bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and domain studies in Alnico 5 and Alnico 7 (abstract)
Authors: Hetherington M. G. , Cerezo A. , Jakubovics J. P. , Smith G. D. W.
Published: July 2002

Magnetization processes in Alnico alloys depend on details of the microstructure on a very fine scale. In this paper, we report the results of studies carried out in more detail and at higher resolution than any previous study. Field ion microscopy (FIM) and atom probe microanalysis (AP) were used for microstructure studies, and high-voltage electron microscopy (HVEM) for studies of both the microstructure and magnetization processes. The composition of the two phases was studied with the new VG Scientific FIM100 AP recently installed in Oxford. Its high mass resolution and vacuum of 10−11 mbar have enabled the composition of the two phases to be accurately determined. The results differ significantly from another recent determination. Information has also been obtained on the ordering of both phases, their interconnectivity and the nature of the interfaces between them. Both phases were found to be partially ordered. In Alnico 5, both isolated and interconnected particles were found. The HVEM has been used to study the microstructure over larger areas, and to study the domain structure. In Alnico 7, particles of the strongly magnetic phase appeared to be more isolated than in Alnico 5, but this result is still to be confirmed by AP. It has also been possible to carry out in situ magnetization studies in the HVEM on specimens heat treated to reduce the coercivity. In Alnico 5, domain wall motion has been observed. In Alnico 7, domains have been observed for the first time. A new model for the coercivity is proposed in the light of these results, which agrees well with both the present results and those of other workers. Studies continuing at present should enable the differences between the magnetic properties of Alnico 5 and Alnico 7 to be explained.
Effect of additional element (Fe, Zr, Ta) for Co-Cr films deposited by targets facing type of sputtering
Authors: Naoe M. , Matsuoka M. , Hoshi Y.
Published: July 2002

In order to improve both magnetic properties and wear resistance of Co-Cr films for perpendicular magnetic recording media, the effect of the addition of a small amount of Fe, Zr, and Ta to the Co-Cr binary alloy films has been investigated. They were deposited with a targets facing type sputtering (TFTS) apparatus. (i) The addition of a small amount of Fe (<5 at. %) causes a significant decrease of the effective perpendicular magnetic anisotropy K⊥ (K⊥=Ku−2πM2s). The K⊥ has a negative value at Fe content above 1 at. %. Consequently, the recording characteristics become worse as Fe content increases. (ii) The addition of Zr leads to a remarkable decrease of grain size and improvement of surface smoothness along with an increase of wear resistance. It also causes evident decrease in Ku and saturation magnetization Ms. However, both K⊥ and remanence ratio Mr⊥/Mr∥ are increased by the addition of a small amount of Zr up to 0.5 at. %, though they decrease steeply with further increase of Zr content above 1 at. %. (iii) The addition of Ta shows almost the same tendency as Zr for the film structure and wear resistance. It also causes the decrease of Ku. But the K⊥ increases with an increase of Ta content up to 0.5 at. % and takes nearly constant value at Ta content above 0.5 at. %, since the Ms of the film decreases remarkably as Ta content increases. Mr⊥/Mr∥ increases gradually from 2.5 to 3.6 as Ta content increases. Consequently, the addition of a small amount of Ta is effective for improving both recording characteristics and wear resistance.
Dependence of magnetic properties of Co-Pt films on sputtering conditions
Authors: Hoshi Y. , Matsuoka M. , Naoe M.
Published: July 2002

Magnetic properties, Young’s modulus, and corrosion resistance of Co-Pt films deposited by targets-facing type of sputtering (TFTS) have been investigated. The films deposited at a Ar gas pressure PAr of 2 mTorr present good surface smoothness and dense texture. The c axis of the hexagonal crystallites in the film orients normal to the film plane. The films have nearly the same value of  Young’s modulus (≊17×1011 dyn/cm2) as that of the bulk Co-Pt alloy. On the other hand, the films deposited at PAr of 30 mTorr exhibit rough surface and columnar structure and do not exhibit any preferred orientation of crystallites. In addition, they have a small value of Young’s modulus (≊5×1011 dyn/cm2) and poor corrosion resistance compared with the film deposited at low PAr. They have coercive force Hc larger than 1 kOe, which is mainly caused by their porous structure. Besides, the Co-Pt films have large in-plane uniaxial magnetic anisotropy, which is caused by both dc magnetic field applied to substrate during deposition and oblique incidence of sputtered particles upon substrate.
Evidence for the mechanism causing growth-induced anisotropy in YBiCaGeSi-IG
Authors: Wen Weiguang , Guan Guixian , Zhou Huiping , Zhang Yujie , Zhen Jianguo , Lee Zo-Yi
Published: July 2002

