bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of light on individual defect noise in a-Si:H/a-SiNx:H double barrier structures
Authors: Teuschler T. , Hundhausen M. , Ley L.
Published: July 2002

A report on the influence of light on random telegraphic noise (RTN) in the current through a-Si:H/a-SiNx:H double barrier structures is given. Upon illumination with a focused He-Ne laser the spectral power density of the noise as well as the individual switching times are affected. Different regimes are observed: For sufficiently low light intensity the emission time constant τ̄e of the trap responsible for RTN decreases for increasing light intensity, whereas the capture time constant τ̄c remains nearly unaffected. For medium intensity illumination RTN disappears during illumination but recovers after its termination. Under high intensity illumination RTN vanishes and as a result the spectral power density of the unilluminated sample changes from a Lorentzian (typical for RTN) to a 1/f-like behavior. This unilluminated non-RTN state is metastable, i.e., the RTN state can be recovered by moderate thermal annealing.
Alloy broadening in photoluminescence spectra of GaxIn1−xAsyP1−y lattice matched to InP
Authors: Benzaquen R. , Charbonneau S. , Sawadsky N. , Roth A. P. , Leonelli R. , Hobbs L. , Knight G.
Published: July 2002

Low temperature photoluminescence measurements of GaxIn1−xAsyP1−y alloys nearly lattice matched to InP to study the line broadening of the observed band to band and near band gap transitions in these materials were performed. We find that the dominant broadening mechanism is alloy broadening that originates from the spatial fluctuations of the band gap energy due to random anion and cation distribution. A model that assumes that occupation of the group-III sites by Ga and In atoms and of the group-V sites by As and P atoms occurs randomly, is fitted to the photoluminescence spectra of our samples. This provides an excellent description of the experimental results.
Enhanced collimation in narrow channels fabricated by focused-ion-beam implantation
Authors: Bever T. , Hirayama Y. , Tarucha S.
Published: July 2002

We investigate the collimation factor of narrow channels defined by focused-ion-beam insulation writing in the highly mobile two-dimensional electron gas of an AlGaAs/GaAs heterostructure. We show that the degree of collimation can be enhanced by appropriate channel design. Additional boundary roughness caused by selective implantation of ions along the channel boundary considerably increases the collimation.
X-ray topographic study on dislocation configuration around indentation in a plastic region of Si single crystal
Authors: Yoshioka M. , Kawamura K.
Published: July 2002

This paper describes the dislocation configuration around an indentation on the (111) surface of a Si single crystal. X-ray Lang topography was used. The Burgers vector was identified for each section of the dislocation clustering region based on the change of the contrast of the diffraction pattern with various diffraction vectors. Additionally, the mechanism of dislocation interaction was discussed resulting in the observed configuration. The following results were obtained. The dislocation clustering region was divided into the inner and the outer territories, each of which was further divided into several sections with different Burgers vectors. It was assured that dislocations in the outer territory were perfect, while they split into partial dislocations in the inner territory. Therefore dislocation interactions were possible in the inner territory resulting in stair-rod dislocations. The observed configuration could be explained by the mechanism of the dislocation interaction.
Correlation of interface recombination and dislocation density at GalnP/GaAs heterojunctions
Authors: Müllenborn M. , Matney K. , Goorsky M. S. , Haegel N. M. , Vernon S. M.
Published: July 2002

Lifetimes at Ga1−xInxP/GaAs heterojunction interfaces determined by photoluminescence power dependence measurements and diffusion model calculations have been correlated to dislocation densities derived from high-resolution x-ray diffraction measurements. The diffusion model calculations are used to determine lifetimes in the region of misfit dislocations by fitting experimental power dependencies of buried-layer photoluminescence. High-resolution x-ray diffraction reveals dislocation densities through the broadening of diffraction peaks due to slight lattice tilts introduced by the dislocations. Lifetimes and dislocation density per dislocation length are correlated to show the functional relationship between the dislocation density and the density of the lifetime-limiting recombination center at the interface.
Depth-dependent lattice parameter variation and stress-induced magnetic anisotropy of ultrathin Dy2BiFe4GaO12 garnet films deposited on the glass substrate by pyrolysis
Authors: Lee Jung H. , Choo Woong K. , Kim Yong S. , Yun Doo W.
Published: July 2002

Lattice parameter variation as a function of depth from the free surface of ultrathin Dy2BiFe4GaO12 garnet films for magneto-optic application has been investigated. These thin films were synthesized by pyrolysis on the glass substrate and annealed at 660 °C in the glass transition range. The lattice parameters were determined by grazing incidence x-ray in asymmetric Bragg diffraction. X-ray diffraction results show that film stress is compressively greater near the glass/film interface and becomes smaller in magnitude toward the free-film surface. This observation has been interpreted as a result of softening of the glass substrate during annealing in the glass transition range and the subsequent larger shrinkage of the glass substrate with respect to the deposited crystalline film upon cooling. The thermal expansion difference between the substrate and the deposited film can in turn cause the stress-induced magnetic anisotropy. The induced magnetic anisotropy factor Ku has the maximum value above a threshold film thickness, about 600 Å. Down to this limit, Ku increases with the decreasing film thickness.
Harmonic mixing at mm waveband in a high temperature superconducting grain boundary Josephson junction
Authors: Wang H. B. , Xu W. W. , Cheng Q. H. , Wu P. H. , Luo Y. J. , Ye H. , Zhang J. M.
Published: July 2002

