bluuebunny/crossref_metadata_2025 huggingface dataset:
Compositional dependence of properties of Bi2−yPbySr3−xCaxCu2O8+z films grown by liquid phase epitaxy
Authors: Balestrino G. , Marinelli M. , Milani E. , Paoletti A. , Paroli P.
Published: July 2002

The growth of Bi2−yPbySr3−xCaxCu2O8+z films by liquid phase epitaxy is illustrated. Films are shown to be good single crystals epitaxial relative to the substrate. Films stoichiometry was varied changing the melt composition. The effects of the Ca and Pb stoichiometry on both the structural and superconducting properties are discussed. The c lattice parameter of the films was found to increase linearly with the Ca content per formula unit with a slope of 0.3 A each 0.5 Ca atoms per formula unit. No sizeable changes in the superconducting properties were found for films with a Ca content between 0.8 and 1.3 atoms per formula unit. Lead doping is shown to decrease the transition temperature without broadening the transition itself. 0.4 lead atoms per formula unit decreased the transition temperature down to 69 K.
dc electrical behavior of polymers used in electro-optic devices
Authors: Ling Hung C. , Holland W. R. , Gordon H. M.
Published: July 2002

We have measured the temperature and electric field dependence of the direct current (dc) electrical resistivity of several electro-optic polymers, in addition to pure polymethyl methacrylate (PMMA) and a commercial acrylate, UV-15. All the polymers exhibit a decrease in resistivity, to different degrees, with increasing temperature between room temperature and 130 °C. The results show that in a sandwich of multiple layers, the high temperature resistivity mismatch between individual layers results in field concentration in the layer with the highest electrical resistivity. This can be used to explain the enhanced electro-optic coefficient measured in electro-optic devices consisting of a sandwich of UV-15/copolymer/UV-15. In PMMA, we observed a saddle region in the temperature dependence of resistivity between 67 and 78 °C. Outside the saddle region, the resistivity of PMMA follows an Arrhenius relationship, with an activation energy of 1.0 eV. This saddle region is broadened in the nitro and DCV copolymers. A mechanism in which the motion of side chains hinders the interchain hopping of conducting species is proposed to explain our data.
Planar solidification in a finite slab: Effects of density change
Authors: Charach Ch. , Zarmi Y.
Published: July 2002

Planar solidification in a slab of finite thickness, cooled from below, is addressed. The solid density is supposed to be greater than the liquid density. The fluid flows toward the moving phase-change front, accompanied by heat transfer in the emerging solid, in the liquid and cavity, resulting due to the contraction of the volume of the material, are analyzed. The Rubinstein transformation, which immobilizes the interface, is modified in order to take the density change into account. It enables one to reduce the problem to that without the density change. Several approximate analytic solutions for transient solidification, some of which are new even for equal solid and liquid densities, are presented.
Neutron production in dense x-pinch plasmas produced from deuterated polyethylene fibers
Authors: Mittal K. C. , Kalantar D. H. , Qi N. , Hammer D. A. , Gerber K. A. , Sethian J. D.
Published: July 2002

A novel intense source of 2.45 MeV neutrons is described. Exploratory experiments with deuterated polyethylene fibers in an x-pinch configuration have been performed using 370-kA, 80-ns current pulses. Up to 4.5×108 neutrons per pulse have been produced. Compared to a z pinch, an x pinch produced about the same number of neutrons for the same current, but the x-pinch neutron source may be 1 mm or less in diameter.
Ion saturation currents to spherical and cylindrical electrostatic probes in collisional plasmas
Authors: Benilov M. S. , Rogov B. V.
Published: July 2002

Simple analytical formulas are discussed relating ion saturation currents to cylindrical or spherical electrostatic probes and the charged particle concentration in an undisturbed plasma. It is shown that normalized values of saturation currents may be approximately considered as universal functions of the diffusive Peclet number (which characterizes the normalized velocity of the plasma flow past the probe), the form of these functions being independent of the species of neutral component of plasma, the species of ions, parameters of undisturbed plasma, etc. A comparison with a large set of various experimental data available in the literature is presented. It is shown that the above formulas describe most of these data with the accuracy of a factor of 3.
Development of the Gd(0001) band structure with film thickness
Authors: Li Dongqi , Hutchings C. W. , Dowben P. A. , Wu Rong-Tzong , Hwang C. , Onellion M. , Andrews A. B. , Erskine J. L.
Published: July 2002

By growing gadolinium films on W(110), it has been possible to observe the development of the Gd(0001) band structure with increasing film thickness. The changes in the 5d bands as a result of exposure to oxygen or the development of the valence-band structure with increasing film thickness lead to changes in the 5p multiplet oscillator strengths. These changes are a result of the influence of the band structure upon the final-state effects that give rise to such multiplet structures. This study provides conclusive evidence that there is a 5d contribution to the shallow 5p multiplet photoemission core-level structure.
Calculated ground-state properties of ternary uranium compounds
Authors: Gasche T. , Auluck S. , Brooks M. S. S. , Johansson B.
Published: July 2002

