bluuebunny/crossref_metadata_2025 huggingface dataset:
The thermal behavior of the critical magnetic field in amorphous ribbons
Authors: Montes de Oca R. , Amano E. , Valenzuela R.
Published: July 2002

Initial magnetization curves of soft magnetic amorphous ribbons are essentially similar to their polycrystalline counterpart. They exhibit a nearly linear reversible magnetization behavior at low magnetic applied field, as well as an irreversible, hysteretic range for high applied fields, above a well-defined ‘‘critical field.’’ In the domain-wall size model approach for polycrystalline materials, the critical magnetic field is related to the depinning of the magnetic domain wall. For lower applied fields, the magnetic domain wall is pinned to the grain boundaries and the net magnetization is produced by a bulging mechanism; for higher applied fields, a depinning and displacement mechanism is responsible for the important magnetization increase. In this paper we present a study of the temperature dependence of the critical magnetic field in Vitrovac-type magnetic amorphous ribbons, from 80 up to 500 K. Taking into account the geometry of the toroidally wound amorphous ribbon we assume that the magnetic domain-wall pinning occurs at the external surface of the sample. We compare these results with experimental results obtained on polycrystalline nickel ferrite. The general behavior of the critical fields as a function of temperature are very similar in spite of the large differences in materials, except for the high-temperature region where relaxation phenomena seem to take place in the amorphous ribbons.
Al2O3 additions to Fe-Nd-B magnets: Can pinning be achieved? (abstract)
Authors: Ramesh R. , Thomas G. , Ma B. M.
Published: July 2002

One of the aspects currently under investigation in Fe-Nd-B magnets is that of the temperature dependence of iHc and Br, which are quite high. In this paper a method to overcome this is suggested. It is well known that pinning of domain walls by a second phase, whose magnetic properties are vastly different from those of the matrix, can be very effective when the particle size is about equal to the wall width. With this knowledge, 300-Å nominal size Al2O3 particles have been added to Fe-Nd-B in order to improve its iHc as well as the temperature dependence. For a 1 wt. % addition, a 10% increase in the iHc was noted. Results of magnetic property measurements, microstructural observations as well as Lorentz microscopy will be presented in this paper.
The microstructure of iron oxide thin films
Authors: Hwang Cherngye , Chen Mao-Min , Castillo Gilbert
Published: July 2002

The microstructural dependence of iron oxide thin films on the film preparation conditions has been systematically evaluated. The main process parameters in this study were substrate temperature, which varied from room temperature to 325 °C, and oxygen flow rate, which was from 3.0 to 9.5 sccm. For the oxygen flow rate below 6.0 sccm during deposition, the crystalline grains are columnar as shown by cross-section TEM. The columnar structure varied with the deposition temperature. For lower deposition temperature, the columnar diameter is nearly constant across the entire thickness (1000 Å) of the film; increasing the temperature tends to increase the diameter of columnar grains along the thickness of the film toward the top surface. It was also noted that the microvoids between columns were present only in the room-temperature deposited films. These voids are believed due to the shadowing effect, and resulted from the low surface atomic mobility at low deposition temperature. For higher oxygen flow rate (>8.5 sccm) the columnar structure no longer existed; instead, large α-Fe2O3 grains are present in a rather diffuse amorphouslike matrix which is believed to consist of numerous very small microcrystalline Fe3O4 particles as evidenced by the electron diffraction patterns. The postoxidization treatment was found to have very little effect on both grain size and the crystalline texture of the as-deposited thin films. However, an additional surface oxide layer of about 70 Å was seen after the oxidation process. This oxide layer was found to be polycrystalline in nature and was speculated to have resulted from the iron atoms which diffused to the surface and were subsequently oxidized to form this layer.
Magnetic profile in Tb-Fe and Tb-Fe/Ni-Fe bilayer films (abstract)
Authors: Hilleke R. O. , Felcher G. P. , Hellman F. , Gyorgy E. M.
Published: July 2002

Films of bilayers Tb0.18-Fe0.82/Ni0.83Fe0.17 show unidirectional anisotropy. This occurs when Tb-Fe is deposited in such a way that the easy axis of its magnetization is tilted at a small angle with respect to the normal to both the film plane and the Ni-Fe moment.1 The in-plane magnetization was tested by polarized neutron reflection2 with the aim of determining if and at which depth a 90° wall is present. Measurements were taken on a single ‘‘tilted’’ layer of Tb-Fe. This already shows an asymmetric magnetization: M∥=+28 G in H∥=+100 Oe and M=+7 G in H∥−100 Oe. The magnetization is fairly uniform along the thickness of 900 Å. For a bilayered sample (obtained by adding a 300-Å overlayer of Ni-Fe on the top of Tb-Fe) the in-plane magnetization is almost entirely contained in the Ni-Fe layer which has a magnetization M∥=450 G. Tb-Fe is still magnetized perpendicular to the film, except possibly at the interface, for a thickness of less than 200 Å.
Numerical micromagnetics by the finite element method. II
Authors: Fredkin D. R. , Koehler T. R.
Published: July 2002

We describe a numerical approach to micromagnetic problems based on the finite element method. We discuss a convergence difficulty in three dimensions and we propose a solution which retains the local character of the numerical method. The shape anisotropy of each element is treated on the same footing as the crystalline anisotropy. Some tests of the validity of our original method in two dimensions are also described.
Magnetic filtration of submicron hematite particles
Authors: Haque M. F. , Aidun R. , Moyer C. , Arajs S.
Published: July 2002