Using a high Tc superconducting grain boundary Josephson junction, harmonic mixing experiments in the mm waveband were carried out, aiming at as large a harmonic number and as high a signal frequency as possible. The dependencies of intermediate frequency output on dc bias, harmonic number, frequency of local oscillator (LO), and other parameters were carefully studied. Until now, our best result was the mixing between the signal at 95 GHz and the 105th harmonic of LO at about 900 MHz. Preliminary experiments using a high Tc harmonic mixer and phase-locking loop were tried to stabilize the frequency of a mm wave source.
Curvature in boron-doped silicon and other compositionally graded single crystals
Authors: Holloway H.
Published: July 2002

A solution is given for the curvature of a semiconductor element that is strained by substitutional incorporation of a dopant with an arbitrary concentration profile. The result is especially applicable to silicon that is heavily doped with boron to form an etch stop during fabrication of thin structures. For the case without misfit dislocations it is shown that the solution for a linear profile is a good approximation for a range of nonlinear dopant profiles and especially so for the erfc profile that arises from Fickian diffusion with a constant surface concentration.
Reduction of interfilament contact loss in Nb3Sn superconductor wires
Authors: Goldfarb R. B. , Itoh K.
Published: July 2002

Interfilament contact in Nb3Sn wires made by the internal-tin-diffusion process causes excess hysteresis loss beyond the intrinsic magnetic hysteresis loss of the filaments. In analogy with eddy-current and proximity-effect coupling losses, the excess contact loss can be reduced by decreasing the twist-pitch length of the filaments in the wire. One consequence of interfilament contact is that volume magnetization measurements are strongly dependent on sample length below about one twist pitch. We define a characteristic length whose reciprocal is equal to the sum of the reciprocals of the sample length and the twist pitch. Hysteresis loss is a universal function of characteristic length for different sample lengths and twist pitches. We discuss several experimental parameters for the magnetic determination of hysteresis loss.
Photoacoustic investigation of first- and second-order phase transitions in molecular crystals
Authors: Bonno B. , Laporte J. L. , Rousset Y.
Published: July 2002

Phase transitions in a single molecular crystal of thiourea and 4,4′-dichlorobenzophenone are investigated in the temperature range 160–210 K by means of photoacoustic detection. First, as well as second, order phase transitions are observed. The results are discussed on the basis of Rosencwaig–Gersho and Korpiun–Tilgner models.
Microstructural stability of metastable amorphous and crystalline Ge1−xSnx alloys
Authors: Lee Susanne M.
Published: July 2002

Amorphous Ge0.75Sn0.25 films, nominally 2000 Å thick, were produced by rf sputtering. The films were transformed to polycrystalline samples with no observable phase segregated β-Sn. The mechanisms of formation of this phase and subsequent phases as a function of temperature were studied with differential scanning calorimetry and transmission electron microscopy. Through these measurements we were able to identify a volume in parameter space from which polycrystalline alloys could be nucleated and grown without simultaneous Sn segregation.
Morphological model of the electrical anisotropy of a conducting polypyrrole
Authors: Montemayor M. C. , Vazquez L. , Fatás E.
Published: July 2002

From impedance measurements of conducting polypyrrole (Ppy) films prepared electrochemically, it is shown that there is a high anisotropy of the capacitive behavior of these films parallel and perpendicular to the substrate directions, making this behavior dependent on the rate of electropolymerization. A simple morphological model based on the arrangement of the Ppy chains explaining this fact is proposed. This model is corroborated by scanning tunneling microscopy measurements.
Thermal-optical switching of a silicon based interference filter
Authors: Augustine B. H. , Feng S. T. , Irene E. A. , Ray M. A.
Published: July 2002

Thermal-optical switching using a silicon based interference filter fabricated by plasma enhanced chemical vapor deposition is reported. A five film structure using high index films of amorphous Si and low index films of SiO2 comprised the device which yielded detector limited 40 ns rise time switching. Operation is in the near infrared spectral region with probe wavelengths of 810 nm and 1.152 μm. A 56% contrast ratio is reported when pumped by a 10.6 μm CO2 pulsed laser. Lower contrast switching was also demonstrated with a Nd:YAG pumped dye laser tunable from 600 to 700 nm. In addition, it is demonstrated that atomic layer thickness precision is not necessary, and several improvements that can further enhance device performance are suggested.
Properties of amorphous silicon/amorphous silicon-germanium multilayers
Authors: Conde J. P. , Chu V. , Shen D. S. , Wagner S.
Published: July 2002

A comprehensive study of multilayer structures made of hydrogenated and fluorinated amorphous silicon and its alloy with germanium, a-Si:H,F/a-Si,Ge:H,F, is reported. After briefly describing the deposition process and the chemical composition of the samples, the optical and the electronic properties of the multilayers are concentrated on. Raman scattering spectra suggest mixing over a 1-nm-thick interfacial layer. Auger electron spectra combined with sputter profiling and x-ray linewidth are compatible with this observation. The rise in optical band gap observed as the a-Si,Ge:H,F well layer thickness is reduced below 5 nm is also compatible with this interfacial mixing. No extra defect states above the detection limit of 2×1010 cm−2 are associated with the interfaces. Electron transport parallel to the layers takes place in the well layers. Perpendicular electron and hole transport is dominated by elastic tunneling through thin (<5 nm) barrier layers, and by thermal emission over thicker barriers.
Effects of air leaks on XeCl laser performance
Authors: Gabzdyl J. , Cleaver K. , Stevenson A. , O’Key M. A. , Osborne M. R.
Published: July 2002

