bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic extended x-ray absorption fine structure of transition metal films and alloys (abstract)
Authors: Idzerda Y. U. , Chakarian V. , Kemner K. M. , Elam W. T.
Published: July 2002

A very large helicity dependence of the extended x-ray absorption fine structure (EXAFS) above the L2,3 edges of the ferromagnetic transition metals Fe, Co, and Ni are observed. Transmission measurements of circularly polarized soft x rays through thin films of bcc Fe, hcp Co, fcc Ni, and FexNi1−x alloys deposited on ultrathin, semitransparent substrates show L-edge magnetic EXAFS (MEXAFS) oscillations nearly two orders of magnitude larger than the respective K-edge MEXAFS oscillations. Surprisingly, comparing the EXAFS and MEXAFS oscillations, after separation of the combined L2 and L3 spectra by an iterative deconvolution, show a linear dependence of the MEXAFS intensity on the spin moment of the scattering atom. Furthermore, the resulting fourier transforms show that, for the MEXAFS, the scattering paths traditionally associated with multiple scattering paths are enhanced compared to the L-edge EXAFS, suggesting the increased importance of multiple scattering in MEXAFS.
Modeling a magnetomechanical drive by a coupled magnetic, electric, and mechanical lumped circuit approach
Authors: Holmberg P. , Bergqvist A. , Engdahl G.
Published: July 2002

In electromagnetic drives and actuators electric, magnetic, and mechanical phenomena have to be solved for simultaneously. Moreover, the device is frequently fed by a power supply including components of power electronics. This article shows how the magnetomechanical drive can be modeled by lumped circuit elements and then be simulated together with the external electrical circuit and a mechanical load in a circuit simulation package. The circuit is easily designed and it considers both eddy currents and hysteresis in the magnetic device by means of a dual Cauer circuit.
Numerical analyses of magnetic field and force in toroidal superconducting magnetic energy storage using unit coils (abstract)
Authors: Kanamaru Y. , Nakayama T. , Amemiya Y.
Published: July 2002

Superconducting magnetic energy storage (SMES) is more useful than other systems of electric energy storage because of its larger amounts of stored energy and its higher efficiency. There are two types of SMES. One is the solenoid type and the other is the toroidal type. Some models of solenoid-type SMES are designed in the U.S. and in Japan. But the large scale SMES causes a high magnetic field in the living environment, and causes the erroneous operation of electronic equipment. The authors studied some suitable designs of magnetic shielding for the solenoidal-type SMES to reduce the magnetic field in the living environment.12 The toiroidal type SMES is studied in this article. The magnetic leakage flux of the toiroidal-type SMES is generally lower than that of the solenoid-type SMES. The toroidal-type SMES is constructed of unit coils, which are convenient for construction. The magnetic leakage flux occurs between unit coils. The electromagnetic force of the coils is very strong. Therefore analyses of the leakage flux and electromagnetic force are important to the design of SMES. The authors studied the number, radius, and length of unit coils. The storage energy is 5 G Wh. The numerical analyses of magnetic fields in the toroidal type SMES are obtained by analytical solutions.
Correlation between magnetic and mechanical properties of molded iron particle cores
Authors: Namkung M. , Bryant R. G. , Wincheski B. , Buchman A.
Published: July 2002

In order to optimize the molding conditions of polyimide bound iron particle cores, it is necessary to understand the combined effects of temperature and pressure on the mechanical and magnetic properties. In the present study the major core specimens were molded at 250, 300, and 350 °C under 82, 102, and 129 MPa. To avoid the anisotropy due to the uniaxial pressure induced directional ordering, spherical iron particles were used. The results showed that the density, hardness, and rupture strength are generally increasing functions of molding pressure and temperature, but the correlation is rather weak probably due to the presence of pores within the specimens. The maximum permeability of these cores vary in a range 30–110. By annealing selected core specimens at an elevated temperature, however, the maximum permeabilities increased to 900–1400 without noticeably changing the density. The magnetization curves of the annealed specimens show unmistakable evidence of domain wall motion suggesting the formation of a network allowing macroscopic propagation of domain walls. The results also indicate that the state of particle matrix interface may significantly contribute to the overall magnetic properties of molded cores since annealing particles alone is known to increase the maximum permeability by a factor of 2–4.
Bloch wall phase transition in the anisotropic spherical model (abstract)
Authors: Garanin D. A.
Published: July 2002

The temperature-induced second-order phase transition from Bloch to linear (Ising-like) domain walls in uniaxial ferromagnets was predicted theoretically1 within the mean-field approximation and observed in the dynamic susceptibility experiments on Sr hexaferrite.2 Here the fluctuational effects at this phase transition are investigated for the exactly solvable anisotropic model of D-component classical spin vectors in the limit D→∞. This anisotropic spherical model is equivalent to the common spherical model in the homogeneous case, but deviates from it and is free from nonphysical behavior in a general inhomogeneous situation. It is shown that the thermal fluctuations of the transverse magnetization in the wall (the Bloch wall order parameter) result in the diminishing of the domain wall transition temperature TB in comparison to its mean-field value, thus favoring the existence of linear walls. For ensuring finite values of TB, an additional anisotropy in the basal plane x, y is required: In purely uniaxial ferromagnets a domain wall behaves like a two-dimensional system with a continuous spin symmetry and does not order into the Bloch wall at any nonzero temperature. The theory qualitatively explains the fact that the value TB=0.99Tc measured on the Sr hexaferrite2 is substantially more remote from Tc than the mean-field estimation TB=0.996Tc, as well as some other characteristics of domain wall relaxation in the critical region.
Evolution of the electronic specific heat of (La1−xCex)3Al
Authors: Azechi L. S. , Medina A. N. , Gandra F. G.
Published: July 2002

