bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of argon characteristics in ion physical vapor deposition using molecular dynamics simulation
Authors: Hwang Chi-Chuan , Huang Gwo-Jiunn , Chang Jee-Gong , Ju Shin-Pon
Published: July 2002

This article uses molecular dynamics simulation to investigate the role of Ar ions in the ion physical vapor deposition (IPVD) process for different Ar+-to-Cu+ ratios, and to analyze the influence of different Ar+-to-Cu+ ratios on the trench filling morphology. Also compared are the trench filling morphology observed for the IPVD process with that found in the conventional collimated magnetron deposition process. The molecular dynamics simulation includes a trench model and a deposition model, and uses the many-body, tight-binding potential method to represent the interatomic force acting among neutral atoms. The interatomic force acting between the ions and the neutral atoms is modeled by the pairwise Moliere potential method. The simulation indicates that the incident Ar ions influence the trench filling mechanisms in two significant ways; peeling of the cluster atoms, which promotes migration of the cluster atoms along the sidewall, and breaking of the bridge which forms when two clusters of atoms join. Both phenomena are beneficial since they promote a more complete filling of the trench.
Ultrafast switching of magnetic nanoelements using a rotating field
Authors: Fidler J. , Schrefl T. , Tsiantos V. D. , Scholz W. , Suess D. , Forster H.
Published: July 2002

Nanostructured granular Ni80Fe20 and Co films are studied using a 3D hybrid finite element/boundary element model. Switching dynamics are calculated for external fields applied unidirectional after a rise time of 0.1 ns and for a 10 GHz rotational field with a field strength of Hext=0.2 Js/μ0 (160 kA/m for NiFe and 280 kA/m for Co). The transient magnetization patterns show that reversal in the unidirectional field proceeds by the nucleation and propagation of end domains towards the center of the element. The switching time strongly depends on the Gilbert damping parameter α. Materials with uniaxial anisotropy (Co), require larger field, but exhibit shorter switching times. Reversal in rotational fields involves inhomogeneous rotation of the end domains towards the rotational field direction leading to partial flux-closure structures. Shorter switching times are obtained by the application of the 10 GHz rotational field (tsw=0.05 ns). Precessional oscillation effects after abruptly switching off the external field which occurred in the NiFe square element, were suppressed in the granular Co film. Reducing the field to zero slowly inhibits the high frequency excitations in NiFe.
Synthesis and magnetic properties of CoPt–poly(methylmethacrylate) nanostructured composite material
Authors: Fang Jiye , Tung L. D. , Stokes Kevin L. , He Jibao , Caruntu Daniela , Zhou Weilie L. , O’Connor Charles J.
Published: July 2002

We have prepared nanometer-sized CoPt particles dispersed in a poly(methyl methacrylate) (PMMA) matrix, as a novel nanostructured magnetic plastic, through a soft chemical processing route. In this work, CoPt nanoparticles were successfully synthesized from a solution phase reduction system in the presence of capping ligands and stabilizing agents at high temperature. The CoPt nanoparticles were annealed at 400 °C for 3 h, and were subsequently re-dispersed in methylmethacrylate (monomer). The polymerization was induced by a UV source and the hardness of final product was adjusted by varying the amount of monomeric cross-link agent. Annealed bare CoPt nanoparticles as a “core” material and CoPt–PMMA composite material were characterized by using energy dispersive spectroscopy, transmission electron microscopy, and x-ray diffraction, indicating that we are able to prepare CoPt nanoparticles with <10 nm in diameter (after annealing) by employing this high temperature colloidal processing method. Magnetic investigation of this CoPt–PMMA material indicates an intrinsic coercivity of 300 Oe at 300 K and 1665 Oe at 5 K.
Renormalization of Poincaré transformations in Hamiltonian semiclassical field theory
Authors: Shvedov O. Yu.
Published: July 2002

Semiclassical Hamiltonian field theory is investigated from the axiomatic point of view. A notion of a semiclassical state is introduced. An “elementary” semiclassical state is specified by a set of classical field configurations and quantum states in this external field. “Composed” semiclassical states viewed as formal superpositions of “elementary” states are nontrivial only if the Maslov isotropic condition is satisfied; the inner product of “composed” semiclassical states is degenerate. The mathematical proof of Poincaré invariance of semiclassical field theory is obtained for “elementary” and “composed” semiclassical states. The notion of semiclassical field is introduced; its Poincaré invariance is also mathematically proved.
Dielectric functions and optical bandgaps of high-K dielectrics for metal-oxide-semiconductor field-effect transistors by far ultraviolet spectroscopic ellipsometry
Authors: Lim Seung-Gu , Kriventsov Stas , Jackson Thomas N. , Haeni J. H. , Schlom D. G. , Balbashov A. M. , Uecker R. , Reiche P. , Freeouf J. L. , Lucovsky G.
Published: July 2002