The compounds UTAl (T=Fe,Co,Ni,Ru,Rh,Ir,Pt) crystallize in the hexagonal ZrNiAl structure. Measurements suggest that the 5f electrons in these compounds are itinerant [V. Sechovsky and L. Havela, in Ferromagnetic Materials, edited by E. P. Wohlfarth and K. H. J. Buschow (North-Holland, Amsterdam, 1988), Vol. 4, p. 309]. From self-consistent linear muffin-tin orbital energy-band calculations for the compounds the transition to magnetism across the series is explained in terms of the calculated Stoner products. Inclusion of spin-orbit interaction leads to an induced orbital moment in URhAl, consistent with the experimental observation that the magnetic properties of these compounds are highly anisotropic [V. Sechovsky and L. Havela, in Ferromagnetic Materials, edited by E. P. Wohlfarth and K. H. J. Buschow (North-Holland, Amsterdam, 1988), Vol. 4, p. 309].
Calculated spin and orbital moments in UNi2
Authors: Severin L. , Johansson B. , Nordström L. , Brooks M. S. S.
Published: July 2002

For the hexagonal ferromagnet UNi2, an unusual 5f form factor for uranium has been observed, indicating a large orbital contribution to the total moment. We report on self-consistent electronic structure calculations for the hexagonal Laves phase (C14) compound UNi2, taking both spin and orbital contributions to the total moment into account. In a constrained calculation, where the spin moment is chosen to agree with experiment, very good agreement with the experimental form factor is obtained. In the analysis of the form factor both the 6d and the 5f electrons are taken into account giving improved agreement with experiment.
Analysis of a quadrupole bonded Nd–Fe–B magnetic roller
Authors: Fang Wen-Ling , Huang Der-Ray
Published: July 2002

Magnetic rollers have been widely used in xerographic processes to transport the toners. Conventionally, magnetic rollers were made from extruded Ba- (or Sr-) ferrite with energy product 1.4–1.8 MGOe. Recently, a magnetic roller with stronger field and smaller size is required by some laser printers or copiers. The MQ1 powder was used in designing a new bonded Nd–Fe–B magnetic roller with energy product about 3 MGOe. The distribution of the radial magnetic field of the quadrupole magnetic roller was measured by a Hall probe over the surface. The theoretical simulation was calculated by using the ANSYS Version 4.4 software. The error of the peak positions and the wave widths of the quadrupoles between the theoretical and experimental data is within 5°. The error of the peak value between theoretical analysis and experimental measurement is within 10%. The theoretical analysis of the magnetic roller is very useful for designing a new magnetic roller.
Degradation of melt-processed Y-Ba-Cu-O in the presence of moisture
Authors: Spyker R. L. , Kozlowski G.
Published: July 2002

Degradation of melt-processed Y1Ba2Cu3O7−x has been observed when the superconducting material is subjected to prolonged contact with moisture. This degradation manifests itself in a reduction in the critical current level. Results indicate that connections between grains degrade faster than the intragranular material itself. After prolonged exposure the material will eventually break apart into individual grains which are still superconducting.
High transport J
c and magnetization in textured Bi-Pb-Sr-Ca-Cu-O superconductors
Authors: Tiefel T. H. , Jin S.
Published: July 2002

High transport Jc is essential for major bulk applications of the high-Tc superconductors. In this paper, we report transport critical current and magnetization behavior in c-axis textured Bi-Pb-Sr-Ca-Cu-O superconductor ribbons. The highly oriented layer structure was achieved by a combination processing of spray coating on silver foil, cold rolling, and partial melting. Transport Jc values as high as 2.3 × 105 A/cm2 at 4.2 K, H=8 T (H⊥ab) have been obtained, which is one of the highest reported so far. The high Jc at H≥ (R18)5 T is maintained to temperatures near 20 K. A comparison of Jc (transport) and Jc (magnetization) indicates that the size scale of the circulating supercurrent loop in the Bean model nearly corresponds to the whole sample dimension rather than the orders-of-magnitude-smaller grain size, thus demonstrating that the a-b grain boundaries in the melt-processed ribbons are not weak links. A similar bulk processing technique with more extensive deformation can also be used to produce weak-link-free thin films, as demonstrated by preparation of ∼3000-Å-thick films. Since epitaxial growth from single crystal substrates is not required, the technique may be suitable for high-speed, low-cost production of large area thin films.
Strong magneto-optical enhancement in highly Ce-substituted iron garnet films by sputtering (abstract)
Authors: Gomi M. , Furuyama H. , Abe M.
Published: July 2002

Recently we succeeded in growing epitaxial films of Ce-substituted iron garnet (Y3−xCexFe5O12) with so much substitution as up to x=1.5, which strongly enhances magneto-optical (MO) effect in the near IR region around hν=1.4 eV.1 The enhancement per Ce ion surpasses that by Bi3+ ion in the IR region which has been the champion of the MO enhancement for 20 years. In this study we have measured the Faraday effect of the Ce-substituted garnet films in an extended photon energy range of hν=1–4 eV in order to elucidate the role of Ce3+ in the MO enhancement. The films (R3−xCexFe5O12: R=Y, Gd, Yb, x=0–3.0) were epitaxially grown in situ on Gd3Ga5O12 (GGG) and Nd3Ga5O12 (NGG) single-crystal substrates by conventional rf diode sputtering. For R=Y the Ce substitution was successfully extended to x=2.5 by sputtering under the reduced atmosphere of Ar+H2. The Ce substitution prominently enhanced Faraday effect not only in the IR region at hν=1.4 eV but also in the UV region at hν=3.1 eV, both having a paramagnetic dispersion relation with nearly equal magnitude though opposite in sign. We also found a new optical absorption due to Ce3+ at hν =2.0 eV which does not enhance the Faraday effect.
Properties of bonded anisotropic magnets
Authors: Panchanathan V. , McMullen A. T. , Croat J. J. , Doser M. , Ribitch R. W.
Published: July 2002

