bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic detection for underground pipes (abstract)
Authors: Wasa Y. , Miyamoto Y. , Kondo Y. , Mori K. , Yamauchi F.
Published: July 2002

Magnetic detection has been investigated for use in detecting the location of underground pipelines, such as gas and water lines, by inputting a signal current into a pipeline and detecting magnetic field (≲100 μG) generated by that current. Measurement factors necessary for accurate detection have been experimentally determined and are discussed. From measurements made on signal current distribution (the current flowing in pipes and leaking from them to ground), it has been concluded that detection error is caused by the leakage current, namely, the current to ground. The detection error is due to the noncenter symmetric distribution of the ground current flowing around a pipe. Even though the ground current is inevitable when flowing a signal current into pipes, it is possible to reduce the error by reducing the nonsymmetry by lowering the signal frequency below 10 kHz in this work. The ground current distribution was obtained by measuring the potential difference between two electrodes, both of which were rod shaped and inserted in the ground to the same depth. At low frequencies below 10 kHz, the ground current distribution in a cross section perpendicular to the pipe showed a rather center symmetry around the pipe, while at high frequencies the distribution changed to a noncenter symmetry with a significant current increase in a region near the ground surface. The drastic change in the distribution of the ground current was also confirmed by magnetic field distribution measurements conducted on the ground using three orthogonally arranged magnetic sensors, each with a sensitivity of 1 μG.
Magnetic behavior of CuBr2⋅2DMSO, a quasi-Heisenberg S=(1)/(2) antiferromagnetic chain
Authors: Landee C. P. , Greeney R. E. , Teh A. T. , Lamas A. C.
Published: July 2002

We report the results of low-temperature susceptibility and magnetization studies of both protonated and deuterated samples of the title compound, CDB. The single-crystal susceptibilities can be modeled as arising from a 1-d Heisenberg S= (1)/(2) chain with an exchange constant J/k=−11.3±0.3 K. This value is consistent with that determined previously from birefringence measurements. The susceptibilities along the a and c axes show indications of spin canting. At 1.5±0.1 K, there are distinct changes in slope in the susceptibilities. The results are similar for the two versions, but the feature is more pronounced for the deuterated compound. This anomaly is consistent with the existence of the critical temperature found in deuterated CDB by neutron scattering. An additional feature is found near 2.6 K in the protonated version; its origin is unclear.
Oxocuprates: A structural and magnetic zoo
Authors: Ramakrishna B. L. , Ong E. W.
Published: July 2002

We have attempted a magnetostructural correlation for the oxocuprates: Y2Cu2O5, BaCuO2, Y2BaCuO5, and YBa2Cu3O6, all of which are closely related to the new high-Tc superconductors. It was found that this series of compounds has interesting combinations of ferro- and antiferromagnetic interactions as a consequence of the structural and electronic variety of copper. Y2Cu2O5 and Y2BaCuO5 were shown to be chain and layer magnetic systems, respectively. BaCuO2, a complicated 3D structure, has interesting effects of exchange interaction manifested in the temperature-dependent EPR spectrum. YBa2Cu3O6 has been shown to possess a Néel point at 450 K from EPR intensity variation with temperature.
A novel self-shielding permanent-magnet rotor assembly
Authors: Potenziani II E. , Leupold H. A. , Basarab D. J.
Published: July 2002

The use of permanent magnets in brushless motors and generators is highly desirable in that they have great potential for reducing weight and increasing efficiency. A self-shielding cylindrical permanent-magnet assembly has been designed and was found to produce high fields at the outer magnet surface and very little flux leakage into the interior rotor space. Construction of this assembly is simplified because it is composed of magnets of simple triangular cross sections, which have only four distinct orientations. The self-shielding nature of the design obviates any need for ferromagnetic material for flux shaping or shielding, thus simplifying greatly the mathematical analysis of the design and reducing its weight and bulk. Finite element methods are used to analyze a hypothetical permanent-magnet rotor assembly with regard to various design parameters.
Hysteresis model for polycrystalline high-T
c superconductors
Authors: Stancil D. D. , Schlesinger T. E. , Stamper A. K. , Wong D.
Published: July 2002

The hysteresis exhibited by ceramic superconductors can be modeled using a phenomenological critical current density of the form Jc=α/(B0+B) with suitable extensions. At low temperatures (near 4 K), satisfactory results can be obtained using this form and neglecting the equilibrium magnetization. However, we show that at higher temperatures the incorporation of the equilibrium magnetization becomes more important. At 77 K, the commonly observed shape of the curves is dominated by the equilibrium magnetization. An approximate model including the equilibrium magnetization is described and compared to measurements made at 77 K.
Magnetic behavior of Ho1Ba2(Cu1−xFex)3O7−y
Authors: Violet C. E. , Hahn P. A. , Datta T. , Almasan C. , Estrada J.
Published: July 2002

We have carried out dc magnetization (x=0 and 0.05) and 57Fe Mössbauer spectroscopy (x=0.05) measurements of Ho1Ba2(Cu1−x Fex)3O7−y , between room temperature (RT) and 4.2 K. Based on x-ray diffraction results all samples are single phase, and either orthorhombic (x=0) or tegragonal (x=0.05). Magnetization measurements determined the onset Tc to be either 90 K (orthorhombic) or 48 K (tetragonal). Mössbauer spectra between RT and 20 K are nearly identical, each consisting of three superposed quadrupole doublets. As the temperature is lowered below about 10 K the Mössbauer spectra exhibit paramagnetic relaxation. The relaxation time increases by about two orders of magnitude as the temperature decreases from 10 to 4.2 K. No magnetic ordering of the Fe moments was observed.
Reproducible sputtering and properties of Y-Ba-Cu-O films of various thicknesses (abstract)
Authors: Luborsky F. E. , Kwasnick R. F. , Borst K. , Garbauskas M. F. , Hall E. L. , Curran M. J.
Published: July 2002