The specific heat of (La1−xCex)3Al was measured in the temperature range from 2 to 30 K as function of the Ce concentration. The electronic specific heat for small x is close to the normal metal value (14 mJ/K2 mol f.u.), increasing to a maximum of 410 mJ/K2 mol Ce for x∼0.4, characterizing a heavy-fermion behavior around this concentration. Above this critical concentration, the electronic specific heat decreases to 140 mJ/K2 mol Ce for x=1. From the fitting of the experimental data to Debye and Schottky type Kondo and crystal field contributions we estimated the Kondo temperature, θD, Δ1, and Δ2. TK was found to increase with Ce concentration. Our results are interpreted in view of the competition between Kondo effect and Ruderman–Kittel–Kasuya–Yosida interaction.
Effect of barium cuprate on high temperature superconductors
Authors: Seyoum H. M. , Melamud M. , Wong-Ng W. , Bennett L. H. , Swartzendruber L. J. , Cook L. , Brown H. J.
Published: July 2002

BaCuO2 has a pronounced effect on the magnetization data of high-Tc superconductors. By subtracting the estimated magnetic contribution of BaCuO2 present in the superconducting samples, the susceptibility is seen to be purely diamagnetic.
Thermal stability of coated two phase magnets
Authors: Lee Ching-Ming , Chang Ching-Ray
Published: July 2002

A possible way to make high energy product magnets with surface coated soft phase based grains was proposed. It was proven theoretically that the energy product can easily achieve 70 MGOe with reasonable packing density and particle diameter. Here we analyze the thermal stability for these two phase magnets using a master equation with two metastable states for an individual grain, and then including the interaction from an oriented array. The result shows that an energy product of 60 MGOe can be maintained up to 400 K for a Nd2Fe14B/α-Fe system at packing density 0.8.
Short-time dynamics of correlated magnetic moments in superparamagnetic Cu–Co melt spun alloys exhibiting giant magnetoresistance
Authors: Allia P. , Tiberto P. , Vinai F.
Published: July 2002

Evidence for correlation among superparamagnetic particles in melt-spun Cu100−xCox systems (x=5–20) exhibiting a giant magnetoresistance is obtained by plotting this quantity as a function of reduced magnetization. Two ranges, Rθ(He) and Rθ(He), have been recently introduced to describe the extent of correlation among angles of tilt (θ) and of twist (φ) of superparamagnetic moments precessing around a local field axis. The angle of tilt appears to be spatially correlated over a distance larger by a factor of 3 than the angle of twist. This difference is explained by analyzing the short-time dynamics of magnetic moments in superparamagnetic granular systems with long-range interactions (of dipolar and the RKKY-like type). The typical time constants characterizing the process of scattering of conduction electrons by adjacent magnetic moments (electronic time of flight, relaxation times for θ and φ) are discussed in detail. An explicit expression for Rφ(H) is obtained by considering the competition between a magnetic interaction favoring parallel (or antiparallel) alignment or adjacent moments, and thermal disturbances resulting in a continuous loss of the phase coherence.
Transmission electron microscopy of as-quenched inert gas atomized particles: Effect of alloying additions in Nd2Fe14B
Authors: Wang J.-Y. , Lewis L. H. , Zhu Y. , Welch D. O. , Sellers C. H. , Branagan D. J. , Panchanathan V.
Published: July 2002

It is known that the addition of alloying elements to the Nd2Fe14B-based alloys significantly inhibits the onset of the crystallization in particles produced by the inert gas atomization (IGA) process. Transmission electron microscopy (TEM) was performed on a selection of as-atomized particles synthesized by IGA methods with the addition of 3 wt % TiC. TEM samples were successfully prepared using the wedge technique. Large particles (>10 μm) tend to consist of well-defined grains of Nd2Fe14B while the submicron size particles are generally amorphous and particles with diameter d in the size range, 1 μm<d<10 μm, contain nanocrystallites dispersed evenly throughout the amorphous matrix. The selected area electron diffraction pattern of the nanocrystallites in powder particles with diameters below 10 μm generally show three or more diffused diffraction rings that are indicative of α-Fe, with a particulate size of several tens of angstroms. These observations demonstrate that while the alloying addition of Ti and C in the IGA process significantly suppresses the formation of properitectic α-Fe in the Nd2Fe14B alloy, they do not completely prevent it.
Formation and magnetic properties of TbCu7-type RFe7 compounds and their nitrides (R=Tb and Dy)
Authors: Yang Jun , Mao Ou , Altounian Z.
Published: July 2002