The effects of traces of oxygen and nitrogen on the initial laser power and on the gas lifetime of a xenon chloride excimer laser have been studied. When present in atmospheric proportions, nitrogen is found to have the dominant deleterious effect. The reaction, under laser conditions, with HCl and H2 forming the benign precipitate NH+4Cl− is observed. With HCl injections, a N2 contaminated gas mixture is found to be ‘‘self-purifying’’ over periods of ∼2×106 shots. The effects of O2 contamination can also be largely counteracted by HCl injections. Conversely, injection of HCl into an old, but not intentionally contaminated, gas mixture causes a decline in the laser power.
Surface reconstruction of hydrogen annealed (100) silicon
Authors: Bender H. , Verhaverbeke S. , Caymax M. , Vatel O. , Heyns M. M.
Published: July 2002

The hydrogen termination and surface reconstruction of (100) silicon annealed at high temperature in a H2 atmosphere at 1 bar is investigated with multiple internal reflection infrared spectroscopy and atomic force microscopy. The surface flattens and becomes 2×1 reconstructed and terminated by strained monohydrides. This surface is shown to be very stable against contamination and oxidation.
Liquid phase epitaxy growth of Pb1−xSnxSe1−yTey alloys lattice matched with BaF2
Authors: McCann Patrick J. , Zhong Dongfan
Published: July 2002

IV–VI semiconductor quaternary alloys lattice matched with BaF2 substrates have been grown by liquid phase epitaxy. X-ray diffraction analysis shows that liquid (Pb1−xLSnxL)0.99 (Se1−yLTeyL)0.01 solutions produce Pb1−xSSnxSSe1−ySTeyS alloys lattice matched with the substrate when yL=60%, 58%, and 57%, and xL=20%, 40%, and 60%, respectively. These data, which can be used to fabricate lattice-matched heterostructure optoelectronic devices covering the 6–30 μm spectral range, show that smaller tellurium concentrations in the liquid growth solution yield lattice-matched alloys as the tin content increases. This is despite the fact that the tellurium content in the isoperiodic solid solution alloy increases with tin content. This result suggests that the chemical potential of tellurium in Pb1−xSSnxSSe1−ySTeyS solid solutions decreases as tin and tellurium concentrations increase. It is argued that this highly nonideal behavior is due to the decreasing strain energy driven segregation of tellurium from the solid to the liquid as the tin concentration increases.
Eddy-current interaction with an ideal crack. I. The forward problem
Authors: Bowler J. R.
Published: July 2002

The impedance of an eddy-current probe changes when the current it induces in an electrical conductor is perturbed by a flaw such as a crack. In predicting the probe signals, it is expedient to introduce idealizations about the nature of the flaw. Eddy-current interaction is considered with an ideal crack having a negligible opening and acting as a impenetrable barrier to electric current. The barrier gives rise to a discontinuity in the electromagnetic field that has been calculated by finding an equivalent electrical source distribution that produces the same effect. The choice of source is between a current dipole layer or a magnetic dipole layer; either will give the required jump in the electric field at the crack. Here a current dipole layer is used. The strength of the equivalent source distribution has been found by solving a boundary integral equation with a singular kernel. From the solution, the probe impedance due to the crack has been evaluated. Although analytical solutions are possible for special cases, numerical approximations are needed for cracks of arbitrary shape. Following a moment method scheme, numerical predictions have been made for both rectangular and semielliptical ideal cracks. These predictions have been compared with experiments performed on narrow slots used to simulate ideal cracks. Good agreement has been found between the calculations and the measurements.
Effect of plasma shielding in laser ultrasonics: Optoacoustic characterization
Authors: Hrovatin Rok , Možina Janez
Published: July 2002

Simultaneous measurements of laser excited ultrasonic waves in a solid sample and in the surrounding air are used for characterizing plasma absorption and the plasma shielding effect. Typical modifications of ultrasonic waves are discussed and the acoustic energy distribution between the solid and the atmosphere is assessed by a comparative analysis of optoacoustic responses received from both probes.
Structural and optical properties in ZnTe/GaAs strained heterostructures grown by temperature-gradient vapor transport deposition
Authors: Lee J. H. , Jang K. S. , Shin C. S. , Park H. L. , Kim T. W.
Published: July 2002

A lattice-mismatched ZnTe epilayer on a GaAs(100) substrate was grown by the simple method of temperature-gradient vapor deposition. X-ray diffractometry measurements were performed to investigate the structural properties of the ZnTe layer. Raman spectroscopy measurements showed that there was a lattice mismatch between the ZnTe epitaxial layer and the GaAs substrate. Reflectivity and photoreflectance measurements clearly revealed the splitting of the valence-band maximum, and photoluminescence measurements showed several resonant excitations of the ZnTe. The binding energies of the light holes and heavy holes determined from the splittings are in reasonable agreement with the bulk values.
Room temperature photoluminescence in the 1 μm region from InAs monolayer structures
Authors: Dosanjh S. S. , Hart L. , Nayak R. , Joyce B. A.
Published: July 2002