High-energy product anisotropic Nd-Fe-B permanent magnets can be prepared by consolidation and hot-deforming melt-spun material. One feature of this type of magnet is that it can be converted into stable powders for subsequent processing into anisotropic bonded magnets. The stability of this powder is attributed to the much smaller crystalline size of the rapidly solidified materials compared to that of sintered magnets. In this work, the properties of anisotropic bonded magnets made from powders produced by hydrogen decrepitation and by a mechanical crushing process are given. Energy products of 15–18 MGOe have been achieved by compression molding techniques. Long-term thermal stability at 100 and 125 °C of bonded magnets using various binders are given. Transmission electron microscopy studies of the anisotropic powder indicate the microstructure to be similar to the hot-deformed precursor material.
Microstructures and magnetic properties of anisotropic Nd-Fe-B magnets produced by splat quenching
Authors: Harada Tetsuji , Ando Teiichi , O’Handley Robert C. , Grant Nicholas J.
Published: July 2002

Crystallographic alignment of the Nd2Fe14B phase was achieved in a Nd15Fe77B8 alloy by splat quenching. Nd-Fe-B magnets produced by splat quenching had a columnar dendritic structure with the growth direction aligned normal to the chilled surfaces of the splats. X-ray diffraction showed that the dendrites were the magnetic Nd2Fe14B phase with their growth direction parallel to the c axis of Nd2Fe14B. The coercivity of the Nd-Fe-B magnets with dendritic structures increased with decreasing dendrite arm spacing. At higher solidification rates the dendritic structures were replaced with equiaxed Nd2Fe14B structures, and with an amorphous structure at the highest quench rates, which resulted in low values of coercivity. Splats with columnar dendritic structures showed a magnetic anisotropy characterized by higher remanence and energy product values in the growth direction of the dendrites.
Die-upset rare-earth iron-boron ingot: Coercivity dependence on composition and heat treatment
Authors: Krentz J. E. , Lee R. W. , Waldo R. A.
Published: July 2002

Rapid solidification (melt spinning) and powder metallurgy (sintering) methods have been successfully developed to fabricate excellent permanent magnets from RE2Fe14B-based alloys (RE=rare earth). Hot deformation of a chill-cast ingot is a potentially simpler and less costly method. However, development of this method will require better understanding of the coercivity mechanisms in this form of the magnet material. Toward this end, this paper reports results of a study of the dependence of the room-temperature demagnetization of a die-upset chill-cast ingot on composition and postpress heat treatment. Substitution of Pr for Nd and Cu for Fe results in smaller 2:14:1 grain size which leads to improved magnetic alignment and higher coercivity in a die-upset ingot. Postpress heat treatment produces a reversible order of magnitude coercivity change from a low-coercivity state (quench from 1000 °C) to a high-coercivity state (quench from 600 °C). This large effect is discussed in the light of electron probe analyses of the grain boundaries. A contributor to coercivity in these materials appears to be the REFe2 component of the eutectic.
Magnetic properties and thermal stability of Fe-Zr-N/Si-N and Fe-Ta-N/Si-N multilayer film (abstract)
Authors: Hoshi Y. , Naoe M.
Published: July 2002

It has been shown that Fe-N/Si-N multilayer films has excellent soft magnetic properties, but their properties are deteriorated easily by increasing the temperature above 400 °C.1 In this study, we added a small amount of Zr and Ta to the Fe-N layer to improve their thermal stability of the soft magnetic properties. Multilayer films about 3000 Å thick were deposited by an opposed target sputtering apparatus on glass slide substrates. Thickness of the Si-N layer was fixed at 50 Å, while those of the Fe-Zr-N (or Fe-Ta-N) layer TFe-N was changed in the range from 200 to 1000 Å. For control of the film composition, a composite target was used. The area ratio of the Zr (or Ta) plate to total target area was changed in the range 0∼4.8%. Figure 1 shows the changes in coercivity Hc and saturation magnetization Ms of the Fe-Zr-N/Si-N film with annealing temperature. The changes in x-ray diffraction patterns of these films are shown in Fig. 2. It is evident from these figures that the crystal growth in the films obtained by the sputtering of 4.8%: Zr-Fe target is significantly suppressed, though the film obtained by the sputtering of 3.2%: Zr is crystallized at a temperature below 400 °C. Soft magnetic properties of the 4.8%: Zr film are not deteriorated by the annealing at the temperature up to 550 °C. Saturation magnetization has a tendency to increase as the annealing temperature increases. Similar results are obtained in the addition of Ta.
Generic source of perpendicular anisotropy in amorphous rare earth-transition metal films: Analytical results
Authors: Fu H. , Mansuripur M. , Meystre P.
Published: July 2002

We derive an analytical expression for the intrinsic perpendicular anisotropy density Ku produced by surface magnetic dipolar interactions in amorphous rare earth-transition metal thin films.
ac impedance at the superconducting vortex glass transition (invited) (abstract)
Authors: Olsson H. K. , Koch R. H. , Eidelloth W. , Robertazzi R. P.
Published: July 2002