Magnetic filtration of submicron (65.5 nm) hematite particles passed in aqueous solution through a bed of stainless-steel spheres has been investigated under conditions of constant flow rate (∼3 cm/min) and fixed solution pH(=11). Measurements were taken as a function of field strength for magnetic fields up to several kOe in both the longitudinal and transverse orientation, and for collecting spheres in three different sizes ranging from about 50 to 200 μm. Filtration efficiency increases with field strength up to a saturation value which depends upon specific system characteristics (size and composition of the collecting elements, field orientation, etc.). The recovery of the filtered particles also was studied and found to vary with applied field and collector characteristics. The results are interpreted on the basis of current theories of magnetic filtration.
Controlling Bloch lines and domain chopping for multiple stripes aligned in parallel
Authors: Matsuyama K. , Nakamura K. , Asada H. , Suzuki T. , Fujimoto K. , Konishi S.
Published: July 2002

Controlling vertical Bloch line (VBL) position and stripe domain chopping in multiple stripe domains, aligned in parallel by a period of 12 μm, are studied experimentally using a 5-μm bubble garnet film. Patterned high coercive-force CoPt films aligned in parallel are used for stabilizing the stripe domain. During the stripe stretching process, the VBL motion at the stripe head was controlled by the dc conductor current to get two different wall states: one with a VBL at the stripe head and the other without VBL. Stripe chopping experiments for VBL detection have been performed using hairpin and meandering conductors. We found that the meandering conductor presents excellent characteristics; the bias field margin and the chopping pulse amplitude margin are 58 Oe±6% and 133 mA±11%, respectively, for one stripe. VBL generation by the meandering conductor has also been studied using the same sample.
Magnetic anisotropy energy in single crystal Y1.8Er0.2Fe14B (invited) (abstract)
Authors: Williams C. M. , Koon N. C. , Das B. N.
Published: July 2002

There has been considerable interest in tetragonal R2Fe14B compounds as a basis for a new class of permanent magnet materials because of the unusually large energy products they exhibit at room temperature for certain rare-earth substitutions. The origin of the high-energy products is directly related to the large saturation magnetization and magnetic anisotropy energy. The magnetocrystalline anisotropy energy is believed to be directly related to an interaction between the 4f-electrons and the crystal field: however, to date few if any direct comparisons have been made between the experimental magnetic anisotropy and crystal field theory. The reason being that the large anisotropy energy makes it very difficult to use conventional torque magnetometry techniques to determine the angular dependence of the magnetic free energy, particularly at low temperatures where the higher-order terms become important. In this investigation we determine the angular dependence of the magnetic free energy as a function of temperature for Y1.8Er0.2Fe14B using high field (6 T) torque magnetometry techniques and make a direct comparison of the free energy with the energy calculated using a model based on crystal field theory. Y1.8Er0.2Fe14B was chosen because the Fe and Er sublattice anisotropy energies nearly cancel at low temperatures making it possible to measure anisotropy. Excellent agreement was obtained between the model and experiment.
A Permalloy-access bubble-memory dual-function gate
Authors: Kelly J. R.
Published: July 2002

A combined write and read gate with a major-track period of 29 μm is described. Characterization results from −20 to 75 °C are presented for both swap and replicate functions. With the exception of the replicate pulse phase, the gate has excellent bias, drive, and current margins over the entire temperature range. The replicate phase is found to have two distinct failure modes. A gate variation which permits separate pulsing of the swap transfer-in and transfer-out (double-pulse swap) is also described. This design eliminates the ubiquitous low-bias–high-swap-amplitude failure mode. Finally, a 16-Mbit architecture which utilizes the dual function gate is described. The architecture has a 10-ms access time and 800-kbit/s data transfer rate (at 100-kHz rotating field frequency).
Magnetic study of acetamidinium tetrachlorocuprate II
Authors: Landenburger L. , Rubenacker Gerald V. , Drumheller John E. , Lin Wan Ke , Emerson K.
Published: July 2002

Magnetic susceptibility measurements of the tetrahedrally coordinated system [(CH3C(NH2)2]2CuCl4 show it to be a weak pseudo-one-dimensional antiferromagnet with the dominant exchange, J2/kB =−2.15 K, directed along chains of magnetic Cu++ ions. A weaker intraplanar exchange, J1/kB =0.66 K, indicates ferromagnetic ordering between chains. Susceptibility data reveal an unexpected double peak at 2.5 and 1.8 K, suggesting the interesting possibility of two phase transitions corresponding to antiferromagnetic ordering of different sublattice pairs. Consistent with crystallographic data, these sublattice pairs are formed by two crystallographically distinct distorted tetrahedral CuCl4 groups linked into chains by intermediate acetamidinium ions. This interpretation is consistent with critical electron paramagnetic resonance linewidth broadening of two separate resonances at the two reported temperatures.
Electronic properties of Co1−xCrx
Authors: Nelson J. S. , Fong C. Y. , Batra Inder P.
Published: July 2002

