bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin-cluster effects in the spin glass Fe2−xTi1+xO5 as observed by transverse-field muon-spin relaxation (abstract)
Authors: Boekema C. , Flint J. A. , Weathersby S. P. , Lichti R. L. , Chan K. C. , Cooke D. W. , Hutson R. L. , Schillaci M. E. , Rempp H. , Brabers V. A. M. , Oostens J.
Published: July 2002

Transverse-field muon-spin-relaxation (μSR) experiments on the anisotropic spin glass Fe2−xTe1+xO5 were performed near and below the spin-glass temperature (x=0.25; Tg=43.5 K). Earlier1 single-crystal work has indicated that spin-cluster effects are present in zero field slightly above the glass temperature. The effect of a transverse-field (B⊥) upon the spin-glass transition and state has been studied by measuring the temperature dependencies of the muon hyperfine parameters at B⊥=5 kOe, and the field dependencies at 7, 17, and 49 K. The B⊥ direction has been chosen to be perpendicular to the c axis. Spin-cluster effects, as signaled by anomalous muon-spin relaxation, have been observed above 44 K in 5 kOe transverse field; further, exponential muon-spin relaxation above 60 K is observed as expected for a paramagnet. A substantial difference in the field dependence of the relaxation rate is seen between 49 K data and data taken at temperatures (7 and 17 K) well below Tg. A shift in Tg due to an applied magnetic field (⊥ c axis) has not been observed. These single-crystal μSR results will be compared with earlier μSR work on metallic spin glasses, where in polycrystalline samples no spin-cluster effects have been observed.2
To what extent does the resonant level model describe heavy-fermion systems?
Authors: Edelstein A. S.
Published: July 2002

The resonant level model is applied to the heavy-fermion systems CeCu6 and CeAl3. It is demonstrated that the resonant level model, if suitably generalized to include crystal-field effects, provides an approximate fit to both the specific heat and susceptibility. This is accomplished by including the effects of the larger energies, the crystal-field splittings, first. The Kondo effect is assumed to dominate the behavior of the magnetization in the easy direction. To simulate the effect of spin fluctuations and to fit the low-temperature CeAl3 data, a temperature-dependent width is postulated.
Magnetic anisotropy in SmCo amorphous films
Authors: Numata Takuhisa , Kiriyama Hideki , Inokuchi Seiji , Sakurai Yoshifumi
Published: July 2002

Magnetic anisotropy in sputter-deposited SmxCo100−x amorphous films depended on the substrate temperature even for a narrow composition range of 18≤x≤26. Deposition between 90 and 140 °C brought a negative perpendicular anisotropy. All the films were magnetically isotropic in the film plane with zero torque curve for a field rotated in the film plane, suggesting that the negative perpendicular anisotropy did not come from easy axes of uniaxial anisotropy due to some structures being in the film plane. A large negative anisotropy vanished after annealing. On the other hand, a positive anisotropy which overcomes the demagnetizing energy was induced by a deposition at 60–90 °C. Films with a positive perpendicular anisotropy had a relatively large electric resistivity and hence a large Hall resistivity. The magnetostriction measurement showed that a stress (film/substrate)-induced anisotropy did not play an important role in both positive and negative perpendicular anisotropies. A possible origin of the large negative anisotropy is internal stress and that of the positive anisotropy is some microstructure which appears at a substrate temperature of 60–90 °C, at which temperature the internal stress may be reduced.
The influence of hydrogen on a hyperfine field of the amorphous alloy Fe83.3B11.2Si3.5C2 (abstract)
Authors: Gui RongLi , Chen WenZhi , Llo KaiYuan
Published: July 2002

We present our results about the influence of hydrogen on the alloy Fe83.3B11.2Si3.5C2. The samples were hydrogenated by electrolysis and recovered at room temperature for different length of time. Sample A contains no hydrogen and B–E is recovered 1, 10, 80, and 130 h, respectively, after charging. The result of Mössbauer effect spectrum of 57Fe of these samples with different contents of hydrogen has demonstrated that the structure in alloy has changed and adjusted, and the conditions of nearest-neighbor numbers (nnn) of Fe atoms have changed as well as. The hydrogen has made the average hyperfine field 〈Hhf〉 from 251 to 263 kOe. With the Günser method11 we have analyzed and compared the HFD curves obtained from the Hesse program, and found that nearly every peak in the HFD curves has moved to a higher field after charging, then returned during recovery (Fig. 1). The peak corresponding to the atoms which have 10 nnn atoms is more sensitive to hydrogen, and the hydrogen charging was mostly infiltrated into the polyhedral that has 10 nnn atoms. These results were in correspondence with the conclusion of the measurement of the saturated magnetization.
Spin reorientation processes in hard magnetic pseudoternaries (ErxNd1−x)2Fe14B
Authors: Ibarra M. R. , Marquina C. , Algarabel P. A. , Arnaudas J. I. , del Moral A.
Published: July 2002