We find scaling behavior of the linear ac impedance consistent with a transition into a vortex glass state in measurements on cuprate YBaCuO superconducting thin films in large magnetic fields, H≳Hcl. The films were measured in the frequency range from 100 kHz to 500 MHz. At the vortex glass transition temperature, Tg, and in the ac linear regime we find scaling behavior of the impedance amplitude, ‖Z‖∝ω0.83, and a frequency-independent phase, φ=74°. The measured frequency dependence, ‖Z‖∝ω(2−d+z)/z, and phase φ=(π/2)(2−d+z)/z is consistent within experimental error of the value of the critical exponent z obtained from dc current-voltage measurements on the same sample. At higher temperatures and still in the linear regime, we find scaling behavior of a temperature-dependent crossover frequency to the critical regime, Ω(T−Tg), and at Tg, scaling behavior of a current density which sets the size of the linear regime, J0(ω, T=Tg). Within experimental error, all of these results are in excellent agreement with predictions for the ac impedance of the vortex glass phase transition in large magnetic fields.
Single-crystal growth and magnetic properties of La2CuO4 and related compounds (T, T*, and T′ phases) (invited) (abstract)
Authors: Cheong S-W.
Published: July 2002

We have performed magnetic, transport, and optical measurements on well-characterized crystals of (un)doped La2CuO4-related compounds, so-called T, T* and T′ phases, in order to understand the physical properties of quasi-2D S=1/2 antiferromagnet with/without added carriers. Single crystals of the (un)doped single-layer cuprates with large in-plane dimension and optically flat surface have been grown by the flux technique with CuO excess. Ways to control and measure dopant level in the crystals will be discussed. Our various measurements of magnetism in the pristine compounds indicate that magnetic phenomena in the insulating layer systems are qualitatively understandable in terms of classical spin models of 2D S=1/2 antiferromagnet, that is, quantum fluctuation effects, expected to be large in S=1/2 systems, are only perturbative. In this context, we discuss results of various investigations such as studies of magnetic dilution effects, field-induced transition, two-magnon scattering, and inelastic neutron scattering. Optical spectra have been measured over a wide range of energies and carrier densities. In undoped crystals, one simple excitation is the electron-hole pair at the edge of a charge transfer gap, whose energy scales with the Cu-O spacing. With a few added carriers, additional excitations appear due to the formation of impurity bands. We discuss a possible relationship between the excitations and spin dynamics.
Transition between the ferromagnetic, paramagnetic, and spin glass in Fe-Al alloys (abstract)
Authors: Zhi Q. Z. , Thomas L. K.
Published: July 2002

In a certain concentration range the Fe-Al alloys undergo a complex magnetic transition.1,2 In this paper the magnetic phase diagram and behavior of Fe1−xAlx (x=29–34) alloys with the (Fe3Al)- and (FeAl)-type atomic order at low temperature have been investigated by alternating low-field susceptibility and steady-field magnetization measurements. The results have shown that the superparamagnetic transition of the alloys with (FeAl)- and (Fe3Al)-type crystal structure extend from 30.0 to slightly above 30.5 at. % Al and between 30.3 and 30.9 at. % Al, respectively. The type of ordered structure has an obvious influence on the freezing temperature Tf and reversed Curie temperature T0. The superparamagnetic range in the double transition with (FeAl)-type order is wider than those with (Fe3Al)-type order so that the magnetic phase diagram is moved in Fe-rich direction. The alloys with different type order have the different ranges of the multicritical point. It can be understood on the basis of the calculation that the ferromagnetic exchange is increased during the transition from (FeAl)- to (Fe3Al)-type ordered structure. The results are interpreted as the relative complete ability between the nearest-neighbor Fe-Fe ferromagnetic exchange and the further-neighbor Fe-Fe ferromagnetic exchange and the further-neighbor Fe-Al-Fe antiferromagnetic superexchange being changed.
Spin-reorientation phenomena in (TbxEr1−x)TiFe11 systems
Authors: Zhang L. Y. , Ma B. M. , Zheng Y. , Wallace W. E.
Published: July 2002

Spin-reorientation phenomena in (TbxEr1−x)TiFe11 systems have been studied over the temperature range from 20 to 1000 K using susceptibility measurement. In this alloy series, the lattice constants, both a and c, increase with increasing x, as expected from the lanthanide contraction. For x<0.5, the (TbxEr1−x)TiFe11 systems were found to exhibit axial-to-conical spin-reorientation transitions with a Tsr decrease with increasing x. However, for x≳0.5, the spin-reorientation transitions have been found to be axial-to-planar, on cooling, and the Tsr increases with increasing x. The magnetic phase diagram of (TbxEr1−x)TiFe11 has been constructed.
The recursion method applied to the T=0 dynamics of the 1D s=1/2 Heisenberg and XY models
Authors: Viswanath V. S. , Müller Gerhard
Published: July 2002

The frequency-dependent spin autocorrelation functions for the 1D s=1/2 Heisenberg and XY models at zero temperature are determined by the recursion method. These applications further demonstrate the efficacy of a new calculational scheme developed for the termination of continued fractions. A special feature of the recursion method highlighted here is its capability to predict the exponent of the infrared singularities in spectral densities.
Hard-spin mean-field theory: Formulation for Ising, XY, and other models
Authors: Netz Roland R. , Berker A. Nihat
Published: July 2002

A new type of mean-field theory, that incorporates the hard-spin conditions of local degrees of freedom, is generally formulated for arbitrary types of local degrees of freedom. The method is implemented by solving its set of coupled equations for the local distribution functions and densities, either analytically and numerically, or by Monte Carlo sampling (‘‘Monte Carlo mean-field theory’’). Excellent results are obtained for frustrated Ising models in two and three dimensions. An explicit formulation is given for XY models.
Structural and magnetic properties of stage 2 CocMn1−cCl2-graphite intercalation compounds
Authors: Suzuki Masatsugu , Suzuki Itsuko S. , Khemai Floyd , Burr Charles R.
Published: July 2002