One goal of this work was to develop a reproducible method of preparing high quality Y-Ba-Cu-O superconducting films and to study their properties versus thickness. This was accomplished by rf diode sputtering from a single target. Twenty-seven depositions were made using a target containing 8.9-at. % Y, 37.3-at. % Ba, and 53.8-at. % Cu. Film thicknesses ranged from 0.09 to 2.4 μm. The film compositions obtained were 15.6±1.0-at. % Y, 35.8±1.0-at. % Ba, and 48.7±1.7-at. % Cu for the mean and standard deviation. The films were amorphous as deposited and crystallized by annealing in O2 at 915 °C. X-ray diffraction, transmission electron microscopy, and scanning electron microscopy indicated that, on (100)SrTiO3 substrates, films with thickness less than ∼0.25 μm were epitaxially oriented with their c axis perpendicular to the substrate. Films on (110)SrTiO3 were oriented with their c axis parallel to the substrate. On (100)SrTiO3, zero resistance was achieved in 30 samples from 27 runs at 85.6±1.4 K with a transition width (10%–90%) of 1.8±1.1 K independent of thickness. Results for deposition on a variety of other substrates were more variable. Diamagnetic shielding of up to 38% was calculated from the initial slope of M vs H. This low value was attributed to the presence of second phases and a significant diffusion layer thickness, both observed by transmission electron microscopy. Critical currents, measured by transport using a four-point probe, reached 8.1×105 A/cm2 at 77.35 K for a 0.2-μm film deposited on (100)SrTiO3 . Comparable values were obtained by calculation from the M-H hysteresis loop, from which we infer that there are either continuous epitaxial sheets of c axis oriented 123 or, if there are grain boundaries, the coupling across them is strong.
Low-field microwave absorption in high-T
c superconducting oxides
Authors: Ramakrishna B. L. , Ong E. W. , Iqbal Z.
Published: July 2002

Low-field nonresonant microwave absorption in an electron paramagnetic resonance spectrometer has been observed in the superconducting state of different samples of the new high-Tc oxides, YBa2Cu3O7−x (powder pellets and single crystals), La1.8Sr0.2CuO4 , and Bi-Sr-Ca-Cu-O. It has been attributed to flux slippage occurring at the Josephson junctions existing in the granular composite materials. The dependence on particle size, temperature, microwave power, dc modulation amplitude, and magnetic field has been studied.
Local moments, diamagnetism, and time-dependent magnetic response of high-temperature superconductors
Authors: Földeáki M. , McHenry M. E. , Kalonji G. , O’Handley R. C.
Published: July 2002

The magnetic properties of high-Tc superconductors RBa2 Cu3O7−δ with R=Y, Gd were investigated in the temperature range 4.2–300 K. To first order, no interaction was found between superconductivity and paramagnetism in the zero-field-cooled state of the Gd-doped samples: after correction for the Curie–Weiss magnetization, the diamagnetism of these samples is very close to that of the Y-doped samples. This suggests that the superconducting screening of an applied field has little effect on the field seen by the R species. The diamagnetic screening is found to be strongly time dependent due to flux penetration, whereas the magnetic ions see the applied field without delay.
Nonequilibrium dynamics of spin glasses and the observability of spin-glass correlations in simple magnetic scattering (invited)
Authors: Huse David A.
Published: July 2002

A theory, developed in collaboration with Fisher, of the nonequilibrium behavior of spin glasses for temperatures, T, below the ordering temperature, Tg, is first reviewed. The magnetic structure factor, S(q), of a spin glass that is magnetized either due to the presence of a uniform magnetic field, h, or due to having been field cooled to TTg, h=0, and 0<q≪ξ−1s, where ξs is the correlation length of any short-range (e.g., spin-density wave, ferro- or antiferromagnetic) order, d2S(q)/dh2∝−ĜEA(q), where ĜEA(q) is the Fourier transform of the usual Edwards–Anderson (spin-glass) correlation function. Thus, one can, in principle, directly measure (a) the spin-glass correlation length when the sample is at equilibrium, and (b) the nonequilibrium spin-glass correlation length (domain size) when the sample is in a nonequilibrium state produced by field cooling.
Structure and magnetic properties of nanostructured Dy/transition-metal multilayered films
Authors: Shan Z. S. , Sellmyer D. J.
Published: July 2002

We report the results of magnetic and microstructural studies for T/Dy (T=Fe, Co, Ni) compositionally modulated films prepared in a multiple-gun sputtering system. The perpendicular anisotropy and magnetization were measured systematically for X-Å Fe/Y-Å Dy and X-Å Co/Y-Å Dy films. The layer-thickness dependence of the magnetization for Co/Dy and Fe/Dy was interpreted in terms of the antiparallel coupling between transition-metal and Dy magnetic moments. For Co/Dy films the ranges of X and Y required for perpendicular anisotropy were determined. A comparision of the structural and magnetic properties of Ni/Dy, Co/Dy, and Fe/Dy is given and the origin of the perpendicular anisotropy is discussed.
FMR in evaporated single and multilayer thin Fe films
Authors: Layadi A. , Artman J. O. , Hall B. O. , Hoffman R. A. , Jensen C. L. , Chakrabarti D. J. , Saunders D. A.
Published: July 2002