(InAs)1(GaAs)2 superlattice structures have been grown on GaAs(001) using molecular beam epitaxy and the photoluminescence experiments performed on them demonstrate that it is possible to modify the band gap of the binary InAs/GaAs system from 0.85 to 1.07 μm at 13 K. Most importantly, by annealing the sample in a hydrogen plasma, impurities as well as nonradiative centers are passivated, allowing intrinsic luminescence to be observed up to 1.14 μm at room temperature. X-ray diffraction measurements also performed show that the as-grown samples are indeed superlattices consisting of InAs and GaAs layers of thickness 1 and 2 monolayers, respectively.
An analytical saturation region model for amorphous silicon thin film transistors using a quasi-two-dimensional and an effective temperature approach
Authors: Chen S. S. , Kuo J. B.
Published: July 2002

This paper reports an analytical saturation region model for amorphous silicon thin film transistors using a quasi-two-dimensional and an effective temperature approach. As verified by the published data, this analytical saturation region model provides an accurate prediction on the drain current characteristics of an amorphous silicon thin film transistor.
Nitrogen effect in mechanical alloying of immiscible Cu-V: Extended x-ray absorption fine structure study
Authors: Sakurai Kenji , Lee Chung Hyo , Kuroda Nariko , Fukunaga Toshiharu , Mizutani Uichiro
Published: July 2002

A mixture of pure metallic powders of Cu and V has been mechanically alloyed by ball milling in a nitrogen atmosphere instead of a conventional inert gas. A strongly disordered phase of Cu30V70-N was obtained, in spite of the immiscibility of Cu and V. The change of local structure around each atom was investigated by the extended x-ray absorption fine structure technique. It was found that a nitriding reaction proceeds in the crystalline Cu-V supersaturated solid solution, which is formed at the early stage.
Optical, electrical, and photoelectrical properties of sputtered thin amorphous Zn3P2 films
Authors: Weber A. , Sutter P. , von Känel H.
Published: July 2002

Amorphous zinc-phosphide films have been prepared by reactive rf sputtering of zinc in a PH3-containing argon atmosphere. Transmittance and reflectance measurements were used to calculate the refractive index n and the extinction coefficient k as functions of wavelength. The absorption coefficient α was calculated and an optical gap of 1.60 eV was deduced. The benchmark energy E04, where the absorption reaches 104 cm−1, is at 1.75 eV. The measurement of the dark conductivity yielded an activation energy around 0.7 eV, near optical midgap. The magnitude of the pre-exponential factor of the conductivity and the sign of the thermopower indicate that carrier transport is due to conduction in extended valence-band states. The photoconductivity is much higher than the dark conductivity at room temperature. A gain of 103 was obtained by illumination with 100 mW cm−2 white tungsten lamp radiation. From the temperature dependence of the photoconductivity, activation energies of 0.18 and 0.3 eV can be deduced.
Characteristics of Ta and Ta-Al alloy Schottky contacts to n-GaAs
Authors: Huang T. S. , Jean S. M.
Published: July 2002

The metallurgical stability and the electrical characteristics of Ta and Ta-Al alloy metallizations on n-GaAs have been investigated. The compositions of electron-gun-evaporated alloy films were Ta55Al45, Ta37Al63, and Ta30Al70. The contacts were annealed by rapid thermal processing in the temperature range 400–900 °C for 20 s. X-ray diffraction, transmission electron microscopy, and Auger depth profiling analysis were used to study the structural properties. The sheet resistance and the electrical characteristics of the Schottky diodes were assessed using four-point probe and current-voltage measurements, respectively. The Ta-Al alloy metallizations were substantially more stable than pure Ta. The interfaces of Ta-Al/GaAs contacts were metallurgically stable and the surface remained smooth and lustrous up to 900 °C anneal, while interfacial reactions occurred and the surface became rough in Ta/GaAs contact after annealing above 600 °C. The Schottky barrier heights of all thermally stable Ta-Al/GaAs diodes increased with temperature after annealing above 700 °C. The variation of the electrical characteristics of the contacts as a function of annealing temperature can be correlated to the crystallization transformation of the film, and the interfacial diffusion and reaction.
Normal domains in large multifilamentary composite superconductors
Authors: Kovner V. S. , Mints R. G.
Published: July 2002

We study the dynamics of normal domains in a multifilamentary composite superconductor with a large amount of stabilizer outside the multifilamentary area. We consider the case when there is a transition layer with high thermal and electrical resistance between the superconductor and the stabilizer. We show the existence of localized and propagating normal domains in these composites. We derive an implicit expression for the propagation velocity of a normal domain.
The testing of action of chemical extracts on soils by magnetic methods (abstract)
Authors: Babanin Vyacheslav F. , Shpilkina Irina V. , Ivanov Alexandr V.
Published: July 2002

The participation of soil iron in the formation of physics-chemical features in feed of plants and microorganisms is well known. Because of the active role of Fe in soil landscapes the Fe state is taken into account in investigations of the genesis of soils. In spite of a relatively high content of iron in soils up to 40%–45% (relative to Fe) its numerical forms are diagnosed in a complex way by Ronthgen diffractometry, differential thermal analysis, and microscopy. Thus, chemical extracts are widely used in soil science. Extracted Fe is considered to be of amorphous, strong or weak crystallized forms. These gradations are of wide use but they are not correct. This is established by some authors by means of magnetic measurements and Mössbauer spectroscopy [Jeanory et al., Sci. Solids 135 (1986)] before and after magnetic separation and chemical extracts [Fine and Singer, Soil Sci. Soc. Am. J. 53, 191 (1989)]. We used the measurements of magnetic susceptibility and saturation and nuclear gamma resonance for the usual soils and electron paramagnetic resonance for weak magnetic Fe containing minerals (before the extract). Our results are comparable with the above research and lead to the next conclusions: (1) ordered alternations of magnetic parameters and results of action of extracts are absent; (2) the Mehra–Jackson extract (sometimes the Tamm’s extract) often extracts the crystallized magneticordered and paramagnetic silicate and superparamagnetic forms of Fe; (3) magnetic susceptibility and magnetic saturation increase in some types of soils (brown earth, ferralsol, alluvial soil) at dissolution of the alumosilicate part of soils because of enrichment by chemically strong particles of magnetite; (4) the conclusions on extracts (as far as crystallized silicate amorphous forms) do not have generalized characteristics.
Dislocation etching of flux grown strontium hexaferrite single crystals (abstract)
Authors: Raina Urvashi , Bhat Sushma , Kotru P. N. , Licci F.
Published: July 2002

