C exhibit increasing intergranular isolation of about 10 Å and thus lower exchange. Coercivity varies linearly but exchange drops abruptly at high temperature. Other mechanisms besides exchange contribute to the coercivity variation.
Anisotropy studies of AFM coupled MBE grown Co/Cu(001) superlattices
Authors: Bröhl K. , Nunzio S. Di , Schreiber F. , Zeidler Th. , Zabel H.
Published: July 2002

We have studied the anisotropy behavior of antiferromagnetically (AFM) coupled fcc Co/Cu(001) sandwiches and superlattices. Magneto-optical Kerr effect measurements on samples with Cu film thicknesses in the range of the second antiferromagnetic maximum reveal characteristic shapes of the hysteresis loops in close agreement with theoretical predictions. For the AFM coupled samples we infer antiparallel spin orientations in remanence perpendicular to the originally applied magnetic field direction. Changing the magnetic layer thickness and maintaining a constant thickness of the spacer completely alters the shape of the hysteresis loops. The loops of weakly coupled AFM layers show characteristic steps, indicative for a rather unusual nonsymmetric spin state. This behavior can be explained by the competing effects of anisotropy with the exchange coupling.
Polarization analysis of magnons in CsMnI3
Authors: Tun Z. , Hsu T. C. , Lussier J-G.
Published: July 2002

A polarized neutron scattering experiment on CsMnI3 shows previously unseen magnons at wave vectors (1/3,1/3,1) and (001), and also shows that the single-ion anisotropy for this material is substantially larger than previously reported. Linear spin wave theory can adequately describe the observed magnon frequencies.
Wet-process preparation of amorphous Y-Fe oxide films ferromagnetic at room temperature
Authors: Zhang Q. , Itoh T. , Abe M. , Zhang M. J.
Published: July 2002

Yttrium iron ferrite films of amorphous structure (as examined by x-ray diffraction), having ferromagnetic moment at room temperature, are successfully synthesized from an aqueous solution by a ferrite plating method in which the substrate is heated by Xe-lamp beams. The atomic ratio of Y/Fe in the films is adjusted to Y/Fe=0.6, as in Y3Fe5O12, by properly choosing the atomic ratio (Y/Fe=3.5) in the reaction solution. The magnetization of the films at room temperature is 10–40 emu/cc, several times smaller than that observed for crystalline YIG. It exhibited, however, a paramagnetic Mössbauer spectrum at room temperature, suggesting that the weak magnetization is ascribed to the magnetic impurity phase whose concentration is too small to be discerned by x-ray diffraction and Mössbauer measurements. The spectrum has an isomer shift of 0.22 mm/sec at 300 K and a hyperfine field splitting of 462 kOe at 12 K, indicating that the Fe ions are in a trivalent high spin state.
Magnetic thin-film media response in presence of displacement eddy currents
Authors: Geri A. , Salvini A. , Veca G. M.
Published: July 2002

Experimental tests have shown that macroscopic multilayer thin films excited by high-frequency magnetic field present permeance resonances. This unexpected behavior exists, even if the thickness of the magnetic films is smaller than the skin depth: in fact, for this condition, eddy currents within laminated magnetic sample should be inhibited. This phenomenon can be justified, observing that, for small thickness of the insulating interlayer, capacitive eddy currents across the dielectric layers begin to circulate between magnetic films. To predict the displacement eddy currents in macroscopic magnetic laminates some authors have provided various computational models based on different theoretical approaches. In particular, the computation of the effective complex permeability has been pointed out by means of coupled Maxwell’s equations, both in differential form and in an integral one. In a previous work we have proposed and validated a circuit model able to simulate the behavior of magnetic samples in the frequency domain. In this paper we present an extensive comparative analysis between our model and the previous ones. The calculations provide the magnitude and the phase of the effective permeability of a laminate with 30 permalloy-ZrO2 film pairs. The simulations have been performed over the frequency range of 1–100 MHz and for different geometries. The results of the simulations have been also compared with those provided by experimental tests available in literature. The main goal of this study is to evaluate the performance and reliability of each model.
Three-dimensional iterative solution for the multiconductor eddy current and free surface calculations
Authors: Ahmed M. Ramadan , Ali K. F. , Moustafa Ibrahim
Published: July 2002