We have used ferromagnetic resonance (FMR) at 33 GHz to study the properties of a number of evaporated thin Fe film systems. Values for effective anisotropy field HKeff , g value, and exchange constant A were derived. For Fe on glass, ‖HKeff ‖ was found to increase with increasing thickness. These changes were attributed to stress which decreased with film thickness. The presence of a Cu or a Ti underlayer did not seem to affect HKeff for films grown at room temperature. However, Fe/Ti/glass films made at higher substrate temperatures, Ts, did show an increase in ‖HKeff ‖. The appearance of a spin-wave mode in the Fe films enables us to compute the exchange constant A for Fe, A=(2.12±0.14)×10−6 ergs cm−1. The coupling between two thin Fe films through an intervening Cu layer was investigated. A model predicting the number and position of the peaks in the spectrum as a function of coupling is presented. From experiment it was observed that the coupling remains almost constant through the 50–5-nm Cu thickness range but rises sharply at 2-nm Cu thickness.
Magnetic characteristics of 3d transition-metal–mica intercalation compounds
Authors: Takahashi M. , Ishio S. , Onuki S. , Ohtsuka K. , Suda M. , Ono M.
Published: July 2002

The magnetic properties of the M-mica intercalation compounds (M=Mn,Fe,Co, and Ni) in which M elements form a two-dimensional lattice between mica layers have been investigated. The content of the intercalated M element, x, was varied up to about 22 wt. %, which is about 81% with respect to the upper limit of x. The ac susceptibility measurements revealed the magnetic ordering around 10 K for the Fe- (x≥8.0 wt. %), Co- (x≥7.4 wt. %), and Ni-mica intercalation compounds, but did not for the Mn-mica. These magnetic orders are considered to be the two-dimensional ones, caused from the intralayer superexchange interaction between M2+ (and Fe3+) ions.
Canted ferrimagnetism in Ca2+Sc3+ substituted yttrium-iron-garnet
Authors: Pardavi-Horváth M. , Thavendrarajah A. , Wigen P. E. , DeGasperis P.
Published: July 2002

The temperature dependence of the magnetization of Y3−y−zCayLuzFe5−xScxO12 (0.6≤x≤1.2, 0≤y≤0.3, 0≤z≤0.9) epitaxial garnet films was measured from 4.2 K up to the Curie temperature. For x=0.7 and T≥50 K, 4πMs is enhanced by about 10% compared to the magnetization of Sc0.7 YIG. At T<50 K, a reduction of the magnetization, increasing with increasing substitution, was observed for all the measured samples. Agreement between the experimental results and molecular field models was obtained by taking into account the canting of the unsubstituted sublattice, the presence of charge compensating Fe4+ ions, a low-temperature ordering of Fe3+ ions with less than two magnetic nearest neighbors, and assuming a lattice parameter-dependent exchange interaction ratio with d(Jdd/Jad)/da =28 nm.−1 For x=1.2 and T<10 K the magnetization can be influenced by cooling through the Curie point in a magnetic field.
Thermal change of magnetic loss in preilluminated yttrium-iron-garnet single crystal
Authors: Hisatake K. , Matsubara I. , Maeda K. , Fujihara T. , Ichinose N.
Published: July 2002

A photoinduced decrease in permeability μ′ is observed over 90% in a highly pure single crystal of yttrium-iron-garnet (YIG) grown by a floating zone method. Even after the illumination is removed, the influence remains up to 230 K. By annealing under oxygen atmosphere in the preparation stage, the magnitude of the effect is reduced to 40%. On warming after the sample is illuminated by a flash lamp at 77 K, the imaginary part of permeability μ″ below 10 kHz is found to show the double peaks, activation energies of which are 0.1 and 0.3 eV, respectively. Besides, it has been observed that the dependence of magnitude of each peak on the strength of illumination is different. These features are discussed in terms of one or two electron F-type defects (oxygen vacancy) and photoexcited two levels.
Chemically homogeneous fine-grained Mn-Zn ferrites by spray drying (abstract)
Authors: Kumar K. , Petrovich A. , Williams C. , VanderSande J. B.
Published: July 2002

Chemically and structurally uniform Mn-Zn ferrites have been produced using powders synthesized by the spray decomposition of mixed, aqueous Mn, Fe, and Zn nitrate solutions. The particle size of the as-formed powder depended strongly on the metal ion concentration in solution; higher concentrations produced larger sizes. The as-formed particles are spherical, internally hollow, and consisted mostly of Fe2O3. A 900 °C, 6-h argon treatment removed the internal void space and converted the particles mostly to the ferrite spinel phase. Sintering of compacts from heat-treated powders produced microstructures superior to those from as-formed powders. Uniform, fine-grained materials, with a densification level comparable to that of commercial sintered ferrite, have been produced at the very low sintering temperature of 1100 °C. Preliminary work indicates that a higher initial permeability is obtained when a higher sintering temperature was used and the level of its disaccommodation depended on the oxygen partial pressure present during sintering. Both ‘‘accommodation’’ and disaccommodation were observed in the permeability; their magnitudes depended on the peak value of the applied excitation field.
Influence of high-temperature annealing on magnetic aftereffects in vacancy-doped magnetite (abstract)
Authors: Rivas J. , Castro J. , Blythe H. J. , Iñíguez J. , de Francisco C.
Published: July 2002

