bluuebunny/crossref_metadata_2025 huggingface dataset:
Determination of minority-carrier diffusion length by integral properties of electron-beam-induced current profiles
Authors: Cavalcoli D. , Cavallini A. , Castaldini A.
Published: July 2002

The diffusion length of minority carriers in n-type floating-zone Si samples is obtained with the electron-beam-induced current technique in planar configuration. The charge collection current data as a function of the beam-junction distance are analyzed on the basis of the ‘‘moment method’’ developed by Donolato [C. Donolato, Solid-State Electron. 28, 1143 (1985)], which is based on the calculation of the variance of the derivative of the current profile. With respect to other methods reported in literature, this has the advantage that it requires no assumptions on the surface recombination velocity and thus provides a diffusion length value free from its influence. The data are also analyzed with the asymptotic method, which requires conventional assumptions on the surface recombination velocity. The comparison between the results has allowed us to test the capabilities of the above-mentioned method. Particular attention is paid to the injection level and its influence on bulk and surface properties.
Positive-charge trapping in nitrided oxide and reoxidized nitrided oxide gate dielectrics
Authors: Krisch K. S. , Gross B. J. , Sodini C. G.
Published: July 2002

The charge-trapping characteristics of nitrided oxide and reoxidized nitrided oxide (ROXNOX) gate dielectrics following constant-current stressing are studied, with an emphasis on the behavior of positive trapped charge. The positive charge is attributed to slow donor states, which are created and ionized during electrical stress. Slow donor states are shown to be responsible for a reversible, bias- and temperature-dependent charge relaxation that is observed following electrical stress. The number of slow donor states created during stress is found to be a function of the nitridation and reoxidation conditions. Using optimized process conditions, ROXNOX dielectrics can be grown with essentially no slow donor states and, hence, with little relaxation.
Reduction of flux creep in spite of a j
c decrease in YBa2Cu3O7−δ after neutron irradiation
Authors: Schindler W.
Published: July 2002

YBa2Cu3O7−δ single crystals with Tc=90.5 K and different transition width have been irradiated with fast neutrons (E≳0.1 MeV) and a fluence of Φ⋅t=2×1017 cm−2. The flux-creep dM/dlnt at B=0.5 T is reduced at any temperature up to T=60 K by a factor of about 2. Correspondingly, the effective pinning potential Ueff is enhanced up to 100kBT at low temperatures and 50kBT at T=77 K, independent of an increase or decrease of the magnetization current density after irradiation. Therefore, the enhancement of Ueff may not in every case be related to a jc increase, which is also determined by the number of pinning centers or a certain defect structure, which may not necessarily show deep pinning potentials. The results can be explained within the conventional flux creep theory and are in a good agreement with recent considerations of the role of electronic anisotropy in the dissipative behavior of YBa2Cu3O7−δ.
Theory of the effect of magnetic field on the excitonic photoluminescence linewidth in semiconductor alloys
Authors: Mena R. A. , Sanders G. D. , Bajaj K. K. , Dudley S. C.
Published: July 2002

We report a calculation on the effect of the magnetic field on the excitonic photoluminescence linewidth in intentionally undoped semiconductor alloys. We assume that the dominant mechanism for line broadening is due to the potential fluctuations caused by the disorder of the components of the alloy. Variations in the local concentrations from the global value are accounted for by using statistical mechanical arguments developed by Lifshitz [Adv. Physics 13, 483 (1965)] and then related to the linewidth. When a magnetic field is applied to the system, the effective volume of the optical probe, namely, the exciton, is reduced, causing it to become more responsive to the statistical potential fluctuations. This results in the broadening of the photoluminescence line as a function of the magnetic field. Variation of the excitonic linewidth as a function of the magnetic field and alloy composition in AlxGa1−x As is presented.
Bismuth- and aluminum-substituted YIG single-crystal films on modified gadolinium gallium garnet single-crystal substrates
Authors: Matsumoto Koji , Sasaki Satoshi , Yamanobe Yasunori , Yamaguchi Kazuhiro , Fujii Toshitaka , Asahara Yousuke
Published: July 2002

Bismuth- and aluminum-substituted yttrium iron garnet single-crystal films with the nominal composition of Y1.5Bi1.5Fe4.2Al0.8O12 (Bi,Al:YIG) were prepared by spin coating a gel on the (111) plane of (GdCa)3(GaMgZn)5O12 single-crystal garnet plates. Crystallinity of the films varies with temperature and time of heat treatment in air after gel coating. Single-crystal films were obtained at Ta=650 °C for 4 h. The onset temperature for crystal growth is about 560 °C, which is about 400 °C lower than that of liquid-phase epitaxy. The crystal-growth process of single-crystal Bi,Al:YIG films was examined by measuring crystallographic structures as well as the magneto-optical Faraday effect. The internal stress giving rise to magnetic uniaxial anisotropy to align the magnetization normal to the film plane plays an important role for completion of single-crystal growth throughout the film.
Theory of guided-wave frequency tripling in the form of coherent Čerenkov radiation: Application to ultraviolet light generation
Authors: Hayata K. , Matsumura H. , Koshiba M.
Published: July 2002

