bluuebunny/crossref_metadata_2025 huggingface dataset:
Gap density of states in amorphous silicon-germanium alloy: Influence on photothermal deflection spectroscopy and steady-state conductivity measurements
Authors: Della Sala D. , Reita C. , Conte G. , Galluzzi F. , Grillo G.
Published: July 2002

A series of amorphous hydrogenated silicon-germanium films has been produced by the glow-discharge dissociation of a GeH4 +SiH4 +H2 gas mixture. The subgap optical absorption has been measured with the photothermal deflection spectroscopy (PDS) technique, and the results are discussed and referred to a model density of states. The density of defects has been found meaningfully correlated to the bulk material, despite a number of possible complications intrinsic of the PDS technique and/or of the material itself, which can potentially prevent the correct determination of the density of defects from the subgap optical absorption. Namely, the defect density ranges from 1016 cm−3 in a-Si:H to 5×1017 cm−3 in a Ge:H, whereas the Urbach tail width is only slightly increased from 50 to 70 meV. The amount of disorder and the defect density of the material are compared to the predictions of an available thermodynamical model: the increasing number of defects brought about by germanium results in being an intrinsic feature of the material. Furthermore, the impact of the variable concentration of silicon and germanium dangling-bond states on the position of the Fermi level has been studied by means of the same model density of states: a noticeable correlation was found between the activation energy of the steady-state dark conductivity (EA ) and the volume density of silicon and germanium dangling bonds (Nd ). In other words, the three-step trend of EA vs x can be considered to be a fingerprint of the separate dangling-bond densities in germanium and silicon. These can be deconvolved, provided that the dangling-bond states in the forbidden energy gap are known as a function of the alloy composition.
Effects of substituted elements into the Cr layer on a CoNiCr/Cr sputtered hard disk
Authors: Tani N. , Hashimoto M. , Murata Y. , Ishikawa M. , Ota Y. , Nakamura K.
Published: July 2002

A study was made on the effects of elements substituted into the Cr layer on a CoNiCr/Cr sputtered hard disk. Among the various elements tried, Si, Gd, Ce, and Cu were found to increase the coercive force in the film. For Si and Gd, alloy targets of Cr-Si and Cr-Gd were prepared, and the deposited films indicated an increase of the coercive force by about 150 Oe over those without Si or Gd element.
Compositional and magnetic properties of iron nitride thin films
Authors: Mosca D. H. , Dionisio P. H. , Schreiner W. H. , Baumvol I. J. R. , Achete C.
Published: July 2002

The compositional and magnetic properties of iron-nitride thin films deposited by dc reactive magnetron sputtering under various nitrogen partial pressure conditions have been investigated by x-ray diffraction, Mössbauer and Auger electron spectroscopy as well as magnetic measurements. The x-ray diffraction patterns indicate a mixed phase composition. 57Fe Mössbauer spectroscopy shows that part of the nitrogen atoms are randomly distributed on interstitial sites with the formation of nonstoichiometric compounds. The excessive width of the Mössbauer lines indicates the degree of disorder of the different iron nitride precipitates. The nitrogen concentration as a function of depth is obtained by sputter-etched Auger electron spectroscopy. Furthermore, the ferromagnetic films show moderate saturation magnetization and coercivities at room temperature as compared with pure iron thin films.
X-ray pole-figure analyses of YBa2Cu3O7−x thin film on SrTiO3(100) prepared by rf diode sputtering
Authors: He Y.-L. , Wang G.-C. , Drehman A. J. , Jin H.-S.
Published: July 2002

The structural properties of a high-temeprature superconducting textured YBa2Cu3O7−x thin film on a SrTiO3(100) substrate have been studied by reflection x-ray pole-figure methods, which can elucidate the degree of preferred orientations of the crystallites in polycrystalline materials and the relative orientations and lateral lattice alignments of the film with respect to the substrate. The specimen was fabricated on a SrTiO3(100) substrate by rf diode sputter deposition and subsequent furnace annealing in flowing oxygen. The film was found to be more preferentially a axis oriented than c axis oriented with a grain ratio of about 4:1. The a-axis-oriented grains are heavily twinned and the twinning structure is reflection about the (013) plane. The pole figures of the c-axis-oriented grains are consistent with the (110) reflection twinning structure. Nevertheless, the crystal axes of both types of oriented grains are aligned with those of the substrate. In addition, the interface matching of the film with respect to the substrate is discussed.
Hysteresis in model spin system
Authors: Rao Madan , Krishnamurthy H. R. , Pandit Rahul
Published: July 2002

The aim of this paper is to construct a nonequilibrium statistical-mechanics theory to study hysteresis in ferromagnetic systems. We study the hysteretic response of model spin systems to periodic magnetic fields H(t) as a function of the amplitude H0 and frequency Ω. At fixed H0, we find conventional, squarelike hysteresis loops at low Ω, and rounded, roughly elliptical loops at high Ω, in agreement with experiments. For the O(N→∞), d=3, (Φ2)2 model with Langevin dynamics, we find a novel scaling behavior for the area A of the hysteresis loop, of the form A∝H0.660Ω0.33. We carry out a Monte Carlo simulation of the hysteretic response of the two-dimensional, nearest-neighbor, ferromagnetic Ising model. These results agree qualitatively with the results obtained for the O(N) model.
Effects of magnetic fields on combustion (abstract)
Authors: Ueno S.
Published: July 2002