Stage 2 CocMn1−cCl2-graphite intercalation compounds (0≤c≤1) approximate two-dimensional site-random XY spin systems with a competition between ferromagnetic [J(Co–Co) and J(Co–Mn)], and antiferromagnetic exchange interactions [J(Mn–Mn)]. The magnetic phase diagram and critical behavior of these compounds are studied by means of ac and dc magnetic susceptibility. For c≥ (R18)0.45 the phase transition occurs between the paramagnetic phase and the ferromagnetic phase. The critical exponents of γ and β do not change with dilution of Mn atoms: γ=2.31 and β=0.085 for c=0.90.
Change of magnetic properties of Th2Fe17 due to interstitial solution of C and N
Authors: Jacobs T. H. , Long Gary J. , Pringle O. Allan , Grandjean F. , Buschow K. H. J.
Published: July 2002

The changes in magnetic and crystallographic properties in the series Th2Fe17Cx and Th2Fe17Nx have been studied. The changes in the latter series were also studied by 57Fe Mössbauer spectroscopy. The ultimate enhancements of the saturation moments in these series are 13% and 24%, respectively. This is much larger than observed previously in the corresponding rare-earth compounds, although the Curie temperature enhancements are of comparable magnitude. In the Th–Fe–C system a novel compound of the BaCd11 type was found, having a Curie temperature around 370 K.
Magnetism of (Sm,R)2Fe17Ny (R=Y, Tb or mischmetal)
Authors: Huang M. Q. , Zheng Y. , Miller K. , Elbicki J. M. , Sankar S. G. , Wallace W. E.
Published: July 2002

Magnetic properties are reported for nitrides of the formula (Sm1−xRx)2Fe17Ny, where R=Y, Tb, or mischmetal and y=2.5 to 2.8. Substantial replacement of Sm by R is observed for Sm2Fe17−60% by mischmetal and 100% by Y or Tb. In all cases nitrogenation expands the lattice and increases Tc by 300 to 400 K. Magnetization decreases as Sm is replaced by Tb but increases when Y is the dopant. The latter implies antiferromagnetic coupling in Sm2Fe17. The uniaxial anisotropy observed for Sm2Fe17Ny is weakened by replacing Sm with Tb or Y. The weakening is greater in the case of Tb; this follows since the Tb crystal field interaction opposes that of Sm, whereas Y acts essentially as a mere diluent. If dilution were the only effect, HA would fall linearly with composition. Behavior approaching this is observed. Some of the systems appear to be of interest for permanent magnet fabrication.
Microstructure and magnetic behavior of granular Co-BN films
Authors: Tsoukatos A. , Hadjipanayis G. C.
Published: July 2002

Cox(BN)100−x films with x=30–90 at. % were prepared by dc magnetron sputtering. X-ray and TEM data show the presence of (002) α-Co(hcp) in the as-grown Co–BN films, and (101) α-Co in their annealed counterparts. dc susceptibility data in the as-deposited films showed a magnetic transition that is a function of the Co volume fraction in the film. The coercivities of the Co–BN films were found to depend on the particle size and metal volume fraction.
Monolayer magnetism of 3d transition metals in Ag, Au, Pd, and Pt hosts: Systematics of local moment variation
Authors: McHenry M. E. , MacLaren J. M. , Clougherty D. P.
Published: July 2002

Electronic and magnetic properties of T/Aun, T/Agn (T=Cr, Mn, Fe, Co, and Ni), Fe/Pdn and Fe/Ptn multilayers and sandwiches have been computed using the layer Korringa–Kohn–Rostoker (LKKR) band-structure technique. Enhanced (as compared with bulk) 2D T magnetism is observed in all Cr, Mn, and Fe/host configurations, consistent with weak coupling between Cr, Mn, and Fe d bands and those of the noble metal (NM) hosts and consequently d bandwidths which are exceeded by the exchange splitting. Fe and Cr moments vary systematically with the number of mediating Ag or Au planes and the Fermi energy of the system. These systematics are explained by considering the variation of the Fermi energy (EF) with composition as well as constraints of charge neutrality and strong (single-band) ferromagnetism. For Fe in Pt and Pd hosts, d-d hybridization leads to a nearly invariant Fe moment as a function of the number of mediating Pd or Pt planes but with large induced moments on the host.
The effect of a parasite hybridizer on the magnetic behavior of partially delocalized transition shell systems (abstract)
Authors: Sanchez-Castro C. , Cooper B. R. , Bedell K. S.
Published: July 2002

We have investigated how the behavior of a transition shell atomic species (species A) with orbital magnetism, driven by hybridization-mediated interactions via a sea of band electrons, is modified by the addition of a second parasite hybridizer (species B). Our approach involves a two-stage procedure. First, we calculate the modification of the band electron sea by hybridization with B by using a slave boson formalism. Second, the modifications in the A-A interionic interactions driving the orbital magnetic ordering are calculated by applying a Schrieffer–Wolff transformation on the renormalized Anderson lattice hamiltonian obtained from the first stage. The new A-A interactions have a different radial dependence (range factor) which depends in a nonlinear way on the band-B hybridization strength: and the consequences of this change on the magnetic ordering are studied using a mean-field approximation. This enables us to model the reduction in the magnetic ordering caused by competing parasite hybridization, and the dependence of this reduction on the relative hybridization strengths of the two species.
High frequency characteristics of annealed Co-base amorphous alloy ribbons
Authors: Tsai C. S. , Yang W. J. , Leu M. S. , Lin C. S.
Published: July 2002