In this study the mechanism causing growth-induced anisotropy Kug in YBiCaGeSi-IG has been discussed and elucidated using the stepwise regression method by computer. In the stepwise regression analysis of a lot of the experimental data, we take Kug as a dependent variable Y, and Bi content, growth temperature Tg, film growth rate Vg, film thickness h, saturation magnetization 4πMs, rotation rate of substrates, Y content as predictors, X1, X2, X3, X4, X5, X6, X7, respectively. In our experiments, Bi content and saturation magnetization 4πMs of the samples were changed from 0.20 to 0.42 and from 330 G to 1008 G, respectively. When F-to-enter threshold F=0.5, 1, 2, 3, 4, the regression Eq. (3) is obtained as follows: Kug=−3.34×104+14.75×104Bi+33.43×4πM where multiple correlation coefficient R=0.86, standard error S3=0.675×104. Since F=15.6>F0.01(2,11)=7.21 for the regression Eq. (3), it is significant at α=0.01 level of significance. This shows that there is an approximate linear relation between growth-induced anisotropy Kug and Bi content in films, and saturation magnetization 4πMs in YBiCaGeSi-IG material.
A large anisotropy field change induced by annealing in heavily He+/Ne+-implanted garnet films (abstract)
Authors: Imura R. , Ikeda T. , Sugita Y. , Suzuki R.
Published: July 2002

It is well known that the effective anisotropy field change Δ(Hk−4πMs) in as-He+/Ne+-implanted garnet films reaches a maximum value (2500 Oe) and then decreases with increasing the ion dose. It has been also reported that the Δ(Hk−4πMs) is recovered to the maximum value by annealing in the heavily implanted films. We have found an anomalous increase in Δ(Hk−4πMs) for the films which are heavily implanted with He+ or Ne+ and subsequently annealed at high temperature (350–600 °C). With annealing, Δ(Hk−4πMs) increases with annealing time and reaches a maximum value (5000 Oe for He+ implantation). It should be noticed that this maximum value is 2500 Oe larger than that in as-implanted films. This anomalous increase has been observed only for the films whose initial strain is more than about 1.5%. This effect has not been observed in heavily H+2 implanted films. This difference may be related to the type of damage induced by He+/Ne+ implantation and H+2 implantation. Using the above-mentioned effect, 4-μm-period ion-implanted propagation tracks have been fabricated and tested . The ion implantation condition was 50 keV/1×1014 Ne cm−2+200 keV/4.5×1014 Ne cm−2. Δ(Hk−4πMs) in the as-implanted film was 1900 Oe. After 560 °C annealing, it increased to 3700 Oe. For the 4-μm-period contiguous disk propagation tracks, 10% bias field margin has been obtained.
The feasibility of silicon on garnet technology
Authors: Rasky P. H. L. , Greve D. W. , Kryder M. H. , Dutta S.
Published: July 2002

The feasibility of combining silicon and magnetic bubble technologies is demonstrated in this paper. Functional MOSFETs have been fabricated on top of bubble films coated with 1 μm thick SiO2 layers. The large grain silicon necessary for these devices is obtained by laser recrystallization of polycrystalline silicon (polysilicon). The laser recrystallization process causes changes in the magnetic properties of the bubble film; however, these changes can be reversed by subsequent thermal anneals. The required temperature treatments after laser annealing are compatible with the MOSFET fabrication process.
Structural and magnetic properties of Nd2Fe14B (invited)
Authors: Herbst J. F. , Croat J. J. , Yelon W. B.
Published: July 2002

We describe detailed analyses of neutron powder diffraction data on Nd2Fe14B at several temperatures and discuss relationships between the crystal structure and the magnetic properties via comparison with other rare earth-transition metal systems, Nd2Fe17 in particular. Diffraction studies have also been performed on optimum energy product melt-spun Nd-Fe-B ribbons. Those results demonstrate that the ribbons are comprised of Nd2Fe14B particles with diameters of a few hundred angstroms.
Excitation and scattering of guided modes on a dielectric cylinder with a periodically varying radius
Authors: Wlodarczyk Marek T. , Seshadri S. R.
Published: July 2002

The excitation and scattering of guided modes on a cylindrical dielectric waveguide with a corrugated surface is investigated. The interactions between the finite number of radiation modes and an infinite number of surface modes are considered with the consequence that both the amplitude and phase of the interacting modes are evaluated. The excitation by a two-dimensional beam is analyzed and the transverse electric and transverse magnetic modes are investigated. The power conservation relation of a corrugated cylinder is established and the reciprocity relations are investigated in general terms starting from the principle of time reversal. The fields of a finite length corrugated cylinder are used to obtain the far-field radiation pattern and treat its frequency characteristics. The effects of dielectric permittivity, dielectric losses, dephasing measure, and the grating profile are investigated.
Efficient flashlamp-pumped IBr laser
Authors: Zapata L. E. , De Young R. J.
Published: July 2002

The operating characteristics and scaling parameters of a flashlamp-pumped, 4-m-long IBr laser were investigated to further evaluate its potential as a solar-pumped laser. A peak power of 3 kW/cm2 at 2.7 μm was achieved at 4-Torr IBr pressure. A gain of 0.07 m−1 was measured at a maximum capacitor discharge energy of 4 kJ. The threshold input power necessary for lasing was found to decrease by a factor of 4 and the laser pulse width increased fourfold as the active gain length was increased from 1 to 4 m. A maximum pulse width of 120 μs was achieved with 10-Torr argon diluent added to 4-Torr IBr. Quenching of the excited state by the parent molecule was shown to be unimportant for pressures less than 4-Torr IBr. An intrinsic efficiency in the range of 12% has been measured for flashlamp-pumped IBr.
Steady-state temperature profiles in narrow thin-film conductors
Authors: Shirley C. G.
Published: July 2002