In the three-dimensional (3-D) eddy current calculations, the obtaining of an accurate numerical solution with reasonable size and less computation efforts is still undertaken in many recent articles. Nowadays, such a solution becomes urgently required for designing and developing the electromagnetic confinement application, where the problem is not only 3-D but also involves more than one conducting region having a free boundary that is unknown a priori. For this class of applications, the present paper is devoted to discuss the developing of a 3-D iterative solution proposed for the analysis of an electromagnetic continuous casting (EMC) of an aluminum rectangular ingot installed in the Egyptalum Company. This solution is based on a derived 3-D Boundary Element (BE)—Impedance Boundary Condition (IBC) formulation, which leads to a significant reduction in the CPU time and the calculation efforts, as compared to the use of the regular BE formulation. In the present iterative solution, the IBC is applied to the resistively molten aluminum region, while the full BE formulation is used to present the field shaping screen. The validity of this iterative solution is tested by predicting the equilibrium meniscus shape of the free surface for an EMC mold having the size of 1050×280 mm for which experimental measurements for both the meniscus and the total active power supplied are available. Numerical results showing the magnetic flux density distributions over the boundaries of this mold are presented. The corresponding total surface power induced are estimated and compared with the corresponding actual (experimental) values. Also, the meniscus of the molten aluminum free surface is predicted and compared as well.
Component-resolved imaging of surface magnetic fields
Authors: Gomez R. D. , Burke E. R. , Mayergoyz I. D.
Published: July 2002

Successful imaging is demonstrated of the three individual Cartesian components of the vector magnetic field from a magnetized surface. This is accomplished by exploiting the capability of the magnetic force scanning tunneling microscope to generate two-dimensional mapping of definite combinations of orthogonal magnetic-field components. This method is applied to well-characterized patterns on thin-film longitudinal recording media and some peculiar characteristics of recorded magnetization patterns are found, including the presence of a significant cross-track magnetization component persisting along the track edges. The experimental approach and the unique physical insights acquired by simultaneously investigating individual magnetic-field components are discussed.
Microwave magnetic envelope solitons: Threshold powers and soliton numbers (abstract)
Authors: Nash J. M. , Chen M. , Tsankov M. A. , Patton C. E.
Published: July 2002

Microwave envelope solitons may be generated in thin yttrium iron garnet (YIG) films by microwave pulses if the input power is above some threshold power Pth. Above Pth, single solitons or multiple solitons may be generated. De Gasperis and co-workers have examined Pth versus input microwave pulse length τ without regard to the number of solitons actually generated.1 Kalinikos and co-workers have extracted a soliton number from actual profiles.2 Collectively, these works demonstrate that both the number of solitons and the threshold power for the generation of those solitons depends on τ. In this work, Pth vs τ data are analyzed to obtain a soliton number index N. This index has a quantitative basis in soliton theory and represents a significant improvement over a qualitative profile based determination. Measurements were made on a 7.2 μm YIG film in a microstrip delay line structure. Microwave pulses 5–50 ns wide and at a carrier frequency of 5.78 GHz were used to generate backward volume wave solitons. Deviations from a linear response of the measured peak output power were observed above some Pth for each τ value. Plots of Pth vs 1/τ2 show three linear regimes that correspond to three distinct values of N, N=1 for 5 ns<τ<10 ns, N=2 for 20 ns<τ<30 ns, and N=3–4 for 30 ns<τ<50 ns. Even when experimental conditions mask the number of distinguishable peaks in a given profile, the threshold power may be used to determine the number of solitons present.
Calculation of giant third-order nonlinear susceptibilities due to excitonic processes in rectangular GaAs quantum well wires
Authors: Madarasz Frank L. , Szmulowicz Frank , Hopkins F. Kenneth , Dorsey Donald L.
Published: July 2002

Exciton and biexciton biding energies and wave functions are calculated variationally for rectangular GaAs quantum well wires in an effective mass approximation. Coulomb interaction terms are treated exactly in their full three-dimensional form throughout the calculation, a more physically realistic procedure than employed in previous calculations that used effective one-dimensional potentials. Our treatment is unique in the use of a two-dimensional Fourier expansion of the Coulomb potential, that removes the difficulty of dealing with the 1/r singularity and considerably reduces the computational effort. Using the results of exciton and biexciton calculations and following the approach of T. Ishihara [Phys. Status Solidi 159, 371 (1990)] in order to eliminate the dimensional dependence of the third-order nonlinear optical susceptibility χ(3), we estimate its magnitude for near-resonant excitonic absorption. We obtain χ(3)’s on the order of 10−1–1 esu for various wire sizes.
Reduction in particle density of laser-deposited YBa2Cu3O7 thin films by low-energy ultraviolet radiation
Authors: Harkness S. D. , Singh R. K.
Published: July 2002