A useful wave-optics solution is derived for the Čerenkov mode calculation of optical third-harmonic signals that are generated in a multilayer planar optical waveguide. With this modal solution, the ultimate performance of the planar-configuration frequency tripler, being phase matched in the form of coherent Čerenkov radiation, is predictable. Numerical results are shown for the third-harmonic ultraviolet light generation in a planar glass waveguide loaded by a polydiacetylene Langmuir–Blodgett deposited thin film. Furthermore, the possibility of pronounced activation of the third-harmonic radiation from a glass waveguide pumped by an intense laser beam is suggested through field calculations based on a laser-induced damage model. In addition, loss analysis that includes both one- and two-photon absorptions is made by means of a phenomenological propagation model using coupled rate equations.
Deep levels in Si- and Be-coimplanted GaAs
Authors: Cho Hoon Young , Kim Eun Kyu , Min Suk-Ki
Published: July 2002

Deep levels and electrical properties in Si- and Be-coimplanted semi-insulating GaAs, grown by liquid-encapsulated Czochralski methods, were investigated. The Si implantation with a dose of 8×1012 ions cm−2 and energy of 65 keV was performed into GaAs already implanted with a Be dose of 2×1012 cm−2 and 90 keV for the purpose of an abrupt implant profile in a deeper region. During the Be coimplantation, an electron deep level at 0.62 eV below the conduction band and a hole deep level at 0.68 eV above the valence band were newly observed. In the Be-implanted region of ion-implanted GaAs, the deep levels Ec − 0.62 eV and Ev + 0.68 eV dominate, but are not found in the bulk. From this work, it is suggested that the Ec − 0.62 eV trap could be the defect due to the implantation damage and that the Ev + 0.68 eV trap could be the Be complex related to a Si dose during the implantation.
Magneto-optic measurements of the effects of crystalline anisotropy in ion-implanted layers of garnets
Authors: Fernandez-de-Castro J. J. , Kryder M. H.
Published: July 2002

A magneto-optic photometer system was designed, constructed, and used to characterizein-plane magnetization in ion-implanted magnetic bubble memory devices. The system utilized the Faraday magneto-optic effect. A model of the in-plane driving layer was developed and used to explain the experimental results. Data were taken on the magnitude, orientation, and symmetry of the magneto-crystalline anisotropy for threefold symmetric (111) films. The experimental results were correlated with a theoretical model from which computer solutions were obtained. The crystalline anisotropy constant (‖K1‖) of 3150 ergs/cm3 was determined for the (111) oriented film. Hysteresis loops with very low coercive force (Hc<5 Oe) were measured, indicating that magnetic domain wall motion was responsible for the magnetization process when the in-plane field was applied inside the critical curve.
Coalescence of buried CoSi2 layers formed by mesotaxy in Si(111)
Authors: Hsieh Yong-Fen , Hull Robert , White Alice E. , Short Kenneth T.
Published: July 2002

Evolution and microstructure of buried CoSi2 layers formed by 100-keV Co+ implantation at 350 °C into Si(111) are systematically studied in this work. Implant doses ranged from 1 × 1016 to 1.6 × 1017 cm−2. Three types of CoSi2 precipitates are observed during the mesotaxial process: A type (fully aligned with the host lattice), B0 type (twinned on the (111) plane parallel to the surface), and B1,2,3 type (twinned on one of the three {111} planes inclined to the surface). The fraction (probability of occurrence) of each type varies with both the implantation and annealing conditions. The critical dose required to form a continuous layer after 600+1000 °C annealing is found to be the same, ≊ 1.1 × 1017 cm−2, in both (111) and (001) substrates, despite pronounced differences in precipitate morphology. Formation of a continuous, twinned (B0 type), buried layer after 600+1000 °C annealing is shown to be possible in (111) samples implanted at the critical dose.
Photo-Hall studies of high-purity GaAs
Authors: Kim M. H. , Plano M. A. , Haase M. A. , Stillman G. E. , Wang W. I.
Published: July 2002

High-purity GaAs layers which are nearly or fully depleted of carriers at low temperatures, due to surface and interface depletion effects, can be characterized electrically by utilizing the phenomenon of persistent photoconductivity. To facilitate electrical measurements of such layers, at 4.2 K the sample is momentarily illuminated by above band-gap light, which causes a reduction in the surface and interface depletion region. After illumination the effects of the photoinduced charge neutral region persist until at some higher temperature, the charge distribution in the sample relaxes back to its original equilibrium state. Results of variable temperature Hall-effect measurements performed under these conditions show that the sheet carrier concentration is increased as compared to measurements obtained in the dark but that the mobility is unchanged. The increase in the sheet carrier concentration after illumination results from the decrease of the surface and interface depletion widths. Such measurements can provide a method for judging the quality of layers that are fully depleted of carriers. The mobility of a high-purity GaAs layer which becomes fully depleted of carriers at low temperatures in the dark, measures 180 000 cm2/V s at 77 K by this method. Photocapacitance-voltage profiling measurements clearly show the change in the depletion widths. A model is presented which accurately depicts the temperature dependence of the band-bending potentials at the surface and interface after illumination with above band-gap light.
Anomalous deuterium trapping in evaporated iron films studied by positron annihilation
Authors: Wistrom R. E. , Bo/rgesen P. , Sass S. L. , Nielsen B. , Leung T. C. , Lynn K. G.
Published: July 2002

Forward recoil energy spectroscopy showed that thin, evaporated Fe films trap anomalously large quantities of deuterium. Positron annihilation was used to investigate how the film microstructure influenced this trapping. Polycrystalline films trapped more deuterium and contained more open volume defects than single-crystal films. Annealing reduced both trap and open volume defect concentrations. These results strongly suggest that coalescence voids produced during the thin-film deposition were the sites for the trapping of deuterium.
In situ laser deposition of superconducting YBa2Cu3O7−x thin films on GaAs substrates
Authors: Lee S. Y. , Jia Q. X. , Anderson W. A. , Shaw D. T.
Published: July 2002