A well-defined new magnetic relaxation phenomenon has recently1 been reported at high temperatures (400–500 K) in polycrystalline magnetite samples of composition Fe3−ΔO4 (10−5<Δ<10−1). We have found that when the temperature of such samples is raised to 650 K or more, on a second measurement of the aftereffects, this magnetic relaxation is found to have almost completely annealed out. This paper presents measurements of ac initial susceptibility and magnetic disaccommodation reflecting this annealing phenomenon. The influence of high-temperature annealing on magnetic properties is attributed to the attainment of a new thermodynamic equilibrium.
ac electrical transport properties of magnetite (abstract)
Authors: Rasmussen R. J. , Honig J. M.
Published: July 2002

Electrical transport properties of synthetic magnetite (Fe3(1−δ)O4) single crystals of controlled stoichiometry have been characterized by ac impedance measurements between 5 Hz and 10 MHz, as a function of temperature (77 K<T<300 K) above and below Verwey temperatures (Tv) of first- (δ≊0) and second-order (δ≊0.005) transitions. The low-frequency impedence is in agreement with results obtained by dc methods. For T<Tv, samples in both composition regimes exhibit weak frequency dependence. Above the magnetic isotropic temperature (Tm≊130 K), the high-frequency impedance increases with relatively constant phase angle. Local maxima at high frequencies are observed in log ‖z‖−1/T space, at temperatures corresponding to Tm. In this projection, the δ≊0.005 sample exhibits an anomalous frequency dependence at approximately 250 K. Between Tm and Tv, the frequency dependence diminishes with decreasing temperature, vanishing at roughly 110 K. Above Tv, the observed behavior is shown to be a function of permeability, which has no influence below Tv. For T<Tv, the results support an adiabatic hopping conduction mechanism.
Fabrication of an inductor using amorphous films with a multilayered structure
Authors: Kamo Y. , Kikuchi S. , Shimada Y.
Published: July 2002

By making use of the high permeability and the excellent high-frequency characteristics of Co-metal amorphous multilayered films, an inductor was fabricated. In order to improve the high-frequency characteristics, stripe patterned films were studied. The inductor consists of two of these films and a ferrite yoke. The value of inductance and quality factor were measured in the frequency range of 0.01–200 MHz. Although the value of the present inductance is small compared with other small size inductors developed so far, excellent high-frequency characteristics may be expected if an inductor is fabricated composed solely of these multilayered films.
A new dc-CT utilizing the skin effect of a conducting current in a small magnetic pipe
Authors: Yamaguchi Masahiro , Hojo Hiroyuki , Matsuki Hidetoshi , Watanabe Tadaaki , Murakami Koichi
Published: July 2002

This paper proposes a new method for noncontact measurement of the dc current. This device utilizes the skin effect of an ac current flowing in a ferromagnetic pipe with an amorphous-tape wound structure. The dc current controls the skin depth of the ac current. This dc-current transformer (CT) has no winding and outputs the difference between the terminal voltage of the pipe and the induced voltage in a one-turn coil. The ac current does not affect the dc line because of axis symmetry. A linear relation between the output and dc current is obtained when an appropriate ac drive frequency is selected. Improvement of gain can be attained by reducing the diameter. It is clarified that the magnetic pipe is applicable for a dc-CT with a small size.
Distance sensor using a cloth inductor
Authors: Yamamoto T. , Matsuki H. , Murakami K.
Published: July 2002

A new distance sensor is presented using a cloth inductor combined with a magnet. The sensor, reported in this paper, makes use of the characteristics of the cloth inductor. A distance sensor using a cloth inductor has superior characteristics due to the cloth inductor. The cloth inductor has two great characteristics: a plain shape and a closed magnetic path. The sensor also has a very plain shape (thickness<0.6 mm), a high signal-to-noise ratio, and is independent of the nearby magnetic substance.
Two c-core type orthogonal-core using a Fe-6.5 wt. % Si sheet and its application to power converters
Authors: Ichinokura O. , Watanabe T. , Murakami K. , Takada Y.
Published: July 2002

This paper describes a two c-core type orthogonal-core made of Fe-6.5 wt. % Si sheet and its application to power converters. The orthogonal-core can be used in the high-frequency region because a Fe-6.5 wt. % Si sheet has superior soft magnetic properties including high permeability and low core loss. Using the orthogonal-core, we constructed a parametric oscillation type dc-ac converter. The dc-ac converter had voltage regulation, overload protection, noise rejection, and almost sinusoidal output. Good efficiency was obtained in the frequency range from 400 Hz to 1 kHz. Furthermore, we propose a dc-dc converter for coupling two independent dc power sources. The dc-dc coupling converter has bilateral power transfer and ease of controlling the transferred power. The basic operation of the dc-dc coupling converter is described.
Spin-wave localization in ferromagnets with random anisotropy
Authors: Serota R. A.
Published: July 2002

We argue that in a three-dimensional Heisenberg ferromagnet with weak random-axes anisotropy and large magnetization, induced by the magnetic field, the low-frequency spin waves will be localized. Two regimes are distinguished: in smaller fields, the regime with the field-dependent correlations of the transverse magnetization, i.e., the ferromagnet with wandering axis (FWA); in larger fields, the mean-field (MF) regime with the transverse magnetization uncorrelated from site to site. Using the approach developed for ferromagnets with uniaxial random-strength anisotropy, we find that the mobility edge in both FWA and MF regimes scales as λmob∝(ΔM/M)−1. Here λ is the spin wavelength and ΔM is the deviation from the saturation magnetization M. It is known that ΔM∝H−1/2 in the FWA regime and ΔM∝H−2 in the MF regime. Thus, the mobility edge can be tuned by the magnetic field.
Fractal analysis of magnetic aftereffects in the amorphous alloy Fe40Ni40P14B6 at 500 K (abstract)
Authors: Rivas J. , López-Quintela M. A. , Walz F. , Kronmüller H.
Published: July 2002