The rapidly quenched amorphous Co-base alloy CobalFe4Ni2Si15B14 (Metglas 2714A) is a suitable material for the magnetic core operating in a high frequency. Appreciable reduction in core loss and increase in permeability of this material can be achieved by proper heat treatment. In this study, data from differential scanning calorimetry (DSC) and high frequency magnetic properties of samples annealed at different temperatures is presented. The results show that magnetic core loss at 50 kHz and 0.4 T decreases as annealing temperature (Ta) increases from 400 to 753 K, and it reaches a minimum with an anomaly factor η of 1.5 at annealing temperature of 753 K. Initial permeability μi behaves more complicately and reach the maximum value of 24000 at the same temperature, which is 50 K lower than the crystallization temperature (Tx = 823 K). This improvement of high frequency magnetic properties is attributed to the presence of small nuclei precipitated during heat treatment. The fraction of crystalline part in the amorphous matrix for optimum high frequency properties is 5%–6%, as estimated from the DSC data.
Magnetic and magnetotransport of amorphous U-As films
Authors: Plaskett T. S. , McGuire T. R. , Fumagalli P. , Gambino R. J. , Bojarczuk N. A.
Published: July 2002

Amorphous thin films of UxAs100−x are ferromagnetic for U-rich compositions, 49≤x≤75, with a magnetic moment of 0.2 to 0.4 μB per U atom and Curie temperatures, Tc, up to 120 K. Large resistivities are found at 5 K for compositions x<51, indicating semiconducting properties for low U content. For the highest Tc, the anomalous Hall angle is θH = 12° and the anomalous Hall coefficient is RS ≊ 10−7 Ω cm/G. Maximum polar Kerr rotation for U62As38 is −2.0° at 1-eV photon energy. The properties of U-As amorphous films are similar in many respects to those of amorphous U-Sb, except that the maximum values of these properties occur at higher U contents. The results are discussed in terms of spin-orbit interactions.
Magnetoresistance of paramagnetic metallic layers sandwiched between ferromagnetic layers
Authors: Garcia N. , Hernando A.
Published: July 2002

Experimental results on magnetoresistance of Fe/Cr/Fe trilayers and multilayers show a large enhancement of this magnitude for a thickness of approximately 10 layers and decreases exponentially with the number of layers. In this work it is proposed that the key point to understand these experiments may lay in the fact that the exchange field of the ferromagnets penetrates in the paramagnet as has recently been proposed by the authors to explain coupling energies in trilayers. Even if the decay length of the penetrating field is small, of the order of nearest neighbors in Fe, its magnitude is large (1000 T), larger than any applied saturation field. The ferromagnetic and antiferromagnetic configurations give rise to two different field configurations and therefore to two different values of the resistance. In the opinion of the authors this is controlled by the effective section that the electrons can go. Also, it is not doubtful that the magnetoresistance is large but that the magnetic field (scattering spin potential) that the electrons see is large. It is found that the magnetoresistance is very much structure or roughness dependent and increases, in first approximation, with its amplitude. The magnetoresistance depends exponentially with the number of paramagnetic layers with a 10–20-Å decay length, but does not oscillate; it is a smooth function.
Neutron measurements on an epitaxial thin film of YBaCuO
Authors: Crow M. L. , Pickart S. J. , Nunes A. C. , McGuire T. R. , Gupta A.
Published: July 2002

We report evidence for an ordered flux line lattice in a 2-μm epitaxial film of YBaCuO from both neutron depolarization and diffraction measurements. Depolarization occurred when field cooling was done normal to the film plane but not within it; this is consistent with frozen-in vortices. Evidence for ordering of the flux lines comes from intensity maxima observed in difference patterns between field cooled and zero field cooled conditions.
Analysis of the normal-state magnetic susceptibility of La2−xSrxCuO4+y (abstract)
Authors: Filipkowski M. E. , Budnick J. I.
Published: July 2002

We describe a quantitative analysis of the low-temperature (T<300 K) susceptibility [χ(T)] of La2−xSrxCuO4+y for dopant concentrations in the vicinity of the superconducting phase boundary (SPB) at x=0.055. This analysis is based on a phenomenological model for the temperature dependence consisting of a Curie-like 1/T term plus a term linear in T. We find that the former exhibits nontrivial doping dependence at the SPB, while the T-linear part accepts decomposition into a Pauli contribution and a portion which can be understood using spin-wave theory.
Muon spin relaxation in the heavy fermion system UPt3
Authors: Luke G. M. , Le L. P. , Sternlieb B. J. , Wu W. D. , Uemura Y. J. , Dalichaouch Y. , Lee B. W. , Maple M. B. , Seaman C. L. , Armstrong P. E. , Ellis R. W. , Fisk Z.
Published: July 2002

We report muon spin rotation/relaxation (μSR) measurements of the heavy fermion superconductor UPt3 in external fields Hext∥ĉ. We find that the muon Knight shift is unchanged in the superconducting state, consistent with odd-parity pairing (such as p wave). The transverse field relaxation is observed to be strongly field dependent, decreasing with increasing field. Below Tc the increase is barely detectable in an applied field of 4 kG∥ĉ. On the basis of the high field measurements, we estimate the low temperature penetration depth to be λ(T→0)≥ (R18)11 000 Å.
Effect of residence time on microwave plasma chemical vapor deposition of diamond
Authors: Celii F. G. , White D. , Purdes A. J.
Published: July 2002