DyFe x and TbFex alloys with x=7, 7.7, and 9 were mechanically alloyed followed by annealing in an attempt to prepare TbCu7-type DyFe7 and TbFe7 compounds. X-ray-diffraction and thermomagnetic measurements show that single-phase TbCu7-type TbFe7 can be obtained for all three compositions, while DyFe7 was formed for x=7.7 and 9 when annealed in the temperature range from 650 to 850 °C. The Curie temperature (Tc) of the TbCu7-type phase shows no obvious variation with Fe content, but decreases with annealing temperature. For DyFe7.7 and TbFe7.7, their respective Curie temperatures are reduced from 160 and 185 °C by annealing at 700 °C for 3 h to 140 and 160 °C after annealing at 850 °C for 3 h. Magnetometry measurements reveal that the TbCu7-type phase is a soft phase with a room-temperature coercivity of less than 500 Oe. Nitriding the TbCu7-type phase results in lattice expansions without changing the crystal structure. However, nitriding increases the Curie temperatures dramatically to 465 and 450 °C for TbFe7.7Ny and DyFe7.7Ny, respectively. Furthermore, nitriding greatly enhanced the coercivities of TbCu7-type compounds, reaching values of 3.75 and 4.0 kOe for TbFe7.7Ny and DyFe7.7Ny, respectively. The nitrides with optimum coercivities are single-phase TbCu7-type compounds with an average grain size of 10–15 nm as estimated from Bragg peak broadening. A coercivity mechanism based on contributions from the random anisotropy of the R3+ ions and the crystalline anisotropy is proposed to explain the observed effects.
X-ray absorption fine structure of samarium-doped borate glasses
Authors: Shimizugawa Yutaka , Sawaguchi Naoya , Kawamura Katsuyuki , Hirao Kazuyuki
Published: July 2002

Samarium LIII x-ray absorption fine structure spectra for both Sm2+ and Sm3+-doped (100-X)B2O3 XNa2O (X=10,15,20) glasses and both Sm2+ and Sm3+-doped 85B2O3 (15-X)Al2O3 XNa2O (X=5,10) glasses were measured using synchrotron radiation. The oxygen coordination number of samarium in Sm2+-doped glass is different from that of the Sm3+-doped glass with the same composition while the nearest neighbor Sm–O distances are closely the same. The change of coordination numbers with alkali or aluminum addition was related to the variation of the optical hole width of Sm2+-doped glasses.
(001) GaAs substrate preparation for direct ZnSe heteroepitaxy
Authors: Bousquet V. , Ongaretto C. , Laügt M. , Behringer M. , Tournié E. , Faurie J.-P.
Published: July 2002

We have investigated the influence of the (001) GaAs substrate preparation on the first stages of ZnSe heteroepitaxial growth by molecular beam epitaxy. We show that three different GaAs reconstructions occur depending on the ex situ substrate preparation, the Se residual pressure in the growth chamber and the temperature of heating. After deoxidation, an epiready substrate leads to a (2×1)-reconstructed surface at high temperature (∼600 °C) which turns into an unreconstructed surface when cooling down to the growth temperature (280 °C). An etched substrate, on the other hand, exhibits a (2×3) or a (4×3) reconstruction depending on the temperature reached during deoxidation. Both reconstructions are stable upon cooling down to the growth temperature. Direct nucleation of ZnSe on such deoxidized substrates leads to three-dimensional (3D), quasi two-dimensional (2D) and purely 2D growth modes on the unreconstructed, (2×3) and (4×3) reconstructed surfaces, respectively. Very pronounced oscillations of the reflection high-energy electron diffraction intensity are observed during nucleation on the (4×3) surface. Excellent agreement is obtained between simulated and experimental x-ray rocking curves for pseudomorphic layers grown on a (4×3) starting surface. In addition, their low-temperature photoluminescence spectra are dominated by free exciton recombinations without any defect-related line. Our results thus demonstrate that we have achieved a substantial improvement of ZnSe heteroepitaxy on bare GaAs substrates.
Effect of water absorption of dielectric underlayers on crystal orientation in Al–Si–Cu/Ti/TiN/Ti metallization
Authors: Yoshida Tomoyuki , Hashimoto Shoji , Hosokawa Hideki , Ohwaki Takeshi , Mitsushima Yasuichi , Taga Yasunori
Published: July 2002

The influence of the exposure of underlying dielectric (phophosilicate glass and borophosphosilicate glass) films to a humid air ambient on crystallographic orientations in Al–Si–Cu/Ti/TiN/Ti layered structures has been investigated as a function of the boron content and exposure time of the dielectric films. The Al(111) orientation in the layered structures was found to improve drastically with increasing boron content and exposure time of the dielectric films. The full width at half maximum value of an Al(111) x-ray rocking curve reached less than 1°. It was also found that the Al–Si–Cu surface becomes smoother and the average grain size increases as the Al(111) orientation improves. The improved Al(111) orientation was attributed to the improved Ti(002) orientation of the bottom Ti films. The mechanism of the improved Ti(002) orientation was investigated. It was confirmed that the improved orientation is closely related with the surface concentration of the absorbed water in the dielectric films. Further, it was demonstrated that interconnects fabricated from the improved layered structure have excellent electromigration performance.
Comment on “Quantum-well infrared detectors” [J. Appl. Phys. 74, R18 (1993)]
Authors: Nathan Vaidya
Published: July 2002

Three errors in the equations for dark current in quantum well infrared photodetectors suggested in a recent paper by Levine [J. Appl. Phys. 74, R18 (1993)] are pointed out and corrected.
A simple model of the adhesive failure of a layer: Cohesive effects
Authors: Ferer M. , Smith Duane H.
Published: July 2002