We have observed a phenomenon that candle flames are pressed down by magnetic fields. We have also observed that flows of gases such as carbon dioxide and oxygen are blocked by magnetic fields. A model, called a ‘‘magnetic curtain,’’ has been introduced to explain these phenomena. The magnetic curtain is a wall of air which is produced by magnetic fields. We have demonstrated an experiment to show that candle flames are quenched by the magnetic curtain. The present study focuses on the mechanism of the phenomena involving quenching of flames using magnetic fields. An electromagnet with a pair of columnar magnetic poles in which inner sidepieces were hollowed out was used first. Magnetic fields of 1.5 T at the brim gave a gradient of 50–300 T/m in the direction perpendicular to the pole axis. Alcohol was burned in the hollowed space between magnetic poles. Gases around flames in the hollowed space were sampled into gas sensors through an inhalation nozzle. Oxygen, carbon dioxide, and carbon monoxide were simultaneously measured during the combustion of methanol and ethanol. During magnetic field exposures, oxygen concentration decreased, whereas concentrations of carbon dioxide and carbon monoxide increased. However, when flames were quenced in a few seconds, oxygen concentration in the hallowed space was not changed, and very little of carbon dioxide and carbon monoxide were produced. The interception of a small amount of oxygen near the surface of the flames may quench flames. Emission spectra of flames of methanol and ethanol were measured before, during, and after magnetic field exposures, using both uniform and gradient magnetic fields. Intensity of the OH radical was not changed by magnetic fields up to 1.6 T, whereas the emission intensity was increased when the product of magnetic fields and the gradient increased.
Anomalous spin-wave excitations in a one-dimensional Dzyaloshinski–Moriya antiferromagnet
Authors: Xia Qing , Riseborough Peter S.
Published: July 2002

The dynamics of a one-dimensional Heisenberg antiferromagnet with a small Dzyaloshinski–Moriya component to the exchange interaction is considered. The spin rotational invariance within the easy plane is broken by the application of a weak magnetic field in the easy plane. The nature of the spin-wave excitations of the quantum spin system is investigated, and pronounced anomalies in the single-spin-wave spectrum at fields comparable to the anisotropy in the exchange interaction are found. These anomalies are of quantum character and are related to the resonance between the single-spin-wave and the two-spin-wave excitations. The implications for the two-spin-wave bound states are discussed.
Magnetization of ferromagnetic amorphous alloys modified by a high-frequency magnetic field (abstract)
Authors: Huang Der-Ray , Li James C. M.
Published: July 2002

The critical magnetic field Hcr for the Barkhausen effect of ferromagnetic amorphous alloys can be modified and reduced by applying ac high-frequency magnetic fields. Both straight and toroidal specimens of amorphous ribbons Fe78B13Si9 (Allied 2605S2) and Fe40Ni38Mo4B18 (Allied 2826MB) were used in our experiment. The waveforms of ac magnetic fields were sine, triangular, or square waves, and the directions of the applied ac magnetic field were either parallel or perpendicular to the length direction of the specimen. For as-cast Fe78B13Si9, applying ac magnetic fields of 100 Hz–1 kHz and magnitudes 0.1–0.3 Oe, the critical magnetic field of the specimen could be reduced from 0.075 to 0.02 Oe under the same exciting field and magnetic induction. For as-cast Fe40Ni38Mo4B18, applying ac magnetic field of 100 Hz–1 kHz and magnitudes 0.1–0.3 Oe, could reduce the Hcr from 0.06 to ≤0.01 Oe under the same exciting field and magnetic induction. If the specimens were heat treated first by ac Joule heating and then applying the same ac magnetic fields when measuring the B-H curves, the critical magnetic fields could be reduced to lower than 0.001 Oe under the same exciting magnetic field and magnetic induction. By using a suitable frequency and magnitude of the ac magnetic field, we observed a magnetic behavior similar to superparamagnetism (i.e., coercive force Hc=0).
Theory of antiferromagnetic multilayers with quantum Heisenberg spins
Authors: Diep H. T.
Published: July 2002

Magnetic properties of antiferromagnetic multilayers with quantum Heisenberg spins at finite temperatures are investigated by a Green function method. The system consists of alternate A and B layers of square lattice, with spins 1/2 and 1, respectively. Staggered layer magnetizations are shown as functions of temperature for different sets of interactions. Monte Carlo results for the corresponding system with classical spins are also shown for comparison.
New opportunities in spin-polarized photoemission spectroscopy (invited)
Authors: Erskine J. L. , Fink R. L.
Published: July 2002