The non-spin-polarized mixed-basis self-consistent pseudopotential method has been used to investigate the electronic properties of hexagonal close packed Co1−xCrx alloys. For x=0.0, 0.25, and 0.5, total charge densities, effective charges, and band structures are reported. The effects of in-plane (a-axis) and c-axis stresses on the electronic properties have been investigated. The charge transfer from Cr to Co, which is about 0.04 electrons per Co/Cr bond, does not show large changes with stress. For x<0.25, we can expect that the band structure of Co will not show significant changes with alloying.
Fractional quantized nesting for the spin-density waves induced by a magnetic field
Authors: Faini G. , Pesty F. , Garoche P.
Published: July 2002

Recent experiments on magnetic field-induced spin-density waves (SDW) in the highly anisotropic organic conductor (TMTSF)2ClO4 have led us to build from thermodynamic data a phase diagram with a series of magnetic subphases. This series of transitions results from the jump of the nesting vector of the SDW. In this paper we relate our investigations of the phase diagram by magnetocaloric experiments. The measurement of the entropy variations were performed at fixed temperature by sweeping the magnetic field on an oriented single crystal. A vanishing latent heat is observed at the transition between different subphases, but this experiment reveals that each subphase is split by several phase transitions. This new complexity explains the discrepancy between phase diagrams obtained from various techniques. It is proposed that a third characteristic length, the lattice periodicity, is responsible for this complexity, thus implying a fractional quantization of the SDW wave vector.
Thermodynamic investigations of the field-induced spin-density wave: Significant departure from Bardeen–Cooper–Schrieffer behavior at high field
Authors: Pesty F. , Faini G. , Garoche P.
Published: July 2002

We have investigated the field-induced spin-density wave (FISDW) state of the quasi-one-dimensional organic conductor (TMTSF)2ClO4 by means of calorimetric experiments. Specific heat measurements were performed at low temperature and in fixed magnetic fields up to 10 T. The specific heat jump at the metal-FISDW transition is found to exhibit an oscillatory behavior as the field is varied: First, the jump goes through a series of discontinuities at the reentrance points of the phase diagram, corresponding to the transitions between two magnetic subphases. Next, around 10 T, a second-order phase transition occurs 1 K above the first-order line deduced from the magnetization data. Finally, in the same field range, the jump value deviates significantly from the Bardeen–Cooper–Schrieffer (BCS) prediction and rises up to about four times the BCS value at 10 T. Such a behavior appears to be in a strong departure from our present understanding of the field-induced magnetic ordering and seems to invalidate the weak-coupling limit in use up to now for the description of the Bechgaard salts.
5f magnetism in (U,Th)CoSn
Authors: Sechovsky V. , Havela L. , Hilscher G. , Pillmayr N. , Andreev A. V. , Veenhuizen P. A. , de Boer F. R.
Published: July 2002

As part of an investigation of UTX compounds (T represents a transition metal and X represents an element out of the group Al, Ga, Sn) we performed magnetic susceptibility, magnetization, and specific-heat measurements on the pseudoternary system (U,Th)CoSn. The results are discussed in terms of a varying 5f-electron density of states at EF which is controlled by the U concentration.
Spectrally correct finite element operators for electromagnetic vector fields
Authors: Pinchuk A. R. , Crowley C. W. , Silvester P. P. , Ferrari R. L.
Published: July 2002

A single finite element formulation using the magnetic (H) field vector directly is proposed for analysis of electromagnetic fields throughout the frequency spectrum. Results for waveguide and cavity analysis, as well as recent solutions to benchmark low-frequency eddy current examples such as the ‘‘Bath cube,’’ demonstrate the flexibility of the formulation. Applying earlier finite element methods to vector Helmholtz or diffusion equation problems, various workers have obtained incorrect solutions because the eigenmode spectra of the discrete (finite element) operators for such problems may contain eigenvalues and eigenmodes which do not correspond to modes of the underlying continuum (physical) problem. Such ‘‘spurious’’ modes have long been documented in high-frequency modal analysis. They are clearly identified as the cause for error in deterministic problems. Error is avoided by employing finite element operators whose spectra contain no spurious components. Application of the formulation may be limited by computer round-off at matrix assembly which affects solenoidality of magnetic fields in the solutions. Furthermore, the extreme values encountered in low-frequency eddy current analyses lead to ill conditioning and information loss and subsequent unreliability of the solution. These numerical instabilities may be overcome by parametric adjustment of permittivities, or by increased computer word length.
Theory of magnetic imaging by STM force microscopy (invited) (abstract)
Authors: Sáenz J. J. , García N.
Published: July 2002

Recently, we have proposed1 a new method to obtain information about local surface magnetic properties, based on the idea of measuring magnetic forces with an STM force microscope.2 In this work, we present a theoretical analysis of the magnetic topography as despicted by this magnetic force microscope (MFM). In order to study the resolution and practical limits of this new technique, we simulate MFM results for different magnetic configurations. The influence of surface roughness on the magnetic resolution is also discussed. We show that lateral resolutions of 0.01 μm can be achieved with this technique. Recent MFM experiments are also analyzed.
7-mil-thick high-permeability grain-oriented silicon steel sheet
Authors: Iwayama K. , Ueno K. , Yoshitomi Y. , Nakayama H. , Kumano T.
Published: July 2002