Temperature profiles in sufficiently narrow thin-film conductors can be computed in a quasi-one-dimensional model. The model applies when the linewidth is less than a thermal decay length. We discuss the thermal decay length as a function of geometrical and material parameters and find that many practical cases satisfy the narrow stripe criterion. Fringing effects are included in the model. Three specific examples are discussed: (i) the temperature of an isolated stripe, including fringing, (ii) temperature profiles near junctions of narrow stripes, and (iii) temperature profiles at the junction of a narrow tap and a wide stripe. The simplicity of the model makes it convenient for the design of electromigration experiments, for programmable read-only memory fusing current calculations, etc. Examples and graphs are given for the case of passivated aluminum on SiO2. The graphs are useful for estimation of thermal parameters without calculation.
An example of energy straggling in an ion accelerator
Authors: Raridon R. J. , Whealton J. H. , Wooten J. W. , McGaffey R. W. , Wooten D. E. , Tsai C. C.
Published: July 2002

We solve the Poisson–Vlasov equations for volume-produced ions, fast neutrals, and backstreaming electrons in a Mirror Fusion Test Facility 80-keV preprototype neutral beam source. Neutral pressure distributions are estimated from known gas feed rates and calculated accelerator column conductance, and are calibrated by comparing measured and calculated electron backstreaming power (computed by solving another Vlasov equation). The depletion of atomic yield from these volume processes is computed for sources in which the atomic yield is 100% in the extraction region. The energy distribution of neutrals and ions is also established.
Experimental bounds on band-gap narrowing set by high open circuit voltage silicon solar cells
Authors: Blakers A. W. , Green M. A. , Keller E. M.
Published: July 2002

It has commonly been reported that the energy band gap in heavily doped silicon is smaller than in lightly doped silicon. The very high open circuit voltages recently achieved in metal-insulator-n-type-p-type (MINP) solar cells, in excess of 680 mV (AM1, 300 K), can be used to put constraints upon the magnitude of such band-gap narrowing. It was determined that most recombination in high open circuit voltage MINP cells occurred in the base region. An exact numerical analysis was then performed of the emitter region. To achieve this, a critical review of the literature was undertaken to determine the values of various material parameters in heavily doped silicon. The review of the literature on hole minority carrier lifetimes and mobilities revealed that some recent studies may be seriously in error. The result of the numerical analysis was that most published models of band-gap narrowing, or extrapolations from band-gap narrowing models, are inconsistent with the open circuit voltage achieved in MINP solar cells. The conclusion is that most band-gap narrowing models overestimate band-gap narrowing at the surface of phosphorus doped MINP solar cell emitters by 60 meV or more.
Infrared pulsed stimulation of ZnS:Cu,Pb phosphor
Authors: Scheps Richard , Hanson Frank
Published: July 2002

The transient emission spectrum and spectrally resolved decay rates are reported for room-temperature ZnS:Cu,Pb phosphor powder excited at 365 nm and stimulated at 700 nm with an 8-nsec full width at half maximum laser pulse. The transient emission spectrum contains bands due to the lead intra-atomic transition and the self-activated ZnS recombination spectrum. No emission due to copper is observed. Decay rates do not vary with wavelength and decay curves are not exponential. The data are interpreted using a qualitative model for excitation and transient stimulation in the phosphor.
X-ray diffraction and ion backscattering study of thermally annealed Pd/SiC and Ni/SiC
Authors: Pai C. S. , Hanson C. M. , Lau S. S.
Published: July 2002

The reactions of Pd/SiC and Ni/SiC samples during thermal annealing are investigated by x-ray diffraction (Read camera) and MeV ion backscattering spectrometry. Metal rich silicides, Pd3Si and Ni31Si12, are found to form first, followed by the formation of Pd3Si and Ni2Si at consecutively high temperature annealing. The reaction temperatures of Pd/SiC and Ni/SiC samples are much higher compared to those of Pd/Si and Ni/Si samples. Carbon compounds were not detected in either the Pd/SiC or Ni/SiC systems within the temperature range investigated in this study.
1/f noise and the field effect in gated resistors
Authors: Garfunkel G. A. , Weissman M. B.
Published: July 2002

A quantitative connection is made between the time-dependent field effect and 1/f noise in semiconductor devices exhibiting surface state occupancy fluctuations. Noise and ac field effect measurements were made on a gated silicon-on-sapphire resistor, providing direct evidence of a surface state contribution of ∼10% of the net 1/f noise.
Steady-state currents in p-n junction filaments or grains in case of large surface recombination velocities at lateral surfaces
Authors: von Roos Oldwig , Lindholm Fredrik A.
Published: July 2002

Recently it has been pointed out that the saturation current of a semiconductor filament which constitutes part of a p-n junction diverges when the surface recombination velocity at the faces becomes infinitely large. Here we point out that this is to be expected on physical grounds since, whenever the carrier concentration is kept off equilibrium by an outside agent and at the same time recombination life times, in the bulk or in surface layers, tend to zero, concentration gradients tend to infinity. As also previously noted, the situation can be remedied by using realistic (finite) surface recombination velocities in model calculations. However, this procedure leads to mathematical complexities which have been circumvented recently by the introduction of a ‘‘heuristic’’ approach. It is the aim of this paper to assess the validity of the heuristic approach by means of detailed and exact calculations. OFF
Photochromic effect in MgO containing Li and Ni impurities
Authors: Mondragón M. A. , Muñoz P. E. , Boldú J. L.
Published: July 2002