The effect of the different kinds of anisotropies (axial, conical, and planar) competing in the same compound with different grades of influence with the concentration, x, produces a wide range of peculiar behaviors. We have studied the magnetic anisotropy in this series by means of the thermal evolution of the spin reorientation transition (SRT) with concentration. We have measured the ac initial magnetic susceptibility for the concentrations x=0, 0.2, 0.4, 0.6, 0.8, 0.9, and 1. The results clearly show peaklike anomalies which allow us to obtain the critical temperature for the phase transition. We have also measured the magnetization parallel and perpendicular to the applied magnetic field on magnetically aligned powder samples in order to determine the thermal evolution of the orientation of the easy magnetization direction. The compounds with intermediate concentrations (0.2≤x≤0.8) present two peaklike anomalies in the range of temperature measured (3.5–350 K), which have been associated with critical phenomena related to the SRT (axial→cone 1 and cone 1→cone 2). The remaining concentrations display SRT axial→planar in the case of Er-rich compounds and axial→cone in the Nd-rich ones.
Magnetic properties of La2(Fe1−xCox)14B and Nd2(Fe1−xCox)14B
Authors: Villas-Boas V. , Missell F. P. , da Cunha S. F.
Published: July 2002

Samples of composition Nd15(Fe1−xCox)77B8 and La15(Fe1−xCox)77B8 were produced by arc melting and subjected to prolonged heat treatments. Metallographic analysis and x-ray diffraction revealed the presence of the magnetic La2(Fe1−xCox)14B phase in the La-based materials; lattice parameters for x=0–1 were determined. High-temperature magnetization measurements allowed the Curie temperature Tc to be determined. The substitution of nonmagnetic La for Nd results in a nearly constant decrease (ΔTc≊40 K) in the ordering temperature of these compounds, in contrast to the results of Y substitution. A molecular field analysis of the data shows that 3d-4f  exchange is relatively constant with increasing Co substitution, while 3d-3d exchange increases sharply. These measurements are compared with results in Fe-rich La15(Fe1−xMnx)77B8 and Nd15(Fe1−xMnx)77B8.
Fabrication of transparent iron-oxide films by means of sol-gel synthesis (abstract)
Authors: Yamaguchi K. , Fujii T. , Kuranouchi S. , Kaneko A.
Published: July 2002

Transparent iron-oxide films were fabricated by sol-gel synthesis using a solution of ferric nitrate (III) dissolved in ethylene glycol.1 The solution was kept at 80 °C and stirred constantly in a nitrogen atmosphere. The gel with an appropriate viscosity was spin coated on soft glass plates, then dried and heated in air at various temperatures for 5 h. The films thus prepared are about 0.2 μm thick, amber colored, and especially transparent in the near-infrared region, whose transmittance exceeds 90%. Maximum saturation magnetization 4πMs=0.74 kG [curve (a)] was obtained by annealing at 450 °C, which is still insufficient to use practical application. Reduction heat treatment in a hydrogen atmosphere is found to be very effective to improve magnetic properties: 4πMs is increased to 3 kG [curve (b)], which is about four times as large as the previous one, but the films become semitransparent due to formation of magnetite particles. Original high transmittance recovers by successive annealing in air at 400 °C without any degradation of magnetic properties [curve (c)], where diffraction peaks of maghemite were observed. This strongly suggests that magnetic anisotropy may be arbitrarily controlled by forming linear chains of ferromagnetic particle clusters through reduction heat treatment in a magnetic field. Faraday rotation θF of the samples was also measured. These films are promising as a new type magneto-optic material.
Spin-wave linewidth of Ga-substituted YIG
Authors: Tang Yi , Yin Guang-jun
Published: July 2002

In this paper the first-order spin-wave instability threshold hc and the spin-wave linewidth ΔHk were studied in a series of single YIG and Ga-YIG crystal spheres at room temperature and at X band. The experimental results show that the k and θk dependence of ΔHk can be expressed as ΔHk=A+B sin2 2θk+Ck, and ΔHk(k=0, θk=π/2) increases linearly with the increase of the concentration of Ga substituted in YIG.
Nonuniform ac magnetostriction in metallic glass: Model and measurement using a fiber-optic strain gauge (abstract)
Authors: Koo K. P. , Dagenais D. M. , Bucholtz F. , Dandridge A.
Published: July 2002

The performance of magnetic transducers using soft magnetic materials such as metallic glass is degraded by static thermal or mechanical stresses,1 demagnetization, and magnetic hysteresis. We have investigated these effects using a distributed parameter model for the ac magnetostrictive response and have measured the response experimentally in strip and cylindrical samples of Metglas 2605 S2, using a fiber-optic strain gauge. The model assumes a two-element system with a different coercive field and a relative ac phase delay between the two elements, and an asymmetry in the ac response. The measurement technique uses an optical fiber interferometer to measure the small-signal ac magnetostrictive response as a function of a relatively large dc magnetic field scan. From a single measurement we determine the spread of the coercive magnetic field and the relative phase in the ac responses over the entire magnetic sample. Further measurements confirm the predictions of the model such as a residual signal at the ac modulation frequency.
Relation between dynamic domain wall movement and crystal orientation in advanced grain-oriented silicon steel
Authors: Yabumoto M. , Matsuo Y. , Kobayashi H. , Nozawa T.
Published: July 2002

Dynamic domain wall movements in advanced grain-oriented silicon steel (GO) magnetized in alternating fields of 50 Hz were observed using the line-sampling stroboscopic technique in a scanning electron microscope. Domain wall interactions among grains were investigated in relation to the differences in crystal orientation. Several kinds of GO which differed in permeability and iron loss, and GO artifically domain refined were examined. It was shown that an essential factor to obtain lower losses in GO is uniform domain wall movements in each grain. Differences of wall displacement speeds among grains were smaller in GO with orientation near (110) [001] than in GO with orientation deviated from (110) [001]. After artificial domain refining these differences became much smaller, and subsequently much lower losses were obtained in GO with orientation near (110) [001].
Nonlinear dynamics of spin waves (invited)
Authors: Jeffries Carson D. , Bryant Paul H. , Nakamura Katsuhiro
Published: July 2002