A new high-permeability, grain-oriented 3% silicon steel sheet of 7-mil or 0.18-mm gauge was developed by solving such problems as increasing difficulty in secondary recrystallization with decreasing sheet thickness. Typical magnetic properties of the sheet are an induction (B10) of 1.93 T at a magnetizing force of 1000 A/M and a core loss (W13/60) of 0.245 W/lb at a frequency of 60 Hz and at an induction of 1.3 T. The core loss can be reduced further to 0.220 W/lb if the sheet is treated by an artificial permanent domain control technique. When the price and other properties are also taken into account, this very low core loss seems to favor the 7-mil silicon steel sheet over amorphous metals.
Effects of the viscosity field on the Barkhausen noise of amorphous ferromagnetic materials
Authors: Celasco M. , Mazzetti P. , Masoero A. , Stepanescu A.
Published: July 2002

Contrary to the case of crystalline or polycrystalline materials, the magnetic aftereffect is almost always present in amorphous ferromagnetic materials. This fact makes the study of its influence very important in order to understand the magnetization dynamics of these materials, which have a growing technological interest. Experimental results prove the existence of a strong correlation between the magnetic aftereffect and the Barkhausen noise. In the present paper a theoretical study of the effect of the viscosity field on the power spectrum of the magnetization noise in amorphous materials will be given. Comparison with the available experimental results will also be made, showing a rather good agreement between theory and experiment.
A hybrid method for eddy current open-boundary field computation
Authors: Chari M. V. K. , Bedrosian G.
Published: July 2002

Open-boundary problems are encountered in the analysis of electric and magnetic fields in engineering applications. Examples of these are dielectric stresses in electrostatic applications, eddy current fields due to shielded power cables and bus ducts, induction heating, and magnetic levitation. Discretization of the total field region is computationally unwieldy. Bounding the field region, on the other hand, by a diamagnetic boundary imposes the effect of artificial sources. A hybrid approach to solving the field problem which combines the traditional finite element method for the interior with harmonic functions for the potential solution in the exterior region is presented. The method is applied to illustrative eddy current problems.
Growth of the fractal patterns in Ni-Zr thin films during ion-solid interaction
Authors: Huang L. J. , Ding J. R. , Li H-D. , Liu B. X.
Published: July 2002

An experimental study of the growth of fractal patterns during ion beam-solid interaction in the Ni-Zr alloy system is reported. The observed fractal patterns in the alloy films feature both isotropic and anisotropic characters depending on their growth surroundings. The fractal dimension of the isotropic fractal patterns is determined to be 1.4±0.1. The possible growth mechanism of the observed patterns is discussed.
A comparison of perpendicular and longitudinal recording
Authors: Perlov C. M. , Christner J. A. , Lopez O.
Published: July 2002

Based on the projected error rate, an optimistic figure of merit is established which applies to general pulse shapes. This figure of merit is used to compare the performance of thin-film longitudinal and double-layer perpendicular recording systems. Although the precise comparison depends on the details of the dominant noise mechanism, there does not appear to be a significant advantage to double-layer perpendicular recording for rigid disk products.
Magnetic-structural development in Co-Cr films for perpendicular recording media
Authors: Lee J.-W. , Demczyk B. G. , Mountfield K. R. , Laughlin D. E.
Published: July 2002

Transmission electron microscopy (TEM) was employed to examine the relation between microstructure and the corresponding magnetic domain structure in Co-Cr films. Emphasis has been placed on the influence of crystallographic orientation on the magnetic domain morphology. Examination of thin samples (7.5–35 nm) reveals that randomly oriented small grains form in-plane domain structures with cross-tie walls, magnetic ripple structure, and Bloch lines. As the film thickness increases (40–50 nm), the grains become well oriented along their c axes and the corresponding domain structures are comprised of the stripe-type characteristic of perpendicular domains. The magnetic domain structures will be discussed in terms of crystallographic orientation and microstructural defects.
Stress-induced anisotropy in Co-Cr thin films
Authors: Mitchell P. V. , Mountfield K. R. , Artman J. O.
Published: July 2002

A modified Varian dc magnetron sputtering system was used at an Ar pressure of 2 mTorr to prepare a sequence of 500-nm-thick Co78Cr22 films. From run to run the substrate temperature Ts was varied from close to room temperature to an upper limit of 300 °C. With a 33-GHz ferromagnetic resonance (FMR) spectrometer the effective anisotropy field, HKeff, was measured for films both as-deposited and removed from the substrate. The differences in effective field, ΔHKeff, were attributed to stress-induced anisotropy. The stress σ was determined by the disk flexure method. From σ and ΔHKeff we determined the magnetostrictive constant, Aλs. Usually A is assigned the value 3/2. p-type (‘‘bulk’’) Co-Cr is characterized by a negative λs, n1-type (‘‘transition layer’’) by a positive λs. Consequently, the tensile-type stress associated with our deposition scheme increases the positive effective anisotropy of p-type film constituents (by as much as 50%) and also increases (in a negative sense) the negative effective anisotropy of n1-type film constituents (by as much as 20%)! Since the relative p- and n-type proportions vary with Ts, the ‘‘average’’ λs found by conventional methods would vary correspondingly. Also, with the addition of 4πMs data, we determine the intrinsic magnetocrystalline anisotropy fields of the film constituents. At Ts =155 °C the intrinsic p-type magnetocrystalline anisotropy field is 85% that of pure cobalt.
Current-driven Josephson junction phase transitions
Authors: Drummond P. D.
Published: July 2002