A reversible photochromic effect is observed in thermochemically reduced MgO crystals containing both lithium and nickel impurities. Electron paramagnetic resonance and optical absorption techniques are used to study the charge-transfer mechanisms.
Influence of Pt atoms on the low temperature formation of epitaxial Pd monosilicide
Authors: Kawarada H. , Mizugaki K. , Ohdomari I.
Published: July 2002

The effect of Pt concentration in Pd thin films on the nucleation and growth of PdSi and PdxPt1−xSi (ternary monosilicide) has been investigated by transmission electron microscopy (TEM). Low concentration of Pt (10 at. %) in Pd film enhances PdSi formation at lower temperature than previously reported. It has been proposed that PdSi formation is governed by its slow nucleation. However, in our studies, the nucleation of PtSi, which is substituted for that of PdSi, triggers the subsequent PdSi growth at low temperatures. High concentration of Pt (55 at. %) in Pd-Pt alloy film lowers the temperature of the phase transformation from metal-rich silicide to monosilicide (PdxPt1−xSi). The temperature is the same as that of PtSi formation. In both cases, the monosilicide layers (about 20 nm) have an epitaxial relationship with (111) Si substrates.
Defect states in p-type silicon crystals induced by plastic deformation
Authors: Ono Haruhiko , Sumino Koji
Published: July 2002

Deep defect states in p-type silicon crystals induced by plastic deformation at 750 °C are investigated by means of deep level transient spectroscopy. Several kinds of hole traps having different energy levels within the band gap are introduced simultaneously by deformation. The main three are denoted DH(0.24), DH(0.33), and DH(0.56). The hole concentration versus temperature relations in plastically deformed p-type silicon crystals measured in a previous paper are interpreted in terms of the defect levels found in this work. Annealing behaviors of the defect states are followed and are compared with those induced by electron irradiation. DH(0.33) is proposed to be due to jogs and kinks while DH(0.24) and DH(0.56) to agglomerations of point defects that result from dislocation debris.
Spectral density due to the fluctuation of the total number of carriers in a semiconductor
Authors: Suh Chung H.
Published: July 2002

By applying stochastics and thermodynamics, a formulation for deriving the spectral density due to the fluctuation of the total number of carriers in a semiconductor is suggested. From establishing and solving the master equations concerning the involved conditional probability functions, the autocorrelation and the cross correlation of the occupancy fluctuations can be obtained. The derived form of the spectral density due to the fluctuation of the total number of carriers is proportional to the equilibrium total number of carriers in the semiconductor, and becomes 1/f noise spectrum when the power index of the relaxation times is large.
Shubnikov–de Haas effect in indium-doped PbTe films
Authors: Martinez Antonio , Davis John L. , Houston Bland
Published: July 2002

Shubnikov–de Haas oscillations in the magnetoresistance were observed in n-type, (111)-oriented PbTe films doped with approximately 0.25 at. % indium. Analysis of the data led to a Dingle temperature of 9±1 K and a transverse effective mass of 0.049±0.0006 me with a carrier concentration of 7.0×1024 m−3. It was found that the substrate-induced strain caused significant carrier transfer to the valley with main axis perpendicular to the film plane. Unexplained frequencies observed may indicate the occurrence of a phase transition.
Fe and Cr doping of liquid-phase epitaxial In0.53Ga0.47As/InP
Authors: Rao Mulpuri V. , Bhattacharya Pallab K.
Published: July 2002

Fe and Cr doping of liquid-phase epitaxial In0.53Ga0.47As grown at 650 °C on InP substrates have been investigated. Varying amounts of high-purity Fe and Cr have been added to the growth melt. The resistivity of Fe-doped layers increases with increase of Fe added to the melt, and layers with ND−NA as low as 2.0×1012 cm−3 can be grown consistently. From analysis of temperature-dependent Hall data on conducting Fe-doped samples, the Fe acceptor ionization energy is found to be 0.46 eV. No additional feature is seen in the 4 K band-edge photoluminescence spectra of Fe-doped layers. Cr doping seems to produce donorlike behavior and the electron concentration increases monotonically with increased addition of Cr to the melt. An additional peak, separated from the band-gap energy by 24 meV is seen in the photoluminescence spectra of Cr-doped samples. It is believed that Cr itself, or a complex defect involving Cr is responsible for the formation of a donorlike center.
Photoconductance transient response in polycrystalline silicon
Authors: Poon E. , Hwang W. , Yang E. S. , Evans H. L.
Published: July 2002

The photoconductance transient response in polycrystalline silicon has been studied theoretically and experimentally. Shockley–Read–Hall statistics are used to describe the emission and capture processes at the grain-boundary traps. Under appropriate conditions, the minority carrier capture and emission time constants of the grain-boundary trap can be directly obtained from the photoconductance transient response. The photoconductance method is therefore useful for studying grain-boundary deep level states. The special case when a focused laser spot is employed is also discussed. From the experimental data obtained from large-grain Wacker polycrystalline silicon, we have discovered a donor-like level at 0.48 eV below the conduction band with a concentration of 2×1010 cm−2. The electron (minority carrier) lifetime is found to be about 6×10−10–10−9 s.
Infrared spectral distribution of photoconductivity and up-conversion in GaP light emitting diodes
Authors: Moser K. , Wahl S. , Eisfeld W. , Prettl W.
Published: July 2002