Highly c-axis oriented superconducting YBa2Cu3O7−x (YBCO) thin films with a zero-resistance temperature of 85.5 K and a critical current density of 1.9×103 A/cm2 at 77 K and zero field, respectively, have been deposited on GaAs substrates by in situ laser ablation. A barrier layer using a combination of yttrium-stabilized ZrO2 (YSZ) and Si3N4 proved to be a most successful buffer on GaAs when YBCO was deposited at relatively high temperature, around 650 °C. The electrical properties of the YBCO films were very dependent on YSZ deposition conditions. The electrical and structural relationship between YBCO films and the YSZ deposition conditions is further investigated by cross-section scanning electron microscopy and Auger electron spectroscopy depth profiling.
Analysis of Rayleigh light scattering of semidilute polymer solutions and gels
Authors: Hino Toshiaki , Soane David S.
Published: July 2002

This paper deals with two major problems often encountered in analyzing the measured autocorrelation functions in photon correlation spectroscopy of semidilute polymer solutions and gels: partial heterodyning and the interpretation of slow relaxation modes. These topics are discussed in the context of measurements of semidilute aqueous polyacrylamide solutions and gels used as electrophoresis media. Following a review of basic principles of Rayleigh light scattering and photon correlation spectroscopy, data analysis procedures, including the constrained Laplace inversion program contin, are first re-examined by presenting the results from aqueous latex standard solutions. The method to analyze the partial heterodyne autocorrelation function is then presented and tested against the simulated partial heterodyne autocorrelation functions. Finally, the recently observed slow relaxation modes in polyacrylamide solutions are examined in detail with a test of contin against the simulated autocorrelation functions consisting of a trimodal distribution of relaxation rates. The results confirm that the slow relaxation modes detected in polyacrylamide solutions are indeed physical modes originating from structural relaxation and interdiffusion.
Properties of YBa2Cu3O7−δ films upon low fluence laser irradiation
Authors: Dye R. C. , Foltyn S. R. , Wu X. D. , Peterson E. J. , Muenchausen R. E. , Nogar N. S.
Published: July 2002

The electrical responses and crystallinity of YBa2Cu3O7−δ films were measured as a function of excimer laser exposure (308 nm) and laser fluences ranging from 20 to 150 mJ/cm2. Tc and Jc were measured with an inductive technique and with standard dc transport measurements. The crystallinity of the films, as determined by Rutherford backscattering spectrometry, scanning electron microscopy, and x-ray diffraction, was altered by the formation of a degraded surface layer, even at fluences well below the melting threshold. The critical current of a film can be modified with a high degree of accuracy and can be correlated with a boundary layer in the film. This allows for the critical current to be decreased over three orders of magnitude with a resolution of 255 A/cm2 per laser shot.
High-pressure phases of boron nitride grown by laser-assisted plasma chemical vapor deposition from BCl3+NH3+H2+Ar
Authors: Komatsu Shojiro , Moriyoshi Yusuke , Kasamatsu Mitsuo , Yamada Kawakatsu
Published: July 2002

By using a newly designed collimated plasma beam reactor, plasma-enhanced chemical vapor deposition from BCl3+NH3+H2+Ar with the surface irradiated by a 193-nm excimer laser at a pressure of 2.8 Torr and substrate temperatures of 500–900 °C yielded BN films with the following texture as revealed by transmission electron diffractometry (TED), transmission electron microscopy, scanning electron microscopy, and Fourier-transformed infrared spectroscopy: (1) a thin-film part which consists of 10-nm-sized crystallites with a sp2-bonded structure grown on the substrate, namely, a sp2 100 Å layer; (2) polycrystalline parts with cBN or wBN structure, depending on the condition, embedded in a sp2 100 Å layer; (3) crystallites, though found infrequently, grown to be much larger than the sp2 100 Å layer thickness. The TED pattern of the polycrystalline wBN was particularly in agreement with the standard data.
A study of the magneto-optical Kerr effect in layered films
Authors: Xu Yongbing , Zhai Hongru , Lu Mu
Published: July 2002

Different concepts toward enhancement of magneto-optical Kerr effect in layered films are discussed and compared. A method of designing the layered films is proposed.
X-ray irradiation effects on superconductivity of cuprate superconductor thin films
Authors: Kohiki Shigemi , Hatta Shin-ichiro , Setsune Kentaro , Wasa Kiyotaka , Sakai Masahiro , Fukushima Sei , Gohshi Yoichi
Published: July 2002

The critical current density and flux activation energy of the cuprate superconductor thin films degraded with the increase of x-ray irradiation time. The enlargement of critical current density with the creation of strong pinning sites resulted from the oxygen annealing of the x-ray irradiated films. The electronic state calculation revealed that the oxygen defects could interact with visual light and form color centers in the x-ray irradiated film. The x-ray irradiation process followed by annealing in oxygen provides effective method to control the characteristics of the superconductor thin films.
Electromagnetic radiation from abrupt current changes in electrical discharges
Authors: Kadish A. , Maier William B.
Published: July 2002

