bluuebunny/crossref_metadata_2025 huggingface dataset:
Polarized neutron study of TmZn
Authors: Givord D. , Morin P. , Schmitt D.
Published: February 2003

The rare-earth intermetallic compound TmZn shows a first-order quadrupolar transition from a cubic to a tetragonal phase at TQ = 8.55 K, while it orders ferromagnetically at TC = 8.12 K. In addition, a first-order paraferromagnetic transition is induced by a magnetic field above TQ. All these properties have been analyzed within a model including quadrupolar pair interactions between Tm3+ ions. We have undertaken a study of polarized neutron scattering in order to test such a model as well as to determine the band magnetization. It turns out that (i) the contribution of the conduction electrons to the magnetization is small; (ii) the 4f form factor in the nonordered phase is well described with our model; (iii) the 4f factor in the ferromagnetic phase may be interpreted within the same model, but the results are incompatible with results of magnetic excitation experiments.
Electrical resistivity, low-field magnetization, and x-ray studies in the Dy-Sm alloy system
Authors: Caton R. , Arajs Sigurds , McDermott A. , Brown K. W.
Published: February 2003

Electrical resistivity (ρ) and low-field magnetization (σ) have been investigated as a function of temperature (T) on Dy-Sm alloys containing 5, 10, 20, 40, and 80 at.% Sm. Anomalies in the ρ vs T and σ vs T curve have been used to determine the magnetic transitions in this system. A magnetic phase diagram for the Dy-rich alloys has been proposed. X-ray studies have been employed to establish the structural features of this system.
Effect of pressure on the Néel temperature in Cr-Ga
Authors: Kaneko T. , Shirakawa K. , Fukamichi K.
Published: February 2003

The effect of hydrostatic pressure on the magnetic transitions of Cr-Ga alloys has been investigated. The shift of the transition temperatures has been determined from the temperature dependence of the electrical resistivity. The transition temperatures linearly decrease with increasing hydrostatic pressure. In the electrical resistivity curves of Cr-1.06 and Cr-1.50 at.% Ga alloys, two transition temperatures have been observed. One is the transition from the paramagnetic state to the commensurate antiferromagnetic state, accompanying a very large magnitude of the pressure coefficient. Another is the transition from the paramagnetic state to the incommensurate antiferromagnetic state. The concentration dependences of the Néel temperature and the pressure coefficient exhibit a similar tendency above 1 at.% Ga. From the present results, the triple point in the magnetic phase diagram is expected to be 260 K at 0.9 at.% Ga.
ac susceptibility technique for characterizing magnetic bubble films (invited)
Authors: Maartense I.
Published: February 2003

A simple susceptibility method is described in terms of its use for rapid measurement of the static parameters of bubble films. Quantities which can be measured include the initial susceptibility, coercivity, and stability fields of domain patterns, exchange constant and anisotropy fields of storage layers, and uniaxial and cubic anisotropy fields of ion-implanted layers.
An improved BiYIG composition for one-micron bubbles
Authors: Luther L. C. , LeCraw R. C. , Dillon J. F. , Wolfe R.
Published: February 2003

Robertson et al.1 have described a Ga-substituted BiYLuIG composition with very narrow linewidth, high Faraday contrast, and low coercivity. In this work, the temperature dependence of magnetic properties has been improved by replacement of the Ga in the above material by Ca,Si. The approximate composition of the improved material is Y1.9Bi0.5Ca0.6Fe4.4Si0.6O12, and it has a 4πM of 800 G at RT. The Curie temperature is 525 °K higher than that of the Ga-substituted equivalent. An anisotropy energy of 75 000 erg/cm3 and a stability factor Q of 3.8 have been measured. The temperature dependence of the collapse field was reduced from −0.35% to −0.22% per degree. The magnetostrictive coefficient λ111 was measured and used to estimate strain corrections to the anisotropy energy. The growth-induced anisotropy was correlated with Bi content. The Faraday rotation was measured at RT and at 1.4 °K over the range (1.5–2)×104 cm−1. In triply implanted films, bubble propagation has been observed on 4-μm period Ion Implanted Propagation Patterns with wide margins and normal symmetry properties.
Growth-induced anisotropy and damping versus temperature in narrow linewidth, 1-μm YIG(Bi, Ca, Si) bubble films
Authors: LeCraw R. C. , Luther L. C. , Gyorgy E. M.
Published: February 2003

The variation of growth-induced anisotropy Ku and damping with temperature are reported in 1-μm films of (YBiCa)3(FeSi)5O12 having very narrow FMR linewidths. In contrast to a more conventional Lu-Sm type 1-μm bubble film, Ku is found to vary much more slowly with temperature (approximately as M2) in the Bi-containing film with no magnetic rare earths. Also, the important bubble parameter Δℓ/ΔT, where ℓ is the material length, is found to be smaller than that of the Lu-Sm type material and of opposite sign. Significant improvements in device temperature stability and operating speeds are expected in the YIG(Bi) system.
High-frequency propagation and failure of contiguous disk magnetic bubble devices
Authors: Zhang S. J. , Humphrey F. B.
Published: February 2003