The existence of current-driven phase transitions in Josephson junction systems is treated using an analytic theory. An arbitrary impedance in parallel with the junction is included. The theory is a singular perturbation expansion around the known solutions for a resistively shunted junction. A number of multistable solutions can occur, depending on the external resonances and their Q values. The results are calculated specifically in the case of a single junction coupled to a waveguide. The nature of the transitions that occur during a current sweep is predicted to depend crucially on the relative sizes of the junction shunt resistance and the waveguide characteristic impedance. Good agreement with experimental observations of multistability is obtained when the series inductance of the shunt resistor is included. This decreases the effective Q of the waveguide at high input current levels, giving an extended multistable region relative to the case of no series inductance. The transitions that occur for nearly equal shunt resistance and characteristic impedance appear to offer the potential for high-speed frequency-modulated switching devices.
The fabrication of TiN films by reactive evaporation and rapid thermal annealing
Authors: Repeta M. , Dignard-Bailey L. , Currie J. F. , Brebner J. L. , Barla K.
Published: July 2002

A process for the fabrication of TiN films compatible with GaAs processing has been developed. The process involves the reactive evaporation of TiN films with a substrate temperature below 100 °C, and a subsequent rapid thermal anneal with quartz halogen lamps for periods of 10–30 s at 300–1100 °C. This method minimizes the oxygen content (4%–8%), and, therefore, minimizes both the electrical resistivity of the TiN films, and the thermal degradation of the underlying GaAs substrate. Annealing TiN at 600 °C for 10 s in forming gas yields TiN sheet resistivity of 190 μΩ cm. The lowest resistivity obtained with this process is 40 μΩ cm at 1100 °C.
Reflection electron microscopy observation of the Si-SiO2 interface
Authors: Honda Kouichirou , Takizawa Ritsuo , Ohsawa Akira
Published: July 2002

The Si-SiO2 interface was studied by reflection electron microscopy (REM) in two situations: (1) through a partially etched oxide film, and (2) after removal of the oxide. We also used high-resolution cross-sectional transmission electron microscopy (HR-XTEM). A roughness of 5.0–15.0 nm in height and 0.7–2.0 μm in width could be resolved through the 2.0-nm oxide film, and the same roughness could be resolved after the oxide was removed. It was made clear that step intervals less than 50.0 nm cannot be resolved by REM, because of the lowering of the resolution due to the foreshortening. It is believed that the fringelike pattern observed after the oxide was removed reflects small steps, but they are not an accurate reflection of the steps at the interface, as observed by HR-XTEM. REM after removal of the oxide has been confirmed as being an effective means of observing the Si-SiO2 interface.
Photoinduced degradation of reverse-biased small-area a-Si:H Schottky barriers
Authors: Hanrieder Wolfgang , Mader Gerhard , Meixner Hans
Published: July 2002

Photoinduced changes (Staebler–Wronski effect) in the photocurrent and dark current of a reverse-biased small-area Schottky barrier made from amorphous silicon are investigated. The well-known, small reductions in the photocurrent are contrasted with the large increases in the dark bias current. This behavior of the dark bias current is a new phenomenon and cannot be explained on the basis of a bulk mechanism. The indications are that even under high bias voltages recombination processes take place close to the interface and give rise to thermally reversible changes of the gap density-of-states. Special attention is paid to the bias voltage and wavelength dependence of the degradation effect. The results are discussed in qualitative terms.
The temporal stability of electrodeless breakdown discharges near threshold
Authors: Curzon F. L.
Published: July 2002

Repetitive electrodeless discharges can occur in an alternating field if the field amplitude E′A exceeds a threshold value ET. In this work it is shown that stable repetitive operation requires that EA exceed ET by an amount which depends on the waveform of the applied field.
An optically controlled closing and opening semiconductor switch
Authors: Schoenbach K. H. , Lakdawala V. K. , Germer R. , Ko S. T.
Published: July 2002

A concept for a bulk semiconductor switch is presented, where the conductivity is increased and reduced, respectively, through illumination with light of different wavelengths. The increase in conductivity is accomplished by electron ionization from deep centers and generation of bound holes. The reduction of conductivity is obtained by hole ionization from the excited centers and subsequent recombination of free electrons and holes. The transient behavior of electron and hole density in a high power semiconductor (GaAs:Cu) switch is computed by means of a rate equation model. Changes in conductivity by five orders of magnitude can be obtained.
Growth behavior during nonplanar metalorganic vapor phase epitaxy
Authors: Demeester P. , Van Daele P. , Baets R.
Published: July 2002

The growth behavior during nonplanar metalorganic vapor phase epitaxy on patterned GaAs substrates was investigated by using a periodic structure of GaAs/AlGaAs layers. At the channel edges, nongrowing and slow growing low-index planes were observed, indicating local kinetic limitation of growth. A number of different channel orientations were studied and a theoretical model was used to explain the resulting growth planes. The kinetic limitation is further demonstrated by the temperature dependence of the growth behavior and by the use of different profiles. The influence of misoriented substrates is discussed. A reduction of the growth velocity was observed in the channels as compared with the surrounding area.
Mixing of Pt-René N4 alloy under Pt+ bombardment
Authors: Srinivasan V. , Bhattacharya R. S.
Published: July 2002