A far ultraviolet (UV) spectroscopic ellipsometer system working up to 9 eV has been developed, and applied to characterize high-K-dielectric materials. These materials have been gaining greater attention as possible substitutes for SiO2 as gate dielectrics in aggressively scaled silicon devices. The optical properties of four representative high-K bulk crystalline dielectrics, LaAlO3, Y2O3-stabilized HfO2 (Y2O3)0.15–(HfO2)0.85, GdScO3, and SmScO3, were investigated with far UV spectroscopic ellipsometry and visible-near UV optical transmission measurements. Optical dielectric functions and optical band gap energies for these materials are obtained from these studies. The spectroscopic data have been interpreted in terms of a universal electronic structure energy scheme developed form ab initio quantum chemical calculations. The spectroscopic data and results provide information that is needed to select viable alternative dielectric candidate materials with adequate band gaps, and conduction and valence band offset energies for this application, and additionally to provide an optical metrology for gate dielectric films on silicon substrates.
Experimental study of granular surface flows via a fast camera: A continuous description
Authors: Bonamy D. , Daviaud F. , Laurent L.
Published: July 2002

Depth averaged conservation equations are written for granular surface flows. Their application to the study of steady surface flows in a rotating drum allows to find experimentally the constitutive relations needed to close these equations from measurements of the velocity profile in the flowing layer at the center of the drum and from the flowing layer thickness and the static/flowing boundary profiles. The velocity varies linearly with depth, with a gradient independent of both the flowing layer thickness and the static/flowing boundary local slope. The first two closure relations relating the flow rate and the momentum flux to the flowing layer thickness and the slope are then deduced. Measurements of the profile of the flowing layer thickness and the static/flowing boundary in the whole drum explicitly give the last relation concerning the force acting on the flowing layer. Finally, these closure relations are compared to existing continuous models of surface flows.
Exact evolution equations for SU(2) quasidistribution functions
Authors: Klimov A. B.
Published: July 2002

We derive an exact (differential) evolution equation for a class of SU(2) quasiprobability distribution functions. Linear and quadratic cases are considered as well as the quasiclassical limit of the large dimension of representation, S≫1.
Determination of aluminum diffusion parameters in silicon
Authors: Krause O. , Ryssel H. , Pichler P.
Published: July 2002

Aluminum as the fastest diffusing acceptor dopant in silicon is commonly used for the fabrication of power semiconductors with p–n junction depths ranging from some microns to more than a hundred microns. Although long used, its diffusion behavior was not sufficiently characterized to support computer–aided design of devices. In this work, the intrinsic diffusion of aluminum was investigated in the temperature range from 850 to 1290 °C. Combining nitridation and oxidation experiments, the fractional diffusivity via self-interstitials was determined. By diffusion in high-concentration boron- and phosphorus-doped silicon the behavior of aluminum under extrinsic conditions was investigated.
Principle and application of a thermal probe to reactive plasmas
Authors: Stamate E. , Sugai H. , Ohe K.
Published: July 2002

A thermal probe for plasma diagnostics is introduced. The method is based upon measuring the equilibrium temperature of a conducting sphere as a function of its applied bias. The resulting temperature–voltage characteristic is processed using a theoretical model that accounts for charge and thermodynamic balance. The thermal probe is capable of detecting negative ions and shows sensitivity to certain chemical reactions. Measurements performed in Ar, Ar/SF6, and O2 show good agreement among the plasma parameters using thermal and Langmuir probes.
Characterization of a model Ziegler–Natta catalyst for ethylene polymerization
Authors: Schmidt J. , Risse T. , Hamann H. , Freund H.-J.
Published: July 2002

Based on the work of the Somorjai group [Magni and Somorjai, Catal. Lett. 35, 205 (1995)] we have prepared a thin well ordered MgCl2(001) film by MgCl2 evaporation from a Knudsen cell. This film does not absorb TiCl4 at room temperature if it is not activated by increasing the defect density via electron or ion bombardment. The nature of some of the defects created is characterized by in situ ESR measurements and Auger spectroscopy. Paramagnetic surface defects are altered by the bonding of TiCl4 to the surface as observed by ESR spectroscopy. Ti3+ centers are detected if particularly severely defected MgCl2 layers are prepared. Reactivity studies show however, that these species are not correlated with polymerization activity. Interaction with aluminum alkyl leads to the formation of the active catalyst and we observe for the first time directly ethyl radicals formed from trimethyl-aluminum in an abstraction process which may be formulated as TiCl4/surface+AlMe3→Me−TiCl3/surface+AlMe2Cl, Me−TiCl3/surface→TiCl3/surface+Me⋅, and Me⋅+Me3Al→C2H5⋅+AlH(Me)2. The presence of the aluminum alkyl is observed via in situ IRAS in the same apparatus.
Multifractal scaling in a Sierpinski gasket
Authors: Tong P. Y. , Yu K. W.
Published: July 2002

The distribution of conductance jumps ΔG in a Sierpinski gasket (SG) has been calculated. Using an exact renormalization scheme, the conductance jumps are obtained up to the ninth generation. It is found that the distribution of ΔG is multifractal. A comparison is also made between the SG spectrum and that of the percolation backbone of a random resistor network at the percolation threshold. Excellent agreement between the two spectra is found.
High-efficiency GaAs0.7P0.3 solar cell on a transparent GaP wafer
Authors: Fraas L. M. , Cape J. A. , McLeod P. S. , Partain L. D.
Published: July 2002

The fabrication of a high performance GaAs0.7P0.3 solar cell on a transparent GaP substrate with an AM1.5 efficiency of 15.4% for a concentration ratio of 30× is reported for the first time. The measured transparency of the GaP substrate allows these cells to be mechanically stacked on silicon solar cells in a manner that should yield combined conversion efficiencies well over 25%. This mechanically stacked two-band-gap cell design is particularly attractive because it utilizes the already well-developed Si solar cell and because the materials foundation for the GaAs0.7P0.3 on GaP cell has been laid by work on light emitting diodes.
Submillimeter wave absorption of n-type InSb at low temperatures
Authors: Brown Elliott R.
Published: July 2002

