bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetizability of Nd-Fe-B-type magnets with Dy additions
Authors: Tokunaga M. , Endoh M. , Harada H. , Trout S. R.
Published: July 2002

Many alloying additions have been made into Nd-Fe-B-type magnets to alter their permanent magnet properties, in particular for applications above 100 °C. To this end, a common practice has been to add Dy, increasing Hci [M. Sagawa, S. Fujimura, H. Yamamoto, H. Matsuura, and K. Hiraga, IEEE Trans. Magn. 20, 1584 (1984); M. Tokunaga, M. Meguro, M. Endoh, S. Tanigawa, and H. Harada, ibid. 20, 1964 (1985)]. It is not unusual to find Hci >20 kOe in these substituted alloys. This approach has caused a dilemma. In some cases, increasing Hci above 20 kOe makes the alloy more difficult to magnetize and therefore less useful when the field available for magnetizing is 25 kOe or less. We have examined the effect of various alloying additions and heat treatment on the magnetizability of substituted Nd-Fe-B alloys. We show that high Hci at room temperature is not a necessary requirement to have Hci >6 kOe at 150 °C. We discuss the factors affecting the magnetizability of Nd-Fe-B-type magnets.
Magnetic birefringence of two S=1/2 Heisenberg antiferromagnetic chains
Authors: Lamas A. C. , Landee C. P.
Published: July 2002

The compounds CuX2⋅2DMSO (X=Cl,Br; DMSO=[(CH3)2SO]) are being studied as model compounds for the S= 1/2 Heisenberg antiferromagnetic linear chain system (HB AF). This report presents the results of birefringence measurements on both the bromide (CDB) and the chloride (CDC) between 3.5 and 250 K. The temperature derivative of the birefringence has been compared to the theoretical predictions for the magnetic specific heat of the model. Both protonated and deuterated versions were studied but no significant differences were observed. Both the (001) and (010) faces of CDB were studied; the results were different but both sets of data correspond to the specific heat of the HB AF with an exchange constant of JBr =−11.4±0.3 K. The exchange strength found for CDC was JCl =−8.1±0.3 K. These values are consistent with those found from magnetic measurements. It was necessary to account for nonmagnetic contributions to the birefringence. The presence of small amounts of exchange anisotropy could not be detected in the data.
Neutron scattering investigation of a quasi-two-dimensional planar ferromagnet
Authors: Wiesler D. G. , Zabel H.
Published: July 2002

The magnetic ordering of stage-2 CoCl2-graphite intercalation compound has been investigated by neutron diffraction. This compound is a layered structure, with ferromagnetic coupling between xy-type spins within the same layer and a much weaker antiferromagnetic coupling between successive layers. The interplanar coupling is sufficiently weak that the ordering occurs in two steps, leaving a temperature window between Tl≊8.8 K and Tu≊9.4 K where the ordering is purely two dimensional. Below Tl the spins become weakly correlated along the c axis, but this correlation never grows beyond two magnetic layers. We have measured the static spin correlation function by neutron scattering. At all relevant temperatures the scattering is markedly two dimensional and consists of two parts: a short-range order term with maximum correlation length and intensity at Tu, and a sharp Bragg-like ridge of constant width, which vanishes above Tu and relates to either long-range order or a power-law decay of the order parameter. Results will be analyzed in light of current theories, in particular, of the vortex binding mechanism proposed by Kosterlitz and Thouless.
Effects of chemical and magnetic disorder in Fe0.50Mn0.50
Authors: Johnson D. D. , Pinski F. J. , Stocks G. M.
Published: July 2002

We present the results of first-principles calculations of the total energy and spin-polarized electronic structure of disordered fcc Fe0.50Mn0.50. These self-consistent calculations were performed using the Korringa–Kohn–Rostoker method and the coherent-potential approximation (KKR-CPA), using the local-spin-density approximation to treat exchange and correlation. We use a lattice constant of a=6.80 a.u.; information about stability can be inferred from calculated pressure and energy. The moments on the Fe and Mn sites are large but antiparallel to each other, resulting in a small net magnetization. A comparison of the electronic structure is made for fcc Fe, Mn, and FeMn in both the ferromagnetic and disordered local moment states.
Temperature dependence of magnetization time decay in particulate magnetic media (abstract)
Authors: Oseroff S. B. , Dai Z. , Chan C. H. , Tobin V. M. , Schultz S.
Published: July 2002

We report on magnetization time decay (MTD) data on several commercial and experimental tapes, γ-Fe2O3 (as a function of packing fraction), Co-doped γ-Fe2O3, and CrO2, measured from 2 to 400 K between 1 s and 104 s. We have found that the decay of the magnetization with time, for a given temperature, does not follow a simple log t relation. At each temperature we analyze our data with an empirical model,1 which relates values of coercive field, Hc, obtained with a 60-Hz B-H looper to that measured with a slow VSM field cycle (i.e., over ten orders of magnitude of time). Particular emphasis will be given to the nature of the MTD in these samples when extrapolated to zero temperature. These data will be compared to that previously reported,2 and the role of possible nonthermal mechanisms will be discussed.
Effective linewidth measurements at 36 GHz in hexagonal and cubic ferrites
Authors: Wilber W. D. , Silber L. M.
Published: July 2002