The mixing rates of the Ni-Pt and René N4-Pt systems under high-energy ion bombardment were measured using Rutherford backscattering spectroscopy. The mixing was induced by various fluences of 1-MeV Pt+ ions. The extent of mixing in René N4-Pt was the same as in Ni-Pt, suggesting the absence of any effects of high voume fraction of ordered second phase (gamma prime) on the mixing phenomenon in the former system. The amounts of mixing predicted by the model based on thermochemical effects were very close to those measured, while cascade collision theory could account for only 2%–3% of the mixing.
Domain size measurements on GdTbFe-based thin-film structures for magneto-optical recording
Authors: Zeper W. B. , Spruijt A. M. J.
Published: July 2002

The dependence of the domain size and domain size scattering on the write energy and the external magnetic field is studied for GdTbFe magneto-optical recording disks. It is found that with respect to the carrier-to-noise ratio the optimum write field is 200–300 Oe and the best write energy is above 0.5 nJ per laser pulse. The write noise is mainly caused by the domain size scattering. Variation of the thickness of the Al layer has little influence on the domain size: by making the Al layer thicker, the domain becomes only slightly smaller. The domain formation is well described by a two-stage model: domain nucleation and domain wall motion towards its final position.
Control of carrier lifetimes in PbTe doping superlattices
Authors: Bauer G. , Oswald J. , Goltsos W. , Nurmikko A. V.
Published: July 2002

Following subnanosecond pulsed laser excitation, time-resolved photoconductivity has been measured in PbTe doping superlattices in the temperature range 50–200 K. The carrier lifetime changes drastically by about three orders of magnitude during the recombination processes indicating an instantaneous lifetime which varies from a ns time scale up to about 1 μs. The temporal evolution is explained by the initially complete flattening of the built-in superlattice electrostatic potential and its recovery with the decrease in the nonequilibrium carrier concentration. The temperature dependence of the recombination is determined by both the bulk band structure of PbTe and the superlattice potential. The effective lifetime initially increases with temperature due to a decrease in the electron-hole recombination by tunneling, but decreases at higher temperatures where a thermal activation process dominates.
Functional dependencies of the Cu XXVIII line power output coincident with a nuclear transition in 169Tm
Authors: Coulter M. C. , Apruzese J. P. , Kepple P. C.
Published: July 2002

The feasibility of using the He-α line of Cu XXVIII at 8.394 keV to pump the 8.410-keV nuclear transition from the ground level to the (3/2)+ level in 169Tm is examined using a collisional-radiative-equilibrium plasma atomic model. Numerical calculations of the He-α line power output are presented for various density, temperature, and size conditions for both laser-imploded and Z-pinch plasmas. The interplay between the density, opacity broadening, and the radiating surface area in overcoming the 16 eV difference in transition energies is analyzed.
Heat treatment effects on an In-GaAs ohmic contact
Authors: Otsuki T. , Aoki H. , Takagi H. , Kano G.
Published: July 2002

Heat treatment effects on an In-GaAs ohmic contact are reported. Our finding is that the contact resistance of In to GaAs exhibits a practically insignificant increase after a heat treatment at a temperature of up to 900 °C. Results of secondary ion mass spectroscopy analysis show that the diffusion constant of In in GaAs is 3.3×10−5 exp(−1.9/kT) cm2/s. Moreover, a thermodynamic analysis gives the result that an InGaAs layer is formed between GaAs and In during the course of the heat treatment process. It is concluded from the above two analyses that the high stability of the contact resistance we have found is attributable to the low diffusion constant of In in GaAs and to the growth of an InGaAs interfacial layer.
Fluxon propagation on a parallel array of microbridge-type Josephson junctions
Authors: Hontsu Shigeki , Ishii Junya
Published: July 2002

This report describes the experimental results and theoretical considerations of the dynamic behavior and propagation of fluxons on a parallel array of the Nb microbridge-type Josephson junctions. A parallel array has 10 junctions. The spacing between adjacent junctions in an array is any one of three kinds, 2, 20, and 100 μm. For the array with 2 or 20 μm spacing, the dc current-voltage (I-V) characteristic includes a bending affecting the propagation of fluxons. In addition, the oscillation caused by the propagation of fluxons appears if impulse voltage is applied to the input terminal of the array. For the array with 100 μm spacing, on the other hand, the phenomena described above never occur. This report makes the mechanism producing these phenomena clear by numerical calculation of the equation on the equivalent circuit of the array including the measurement circuit.
Nonlinear temperature dependence of the refractive index of polycrystalline silicon films and the influence of microstructural disorder
Authors: Chandrasekhar S. , Vengurlekar A. S. , Roy S. K. , Karulkar V. T.
Published: July 2002

The optical properties of thin films are known to be affected by microstructural inhomogeneities. In this paper we study, using ellipsometry, the influence of microstructural disorder on the refractive index at 632.8 nm and on its dependence on temperature in the range 300–700 K in the case of thin noncrystalline low-pressure chemical-vapor deposition silicon films. It is found that films with large amorphous component have a behavior distinct from that shown by polycrystalline films. In particular, both the refractive index n and the thermo-optic coefficient dn/dT at room temperature have larger values for amorphous films than for polysilicon films. Furthermore, the thermo-optic coefficient dn/dT is found to vanish at about 500 K in the case of highly noncrystalline films.
GaP/Si heteroepitaxy by complex ion beam sputtering
Authors: Ishizuka F. , Yoshizawa H. , Itoh T.
Published: July 2002