A fine-scale model is developed for the removal of an adhesive layer by a uniform stress. The initial motivation of this modeling project was a description of the removal of a layer of filter cake from cylindrical filters by backpulse cleaning. The model includes the bonding forces of adhesion between the layer and a substrate, as well as the forces of cohesion between imaginary “gridblocks’’ within the layer. For stresses greater than a threshold value, some of the layer is removed, with the fraction removed depending upon the stress, the average adhesive and cohesive forces, and the distribution of these forces about their average. The cohesive forces reduce the threshold well below the average strength of the adhesive force, because they increase the stress near broken adhesive bonds. The cohesive forces also sharpen the threshold in the cleaning pressure significantly, so that the threshold is very much sharper than the distribution of adhesive strengths. For moderate filter cake thickness (moderately strong cohesive forces), the threshold becomes steplike, with no cleaning just below the threshold and complete cleaning at the threshold and above. The model also provides the pressure dependence of the size and shape distributions for the fragments of the filter cake layer removed from the filter, enabling the model to address questions of cleaning efficiency, “patchy cleaning,’’ re-entrainment, and trapping of large cake-fragments in the filter vessel.
Magneto-optical spectra of (Mn1−xFex)Pt3 ordered alloy films
Authors: Kato T. , Iwata S. , Yasui M. , Tsunashima S.
Published: July 2002

The magnetic and magneto-optical properties have been investigated for ordered (Mn1−xFex)Pt3 alloy (0<x<0.6) films, prepared by annealing (Mn-Fe)/Pt multilayer films at 800 °C. The Kerr spectrum of the MnPt3 film had a large negative peak value of −1.18° at 1.24 eV, and showed a small positive peak around 3.2 eV. With increasing Fe content x, the peak value at 1.24 eV decreased in magnitude and the position of the peak shifted towards lower energy side. Furthermore, another peak appeared in the Kerr spectra around 2.3 eV for x>0.24. The spectral analysis of the diagonal component of dielectric tensor and the off-diagonal component of conductivity tensor showed that all the peaks mentioned above were attributed to interband transitions.
On the effect of pore pressure on the isotropic behavior of saturated porous media
Authors: Kytömaa H. , Kataja M. , Timonen J.
Published: July 2002

This paper analyzes the small strain elasticity of fluid saturated porous media and the influence of the fluid static pressure, or pore pressure, on their isotropic constitutive properties. The porous medium is modelled as a lattice assembly of monodisperse spheres that interact through Hertz contacts. The size of the spheres and hence the matrix volume at zero solids stress are shown to be influenced by the pore pressure. Consequently, the structural pressure generated by elastic Hertzian contact deformations is shown to depend on both the volume occupied by the matrix and the pore pressure. This result is then generalized for random assemblies of spheres by using an isotropic constitutive law that is realistic for dry sands. The present findings suggest that the contributions of pore pressure and structural pressure to the total stress do not have a constant weighting as is often assumed, but one that is sensitive to the deformation state of the matrix. The theory also captures the characteristic loss of matrix stiffness during liquefaction at sufficiently elevated pore pressures.
Numerical studies of annealed non-stoichiometric low temperature grown GaAs
Authors: Kreskovsky J. P. , Grubin H. L.
Published: July 2002

The means by which deep traps in annealed low temperature molecular beam epitaxy grown GaAs are responsible for its remarkable semi-insulating and short lifetime properties has been the subject of much discussion. For example, while low dc bias and high speed phototransient measurements can be explained as consequences of a homogeneous trap distribution in the non-stoichiometric material, experiments demonstrating the presence of electrically active precipitates must be dealt with. The study below, which is numerical, concludes that a consistent argument based on the presence of electrically active precipitates, coupled to a surrounding distribution of traps, will account for much of the observed experimental phenomena.
Optical absorption of ReS2 and ReSe2 single crystals
Authors: Ho C. H. , Liao P. C. , Huang Y. S. , Yang T. R. , Tiong K. K.
Published: July 2002

The optical absorption of synthetic ReS2 and ReSe2 single crystals is reported over a temperature range from 25 to 300 K. Analysis reveals that the absorption edges of ReS2 and ReSe2 are indirect allowed transitions. The indirect band gaps at various temperatures are determined and their temperature dependence is analyzed by the Varshni equation [Physica 34, 149 (1967)] and an empirical expression proposed by O’Donnel and Chen [Appl. Phys. Lett. 58, 2924 (1991)]. The parameters that describe the temperature dependence of energy gaps of these two materials are evaluated and discussed.
Effect of Ge on the segregation of B in Si(100) and Si(110)
Authors: Thompson P. E. , Silvestre C. , Jernigan G. , Hobart K. , Simons D. S. , Gregg M. R.
Published: July 2002

The segregation of B from Si1−xGex quantum wells grown using molecular beam epitaxy on Si(100) and Si(110) was investigated using secondary ion mass spectrometry. When a 3 nm B doping slab (n=1019/cm3) was placed in the center of a 6 nm Si1−xGex quantum well, the B profiles had two distinct exponential decay lengths, ΔSiGe, the Ge-controlled B decay length and ΔSi, the B decay length normally measured in Si. ΔSiGe was the same for Si(100) and Si(110) and independent of Ge concentration in the well for 0.1⩽x⩽0.5. As the Ge concentration was increased in the well, the location of the transition point, from ΔSiGe to ΔSi, which was always found far outside of the SiGe quantum well, increased in distance from the center of the well.
Effects of traps and shallow acceptors on the steady-state photoluminescence of quantum-well wires
Authors: Pérez-Merchancano S. T. , de Dios-Leyva M. , Oliveira L. E.
Published: July 2002