Hexagonal hard ferrites like SrFe12O19 are technically interesting materials not only because they are the traditional permanent magnets but also as emerging magnetic recording media and as potential magneto-optic devices. For these reasons the study of dislocations in these samples is quite significant. Flux grown single crystals of SrFe12O19 are etched in 37% HNO3 at 100 °C and 85% H3P4 at 120 °C. These two etchants produce hexagonal pits on (001) planes that are established as dislocation etchants by performing the following experiments: (1) successive etching for prolonged periods resulting in persistent point bottomed etch pits at all the stages; (2) etching of matched (0001) cleavages in similar, as well as dissimilar, etchants which produce 1:1 corresponding point bottomed etch pits on a pair of the matched cleavages; (3) etching of low angle grain boundaries which consist of a grid of equally spaced edge dislocations. An equally spaced row of etch pits is obtained along the grain boundaries. Hexagonal etch pits with smooth sloping planes are normally produced. Among such pits, unusual etch pattern features including pits with rythmically and irrythmically spaced terracings, eccentric pits, small point bottomed pits within a large flat bottomed pit with differing geometrical centers, and flat bottomed pits with beaked centers, are obtained. Unusual deviations from the perfect match of etch patterns on certain matched (0001) cleavages are examined critically. It is thought that these unusual etch patterns are due to bending, branching, and stepping of dislocations. The terracing of pits is attributed to the segregation of impurities along dislocation lines.
Dipole-dipole interactions in KEr(MoO4)2 (abstract)
Authors: Anders A. G. , Volotskii S. V. , Zubkov O. E.
Published: July 2002

The model of a dipole-dipole magnet previously developed1,2 has applied to a KEr(MoO4)2 crystal with two paramagnetic ions in an orthorhombic unit cell. The erbium ion in the compound has a large anisotropy of an effective g tensor which, in turn, leads to Ising-like behavior in the magnetic subsystem. As had been done earlier,2 we had calculated the dipole configuration with the lowest energy, thus obtaining the ground-state structure that would appear at the magnetic phase transition. This dipole structure consists of ferromagnetic chains aligned along the c axis and antiferromagnetically coupled along a and b axes. The results were compared with recently done measurements of magnetic moment and low-temperature magnetic susceptibility.3 Calculated dipole ground energy E min=−1.325 K is in reasonable agreement with the experimental value of Tn=0.9 K. The obtained easy-axis direction along the c axis also agreed with experiment. The phase transition observed in crystal at H∥c in our model results in a transition to a ferromagnetic structure with Hcr=700 Oe. The last agreed with measured Hcr=800 Oe so one should conclude that a pure dipole model could well describe the main features of KEr(MoO4)2. At the same time our model could not explain the other phase transition that took place at H=1.5 kOe(H∥a). To understand this transition one probably should also consider a small anisotropic exchange interaction.
Influence of ultraworking frequency alternating weaking magnetic field on the microvasculture of mice (abstract)
Authors: Yang Ningjiang , Zhang Changmin
Published: July 2002

The physical effect produced by the ultraworking frequency alternating weaking magnetic field (UWFAWM) is demagnetization. We used two methods to study the influence of UWFAWM on the microvasculture of Kunmin mice. Method 1 (in vivo) included 21 mice (the experimental group 11 and the control group 10). Method 2 (in vitro) included 25 mice (the experimental group 13, the control group 12). Each group was put in the coil of the JDM-1 Type Demagnetometer which produced UWFAWM. The coil was electrified for the experimental groups, but not for the control groups, for 20 min, once a day. (1) Method 1. On the 10th day of demagnetization, the surface microvascultural diameters of liver and mesenterium were measured in two groups.1 The results showed that those in the experimental group (25.05±3.92 μm and 24.44±4. 7 μm, respectively) were markedly greater than those in the control group (10.70±1.72 μm and 18.37±1.93 μm, respectively. (2) Method 2. On the 40th day of demagnetizing, we killed all mice and immediately preserved the brain, heart, lung, liver, kidney, stomach, intestine, and submandibular gland in 10% formalin, then used continuous paraffin sections of 5 μm and HE stain, and measured the microvascular diameter of each group.2 The results showed that mean diameters of the organs in the experimental group were also significantly greater than those in the control group (p<0.01). This study confirms that UWFAWM can dilate the microvascultures of various organs, resulting in local aterial hyperemia of the organ, advance local tissue metabolism, and an increase in organic function, thus providing a basis for treating some diseases and for health care.
35Cl nuclear-magnetic-resonance study of magnetic ordering in Sr2CuO2Cl2 single crystal
Authors: Corti M. , Borsa F. , Miller L. L. , Rigamonti A.
Published: July 2002