We have investigated the sputter deposition using a complex ion beam formed with the mixture of Xe and PH3 to grow GaP epitaxial films on Si substrates. The complex ion beam was formed by the cold cathode ion source into which Xe and PH3 gases were fed via variable-leak valves. To reduce the ion beam irradiation damage in the deposited film, the Si substrate was arranged in parallel to the polycrystalline GaP target which was sputtered by the oblique irradiation of the ion beam. The ion beam acceleration voltage was kept at 6.5 kV and the ion beam current density was about 100 μA/cm2 on the GaP target. The GaP films were deposited at a chamber pressure of 2×10−5 Torr, and the substrate temperature was selected between 400 and 600 °C. The crystalline quality of the deposited GaP films was examined by the reflection high-energy electron diffraction and the surface morphology was observed by the scanning electron microscope. Single-crystalline GaP films were not obtained by the Ar+ or Xe+ ion beam sputter deposition, but were obtained by the complex ion beam sputter deposition using the gas mixture of Xe:PH3 =1:1 as a source gas at a substrate temperature of 500 °C, and also by the PH3 ion beam sputter deposition. The surface morphologies of the GaP films grown by the complex ion beam sputtering were smoother compared with those films deposited by the Ar+ or Xe+ ion beam sputtering.
Si-ion implantation in GaAs and AlxGa1−xAs
Authors: Adachi Sadao
Published: July 2002

A comprehensive study of Si implants (5×1013 cm−2, 150 keV) in GaAs and Al0.3Ga0.7As is made with the use of Hall-effect measurements. A significant annealing-temperature dependence of the electrical activation is observed. For GaAs, a clear Arrhenius plot is implied by the data, and it gives an activation energy of ∼0.79 eV. For Al0.3Ga0.7As, the electrical activation occurs dramatically from 800 °C and saturates at approximately 875 °C. Temperature-scanned Hall-effect measurements indicate that for GaAs the electron concentration is nearly temperature independent, which suggests highly degenerate electron statistics. For Al0.3Ga0.7As, the freezeout of electrons is an exponential function of temperature between 170 and 300 K, which provides a donor ionization energy of ∼110 meV. Low-temperature (4.2 K) photoluminescence measurements reveal that Si-ion implantation produces a new emission band at 1.46 eV in GaAs and strongly enhances the intensity of the 1.84-eV band in Al0.3Ga0.7As. These bands may be due to defect-impurity (Si) related transitions in GaAs and Si-donor–Si-acceptor pair recombination in Al0.3Ga0.7As.
Spin-polarized electron energy-loss spectroscopy of metastable bcc cobalt films (abstract)
Authors: Lind D. M. , Idzerda Y. U. , Prinz G. A. , Jonker B. T. , Krebs J. J.
Published: July 2002

Recent developments now allow for the study of the spin dependence of electron energy-loss features for scattering from magnetized ferromagnetic materials. Particular interest in such studies has been focused on Stoner (or spin-flip) excitations1 because of their fundamental nature as well as their proposed role in the polarization enhancement for low energy secondary electron emission from ferromagnets.2 We have performed spin-polarized electron energy loss spectroscopy (SPEELS) on thin (∼40-Å) metastable bcc Co(110) films which have been grown by e-beam evaporation on atomically clean GaAs(110) substrates. Surface order and cleanliness of the substrate and grown film are

monitored by LEED and AES. Details of the bcc Co deposition, growth, and characterization have been reported elsewhere.3 After growth, the thin ferromagnetic films are magnetized to near-saturation remanence magnetization along the in-plane [001] (magnetically easy) direction3 by placement in the center of a pulsed coil. The spin-polarized primary electron beam is obtained by photoemission from a negative electron affinity GaAs surface excited by circularly polarized light. The direction of polarization of the electron beam is easily reversed without changing the beam intensity or transport characteristics. The degree of polarization of the source is estimated to be 28–30%. The scattering geometry is chosen so that only the energy-loss spectrum of the specularly reflected beam is measured by a hemispherical energy analyzer. We obtain spin dependent loss spectra for specularly reflected electron beams for a range of primary beam energies. Two polarization dependent features are observed in the energy-loss spectra, a shoulder at 1.6 eV and a well-defined peak at 2.8 eV. The data obtained is normalized to the measured elastic peak intensity, which is assumed to be the same for both spin polarization directions. Polarization analysis shows both features to be due almost entirely to inelastic scattering of incident electrons polarized parallel to the spin-down (minority) direction. The FWHM of both features are quite narrow, suggesting a near rigid exchange splitting for the bcc Co bands. The magnetization reversal behavior and the energy dependence of these spin-dependent features are consistant with the behavior of Stoner excitations. We have tentatively identified the feature at 1.6 eV as the primary Stoner excitation which implies the exchange splitting for bcc Co is also 1.6 eV. The higher-energy peak is most likely a second peak in the Stoner density-of-states.4 Additional theoretical calculations are being performed to verify these identifications.5
Spin-glass transition in the random anisotropy axis model
Authors: Chakrabarti Amitabha
Published: July 2002