The spectral distribution of photoconductivity and infrared excited electroluminescence has been determined in GaP light emitting diodes at low temperatures by conventional infrared spectroscopic techniques. The observed photoresponse was found to be caused by ionization of shallow donors only, showing a peak sensitivity of 20 mA/W at 13-μm wavelength. Spectral structures for photon energies lower than the binding energies of shallow donors are attributed to electric field assisted photoionization. An external quantum efficiency of 3×10−3 was obtained being largely independent on the bias voltage and the wavelength of infrared stimulation.
Temperature dependence of carrier lifetime and Auger recombination in 1.3 μm InGaAsP
Authors: Sermage B. , Heritage J. P. , Dutta N. K.
Published: July 2002

Carrier lifetime has been measured by the luminescence decay of a 1.3-μm-InGaAsP layer excited by a mode locked YAG laser at 1.06 μm. The measurements have been done as a function of excitation intensity for nearly three orders of magnitude of carrier concentration (4×1016–2×1019 cm−3) and for different temperatures (between 32 and 346 K). At low and moderate carrier density, the lifetime τ follows the variation with excitation of the theoretical radiative lifetime. At high carrier density (above 1018 cm−3) the carrier decay rate increases more rapidly than the radiative one and around room temperature this can be accounted for by an additional recombination mechanism whose variation with excitation is typical of an Auger process. The Auger coefficient (Ca=2.6×10−29 cm6 s−1) does not vary with temperature within experimental uncertainty. This suggests that though Auger recombination is for a large part responsible for the low T0 value of 1.3-μm InGaAsP lasers, the temperature dependence of the Auger coefficient does not contribute to it.
Impurity doping properties of hydrofluorinated amorphous silicon produced by intermediate species SiF2
Authors: Matsumura Hideki , Ihara Hisanori , Uesugi Takashi
Published: July 2002

Electrical and optical properties of boron- or phosphorus-doped new hydrofluorinated amorphous silicon (a-Si:F:H) are experimentally studied. This new a-Si:F:H is produced by using intermediate species SiF2 and H2 gas mixture instead of using SiH4 gas or SiF4 and H2 gas mixture. It is found that the doping efficiency for boron or phosphorus in this a-Si:F:H film is slightly better than that of conventional hydrogenated amorphous silicon (a-Si:H), and also that the optical band gap of this a-Si:F:H hardly changes for the increase of conductivity due to boron doping while that of a-Si:H is apparently decreased.
Defect analysis in polycrystalline silicon solar cells
Authors: Sastry O. S. , Dutta V. , Mukerjee A. K. , Chopra K. L.
Published: July 2002

Localized bulk defects like diffusion length variations and structural defects like grain boundaries are analyzed in polycrystalline silicon solar cells using laser scanning and deep level transient spectroscopy techniques. The effect of hydrogen passivation on the role of grain boundaries has been studied.
Graphical method to include temperature variation of activation energy in Hall data analysis
Authors: Iyer Suman B. , Kumar Vikram
Published: July 2002

A graphical method is presented for Hall data analysis, including the temperature variation of activation energy due to screening. This method removes the discrepancies noted in the analysis of recently reported Hall data on Si(In).
Driven diffusion including radial exchanges with the environment
Authors: Zee R. H. , Blair J. M.
Published: July 2002

The time-dependent partial differential equation governing the two-dimensional driven diffusion in a cylindrical rod is solved analytically with an exchange strength at the surface that is either (i) proportional to the local surface concentration, or (ii) a constant. Both solutions are in the form of infinite series containing Bessel functions. Results from these calculations can be used to determine various thermodynamic properties of a solute in a homogeneous solid solution.
Annealing behavior of light-induced defects in boron-doped hydrogenated amorphous silicon alloys
Authors: den Boer W. , Guha S.
Published: July 2002

Light-induced effects in lightly boron-doped hydrogenated amorphous silicon alloys have been studied in coplanar and sandwich sample configurations. It is observed that metastable changes in these films anneal out at a significantly lower temperature (≤ 100 °C) than in undoped films.
The growth of CdS and Cd1−xZnxS
Authors: Kuwamoto H. , Gunning W. J.
Published: July 2002

CdS and Cd1−xZnxS single crystals have been grown by a modified vapor growth technique. They have high transmission and high resistivity (>1010 Ω cm). The results of transmission measurements are reported.
Optical quenching of the near-intrinsic photocurrent in semi-insulating bulk GaAs
Authors: Jiménez J. , Hernández P. , de Saja J. A. , Bonnafé J.
Published: July 2002

The optical quenching of the photoresponse of GaAs when it is subject to a prolonged 1.15-eV optical excitation is one of the most important properties of the EL2 level in GaAs. Another quenching phenomenon takes place after excitation with photons in the same range, that is the optical quenching of the photoresponse in the near band-edge spectral region. Both quenching effects seem to be strongly correlated with changes in the configuration of the EL2 level, due to variations in the charge state of this level. In this way we can conceive a mechanism where EL2 captures electrostatically shallow levels when it is optically ionized at low temperature. By photoconductivity studies, we have seen that capture of shallow levels is accomplished after EL2 has relaxed to a metastable state EL2* which could be described on the basis of a mechanism similar to that recently proposed by M. Levinson.
Defect property correlations in garnet crystals. II. Electrical conductivity and optical absorption in Ca3Al2Ge3O12
Authors: Rotman S. R. , Tuller H. L. , Roth M. , Linz A.
Published: July 2002