The effects of traps and shallow acceptors on the continuous-wave steady-state photoluminescence of GaAs-(Ga,Al)As quantum-well wires are studied at room temperature. The analysis is based on a quantum-mechanical calculation of the transition rates of radiative recombinations of excited-conduction electrons with free and bound (at acceptors) holes, and on a phenomenological treatment of the nonradiative rates associated with transitions involving conduction electrons falling into traps, and trapped electrons recombining with free holes. The various steady-state radiative and nonradiative e-h recombination lifetimes as function of the cw laser intensity are then obtained, as well as the dependence of the conduction-electron quasi-Fermi level (or chemical potential), and carrier densities on the laser intensity. We have also studied the laser-intensity dependence of various recombination efficiencies and of the integrated photoluminescence intensity. Finally, trap and impurity effects are shown to be quite important in a quantitative understanding of the room temperature steady-state photoluminescence of quantum-well wires.
Controlled temperature broadening of colossal magnetoresistance in a manganite heterostructure
Authors: Kalechofsky N. , Tsui Y.-K. , Reichenbach H. , McGinn P. , Schiffer P.
Published: July 2002

An intrinsic characteristic of the “colossal” magnetoresistance manganite compounds is that the resistance and the magnetoresistance vary strongly with temperature over the small temperature regime in which the magnetoresistance is exceptionally large. We propose a heterostructure constructed of layers of varying composition manganites which extends the regime of large magnetoresistance and greatly broadens the sharp peak in resistance. Data from a prototype heterostructure are presented that demonstrate the effectiveness of this method.
Impression creep of a viscous fluid
Authors: Yang Fuqian , He Xiaoyi , Dembo M. , Li J. C. M.
Published: July 2002

The impression test of a Newtonian fluid under a constant load and for a small Reynolds number flow was simulated by using the finite element method. It is found that the penetration velocity is a constant if the surface tension/viscosity ratio is less than 0.1 cm/s, the product of surface tension and indenter radius is less than 0.05 of the applied load, and the penetration depth is less than 1/3 of the indenter radius. Such constant penetration velocity is proportional to the applied load and inversely proportional to the viscosity and the indenter radius. The stick or slip boundary condition at the interface between the indenter and the fluid has no effect on the penetration velocity under these conditions.
Electron-beam-induced charging of phosphors for low voltage display applications
Authors: Seager C. H. , Warren W. L. , Tallant D. R.
Published: July 2002

Shifts of the surface potential were measured for several commercial phosphors by monitoring secondary and Auger electron spectra during electron beam irradiation at energies between 0.5 and 5 keV. The insulating phosphors charge strongly negative above 2 keV, whereas the conductive ones do not. This charging behavior is exaggerated after prolonged beam exposure. Measurements using two coincident electron beams to control the surface potential demonstrate that aging-enhanced surface charging decreases the phosphor cathodoluminescence. The dependence of the phosphor surface potential on the voltage applied to the metal plate on which they are deposited was also determined. These data suggest the presence of substantial space charge in the phosphors, even at low electron beam energies where no beam-induced shifts of the surface potentials are seen. We suggest that the electric fields due to these near-surface space charge regions are crucial in altering secondary emission and in establishing a steady state charge balance in the case where no currents can flow from the irradiated phosphor surface to the conductive backplane.
Aligned Sm2Fe17−δ Mδ CxNy (M=metal) magnet produced by post-sintering-gas-solid reaction
Authors: Chen X. , Altounian Z. , Ström-Olsen J. O.
Published: July 2002

The principle is discussed for nitriding a sintered Sm2(Fe,M)17Cx (M=metal) intermetallic compound. It is found that a bulk anisotropic magnet with the main composition of Sm2(Fe,M)17CxNy can be formed with a density of about 90% of full density. The physical integrity of the magnet is retained. As an example, an anisotropic magnet with the composition of Sm2Fe16.6Cr0.4C1.2Ny shows a coercivity of 6.3 kOe, a remanence, Mr, of 790 G, and an energy product of 15 MGOe at room temperature.
Brillouin light scattering and ferromagnetic resonance in sputtered NiFe/Cu/NiFe thin films
Authors: Lucena M. A. , de Aguiar F. M. , Rezende S. M. , Azevedo A. , Chesman C. , Parkin S. S. P.
Published: July 2002

The spin-wave spectra of Ni81Fe19(t)/Cu(25 Å)/Ni81Fe19(t) with t=200 and 300 Å are investigated by means of Brillouin light scattering and ferromagnetic resonance. Samples grown on three different substrates, namely, MgO(100), MgO(110), and sapphire(0001), exhibit clear-cut volume and surface modes. Sharp linewidths are signatures of the excellent quality of the samples. Angle-dependent measurements reveal that, while the samples grown on MgO(100) and sapphire(0001) are nearly isotropic, a surprisingly large in-plane uniaxial anisotropy is a characteristic feature of the samples grown on MgO(110). Quantitative agreement between theoretical and experimental results is reported for a realistic set of the samples’ parameters.
Cross track distribution of partial erasure
Authors: Lam T. T. , Zhu J.-G. , Tong H.-C. , Rottmayer R.
Published: July 2002

The extent of partial erasure across a written track is measured experimentally on a spin-stand. Using the combined track profiling-1D/3D method of measuring partial erasure, it is found that partial erasure, or intertransition percolation, does not occur uniformly across the track. The portion of transition near the track edges actually percolates at lower densities than the center portion of the track as recording density increases. The overall partial erasure of the track is mainly attributed to the reduction in signal strength near the track edges, results from the reduced head field gradient near the edges of the head poles. This distribution of partial erasure across the track becomes highly asymmetric at large skew angles, especially in narrow track recording systems. Intertransition percolation becomes more severe on the side of the track that has a wider erase band.
Electron spin resonance and conductivity investigations in the polypyrrole family of polymers
Authors: Singh Ramadhar , Narula Amarjeet K. , Tandon R. P. , Mansingh A. , Chandra Subhas
Published: July 2002