High-frequency propagation and failure of contiguous disk devices in an ion-implanted 3-μm YSmLuCaGe garnet film were investigated by using high-speed optical sampling. The minimum drive field, the bias field operating margin, and the bubble position with respect to the instantaneous rotating field direction were found to change with the frequency of the drive field. The shape and position of bubbles during the propagation were measured so that the instantaneous velocity dependence of the frequency of the drive field could be calculated. This study was done on a selection of different tracks so that the dependence of the geometry of the tracks could be included. It was found that more uniform instantaneous velocity leads to lower minimum drive field and a higher rotating frequency limit. The cause of high-frequency failure was examined and found generally to be the limitation of the maximum velocity of bubbles causing a phase lag greater than 90°. This limitation can be caused either by a low drive or by a saturation velocity.
NDRO detector for ion-implanted bubble devices
Authors: Ekholm D. T. , Bonyhard P. I. , Muehlner D. J. , Nelson T. J.
Published: February 2003

We report on the design and characterization of a nondestructive readout detector for ion-implanted bubble devices. Detection takes place, according to this design, as in previously reported destructive readout detectors in ion-implanted devices.1 The bubble to be detected is stretched into a strip along a magnetoresistive permalloy bar by a current pulse in a hairpin conductor. In our design, however, a second hairpin conductor is added, coplanar with the first one, and a current pulse in this second conductor stretches the end of the bubble to a second propagate track. Finally, a collapse pulse is applied to the first conductor forcing the bubble strip off the permalloy bar. The detector has been produced on 8-μm period circuits using previously reported implant conditions and processing.1 It has been operated at 50 KHz with bias margin ranges typically 20 Oe at 40 Oe rotating field. An error rate at one bias of <5×10−9 has been demonstrated.
Current-access ion-implanted bubble device structure
Authors: Ohta H. , Kryder M. H.
Published: February 2003

A hybrid current-accessed ion-implanted bubble device structure has been demonstrated to circulate bubbles around disk-shaped structures using currents in apertured conductor sheets to access charge walls in ion-implanted layers of garnet. Measurements of the collapse field of bubbles indicate that, with the new structure, magnetic poles produced by charge walls are made to add to the poles produced by currents flowing around apertures in conductor sheets, increasing the potential well of the bubble domains. As a result of the increased potential well the new structure requires less drive. Measurements show that to circulate 1-μm bubbles in a double layer GdTmGaYIG/EuTmGaYIG garnet around 6-μm disks, a linear current density of about 1.4 mA/μm is required, whereas more than 2.6 mA/μm was required in a conventional current-access apertured-sheet device fabricated on the same chip. This difference in minimum drive corresponds to a reduction in power dissipation per unit area by about a factor of 4 in the current-access ion-implanted structure.
Thin-film detector performance on a one megabit magnetic bubble memory
Authors: Silverman P. J. , McEfee P.
Published: February 2003

Magnetic bubble memories have been fabricated with thin-film detectors which have a 4× improvement in signal amplitude over conventional chevron detectors. The detectors have a nominal 20-mV signal at 25 °C when operated in a bridge configuration from a 12-V supply. Random noise on the signal has an rms value of ∼250 μV. The temperature coefficient of the signal is approximately −1%/°C. Signal variation with drive field amplitude is ∼1% for a 1% drive field variation over a ±10% range about nominal (60-Oe) drive. The standard conductor first structure is used, with the thin-film detector situated between two silicon dioxide spacer layers under the conductor metalization. Nominal detector thickness is 50 nm. Relatively high detector resistance (2.5 KΩ) reduces on-chip power dissipation to less than half that of conventional chevron detectors. Contact to the thin-film detector is made through vias in the spacer layer. Metal-to-metal contact between the Al(Cu) conductor metalization and the Permalloy thin-film detector is assured by an in-situ sputter etch prior to Al/(Cu) deposition.
An isotropic particulate medium with additive Hilbert and Fourier field components
Authors: Lemke James U.
Published: February 2003

Interference effects between planar and normal components of magnetization in an isotropic tape are used to separate the contribution of each and address the question of transition lengths for so-called vertical recording. For low level record signals (−4 dB relative to optimum band edge current) and high coercivity isotropic or anisotropic media, the dominant magnetization at short wavelength is found to be normal to the plane (vertical), and the transition length is nonexistent. The isotropic medium supports twice the normal component of the anisotropic medium. Constructive interference of the two components causes apparent departure from the Wallace equations although each component is exactly described by the Wallace model. Increasing current causes a log/linear attenuation which may be caused by factors other than transition length. Using the isotropic tape, densities of 10 000 transitions/mm (250 000 f.c.i.) are seen.
Noise reduction and recording density increase in magnetic-coated disks
Authors: Maeda M. , Ishida S. , Suenaga T. , Ogawa S.
Published: February 2003

We studied the effects of several conditions on noise of medium of magnetic-coated disks and succeeded in reducing the noise significantly. In our study, we focused on nonmagnetic particles and surface roughness and found that: (1) Nonmagnetic particles, like alumina, affect noise unless they are small and as well-dispersed as the magnetic particles. (2) ’’As-coated’’ roughness, meaning the surface roughness before polishing, causes the noise. By eliminating nonmagnetic particles and improving the coating method to reduce the ’’as-coated’’ roughness, we produced extremely low-noise magnetic-coated disks. Using Co adsorbed iron oxide powder (Hc:650 Oe), we obtained high signal to noise ratio (SNR) (40 dB) magnetic-coated disks at a high linear density of 20 000 FRPI.
μSR measurement of rare-earth moment dynamics in the HoxLu1−xRh4B4 ternary alloy system
Authors: Boekema C. , Heffner R. H. , Hutson R. L. , Leon M. , Schillaci M. E. , Smith J. L. , Dodds S. A. , MacLaughlin D. E.
Published: February 2003