Effective linewidth measurements at 36 GHz are reported for barium ferrite, several W-type single-crystal hexagonal ferrites, and for polycrystalline LiZn ferrite. In general, the effective linewidths for the W-type ferrites were relatively large—several hundred oersteds. Values of ΔHeff for the barium ferrite samples were tens of oersteds, similar to the ferromagnetic resonance (FMR) linewidths for these materials. The LiZn samples showed effective linewidths significantly below the FMR values. The results indicate that the two-magnon loss mechanism is the predominant factor in the polycrystalline LiZn, but contributes little to the ferromagnetic loss in single-crystal barium ferrite. The data for the W-type ferrites show that the intrinsic loss for these single-crystals is a significant part of the ferromagnetic resonance linewidth.
Variational principles for three-dimensional magnetostatics based on helicity
Authors: Kotiuga P. R.
Published: July 2002

Following Anderson and Arthurs [Int. J. Electron. 56, 571 (1984)], a variational formulation for three-dimensional magnetostatics based on helicity is considered. The advantages of formulating problems in terms of the magnetic field as opposed to the vector potential are given. It is shown that when the extremal is constrained to be solenoidal and μ=1, the Euler–Lagrange equation of the proposed functional involves a first-order differential operator whose square is the Laplace–Beltrami operator. This implies that the condition number of any discretization is the square root of the corresponding number for the Laplace–Beltrami operator.
The strategic dual image method: An extremely simple procedure for open field problems
Authors: Saito Y. , Takahashi K. , Hayano S.
Published: July 2002

Previously we proposed a new method which is based on the strategic dual image forcing an open boundary to close for the finite element solution of open boundary problems. In this paper the relationship between the strategic dual image and traditional electric image methods is clarified. This leads to a method of determining a hypothetical boundary for our strategic dual image method. Several examples demonstrate the versatility of our new method.
Three-dimensional finite-element analysis of recording heads
Authors: Lowther D. A. , Coughlin T. M.
Published: July 2002

Three-dimensional analysis of recording heads can provide the designer with predictions of head performance which include transverse fringing effects as well as the effects of magnetic nonlinearity. Some of the problems associated with such analysis and the type of results which may be obtained are described together with a possible computer aided design system structure. Finally, three-dimensional results are compared with those from a two-dimensional analysis from a point of view of the head fields.
Evidence for particle interaction effects in Nd-Fe-B ribbons (abstract)
Authors: Pinkerton F. E.
Published: July 2002

A model is developed to describe the magnetization behavior of randomly oriented uniaxial particles, in which it is assumed that the individual Nd2Fe14B crystallites do not interact. The model agrees qualitatively with the observed magnetization behavior of melt-spun Nd-Fe-B ribbons, but significant quantitative violations of the model provide evidence for substantial particle interaction effects in the ribbons. This corroborates earlier transmission electron microscope and magnetization studies in which indications of such effects were reported. A qualitative discussion of the role of particle interactions in the magnetization behavior is presented.
Propagation of an extraordinary wave in a thin ferrite film in the absence of an external magnetic field
Authors: Halchin David J.
Published: July 2002

The propagation of an extraordinary wave in a unbiased ferrite film of (Bi,Lu) yttrium iron garnet is discussed. This, to our knowledge, is the first reported observation of this type of magnetostatic wave propagation. Two separate modes were observed to propagate in the material, with the mode selection resulting from the initial preparation of the film prior to measurement. These modes propagate in different ranges, 4.2–5.1 GHz and 2.63–3.13 GHz, and exhibit different propagation characteristics. The effect of an external magnetic field on the two modes is also reported for three mutually perpendicular direction-of-bias fields. Two of these directions are in-plane and the third is normal to the plane of the ferrite. This material has potential applications for microwave signal processing devices in that they do not require an external magnetic bias field for proper operation. This can greatly reduce the size of present magnetostatic wave devices, as well as allow these devices to acquire a more planar geometry.
Density dependence of noise in thin metallic longitudinal media
Authors: Moon Jaekyun J. , Carley L. Richard , Katti Romney R.
Published: July 2002

The dependence of noise in thin metallic longitudinal disks on the transition density is investigated. The medium noise is modeled in the time domain by assuming that the recorded transitions are subject to random variations in width as well as in position. A time domain measurement technique is developed to estimate the second order statistics of transition width and transition position as a function of recording density. The results indicate that the noise due to the transition width variations predominates over the noise resulting from the position jitter of the written transitions at high densities where the transition spacing approaches the transition width.
The effect of Cr and W nucleation layers on the magnetic properties of CoPt films
Authors: Howard J. K.
Published: July 2002

CoPt and CoCr alloy films have received considerable interest recently for use as recording media in high-density recording technology. Chromium films have been used as nucleation layers to improve the magnetic properties of hcp magnetic alloy films (CoNi, CoNiCr, and CoCr) by increasing the in-plane c-axis preferred orientation. In this investigation, Co80Pt20 magnetic films were deposited onto 1000-Å-thick nucleation layers of chromium, a chromium-vanadium alloy or tungsten. Deposition of Co80Pt20 films onto W produced a significant increase in coercivity compared to the Cr nucleation layers. Coercivity values as high 2400 Oe were observed for the W/Co80Pt20 composite structure compared to about 1900 Oe for the CrV/Co80Pt20 structure.
Spacing dependence of magnetic recording with a single thin-film head and disk (abstract)
Authors: Jefferson C. Michael , Beardsley I. A.
Published: July 2002