35Cl nuclear-magnetic-resonance (NMR) and relaxation measurements have been performed in a Sr2CuO2Cl2 single crystal as a function of orientation between the external magnetic field H0 and the tetragonal c axis. The onset is found of an anisotropic inhomogeneous broadening of the NMR line without paramagnetic shift starting below about 320 K. The broadening is strongly temperature dependent and it increases with increasing H0. The relaxation rate T−11, on the other hand, diverges at TN≂260 K in agreement with previous results in powder sample. It is suggested that the observed broadening is due to the onset at T≳TN of a spontaneous nonzero thermal average of the Cu2+ moment lying in the a-b plane.
Effects of magnetic fields on fibrinolysis
Authors: Iwasaka M. , Ueno S. , Tsuda H.
Published: July 2002

In this study, we investigated the possible effects of magnetic fields on the fibrinolytic process. Fibrin dissolution was observed and the fibrinolytic activities were evaluated. First, fibrinolytic processes in magnetic fields were investigated by the fibrin plate method. We gathered solutions from the dissolved fibrin, and measured mean levels of fibrin degradation products (FDPs) in solutions. Mean levels of FDPs exposed to 8 T magnetic fields were higher than those not exposed to fields. Second, we carried out an experiment to understand how fibrin oriented in a magnetic field dissolves. FDPs in solutions of dissolved fibrins in fibrin plates were assayed. The result was that fibrin gels formed in a magnetic field at 8 T were more soluble than those not formed in a magnetic field. A model based on the diamagnetic properties of macromolecules was explained, and changes of protein concentrations in a solution in gradient magnetic fields were predicted.
Magnetic structures of itinerant electron systems (abstract)
Authors: Kübler J. , Sandratskii L. , Uhl M.
Published: July 2002

Under well-defined conditions itinerant electrons conspire to form magnetic moments that can show a variety of order phenomena in and near the ground state. We describe these quantitatively using energy-band theory which supplies a powerful conceptual and computational tool. Both the density functional and methodological bases are briefly reviewed and results are presented not only for noncollinear antiferromagnetic moment arrangements, but also for states having incommensurate helical order characterized by some wave vector q. In particular, we discuss the static nonuniform, exchange-enhanced magnetic susceptibility obtained for a selected set of transition metals. The observed temperature variation of the electron density of states of bcc iron can be explained just as that of the 5d states of gadolinium. For fcc-iron precipitates we find an incommensurate antiferromagnet ground state as observed by neutron-diffraction experiments. For other frustrated antiferromagnets, like the hexagonal Laves phase ThMn2, we obtain an incommensurate ground state, again in agreement with neutron diffraction experiments. Concerning the INVAR problem we add transverse magnetic fluctuations to the longitudinal fluctuations that recently have been quite successful in explaining magneto-volume anomalies of INVAR. Finally, we discuss the magnetization reversal in magnetic multilayers subject to an applied magnetic field.
A method of increasing magnetic energy of superconducting magnetic energy storage
Authors: Morisue T. , Yajima T.
Published: July 2002

A solenoidal-type superconducting magnetic energy storage (SMES) using ferromagnetic material as an exterior magnetic circuit can store about 30% more magnetic energy than that using no ferromagnetic material. The amount of pure iron needed is 3.4 ton/MJ or 12 000 ton/MWH for the operating magnetic flux density of the solenoid between 4 and 5 T. Low grade ferromagnetic material containing more than 50% pure iron may be available for the SMES.
Anti-Invar in Fe-Ni
Authors: Acet M. , Schneider T. , Zähres H. , Wassermann E. F. , Pepperhoff W.
Published: July 2002

Anti-Invar behavior in a material can be characterized by an anomalously large and a weak temperature-dependent thermal-expansion coefficient, when compared to the respective Grüneisen lattice expansion. It is just the opposite of the Invar effect, which is characterized by an anomalously small thermal-expansion coefficient. Common to Invar and anti-Invar is the fact that both posess moment-volume instabilities. Anti-Invar is observed in the paramagnetic state. It occurs in γ-Fe and in a number of 3d fcc binary and ternary alloys. In FexNi100−x alloys it is observed in the concentration range 70≤x≤100 at. % within the fcc stability range. The effect vanishes as the Invar concentration, x=65 at. %, is approached. To examine the valence electron concentration dependence of the anti-Invar effect the thermal expansion has been measured in the fcc state of FexNi100−x for 63≤x≤100 at. %. Using a model based on moment-volume instabilities in conjunction with a thermal activation process the size of the anti-Invar effect in these alloys has been determined. The volume enhancement is found to decrease with increasing Ni concentration from 2.8% in γ-Fe to 0% at x=65 at. %.
Approach to the electronic structure of antiferromagnets
Authors: Callaway J. , Kanhere D. G. , Kolchin A.
Published: July 2002

A study of a simple band model of a commensurate, two-dimensional antiferromagnet is briefly described. A self-consistent calculation shows a transition from a paramagnetic to a metallic antiferromagnetic state when an interaction is stronger than a critical value. The transition is accompanied by a change in size (large to small) of the Fermi surface. An insulating state may be obtained if there is exactly one electron per site.
Penetration of circularly polarized electromagnetic fields into superconductors with gradual resistive transitions
Authors: Mayergoyz I. D.
Published: July 2002