For a yttrium-iron-garnet sphere at room temperature, an experimental study is made of the first-order Suhl spin-wave instability using perpendicular pumping at 9.2 GHz with the dc field parallel to the [111] crystal axis. The dynamical behavior of the magnetization is observed with high resolution by varying two control parameters, dc field (580<H0<2100 G) and microwave pump power (1<Pin <200 mW). Within this parameter space quite varied behavior is found: (i) onset of the Suhl instability by excitation of a single spin-wave mode with very narrow linewidth (<0.5 G); (ii) when two or more modes are excited, interactions lead to collective oscillations (‘‘auto-oscillations’’) with a systematic dependence of frequency (104–106 Hz) on pump power, these oscillations displaying period-doubling to chaos; (iii) quasiperiodicity, locking, and chaos occur when three or more modes are excited; (iv) abrupt transition to wide band power spectra (i.e., turbulence), with hysteresis; (v) irregular relaxation oscillations and aperiodic spiking behavior. A theoretical model of coupled modes is numerically evaluated and found to exhibit a behavior pattern similar to those observed experimentally.
Magnetic field dependence of surface acoustic wave velocity and attenuation in nickel thin films
Authors: Wiegert R. F. , Levy M.
Published: July 2002

The relative velocity ΔV(H)/V(H=0) and attenuation α(H) responses of 0.6 GHz Rayleigh-mode surface acoustic wave (SAW) pulses propagating through thin (<400 Å) films of nickel were measured as a function of in-film-plane dc magnetic bias field H. The films’ dc magnetoresistive response ΔR(H) was also measured. The sample’s ΔV(H)/V(H=0), α(H), and ΔR(H)/R(H=0) responses could be varied over respective ranges of 0.07%, 80 dB/cm, and 1.4% as H was varied from 0 to 90 Oe. Qualitative and semiquantitative correlations between ΔV(H) and α(H) indicate that the dynamic magnetoelastic coupling theoretically responsible for the previously observed SAW attenuation in nickel films also primarily determines the sample’s relative velocity response. The correlated ΔV(H)/V, α(H), and ΔR(H)/R data provide a useful experimental basis for characterization of dynamic and static magnetoelastic effects in ferromagnetic films.
Electric field effects on HgTe-based quantum wells
Authors: Yang Z. , Furdyna J. K.
Published: July 2002

The electronic states localized in CdTe/HgTe/CdTe quantum wells (QWs) in the presence of an electric field perpendicular to the layers of the QW are investigated theoretically. It is noted that at wavelengths close to the energy gap of the QW the optical properties of the structure change considerably when the field is applied. Such QWs may therefore have potential applications in electro-optical devices at wavelengths beyond 2 μm.
Electron mobilities of AlInAs and AlInAs/InP heterostructures
Authors: Aina Leye , Mattingly Mike
Published: July 2002

Electron mobilities at 300 K as high as 4500 and 9800 cm2 /V s are observed when AlInAs is grown on in situ-grown InP and GaInAs, respectively. These high anomalous mobilities, compared to those of material grown directly on InP substrates, are shown to be due to parallel conduction both in the AlInAs and in the two-dimensional electron gas present at the AlInAs/InP and AlInAs/GaInAs interface. To our knowledge, this is the first report of a two-dimensional electron gas for AlInAs/InP heterostructures. Theoretical estimation of the electron mobilities in AlInAs using realistic values of alloy scattering potentials have been used to show that the true mobilities of electrons in AlInAs are for material grown on InP substrates.
Optical absorption spectroscopy of hydrogen- and deuteron-implanted cadmium fluoride
Authors: Tatarkiewicz J. , Król A. , Breitschwerdt A. , Dobrowolski J.
Published: July 2002

A full-range (visible and infrared) study of the optical properties of CdF2 implanted with hydrogen and deuterium is presented. One strong absorption band was found at 280 nm (4.2 eV), whose intensity is proportional to the radiation damage introduced. Oxidation of CdF2 produces a similar absorption band, which suggests that the electronic transition takes place in an extended defect containing a cadmium vacancy. In the infrared region implanted samples exhibit two bands at about 3200 and 1600 cm−1. We assign these modes to water molecules vibrating on the surface. Measurements at low temperatures (after polishing) revealed weak localized vibrational modes of hydrogen and deuterium at 1550 and 1160 cm−1, respectively. Because of their temperature behavior we assign these lines to the second harmonics of implanted ion vibrations. Calculated oscillator strengths correspond to an effective charge of about 0.5e0 and show decreasing values for higher radiation damage.
A model of fragmentation by nonintersecting cracks
Authors: Fortes M. A. , Andrade P. N.
Published: July 2002

A two-dimensional model of fragmentation by randomly (Poisson) distributed and oriented nonintersecting cracks (T junctions) is discussed and the distribution functions of crack lengths and fragment areas are determined. Both distributions are well described by gamma distribution functions, the one for the fragment areas being very close to a pure exponential except at small fragment sizes, the probability of which decreases with decreasing size. The area distribution predicted by the model is compared with that for intersecting cracks, where the probability increases without limit as the size decreases. Differences are predicted for the distribution of fragment sizes resulting from simultaneous (dynamic) fragmentation and successive fragmentation (comminution).
Shock processing of materials with laser initiated spherically convergent detonations
Authors: Mayer Frederick J. , Fechner Walter B. , Maynard Robert L. , Schmerberg Nancy W. , Wixom Michael R.
Published: July 2002