μSR measurements have been carried out in the ternary rare-earth system HoxLu1−xRh4B4, x = 0, 0.7, and 1, to study the effects of superconductivity and magnetic order on Ho moment dynamics in this alloy series. In nonmagnetic LuRh4B4, muon relaxation is due to nuclear dipolar fields; the decrease of the relaxation rate above ∼200 K is attributed to the onset of muon diffusion at this temperature. In HoRh4B4, the zero-field relaxation rate Λ(T) exhibits a strong maximum well above the magnetic ordering temperature TM = 6.6 K, but no singularity at TM. Instead, the relaxation function develops a form indicative of very slow Ho moment fluctuations below ∼9 K. The high-temperature relaxation rates are too low to be explained by a ferromagnetic mean-field estimate of the exchange frequency; interactions of competing signs may be involved. For x = 0.7, where reentrant superconductivity is observed between TM = 4.1 K and TS = 7.7 K, a shoulder in Λ(T) is observed between TM and TS. This seems to indicate an important effect of superconductivity on Ho moment dynamics.
Mössbauer study of superconducting LaFe4P12
Authors: Shenoy G. K. , Noakes D. R. , Meisner G. P.
Published: February 2003

The ternary compound LaFe4P12 having a ’’filled skutterudite’’ structure is a superconductor with Tc = 4.08 K. We have used the Mössbauer effect of 57Fe to show that the magnetic moment of Fe in LaFe4P12 is less than 0.01μB. The value of the measured isomer shift indicates a spin-paired 3d configuration of Fe. The temperature dependence of the shift and the resonance fraction are used to establish a weak coupling of 3d electrons with the phonons, the coupling parameter being about 0.4 to 0.5.
Antiferromagnetic ordering of TbH2+x
Authors: Arons R. R. , Schaefer W. , Schweizer J.
Published: February 2003

Tb dihydride TbH2+x has been investigated for −0.05<x<0.12 by means of magnetic susceptibility and neutron diffraction measurements. It is shown that both the magnetic structure and the Néel temperature TN depend strongly on x. For x≊−0.05, a commensurate antiferromagnetic structure appears below 15.8 K. For higher concentrations different incommensurate structures are obtained which are stable from TN down to 4 K. The transition from the commensurate into an incommensurate magnetic structure is ascribed to the random occupation of some octahedral sites in the fcc Tb lattice for x≳−0.05.
Ferromagnetic neodymium dihydride
Authors: Carlin Richard L. , Krause L. J. , Lambrecht Armin , Claus H.
Published: February 2003

Two polycrystalline samples of neodymium dihydride have been investigated by both ac-susceptibility and dc-magnetization measurements. The ac susceptibility displays a sharp peak at 5.8±0.1 K, suggestive of the onset of long-range ferromagnetic order. The dc magnetization shows the onset of coercivity and remanence at the same temperature. Arrott plots of the magnetization confirm ferromagnetic order at 5.6 K. However, saturation is not observed at 4.2 K in external fields up to 60 kOe.
Nondispersive magnetostatic forward volume waves under field gradient control
Authors: Morgenthaler F. R.
Published: February 2003

The magnetostatic dispersion relation for a single ferrite strip of width W and thickness d, placed between arbitrarily spaced parallel ground planes, is derived under the assumption that the dc magnetic bias is normal to the plane of the strip but a general polynomial function of the transverse coordinate. Edge wave and volume wave modes are considered separately and both types are found to be susceptible to field gradient control. Assuming N-field gradient coefficients are available for dispersion control, a least-squares procedure can be employed to find that set which best approximates nondispersive (or other desired) propagation over a prescribed bandwidth. As expected, control is best achieved with moderately long magnetostatic wavelengths.
Temperature dependence of the magnetostriction in SmxDy1−xFe2 compounds
Authors: Abbundi R. , Clark A. E. , McMasters O. D.
Published: February 2003

The temperature dependence of the magnetostriction from 80–300 K, as a function of applied field, was investigated in a series of SmxDy1−xFe2 (x = 0.86, 0.70, 0.55, 0.40, and 0.20) polycrystalline compounds. Large strains are observed in Sm0.86Dy0.14Fe2 with λ∥−λ⊥ = −1688×10−6 at room temperature and −2725 ppm at 80 K, as the large negative λ111 found in SmFe2 dominates. The competing anisotropies of SmFe2 and DyFe2 compensate near room temperature in this composition, permitting the magnetostriction at 300 K to saturate at 7 kOe. As one proceeds across the series, the influence of DyFe2 causes a decrease in ‖λ‖ with λ∥−λ⊥ = −77×10−6 at 300 K in Sm0.55Dy0.45Fe2. The field dependence at lower temperatures indicates a rotation of the magnetic moment, resulting in a positive dλ/dH in the high field portion of the curves. The magnetostriction of Sm0.20Dy0.80Fe2 initially shows a negative strain which changes sign as the field is increased. The field curves are far from saturation at all temperatures with λ∥−λ⊥ = 248×10−6 at H = 25 kOe at room temperature. The remanent magnetostriction at 300 K in these compounds provides an estimate that λ100≊−180×10−6 for SmFe2.
Magnetostriction and magnetic anisotropy of field annealed Metglas* 2605 alloys via dc M-H loop measurements under stress
Authors: Spano M. L. , Hathaway K. B. , Savage H. T.
Published: February 2003