Magnetic aftereffects (MAEs) of the initial reluctivity have been measured over times of 1–106 s in the as-quenched state of amorphous alloy Fe40Ni40P14B6 at 500 K. A considerable decrease in the relaxation amplitude observed for times t>103–10 s has been interpreted in terms of a superposition of two different mechanisms resulting from (i) quasi-reversible, local rearrangements of two-level systems, and (ii) irreversible, wide-range order relaxation due to the migration of free volumes.2 Here we report on the results obtained from fractal analysis of the short-time MAE region (t≲200 s). Fitting of the stretched exponential,3 exp[−(t/τ)ρ], (0<β<1), to the experimental data yielded values of ρ in the range 0.15–0.30. This implies a spectral (fracton) dimension d̃ of 0.3–0.6 for this alloy. In terms of a postulated ultrametric distribution of random energy barriers, this means a hierarchy with a low degree of ramification (Z∼1.2).
Atomic structure and thermal stability in amorphous rare-earth–transition-metal magneto-optic alloys (abstract)
Authors: Robinson C. J. , Samant M. G. , Marinero E. E. , Cargill III G. S.
Published: July 2002

The technique of EXAFS has been used to study local atomic structure and thermal stability in amorphous thin-film alloys of TbFe, TbFeCo, TbFeCoAu, and DyFe. The rare-earth–transition-metal (RE-TM) films used were coated on the underside and topside by additional dielectric layers of Si3N4 to prevent oxidation during annealing. The EXAFS data were obtained by direct measurement of sample current in a total electron yield technique of data collection. The applicability of this method of analysis to the particular magneto-optic sample structure used is discussed with results of atomic local site geometry and limitation of the technique. Calculations from Fe K-edge data in TbFe and TbFeCo samples yield an Fe nearest-neighbor distance of 2.50±0.10 Å and an average coordination number of 11.0 representative of a dense random-packed amorphous structure. On annealing to 400 °C a second-nearest-neighbor distance and second shell structure is observed in the radial distribution functions as bccFe precipitates into the amorphous matrix. The addition of small amounts of Au into the RE-TM alloy is shown to stabilize the amorphous structure and prevent this process of atomic rearrangement of Fe through a process of stearic pinning. Analysis of Tb Liii–edge data is also discussed in addition to measurements of magnetic parameters Hc and Ku relevant to application in optical storage media.
Thermal demagnetization and randomness of domain nucleation in single-phase Nd2Fe14B
Authors: Luo Yang , Ji Qigan , Zhang Nin
Published: July 2002

The general behavior of the domain structure in Nd2 Fe14 B as a function of temperature has been reported in an earlier paper [Y. Luo, N. Zhang, and X. Su, Acta Metall. Sin. 23, A136 (1987)]. In order to clarify some details of the temperature variation of domain structure in the basal plane of this material, we have now made observations on a single-phase sample of Nd2 Fe14 B. We find that the optical contrast between antiparallel domains, using the Kerr effect for observation, is approximately proportional to the saturation magnetization; both decrease with increasing temperature. The main basal-plane domains are unchanged by heating, but the supplementary closure domains (cone-shaped reversal domains) change in size and shape, and may even disappear, when the sample is heated above 240 °C. Since the domain nucleation process is to some extent random, the domain pattern is different after each thermal demagnetization cycle above the Curie temperature.
Electron correlation and magnetism in NiTi amorphous alloys near the ferromagnetic transition (abstract)
Authors: Mackay K. D. , Friend R. H.
Published: July 2002

In recent years it has been shown that the transport properties of amorphous metals at low temperatures can be reasonably described using the theories of quantum interference (Q.I.) and electron-electron interactions (E.E.). Normally the E.E. term is much smaller than the Q.I. term except at the lowest temperatures.1 However, in the presence of paramagnons this E.E. term can be considerably enhanced.2 We present measurements of resistivity (0.1–300 K), magnetoresistivity (0–12 T), and Hall coefficient on a series of sputtered NiTi and CuNiSi amorphous alloys with particular emphasis on compositions on the paramagnetic side of the ferromagnetic transition and have analyzed the results in terms of the above theories including the contributions from spin fluctations.
Field and power dependence of auto-oscillations in yttrium-iron-garnet films
Authors: McMichael R. D. , Wigen P. E.
Published: July 2002

The nonlinear response of the magnetic spin system in yttrium-iron-garnet (YIG) thin films to high-power ferromagnetic resonance (FMR) at perpendicular resonance was studied and the results are presented. A diagram of the regions of auto-oscillation of the system as a function of field and power is presented which shows the modes that appear in low-power FMR becoming unstable to auto-oscillations with increased power. The auto-oscillations exhibit periodic, quasiperiodic, period doubling, and chaotic behavior with typical frequencies in the MHz range. The domains of oscillatory behavior due to individual resonance modes are seen to merge and shift to lower fields as power is increased. Possible mechanisms for the behavior are proposed.
The stress dependence of the ΔE effect in Terfenol-D (abstract)
Authors: Savage H. T. , Clark A. E. , Pearson D.
Published: July 2002