The effect of nanosecond pulsed excimer laser irradiation on the particle distribution and density of laser-deposited YBa2Cu3O7 thin films was investigated. High-TC YBa2Cu3O7 superconducting thin films with thicknesses varying from 800 to 2000 Å were deposited on (100) LaAlO3 and (100) yttria stabilized zirconia substrates. The as-deposited films were characterized by a distribution of particles on the film’s surface. The effect of controlled low energy density pulses (fluence, E=50–250 mJ/cm2, wavelength λ=248–308 nm, and pulse duration τ=20–45×10−9 s) on these films was investigated. A significant reduction of particles was observed in films after single pulse irradiation at fluences below 150 mJ/cm2. Multiple pulses did not have any further change on the surface morphology. The possible mechanisms for particle removal are also discussed.
Doping of semi-insulating polycrystalline silicon by B, P, and As implantation and diffusion
Authors: Lombardo S. , Campisano S. U. , Nicotra M.
Published: July 2002

The formation of p- and n-type layers of semi-insulating polycrystalline silicon has been investigated by implantation and diffusion of B, P, and As. At room temperature the material resistivity can be changed by more than six orders of magnitude for both p- and n-type doping. A dramatic decrease of resistivity is observed for dopant concentrations above a threshold level which corresponds to the complete filling of midgap grain-boundary traps. The determination of this critical concentration allows the evaluation of the donor and acceptor grain-boundary trap densities which are found to lie in the range from 7 to 14×1012/cm2. The charged traps produce depletion layers and potential barriers at the grain boundaries; these barriers drive the free-carrier motion under external fields. Above the threshold concentration, the barrier height decreases with the increasing concentration of active dopant, going from ≊0.5 eV to nearly 0 and correspondingly the resistivity drops down. Thermionic emission and tunneling of the carriers through these intergrain barriers are assumed to be the main conduction mechanisms. This assumption fits the temperature dependence of resistivity and the predominance of one mechanism over the other depends upon temperature, oxygen concentration, and doping.
The generalized transmission matrix for electron-wave-optics through biased heterostructures: Quantum device applications
Authors: Kan’an A. M. , Puri A.
Published: July 2002

The transmission matrix approach is generalized to calculate the transmission probability of obliquely incident electrons through arbitrary shape potential profiles. Transmission probability is obtained as a function of the electron energy, the angle of incidence, and the applied voltage across the structure. Applications to electron waveguide and quantum resonant tunneling are outlined. Numerical results are presented for angle dependent resonant tunneling through biased multibarrier GaAs-AlxGa1−xAs heterostructures. As a consequence, various novel quantum devices, i.e., high speed switch, tunable electron wave filter, and electron wave beam splitter are proposed.
Synchrotron powder diffraction study of the low-temperature lattice distortion of PbMo6S8
Authors: François M. , Yvon K. , Cattani D. , Decroux M. , Chevrel R. , Sergent M. , Boudjada S. , Wroblewski Th.
Published: July 2002

Synchrotron and Guinier x-ray powder diffraction data as a function of temperature on a superconducting PbMo6S8 sample (Tc=14.7 K) showed evidence for a subtle structural phase transition at Tl=140 K, leading from a rhombohedral high-temperature to a triclinic low-temperature modification. The transition is incomplete and presents a hysteresis of about 110 K. The triclinic cell parameters obtained at 130 K, a=6.534(9) Å, b=6.532(9) Å, c=6.529(9) Å, α=89.27(8)°, β=89.12(8)°, γ=88.97(8)°, show that the distortion affects mainly the angles (δα/αr=0.3%) and less the edges (δa/ar<0.1%). This result contrasts with previous neutron diffraction work [Phys. Rev. 35, 5365 (1987)] where the distortion was found to be much greater and to affect both the angles and the edges (δa/ar=1.2%, δα/αr=1.2%), and to be of the same order of magnitude than in the MMo6S8 (M=Sr,Ba,Eu) analogues (M=Ba: δa/ar=1.2%,δα/αr=3.5%). Guinier data on an oxygen containing sample having a lower superconducting transition temperature (Tc=10.5 K) showed a smaller distortion that started at lower temperature (Tl=100 K).