Amorphous metallic ribbons annealed in transverse fields have enormous magnetoelastic coupling. An integrating magnetometer was used to measure magnetization M as a function of applied field H and tensile stress T in such ribbons, from which is determined the magnetostriction λs. A simple phenomenological model of moment rotation can account for the linear dependence of M as a function of H at T below 7×105 Pa observed in Metglas 2605SC. From the model we extract λs∼27×10−6 and anisotropy K∼38 J/M3. In stressed 2605CO no linear behavior is observed. This work substantiates previous high values obtained for the coupling factor and ΔE effect.
Specific heat of nickel diglycine dihydrate between 0.5 and 10 K
Authors: Calvo R. , Nascimento O. R. , Torikachvili M. S. , Maple M. B.
Published: February 2003

Specific heat measurements between 0.5 and 10 K on nickel diglycine dihydrate reveal a phase transition at 0.88 K and yield the values D/k = −14.5 K and ‖E‖/k = 1.13 K for the spin Hamiltonian parameters of the Ni2+S = 1 ions. The phase transition is identified as the antiferromagnetic to paramagnetic transition inferred from magnetic susceptibility measurements.
Critical behavior in random anisotropic antiferromagnets
Authors: Belanger D. P. , King A. R. , Jaccarino V.
Published: February 2003

The role of random uniaxial anisotropy on critical behavior has been studied in the antiferromagnetic system FexMn1−xF2 using linear magnetic birefringence. In the pure FeF2 and MnF2 crystals the deduced magnetic specific heat near TN shows no rounding for reduced temperature t as small as 10−4. Except for the effects of concentration gradients, no rounding is observed in the mixed crystals. In fact, for the Fe.75 Mn.25F2 sample, where such gradient effects are minimal, the transition is as sharp as in pure FeF2. Since MnF2 and FeF2 differ primarily in the size of the single ion anisotropy, it is clear that random anisotropy, by itself, does not broaden the transition. If anisotropy were not considered, MnF2 and FeF2 would be expected to have nearly identical TN. Although MnF2 is itself asymptotically Ising-like as T→TN because of its small but finite anisotropy, the larger TN in the more anisotropic FeF2 and the drastic increase in TN with x near x = 0 is attributable to the effects of crossover from Heisenberg to Ising critical behavior.
Magneto-optical determination of magnetic ordering and magnetic structure of CS3MnCl5 below 0.6 K
Authors: Rivoal J. C. , Briat B. , Torre J. P.
Published: February 2003

We report on magneto-optical determination of the magnetic phase transition as well as the magnetic structure of crystalline CS3MnCl5. A new type of optical cryostat, with a closed cycle of He3 has allowed us to study continuously the variation of the absorption bands down to 0.4 K. The temperature variation of hot and cold bands attributed to the 6A1→4E, 4T2 transitions proves that antiferromagnetic ordering arises at 0.6 K. Studying the MCD spectrum of the 6A1→4T2 zero phonon line in low magnetic field, we have observed that the antiferromagnetic phase reverts to paramagnetic state. From this we deduce a value of the weak exchange field (0.9 T) and the energy of the magnon (ω0 = 0.28 cm−1). Using the latter value we show that the origin lines of the 4E and 4T2 states can be fairly well understood in terms of magnon sidebands. In contrast the σ polarized absorption spectra under an applied magnetic field, perpendicular to the c axis, show no discontinuity. A log-log plot of the absorbance versus magnetic field gives clear evidence for a power dependence with an exponent close to two, as expected when the spins are all orthogonal to the direction of the field.
Agglomerate formation in a magnetic fluid
Authors: Chantrell R. W. , Bradbury A. , Popplewell J. , Charles S. W.
Published: February 2003

Monte Carlo techniques have been used to investigate the effects of magnetostatic and repulsive particle interactions on the formation of agglomerates in a magnetic fluid. The dependence on particle size and applied field of the form of the agglomerates was studied using a spatial distribution function which allows a quantitative distinction to be made between clusters and anisotropic chain structures. Magnetization curves have been calculated for magnetic particle sizes varying from 5 to 15 nm with and without magnetostatic interactions. For the larger particle sizes, it was found that the initial susceptibility is reduced in the presence of interactions. This is associated with the presence of pronounced agglomeration in zero field, where open clusters are formed. As the applied field is increased the clusters break up to form long chains aligned in the field direction. At intermediate particle sizes, there is evidence of magnetic field induced agglomeration leading to the formation of dimers and trimers preferentially aligned in the field direction. The smallest particle size showed little evidence of ordering even in strong applied fields, since thermal disordering dominates the situation.
Heat capacity and magnetic studies of graphite intercalated with FeCl3 and NiCl+2
Authors: Onn David G. , Alexander M. Grayson , Ritsko J. J. , Flandrois S.
Published: February 2003

Low-temperature specific heat (Cp) and magnetic susceptibility (χ) for the graphite intercalation compounds C6.2FeCl3 (stage 1) and C17FeCl3 and C11.3NiCl2.13 (stage 2) is reported and analyzed. The FeCl3 compounds show large anomalies in Cp at 4 and 1.7 K, respectively, while the NiCl2 compound shows a peak at 20 K. For the FeCl3 compounds, χ is less than 5×10−6 emu gm−1 at all temperatures, showing only very small anomalies, while the NiCl2 compound shows a very large peak in χ at 16 K. Possible magnetic models for these layered compounds are considered, including a spin-glass or spin-cluster glass state.
Fabrication of a thin film head using polyimide resin and sputtered Ni-Fe films
Authors: Hanazono M. , Narishige S. , Kawakami K. , Saito N. , Takagi M.
Published: February 2003