Electrical conductivity and ionic transference measurements performed at varying temperatures and partial pressures of oxygen show that CALGAR (Ca3Al2Ge3O12), a luminescent garnet, is a mixed ionic-electronic conductor. An activation energy of 1 eV for ionic diffusion is measured. An absorption band at 400 nm, whose magnitude can be controlled by varying the annealing atmosphere, is attributed to an O− center.
Thermoelectric properties of Ga1−xAlxAs
Authors: Hava S. , Hunsperger R.
Published: July 2002

Theoretical and experimental results describing the dependence of the Seebeck and Peltier coefficients on the composition of Ga1−xAlxAs solid solution are given. The Seebeck coefficient for nondegenerately doped n- and p-type Ga1−xAlxAs is given by the simple expressions αn=(k/e)(lnNc/n+2) and αp=−(k/e)(lnNv/p+2), respectively. The dependence of α on the composition of Ga1−xAlxAs solid solutions is linear for p type and nonlinear for n type. This relation is dependent on the type of carrier that is involved in the conduction process, as well as the detailed band structure of the material. For p-type material, two kinds of carriers are involved: heavy and light holes; for n-type material, three kinds of carriers are involved: one direct electron and two indirect electrons. The direct electrons are dominant for Al composition of 0<x<0.3, and the indirect electron is dominant for composition 0.45<x<1. Experimental measurements of the Seebeck coefficient for n- and p-type Ga1−xAlxAs and for AuGe and AuZn resemble the theoretical results.
Electronic conduction in poly(p-phenylene sulfide)
Authors: Tsutsui Tetsuo , Nitta Naoki , Saito Shogo
Published: July 2002

The dark conductivity and photoconductivity of pristine poly(p-phenylene sulfide) (PPS) were investigated under strictly controlled experimental conditions. Apparent dark conductivity of pristine PPS increased by more than a decade after the sample was irradiated with UV light. The appearance of apparent high conductivity was found to originate from thermally released electronic carriers which had been captured in deep trapping sites. Dark conductivity of PPS measured in air was about 4 decades higher than that measured under high vacuum. Oxygen absorbed in PPS samples was found to behave as weak electron acceptors and to assist the production of electronic carriers. Large photoconductivity under steady-state photoirradiation was found.
Electron-beam-induced currents collected by a p-n junction of finite junction depth
Authors: Soukup R. J. , Ekstrand J. P.
Published: July 2002

The hole-electron pair generation region in a semiconductor bombarded by a scanning electron beam can be modeled as a circular cylinder tangent to the semiconductor surface. A cross-sectional plane normal to the cylinder is then examined. Under conditions of high semiconductor surface recombination velocity, a conformal transformation of this plane can be made to yield a geometry in which the method of images can be used to match boundary conditions at the junction and at the semiconductor surface. Thus, a solution for the electron-beam-induced current (EBIC) problem can be found in this manner when the generation region is external to the diffused or implanted region of a finite junction depth. An infinite series of images can be used to solve the problem when the generation region is within the diffused or implanted region under conditions of low, as well as high, surface recombination velocity. Thus, expected EBIC results are presented as a function of junction depth.
Magnetron-sputtered amorphous silicon
Authors: Demichelis F. , Tagliaferro A. , Tresso E. , Rava P.
Published: July 2002

The optical properties of undoped α-Si:H films prepared using magnetron sputtering at different deposition conditions were studied by measuring their transmittance and reflectance between λ=0.25 and λ=1.5 μm and their thickness. The extracted optical constants are interpreted to give values of the band gap. Values of dark conductivity and activation energy are also obtained. The study has been extended to structures SnO2/α-Si:H/substrate. From measurements of transmittance and reflectance of the system optical constants of the components can be extracted.
Self-consistent calculation of stress-induced demagnetization process
Authors: Izawa Fumio
Published: July 2002

The change in a magnetization transition zone in a magnetic recording medium is analyzed under stress application by the self-consistent iterative calculation method. The medium is assumed to be composed of uniaxial single domain magnetic particles with two-dimensional angular distribution of easy axes. Owing to the applied stress, the demagnetizing field temporarily increases at the localized area, because the magnetization distribution changes due to stress-induced easy axes rotation. The applied stress also changes the critical field for irreversible magnetization switching; hence, additional magnetization reversal takes place for particles which suffer critically large demagnetizing field. Consequently, the present simulation can explain the stress-induced demagnetization phenomenon, in which reproduced signal level attenuates as a result of magnetization transition broadening caused by stress.
Perpendicular recording characteristics of ring head and Co-Cr/Co-Zr-Mo double-layer media
Authors: Shiroishi Y. , Tsumita N. , Shiiki K. , Uesaka Y. , Kudo M.
Published: July 2002