We treat electromagnetic radiation from narrow electrical discharges, with particular emphasis on the asymptotic behavior at high frequencies f. We show that discontinuities in the discharge current and its derivatives dominate the high-frequency part of the radiated spectrum. Specifically, when a current discontinuity is present, the envelope of the radiated fields falls off with large f as f −1 for almost all observation angles. If the current is continuous but has discontinuities in its first derivatives, then the envelope of the radiated field falls off as f −(1+1/n) at large f for a range of observation angles. If the discharge current and its first derivatives are continuous, then the radiated fields fall off at least as fast as f −2 at large f. The characteristic high-frequency dependence associated with abrupt current change persists for some large range of f, even when current variation is not precisely abrupt. We illustrate the general results with radiation from AWA discharge models (previously referred to as arc welder’s ansatz models) featuring a constant electric field associated with dissipative discharge processes.
Magnetic laser discharge stabilization scaling to high-pressure systems
Authors: Capjack C. E. , Labun A. H. , Seguin H. J. J. , Bilida W. D.
Published: July 2002

The application of the magnetic discharge stabilization technique to high-pressure laser discharges is investigated. Scaling laws are developed with the help of Monte Carlo simulations for the transverse discharge velocity and for the magnetic field strength that is necessary for discharge stability. The results that are obtained indicate that the required magnetic field strength scales as the pressure squared. Unless a cost-effective means is found for implementing a very strong magnetic field into an electrode design, the magnetic discharge stabilization technique will be mainly relegated to low-pressure systems.
Partially ionized beam deposition of 2-methyl-4-nitroaniline thin films
Authors: Nason T. C. , McDonald J. F. , Lu T.-M.
Published: July 2002

Polycrystalline thin films (1–10 μm) of the nonlinear material 2-methyl-4-nitroaniline were deposited on Ag, Cu, and Si by conventional and partially ionized beam deposition. The use of ions was seen to promote a highly oriented film, with only the single x-ray diffraction orientation (112) being observed at reduced temperatures (−50 °C). The effect of the ions on the physical microstructure of the films was to densify the film and reduce the size of the microcrystals. The films had powderlike optical properties and displayed a strong second harmonic from a Nd:YAG laser.
Tight-binding model for ferromagnetic domain walls in 3d transition metals
Authors: Pinto Marc A. , Valet Thierry R.
Published: July 2002

In this work a quantum-theoretical calculation of ferromagnetic domain walls in 3d transition metals is presented. The model is based on a tight-binding description of the system and the 3d electronic structure is obtained self-consistently by use of the real-space recursion method. A salient feature of this model is that both the orientation and the magnitude of the atomic magnetic moments are free to vary. This is in sharp contrast with classical studies which are based on the a priori assumption that the magnitude of the moment is constant. Preliminary numerical results for a ferromagnetic chain are given.
Electronic structure calculations for Gd32Co68 and Gd18Co82 amorphous alloys
Authors: Tanaka Hiroshi , Takayama Shinji
Published: July 2002

The spin-polarized electronic structures of Gd18Co82 and Gd32Co68 amorphous alloys are calculated self-consistently in order to study their magnetic properties. The calculated electronic-state densities of the Gd and Co d states do not have well-resolved peaks; this is a characteristic of amorphous alloys. The magnetic moments of Co and Gd are 1.51 and 7.16 μB in Gd18Co82, and 1.38 and 7.14 μB in Gd32Co68, respectively. These values show good agreement with experimental data. The exchange splitting of Co d states in Gd32Co68 is smaller than in Gd18Co82, while the density of states at the Fermi level in the former is higher than that in the latter.
Water milling and gas passivation method for production of corrosion resistant Nd-Fe-B-N/C powder and magnets
Authors: Bogatin Y. , Robinson M. , Ormerod J.
Published: July 2002

Nd-Fe-B powder produced by conventional methods is pyrophoric, and exhibits poor corrosion resistance. Magnets made from powder are also susceptible to corrosion. Conventional methods of production are complicated, potentially hazardous, and relatively expensive. A novel, low cost, less hazardous method of producing powder and magnets with high corrosion resistance and Curie point is discussed. Nd-Fe-B alloys are milled in water, vacuum dried, and passivated at a suitable temperature in a nitrogen or carbon dioxide medium. During passivation, a protective layer, comprised of nitride and/or carbide phases, is formed in the surface region of the powder particles. This powder is not pyrophoric, and may be stored in a laboratory air environment for an extended period of time with no loss in magnetic properties. Compacted and sintered magnets produced from this powder are also highly corrosion resistant, and exhibit a higher Curie point compared to conventionally produced magnets. A description of the novel technology, and a discussion of the properties of Nd-Fe-B-C/N powder and magnets is given.
Variable magnetic circuit torque sensor
Authors: Lemarquand G. , Lemarquand V.
Published: July 2002

This paper presents an original torque sensor structure using the properties of magnetic circuits, including permanent magnets. The torque is measured through the torsion of the transmitting shaft. The torsion is proportional to the torque. Considering two points of the shaft on the same line in absence of torque, the information is given by the twisting angle in the presence of a torque. A rotating magnetic circuit yields an angle representative signal. This circuit is deformed by the shaft torsion. The reluctance varies and so does the magnet operating point. The induction is measured in an airgap by a statoric galvanomagnetic device. The magnetic field source is an axial permanent magnet ring. Two iron-toothed rings, fixed to the driving and driven part of the shaft, respectively, and separated by an airgap make up the variable part of the magnetic circuit. The teeth get out of line whenever a torque is applied. The galvanomagnetic device measures an uniform induction and so delivers a modulation free signal, i.e., rotation independent. Because of the periodic toothed structure, the induction varies periodically with the twisting angle. The sense of the variation is the same over half a period or half a pitch. The variation form depends on the teeth design. Operating interval is to be chosen equal to or smaller than the half pitch.
Critical current density and flux pinning dominated by neutron irradiation induced defects in YBa2Cu3O7−x
Authors: Lessure H. S. , Simizu S. , Sankar S. G. , McHenry M. E. , Cost J. R. , Maley M. P.
Published: July 2002