Sputter-deposited Ni-Fe films and planarized polyimide resin (PIQ) were used for fabrication of an eight-turn thin film head. Properties of the head were tested using a disk storage system.
The effect of magnetic fields on crosstie walls in thin iron films observed i
n s
i
t
u in an electrostatic TEM
Authors: Karamon H. , Rempfer G. F. , Dash J. , Takeo M.
Published: February 2003

The effect of magnetic fields on the magnetic domain structure in thin iron films (∼200 Å) has been studied in situ by Lorentz microscopy in an electrostatic transmission electron microscope (TEM). The electrostatic instrument provides a specimen region free of magnetic fields. A special solenoid was placed in the specimen region, coaxial with the optic axis. By tilting the specimen holder a known in-plane component of the field could be applied to the specimen. Studies were made with the in-plane field applied parallel to and perpendicular to the domain walls.
Large stable magnetic domains
Authors: Pulliam G. R. , Ross W. E. , MacNeal B. , Bailey R. F.
Published: February 2003

Large, thin-film single domain areas have been observed, in the absence of a bias field, in garnets with magnetization perpendicular to the film plane.1,2 The domain stability in the work by Krumme1 was attributed to a combination of low saturation magnetization and a low Curie temperature. Uchishiba2 relates the stability in his double layer system to appropriate anisotropy fields in one layer compared to the magnetization in the other layer. A more complete model for large domain stability in a bias field free environment is given in this work. Three distinct stability regimes are predicted by the model and all have been observed experimentally. Areas 3.5-cm in diameter have been made into stable single domains. This was achieved in a material showing a zero bias strip width of 4.5 μm. The single domain diameter was, therefore, 7500 times the equilibrium energy domain width. The technique developed and the model have led to a new means for observing magnetic defects. More importantly, it also offers a means for measuring the strength of the defects. Possible applications of the model are also discussed.
Magnetic, Mössbauer, and catalytic properties of the zeolite catalyst ZSM-5(Fe)
Authors: Obermyer R. T. , Mulay L. N. , Lo C. , Oskooie-Tabrizi M. , Rao V. U. S.
Published: February 2003

Iron-impregnated medium pore zeolite ZSM-5 (pore opening of 5.5 Å) is an efficient catalyst for the conversion of synthesis gas (CO+H2) to high octane gasoline. Activity and selectivity of the ZSM-5 (Fe) depends upon the manner in which Fe is impregnated on ZSM-5. Magnetic and Mössbauer studies were conducted on catalysts prepared by two methods: (a) ferric nitrate impregnation and (b) carbonyl Fe3(CO)12 impregnation on the zeolite. These studies were conducted for various stages of preparation and after use of the catalysts. The carbonyl impregnated sample in the as-prepared form contained ultrafine γ-Fe2O3 of d = 60–66 Å, as evidenced by superparamagnetic behavior seen in magnetic and Mössbauer studies. In contrast, the as-prepared, nitrate impregnated sample showed α-Fe2O3 of approximate particle size of 100 Å. Both samples were reduced to about 80% metallic Fe in flowing H2. On exposure to synthesis gas, the carbonyl impregnated sample yielded a substantial amount of Fe3O4 in addition to χ carbide, wheres the nitrate impregnated sample exhibited ε, χ, and ϑ carbides. The steady catalytic activity and selectivity of the carbonyl impregnated sample can be related to the ultrafine iron dispersions leading to the observed phases in the used catalyst.
Ground state properties of a spin glass model
Authors: Kolan A. J. , Palmer R. G.
Published: February 2003

A new algorithm has been developed to find ground state properties of finite two-dimensional lattices of Ising spins with +J, −J, or O interaction strengths. The algorithm is based on a list of all possible string assignments on a boundary which divides the sample in two. Averaged ground state properties are presented for random lattices in which +J occurs with probability p, −J with probability q, and O with probability r (p+q+r = 1). Evidence for zero temperature phase transitions between paramagnetic, ferromagnetic, antiferromagnetic, and possible spin glass phases is discussed.
Density functional calculation of magnetic susceptibilities
Authors: Callaway J. , Singhal S. P. , Adamowicz L.
Published: February 2003

The transverse wave vector and frequency dependent magnetic susceptibility matrix for ferromagnetic nickel is studied at T = 0 °K using a procedure based on density functional theory. Wave functions and energies from a first principles band calculation are used in numerical evaluations. Some results are presented for the energy dependence of the inelastic neutron scattering cross section.
Use of acoustic emission to detect regions of structural change in metallic glass tape
Authors: Lord A. E. , Tyagi Somdev
Published: February 2003

A method is demonstrated for the rapid detection of localized structural variation in ferromagnetic metallic glass tapes. The method employs the acoustic Barkhausen effect.
Temperature and field dependence of intergrain barriers in polycrystalline n-InSb films
Authors: Dawar A. L. , Sen A. D. , Dewan H. K. , Taneja O.P. , Mathur P. C.
Published: February 2003

Field-effect Hall mobility studies were made on polycrystalline n-type InSb films. The intergrain barrier potential is found to be dependent on both temperature and applied gate field. The experimental results fit well with an intergrain barrier potential of the form φb = φ0(1+αT)(1+αq+bq2), where φ0 is the value of φb at zero gate field and absolute zero temperature, α is the temperature coefficient of φb, and a and b are constants.
Comment on ’’Simulation of high-field transport in GaAs using a Monte Carlo method and pseudopotential band structures’’ and on ’’Band-structure dependent transport and impact ionization in GaAs’’
Authors: Capasso F. , Pearsall T. P. , Thornber K. K. , Nahory R. E. , Pollack M. A. , Bachelet G. B. , Chelikowsky J. R.
Published: February 2003