We describe a new technique for dynamically compressing materials using small scale spherically converging shock waves driven by laser initiated high explosives. This technique uses spherical targets consisting of an outer explosive shell of 1–2 cm diam, and an inner sample core 0.48–0.96 cm diam. The shock waves result from a detonation wave generated near the outer surface of the explosive by a high-power laser. Spherical convergence and shock impedance matching produce ingoing shock waves in the core which have pressure amplitudes much greater than the detonation pressure of the explosive. Shock pressures in the sample core are typically in the range 10–200 GPa depending on the radius, density, and composition of both the explosive layer and the inner core. We discuss the hydrodynamic modeling of our implosion process, the conditions required for laser initiated detonation, and the results of boron nitride and carbon recovery experiments.
Development of a scanning minority-carrier transient spectroscopy technique with optical injection and full transient analysis
Authors: Heiser T. , Mesli A. , Courcelle E. , Siffert P.
Published: July 2002

A scanning minority-carrier transient spectroscopy with optical injection and full transient analysis is developed. The continuity equation is solved with adequate injection and boundary conditions in order to determine the optimum experimental conditions and the corresponding optimum spatial resolution. A numerical treatment is implemented which filters out the noise component of the transient, improving the sensitivity of the technique. It allows us to make a fit to the transient, to check its exponential character and to treat certain cases of nonexponential behavior. The technique is applied first to a step distribution of laser-induced defects and results can be obtained which are in good agreement with theoretical predictions. Finally, the gettering of gold to dislocations during a rapid thermal annealing is illustrated using this technique.
Spectroscopic analysis of insulating crystal fibers
Authors: Buoncristiani A. M. , Byvik C. E. , Albin S.
Published: July 2002

A new technique for investigating the optical properties of solid-state laser materials using single-crystal fibers grown by a laser-heated pedestal-growth technique is described. Single-crystal fiber samples can be prepared more rapidly and less expensively than crystals grown by more conventional methods, however, they are smaller and less uniform making spectroscopic measurements difficult. A simple procedure for extracting the optical absorption and emission spectra of insulating crystal fibers is demonstrated with a titanium-doped sapphire fiber sample; results are comparable to those from Czochralski-grown material.
Light wave interference during laser drilling of polymer coatings
Authors: Pargellis A. N. , Au D. T. W. , Kestenbaum A.
Published: July 2002

A CO2 laser has been used to drill holes in a 150-μm-thick, UV-curable, modified acrylate, polymer coating a copper substrate. A typical hole is 100–150 μm in diameter. The holes in this study were each made with a single laser pulse of 10.6-μm wavelength, duration 100 or 200 μs, and 4–20 mJ energy. Two superimposed sets of periodic ripples have been observed on the hole walls. The shorter wavelength varies from 4.0 μm at the top of the hole to 5.3 μm at the bottom of the hole. The longer wavelength appears to be 13.2 μm and is attenuated as the wave propagates towards the copper substrate. The experimental data are compared with values calculated using a model that considers the interference of a standing wave inside the hole with radiation propagating through the dielectric surrounding the hole. The amplitude (trough-to-peak distance) of the waves in the hole wall is about half the wavelength of the standing waves. The long-wavelength waves (13.2 μm) yield ripples in the wall of 6.5-μm amplitude. These ripples give 13.0 μm (0.5 mils) as an ultimate lower limit for laser drilling holes using the 10.6-μm wavelengths obtained with a CO2 laser. Chemical etching of the polymer causes all of the holes to have thin rims surrounding the top of the hole. This is due to accelerated etching of the less cured polymer material inside the hole. A chemical etching process etches away some of the ripple pattern, particularly near the top of the hole.
Electronic and optical properties of deep levels in iron-doped InAsP alloys
Authors: Huang K. , Wessels B. W.
Published: July 2002

The electronic and optical properties of deep levels in Fe-doped InAsP grown by organometallic vapor phase epitaxy are investigated. Two deep levels associated with Fe are observed in the alloys. From measurements of the temperature dependence of resistivity, photoluminescence, and photoconductivity, the energy levels of iron in the alloys are determined for a wide range of compositions. The variation of the positions of the Fe energy levels as a function of composition is explained in terms of the vacuum-referred binding energies.
Estimation of dopant concentration and surface potential by x-ray photoemission spectroscopy
Authors: Ogama T.
Published: July 2002

Energy band bending in a surface layer of semiconductor can be detected using x-ray photoemission spectroscopy (XPS) from the change in binding energy when a metal layer is deposited on a semiconductor, when the detection angle of photoelectrons is varied, and when excitation sources with different energy are used. It is proposed that combinations of these methods to detect energy band bending can give the estimation of dopant concentration and surface potential caused by energy band bending from XPS measurement only. Numerical examples of these combinations are shown, and the available range of dopant concentration and surface potential using each of these combinations is discussed and compared with one another. It is shown that the improvement in the accuracy to measure binding energy greatly extends the available range of dopant concentration and surface potential in each combination. In practice, the combination of the measurements of the change in binding energy after metal deposition and the change in binding energy with the change in detection angle gives the widest available range.
NMR and NQR studies of copper oxide superconductors (invited)
Authors: Warren W. W. , Walstedt R. E. , Brennert G. F. , Bell R. F. , Cava R. J. , Espinosa G. P.
Published: July 2002