The functional dependence of critical current density (Jc) upon defect density is studied with neutron irradiation of YBa2Cu3O7−x. Identical polycrystalline samples of YBa2Cu3O7−x have been irradiated with fast neutrons (E≳0.1 MeV) in eight steps between 0 and 2.1 × 1018 n/cm2. Critical current densities are obtained from magnetic hysteresis measurements and correlated with defect density measurements obtained from transmission electron microscopy. We observe that despite the existence of a significant degree of hysteresis in the as grown material the hysteretic Jc in the irradiated samples appears to be dominated by a power law dependence on neutron fluence with an exponent of approximately 1/3 over a wide range of temperature, field and fluence.
Magnetoelastic properties of stress-annealed Fe-based metallic glasses
Authors: Freestone J. , Gibbs M. R. J. , Squire P. T.
Published: July 2002

We present data on METGLAS 2605S2 annealed with a combination of dc current and load. The material develops an easy direction at ≳45° to the sample axis, and shows significant magnetostrictive and magnetoelastic response. These results are in contrast to data on material annealed with current or load alone.
Nb-added high-coercivity Nd-Fe-B melt-spun ribbon with high remanence
Authors: Kim Y. B. , Lee K. W. , Kim C. S. , Shin H. C. , Kim T. K. , Okada M. , Homma M.
Published: July 2002

The effects of composition and additives on the microstructures and magnetic properties of Nd-Fe-B melt-spun ribbons were studied. Experimental results have revealed that homogeneous grain structure with fine grain size was obtained on composition close to 2-14-1 stoichiometry with additives. It was also found that Nb was very effective in increasing both remanence and coercivity in a Nd-Fe-B melt-spun ribbon. A high-energy product of 151.2 kJ/m3 (19.0 MGOe) was obtained from an isotropic (Nd0.5Pr0.5)12Fe72Co8B6Nb2 melt-spun ribbon with a remanence of 0.926 T and a coercivity exceeding 1200 kA/m (∼15 kOe).
Ferromagnetic resonance investigations of spin waves in Fe-Ni multilayers
Authors: Kordecki R. , Meckenstock R. , Pelzl J. , Mühlbauer H. , Dumpich G. , Nikitov S.
Published: July 2002

The standing spin-wave resonance (SSWR) at 9.2 GHz has been investigated in a multilayer structure composed of alternating layers of Ni and Fe for the as-prepared sample and at different annealing temperatures between 420 and 570 K. Changes of the resonance field and of the intensity of spin-wave modes with annealing temperature indicate the excitation of a surface mode in the as-prepared sample. Heating of the multilayer above 520 K leads to a spin-wave spectrum which exhibits a behavior corresponding to an alloy with comparable chemical composition. The SSWR fields show a quadratic dependence of the wave number of the spin waves at all annealing temperatures but a drastic change of surface spin pinning with increasing temperature.
Control of exchange coupling for direct overwrite media using Pd metal interlayer
Authors: Hatwar T. K. , Stinson D. G.
Published: July 2002

Several kinds of direct overwrite schemes have been proposed for magneto-optic media. Schemes using weakly coupled multilayers have shown great promise. In these methods, control of exchange coupling is key to realizing overwrite. An intermediate layer between the memory and reference layers is used sometimes to control the degree of exchange coupling and interface wall energy density. For this purpose, GdFeCo layer having in-plane anisotropy has been used previously. However, it is easily oxidized. Also, these multilayer direct overwrite media are comprised of similar materials but with different concentrations of components. The components from one layer may diffuse into the adjacent layer, rendering direct overwrite impossible. We found that easily polarizable metals such as Pd can be used as an interlayer to control the degree of exchange interaction between memory and reference layers. Pd metal has no magnetic moment by itself, but a moment is induced on it when it is in proximity to a magnetic material. This induced magnetic moment can mediate the exchange interaction between the reference and memory layers. Since Pd is noble, a very thin layer of Pd (10–20 Å) is stable and prevents diffusion between the magnetic layers.
Magnetic properties of permalloy-coated organic tubules
Authors: Krebs J. J. , Rubinstein M. , Lubitz P. , Harford M. Z. , Baral S. , Shashidhar R. , Ho Y. S. , Chow G. M. , Qadri S.
Published: July 2002

We present an initial investigation of the ferromagnetic properties of a novel type of magnetic composite, viz., permalloy-coated submicron diameter hollow cylinders or tubules. The tubules form spontaneously from an organic material, a diacetylenic phosopholipid, and were used as templates on which the ferromagnetic material was deposited by electroless deposition. The permalloy-coated tubules were dispersed in an epoxy matrix to measure the magnetization and ferromagnetic resonance (FMR) properties of individual tubules. The nature of the magnetic anisotropy and the FMR spectra observed confirmed that the tubules are well aligned by a magnetic field during the epoxy curing. The FMR spectra are interpreted in terms of a powder pattern distribution of thin-film spectra consistent with the large diameter-to-thickness ratio.
Crystal axis alignment in hot-deformed sintered magnets
Authors: Ohmori K. , Graham C. D.
Published: July 2002