The absorption coefficient of two high-purity n-InSb samples is measured in the 10–40 cm−1 range using Fourier transform spectroscopy. The absorption coefficient spectrum is presented for both samples at 4.2 K. It is also shown for the lower resistance sample cooled to 2.2 K and heated by dc bias to elevated electron gas temperatures of 7.5 and 17.9 K. ac Drude theory gives rather poor agreement with experiment at 2.2 and 4.2 K but does much better when the sample electron gas is heated. In contrast, a simple quantum mechanical theory of absorption based on inverse Bremsstrahlung yields promising agreement at the lower temperatures although its applicability is questionable. The non-Drudian absorption is shown to have a favorable effect on the performance of InSb hot-electron bolometers.
Annealing behavior of hydrogen-implanted magnetic garnet
Authors: Wilts C. H. , Awano H. , Speriosu V. S.
Published: July 2002

Ferromagnetic resonance spectra and x-ray rocking curves were used to measure magnetic and strain profiles of Gd, Tm, Ga substituted yttrium iron garnet films implanted with H2+ at 120 keV and at doses in the range (3–80)×1015 ions/cm2. The maximum strain occurred at a depth of 3600 Å, reaching a value of 2.9% at 40×1015 ions/cm2. At the highest dose, the garnet was amorphous in that region which had highest strain at lower dose. The strain has two components, one due to damage and one due to the presence of the hydrogen atoms. The second component disappears for annealing temperatures above 400 °C, at which temperature the hydrogen has been reported to be largely desorbed. The reduction of the first component with annealing follows the same pattern as other implant elements. The magnetic anisotropy exhibits a large anomalous nonlinear increase with dose. The excess over other implantation elements disappears for annealing temperatures above 400 °C. There is no significant change in gyromagnetic ratio with dose or annealing temperatures up to 600 °C.
Preparation and characteristics of Nb/Al-oxide-Nb tunnel junctions
Authors: Huggins H. A. , Gurvitch M.
Published: July 2002

Preparation and characteristics of refractory Nb/Al-oxide-Nb Josephson tunnel junctions with critical current densities jc from ∼103 to ∼4×104 A/cm2 were studied with respect to junction quality, uniformity, reproducibility and jc control. The key steps leading to improved junction parameters are emphasized and compared with previously used procedures. The results include jmaxc/jminc of 1.2, on a 1-in. chip, Vm up to 56 mV in junctions with jc∼103 A/cm2, and Vm up to 24 mV with jc∼6×103 A/cm2. Good run-to-run reproducibility and control of jc are also demonstrated. In particular, jc is shown to increase by a factor of ∼40 when the oxygen pressure during the in-situ oxidation of the Al overlayer is reduced from 1 to 0.01 Torr.
A generalized time-dependent theory on craze initiation in viscoelastic media
Authors: Chern S. S. , Hsiao C. C.
Published: July 2002

The time-dependent craze failure process of polymers has been investigated. The process is characterized by several stages: deformation, development of microporosity, craze initiation, craze propagation, craze-crack transition, and propagation of crack to final fracture. Using Laurent’s series expansion and convolution integral form of material’s constitutive function, a time-, temperature-, and stress-dependent instability criterion for viscoelastic media has been considered. It is found that under a constant load, an incubation time for craze initiation can be obtained. This incubation time goes to zero for sufficiently high values of stress and approaches to infinity for low values of stress. The crazing stress depends linearly on temperature, and decreases as the test temperature increases toward the glass transition temperature. The interrelationship among the applied stress, craze initiation time, and temperature is then established and a fairly general time-dependent theory on craze or quasifracture initiation in viscoelastic media is formulated.
Transient capacitance study of electron traps in AlGaAs grown with As2
Authors: Mooney P. M. , Fischer R. , Morkoç H.
Published: July 2002

Using transient capacitance spectroscopy we have investigated the effect of growth by molecular-beam epitaxy (MBE) with dimeric As on the concentrations of deep traps in n-type AlGaAs with the Al mole fraction varying from x=0.04 to x=0.36. The substrate temperature dependence of E(0.77), which is the dominant trap in samples with x=0.25 grown at low substrate temperature, is similar for both As2 and As4 and is independent of Al mole fraction for the range investigated. For samples with Al mole fraction greater than 25% the dominant deep traps are the so-called D-X centers. The effect of using As2 is negligible compared to the effects of temperature and Al mole fraction which control the concentrations of the dominant deep traps.
Dark current transients in HgI2 single crystals used as γ- and x-ray spectrometers
Authors: Levi A. , Schieber M. M. , Burshtein Z.
Published: July 2002

Transient characteristics of dark currents have been measured in HgI2 single crystals as functions of voltage and temperature. The existence of a hole trapping center, 0.7 eV deep and of density ∼1015 cm−3, was established, which effectively lowers the hole drift mobility by about seven orders of magnitude. The samples were found to be slightly extrinsic n type, the Fermi level being 0.9 eV deep. The room-temperature electron density was about 2×103 cm−3. The meaning of these characteristics to the performances of HgI2 γ- and x-ray spectrometers is discussed. Particularly, it is suggested that lowering of the HgI2 detector operation temperature to about 0 °C will improve its energy resolution capabilities.
Defect-property correlations in garnet crystals: The electrical conductivity and defect structure of luminescent cerium-doped yttrium aluminum garnet
Authors: Rotman S. R. , Tandon R. P. , Tuller H. L.
Published: July 2002