The read/write and noise characteristics of Co-Cr/Co-Zr-Mo double-layer media are investigated with a conventional Mn-Zn ferrite ring head of 0.3-μm gap length in comparison with single-layer media. Almost the same D50 recording density of 80 kFCI are obtained for both double- and single-layer media with a coercivity of 500 Oe. The double-layer media/ring head combination has superior output and overwrite characteristics but inferior noise characteristics to those of a single-layer/ring head.
A new biasing method for shielded MR head
Authors: Kamo Yoshihisa , Kitada Masahiro , Tsuchiya Hiroshi
Published: July 2002

Reproduced signal waveform changes of magnetoresistive (MR) heads due to head wear are studied through experiments and computer simulations using the finite-element method. The experiments are performed utilizing magnetic tapes and MR heads with permanent-magnet and shunt bias. The change of reproduced signal waveform asymmetry is opposite in these biasing methods. Based on this result, we propose a new biasing MR head which has a structure combining current bias with permanent-magnet bias, and present its advantages.
Analytic model for single pole heads
Authors: Baker Bill , Gloski David , Labmeier Carl , Lee Michael
Published: July 2002

Inner and outer analytic solutions are merged to obtain accurate simple results for main pole driven thin-film heads for perpendicular recording. The variation of the pole tip potential as a function of spacing and the distribution of total flux in the permeable sublayer are derived. The computed frequency response and spacing losses for double-layered media are compared with experimental data from a CoCr sputtered disc.
Particle-like magnetic behavior of rf-sputtered CoCr films
Authors: Wuori E. R. , Judy J. H.
Published: July 2002

This paper summarizes measurements on CoCr films that appear to indicate particle-like behavior of the magnetization reversal. The films studied were rf-diode sputtered onto glass substrates and had a magnetic moment of 400 emu/cm3 (at about 17 at. % Cr content). Particle-like structure of CoCr films has been reported by many authors because of the SEM fracture cross sections which show a columnar microstructure with long thin particles extending through the film thickness. Temperature variations of coercivity and anisotropy fields are found to track approximately indicating that the coercivity is primarily of crystalline origin but also the difference in the slopes of these curves is explained almost exactly by a particle model consistent with the SEM fracture cross sections. Preisach diagrams were constructed from the shear corrected hysteresis loops and found to be extremely narrow. Further, the Preisach data correctly predicts initial magnetization curves. The Preisach diagram results suggest a magnetization reversal model of particles that are magnetically noninteracting except for the sheet demagnetizing fields of the film. Much data exists to support the idea of phase segregation in the CoCr alloy system, again in support of the particle idea. Rotational hysteresis loss measurements were made which indicate magnetization reversal by way of a curling or buckling mechanism, again indicating a particle-like behavior. Coercivity as a function of field angle was measured yielding results consistent with curling or buckling as the primary reversal mechanism. Almost all available data is explained by a model of magnetically isolated particles that interact magnetically only through the film demagnetizing fields and individually reverse by curling or buckling.
Accounting for nonlinear material characteristics in modeling ferroresonant transformers
Authors: Voisine J. T.
Published: July 2002

A mathematical model relating core material properties, including nonlinear magnetization characteristics, to the performance of ferroresonant transformers has been developed. In accomplishing this, other factors such as fabrication destruction factors, leakage flux, air gap characteristics, loading, and coil resistances and self-inductances are also accounted for. From a material manufacturer’s view, knowing such information facilitates isolating sources of performance variations between units of similar design and is therefore highly desirable. The model predicts the primary induction necessary to establish a specified secondary induction and determines peak induction at other points in the magnetic circuit. A study comparing the model with a transformer indicated that each predicted peak induction was within ±5% of the corresponding measured peak induction. A generalized 4-node magnetic circuit having two shunt paths was chosen and modeled. Such a circuit is easily modified facilitating the analyses of numerous other core designs. A computer program designed to run on an HP-41 programmable calculator was also developed and is briefly described.
Computation of optical properties of multilayered media for magneto-optical memories
Authors: Gueugnon C. , Bernstein P. , Lefèbvre R.
Published: July 2002

Amorphous rare-earth/transition metal alloys are efficient materials for high-density magneto-optical memory discs. To optimize the figure of merit F=R×sin2θ (R is the reflection coefficient and θ is the peak to peak Kerr rotation), the alloys are used as very thin films in multilayered structures. Kerr and Faraday effects combined with interference effects enhance F. A computation of numerous parameters (optical and magneto-optical indices and thickness of each layer) is necessary to optimize this structure. The computation we propose is based on the recurrent Heavens’ method taking into account the circular birefringence of the magnetic layer, and leads to realistic values of F. The computation method is outlined in this paper and the agreement between experimental and theoretical results discussed for GdFe alloys.
Magnetic and structural properties of shock-synthesized zinc ferrite
Authors: Venturini E. L. , Morosin B. , Graham R. A.
Published: July 2002

High-pressure shock-wave loading on stoichiometric mixtures of zinc oxide and ferric oxide powders produces partial conversion to a spinel structure zinc ferrite as shown by x-ray diffraction. The ferrite phase is characterized by a substantial saturation magnetization plus a high-field susceptibility. Since stoichiometric ZnFe2O4 is paramagnetic above 10 K, the magnetic behavior of the shock-synthesized spinel demonstrates that it is a zinc-deficient ferrite. X-ray diffraction data confirm that less zinc oxide is consumed than ferric oxide in producing the recovered spinel.
Prediction of flux distribution as a means to nondestructive testing of oil-pipe materials (abstract)
Authors: Sarma Mulukutla S.
Published: July 2002