Although it is known that magnetic recording system performance can be improved by reducing the separation between the head and media, few detailed measurements of the spacing dependence of recording performance (rolloff curves, isolated pulse heights and widths, etc.) have been made. Most measurements reported to date are at low linear velocities using flexible media and deposited oxide layers on the head1 or carbon overcoats of various thicknesses on the flexible disk2 to maintain a given spacing. This paper presents the results of measurements made with a novel device which positions the head at arbitrary (and continuously variable) heights above a rigid magnetic disk operating at a high and constant linear velocity. Separate read and write spacing loss measurements were made using a 3380-type thin-film head and metal film disk at a number of spacings ranging from 0.075 μm (3 μin.) to 0.5 μm (20 μin.). The results are analyzed using head sensitivity functions computed by the boundary element method. Good agreement between theory and data is found at linear densities in excess of 2500 fc/mm. The advantages of magnetic recording at small head/disk spacing are discussed.
Demagnetization process of sintered R17Fe83−xBx magnets (R=Nd or Pr)
Authors: Otani Y. , Miyajima H. , Chikazumi S. , Hirosawa S. , Sagawa M.
Published: July 2002

A series of R-Fe-B (R=Nd or Pr) sintered magnets rich in B relative to R15Fe77B8 were synthesized to investigate the demagnetization processes for various configurations of R2Fe14B grains. The R2Fe14B grains in these magnets are well separated from each other by a surrounding B-rich R1.11Fe4B4 phase. The coercivity of Nd17Fe83−xBx at 320 K is increased from 11 to 18 kOe with an increase of B content from 17 to 37 at. %. With a decrease of temperature from 320 K, the coercivities of Nd-Fe-B magnets for x=17, 30, and 37 at. % exhibit a monotonic increase. However, below 50 K, the coercivity of the magnet with x=37 at. % decreases sharply to 5 kOe. This behavior is interpreted in terms of the ferromagnetic ordering of the Nd1.11Fe4B4 phase at about 20 K.
Electromagnetic field analysis of unbalanced regimes of synchronous machines
Authors: Mayergoyz I. D. , Emad F. P. , Sherif M. A.
Published: July 2002

A new semianalytical technique for the computation of electromagnetic fields in synchronous generators under unbalanced steady-state conditions is presented. This technique is based on the novel idea of slot impedance boundary conditions and it leads to the analytical expressions for electromagnetic fields in terms of spatial harmonics.
Enhancement of perpendicular anisotropy in amorphous GdCo and TbFe films prepared by alternative bias sputtering
Authors: Yamamoto Hiroshi , Tanaka Masaichi , Naoe Masahiko
Published: July 2002

Amorphous GdCo and TbFe films were prepared by a newly devised sputtering technique in which film deposition and ion bombardments were performed alternatively. The changes of the film composition and magnetic properties were focused as a function of the thickness of the layer periodically deposited. It was found that ion bombardments induced by the substrate bias changed the composition only within a few atomic layers near the film surface. At the periodic thickness of about 3 nm, the enhancement of a perpendicular magnetic anisotropy took place in the both cases of GdCo and TbFe films. The new class of perpendicular anisotropy was discussed in relation to the multilayered structure formed by the alternative bias sputtering.
Performance improvement of bubble memories using Bi-substituted bubble films
Authors: Thayamballi P.
Published: July 2002

Epitaxial bubble films which use bismuth instead of rare-earth (RE) ion substitution to achieve the necessary uniaxial anisotropy have been grown with low defect densities. Device performance of 4-Mbit Permalloy bubble memories using Bi-substituted films is compared with those using the standard RE-substituted films. Comparison of the devices in the −55 °C to +120 °C temperature range shows superior performance of the Bi-substituted films. The Bi films show a smaller temperature variation of bubble nucleate and cut currents as well as wider bias-drive operating margins at the temperature extremes. The better operation of Bi-substituted films is attributed to lower temperature coefficient of uniaxial anisotropy and higher Curie temperature.
Band structure of cobalt by an empirical approach
Authors: Nelson J. S. , Fong C. Y. , Perlov C. M.
Published: July 2002

The band structure of hexagonal-close-packed ferromagnetic cobalt has been calculated using a nonlocal empirical pseudopotential method. With the energies in face-centered-cubic cobalt given by Himpsel and Eastman as a reference, the potentials are determined to give the best fit of the photoemission data and magnetic moment. The positions of the dominant peaks in the density of states for the minority spin case agree better with the photoemission (≤0.2 eV) than the ones of the majority spin case (∼0.3 eV). Physical quantities, such as d-band widths, exchange splitting, etc., are also analyzed and compared with experiments and other theories. The difference between most earlier theories and the present calculations are that we have (a) narrower d-band widths and (b) higher p-state energies with respect to the d states.
Bond randomness at Ising criticality
Authors: Singh Rajiv R. P. , Fisher Michael E.
Published: July 2002

A detailed theoretical study of bond or exchange randomness in three dimensions is carried out on the basis of high-temperature series expansions for the ±J Ising model. The results constitute the first stringent test of crossover scaling with φ=α in a model disordered system.
The natural finite element formulation of the impedance boundary condition in shielding structures
Authors: Hoole S. Ratnajeevan H. , Weeber Konrad , Hoole N. Ratnasuneeran G.
Published: July 2002