Electron spin resonance and dc conductivity investigations in the polypyrrole family of polymers support the existence of Mott’s variable range hopping mechanism.
Temperature dependence of noncollinear magnetic coupling in Fe/Cr(001) superlattices
Authors: Ankner J. F. , Kaiser H. , Schreyer A. , Zeidler Th. , Zabel H. , Schäfer M. , Grünberg P.
Published: July 2002

Using polarized-neutron reflectivity, we have measured the temperature dependence of the noncollinear magnetic coupling of ferromagnetic iron across chromium interlayers in two superlattice samples. The first sample, (52 Å Fe/17 Å Cr)9, exhibits a room temperature remanent magnetic structure consisting of successive Fe layer moments aligned at 50° relative to each other. This magnetic structure remains unchanged upon cooling the sample to 42 K. In contrast, a superlattice with a thicker Cr interlayer, [44 Å Fe/88 Å Cr]30, passes in a 20 K-wide transition centered on TN=240 K from a room temperature state with Fe moments aligned at 90° to an uncoupled state. The formation of the incommensurate Cr spin density wave state below TN suppresses the interlayer coupling. The thinner Cr interlayers do not undergo a transition to this bulk structure, hence exhibit no suppression of coupling. In both samples, the coupling strength decreases for temperatures at and above room temperature.
Palladium magnetism in Pd/Fe multilayers studied by x-ray magnetic circular dichroism at the Pd L2,3 edges (abstract)
Authors: Cros V. , Petroff F. , Vogel J. , Fontaine A. , Kappler J. P. , Krill G. , Rogalev A. , Goulon J.
Published: July 2002

We have performed direct measurements of the Pd 4d orbital and spin moments in Pd/Fe multilayers with different Pd interlayer thicknesses, using x-ray magnetic circular dichroism (XMCD) at the L2,3 edges of Pd. The Pd/Fe multilayers were grown by molecular beam epitaxy on MgO (001) substrates and the XMCD experiments were performed on beamline 6 at the ESRF using fluorescence yield detection. We found that the Pd atoms directly at the interface are strongly polarized with a total moment of 0.4 μB/atom. The orbital moments are found to be small (0.0–0.04 μB). The hybridization of the Pd 4d states with the Fe 3d band leads to a small increase in the number of Pd 4d electrons, of about 0.1 electron per Pd atom. The thickness dependence of the XMCD shows that the Pd atoms are magnetically polarized up to four layers from the interface. From the spectral features observed after the L3 and L2 white lines we can also show that the structural Pd/Fe interface is smooth and that in the two atomic layers adjacent to Fe, the Pd atoms have a local structure imposed by the epitaxy on Fe which differs from face centered cubic. The relation between electronic structure and magnetic properties will be discussed.
Temperature dependence of the electrical resistivity of amorphous (Fe1−xCox)78Si9.5B12.5 alloys
Authors: Shen Bao-gen , Guo Hui-qun , Gong Hua-yang , Zhan Wen-shan , Zhao Jian-gao
Published: July 2002

The temperature dependence of the electrical resistivity of amorphous (Fe1−xCox)78Si9.5B12.5 (0⩽×⩽1.0) alloys prepared by a single roller quenching apparatus was studied. The electrical resistivity of the samples was measured by using a usual four-probe method from 4.2 to 300 K. All amorphous alloys investigated here are found to exhibit a resistivity minimum at low temperature. The temperature of resistivity minimum Tmin is found first to increase and then to decrease with increasing Co content x, having a maximum value of 33.5 K at x=0.9. The electrical resistivity exhibits a logarithmic temperature dependence at T<Tmin, and a T2 dependence in the interval Tmin<T<130 K. The resistivity minimum and the −ln T dependence of resistivity below Tmin can be explained by the Kondo-like effect. The temperature dependence of the electrical resistivity above Tmin was discussed by the extended Ziman theory. The Debye temperature θD calculated from the temperature coefficient of electrical resistivity above Tmin is found to be 450±70 K.
Sputter deposited (CoNi)xO1−x composite materials (abstract)
Authors: Yi J. Y. , Rudee M. L. , Berkowitz A. E. , Cheeks T. L.
Published: July 2002

(CoNi) x O 1−x films have been studied extensively for use in high density recording tape media. Fabricated using metal evaporation in a partial pressure of oxygen, these films have exhibited high coercivity with improved corrosion and wear resistance. These attributes appear to be due to the inclined columnar microstructure in which the metal core is surrounded by a magnetic oxide phase. The coercivity could be varied by simply adjusting the atomic ratio of metal to oxide concentration. These properties as well as the possibility of an increased exchange anisotropy field make (Co0.5Ni0.5)xO1−x an interesting material to investigate as a candidate for future high density recording media. We investigated (CoNi)xO1−x composite films using reactive dc magnetron sputtering from a CoNi alloy target in an Ar and O2 environment. The oxide composition of the films was changed by systematically controlling the O2 partial pressure. X-ray diffraction results show that the films consisted of fcc CoNi metal and a fcc oxide phase. The oxide phase consisted of a mixture of NiO, CoO, or CoNiO2. Both the metal and the oxide phase showed a preferential (111) orientation. Calculated using x-ray peak broadening, the crystallite size was observed to decrease from 230 to less than 100 Å with increasing O2 flow rate. Magnetic measurements showed that the saturation magnetization (Ms) decreases from 1000 to 60 emu/cm3 and that the coercivity (Hc) increases from 30 to 300 Oe with increasing O2 flow rate. The easy axis of magnetization appears to be in-plane. Plausible models for the exchanging coupling behavior in composite materials will be discussed.
Magnetic recording performance of keepered media
Authors: Coughlin T. M. , Tang Y. S. , Velu E. M. T. , Lairson B.
Published: July 2002