The conduction mechanisms in cerium-doped yttrium aluminum garnet (Ce:YAG) have been studied as a function of temperature and PO2. ac conductivity and ionic transference measurements show that Ce:YAG is a mixed ionic-electronic conductor with an ionic conductivity characterized by an activation energy of 2.3 eV. A derived thermal band-gap energy of 6.1 eV compares favorably with the optically measured band gap. Conductivity and transference measurements support a defect model with a fixed number of doubly-ionized oxygen vacancies as the primary defect; the energy to produce such vacancies is calculated to be 7.8 eV.
New possibilities for niobium-based Josephson tunneling
Authors: Celaschi S. , Geballe T. H. , Hammond R. H.
Published: July 2002

Preparation of high quality Nb/ZrOx/Pb and Nb/TiOx/Pb Josephson tunnel junctions based on single-crystal niobium thin films is reported. Vm values up to 70 mV, as measured at 4.2 K, were obtained as a result of thermal oxidation of the freshly coated surfaces. The specific capacitance of these junctions varies from 0.010–0.022 pF/μm2, as determined from Fiske modes and the Josephson diffraction patterns. The use of added thermally oxidized metallic coatings on single-crystal Nb surfaces is shown to modify the tunneling parameters systematically and to offer new possibilities for fabricating all refractory metal Josephson devices.
Equivalence of the Lorentz and Ampere force laws in magnetostatics
Authors: Ternan J. G.
Published: July 2002

The Lorentz and Ampere laws are shown to be equivalent in magnetostatics. Both predict equal and opposite forces on complementary parts of a current distribution, and only a normal force on a current element. There is no force along the element. The illusory differences between the two are attributed to the incorrect integration of the differential forms of the laws, and to the inappropriate use of line current elements as sources, instead of surface or volume elements.
Annealing kinetics of the gold-iron complex in silicon
Authors: Brotherton S. D. , Bradley P. , Gill A.
Published: July 2002

Gold and iron are known to interact in silicon at temperatures below ∼400 °C to form gold-iron pairs with band-gap energy levels of Ev +0.434 eV and Ec −0.354 eV. In this work, the details of the formation and dissociation of these pairs were examined and from the equilibrium concentrations a binding energy of 1.22±0.02 eV was deduced. The activation energy of the gold-iron pair formation process was found to be 0.8 eV; when corrections were made to extract the activation energy for the iron diffusion coefficient from the data, a value of 0.42 eV was obtained. This is substantially smaller than the values of 0.7–0.9 eV obtained from iron precipitation and iron-boron pairing studies. It was noted during the higher-temperature dissociation process that there was concurrent precipitation of the iron which caused the dissociation to appear to be a two-stage process. This precipitation also resulted in substantial irreversibility of successive dissociation and pair formation anneals. Finally, it is pointed out that these low-temperature instabilities in the concentration of gold and the deep-level gold-iron complex are likely to result in device instabilities when gold and iron contamination occur.
Transient pulse buildup mechanisms in a synchronously-pumped mode-locked dye laser
Authors: Urisu Tsuneo , Mizushima Yoshihiko
Published: July 2002

Numerical calculations concerning transient pulse buildup processes are performed for a synchronously-pumped mode-locked dye laser system. Rate equations are used, including the amplified spontaneous emission (ASE) term. ASE is required to reach a stationary state. The calculated cavity length detuning characteristics are in good agreement with published observations. The observed large time-bandwidth product and spectral width of the pulse are explained by the shift of the gain spectrum peak with population change. Inhomogeneous broadening in the active medium causes the frequency shift in the pulse.
Photoconductive characterization of undoped, semi-insulating GaAs crystals
Authors: Mita Yoh
Published: July 2002

Extrinsic photoconductivity spatial and spectral distribution characteristics in undoped, semi-insulating GaAs crystal wafers have been investigated and the results are compared with those for optical absorption. The photoconductivity spatial distribution in a single wafer has been shown generally in reverse relation with that for optical absorption.
Linear dose dependence of ion beam mixing of metals on Si
Authors: Poker D. B. , Appleton B. R.
Published: July 2002

Helium backscattering spectroscopy was used to measure ion beam mixing of Au, V, Cr, and Pd on Si after 28Si implantation. The depths of mixing showed linear dose dependences, in contrast to the more commonly observed square-root dependence. Possible reasons for this discrepancy with earlier results are discussed.
Effective conductivity of irregular conducting channeling textures in two dimensions
Authors: Nakamura Mitsunobu
Published: July 2002

An irregular continuous conducting channel, linkage, or chain is formed in a sedimentary rock. The grain boundary of a polycrystalline and the blood vessel in a biological body shape such channels. In a previous paper we researched the effective conductivities of regular channeling textures by the finite element method (FEM) as a first approach to the problem of random channeling textures. In this paper we form irregular channeling patterns by computer simulation. The models are formed by randomly packing insulator squares into a metal sheet without any contact and overlap. We compute, by the FEM, the effective conductivities and compare them with previous results. It makes clear that the models are less conductive than a composite with a regular conducting channel. The conductivities agree well with the results from the granular effective medium approximation and from the extended Watson–Leath equation except when the metallic volume fraction is small.
I-V characteristics of polycrystalline silicon with n+p
n+ structure
Authors: Saito Yoji , Okada Taisuke , Okamura Kazuhisa , Kuwano Hiroshi
Published: July 2002