We have investigated the effects of reactant residence time on the properties of microwave-assisted chemical vapor deposited diamond films. Using a constant gas pressure of 40 Torr and gas composition of 1% CH4 in H2, the total gas flow rate was adjusted from 25 to 800 sccm which corresponds to apparent chamber residence times of 3–100 s for our reactor. The flow rate is one of the few parameters in the microwave plasma deposition system that is decoupled from all others, making this a relatively clean study on the effects of a single process variable. Two distinct types of diamond films were prepared in this work. One set was deposited directly on diamond-seeded silicon wafers. A second set was prepared separately, and under otherwise identical diamond film growth conditions, but deposited on a layer of microcrystalline diamond (MCD). The 5-h growths resulted in continuous polycrystalline diamond films of ∼2 μm thickness which were analyzed with scanning electron microscopy, Raman scattering and photoluminescence (PL) spectroscopies, infrared (IR) transmission, and x-ray diffraction. The Raman and PL spectra, and x-ray diffraction data exhibited flow-dependent behavior, while the electrical resistivity, IR transmission spectra, and deposition rate of the films, as well as the optical emission spectra of the deposition plasmas, were relatively insensitive to the flow rate. The x-ray diffraction results revealed that the diamond films were textured, although the preferred orientation was not particularly related to the surface morphology.

The surfae preparation strongly affected the texture, with films deposited on MCD exhibiting a [110] texture while those on Si had a [111]-preferred orientation. Furthermore, the extent of texture for the films on Si varied with the gas flow rate, unlike that of the films on MCD. The Raman and PL spectra varied with flow for both the films on Si and on MCD. Flow modeling showed the importance of convective flow in our reactor, and the insensitivity of deposition rate on gas flow rate can be rationalized by the flow pattern. The presence of vortices above the growth surface complicates the concept of residence time for this system. We argue that variation in the concentrations of gas-phase diamond growth species, arising from changes in gas residence time, are responsible for the flow-dependent variation in diamond film material properties.
Electrical transport properties of CoSi2 and Co(SixGe1−x)2 films formed by different methods
Authors: Li Bing-Zong , Liu P. , Jiang G. B. , Huang W. N. , Lu X. , Aitken R. G. , Daneshvar K. , Puzerewski M. , Singco G.
Published: July 2002

The electrical transport properties of CoSi2 and Co(SixGe1−x)2 thin films formed by solid state interaction and co-evaporation in the range of 4–300 K were studied. The Hall effect data indicate a hole carrier conduction in all samples. The rapid thermal annealed CoSi2 exhibits a typical metallic conduction with a residual resistivity of 3.3-μΩ-cm and room-temperature (RT) resistivity of 15 μΩ cm. The co-evaporated CoSi2 and Co(Si0.9Ge0.1)2 films after low temperature annealing up to 250 °C show a low resistivity of 70–80 μΩ cm at RT and change little down to 4 K. The hole carrier density of all the samples studied has values close to 2–3×1022 cm−3, while the carrier Hall mobility has large differences.
Correlation of shock initiated and thermally initiated chemical reactions in a 1:1 atomic ratio nickel-silicon mixture
Authors: Krueger Barry R. , Mutz Andrew H. , Vreeland Thad
Published: July 2002

Shock initiated chemical reaction experiments have been performed on a 1:1 atomic ratio mixture of 20- to 45-μm nickel and −325 mesh crystalline silicon powders. It has been observed that no detectable or only minor surface reactions occur between the constituents until a thermal energy threshold is reached, above which the reaction goes to completion. The experiments show the energy difference between virtually no and full reaction is on the order of 5 percent. Differential scanning calorimetery (DSC) of statically pressed powders shows an exothermic reaction beginning at a temperature which decreases with decreasing porosity. Powder, shock compressed to just below the threshold energy, starts to react in the DSC at 621 °C while powder statically pressed to 23% porosity starts to react at about 30 °C higher. Tap density powder starts to react at 891 °C. The DSC reaction initiation temperature of the shock compressed but unreacted powder corresponds to a thermal energy in the powder of 382 J/g which agrees well with the thermal energy produced by a shock wave with the threshold energy (between 384 and 396 J/g). (Thermal energies referenced to 20 °C.) A sharp energy threshold and a direct correlation with DSC results indicates that the mean thermal energy determines whether or not the reaction will propagate in the elemental Ni+Si powder mixture rather than local, particle level conditions. From this it may be concluded that the reaction occurs on a time scale greater than the time constant for thermal diffusion into the particle interiors.
Pyrolytic and photolytic dissociation of trimethylgallium on Si and Au substrates
Authors: Shogen Satoshi , Matsumi Yutaka , Kawasaki Masahiro , Toyoshima Isamu , Okabe Hideo
Published: July 2002

Pyrolytic dissociation of trimethylgallium (TMGa) on Si, Au, and Al substrates was studied at various temperatures from 80 to 670 K by x-ray photoelectron spectroscopy of Ga (3d) and C (1s). The intensity and band profile of carbon and gallium signals from TMGa adsorbed on the substrates were measured. The results indicate that TMGa on Si (111) dissociates into Ga and CH3 on the substrate even at 200 K and CH3 further dissociates into C, CH, and CH2 at higher temperatures. Most carbon and gallium species remain on the Si substrate. Carbon species leave the Au and Al substrate but Ga remains on the surface. The pyrolysis of TMGa on GaAs (100), Si (111), and Si (100) substrates is compared and the mechanism of carbon incorporation in photolysis and pyrolysis is discussed. Photodissociation of a monolayer of TMGa on Si and Au is observed with an incident wavelength of 266 nm; direct absorption by the adsorbed molecules occurs at this wavelength. At 355 nm, photodissociation does not occur.
Profiling of BaTiO3 ion beam sputtering by optical spectroscopy
Authors: Klein J. D. , Yen A.
Published: July 2002