The critical behavior of the Random Anisotropy Axis model (RAM) is studied by the Monte Carlo simulation method in the limit of infinite anisotropy. Finite size scaling analysis of the data for equilibrium averages strongly suggests a zero temperature critical point in two dimensions and a finite temperature phase transition in three dimensions. The values of the critical exponents in both two and three dimensions indicate that RAM belongs to the same universality class as that of short-range Ising spin-glass models.
Linear-exponential functions for eddy current analysis
Authors: Weeber Konrad , Vidyasagar Samuel , Hoole S. Ratnajeevan H.
Published: July 2002

A finite element formulation based on a superposition of linear and exponential interpolation functions is presented for eddy current problems. These special interpolation functions are valid for problems with and without imposed source current. An error calculation demonstrates the skin depth independent and uniformly high accuracy of the linear-exponential interpolation functions and the remarkable reduction in computational effort in comparison with linear interpolation functions.
Upper critical fields of YBa2Cu3O7−δ with 60 and 90 K superconductivity and the weak link effect in the system
Authors: Shi Donglu
Published: July 2002

Upper critical fields Bc2(0) have been measured in dc fields up to 12 T for YBa2Cu3O7−δ samples with 60 and 90 K superconductivity. The data yield (dBc2/dT)T=Tc =1.49 T/K for the 90 K sample and 0.35 T/K for the 60 K sample. The estimated Bc2(0) values are 98 and 15 T for the 90 and 60 K samples, respectively. The weak link effect is associated with the low Tc phase regions in the sample which are caused by shear transformation in the system.
Properties of liquid-phase epitaxy grown Pb1−xSnxTe homostructure diode lasers with Ga-doped cladding layer
Authors: Shahar A. , Zussman A.
Published: July 2002

The properties of homostructure Pb1−xXnxTe diode lasers with tin compositions x=0.126, 0.182, 0.210, and 0.238 fabricated from liquid-phase epitaxy grown p+-p-n+ layer structure with Ga-doped n-type cladding layer were investigated. Threshold current density (Jth) and quantum efficiency (ηext) was measured as a function of temperature in the range 10≤T≤140 K. Current versus voltage (I-V) and product derivative I dV/dI vs I characteristics were measured at T=10 and 40 K. Jth was evaluated from basic principles taking into account intrinsic radiative and nonradiative Auger recombination lifetime, where the last was calculated using both parabolic and nonparabolic energy band structures. Satisfactory agreement was obtained between the calculated and measured Jth for temperatures above 40 K, while at low temperatures the theory underestimates Jth significantly. Using an electrical equivalent model of the diode laser and best fit procedure the I-V and I dV/dI vs I characteristics were analyzed and the various current components and diode laser parameters were obtained. It was qualitatively shown that the discrepancy at low temperatures follows from the presence of large leakage and tunneling currents. The temperature dependence of the observed ηext, which exhibits a maximum between 40 and 50 K, was shown to be related to a filamentary lasing process.
Three and six logic states by the vertical integration of InAlAs/InGaAs resonant tunneling structures
Authors: Potter Robert C. , Lakhani Amir A. , Hier Harry
Published: July 2002

Double-barrier/single-well resonant tunneling structures based on InAlAs/InGaAs were vertically integrated on an InP substrate to obtain devices with multiple negative-differential resistance (NDR) regions. These devices, with either two or five tunneling structures, exhibited uniform current peaks and valleys and also had NDR regions about equally spaced in bias voltage. The devices were used in simple circuits to demonstrate three or six stable logic levels which could be set with current pulses.
Laser-induced reemission of silicon atoms implanted into quartz
Authors: Shimizu Tsutomu , Itoh Noriaki , Matsunami Noriaki
Published: July 2002

Reemission of Si atoms implanted into SiO2 by both pulse-laser irradiation and thermal annealing has been investigated using the techniques of optical absorption and Rutherford backscattering. It is found that, even though the number of Si atoms in the surface is reduced in both cases, laser irradiation shifts the distribution of implanted Si atoms toward the surface, whereas thermal annealing shifts the distribution backward. The results are explained in terms of thermal diffusion arising from a temperature gradient induced by nonuniform optical absorption.
Organic-on-inorganic semiconductor heterojunctions: Energy-band discontinuities, quasi-Fermi levels, and carrier velocities
Authors: Forrest S. R. , So F. F.
Published: July 2002

Organic-on-inorganic semiconductor heterojunctions (OI-HJs) exhibit rectification whereby the current-voltage characteristics are limited by the properties of the inorganic semiconductor substrate and the magnitude of the energy barrier at the heterointerface. In this paper we calculate the potential distribution and the quasi-Fermi level energy (or imref) across the OI diode bulk. Both ohmic as well as space-charge-limited conduction regimes of the organic thin film are considered. Previous work considered the OI-HJ to be similar to a Schottky, metal-semiconductor contact. While this can give a good approximation to OI-HJ transport processes under some bias regimes, it results in a misleading picture of the position of the imrefs under reverse bias, as well as errors in measurements of the band discontinuity energy at the OI-HJ. Unlike Schottky contacts, the imref in the OI diode is flat throughout the substrate under both low forward and reverse biases. These results are used to calculate carrier velocities within the organic film. The hole velocity is in the range of 100–2000 cm/s under reverse bias and is as high as 105 cm/s under forward bias. Experimental measurements of the energy-band discontinuities are presented that are in agreement with the predictions of the current-voltage model.