Recent theoretical work by Shichijo, Hess, and Stillman on a Monte Carlo simulation of high-field transport and impact ionization in GaAs is examined. The failure of that calculation to reproduce the experimentally well-documented orientation dependence of impact ionization can be directly related to the use of a phonon scattering rate that is unrealistically high. It is shown that such high scattering rates lead, by the uncertainty principle to a large collisional broadening (?0.3 to 0.6 eV) of the conduction band, thus invalidating the Monte Carlo simulation and rendering questionable any attempt to relate transport to the band structure. The important role played by the avalanche region width in the orientation dependence of impact ionization is also discussed.
Reply to ’’Comment on ’Simulation of high-field transport in GaAs using a Monte Carlo method and pseudopotential band structures’ and on ’Band-structure dependent transport and impact ionization in GaAs’ ’’
Authors: Hess K. , Tang J. Y. , Brennan K. , Shichijo H. , Stillman G. E.
Published: February 2003

Using semiclassical Monte Carlo simulations and the band structure as calculated by the empirical pseudopotential method, we show that the electron-phonon scattering rate in GaAs exceeds 1014 s−1. As a consequence, impact ionization of ballistic (lucky) electrons becomes extremely unlikely. The objections of Capasso et al. to our treatment are discussed in detail and shown to be physically of minor importance.
Spectral response of ac photoconductivity in Zn3P2
Authors: Wang Faa-Ching , Bube Richard H.
Published: February 2003

ac (80 Hz) photoconductivity spectral response curves have been measured for seven single crystal samples of Zn3P2 prepared by different preparation techniques and subjected to different heat and surface treatments prior to measurement over the spectral range from 0.6 to 1.2 μm. Surface ac photoconductivity lifetimes range from 0.4 to 40 μsec, and bulk ac photoconductivity lifetimes range from 3 to 100 μsec. Major contributions to the photoconductivity near the band edge of Zn3P2 come from transitions of about 1.41 and 1.52 eV, probably corresponding to direct transitions from the two higher-lying valence bands split by spin-orbit and crystal fields.
Effect of nonparabolicity on amplification of surface phonons in piezoelectric semiconductor films
Authors: Wu Chhi-Chong , Tsai Jensen
Published: February 2003

The effect of nonparabolicity on the amplification of surface phonons in piezoelectric semiconductor films is investigated quantum mechanically in the GHz frequency region. Numerical results are obtained for an n-type GaAs epitaxial layer on a semi-insulating GaAs substrate at 77 °K. Results show that the amplification is enhanced for the nonparabolic band structure due to the nonlinear nature of the energy band in semiconductors.
GaInP grown by molecular beam epitaxy doped with Be and Sn
Authors: Blood P. , Roberts J. S. , Stagg J. P.
Published: February 2003

Using an ancillary flux of Pb atoms, we have grown Be-doped Ga0.5In0.5P on (001) GaAs substrates by molecular beam epitaxy (MBE) with hole concentrations as low as 1016 cm−3, a region previously inaccessible by conventional MBE growth. Sn-doped layers have also been grown by the same technique with similar concentrations of electrons. Room temperature hole mobilities exceed literature values for VPE layers. Deep level spectra have revealed three electron traps with thermal activation energies of 0.15, 0.34, and ∼0.81 eV. The total electron trap concentration was 5.2×1015 cm−3 in a layer with n = 5×1016 cm−3. The dominant mid-gap trap was also detected in n-type layers grown without the Pb flux. The concentration of Pb incorporated in the layer is about 1.5×1017 cm−3 and is uniformly distributed. This corresponds to about 2×10−4 of the incident Pb flux. The presence of Pb on the surface induces a change from a weak 2×1 RED pattern to a sharp 1×2 pattern and we suppose that this modification of the surface structure reduces the concentration of deleterious defect centers.
Coupling of pulsed 0.35-μm laser radiation to aluminum alloys
Authors: Rosen D. I. , Mitteldorf J. , Kothandaraman G. , Pirri A. N. , Pugh E. R.
Published: February 2003

Experiments and theoretical analysis have been performed to investigate the thermal and mechanical coupling of pulsed 0.35-μm laser radiation (τp≊10−6 s) to aluminum targets irradiated in vacuum. Thermal coupling coefficients measured for Al 2024 (as-received and polished) and pure aluminum, and impulse coupling data for polished Al 2024 are presented. We find low fluence (≲5.0 J/cm2) thermal coupling coefficients of 0.4 for as-received Al 2024, 0.2 for polished or laser-cleaned Al 2024, and 0.1 for pure aluminum. Neglecting initial surface layer effects, impulse coupling is shown to result from bulk target vaporization for pulse fluences greater than 10 J/cm2. Measurements are also presented for the plasma formation threshold above aluminum targets irradiated in vacuum at 0.35 μm. An intensity threshold of 6×107 W/cm2 is indicated for a pulse duration of 0.5 μs. The impulse coupling and plasma ignition threshold data are shown to be in good agreement with theoretical model predictions.
Growth kinetics of planar binary diffusion couples: ’’Thin-film case’’ versus ’’bulk cases’’
Authors: Gösele U. , Tu K. N.
Published: February 2003