Critical state-type models of superconducting hysteresis are based on analytical study of penetration of electromagnetic fields into hard superconductors. This study has been carried out under the assumption of ideal (sharp) resistive transition. In the paper, the attempt is made to study the penetration of electromagnetic fields into hard superconductors for gradual resistive transitions described by the ‘‘power law.’’ This requires the solution of nonlinear partial differential equations. It is shown that the exact analytical solution can be found in the case of circular polarization of electromagnetic fields due to the high degree of symmetry of the posed problem. In the limiting case of sharp transition, the obtained solutions are reduced to the solution previously asserted by Bean.
Magnetization density in URu2Si2 and URh2Si2
Authors: Continenza Alessandra , Monachesi Patrizia
Published: July 2002

The magnetic properties of the isostructural compounds URu2Si2 and URh2Si2 are compared in order to ascertain the different role played by Ru vs Rh. The total magnetic moment, obtained by spin-polarized electronic calculations with the full potential augmented plane-wave method within local spin-density approximation, agrees quite satisfactorily with the measured one in URh2Si2, whereas it is orders of magnitude too big in URu2Si2. However, important differences are found among the two compounds: These are the substantial contribution to the total magnetic moment of negative d spin polarization and the larger radial extention and asphericity of the magnetization density (in two crystal planes) in the Ru compound compared to the Rh compound. Also, the f positive spin-polarization density on U differs in the two compounds. This should result in different magnetic form factors in diffraction experiments.
Giant and anisotropic magnetoresistance in single layer Ni66Fe16Co18–Ag films
Authors: Waknis A. , Barnard J. A. , Parker M. R.
Published: July 2002

Single layer Ni66Fe16Co18–Ag thin films were made by cosputtering from a composite Ni66Fe16Co18–Ag target. At the silver rich end of the composition range (≊57%–80 at. % Ag) we have found ‘‘giant’’ magnetoresistance (a maximum of ≊9% at room temperature at ≊72 at. % Ag after annealing at 300 °C for 1/2 h), while in the midcomposition range (≊42–≊57 at. % Ag), we have observed anisotropic magnetoresistance.
Disappearance of three-dimensional magnetic ordering in Gd2CuO4
Authors: Chattopadhyay T. , Brown P. J. , Roessli B.
Published: July 2002

The magnetic ordering of an isotope (158Gd) enriched Gd2CuO4 single crystal has been investigated by neutron diffraction in the temperature range 1.5–50 K. The three-dimensional magnetic order of the Cu sublattice is found to disappear abruptly in a narrow temperature range close to 7 K which is just above the ordering temperature of the Gd sublattice [TN(Gd)=6.4 K]. This result is thought to be intimately related to the structural distortion of the CuO planes which gives rise to weak ferromagnetism. The lack of three-dimensional order in the structural distortion imposes itself on the antiferromagnetic arrangement of the Cu sublattice through the Cu-Gd and Gd-Gd interactions and the different and incompatible wave vectors of the Cu and Gd magnetic sublattices.
Micromagnetic studies of medium noise mechanisms
Authors: Che Xiaodong , Bertram H. Neal
Published: July 2002

For a granular thin-film medium, the total noise is determined by intergranular interactions and local anisotropy fields. Among these two factors, the effect of local anisotropy on medium noise is relatively less clear. A micromagnetic model is used to study four kinds of media with different anisotropy distributions. Perpendicular anisotropy is examined in two of the four media: One has a uniform perpendicular component for all grains, the other has some perpendicular grains randomly distributed. It is found that if exchange coupling is absent, the medium with the most uniformly distributed crystalline anisotropy has the lowest noise. Otherwise, the medium with the most nonuniformly distributed anisotropy yields the lowest noise.
Thermoelectric power studies of a Nd1.82−xSrxCe0.18CuOy superconducting system (abstract)
Authors: Singh Okram G. , Padalia B. D. , Prakash Om , Moorthy V. N. , Narlikar Anant V.
Published: July 2002

We have reported recently on the revival of superconductivity in Nd1.82Ce0.18CuOy by doping with a divalent alkaline earth element. The doped superconductor Nd1.82−xSrxCe0.18CuOy has a Nd2CuO4 (T′-type) structure. This system possesses a normal state metallic resistivity [ρ(T)] in polycrystalline form. The ρ(T) versus temperature (T) plots are, in general, linear. We report here the results of our studies of ρ(T) and thermopower S(T) and their dependence on the lattice oxygen content (y) that is a function of the Sr-content x. The dρ(T)/dT improves and then deteriorates with an increase in y. However, the thermopower behavior is a more complicated function of y (or x) and its results indicate that the majority of the charge carriers are electronlike. The thermopower (in absolute value) of the superconducting Nd1.73Sr0.09Ce0.18CuO3.97 compound gradually decreases from 250 to 150 K, remains almost constant from 150 to 75 K, decreases very fast below 75 K, and shows negative dS/dT. The overall feature of the S vs T plot suggests that the main contribution to S is from diffusion. Unlike reduced Nd1.82Ce0.18CuO4.01 and other electron-doped superconductors, we have not observed a peak near the transition temperature (Tc) on the higher temperature side of the S vs T plot of the present sample. An attempt is made to explain the salient features of the thermopower.
The magnetic and superconducting properties of Pb2Sr2(R/Ca)Cu3O8, R=Pr, Ce, and Cm (abstract)
Authors: Xue J. Simon , Williams C. W. , Soderholm L.
Published: July 2002