Using low flying and proximity inductive heads, keepered media show improved on- and off-track performance leading us to conclude that a greater than 20% areal density improvement is possible with a keeper layer over the magnetic storage layer. For Sendust keeper layers there is an optimal range of thickness and an optimal bias point for best performance. There are both amplitude and timing asymmetries that are functions of the read-back bias. For a peak detect channel the best performance corresponds to the minimum timing asymmetry although this is not the point where the pulses are narrowest. Keepered media may have an advantage in total jitter and partial erasure. NLTS is almost identical for keepered versus unkeepered media.
Modeling of yoke giant magnetoresistance heads
Authors: Wei Yi , Jones R. E. , Kryder M. H.
Published: July 2002

Yoke giant magnetoresistance (GMR) heads are of interest for ultrahigh density recording. To optimize the design and efficiency of these heads, a comprehensive model was developed in which the total efficiency is the product of ratios of several fluxes in the head structure. The model consists of a network of shunt reluctances, which provide flux paths between the top and bottom yoke films, and series reluctances, which represent the yoke and GMR sensor films plus yoke-sensor overlap contacts. Expressions for individual reluctances are derived from a transmission line analysis of variable gap head segments, the series reluctances of magnetic films, and an analysis of flux leakage between the yoke and sensor films. A sensitivity analysis was performed for several parameters. The efficiency was found to be sensitive to the throat height and the planar area of the yoke-sensor contact. The model predicts a 53.6% efficiency for a 10 Gbit/in.2 head with a 1 μm throat height and a 2 μm yoke-sensor overlap. Assuming a GMR sensitivity of 0.2%/Oe and the above efficiency, a 580 μV p-p output will result from a 0.5 memu/cm2 media.
Effect of partial site occupation on the magnetic properties of Nd2Fe17−xSix by supercell calculation
Authors: Huang Ming-Zhu , Ching W. Y. , Gu Zong-Quan
Published: July 2002

The magnetic properties of the Nd2Fe17−xSix intermetallic compounds are studied by means of spin-polarized supercell calculations in which the selected sites of substitution are close to the situations in real samples. It is shown that the average Fe moment increases with x and saturates near x=3. This correlates quite well with the experimental dependence of Tc on x. The difference between supercell and unit cell calculations are pointed out and the influence of Si atoms on the density of states of the nearby Fe atoms is emphasized.
Artificial molecule realization of a magnetic wall
Authors: Ziolkowski Richard W. , Auzanneau Fabrice
Published: July 2002

The design of magnetic materials can be achieved with artificial magnetic molecules formed by electrically small loop antennas loaded with passive electrical circuit elements. A time derivative Lorentz material response is achieved with a series resistor and capacitor load. It is shown that the parameters of this magnetic molecule can be selected to yield a time derivative Lorentz material that acts as a highly conducting magnetic wall.
Characterization of the temperature dependent phase transition of evaporated Ti films on diamond: Phase identification using maximum entropy data analysis
Authors: Miller S. , Fischer R. , Plank H. , Roth J. , Dose V.
Published: July 2002

The carbidization of thin Ti films on natural diamond has been investigated in the temperature range between room temperature and 700 °C using x-ray-photoelectron-spectroscopy. It is possible to separate chemical phases in Ti 2p3/2 electron peaks after deconvolution of the spectrometer’s broadening function. We employ Bayesian information, using maximum entropy prior information. The apparatus function is derived from measured spectra of the Fermi edge of a silver sample. Data analysis of reconstructed Ti 2p3/2 core level spectra shows that, with increasing temperature, Ti films are transformed from metallic Ti to a mixed phase consisting of metallic Ti and TiC0.56. No carbidic phase is found with a ratio of carbidic C to Ti smaller than 0.56. The metallic layer is fully transformed to TiC0.56 at 430 °C. At higher temperatures, the concentration ratio of carbidic C to Ti depends nearly linearly on temperature.
Characteristics of an indium antimonide metal-insulator-semiconductor structure prepared by remote plasma enhanced chemical vapor deposition
Authors: Lee Jae-Gon , Choi Sie-Young , Park Sang-Jun
Published: July 2002

Silicon dioxide (SiO2) films on indium antimonide (InSb) were prepared using remote plasma enhanced chemical vapor deposition. The structural characteristics of the SiO2 films and the electrical characteristics of the metal-insulator-semiconductor (MIS) structures were examined. The SiO2 films, as evaluated by Auger electron spectroscopy, showed that the atomic ratio of silicon to oxygen was 0.5 and the composition was uniform throughout the oxide film. The leakage current density at 1 MV/cm was about 22 nA/cm2, the breakdown electric field of the MIS capacitor using SiO2 film deposited at 105 °C was about 3.5 MV/cm, and the interface-state density at midband gap extracted from the 1 MHz capacitance-voltage measurement was about 2×1011 cm−2 eV−1.
Stabilization of a cold cathode electron beam glow discharge for surface treatment
Authors: Mingolo N. , González C. R. , Martı́nez O. E. , Rocca J. J.
Published: July 2002

We have demonstrated that the reproducibility of electron beam pulses generated by a high power, cold cathode glow discharge is greatly improved by adding a small continuous keep-alive discharge current. A current of the order of 200 μA was found to limit the shot to shot current variation to within 1.5%. This stabilization in turn reduces by an order of magnitude the fluctuations of the energy density deposited on the target, demonstrating a reliable energy source for surface treatment.
Physical properties of BeAl6O10 single crystals
Authors: Pestryakov E. V. , Petrov V. V. , Zubrinov I. I. , Semenov V. I. , Trunov V. I. , Kirpichnikov A. V. , Alimpiev A. I.
Published: July 2002