The optical emission spectra resulting from argon ion beam sputtering a BaTiO3 target were observed as a function of position. A collimated optical fiber bundle parallel to the plane of the sputter target was translated vertically and horizontally to spectroscopically profile the sputter process. The Ar contours provide an image of the incident beam and its distortion by the presence of the target. Comparison of the Ar and O contours indicate that the oxygen atmosphere in the vicinity of the target is determined by sputtering events as well as the incident beam. The shapes of the Ba and Ti contours are elliptical with some slight differences in intensity gradients.
Impact ionization, recombination, and visible light emission in AlGaAs/GaAs high electron mobility transistorsa)
Authors: Zanoni Enrico , Paccagnella Alessandro , Pisoni Pietro , Telaroli Paolo , Tedesco Carlo , Canali Claudio , Testa Nicoletta , Manfredi Manfredo
Published: July 2002

This communication describes a detailed experimental investigation of light emitted from AlGaAs/GaAs high electron mobility transistors biased at high drain voltages where impact ionization occurs. We present the electroluminescence spectra in 1.1–3.1 eV energy range. The strong correlation of the integrated intensity of photons with hν≳1.7 eV with the product of hole current generated by impact ionization and of electron current indicates that the recombination process is the main mechanism for visible light emission.
Time-resolved reflectivity measurements of temperature distributions during swept-line electron-beam heating of silicon
Authors: England J. M. C. , Zissis N. , Timans P. J. , Ahmed H.
Published: July 2002

Experiments have been carried out to determine the temperature distributions induced during swept-line electron-beam heating of silicon. In situ measurements of the reflectivity were used to determine the temperature rise, using as a basis the rise in reflectivity exhibited by silicon with increasing temperature. Sweep speeds between 10 and 60 cm/s were studied using line beams between 60 and 300 μm wide. The experimental results were compared with analytic one- and two-dimensional models assuming constant thermal properties, and with a one-dimensional (1D) numerical model which takes into account the variation of heat capacity and thermal conductivity with temperature. The analytic models were used to show the range of conditions over which the 1D approximation could be applied and to quantify the errors introduced as this approximation breaks down. The experimentally measured peak temperatures and those predicted by the numerical model were found to agree to within 5% for conditions where the heat flow was in the 1D regime. For other conditions, the experimental and numerical results were found to differ, but the size of this discrepancy was consistent with the errors introduced by making the 1D approximation in the numerical model.
Surface breakdown of silicon
Authors: Feuerstein R. J. , Senitzky B.
Published: July 2002

The surface electrical breakdown of n+nn+ rectangular solid blocks of silicon have been investigated. These studies were conducted in air at pressures of 10−6 Torr and 1 atm, and in transformer oil, ethylene glycol, and de-ionized water, with pulsed electrical excitation. In addition, one sample had one contact end coated with a material having a large dielectric constant. It was found that the breakdown voltage of these devices increased as the dielectric constant of the ambient increased. Glow discharge cleaning of the surface in vacuum had no effect on the breakdown voltage. Based on these results a theory of surface charging leading to field enhancement along the surface is presented. Furthermore, the surface charge perturbs the space-charge region at the n+n anode junction such that the field at the junction increases more along the surface than in the bulk. As the field increases, it is hypothesized that collision ionization occurs, leading to avalanche breakdown. It is shown that a large dielectric constant material in contact with the surface near the junction can lead to significant improvement in the voltage holdoff capability of the silicon blocks.
Study of electrical damage in GaAs induced by SiCl4 reactive ion etching
Authors: Lootens D. , Van Daele P. , Demeester P. , Clauws P.
Published: July 2002

In the last decade reactive ion etching has become a very important tool for the patterning of submicron features. Although the particle energies involved in this etching process are relatively low, they still are high enough to alter the characteristics of semiconductor materials. In this paper we report on the electrical damage in n- and p-type GaAs induced by SiCl4 reactive ion etching. We found that the etching process causes significant electrical damage extending hundreds of nm deep in the p-GaAs but in n-GaAs only minor changes are observed. The changes in p-GaAs are thought to be due to the formation of EL2 point defects in a concentration comparable to the dopant concentration. Possible explanations for the observed differences in damage between p- and n-type material are given.
A predictive model of electron and hole decay in silicon-nitride-oxide-silicon nonvolatile memory transistors experiencing arbitrary thermal environments
Authors: Miller S. L. , McWhorter P. J.
Published: July 2002

A model is presented which accurately predicts the threshold voltage decay of both the excess electron and excess hole logic states of silicon-nitride-oxide-silicon nonvolatile memory transistors in thermally varying environments. The model predictions require as inputs the initial occupied trap distributions for both trapped holes and trapped electrons. A technique is presented to determine all model parameters, including the initial occupied trap distributions, by performing a single practical experiment with a specific thermal scenario. Once the model parameters are determined by this single experiment, the threshold voltage is predicted (with no adjustable parameters) for arbitrary time dependent thermal environments. Retention experiments are performed for a wide range of thermal environments which are changed during the charge decay process. The accuracy of the model predictions is verified by experimental data.