The series of compounds Pb2Sr2(R/Ca)Cu3O8, (R=Ce-Tm) are known to superconduct at temperatures as high as Tc=84 K. We have studied the relationship between superconductivity and magnetism in the Ce and Pr analogs. In addition, we report the synthetic route and the magnetic properties of the actinide analog Pb2Sr2(Cm/Ca)Cu3O8. The parent compound Pb2Sr2CmCu3O8 is not a superconductor, but shows evidence of long range magnetic ordering at about 18 K. This is a much higher temperature than is observed for any of the other R-ion parent compounds. These results will be discussed in terms of the different hybridization and bonding properties of the 4f and 5f electrons, and how these differences influence superconductivity. These results will be compared with the Pr and Cm analogs of the other superconducting series RBa2Cu3O7 and R2−xThxCuO4.
Restoration of the continuous phase transition in the vortex state due to the lattice translational symmetry: Large-N limit (abstract)
Authors: Shalaev Boris N. , Ktitorov Sergey A.
Published: July 2002

The critical behavior of type II superconductors (SC) near the upper critical magnetic field is studied. The order parameter fluctuations in type II SC near the upper critical magnetic field were shown to destroy the off-diagonal long-range order (ODLRO) in d<4 dimensions. In the report this result is proved to be valid in the 1/N expansion. Thus, there is a serious controversy between the experimentally observed phase coherence in SC and theoretical results forbidding a spontaneous breakdown of the U(1) symmetry. Lattice effects breaking the continuous translational magnetic symmetry and suppressing the dimensional reduction effect are shown to be responsible for the existence of the ODLRO. The lattice Hamiltonian of the uniformly frustrated O(2N) symmetric nonlinear sigma model is used to obtain the effective Ginzburg–Landau action which is analyzed in the large N limit. It is shown that the continuous phase transition does indeed occur with critical exponents being universal and identical to those of a superconductor with H=0.
Magnetic structure determination for Fe3O4/NiO superlattices by neutron diffraction techniques (abstract)
Authors: Borchers J. A. , Erwin R. W. , Ankner J. F. , Berry S. D. , Lind D. M. , Lochner E. , Shaw K. A.
Published: July 2002

Neutron diffraction measurements reveal the nature of the magnetic structure in Fe3O4/NiO superlattices grown by molecular beam epitaxy. By taking advantage of differences between the spinel and rocksalt crystalline symmetries, we have separated the magnetic order parameters of the Fe3O4 and NiO bilayer components. The NiO antiferromagnetic order develops at temperatures 10–150 K greater than TNéel for bulk (520 K) due to exchange coupling of the Ni spins to the Fe3O4 (TCurie=858 K) at the superlattice interfaces. The resultant scaling of the NiO transition temperature with the bilayer composition is consistent with expectations from mean-field treatments for a modulated magnetic material. In addition, the NiO spin order propagates coherently through several superlattice bilayers, while the magnetic coherence of the Fe3O4 is limited by a random stacking of the spinel unit cell at the interfaces when the NiO interlayers are thicker than ≊15 Å. A model for the diffraction data, based upon a Hendricks–Teller description of the interfacial disorder, demonstrates that the observed broadening of selected crystalline and magnetic reflections originates directly from these stacking faults. Combining the high angle diffraction results with those from polarized-beam reflectivity analysis, we extract specific information about the moment distribution in these superlattices and qualitatively explain the evolution of the magnetic structure with temperature.
Mechanical properties of hot-rolled Pr-Fe-B-Cu magnets
Authors: Arai A. , Kobayashi O. , Takagi F. , Akioka K. , Shimoda T.
Published: July 2002

Mechanical strength and properties of thin plates were investigated for hot-rolled Pr-Fe-B-Cu magnets. Tensile strengths of the hot-rolled magnets were more than 23.7 kg f/mm2. Bending tests were also applied and the strength of 37.7 kg f/mm2 was obtained. The strengths obtained are definitely higher than that of commercial Nd-based sintered magnets. It was found that the mechanical strengths were enhanced by Pr2Fe14B grain refinement caused by Cu addition. Related to high mechanical strength, hot-rolled Pr-Fe-B-Cu magnets show excellent machinability. Thin plate magnets up to 0.1 mm in thickness with fairly large surface area were produced without any cracking. Moderate energy products better than 20 MGOe were achieved by heat treatment after machining.
Ferromagnetic resonance studies of granular materials (abstract)
Authors: Rubinstein Mark , Das Badri , Chrisey D. B. , Horwitz J. , Koon N. C.
Published: July 2002

We have investigated the ferromagnetic resonance (FMR) spectra of several granular alloys displaying giant magnetoresistance (GMR). For this task, we have produced melt-spun ribbons of Fe5Co15Cu80 and Co20Cu80 by rapid quenching and thin films of Co80Cu20 by pulsed laser deposition. The salient feature of the FMR spectra is the increase of the resonance linewidth as a function of increasing annealing temperature. We have deconvoluted the FMR spectra to a single-domain powder pattern and a multidomain powder pattern. As a function of annealing temperature, the GMR of these samples attains a maximum value. Near the peak of the GMR curve, the FMR spectrum reveals that the ferromagnetic particles are half mono- and half multidomain. Since the maximum size of a single-domain particle is known, this enables us to estimate the spin diffusion length of the Cu conduction electrons. We have also demonstrated, theoretically and experimentally, that the appropriate demagnetizing field to apply to the ensemble of spherical magnetic particles that comprise our granular thin film is simply the field corresponding to the average magnetization.