The study of shielding configurations requires an analysis of ac electromagnetic fields. However, the fine meshes required within the shield make ac analysis uneconomic and a static analysis is usually employed. In this paper, the impedance boundary condition, cast in vector potential form as a general Neumann condition, is naturally imposed through Galerkin’s method to eliminate eddy currents from the domain. This allows a more exact ac analysis to be employed.
The quest for a polymeric ferromagnet: A new polymorph of 1,4-bis(2,2,6,6-tetramethyl-4-oxy-4-piperidyl-1-oxy)butadiyne (invited)
Authors: Miller Joel S. , Calabrese Joseph C. , Glatzhofer Daniel T. , Epstein Arthur J.
Published: July 2002

A new polymorph of 1,4-bis(2,2,6,6-tetramethyl-4-oxy-4-piperidyl-1-oxy)butadiyne has been prepared and characterized by x-ray diffraction, infrared and Raman spectroscopies, and magnetic susceptibility. Unlike the Pccn-α phase, the β phase belongs to the Pca21 space group [a=14.265(1) Å, b=8.079 (3) Å, and c=18.865(2) Å, V=2174.1 Å3, Z=4, T=−100 °C, Ru=4.8%, Rw=5.0%). The C 3/4 C, CC–CC, and NO distances are 1.201, 1.391, and 1.293 Å, respectively. The only intermolecular interactions are 1.844-Å–OH ⋅ ⋅ ⋅ ON hydrogen bonding interactions. The vibrations νOH,NH =3289, 3070, 3021, νNO(IR) =1341, and νC 3/4 C (Raman) =2236 cm−1 are present. The solid-state motif is that of pleated sheets. UV, electron beam, and γ-ray induced polymerization has not been achieved; however, thermal treatment turns the crystals black. Thermogravimetric analysis under nitrogen reveals an explosive decomposition at ∼140 °C. Between 2 and 300 K the susceptibility obeys the Curie–Weiss expression with Θ=−2.75 K. The effective moment is 2.47μB per molecule which is consistent with two independent S= 1/2 spins per molecule. Upon thermal treatment (17 h at 90 °C) the resultant black material exhibits a reduced Curie–Weiss susceptibility of 1.12μB and Θ=−2.87 K. Unlike the α phase evidence for ferromagnetic behavior has not been observed.
Ferromagnetism in molecular materials: Decamethylferrocenium tetracyanoethanide (DMeFc) (TCNE) (invited)
Authors: Epstein A. J. , Chittipeddi Sailesh , Chakraborty A. , Miller Joel S.
Published: July 2002

Ferromagnetism has only recently been observed in molecular materials. We present here a summary of the ferromagnetic phenomena observed in the molecular charge transfer salt, decamethylferrocenium tetracyanoethanide (DMeFc)(TCNE), and related compounds. A spontaneous magnetization is observed in this material for T<4.8 K, with a saturation moment in agreement with alignment of individual spins localized on the DMeFc+⋅ and TCNE−⋅ ions. A comparison of these results with analogous charge transfer salts is presented. Models for the magnetic interaction in the charge transfer salts and the preparation of other molecular and/or polymeric materials with ferromagnetic exchange are presented.
Microanalysis of nonoriented P containing silicon steel
Authors: Liu Puru , Li Fulin , Chen Liang , Li Institute Zhenchun
Published: July 2002

Texture determination, Si, P distribution, and microstructural analyses were made for the nonoriented P containing silicon steel (DW1) by x-ray diffractometer (XRD), electron probe microanalyzer (EPMA), and transmission-electron microscope (TEM), respectively. DW1 is a new electrical steel designed by WISCo. It contains about 0.05% Si and 0.11% P [L. He, D. Fei, and P. Liu, in the Second International Conference on the Physical Metallurgy of Electrical Steel, New York, 1985 (unpublished)]. The textures were measured for samples decarburization-annealed at different temperatures such as 710, 750, 820, and 860 °C. According to the ratio of (100) and the magnetic properties of DW1, we found that the optimum result was obtained at 820 °C. It was found from the result of EPMA measurements that the distribution of Si and P is homogeneous without any grain boundary segregation. The microstructure shows that coarse precipitates of AlN an MnS were present in the hot rolled strip and remained in the strip after 1020 °C solid solution treatment but dissolved after 1120 °C. It also shows that 710 °C isn’t the efficient decarburizing annealing temperature because there are some inclusions precipitated along grain boundaries in the sheet after decarburization-annealed at that temperature. The structure of this type must be harmful to the properties of materials.
Use of resistivity and magnetic measurements to monitor recrystallization of metallic glasses
Authors: Fish G. E. , Hasegawa R.
Published: July 2002

It is shown that resistivity and magnetization measurements can be used to monitor the controlled devitrification of metallic glasses. These measurements are especially useful in the case of Fe-based metallic glasses to be used at high frequency. In these materials, transformation of about 1 vol. % of the amorphous matrix into crystalline α-Fe is known to produce enhanced magnetic properties. Magnetic techniques are especially sensitive when the heat treatment is carried out above the Curie temperature of the amorphous matrix but below the Curie temperature of the α-Fe precipitates.
Vector Preisach and the moving model
Authors: Della Torre Edward , Kádár György
Published: July 2002