6 3 , 6 5Cu NMR and NQR measurements reveal remarkably different electronic character at the Cu(1) chain and Cu(2) plane sites in YBa2Cu3O7.0. In the normal state, spin-lattice relaxation rates at both sites are strongly enhanced relative to estimated d-band Korringa (T1) rates, but have sharply different temperature dependencies. Moreover, T1 anisotropy is greater than an enhanced Korringa model can account for. Below Tc, the temperature dependencies reveal significantly different spectra for quasiparticle excitation at the two sites with the strongest apparent energy gap occurring for the planar Cu(2) sites. At reduced oxygen content (YBa2Cu3O6.7) the relaxation at the Cu(1) sites is only slightly (∼30%) less than observed for YBa2Cu3O7.0 while the rates for the resonance at the frequency of the Cu(2) sites in YBa2Cu3O7.0 exhibit a large (∼2000 ×) decrease for a minority of planar Cu(2) sites indicates that these sites are electronically inactive. NMR shift measurements are used to analyze the susceptibility of YBa2Cu3O7.0 and obtain an upper limit for the electronic density of states.
Optical birefringence and successive phase transitions of hexagonal ABX3 -type antiferromagnets with spin frustration
Authors: Iio K. , Sano M. , Tanaka H. , Nagata K.
Published: July 2002

To investigate the successive ordering processes of the triangular lattice antiferromagnet CsNiCl3, a Heisenberg system with an easy-axis anisotropy, optical birefringence has been studied on various hexagonal ABX3 systems involving other types of anisotropy. The birefringence for light propagating along the c axis clearly shows that the basal plane component of spins in CsNiCl3 is ordered below the lower Néel point TN2. A cusplike anomaly in the temperature dependence of the birefringence for light propagating perpendicular to the c axis is observed at the upper Néel point TN1 of the Heisenberg system with an easy-axis anisotropy. A plausible explanation for this anomaly is presented in connection with a spin frustration effect.
Superconducting properties of melt-cast Bi-Sr-Ca-Cu-O (abstract)
Authors: Goldfarb R. B. , Ciszek T. F. , Evans C. D.
Published: July 2002

Sintered solid copper-oxide superconductors generally have an intergranular coupling component that is evident in curves of ac susceptibility versus temperature: a broad peak in the imaginary (loss) part, χ″, and a corresponding inflection in the real part, χ′.1 Polycrystalline Bi-Sr-Ca-Cu-O samples have been prepared from the melt. They are very different from typical sintered materials. Some have a single superconducting phase, while others have two superconducting phases. Most of the superconducting platelets are partially surrounded by nonsuperconducting material.2 An unusual feature of the susceptibility curves is that they show almost no coupling losses. This might be explained if the superconducting grains were isolated from each other, as is the case in susceptibility measurements of powdered superconductors.3 However, the characteristics of the melt-cast samples differ from those of powdered samples in three ways. (1) The resistivity goes to zero at low temperatures, which indicates some connectivity between crystallites. (2) χ′ approaches −1 at low temperature, indicating substantial bulk shielding. (3) χ′ decreases in magnitude with increasing field at low temperature, an effect not seen in powdered samples. We therefore believe that there is substantial superconductor grain-to-grain coupling, even though the susceptibility curves show little evidence of the usual intergranular coupling losses. We conclude that the coupling component in these melt-cast samples is virtually lossless.
Homogeneous fine-grained Mn-Zn ferrites by sintering of colloidally precipitated powders
Authors: Petrovich A. , Kumar K. , Williams C.
Published: July 2002

Colloidally precipitated powders were investigated for the synthesis of chemically homogeneous, uniformly fine-grained Mn-Zn ferrites. The process consists of the atomized dispersion of an aqueous solution of Mn, Zn, and Fe nitrates in an agitated solution of 1M ammonium hydroxide. This results in the coprecipitation of a fine colloidal mixture of Mn, Zn, and Fe hydroxides. The mixture is filtered, washed, dried, and heat treated to form agglomerated powders. The agglomerated powders are reduced in size and sintered after cold compaction. Sintering was performed at temperatures of 1100–1250 °C with oxygen partial pressures from 0 to 500 ppm in argon. Magnetic permeability and disaccommodation were measured on selected samples after an initial 0.5–5.0 Oe decaying sinusoidal field was applied to the specimens to excite time varying permeability. The permeability variation depended strongly on the magnitude of this excitation; both disaccommodation and accommodation were observed. The duplex structure typically associated with severe discontinuous grain growth was not observed for either of the two compositions examined over the range of sintering temperatures studied. Low levels of porosity were seen in samples sintered at 1150 and 1250 °C.
Effects of Co addition on the temperature dependence of the intrinsic coercivity in Pr-Fe-B sintered magnets
Authors: Hirosawa Satoshi , Sagawa Masato
Published: July 2002

Temperature dependence of the intrinsic coercivity (HcI ) of Pr17 (Fe0.9 Co0.1 )83−x Bx has been measured above room temperature and analyzed by expressing HcI as the difference between a term proportional to the anisotropy field (HA ) and a term corresponding to a local demagnetization field. The fraction in HA available as an impeding force against nucleation of inverse domains does not appear to be decreased by the Co addition in a magnet with a high boron content, indicating that magnetic correlation of hard magnetic particles is one of the key parameters which determines HcI in this type of magnet. It is also shown that changes in the local demagnetization field account for the heat treatment effects.
Chemical dry etching of GaAs and InP by Cl2 using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy system
Authors: Furuhata N. , Miyamoto H. , Okamoto A. , Ohata K.
Published: July 2002