It is proposed that interfacial reaction barriers in binary A/B diffusion couples lead to the absence of phases predicted by the equilibrium phase diagram, provided that the diffusion zones are sufficiently thin (thin-film case). With increasing thickness of the diffusion zones the influence of interfacial reaction barriers decreases and the simultaneous existence of diffusion-controlled growth of all equilibrium phases is expected (bulk case). Selective growth of the first and second phases and the effect of impurities are discussed with the influence of interfacial reaction barriers and with references to the known cases of silicide formation.
Pulsed laser annealing of rf sputtered amorphous Si-H films doped with arsenic
Authors: Fogarassy E. , Stuck R. , Toulemonde M. , Bruyere J. C. , Siffert P.
Published: February 2003

Arsenic doped amorphous silicon layers have been deposited on silicon single crystals by rf cathodic sputtering of a silicon target in a reactive argon-hydrogen mixture, and annealed with a Q-switched ruby laser. Topographic analysis of the laser irradiated layers indicate that a crater is formed due to an evaporation of material which could be related to the presence of a high concentration of argon in these deposited films. Furthermore, Rutherford Backscattering experiments showed that a highly disordered surface layer is left after irradiation due probably to an inhibition of the recrystallization by the presence of hydrogen as revealed by nuclear reaction analysis. Nevertheless, it was found that below this surface layer arsenic has diffused into the monocrystalline substrate. Therefore, under convenient experimental conditions, (repetitive laser pulses), p-n junctions of good quality could be formed.
Experimental studies of fast deuterons, impurity- and admixture-ions emitted from a plasma focus
Authors: Mozer A. , Sadowski M. , Herold H. , Schmidt H.
Published: February 2003

The energy and mass analysis of ions emitted from a 50-kJ, 18-kV, plasma focus machine was performed with a Thomson analyzer. Energy distribution functions of fast deuterons (E⩽350 keV) and those of impurity ions have been determined. The energy distributions of the O, N, and C impurity ions in different ionization states have similar character. They usually increase exponentially and after reaching the maximum at E/Z≊1.0 MeV they decrease exponentially to E/Z≊1.8 MeV. For deuterons at lower operating pressures (p0⩽2 mbar) the energy distribution measured decreases exponentially from 0.35 to about 3.0 MeV. In some cases, independent of the operating pressure, the maximum energies of the distribution extend to 0.5–1.5 MeV only. With an argon admixture (up to 4.5%) Ar+-Ar7+ ions of energy from 0.5 to 14 MeV are produced.
Pressure determination of mercury discharges from self-reversed spectral lines
Authors: Karabourniotis D. , Damelincourt J. J.
Published: February 2003

A method is introduced for determining the pressure of an optically thick mercury plasma in local thermodynamic equilibrium (LTE) from the depth of the valley at the center of an observed self-reversed line and the distance between self-reversal maxima. The calculations are based on a simplified model for the light source. Experimental results are presented which agree with results obtained previously from the intensity of an optically thin line.
V-I characteristics of a plane disc probe in collisionless streaming plasmas
Authors: Goel S. K. , Gupta P. D. , Bhawalkar D. D.
Published: February 2003

Expansion of high-temperature high-density plasmas produced by focussing high-power lasers on solid targets gives rise to collisionless streaming plasmas with flow velocity U such that Ci ≪U≲Ce, where Ce and Ci are electron and ion thermal velocities, respectively. Dimensionless V-I characteristics of a plane disc probe in such streaming plasmas are obtained. The characteristics show a nonsaturation behavior of the probe current in the electron attracting region of the probe operation. It is observed that in the electron repelling region, the slope of the V-I characteristics increases with the decrease in the probe potential.
Surface flashover of solid dielectric in vacuum
Authors: Pillai A. Sivathanu , Hackam Reuben
Published: February 2003

The surface of a solid dielectric insulator becomes electrically charged when subjected to a high-voltage stress in vacuum. A method for calculating the surface flashover voltage based on the assumption that the discharge occurs in a layer of desorbed gases from the insulator surface is proposed. The electric field strength required to cause surface flashover is calculated by taking into account the secondary electron emission characteristics of the dielectric material. The dependence of the surface flashover field on the insulating material is deduced. A dependence of the flashover voltage on the insulator length to a power law of 0.5 is theoretically predicted. The calculated surface flashover voltage is compared with the previously reported measurements and good agreement is obtained.
Nature of dark defects revealed in InGaAsP/InP double heterostructure light emitting diodes aged at room temperature
Authors: Ueda Osamu , Umebu Itsuo , Yamakoshi Shigenobu , Kotani Tsuyoshi
Published: February 2003

The nature of the dark defects which have appeared in the InGaAsP/InP double heterostructure light emitting diodes aged at room temperature were studied by transmission electron microscopy and other related methods. According to the observation of many diodes by electroluminescence topography, the dark defects were classified into five types: cross-hatched 〈110〉 dark line defects, regular tetragonal 〈110〉 dark line defects, regularly distributed dark spot defects, dark band defects, and dark spot defects whose circumference was bright. These dark defects corresponded to misfit dislocations, stacking faults which originated from the interface between the epitaxial layer and the substrate, precipitate-like spherical defects, mechanical damages induced during epitaxial growth, and alloyed regions produced by the penetration of the electrode metals, respectively. It was found that both the dislocation glide process and the dislocation climb motion due to the nonradiative recombination of the minority carriers which have been often observed in the GaAlAs/GaAs double heterostructure materials occurred only with difficulty in the InGaAsP/InP double heterostructure materials. These phenomena could be well explained by the difference between these materials in term of interaction between impurity atoms and dislocations and/or the electronic state of defects and nonradiative recombination rate at defects.
Atom and carrier depth distributions of beryllium implanted into silicon
Authors: Wilson R. G. , Comas J.
Published: February 2003