The I-V characteristics of polycrystalline silicon with n+pn+ structure are experimentally and theoretically investigated. As the applied voltage increases, a sublinear region appears following the ohmic region in the I-V characteristics. When the applied voltage V increases further, the current increases rapidly, and is finally proportional to V2. We propose a model to explain these characteristics. According to the model, the recombination-generation current flows through the films in a small applied voltage. At large applied voltages, electrons are injected from the n+p junction on the cathode side and holes are injected by tunneling from the n+p junction on the anode side; consequently double injection current flows. The calculated results are in reasonable agreement with experiment.
Annealing of intimate Au-GaAs Schottky barriers: Thick and ultrathin metal films
Authors: Newman N. , Petro W. G. , Kendelewicz T. , Pan S. H. , Eglash S. J. , Spicer W. E.
Published: July 2002

Using valence-band and core-level photoemission spectroscopy (PES) and electrical device measurements, the effects of annealing on Au:n-type (110) GaAs Schottky diodes fabricated in ultrahigh vacuum have been studied. Similiar trends in the annealing-induced changes in the barrier height of Au:n-type GaAs were found for 0.2 and 15 monolayer coverages as determined by PES and for thick film coverages (1000 Å) as determined by current-voltage (I-V) and capacitance-voltage (C-V) measurement techniques. In each case, the barrier height was found to be stable for temperatures between 30 and 200 °C and between 300 and 500 °C; while a gradual decrease in the barrier height was found for annealing temperatures of 200–300 °C. These changes are correlated with the formation of a Au-Ga rich layer at the interface during anneals at 200 to 300 °C. Leakage currents were found to dominate the I-V characteristics in the devices which were annealed above the Au-Ga eutectic temperature. These peripheral leakage currents were eliminated by mesa-etching the devices. This allowed more reliable barrier height determinations using device measurements for higher annealing temperatures than has been previously reported for the Au-GaAs system.
Site-selection spectroscopy and energy transfer studies of Eu3+ ions in glass hosts
Authors: Gang Xu , Powell Richard C.
Published: July 2002

Time-resolved site-selection spectroscopy techniques using a pulsed tunable dye laser were used to investigate the spectral structure and dynamics of Eu3+ ions in six oxide and one fluoride glass hosts. Network modifier ions were found to be important in determining the details of the spectral structure which can be related to the amount of local order in the glass. As the relative order increases, the fluorescence lifetime was found to decrease and the energy transfer rate increase. The transfer rate was found to vary linearly with the predicted ion-ion interaction rate for the oxide glasses. Differences in the temperature and excitation wavelength dependences of the energy transfer rates were found for the different samples.
Epitaxial growth induced by phosphorus tribromide doping of polycrystalline silicon films on silicon
Authors: Knoell R. V. , Murarka S. P.
Published: July 2002

The doping of polycrystalline silicon films is known to structurally change the material, producing larger grains after annealing. The grain growth is especially enhanced during high-temperature doping using a PBr3 or POCl3 dopant source. In this paper, we report our observation of the PBr3-doping induced epitaxial growth in polycrystalline silicon films deposited on silicon substrates and on the silicon in windows etched in the oxide. Epitaxial films contained twins induced by the microcrystals at the substrate-film interface. Models are proposed to explain possible mechanisms for grain growth of undoped and PBr3-doped polysilicon films. Also proposed are possible explanations for the observed microcrystalline growth at the epitaxy-substrate interface and in the epitaxial film itself.
Optical absorption measurements in a new composite material by combined photoacoustic and beam transmission techniques
Authors: Cesar C. L. , Lima C. A. S. , Leite N. F. , Vargas H. , Rubira A. F. , Galembeck F.
Published: July 2002

The absorption coefficient of a highly absorbing (β>105 cm−1) new composite produced in our laboratory, namely manganese dioxide surface-impregnated polyethylene (MnO2–PE) film, has been measured in the visible range. We have employed a combination of concurrently taken photoacoustic and beam transmission data. This combination proved to be an effective means for the optical evaluation of highly absorptive samples which dispenses with the need for prior knowledge of the sample reflectivity. Theoretical interpretation of MnO2–PE absorption profile, with due account of the processes underlining the photoacoustic signal generation, reveals a semiconductor behavior with an estimated effective gap wavelength of 8050 Å. Technical implications of the availability of these highly absorptive flexible films are briefly considered.
Magnetic properties in the system iron–cobalt–aluminum (abstract)
Authors: Jacobs I. S.
Published: July 2002