Damage and contamination-free chemical dry etching of (100)GaAs and (100)InP by Cl2 was demonstrated using a new ultrahigh-vacuum dry-etching molecular-beam-epitaxy (MBE) system. This system consists of a combined etching chamber, an MBE chamber, and a sample preparation chamber, all at ultrahigh vacuum. A mirrorlike surface was obtained after etching at substrate temperatures ranging from 300 to 400 °C for GaAs, and from 200 to 400 °C for InP. In situ reflection high-energy electron diffraction observations were accomplished for GaAs, with a mirrorlike surface after etching, and (2×4) surface reconstruction was observed. Results show that a smooth surface was formed at an atomic level.
Electrical, optical, and structural properties of reactive ion beam sputtered hydrogenated amorphous germanium (a-Ge:H) films
Authors: Bhan Mohan Krishan , Malhotra L. K. , Kashyap Subhash C.
Published: July 2002

Electrical, optical, and structural properties of hydrogenated amorphous germanium (a-Ge:H) films prepared by reactive ion beam sputtering of a high-purity crystalline germanium target under varying deposition conditions have been studied. A detailed description of the deposition setup, preparation procedures, and techniques of property measurement is given. The dependencies on beam voltage, H2:Ar flow ratio, and substrate temperature of the room-temperature dark conductivity, optical band gap, hydrogen content, and ellipsometric and IR data are reported and analyzed. The minimum conductivity (10−4 Ω−1 cm−1) a-Ge:H films have been obtained for H2:Ar flow ratio of 16:1, and beam voltage and substrate temperature of 1000 V and 250 °C, respectively. These films contain a hydrogen concentration of about 11 at. % and show an optical band gap near 1.04 eV. The IR spectra reveal absorption bands corresponding to both monohydride (Ge-H) and dihydride (GeH2) groups for all the samples deposited. The monohydride absorption band is, however, completely absent in the films deposited at 350 °C. X-ray diffraction and spectroscopic ellipsometry analyses show that the films deposited at 350 °C are polycrystalline.
The aging of niobium and tantalum tritides: Evolution of hardness in comparison with other properties
Authors: Schober T. , Dieker C. , Trinkaus H.
Published: July 2002

Vickers hardness measurements on niobium and tantalum tritides of initial composition NbT0.0225 and TaT0.097, respectively, performed over the first 20 months after T charging, are reported and interpreted. For both tritides, the hardness increases monotonically, but in a decelerating rate, with the 3 He concentration built up upon T transmutation. At given 3 He concentration, the increase per unit 3 He concentration is stronger for Nb than for Ta. To interpret the observed hardness evolution, existing hardening theories are adjusted to the present microstructural situations. It is concluded that the microstructure developing on 3 He precipitation is more disperse in the Nb tritide than in the Ta tritide. These findings are supported by conclusions drawn previously from swelling, acoustic emission, and x-ray diffraction measurements of these materials.
Smith–Purcell oscillator in an exponential gain regime
Authors: Schächter Levi , Ron Amiram
Published: July 2002

A Smith–Purcell oscillator with a thick electron beam is analyzed in its exponential gain regime. A general expression is obtained for the dispersion relation of the oscillator, and the threshold current for self-sustained oscillations is found to be less than 1 A for radiation of 1-mm wavelength.
Acousto-optic performance of monomode dilute melt proton exchange waveguiding Bragg cells
Authors: Reid S. A. , Farr A. , Hall A. M. , Varasi M. , Annulli A. , Vannucci A.
Published: July 2002

The acoustic and acousto-optic performance of surface acoustic wave Bragg cells using waveguides fabricated by Ti diffusion and dilute melt proton exchange have been compared. All waveguides were monomode at 0.83 μm, and we report for the first time essentially identical acousto-optic performance for the two waveguides, with no significant degradation of properties being caused by the dilute melt proton exchange process.
Island films resulting from ion bombardment: Spectroscopic ellipsometry and Auger electron spectroscopy
Authors: Armstrong Michael J. , Muller Rolf H.
Published: July 2002

The effects of ion bombardment on the morphology of compact lead films of under 100 nm thickness were investigated by spectroscopic ellipsometry, Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). In contrast to the expected uniform removal of the surface by ion bombardment, on which the determination of composition profiles by AES is based, a nonuniform removal of material with the formation of pits or islands has been found to occur. The pitting is independent of the film preparation or the presence of an oxide overlayer. SEM confirmed the island nature of the surface. Spectroscopic eillipsometer and AES measurements agree well when interpreted in terms of surface coverage. Thus supporting the validity of the coherent superposition model for interpreting ellipsometer measurements of island films.
Effects of magnetic relaxation times on the shielding of a polarized electromagnetic pulse
Authors: Zayek F. , McKnight S. W. , Vittoria C. , Folen V. , Maisch W.
Published: July 2002

The shielding of a polarized electromagnetic pulse by a ferromagnetic thin film is calculated in the case where the magnetization is perpendicular to the incident field’s polarization. The effects of anisotropy, domain interaction, saturation, hysteresis, and magnetization response time are considered. Results show that best shielding occurs when the response time of the ferromagnetic film is the inverse of the rise time of the pulse. At its optimum frequency, a ferromagnetic alloy shields better than a copper film of the same thickness.
Photoacoustic detection of the superconducting transition in high T
c superconductors
Authors: Song Yang Sup , Lee Ho Keun , Chung Nak Sam
Published: July 2002