We have investigated the possibility of hot deformation and crystallographic alignment in initially random (unaligned) sintered magnets which contain less Nd-rich phase and are characterized by better-defined grain boundaries than cast Pr-Fe-B-Cu, but contain more Nd-rich phase and larger grains than rapidly quenched and hot-pressed Nd-Fe-B (General Motors MQ-III). Nonaligned sintered magnets were found to deform at 1000 °C under compressive stresses between 11 and 170 MPa. It was found that the addition of copper changed not only the melting point of the Nd-rich phase but also the surface energy of the liquid and its reaction with graphite. The crystal axis alignment is mainly attributed to the solution and reprecipitation of small grain fragments produced by deformation and by anisotropic crystal growth. A highly oriented structure was obtained in a sample of composition Nd15Fe77B6.5Cu1.5, after 24 h at 1000 °C under a compressive stress of 45 MPa.
Effect of refractory additives on coercivity of sintered (Nd, Dy)(Fe, Co) BM magnets (M=Cr/W/Zr/Nb/Ta) (abstract)
Authors: Lin K. D. , Tzuoo U. C. , Tung J. Y. , Chin T. S.
Published: July 2002

In a trial to develop heat-resistant sintered Nd2Fe14B magnets, a refractory element (Cr/W/Zr/Nb/Ta) was selected as an additive incorporating Dy and Co in the Nd-Fe-B composition. Nd13Dy1.5Fe72−xCo6B7.5Mx alloys (M=Cr/W/Nb/Ta, x=0, or 3.5) were arc-melted, pulverized, compacted, and sintered by the conventional powder metallurgy method. It was found that W/Cr greatly enhances the as-sintered intrinsic coercivity (iHc, in kA/m), e.g., from 510 (x=0) to 810 (W, x=3.5) or 740 (Cr, x=3.5). An additional two-stage annealing at 900 and 600 °C for 1 h each led to an even higher iHc of 1000 (W, x=3.5). While Nb/Ta moderately enhanced as-sintered iHc, and responded less to additional annealing. Temperature coefficients of remanence was found to be greatly improved by the W or Cr addition, e.g., 0.43%/°C for x=0 and 0.06%/°C for M=W, x=3.5 (p=1, 20–150 °C). They are thus very suitable for applications at temperatures up to 150 °C. EPMA analyses showed the possible existence of a M2FeB2 (M=W/Nb/Ta) phase at grain boundaries. Thermomagnetic analyses and detailed microstructure of the sintered and/or annealed magnets are discussed.
Magnetic properties of Ti5Si3 contaminated by Fe during mechanical alloying processes
Authors: Kaczmarek W. A. , Ninham B. W. , Calka A.
Published: July 2002

This is a first systematic report on the magnetic properties of the amorphous and nanocrystalline Fe-(Ti5Si3) system. Using electron microprobe, scanning electron microscopy and by application of ferromagnetic resonance and magnetization measurements it was found that during mechanical alloying iron is introduced to the milling product. In the amorphous state of the material only Fe3+ ions exist, all ferromagnetically coupled, but with a high level of exchange interaction fluctuations. During the annealing-crystallization and diffusion process take place. Thereafter in the crystalline state both Fe3+ and Fe2+ ions are present. The first are located on the surface of grains with established local magnetic moments. The second type, paramagnetic Fe2+, are located in the Ti5Si3 crystal structure.
Wavelength dependencies of the Kerr rotation angle and ellipticity for the magneto-optical recording media
Authors: Zhou Feng Lei , Erwin J. Kevin , Brucker Charles F. , Mansuripur M.
Published: July 2002

Wavelength dependencies of the Kerr rotation angle, ellipticity, and reflectivity are measured for a Co/Pt sample and a series of Co/Pd samples with varying film thicknesses. The interference effects are analyzed by comparing the Kerr spectra of the various Co/Pd samples. The dielectric tensors are measured at 632.8 nm and the thickness dependencies of the Kerr rotation angle, ellipticity, and figure of merit are studied from the experimental and simulated results. The wavelength and thickness dependencies of the magneto-optical properties are studied in order to achieve an understanding of the magneto-optical interactions in the superlattice samples.
Bi-substituted iron garnet films with fine grains prepared by pyrolysis
Authors: Cho J. , Gomi M. , Abe M.
Published: July 2002

Polycrystalline films of Y3−xBixFe5−yAlyO12 (x=0.5–2.0, y=0–1.2) were prepared on glass substrates by pyrolysis combined with spin-coating techniques. SEM and TEM studies revealed that the grain size increases with x but decreases with y. This means that enhancing the magneto-optical effect by increasing x results in large grain size, which causes a strong media noise due to light scattering at grain boundaries. To solve this problem we have made double-layer films. An underlayer of polycrystalline film low in x, hence small in grain size, was first made by a conventional pyrolysis process. On this an upper layer high in x was made. The upper layer was crystallized at a temperature ∼50 °C lower and was ten times smaller in grain size than the single-layer film with an equal x. Furthermore, the upper layer crystallized at the lower temperature (590 °C) was exceedingly homogeneous.
Static and high frequency magnetic properties of amorphous BiFeO3–CuFe2O4 compounds
Authors: Rao B. Uma Maheshwar , Srinivasan G.
Published: July 2002