The ternary alloy family Fe–Co–Al is studied in the body-centered cubic (α) phase for the behavior of structure-insensitive magnetic parameters, out to compositions of 13 wt. % Al and 50 wt. % Co. Interest in this family on the potentially practical side derives from the properties of its separate iron binary systems. Iron–aluminum alloys have been investigated since before the turn of the century and there have been several efforts at commercialization as soft magnetic material. Iron–cobalt alloys have received special attention because of their high saturation magnetization (exceeding that the Fe), as well as for their very high Curie temperatures. However, the ternary system has received only sporadic attention, starting with the phase diagram and Curie point work of Köster one-half century ago and resumed largely for scientific interest in the electronic properties of transition metal alloys. Room-temperature magnetizations on a mass basis and on the more practical volume basis are presented. These expand upon earlier low temperature results. The presence of a broad maximum in magnetization in the Fe–Co binary does not persist beyond about 5 wt. % Al in the ternary family. Curie point results add to the data base and confirm those of Köster including an anomalous increase of Curie point with Al dilution for a certain range of composition. This feature is explained in terms of the bcc–fcc (α–γ) structure transition and the stabilization of the α-phase by Al additions.
Impact of some process variations on NiFe thin films
Authors: Reith T. M. , Davis R. E. , Leavitt J. A.
Published: July 2002

Rutherford backscattering spectrometry (RBS) and Auger electron spectroscopy (AES) are used to detect changes in stoichiometry and impurity incorporation in thin, rf diode sputtered NiFe films as a function of processing variations. Comparisons are made to thin, evaporated NiFe films with respect to oxygen reactivity. Because Ni and Fe are close in atomic weight, RBS, using 2-MeV He incident ions, cannot resolve them. However, by increasing the He incident energy to 4.7 MeV, the (26)Fe(56) and (28)Ni(58) isotopes are resolvable in films thinner than about 250 Å and the actual NiFe thin-film stoichiometry can be calculated. Complementary AES depth profiling measurements indicate Fe enrichment by approximately 5 wt. % as the deposition substrate bias is increased from 0 to −200 V. Magnetic characterization shows a corresponding increase in easy-axis coercivity of more than a factor of 10. Other magnetic parameters are also adversely affected.
Influence of the grain size distribution on the ferromagnetic hysteresis loop (abstract)
Authors: Escobar M. A. , Magaña L. F. , Valenzuela R.
Published: July 2002

We have considered the grain size distribution effects on the magnetic hysteresis loop of polycrystalline ferrites. We use equations given recently to describe the hysteresis loops of ferrite samples represented by a single grain size. We show the effect of several grain size distributions (Dirac, Gaussian, normal logarithmic, etc.) on the hysteresis loop. Finally, a grain size distribution function is simulated in order to fit experimental results obtained in YIG samples.
Domain control by spark ablation
Authors: Beckley P. , Snell D. , Lockhart C.
Published: July 2002

The power loss of grain oriented electrical steel can be usefully reduced by refinement of the ferromagnetic domain structure in cases where overlarge grains support widely spaced domains. Artificial grain boundaries can be produced by laying down lines of ablated spots on the steel surface to generate a stress and atomic disruption pattern which pins domain walls and leads to a smaller wall spacing. A high voltage electrical discharge from capacitors or otherwise can be used to give high enough energy rates and spatial densities to achieve suitably ablated spots on the metal surface. The method is readily adaptable to a production situation.
Study of Bloch wall dynamics and losses in monocrystalline, polycrystalline, and amorphous materials by means of optical techniques (invited)
Authors: Celasco M. , Masoero A. , Mazzetti P. , Stepanescu A.
Published: July 2002

The dynamics of the magnetization process of a ferromagnetic material is in general strongly influenced by interactions between Bloch walls, brought about by internal fields. The resulting stochastic character of the magnetization process has, together with many other effects, an important role in producing the so called excess magnetic loss, found in practically all the ferromagnetic materials undergoing a cyclic magnetization process. Recently an optical technique has been developed which makes use of the Kerr effect, on suitably prepared specimens, to study the Bloch wall dynamics in a wide frequency range (0–100 kHz). Through this technique, and by means of mathematical developments allowing one to evaluate local magnetic losses from the analysis of the optical signal, a rather large amount of information has been obtained on the magnetization dynamics and loss mechanisms in monocrystalline, polycrystalline, and amorphous materials. In particular, in the case of grain-oriented Fe–Si laminations, the correlation existing between Bloch wall interactions and deviations from the Pry and Bean theory of losses, even in well-oriented grains, showing a regular antiparallel domains structure, has been clearly evidenced. In the present paper, this technique, whose main advantage is connected with the possibility of visualizing the domain structure of the region under study, will be described and discussed, together with some of the main results obtained until now.
Intrinsic magnetic properties of R15B7Fe78 compounds
Authors: Yang Ying-Chang , Chen Hai-Ying , Liu Zun-Xiao , Liao Bing , Xing Feng , Ho Wen-Wang
Published: July 2002

Tetragonal R15B7Fe78 (R=MM, Pr, Nd, Sm, Gd, and Y) compounds have been studied by x-ray diffraction and magnetic measurements. The lattice parameters are found to decrease with increasing atomic number of rare-earth elements, whereas the Curie temperatures TC increase monotonically, and the TC of Gd15B7Fe78 is the highest. The saturation magnetization and magnetocrystalline anisotropy were measured with a field up to 70 kOe at the temperature between 1.5 and 300 K. We found that the c axis is the easy axis of magnetization for R=Pr, Gd, and Y; the easy magnetization direction lies in the basal plane for R=Sm; and the direction of easy magnetization changes with temperature for R=Nd.
Magnetic and crystallization studies in amorphous neodymium-cobalt alloys
Authors: Wong C. P. , Gudimetta K. , Dale B. , Hadjipanayis G. C.
Published: July 2002