Photoacoustic measurements for polycrystalline samples of orthorhombic YBa2Cu3O7−x, GdBa2Cu3O7−x, and DyBa2Cu3O7−x have been carried out in the range of temperatures between 85 and 100 K. An anomalous change of photoacoustic signal due to the specific heat anomaly of the superconductor at transition temperature has been observed. The temperature at which the photoacoustic signal intensity changes anomalously has been found to correspond to the offset temperature of superconducting transition in resistivity measurement. The changes of photoacoustic signal have been analyzed using Rosencwaig and Gersho’s theory [J. Appl. Phys. 47, 64 (1976)]. The superconducting transition of the samples was, from the photoacoustic measurements, found to be a second-order transition with no latent heat.
Measurement of pulse lengthening with pulse energy increase in picosecond Nd:YAG laser pulses
Authors: Cutolo Antonello , Zeni Luigi , Berardi Vincenzo , Bruzzese Riccardo , Solimeno Salvatore , Spinelli Nicola
Published: July 2002

Taking advantage of a new technique, we have monitored the relative variations of time duration and mode size as a function of the pulse energy for 30-ps-long Nd:YAG laser pulses. In particular, by carrying out a statistical analysis, we have observed that the pulse time duration is an increasing function of the pulse energy, according to the theoretical modeling of passively mode-locked lasers. The measurements can be easily extended to the femtosecond regime.
Observation of sheath structure near a rf electrode in a magnetized afterglow plasma
Authors: Okuno Yoshihiro , Yagura Shinya , Fujita Hiroharu
Published: July 2002

The sheath structure near a rf electrode has been observed by measuring the spatial profiles of the potential and density in a magnetized afterglow plasma. Dependence of the structure on the rf frequency (10–40 MHz) and elapsed time during the afterglow in a periodic, pulsed rf discharge operation are obtained by a time resolved measuring method. The potential close to the electrode is found to increase with increasing frequency and with elapsed afterglow time, without much change of the density profile. In addition, a slight decrease of the electron temperature has been observed during the afterglow time, although the density is roughly constant.
Raman scattering study of carrier activation in zinc- and silicon-implanted and pulse-laser-annealed GaAs
Authors: Ashokan R. , Jain K. P.
Published: July 2002

This study reports the plasmon-LO-phonon coupled modes observed in the Raman spectra of GaAs implanted with p-type (zinc) and n-type (silicon) implants and then pulse laser annealed. The coupled modes are due to the interaction between LO phonon and free carriers and this allows a rough estimation of the carrier concentration from the frequency and width of the L− coupled modes. The wavelength dependence for λ=1.06 and 0.53 μm of the threshold power density for the best carrier activation is reported here. The width of the depletion layer is estimated in silicon implanted samples for various power densities of 22, 26, and 31 MW/cm.2
Defect-ordered phases in a multiphase Cu-In-Se material
Authors: Tseng B. H. , Wert C. A.
Published: July 2002

Several copper-deficient phases in a Cu-In-Se ingot were identified and characterized by electron diffraction and energy dispersive x-ray analysis. Some were phases already identified by x ray and electron diffraction. A new vacancy-ordered phase with composition close to Cu0.75In2.25Se4 was identified to have a thiogallate-type structure. A phase with composition close to CuIn5Se8 exhibited a polytype structure with both 7- and 14-layer stacking sequences.
Effects of shock waves on metal-semiconductor interfaces
Authors: Sin Wai-Cheong D. , Salansky N. M. , Glass I. I.
Published: July 2002

Extensive interdiffusion was found in metal-semiconductor contacts under shock wave compression. In Al coated Si samples, selected area diffusion began at a pressure of 0.46 GPa and increased with pressure. An interdiffusion coefficient of up to 10 cm2/s was obtained. The diffusion depth was found to vary as the square root of pressure varied. However, no diffusion could be found in pressure treated Sb on Si samples. The results showed that interstitial diffusion in thermal diffusion systems was responsible for the Al-Si interdiffusion. It demonstrated that the dominant diffusion mechanism in thermal diffusion (e.g., interstitial for Al) remains dominant under shock wave pressure diffusion. It also suggested that under shock wave pressure, the interdiffusion of metal-semiconductor contacts may exhibit the same behavior as in the case of thermal diffusion.
Effects of low-level boron doping on the photocurrent of amorphous silicon Schottky photodiodes
Authors: Kakinuma H. , Kasuya Y. , Sakamoto M. , Shibata S.
Published: July 2002

We have measured the photocurrent-electric field (Jph-F) characteristics of slightly boron (B) doped (0≤[B2H6]/[SiH4]≤10 ppm) amorphous silicon (a-Si:H) Schottky photodiodes with a configuration of Cr/a-Si:H/ITO. The measurements were performed with different bias directions and two light wavelengths (555 and 660 nm), and mobility-lifetime (μτ) products were deduced by two methods. One is by fitting the experimental plots to the theoretical curves developed by Crandall [Semiconductors and Semimetals (Academic, Orlando, FL, 1984), Vol. 21, Pt. B, p. 245.]. The other is a new one we have proposed where the transition electric field Ftr, at which Jph changes from space-charge-limited current to the theoretical curve given by Crandall, is applied to the relationship μτFtr=L, where L is the thickness of a-Si:H. It was found that the former method is applicable only where a-Si:H is homogeneously illuminated and no space charge is formed. On the other hand, the latter method is effective where a-Si:H is inhomogeneously illuminated and a space charge is formed in the carrier transit region. The μhτh deduced by the latter method increased from 2×10−9 to 3×10−8 cm2/V when the B-doping ratio was increased from 0 to 3 ppm, but remained nearly constant with further doping. In contrast, μeτe monotonically decreased from 2×10−8 to 2×10−9 cm2/V with increased doping. The (μτ)fit deduced by the former method coincides with the μhτh at doping ratios higher than 3 ppm, but did not at lower doping ratios probably because of a space-charge formation by deep hole trapping and incomplete homogeneous illumination. These changes in μτ are discussed microscopically in terms of the charge state of the dangling bond state.
Anomalous excitation-intensity dependence of photoluminescence properties of an asymmetric coupled quantum well structure
Authors: Tokuda Yasunori , Kanamoto Kyozo , Tsukada Noriaki , Nakayama Takashi
Published: July 2002