The magnetic ordering in amorphous radio-frequency sputtered samples of (1–2x) BiFeO3–x CuFe2O4 with x=0.3 has been studied through magnetization and ferromagnetic resonance (FMR) measurements. Unannealed films sputtered in a mixed oxygen–argon atmosphere show a paramagnetic character at room temperature. In samples annealed in air at high temperatures Ta, one observes a large ferromagnetic moment and a uniaxial anisotropy. Both the room temperature magnetization and anisotropy field increase with Ta until the precipitation of crystalline CuO and Bi2Fe4O9 phases at high temperatures leads to a decrease in the magnetic parameters. The FMR linewidth is found to be dependent on Ta: a rapid increase in the linewidth is seen when crystallization commences. We conclude from low temperature magnetization, Curie temperature, and gyromagnetic ratio data that the ferromagnetic character is due to the formation of ferrimagnetically ordered clusters of copper ferrite.
Correlation between normal flux transfer from lamination to lamination during the magnetization process with static domain structures in grain oriented 3% silicon iron
Authors: Ebrahimi A. , Moses A. J.
Published: July 2002

Grain oriented 3% silicon iron is widely used as magnetic core material in power devices. It is usually assessed on the basis of its magnetic losses when magnetized as single strips or in the Epstein square. When material is built into cores and magnetized, some flux passes normal to the plane of the laminations and increases the losses of transformers and rotating machines. Pairs of strips were placed together and magnetized at 50 and 60 Hz at ac longitudinal flux densities from 1.0 to 1.8 T and the normal flux density, BN transferred between them was calculated from the emfs induced in search coils located between the strips. Static domain structures were observed using a colloidal technique. Values of BN have been correlated with the domain structures, grain size, and boundary effects. BN was found to be dependent on the static wall spacing in adjacent grains and varied between 0.5 and 3.0 mT with a repeatability better than ±5%. Most large grains had low surface magnetic charge at their boundaries and BN was low. The opposite was found where the flux was transferred between small, not so well oriented, grains. This large normal flux transfer between poorly oriented small grains causes small additional losses in laminated cores.
Anisotropy of magnetic vortex pinning in high-T
c superconductors (invited) (abstract)
Authors: Krusin-Elbaum L.
Published: July 2002

There is no consensus as to the nature of the ‘‘irreversibility line’’ or the dynamic depinning transition boundary in H-T plane. The angle-resolved ac χ measurements allow us to probe the anisotropy of this boundary. We review remarkable new observations in single crystals of YBaCuO: one is the splitting of the loss peak in the out-of-phase ac susceptibility as a function of tilt angle between magnetic field and crystal axis, suggesting that vortices conform to the layered structure to form a modulated ‘‘staircase’’ shape. Another is the observation of a new irreversibility collapse transition in H-T plane at low fields near Tc. The new regime may indicate a separate boundary in the magnetic phase diagram, below which the pinning barriers are thermally renormalized so that pinning is significantly reduced or negligible. We discuss these observations in the context of intrinsic pinning and collective effects.
Exchange anisotropy in NiFe layers coupled with multilayered MnFe/MnFeCr (abstract)
Authors: Kung Kenneth T.-Y. , Campbell Richard T.
Published: July 2002

The exchange anisotropy in a ferromagnetic NiFe layer coupled with an antiferromagnetic MnFe layer can be used to stabilize the single domain state of a magnetoresistive sensor,1 but this technology may be limited by the high corrosion sensitivity of MnFe. It is possible to improve the corrosion resistance of MnFe through impurity doping, e.g., MnFeCr with Cr concentrations of 3–12 at. %,2 but this technique will at the same time degrade the exchange anisotropy. In this work, we have investigated the exchange anisotropy in NiFe layers coupled with multilayered MnFe/MnFeCr. The samples had a configuration of glass substrates, followed by a NiFe (300 Å) layer, followed by a MnFe(x Å)/MnFeCr(y Å) multilayer, where the antiferromagnetic multilayer had either MnFe or MnFeCr interfacing with the NiFe and had a fixed total thickness of 240 Å. They were prepared by rf diode sputtering and, after a Ta (200 Å) protective layer deposition, were thermally cycled to a maximum temperature of 250 °C. The results can be summarized as follows: (1) The anisotropy energy, EUA, near the room temperature ranged from 0.03 to 0.10 erg/cm2; it was determined mostly by the antiferromagnetic layer (MnFe or MnFeCr) at the NiFe interface and was essentially independent of the rest of antiferromagnetic structure. (2) The critical temperature, TC, range from 90 to 160 °C; it was determined mostly by the relative amounts of MnFe and MnFeCr in the entire antiferromagnetic structure and not just at the NiFe interface. These results implied that, while one could improve the anisotropy energy at lower temperatures simply by improving the antiferromagnetic layer near the NiFe interface, to improve the anisotropy energy at higher temperatures one must improve the entire antiferromagnetic layer.
Analysis of the magnetic anisotropy in SmCo5 and GdCo5
Authors: Zhao Tie-Song , Jin Han-Min , Grössinger R. , Kou Xuan-Chao , Kirchmayr H. R.
Published: July 2002