The stress dependence of the intrinsic change in Young’s modulus with magnetic field (the ΔE effect, DE) has been measured to 120 MPa in Terfenol-D (Tb0.27Dy0.73Fe2−x, 0<x<0.1) with the field H as a parameter. The sample, prepared by rf rapid zoning,1 consists of slablike dendrites with the [112̄] growth direction determining the longitudinal (stress and field) axis of the sample. A [111] direction is normal to the longitudinal axis. The data (Fig. 1) show an extremely large (eightfold) depression in Young’s modulus, comparable to that found in Fe-based amorphous materials. Earlier measurements on polycrystalline samples yielded DE=1.6. The value of DE observed here is attributed to the ‘‘jumping’’ of the magnetization between two easy axes of magnetization. These directions are stress dependent, parallel to the magnetically easy 〈111〉 directions at low stress. One rotates to a direction 14.75° from the [111] direction at high stress. A calculation of the stiff (high-field) Young’s modulus in the [112̄] direction using ‘‘infinite field’’ single-crystal elastic constants yielded a value of 114 GPa. The lower value in Fig. 1 is consistent with this result since Δc44∼1/H. Calculation of the field dependence of the modulus caused by ‘‘jumping’’ of the moment will be presented.
Detrimental effect of oxidation on magnetic properties of nonoriented electrical steel sheet
Authors: Günther K. , Bölling F. , Huneus H.
Published: July 2002

The conventional final heat treatment of Si+Al alloyed nonoriented electrical steel sheet is a continuous two-stage process with decarburization in the first stage and high-temperature recrystallization annealing in the second. The present investigation shows that this practice has an important detrimental effect on core loss and thus prevents the full optimization of the final product. This is due to the use of wet gas in the first annealing stage which causes harmful oxidation processes and, if nitrogen-containing atmospheres are used, also facilitates subsurface nitration during annealing at high temperatures in the second stage. Therefore, the current development of N. O. grades with superior magnetic properties is based on improved steels with extremely low carbon content, thus avoiding the conventional decarburization annealing with its associated detrimental oxidation processes.
Chaos and chaotic transients in yttrium iron garnet (invited)
Authors: Carroll T. L. , Pecora L. M. , Rachford F. J.
Published: July 2002

Long-lived chaotic transients are a prominent feature of the spin-wave behavior of spheres of yttrium iron garnet (YIG) being perpendicularly pumped in the region of the first-order Suhl instability. These transients may appear after a sudden increase in rf pumping power or during transitions between quasiperiodic auto-oscillations. The transients, which result from the collision of a chaotic attractor with the basins of attraction of multiple stable quasiperiodic attractors, vary in lifetime by more than six orders of magnitude, from milliseconds to hours, as a function of the rf driving field. The average lifetimes of these transients fit an extended Grebogi–Ott–Yorke scaling law. Roughening the surface of the YIG sphere drastically changes the behavior of these transients.
A model for the reflectivity in laser-substrate interactions
Authors: Cohen S. S. , Wyatt P. W.
Published: July 2002

We study the issue of reflectivity in interactions of laser beams with condensed matter substrates. In particular, we discuss the effect that the reflectivity has on the melting of silicon. The theory of the laser-solid interaction expresses the properties of the hot zone that forms in the solid in terms of the beam parameters, such as the power and the spatial profile. The value of the reflectivity determines the actual value of the deposited power, and hence greatly influences the properties of the hot zone. The reflectivity is temperature dependent, and hence it constantly varies during the period in which the laser power rises to its maximum value. Therefore, a meaningful model is required in order to properly account for its effects. We have developed such a dynamical model for the reflectivity. The results of this model compare well with relevant experimental measurements.
Deep levels in p-type GaAs grown by metalorganic vapor phase epitaxy
Authors: Wang P. J. , Kuech T. F. , Tischler M. A. , Mooney P. , Scilla G. , Cardone F.
Published: July 2002

We report a detailed deep level transient spectroscopic study in p-type Mg- and Zn-doped GaAs epitaxial layers grown by metal-organic vapor phase epitaxy. Dependence of deep level structures on doping concentrations and growth temperatures has been investigated. Over a wide range of growth conditions, four hole traps and an electron trap ranging in activation energy from 0.18–0.79 eV were measured in GaAs:Mg while only a single hole trap has been observed in GaAs:Zn.The presence of a certain trap and its concentration in GaAs:Mg depends mainly on the doping concentration in the layers. The total trap concentration in the GaAs:Mg decreases rapidly with doping concentration for p>4×1017 cm−3. The physical and chemical origins of several of these traps have been identified. The Mg-doped GaAs always exhibited a greater concentration of midgap trap levels than the Zn-doped material, regardless of dopant concentration or growth temperature. The overall defect structure and dopant incorporation characteristics indicate that Zn is the preferred dopant species.
Structural and elemental analysis of melt-processible high-temperature superconductors by surface science and x-ray diffraction measurements
Authors: Hermann A. M. , Sheng Z. Z. , El Ali A. , Mooney G. D. , Nelson A. J. , Goral J. , Kazmerski L. L.
Published: July 2002

We report the results of scanning electron microscopy (SEM), microprobe analysis (wavelength dispersive and energy dispersive spectroscopies), secondary-ion mass spectroscopy (SIMS), and x-ray diffraction measurements on a series of melt-processed high critical-temperature superconductors. The superconductors were synthesized through a melt reaction between TbBa2Cu3O7−x and nonstoichiometric rare-earth Ba-Cu-O oxides. The melt-processed samples are dense, largely void-free superconductors with critical temperatures in the 90–95 K range. Microprobe and SIMS data show the absence of Tb in surfaces of the interiors of samples which had been fractured to expose the interior regions. Comparative microprobe and SEM data are included for conventionally prepared sintered samples. Comparative x-ray diffraction studies are presented which show that the melt-processed samples studied have diffraction patterns nearly identical to those of sintered (rare earth)Ba2Cu3O7−x samples. In two of the three Y-based melt-processed superconductors studied, the compound stoichiometry from microprobe analysis is Y1Ba2Cu3O7−x. The evidence presented indicates that the TbBa2Cu3O7−x decomposes during the melt reaction.
Modifications in the one-particle Monte Carlo method for solving the Boltzmann equation with changed variables
Authors: Nedjalkov M. , Vitanov P.
Published: July 2002