The thermal and magnetic properties of amorphous alloys prepared by melt spinning and vapor deposition have been studied in the system Nd100−xCox where 25≤x≤75. It is found that the alloys around the equiatomic composition are the most stable thermally. ac susceptibility studies show that the ordering temperatures of the amorphous phase increase with cobalt content from about 30 K in Nd60Co40 to about 90 K in Nd50Co50. Upon crystallization of the samples four different phases appear with ordering temperatures 24, 105, 140, and 190 K. The phases with ordering temperatures of 24 and 105 K have been identified with Nd3Co and NdCo2, respectively.
Properties of high rate sputtered perpendicular recording media
Authors: Ouchi K. , Iwasaki S.
Published: July 2002

Double layered media for perpendicular magnetic recording were made by dc magnetron sputtering. The coercivity of the Co-Cr layer was independent of deposition rate over the range from 0.006 to 1.2 μm/min, when the substrate temperature was kept constant during sputtering. Micro columnar structure of the Co-Cr film was studied by chemical etching. Only the columns were dissolved leaving the column boundaries showing a microhoneycomb structure. From the composition analysis of the etchant, Cr segregated column boundaries were confirmed to exist even in the high rate sputtered films. The Permalloy back layer with coercivity below 1 Oe shows large noise pulses in the reproducing process. Increasing the coercivity to several Oersteds reduced the noise to the amplifier noise level without changing the signal level. Finally, a high recording performance was obtained for the media made by high rate sputtering.
Influence of deposition conditions on magnetic properties of CoCr thin films
Authors: Snyder J. E. , Kryder M. H.
Published: July 2002

CoCr thin films were sputtered with varying values of target bias, forward power, sputtering rate and argon pressure. Cr content, saturation moment, coercivity, squareness, perpendicular anisotropy Ku, and net anisotropy (Ku−2πM2s) were measured. It was found that perpendicular or in-plane squareness measurements with a VSM were not a useful indicator of perpendicular anisotropy (as determined by torque magnetometry). Net perpendicular anisotropy (Ku−2πM2s) was found to increase with deposition rate. Most films showed positive net perpendicular anisotropy, with no substrate heating necessary other than that provided by the sputtering process. Saturation moment was found to decrease with increasing target bias, a variation not explainable by differences in average Cr content. Perpendicular anisotropy and perpendicular coercivity decreased with increasing target bias also. These results suggest a common microstructural mechanism affecting all three properties. Alternate explanations involving oxidation, Cr distribution (short-range order, or segregation of Cr-rich phases), and argon incorporation could explain these results, but will require further experiments to establish.
Microstructure and exchange anisotropy of Co-CoO films with perpendicular magnetization
Authors: Ohkoshi M. , Tamari K. , Honda S. , Kusuda T.
Published: July 2002

Microstructure and temperature dependence of magnetic properties of Co-CoO films are studied. Columnar microstructure with chains of Co fine particles surrounded by CoO fine particles develops perpendicular to the film plane. Perpendicular anisotropy energy Ku takes a maximum value when the columnar diameter is minimum whose typical value is 1/20 of the film thickness. Change of magnetic domain structure with increasing Ku is studied. The perpendicular magnetization is restricted to the heterogeneous columnar microstructure. The perpendicular coercivity Hc decreases steeply with increasing temperature, that is associated probably with antiferromagnetic nature of CoO. Hc at room temperature increases after an annealing at 400–500 K.
Variation of the temperature coefficient of collapse field in bismuth-based bubble garnets
Authors: Fratello V. J. , Pierce R. D. , Brandle C. D.
Published: July 2002

To achieve wide temperature operation of magnetic bubble devices, the bias magnet field must remain within the material bias margins over the entire temperature range. It is therefore best that the slope of the bubble collapse field be matched to that of the bias magnet field. However, the slope of the collapse field of unmodified Bi:YIG is 50% greater than the slope of the field of the commonly used barium ferrite magnet. We used an approximation to the collapse field formula to show its dependence on magnetization and wall energy and the effect of substitution of various classes of rare earths. In particular, we have tested the effect of additions of Gd, Sm, and Eu on 1-μm Bi:YIG bubble materials. Collapse field, magnetization, and wall energy were fitted to quadratic functions of temperature from −50 to 150 °C. Gd, the traditional slope-reducing additive, affects the collapse field through the magnetization but also introduces substantial nonlinearity, which can lead to large deviations of the collapse field from the bias field at extreme temperatures. Sm introduces a strongly temperature-dependent rare-earth component of anisotropy that reduces the slope of the collapse field through the wall energy. Eu incorporates both these effects and, owing to its singular magnetic properties, results in the most nearly linear temperature dependence of the collapse field and the best approximation to the bias magnet.
Channeling effects on bubble propagation for 8-μm-period ion-implanted propagation patterns
Authors: Wen Weiguang , Guan Guixian , Chao Xiangdong , Wei Juan , Gao Guowei , Wu Zhenyuan , Lee Zo-Yi
Published: July 2002