The temperature dependence of the magnetic anisotropy constant K1 for SmCo5 and GdCo5 is well reproduced by calculations based on a single-ion model taking into account the anisotropies of the R–Co exchange interaction and the Co-sublattice magnetic moment. The anisotropy of the R–Co exchange interaction plays an important role in reproducing the experimental K1(T) for SmCo5 and GdCo5. It is found that the absolute value of the second order crystalline electric field parameter A02 in SmCo5 decreases monotonically with increasing temperature.
Dynamic specific heat near the Curie point of Gd
Authors: Jeong Yoon H. , Bae D. J. , Kwon T. W. , Moon I. K.
Published: July 2002

We have developed a dynamic calorimeter, which can measure thermal properties of a wire or planar sample as a function of frequency over the range of five decades, 0.01 Hz–1 kHz. We have used this calorimeter to study the frequency dependence of the specific heat of gadolinium near the Curie point. There is an indication that the specific heat peak associated with the magnetic phase transition may depend on the measuring frequencies.
Orbital magnetic response of disordered metallic systems with Kondo impurities: Mesoscopic effects
Authors: Zyuzin A. Yu. , Esposito F. P. , Serota R. A.
Published: July 2002

We propose a novel mechanism effecting both the magnitude and the sign of orbital magnetic response in a mesoscopic metallic system, namely, the electron–electron interaction induced via spin-flip scattering from paramagnetic impurities. We evaluate its contribution to the response due to weak localization effects and compare it with the average response of a canonical ensemble of noninteracting electrons and with the localization correction due to the screened Coulomb interaction. We examine both the singly connected (Landau) and multiply connected (Aharonov–Bohm) sample geometries and explain how various contributions to the total magnetic response can be distinguished by their dependences on the magnetic field and the impurity concentration.
Coercivity mechanism in SmFeTi rare-earth magnets
Authors: Hütten A. , Thomas G.
Published: July 2002

The microstructure of SmFeTi magnets has been investigated by electron microscopy and microanalysis. Melt-spun SmFe10Ti consist of two phases; the hard magnetic SmFe11Ti phase (1:12), with the ThMn12 structure, and α-Fe. The origin of the Fe formation and its influence on the magnetic behavior are discussed. The measured temperature dependence of the coercivity is analyzed in terms of nucleation and pinning mechanisms. It is concluded that both models describe reasonably the temperature dependence of the coercivity in the temperature range 300–500 K, namely that the pinning mechanism predominates at higher temperatures, and the nucleation mechanism at lower temperatures. The microstructure of mechanically alloyed Sm28Fe62Ti10 consists of multiphases. The magnetic properties in these specimens are not determined by the (1:12) phase but a new hard magnetic Sm23Fe73Ti4 phase.
Magnetic anisotropy of RFe10Si2 alloys
Authors: Li Qingan , Lu Yi , Zhao Ruwen , Tegus O. , Yang Fuming
Published: July 2002

Magnetocrystalline anisotropy, Curie temperatures, spin reorientation temperatures, and first-order magnetization processes (FOMP) are reported for RFe10Si2 compounds with R=Y, Gd, Tb, Dy, Ho, Er, and Lu. The saturation magnetizations of them at 1.5 K are determined. The value of the R-Fe magnetic-coupling constant JRFe/k, derived by a mean-field analysis of the Curie temperatures, is about −10 K. A tentative spin-phase diagram for the RFe10Si2 series is presented.
Electronic structure and magnetic properties of a new class of hard magnets: R2Fe17Nx(abstract)
Authors: Jaswal S. S. , Sellmyer D. J. , Hadjipanayis G. C. , Yelon W. B.
Published: July 2002

Recently discovered R2 Fe17Nx (R=rare earth, x∼3) compounds look promising as permanent-magnet materials. The addition of N to R2Fe17 compounds almost doubles their Curie temperatures.1 It also give rise to uniaxial anisotropy in the Sm compound. We have performed spin-polarized self-consistent electronic structure calculations in order to understand the magnetic properties. Neutron diffraction and photoemission measurements are used to obtain information on nitrogen site occupancies and electronic structure. For Y2Fe17N3, the calculated site-dependent Fe moments vary significantly from those for Y2Fe17 (up to ∼1.7 μB), and the total moment per cell agrees very well with experiment. The expansion of the lattice due to nitrogenation lowers the overlap among the Fe atoms in the ion-only planes thereby increasing their magnetic moments. This leads to an increase in their interatomic exchange interactions and hence the Curie temperature. The Fe atoms in the vicinity of the N atoms overlap strongly with the latter and thus their moments decrease.2
Exchange and crystal fields in R2Fe14B studied by inelastic neutron scattering (invited)
Authors: Loewenhaupt M. , Sosnowska I.
Published: July 2002

Exchange and crystal fields (CF) acting on R3+ ions in R2Fe14B were investigated by means of inelastic magnetic neutron scattering. Experimental data for R=Pr, Nd, Gd, Tb, Dy, Ho, Er, and Tm are reviewed. Molecular fields H acting on R ions are calculated using neutron-scattering data for the CF models proposed earlier for these compounds based on single-crystal magnetization measurements. For Gd2Fe14B the molecular field acting on the Gd3+ ions was directly determined by inelastic neutron scattering as 2μBHm/kB = 435 K.
Permeability tensor of cubic arrays of magnetic spherical particles
Authors: How H. , Vittoria C.
Published: July 2002

We have calculated the Polder permeability tensor of a composite consisting of cubic arrays of magnetic spherical particles. Magnetic potentials associated with particle-particle interactions have been expressed in terms of multipole fields. The permeability tensor can be then expanded in power series of the particle volume loading. These results are in agreement with other method of calculation involving the free energy of a particle composite.