Modifications in the one-particle Monte Carlo method are described when it is more convenient to change the variables in the Boltzmann equation. The physical interpretation of the coefficients in the equation obtained is shown. An example under the condition of symmetry about the field is considered. The results are compared with those obtained by other methods solving the Boltzmann equation.
Density of states in evaporated amorphous GaSe films using space-charge-limited current measurements
Authors: Micocci G. , Siciliano P. , Tepore A.
Published: July 2002

The gap-state distribution in vacuum-evaporated amorphous GaSe is studied by space-charge-limited current measurements. Samples with In/α-GaSe/In sandwich structures were used to obtain current-voltage characteristics. By using an analytical method the gap-state density N(E) over an energy range extending about 0.16 eV below the thermal equilibrium Fermi level EF0 is calculated. The resulting values are in agreement with the density of states N(EF0) at the Fermi level obtained from the dark-conductivity data for variable range hopping.
Application of computational fluid dynamics methods to a numerical study of electromagnetic wave scattering phenomena
Authors: Ling R. T.
Published: July 2002

The scattering of electromagnetic waves by an obstacle is formulated as a boundary value problem analogous to the fluid dynamic problem of flows past the obstacle. The transformed Helmholtz equation in terms of Debye amplitude functions can be solved numerically in a manner similar to the solution of governing fluid flow equations. The far-field radiation condition and media interface boundary condition can also be enforced in a manner similar to the enforcement of the free-stream condition and flow-tangency condition. Various numerical methods in computational fluid dynamics CFD can be carried over for the computation of scattering characteristics. An example problem of the scattering of plane electromagnetic waves by a perfectly conducting sphere is solved in the frequency domain by a finite difference method based on the concept of generalized scattering amplitude. Numerical results are presented for ka=2.9, where k is the wave number equaling 2π divided by the wavelength and a is the radius of the sphere.
Deuterium interactions in oxygen-implanted copper
Authors: Myers S. M. , Follstaedt D. M.
Published: July 2002

The interaction of deuterium (D) with Cu2O precipitates in Cu was investigated at temperatures between 300–800 K using ion implantation, nuclear-reaction analysis, and transmission electron microscopy. The exothermic reduction reaction between D and Cu2O to form D2O was found to occur readily at temperatures down to 300 K, with appreciable decomposition of the water and D release occurring only above 600 K. These processes, together with much weaker irradiation-defect trapping in the implanted Cu-Cu2O-D alloy, were quantitatively described by using an advanced transport formalism with independently evaluated reaction and trapping enthalpies. Buried oxide sinks formed by ion implantation were shown to provide an advantageous method of measuring hydrogen permeabilities and chemical potentials.
Low field investigation of the gold donor level in silicon by noise and resistance measurements
Authors: Jang S.-L. , Bosman G.
Published: July 2002

The generation-recombination noise spectral density and the resistance of an overcompensated gold-doped silicon p+-p−-p+ resistor with boron dopant concentration Na=1.0×1015 cm−3 are measured as a function of temperature in the low field regime. The temperature dependence of the plateau values of the noise spectra and the resistance are used to extract the trap energy, the hole capture cross section, and the spin degeneracy factor. The values so obtained are in good agreement with published data in the literature, indicating that this method is an accurate technique to investigate deep-level properties.
Strong lumped circuit solitons
Authors: Rosenbluth M. N. , Waltz R. E.
Published: July 2002

The formation, breakup, and temporal compression of strong solitons in a lumped circuit (dispersive) nonlinear LC-transmission line is treated. The strong lumped circuit solitons are characterized by the condition that almost all the signal charges may instantaneously appear on a simple circuit stage and travel much faster than the linear circuit signal speed. Under these conditions, the usual nonlinear Korteweg–de Vries theory of lumped nonlinear transmission lines does not apply. Properties of the soliton structure are derived; in particular, the rate at which energy is radiated for nonuniform parameters (i.e., temporal compression) is calculated and compared with numerical simulation.
Nuclear magnetic resonance imaging as a tool to characterize defect densities in solids
Authors: Suits B. H. , Lutz J. L.
Published: July 2002

Nuclear magnetic resonance imaging methods demonstrate the spatial variation of 23Na signal intensity in NaCl which results from an impact-induced inhomogeneous defect distribution.
1/f noise in ring geometries
Authors: Clevers R. H. M.
Published: July 2002

The effective number of carriers Neff of a sample with ring geometry is recalculated analytically and numerically. The Neff of the sample with ring geometry as calculated by Bisschop (Ph.D. thesis, Eindhoven University of Technology, Eindhoven, 1983, Chap. V) is erroneous. Therefore, the 1/f noise parameter α of 10−7 at 300 K of a p-Si sample with ring geometry given by Bisschop must be replaced by 10−5.
Scattering effects on resonant tunneling in double-barrier heterostructures
Authors: Gu B. , Coluzza C. , Mangiantini M. , Frova A.
Published: July 2002