In our work, channeling effects on bubble propagation for 8-μm-period ion-implanted propagation patterns (I2P2) using the (YBiCa)3 (FeGeSi)5O12 bubble material have been found and studied. The best propagation patterns have been designed in the form of a snake in the experiments. Several kinds of ion sources have been used, such as N-N, N-Ne, Ne-Ne. The effects of injection angles and doses on propagation characteristics will be discussed in this paper. Owing to use of the channeling effects, even if energy does not exceed 200 keV, bubble quasi-static propagation has been realized successfully in N-N, N-Ne, Ne-Ne ion implantation experiments. N-N ion implantation produces better effects for quasi-static propagation with wider margins (30 Oe) of minor loops than the others.
Observation of vertical Bloch line propagation
Authors: Lian M. R. , Humphrey F. B.
Published: July 2002

The presence of vertical Bloch lines in the wall of a stripe domain of a magnetic ‘‘bubble’’ material can be inferred by observing the transient distortion of the straight wall driven by a uniform field. Because the local mobility depends upon local structure in the wall, rapid motion of the straight wall results in transient bulges of the wall. These hard wall bulge sections were seen by applying a large uniform bias field pulse and then observing the transient shape of the initially straight wall using a high speed optical sampling microscope with 10 ns pulse laser illumination. Bulge phenomenon, such as generation, annihilation, and propagation along the stripes were observed in an as-grown sample, Sm0.4Y2.6Ga1.15Fe3.85O12 with a thickness of 6.26 μm, 4πMs=125 Oe, γ=1.54*107 Oe−1, Hk=2190 Oe, α=0.208, and Q has a value of 17. Several different types of bulges have been seen. They can be different in size and can appear either on one side or both sides along the stripe domains. Shorter bulges usually move more slowly and inconsistently. They can be collected in the stripe bend and become longer bulges. Two bulges traveling in the opposite directions along the same stripe will combine into a shorter one or disappear.
Bloch lines generation in moving stripe heads
Authors: Wu J. C. , Humphrey F. B.
Published: July 2002

The generation of vertical Bloch lines (VBL’s) at the head of a moving stripe domain with and without an in-plane field was studied. For an as-grown sample, the velocity saturation is independent of in-plane field direction and the same velocity as an implanted sample when the in-plane field direction is the same as the stray field in the implanted layer. When the in-plane field direction was reversed, the wall saturation velocity is higher. Overshoot starts when the wall velocity approaches the saturation velocity and increases with drive field as the stripe head becomes asymmetrically distorted. Eventually, the stripe will move at an angle. The presence and motion of VBL’s was inferred from the shape of the stripe head during and at the end of the applied pulse field, the bending of the stripe, and the presence of overshoot. In the ion-implanted film, after the generation of a pair of VBL’s on the stripe head, the positive (negative) VBL was pushed into the straight part of the stripe when the in-plane field direction is opposite (parallel) to the stray field direction in the implanted layer at the stripe head. In the as-grown film, which kind of VBL is pushed away seems random and independent of the in-plane field direction and amplitude.
Design consideration for a 2-μm-period ion-implanted propagation track (abstract)
Authors: Satoh Y. , Miyashita T. , Ohashi M. , Betsui K. , Komenou K.
Published: July 2002

We report on the design of ion-implanted propagation tracks with a 2-μm period. Reducing cell size causes increased drive field and margin degradation due to adjacent loop interaction. We investigated the effect of ion-implanted layer properties on these problems. Using conventional photolithography, we fabricated propagation tracks on YSmLuCaGeFeO films with 0.5–0.7 μm bubble diameters by triple implantation of hydrogen and neon ions. After implantation, we exposed the wafers to argon plasma to increase the implantation-induced anisotropy field change (ΔHk), then coated them with rf-sputtered SiO2 film. We next annealed the coated wafers at temperatures ranging from 350 °C to 450 °C. To investigate the effect of the implanted layer thickness and its ratio to LPE film thickness, we proportionally varied the energies of triple implantation at a constant dose. The interaction between adjacent loops and the minimum drive field decreased as the implanted layer thickness decreased. Furthermore, we found that we could reduce the difference in bias field margin between the ion-implanted track and the Permalloy track by decreasing the implanted layer thickness without margin loss. This makes possible to realize high density hybrid devices. A minimum drive field of 38 Oe and bias margin of 68 Oe at a quasi-static drive field of 50 Oe have been obtained. Although the required drive field was larger than that of 4-μm-period tracks, we believe it can be reduced by optimizing LPE film properties and implantation conditions. Inside and outside turns, necessary in folded minor loops, have been successfully designed. Details of designs, including pattern shapes, will be discussed.
High-quality single-crystal Nb and Ta films formed by an ultrahigh vacuum arc method
Authors: Igarashi Yuichiro , Kanayama Michio
Published: July 2002

High-quality epitaxial Nb thin films (thickness, 2000 Å), characterized by flat and clean surfaces, high superconducting critical temperature (max.Tc, 9.44 K), large resistivity ratio (RR, resistivity at room temperature divided by resistivity at 10 K, max.RR, 44), and very small quantities of grains of different orientation, have been formed on sapphire-A and sapphire-C substrates at a relatively low substrate temperature (350–530 °C) using an ultrahigh vacuum arc method (4×10−7– 4×10−6 Pa). Structures and orientations of the films deposited on MgO(100), sapphire-A, and sapphire-C substrates are investigated by means of several techniques and they depend on symmetry properties of the substrates. 200-Å-thick Nb films deposited on the MgO and the sapphire-C substrates showed good crystallinity and planarity. High-quality single-crystal films of Ta (thickness, 90 Å) were formed on single-crystal Nb films (7000 Å) obtained with the sapphire-A plane.