The recently introduced vector Preisach model has the same congruency and accommodation properties as the classic Preisach model does. A study of these properties has indicated that both the moving model and the product model can correct these limitations in the scalar Preisach model. This paper uses the moving model modification to generalize the vector Preisach model so that it can display the congruency property correctly. The new generalized Preisach function is a function of six variables, and at a given point can assume seven possible values.
Very high mobility HgTe films grown on GaAs substrates by molecular-beam epitaxy
Authors: Feldman R. D. , Oron M. , Austin R. F. , Opila R. L.
Published: July 2002

HgTe films have been grown in both the (100) and (111) orientations on (100) GaAs. In agreement with what has been reported for growth on II-VI substrates, we find higher Hall mobilities in (100) films. An 80-K mobility of 92 200 cm2  V−1 s−1 has been achieved. This is higher than has previously been reported for growth on (100) II-VI substrates. The conditions for growing these films are described.
CoCr double-layered media with NiFe and CoZrNb soft-magnetic layers (invited)
Authors: Bernards J. P. C. , Schrauwen C. P. G. , Zieren V. , Luitjens S. B.
Published: July 2002

The magnetic, structural, and recording properties of CoCr double-layered media are investigated. The underlayer materials NiFe (crystalline) and CoZrNb (amorphous) were combined with two different kinds of intermediate layers: Ti (crystalline) and Ge (amorphous). Applying a bias voltage during sputtering of NiFe results in a low coercivity of the NiFe layer and in a high coercivity of the CoCr layer. The structure of the NiFe layer influences the structure of the CoCr layer. A Ti layer between the NiFe and CoCr layers decreases the in-plane remanence of the CoCr layer. The coercivity of all CoZrNb layers is low, independent of the application of a bias voltage. The orientation and structure of CoCr on CoZrNb can be improved by using a Ge intermediate layer, which results in a low coercivity of the CoCr. A Ti intermediate layer increases the coercivity. Ring heads show a dependence of spike noise on the underlayer coercivity and on the applied normal force. A probe-type head shows a dependence of its output on the CoCr coercivity, which may be understood in terms of demagnetization and writing depth.
Ion beam mixing of GaAs with films of Al, Si, and their nitrides
Authors: Fastow R. , Brener R. , Kalish R. , Eizenberg M.
Published: July 2002

Thin films of Al, AlN, Si, and Si3N4 deposited on GaAs substrates were irradiated with silicon ions. The amount of interfacial mixing was found to depend both on the composition of the thin film and on the ion dose. The greatest amount of mixing, as measured by Rutherford backscattering spectrometry and Auger depth profiling, occurred in the Al/GaAs system. Mixing in the Si/GaAs system showed a sublinear dose dependence as well as a deep diffusion of silicon into the substrate. Interfacial phase formation between the aluminum and silicon layers and the GaAs substrate was observed using Auger line shape analysis and low-energy electron loss spectroscopy. Small or negligible mixing was found in the AlN/GaAs and the Si3N4/GaAs systems, presumably due to strong nitrogen bonding in these layers. The data suggest that an optimal cap for through-cap implantation and annealing is a two-layer structure consisting of a thin Si3N4 layer below a thick AlN layer.
The effects of the glass substrate on the properties of rf glow discharge amorphous Si:H thin films
Authors: Koo Y.C. , Perrin R. , Aust K. T. , Zukotynski S. , Kruzelecky R. V.
Published: July 2002

The quality of a rf glow discharge deposited a-Si:H thin film is affected by the substrate material. As a result of ion bombardment, some of the reactive species from the glass substrate are introduced into the deposition chamber by desorption. These species are then adsorbed back into the surface with the decomposed gas and form impurities in the film. The presence of Na-Si and K-Si impurities in the a-Si:H film lowers the electrical conductivity and decreases the film stability.
Magnetic anisotropy in rf sputtered Tb-Fe films
Authors: Krishnan R. , Porte M. , Tessier M. , Vitton J. P. , Le Cars Y.
Published: July 2002

We have studied sputtered amorphous Tb-Fe films by torque magnetometry in the range 10–300 K. M-H loops have also been taken with a vibration sample magnetometer. All the samples studied show uniaxial anisotropy on the order of 1.5×106 erg cm−3. The rotational hysteresis is present. The torque curves for T<80 K show a strong deviation from sin 2θ behavior and makes the extraction of Ku difficult. However, in the range 80–300 K, Ku increases strongly with a decrease in temperature. A strong contribution from magnetoelastic interactions is suggested. As regards magnetization, it increases as T decreases and saturates for T<60 K. The results are discussed.
Observation of optical radiation in the negative differential resistance region of optoelectronic triangular barrier switch
Authors: Mand Ranjit S. , Nakamura Masaru
Published: July 2002

First observation of light emission due to negative differential resistance in a new optoelectronic device called an optoelectronic triangular barrier switch, which displays bistable electrical characteristics, is reported. The light emission is shown to be initiated by controlled reverse breakdown and then sustained by avalanching for the duration of the negative differential resistance part of the device electrical characteristics. The spectral content was measured and has peak emission at 0.85 μm, which corresponds to the band-gap energy of the GaAs. It is shown that the light emission is due to the radiative recombination of electron-hole pairs created by avalanching electrons and not due to the recombination of high-energy electrons and holes.
Ferromagnetic resonance of thin yttrium iron garnet films near a ground plane: Parallel field
Authors: Barak J. , Ruppin R. , Suss J. T.
Published: July 2002