The electrical properties and atom depth distributions of Be implanted into Si were studied as a function of implant fluence and annealing parameters. Beryllium depth distributions are presented for eight implant fluences between 2×1012 and 1.5×1016 cm−2. For the lower fluences (⩽1013 cm−2), associated acceptor profiles were measured by differential C-V profiling and were compared with Be profiles obtained by secondary ion mass spectrometry. Two different modes of thermal redistribution of implanted Be are observed, depending upon whether the implants are above or below the amorphization level (∼1.5×1015 cm−2). Acceptor activity was observed for annealing temperatures between 200 and 900 °C. A maximum acceptor density of 8×1016 cm−3 was measured for a 3×1012 cm−2 implanted and 500 °C annealed sample, with ∼50% of the Be being electrically active. Annealing at 600 °C (3×1012 cm−2 implant) resulted in a redistribution of Be with only ∼12% retention; however, the electrical activation of the retained Be was ∼100%. Be implantation of Si substrates held at 200 and 400 °C with no post-implantation annealing produced essentially the same acceptor distributions as room-temperature implanted substrates that were subsequently annealed at the same temperatures.
Influence of the nonequilibrium vacancies on the diffusion of phosphorus into silicon
Authors: Mathiot D. , Pfister J. C.
Published: February 2003

Using Fair and Tsai’s model, a numerical solution is obtained for the coupled phosphorus and vacancy diffusion equations. It is shown that the supersaturation of vacancies, which enhances the phosphorus diffusion in the tail region, also causes an important backwards contribution to the total phosphorus flux in the surface region. It is thus proved that the diffusion via E centers alone cannot explain the plateau region in the phosphorus profiles, and that another mechanism is needed to describe the diffusion of phosphorus in silicon in the high concentration range.
Preparation and properties of reactively sputtered tungsten oxide films
Authors: Kaneko H. , Miyake K. , Teramoto Y.
Published: February 2003

Properties of reactively sputtered tungsten oxide films for electrochromic display devices have been investigated. The films (2000–23000 Å thick) were formed by rf sputtering from a metallic tungsten target under a constant operating pressure ranging from 5×10−3 to 6×10−2 Torr using a mixture of Ar-4–50% O2. Electrical resistivity of the films formed increases remarkably with increasing oxygen concentration and total operating pressure of the sputtering atmosphere, ranging from 10−3 to 1011 Ω⋅cm. The films 5900–9200 Å thick prepared in a sputtering atmosphere of Ar-10% O2 under a constant operating pressure higher than 2×10−2 Torr are transparent and have a spectral transmittance of about 85% in the visible and infrared region. Optical band gap and refractive index of these films are 3.01–3.08 eV, and 2.2–2.4, respectively. Electrochemichromic properties of the films were also studied using asymmetric cells, and it was found that a good electrochromic performance was achieved usually by the cells composed of the transparent films with a resistivity of 106–1010 Ω⋅cm.
Pulse propagation properties in a high-power CO2 laser system for laser fusion
Authors: Daido H. , Inoue M. , Fujita H. , Matoba M. , Nakai S. , Yamanaka C.
Published: February 2003

The simulation results of nonlinear propagation properties in the CO2 laser system using a simulation model of the SF6 saturable absorbers and the CO2 laser amplifiers agree well with the experimental results. The technical problems of the simultaneous irradiation of multibeams to a target are also discussed.
A semiconductor preionizer for transversely excited atmospheric CO2 lasers
Authors: Rickwood K. R.
Published: February 2003

A novel preionizing system is described, using a semiconductor element. The mode of operation is described with experimental verification. Transversely excited atmospheric pressure laser performance using this system is compared with other published results.
Design of efficient transversely excited sequence CO2 lasers
Authors: Znotins T. A. , Reid J. , Brimacombe R. K.
Published: February 2003

Design criteria for the construction of high-energy transversely excited (TE) sequence CO2 lasers are presented. It is demonstrated that intracavity hot CO2 cells are a simple and efficient means of converting conventional TE CO2 lasers to operation on the sequence transitions. Sequence output energies of 6 J per pulse have been obtained from a 1-m discharge. Factors such as hot cell pressure and degree of excitation in the discharge are shown to be important considerations in the design of TE sequence lasers. Possible applications of high power sequence lasers are discussed.
Helically distorted relativistic electron beam equilibria for free electron laser applications
Authors: Davidson Ronald C. , Uhm Han S.
Published: February 2003

The purpose of this paper is to develop a self-consistent kinetic description of helically distorted relativistic electron beam equilibria for free electron laser applications. In particular, radially confined equilibria are considered for a helically distorted electron beam propagating in the combined transverse wiggler and uniform axial guide fields described by B0 = B0êz +δB = B0êz −δB cos k0zêx −δB sin k0zêy , where B0 = const, δB = const, and λ0 = 2π/k0 = const is the axial wavelength of the wiggler field. It is assumed that the beam density and current are sufficiently small that the equilibrium self fields can be neglected in comparison with B0. In this context, it is found that there are three useful (and exact) invariants (C⊥,Ch,Cz) associated with single-particle motion in the equilibrium field B0êz+δB . These invariants are used to construct radially confined Vlasov equilibria fob(C⊥,Ch,Cz) for an intense relativistic electron beam propagating primarily in the z direction. Examples of both solid and hollow beam equilibria are considered, and it is shown that the transverse wiggler field can have a large modulational influence on the beam envelope, depending on the size of δB/B0.