In this paper we use the transfer matrix approach to investigate the effect of scattering in the well on resonant tunneling in double-barrier heterostructures. We consider a double-barrier heterostructure, in which there is a uniform distribution of scattering centers throughout the well, and use the δ-type function to describe the perturbation potential of the centers. For simplicity, we only consider one dimension. From model calculations of the transmission probability of the system we find, in agreement with experimental observations, that resonant peaks arising from the quantized states in the well are always present, provided the concentration of the scattering centers is not too high. The effect of scattering is to lower the tunneling current and to shift and broaden the peak of the resonant tunneling spectrum.
Photoluminescence decay time studies of type II GaAs/AlAs quantum-well structures
Authors: Dawson P. , Moore K. J. , Foxon C. T. , ‘t Hooft G. W. , van Hal R. P. M.
Published: July 2002

We have investigated the temperature dependence of the photoluminescence (PL) decay kinetics of a series of GaAs/AlAs quantum-well structures where the GaAs thickness was kept constant at 25 Å and the AlAs was varied between 41 and 19 Å. In these structures the band alignment is type II and the dominant photoluminescence process at 4 K is due to recombination of excitons involving electrons confined at the AlAs X point and holes in the GaAs. At 4 K on the low-energy side of the zero-phonon type II transition the PL decay is a single exponential over at least two decades. The time constant of this decay is a strong function of the AlAs layer thickness. The variation of this decay time is described by a change in the oscillator strength of the type II process due to the change in the mixing between the Xz (AlAs) electron states and the Γ (GaAs) electron states. At higher temperatures (T>15 K) the photoluminescence intensity and the decay time decrease very rapidly with increasing temperature. This is due to the increased influence of nonradiative processes as the type II excitons become delocalized.
Effects of Al and Ti interlayers on Sb/(HgCd)Te interface behavior
Authors: Davis G. D. , McKinley J. T. , Kilday D. G. , Margaritondo G.
Published: July 2002

The effects of 0.1 and 0.5-nm Al and 0.02-nm Ti interlayers on the Sb/(HgCd)Te system have been investigated with photoelectron spectroscopy using synchrotron radiation. With no interlayer, the Sb forms an abrupt, uniform overlayer with a stoichiometric interface and causes no change in the band bending induced during the cleaving process. With the two Al interlayers Sb exhibits less uniform deposition and diffuses into the semiconductor enough to reverse the additional band bending caused by Al in-diffusion. It also reacts with the elemental Al of the 0.5-nm interlayer to form AlSb. The increased disruption of the (HgCd)Te surface by the Ti interlayer leads to enhanced out-diffusion of Te in addition to Sb clustering and in-diffusion. In this case, Sb is able to compensate for the inversion occurring during cleavage and returns the surface to a nearly flat-band condition.
High-power operation of 830-nm AlGaAs laser diodes
Authors: Shinozaki K. , Watanabe A. , Furukawa R. , Watanabe N.
Published: July 2002

We have developed a high-power, semicylindrical-shaped waveguide inner stripe laser diode (SCILD) using a current confinement structure. The structure is optimized for high-power operation without catastrophic optical damage (COD) which limits the maximum available optical power. We confirm that the optical electric field shape in the LD waveguide layer obtained from our analysis coincides with the micrograph of the COD on the device facet. The SCILD is emitted in the fundamental transverse mode up to 190 mW. The full beam angles between the half-power points were 10° and 30° in the directions parallel and perpendicular to the junction plane, respectively. The characteristic temperature of the threshold current was 152 K.
High-frequency strain response in ferroelectrics and its measurement using a modified Mach-Zehnder interferometer
Authors: Zhang Q. M. , Jang S. J. , Cross L. E.
Published: July 2002

In this paper we report on a modified Mach-Zehnder interferometer which is capable of measuring the ultrashort time strain response of a sample. Using this instrument, the dispersion of piezoelectric and electrostrictive coefficients of several commonly used ferroelectrics was measured. The strain switching behavior of lead lanthanum zirconate titanate (PLZT) 9/65/35 driven by a square pulse electric field was studied. The results show that the switching rise time of the strain response for PLZT 9/65/35 can be much shorter than 5 μs at a pulse field strength near 25 kV/cm and that the fall time of the strain response is considerably shorter than the rise time in the experimental field strength range.
ZnSe homoepitaxial layers grown at very low temperature by atmospheric pressure metalorganic vapor-phase epitaxy
Authors: Yodo T. , Koyama T. , Ueda H. , Yamashita K.
Published: July 2002

ZnSe homoepitaxial layers with high crystalline quality were grown on (100) ZnSe substrates (grown by the iodine vapor transport method) between 190 and 250 °C. The surface morphologies of homoepitaxial layers (homoepilayers) grown below 250 °C were all mirrorlike. The concentration of self-activated (SA) centers is related to the growth temperature. The band-edge photoluminescence (PL) intensity increases drastically with increasing temperature from 190 up to 210 °C, decreases above 210 °C, and the SA-PL intensity increases monotonically as the growth temperature increases. The mechanism of suppressing the occurrence of SA centers below 250 °C is assumed that the concentration of Zn vacancies diffused from the highly iodine-doped ZnSe substrates into the ZnSe homoepilayers reduces at this temperature region. The SA-PL intensity of the ZnSe homoepilayer with the strongest band-edge emission (grown at 210 °C) is the same or weaker than that of the best ZnSe heteroepitaxial layer (heteroepilayer). Below 200 °C, the FWHM of the ZnSe (400) diffraction is 14 arcsec which is the best value we have ever obtained, though the growth temperature seems to be too low to maintain the crystalline quality. The comparison on the crystalline quality with the ZnSe heteroepilayers is discussed in detail from the viewpoints of the epitaxial growth mechanism.