Parallel field ferromagnetic resonance spectra of an yttrium iron garnet film in the vicinity of a metallic ground plane are presented. The evolution of the spectra with changing film-ground distance is traced continuously over a wide range. The following effects are found to occur at distances of less than about 500 μm: Large shifts of the resonance fields, disappearance and subsequent reappearance of lines, appearance of ‘‘forbidden’’ lines, and crossing of lines. All of these effects are confirmed by a theoretical calculation which relies on the mechanism of excitation of waves which are circulating around the sample.
Photoluminescence characteristics of undoped and terbium chloride doped zinc oxide films deposited by spray pyrolysis
Authors: Falcony C. , Ortiz A. , García M. , Helman J. S.
Published: July 2002

The photoluminescence characteristics of undoped and TbCl3-doped zinc oxide films deposited by the spray pyrolysis technique are reported. Undoped films present the characteristic blue-green emission peak at ∼508 nm observed in single-crystal and powder ZnO. The TbCl3-doped films present a luminescence peak at ∼540 nm. The light emission of the doped films decreases with time of exposure of the sample to the excitation light. The phenomenon is interpreted in terms of a simple model in which a competitive process of hole trapping and phototrapping occurs at a radiative recombination center generated by the TbCl3.
Generation of 130-nm radiation via four-wave mixing in Hg vapor
Authors: Leung K. , Slater R. C.
Published: July 2002

A 2ω1+ω2 four-wave mixing scheme in Hg vapor has been utilized to generate radiation in the 130-nm spectral region that overlaps the strong O-i triplet.
Frequency characteristics of the Mn-doped InP p-n junction
Authors: Takanohashi T. , Tanahashi T. , Sugawara M. , Kamite K. , Nakajima K.
Published: July 2002

Admittance spectroscopy is applied to the analysis of the thermal properties of the Mn acceptor-doped InP grown by liquid-phase epitaxy. The thermal activation energy and capture cross section are determined as ΔET=183 meV and σp=1.8×10−13 cm2, respectively. The cutoff frequency of the emission of holes from the Mn acceptor is 1 GHz at 300 K. It is shown that the small signal frequency characteristic of a buried heterostructure laser is improved at frequencies f>1 GHz by using the Mn-doped p-InP layer for the current blocking region.
Back bias effects on two-dimensional electron gas
Authors: Schuermeyer Fritz L. , Grzyb Joseph A. , Curtis Michael J. , Paulus Michael J. , Cheney Michael E.
Published: July 2002

A new technique is described to study heterostructure field-effect transistors. This technique is based on the application of an electric field perpendicular to the channel via a p-doped substrate. The measurements demonstrate that the centroid of the two-dimensional electron gas resides approximately 10 nm below the heterointerface and that application of a negative substrate potential increases the confinement of these charges towards the interface. A negative substrate voltage decreases the K′ factor of the transistor and also reduces the well capacity. Capacitance voltage measurements confirm that a parasitic channel in the donor layer can be formed and that it is shielded from the substrate by the two-dimensional electron gas.
The effect of accelerating gap geometry on the beam breakup instability in linear induction accelerators
Authors: Miller R. B. , Marder B. M. , Coleman P. D. , Clark R. E.
Published: July 2002

The electron beam in a linear induction accelerator is generally susceptible to growth of the transverse beam breakup instability. In this paper we analyze a new technique for reducing the transverse coupling between the beam and the accelerating cavities, thereby reducing beam breakup growth. The basic idea is that the most worrisome cavity modes can be cutoff by a short section of coaxial transmission line inserted between the cavity structure and the accelerating gap region. We have used the three-dimensional simulation code SOS to analyze this problem. In brief, we find that the technique works, provided that the lowest TE mode cutoff frequency in the coaxial line is greater than the frequency of the most worrisome TM mode of the accelerating cavity.
Interfacial reactions of platinum thin films on (111) and (001) germanium
Authors: Hsieh Y. F. , Chen L. J.
Published: July 2002

A combined plan-view and cross-sectional transmission electron microscope study has been carried out to investigate the interfacial reactions in platinum thin films on germanium. Pt2Ge, PtGe, Pt2Ge3, and PtGe2 were found to form at 160, 250, 350, and 400 °C, respectively. Definite orientation relationships were observed between those of Pt2Ge, PtGe, and PtGe2 and (111)Ge. No epitaxial growth of platinum germanides on (001)Ge was observed. The results were found to be partially different from those obtained in a previous investigation. The discrepancy is attributed to different substrate cleaning schemes prior to the metal film depositions in the two studies. It appears that the growth of platinum germanide epitaxy on (111)Ge is not directly correlated with the lattice matches at germanide/Ge interfaces at room temperature.
Thickness dependence of material quality in GaAs-on-Si grown by metalorganic chemical vapor deposition
Authors: Pearton S. J. , Abernathy C. R. , Caruso R. , Vernon S. M. , Short K. T. , Brown J. M. , Chu S. N. G. , Stavola Michael , Haven V. E.
Published: July 2002

The evolution with increasing layer thickness of the structural and electrical properties of GaAs grown directly on Si or Si-on-insulator (SOI) by metalorganic chemical vapor deposition is reported. There is a substantial improvement in the surface morphology and near-surface crystallinity of the GaAs in thicker films (≥1.5 μm). The implant activation efficiency of 60-keV 29Si ions at a thickness of 4 μm is comparable to that seen in bulk GaAs. The deep level concentration is also observed to decrease with increasing layer thickness. Transmission electron microscopy reveals average defect densities near 108 cm−2 in films deposited either on misoriented or exact (100) Si, and in those grown on SOI.
Correlation between electronic states of O, Cu, and Ba in several high-T
c superconductors
Authors: Horn S. , Cai J. , Shaheen S. A. , Croft M. , Chang C. L. , den Boer M. L.
Published: July 2002