The flux distribution for a given excitation is determined in the cross section of an oil pipe, in its interior and exterior regions, in order to utilize this information eventually for the nondestructive testing of the material of the pipe. A two-dimensional mathematical model is established under certain simplifying assumptions and the grid system is laid out for numerical analysis. The relevant partial differential equations of the magnetic vector potential as well as their difference algorithms are developed. An innovative combination of rectangular and polar grid systems is used to follow the contours of the cross section consisting of the oil pipe and the excitation mechanism made up of a core, coil, and two steel brushes. The reluctivity of ferromagnetic materials is assumed to be a function of the magnetic induction. An iterative procedure consisting of successive-point relaxation of vector potentials with an optimum over-relaxation factor, a block-relaxation method for accelerating the convergence, relaxation of reluctivities with an optimum under-relaxation factor, and a constant monitoring of the convergence of the sum of absolute values of residuals as well as of the absolute value of the maximum residual is described. Computer programs in fortran language are developed and applied to find the flux distribution inside and outside the cross section of the oil pipe for various excitation-current densities. Analytical results are compared with experimental data. Refined analyses including eddy-current and three-dimensional effects are under way.
Solution of three-dimensional boundary value problems for magnetostatics by a constrained Fredholm integral equation
Authors: Mayergoyz I. D. , D’Angelo J. , Crowley C.
Published: July 2002

In this paper, a constrained boundary integral equation is presented for the analysis of three-dimensional magnetostatic problems. This formulation uses a simple layer of charge on the interface surface to represent the permeable object. A constraining condition that sets the total integrated surface charge to zero is used to make this formulation unique. In addition, a method of generating exact analytical solutions for use in validating the boundary element code is presented. A test comparison using this method will be shown.
Dual simple-layer source formulation for two-dimensional eddy current and skin effect problems
Authors: Lean Meng H.
Published: July 2002

The integrodifferential expression resulting from a reformulation of the time-harmonic diffusion equation to accommodate skin effect problems is further transformed, via an approximate average potential A0, to allow solution using a boundary integral technique. Conducting and nonconducting regions are initially separated into subregions. On each subregion boundary a simple-layer distribution of sources is prescribed resulting in a first kind Fredholm integral equation. Dual simple-layer sources are therefore distributed on subregion interfaces. The 2n equations derived from enforcing continuity of normal B̄ and tangential H̄, using point collocation, are added to the current conservation equation for direct solution of the 2n+1 unknowns. This method allows subregion solutions to be decoupled once the sources are determined since the fields in any subregion are adequately prescribed by the corresponding source layer. Curved interfaces are modeled accurately by fourth-order boundary elements. Numerical results, including vector potential distributions and loss ratio and inductance variation with frequency, for a single conductor of circular cross section modeled by four quartic elements are compared with the exact solution. The extension of this technique to noncontacting multiconductor geometries is discussed. It is shown that asymmetric block-sparse matrices are generated for problems made up of more than two subregions.
Novel finite element analysis method using magnetic flux density directly as an unknown variable
Authors: Yamashita H. , Shaikh Z. H. , Nakamae E. , Hammam M. S. A. A.
Published: July 2002

In magnetic field analysis, designers are interested in the magnitude of magnetic flux density. It is common practice to use vector potential as an unknown variable and then differentiate it to obtain the magnetic flux density. This paper uses the magnetic flux density directly as an unknown variable. The formulation of this new method and its application to two-dimensional and axisymmetrical magnetic fields are explained and illustrated. The calculated error of the magnetic flux density by the new technique is compared with that obtained by the traditional finite element method for a model of known solution. The comparison shows that the new method is capable of producing better results than the traditional one in terms of computation time and accuracy. Furthermore, the proposed technique will be useful for the calculation of three-dimensional fields and eddy-current problems.
On finite element force computation from two- and three-dimensional magnetostatic fields
Authors: Hoole S. Ratnajeevan H. , Hoole P. Ratnamahilan P.
Published: July 2002

The mathematics of force computation is well known. However, little literature exists on the practical aspects of its implementation in finite element methods. This paper takes up the issue and shows that the convergence of force with finite element mesh refinement is far behind that of flux density or vector potential. Likewise, the effect of remote boundaries placed at far, but finite, distances is shown to be greater on force. Algorithms are given for the extraction of forces from a field solution for an interactive environment and the force density and Maxwell stress methods compared.
Magnetic field computation in hysteretic media by the finite element method, using the Preisach model
Authors: Ostiguy J.-F. , Silvester P. P.
Published: July 2002

The Preisach hysteresis model is implemented into the finite element method. It is demonstrated that this model is well suited to a scalar potential representation of the field, a fact that has not been fully appreciated so far. Although this clearly eliminates the possibility of dealing exactly with problems involving eddy currents in hysteretic subregions, the computation of the magnetic field when both hysteretic and nonmagnetic current-carrying subregions are present simultaneously can be handled by adopting a hybrid formulation. This allows complete field solutions in reactor or transformer problems. Finally, it is shown how position-dependent remanent magnetization can be dealt with in a straightforward manner, without the need to use both volume and surface elements simultaneously, and without any assumption on the order of the interpolation polynomials for the potential. The method is also applicable to permanent magnet problems for which an accurate representation of the spatial dependence of remanent magnetization is important.