Single crystals of BeAl6O10, beryllium hexaaluminate, were grown by the Czochralski method. The optical, acousto-optical, elastic, and a number of thermo-mechanical properties of bulk crystals of BeAl6O10 were investigated in comparison with crystal of BeAl2O4, chrysoberyl. It has been demonstrated that this material is the promising host for active media of tunable solid state lasers.
Conoscopic interferometry of wafers for surface-acoustic wave devices
Authors: Äyräs P. , Friberg A. T. , Kaivola M. , Salomaa M. M.
Published: July 2002

We show that in interpreting the conoscopic interference fringes, one should exercise care in employing approximate expressions which fail for certain crystal cuts. In this paper, we study 64°- and 128°-rotated Y-cut and Z-cut LiNbO3 wafers. We show that the error made in using the approximate formulae for the samples is more than 25% and that one has to use exact formulae in order to attain quantitative agreement with the experimental data.
Simulation of pulse height spectra in ion beam induced charge microscopy of polycrystalline silicon
Authors: Donolato C. , Nipoti R.
Published: July 2002

This article describes computer simulations of the charge pulse height spectra that are obtained by irradiating selected regions of a polycrystalline silicon solar cell by a 2 MeV He+microbeam. The spectra are calculated in terms of the energy loss function of the ions and the distribution of the charge collection probability at a grain boundary, and illustrate the effect of the interface recombination velocity of the grain boundary and the bulk diffusion length. The simulations are compared with some experimental spectra to demonstrate the applicability of the theory. The method can be extended to the analysis of other semiconductor defects or more complex devices.
Dielectric characterization of the phase transitions in Pb1−y/2(Zr1−xTix)1−yNbyO3(0.03⩽x⩽0.04, 0.02⩽y⩽0.05)
Authors: Duan Ning , Cereceda Noé , Noheda Beatriz , Gonzalo Julio A.
Published: July 2002

The Curie temperature and the ideal thermal hysteresis of Pb1−y/2(Zr1−xTix)1−yNbyO3 (0.03 ⩽x⩽0.04, 0.02⩽y⩽0.05) ferroelectric ceramics have been investigated as a function of composition at the FRH–PC phase transition. Experimental results are analyzed using the generalized effective field approach and taking into account the composition dependence of the dimensionless parameters g and h corresponding to the second and third terms in the generalized effective field expansion. With this approach we can describe reasonably well the composition dependence of TC(x,y) at the FRH–PC transition and thermal hysteresis ΔT(x,y) in the narrow range of compositions investigated. The effects of the oxygen octahedra tilt in the dielectric constant at the FRL–FRH transition have also been investigated as a function of composition.
Hump-shaped internal collection efficiency of degraded a-Si:H p-i-n solar cells
Authors: Smole F. , Topič M. , Furlan J. , Kusian W.
Published: July 2002

Measured internal collection efficiency (ICE) characteristics of annealed and degraded a-Si:H p-i-n solar cells were used for an analysis of their internal behavior. Using the numerical simulator ASPIN, simulations were performed in order to fit and explain pronounced hump-shaped voltage-dependent ICE characteristics of degraded structures under weak short-wavelength illumination. Agreement with measured ICE characteristics for a degraded cell was obtained only if in addition to the introduction of light-induced dangling bond defect states, their capture cross sections were also increased, in particular the capture cross section for the charged defect states were increased. This caused a change in the occupancy of defect states at the p-i interface and front part of the i layer under forward biases. Consequently, the electric field in the front part of the cell was sustained under higher forward biases, resulting in recovery of the ICE.
Reactivation kinetics of boron acceptors in hydrogenated silicon during zero bias anneal
Authors: Majumdar Amlan , Balasubramanian Sathya , Venkataraman V. , Balasubramanian N.
Published: July 2002

The reactivation kinetics of passivated boron acceptors in hydrogenated silicon during zero bias annealing in the temperature range of 65–130 °C are reported. For large annealing times and high annealing temperatures, the reactivation process follows second-order kinetics and is rate limited by a thermally activated H̃2 complex formation process. For short annealing times and low annealing temperatures, the reactivation rate is found to be larger than that due to H̃2 complex formation alone. We conclude that the faster reactivation is caused by the diffusion of the liberated hydrogen atoms into the bulk as well as H̃2 complex formation. The effective diffusion coefficient of hydrogen is measured and found to obey the Arrhenius relation with an activation energy (1.41±0.1) eV.
How endoreversible thermodynamics relates to Onsager’s nonequilibrium thermodynamics
Authors: Verhas J. , De Vos A.
Published: July 2002

Using the well explored endoreversible heat engine as an example, this article shows how an endoreversible model fits the general framework of nonlinear nonequilibrium thermodynamics. The heuristic power of endoreversible thermodynamics is stressed.
Electron refrigeration in the tunneling approach
Authors: Müller Heinz-Olaf , Chao K. A.
Published: July 2002

The performance of electron refrigeration by means of tunnel junctions between superconducting and normal-metal electrodes is studied theoretically. A suitable approximation of the basic expression for the heat current across the tunnel junctions allows the investigation of the main features of the device such as its optimal bias voltage, its maximal heat current, its optimal working point, and the maximal temperature reduction. The theoretical results are compared with those of a recent experiment.