X-ray photoemission measurements of Y-, Sm-, Eu-, and Yb-based high-temperature superconductors show a clear correlation between Cu 2p satellite features, which previous work has shown are associated with materials which exhibit superconductivity, and a high-binding-energy peak in the O 1s spectrum. In samples with varying oxygen content the intensity of the Cu 2p satellites changes, reflecting the Cu valence which varies between 1+ and 2+. The high-binding-energy O peak appears to track the Cu valence. This high-binding-energy peak may be indicative of the presence of O 2p holes, suggested in some models as necessary for superconductivity. The Ba 3d peak position also changes systematically with the Cu valence.
Dependence of growth length of single silicon crystals on scanning direction of laser beam in lateral seeding process
Authors: Fujii Eiji , Senda Kohji , Emoto Fumiaki , Hiroshima Yoshimitsu
Published: July 2002

The growth length of single silicon crystals obtained by laser annealing was investigated in detail as a function of the scanning direction of the laser beam in the lateral seeding process on (100), (110), and (111) silicon substrates. It was found that the scanning direction 〈110〉 on a (100) substrate offers the largest growth length. An attempt has been made to interpret this result on the basis of a {111} facet formation model.
Semiclassical derivation of Handel’s expression for the Hooge parameter
Authors: van der Ziel Aldert
Published: July 2002

A semiclassical derivation is given of Handel’s expression [Phys. Rev. Lett. 34, 1492 (1975); Phys. Rev. A 22, 745 (1980); Phys. Rev. A 26, 586 (1982)] for the Hooge [Phys. Lett. A 29, 139 (1969); Physica 83B, 19 (1976)] parameter αH. This may explain why Handel’s expression for αH always agrees with the experimental data, despite the fact that there seem to be serious objections to Handel’s derivation of his results.
Scaling, material, and design characteristics of the permeable base transistor
Authors: Meyyappan M. , Kreskovsky J. P. , Grubin H. L.
Published: July 2002

Numerical simulation of the gallium arsenide permeable base transistor has been performed through solutions to the drift and diffusion equations in two dimensions. First, scaling of the device to increase the current and frequency has been investigated. The various scaling approaches used are discussed in detail. Second, the sensitivity of the device performance to the device parameters such as base penetration, channel opening, etc., has been studied. Third, the effect of material characteristics on the cutoff frequency has been investigated. A new design incorporating a semi-insulating region around the base is proposed and studied in detail. This new design is shown to reduce the amount of unwanted stored charge upstream of the base and to result in increased cutoff frequencies.
Pulsed-laser-induced reactive alloying of Fe-W system under benzene
Authors: Ghaisas Smita , Chaudhari S. M. , Kanetkar S. M. , Ghaisas S. V. , Kulkarni V. N.
Published: July 2002

Reactive alloying of the Fe-W system under benzene by use of pulsed laser treatment is demonstrated. The as-deposited and processed samples were characterized by employing the techniques of low-angle x-ray diffraction, Rutherford backscattering, conversion electron Mössbauer spectroscopy, and x-ray photoelectron spectroscopy. Formation of ternary phase FeW3C is observed at a lower fluence while its amorphization is observed at a higher fluence.
Absolute excited state and ion densities from two- and three-photon processes in some 6p levels of atomic krypton
Authors: Khambatta Noshir M. , Oertel John A. , Silk Robert , Radziemski Leon J. , Mack Joseph M.
Published: July 2002

Neutral krypton atoms are excited from the ground state to the 4p56p[3/2]2 state by two-photon absorption from an ArF excimer laser operating at 193.41 nm. The third photon ionizes the krypton atoms. Excitation and ionization yields are theoretically computed employing the standard laser rate-equations analysis. Measurements are made on both the excitation and ionization yields. The experimental results are in good agreement with the theoretical predictions of our formulations, as well as with those of other authors.
The Pierce diode with an external circuit: Simulations in the linear regime
Authors: Lawson William S.
Published: July 2002

The linear theory for the eigenfrequencies of the extended Pierce diode for resistive, capacitive, and inductive external circuits is tested via computer simulation with the pdw1 code, and is verified to within the accuracy of the simulation (between 1% and 0.01% depending on the circumstances). The simulations were remarkably inexpensive in terms of computer time, and could have been performed on a personal computer.
Plasma- and gas-surface interactions during the chemical vapor deposition of tungsten from H2/WF6
Authors: Green W. M. , Hess D. W. , Oldham W. G.
Published: July 2002

Ion and neutral species were sampled from a H2/WF6 tungsten deposition atmosphere (with and without plasma enhancement) by a line-of-sight quadrupole mass spectrometer and cylindrical mirror ion energy analyzer. These diagnostics were used to investigate the influence of neutral and ion flux on the resistivity and morphology of α- and β-tungsten films. In all depositions, WF, WF2, and WF6 were the principle tungsten-fluorine species while WF+5 was the primary plasma-generated ion. Variation of α-tungsten film properties with thickness was dominated by impurities and defects incorporated early in the deposition and by domain size. Plasma-enhanced chemical vapor-deposited films exhibited lower resistivity, and higher temperature coefficient of resistivity and domain size compared to low-pressure chemical vapor deposition films. The variation of α-tungsten properties with increasing ion-bombardment energies was consistent with enhanced sputtering and damage production. Low-resistivity small-domain films were deposited at low frequencies while low-energy high-current bombardment conditions were conducive to domain growth. Nucleation and growth of β tungsten required oxygen rather than fluorine impurities.
Townsend coefficients for electron scattering over dielectric surfaces
Authors: Peck Timothy L. , Kushner Mark J.
Published: July 2002