We report anomalous emission peak shifts as a function of excitation intensity in photoluminescence spectra from a p-i-n structure where asymmetric coupled quantum wells are embedded in the intrinsic region. Emission behavior can be explained in terms of an anticrossing of quantized levels: this occurs when the energy-band structure automatically becomes flat by means of reduction of the internal electric field by photogenerated carriers. This result may be of significance in creating novel all-optical devices where transition energies are able to be optically modulated.
Optical switching in the semiconductor directional coupler with saturated gain
Authors: Hwu R. J.
Published: July 2002

A detailed theoretical study of optical switching by gain saturation-induced phase shift in semiconductor directional couplers has been carried out by solving the electromagnetic equation for a spatially inhomogeneous refractive index distribution using the method of Yeh, Brown, and Szejn [Appl. Opt. 18, 489 (1979)]. The gain saturation-induced phase shift is calculated as a function of the antiguidance factor, injection current density, and input power. The results clearly show that the antiguidance factor and injection current density drastically affect the phase shift. However, the phase shift has only a weak dependence on the input power. In addition, it is also shown that the phase shift is proportional to the antiguidance factor and injection current density for a constant input power. Based on the results presented, the future of optical gain saturation-induced light switching in directional couplers should prove to be very promising.
Consideration on the void generation mechanism in electron-beam recrystallized silicon-on-insulator films
Authors: Horita Susumu , Ishiwara Hiroshi
Published: July 2002

Void generation phenomena in silicon-on-insulator (SOI) films are investigated in the pseudoline electron-beam(e-beam) recrystallization method, in which a linear molten zone is formed by a fast-scanned spot e beam. Then, based on these experimental results, a qualitative model is proposed, which describes that the formation of isolated molten spots in the SOI films due to the heat-sink effect of the seed regions and the subsequent volume shrinkage or contraction of Si due to melting are essential in the void generation. In derivation of this model, the initial process of the void generation is discussed from a viewpoint of thermodynamics. Finally, using this model it is shown that the perforation seed structure, in which rectangular or circular seed regions are separately arranged along a line, is effective for suppressing the void generation.
Nature of the oscillatory surface smoothness and its consequence during molecular-beam epitaxy of strained layers: A computer simulation study
Authors: Ghaisas S. V. , Madhukar A.
Published: July 2002

Computer simulations show that differences in the molecular-anion incorporation rates at cluster edges (steps) and terraces during molecular-beam-epitaxical growth of compound semiconductors, if present, give rise to a double-peak damped oscillatory behavior of the growth front smoothness at sufficiently low anion pressures. For lattice-mismatched systems such differences can be enhanced by the difference in strain at cluster edges and at terraces. Only under such a situation is the dynamics of the surface smoothness found to be similar to the reported double-peak structure in reflection high-energy electron-diffraction specular-beam intensity during growth of Inx Ga1−x As on GaAs(100).
Influence of crack velocity thresholds on stabilized nonequilibrium fracture
Authors: Cook Robert F.
Published: July 2002

The time dependence for crack extension in stabilizing mechanical energy release rate fields has been analyzed, including the thermodynamic threshold for crack motion. Analyses based on crack velocity relations ignoring the threshold predict cessation of crack motion only at infinite crack lengths, in clear contrast to experimental observations. The new analysis predicts that crack motion will cease at finite crack lengths, in accord with experimental results, and includes the zero threshold result as an asymptotic limit.
Low-resistivity, YBa2Cu3O7-to-silver electrical contacts by plasma spraying
Authors: Katz J. D. , Willis J. O. , Maley M. P. , Castro R. G.
Published: July 2002

A simple cost-effective method has been developed for the fabrication of low-resistivity contacts for high-temperature superconducting ceramics. Surface resistivities have been measured for the contacts in the 10−8 Ω cm2 range at 76 K. The fabrication method involves application of a silver pad to the ceramic by plasma spraying and then attachment of leads by soldering.
Transport in reversibly laser-modified YBa2Cu3O7−x superconducting thin films
Authors: Krchnavek Robert R. , Chan Siu-Wai , Rogers C. T. , De Rosa F. , Kelly M. K. , Miceli P. F. , Allen S. J.
Published: July 2002

A focused argon ion laser beam in a controlled ambient is used to modify the transport properties of superconducting YBa2Cu3O7−x thin films. The laser-modified region shows a sharp transition temperature (Tc≊76 K) that is reduced from the unmodified regions of the film (Tc≊87 K). In situ monitoring of the room-temperature electrical resistance is used to control the laser processing and prevent formation of the semiconducting phase. The original properties of the superconducting film can be recovered by plasma oxidation indicating that the laser-induced phase is oxygen deficient.