A method for describing the probability of initiating flashover discharges across dielectric surfaces is presented in which we define a transport coefficient for electron multiplication similar to the Townsend coefficient used for gas discharges. The coefficient is a function of the scaling parameter (charge released from the cathode)/(cathode-anode separation) and is also a measure of the growth of the sheath on the dielectric surface resulting from electron scattering. We discuss results for when the source of seed electrons does not necessarily depend upon field emission at the cathode-vacuum-dielectric triple point. This may occur when the surface is illuminated by UV radiation. For these conditions, there is a different functional dependence of flashover probability on voltage and geometry (e.g., thickness of the insulator) than when field emission provides the seed electrons. As a result, criteria previously used to predict flashover discharges may not apply.
Circuit model of surface arcing
Authors: Robiscoe R. T. , Sui Zhifeng
Published: July 2002

An electrical breakdown on a highly charged dielectric surface can result in a discharge along the surface, i.e., a flashover arc. We construct a simple circuit model for such an arc: the discharge of a capacitor C (related to the initial charged area) through a series inductor L and resistor R (related to the arc considered as a plasma). The arc current assumes a very simple form over most of its dynamic range, and such measured arc quantities as total charge transport, pulse width, peak current, and rise time are easily calculated. Moreover, straightforward a priori estimates of C, L, and R values give calculated arc quantities in good agreement with observation, for both typical magnitudes and areal scaling. We also analyze the effect on areal scaling of allowing the arc resistance R to ‘‘switch’’ during the evolution of the arc, from a small value characteristic of the arc plasma to a large value characteristic of the dielectric surface. Finally, we consider some aspects of the electromagnetic radiation generated by the arc.
Parallel-processing single-beam Fourier-imaging thermal-wave microscopes: Line-heating systems
Authors: Lörincz A.
Published: July 2002

Thermal-wave microscopes are generally restricted in speed by their long integration times and the point-by-point scanning mode. In this paper the properties of Fourier-imaging line-heating thermal-wave microscopes are considered. These new microscopes can overcome the speed limit by offering a parallel-processing mode for points placed along a narrow line, determined by the resolution of the optical system. The method allows single-beam arrangement, i.e., the reflected part of the heating beam is the means for detection. In particular, the dark-field and the phase-contrast techniques are studied.
Electron transfer between regions with different confining potentials
Authors: Frohne R. , Datta S.
Published: July 2002

A practical numerical method is presented for obtaining the scattering matrix for an electron at a junction between two regions having different confining potentials in the transverse direction. The scattering matrix should find general use in models describing electron transport in semiconductor microstructures whenever changes in channel dimensions or structure are important. As an illustrative example, the method is applied to electron transfer from a narrow channel into a wide contact including the effects of the contact potential.
Magnetic properties of Ni/Fe//SiO2 multilayer film
Authors: Nagai Yasuhiro , Senda Masakatsu
Published: July 2002

This paper presents an experimental investigation into the magnetic properties of Ni/Fe//SiO2 multilayer films. An increase in magnetic anisotropy and a decrease in hard-axis coercivity are observed with decreasing the Ni/Fe layer thickness in Ni/Fe//SiO2 multilayer films. By sandwiching thinner Ni/Fe and 5-nm SiO2 layers together, relative permeability is tremendously increased to a range of 3500–4500. This permeability improvement corresponds well to the minor loop in the M-H characteristics. The magnetic domain observation indicates that the domain structure is widely changed, and several 180° and reduced 90° walls exist in the pole tip of thin-film head patterns. The higher relative permeability of over 3000 and the higher saturation magnetization of 1.7 T are confirmed in the thickness range of 0.1–2.0 μm.
Comparative studies of defects in GaAs on silicon substrates using electron-beam-induced current and transmission electron microscopy
Authors: Humphreys T. P. , Hamaguchi N. , Bedair S. M. , Tarn J. C. L. , El-Masry N. , Radzimski Z. J.
Published: July 2002

We report the use of electron-beam-induced current imaging and transmission electron microscopy techniques to examine defects in heteroepitaxial films of GaAs on Si. The electron-beam-induced current method has been successfully applied to obtain dark spot micrographs revealing the distribution of electrically active defects in the GaAs epilayer. Relatively large areas of dark contrast corresponding to regions of high defect density (enhanced recombination) have been identified. In contrast, within the intervening regions between these electrically active centers, areas associated with uniform electrical quality have been observed. Furthermore, in a comparative study of the microstructural character of defects using transmission electron microscopy, we have also identified corresponding regions of high and low defect density. The role of electrically active defects in determining the minority carrier lifetimes and diffusion lengths in the GaAs epilayer is also discussed. Moreover, it has been demonstrated that an electron-beam-induced current technique is an appropriate alternative to transmission electron microscopy in delineating the contribution and distribution of electrically active of defects in large-area heteroepitaxial GaAs on silicon samples.