New opportunities for probing magnetism and magnetic materials are emerging as a result of improved electron-spin detectors, broad advances in materials synthesis and characterization techniques, and refinements in spin-sensitive spectroscopic techniques. A multi-investigator group is currently commissioning a spin-polarized photoemission beamline at the National Synchrotron Light Source that has been designed to synthesize and study magnetic materials. The beamline exploits the significant increase in synchrotron radiation flux that is emitted from a magnetic insertion device. Key issues and new opportunities for advancing the understanding of magnetism and magnetic materials using this facility are addressed.
Effects of magnetic and structural properties on magnetoresistance in amorphous TbFeCo
Authors: Yumoto S. , Hidaka Y. , Okada O.
Published: July 2002

An extraordinary magnetoresistance effect, linearly dependent on the external magnetic field, is observed in amorphous TbFeCo films. The electrical resistance jumps by δρ at magnetization reversal. δρ depends on Tb concentration and it becomes nearly zero at about Tb 26 at. % concentration. To clarify the Tb concentration dependence of δρ, the magnetic properties and the heat treatment effect are examined. It is found that the magnetic anisotropy field (Hk ) is maximum at about Tb 26 at. % and the gradient of linear magnetoresistance, δρ/(ρ0Hc), is proportional to the −Hk+ const, where ρ0 is the electric resistance in zero field, Hc is the coercive force, and the constant is about 100 kOe. The structural relaxation, a coercive force change by the heat treatment up to 200 °C, is examined. It is found that as δρ/(ρ0Hc) in the as-sputtered state decreases, the coercive force change by the heat treatment decreases. The coercive force change is minimum at about Tb 26 at. %, where δρ/(ρ0Hc) becomes zero. These results mean that linear magnetoresistance is related to structure relaxation by heat treatment. The δρ disappearance at about Tb 26 at. % is based on the stable structure against heat treatment and the largest magnetic anisotropy field.
Random magnetic anisotropy: Switching and coercivity behavior
Authors: Creswell A. , Paul D. I.
Published: July 2002

Starting from a Hamiltonian based on the random magnetic anisotropy model to describe the magnetic characteristics of amorphous materials such as TbFe2, we determine the low-temperature dependence of the coercivity as well as the magnetization dynamics of these materials. Our model features clusters, each characterized by its anisotropy direction. The exchange energy term entering the Hamiltonian is represented by an effective exchange interaction acting in the intercluster regions. Our Hamiltonian has a minimum in each of the two opposite hemispheres defined by the applied field. We derive the temperature-dependent coercivity by calculating the field necessary to have the one metastable minimum disappear. Our results agree well with experimental data for reasonable values of the parameters. We study the dynamics of the magnetization at 0 K by performing a numerical integration of the equations of motion derived from our Hamiltonian augmented by a Gilbert and Kelly damping term. The average magnetization of the material is reevaluated at each integration step in order for the mean-field approximation for exchange to remain physically meaningful. We obtain the time dependence of the magnetization, determine the switching fields and switching times, and study the influence of the exchange on the results.
A parallel conjugate gradients algorithm for finite element analysis of electromagnetic fields
Authors: Mahinthakumar G. , Hoole S. Ratnajeevan H.
Published: July 2002

The exploitation of parallel and vector machine architectures provides new means of speeding up the finite element analysis of electromagnetic field problems. In this paper most operations in an iteration of the conjugate gradient algorithm are parallelized individually. New parallel algorithms appropriate to finite element data storage schemes are presented for Cholesky splitting of the coefficient matrix, sparse matrix multiplication, forward elimination, backward substitution, vector multiplication and vector addition. A Sequent Symmetry 81 parallel computer operating with four processors was employed for this purpose. Interestingly, it was found that parallelization profoundly improves the speed only when the matrix size is large. For relatively small matrices, the time required to allocate processors does away with the advantage of parallel computation.
Faster open-boundary magnetic field computation using the strategic dual image and Voronoi–Delaunay transformation methods
Authors: Saito Y. , Nakazawa Y. , Hayano S.
Published: July 2002

In order to obtain the finite element solutions of open-boundary magnetic field problems, we have previously proposed a strategic dual image (SDI) method. This SDI method requires the use of a specific shape of hypothetical boundary so that it sometimes requires a solution of a king size system of equations. To remove this deficiency, this paper proposes an efficient implementation technique of the SDI method based on a Voronoi–Delaunay transformation. As a result, it is revealed that a king-size system of equations can be dramatically reduced to a small size system of equations.
Force calculations with three-dimensional scalar potential based finite-element programs (abstract)
Authors: Lowther D. A. , Forghani B.
Published: July 2002

In the design of many electromagnetomechanical devices one of the prime parameters of interest is the mechanical force of torque produced by the device. The generated forces are of interest in two forms. The first is the distribution, which might be used to indicate a particular loading on some part of the structure; the second is a global value which appears at the mechanical interface. It is with the calculation of the latter that this paper is concerned. Much has been published concerning force calculations in two-dimensional solutions and it is the intention of this paper to discuss the extension of these methods to three-dimensional, scalar potential based analyses and to give examples of computed and measured results on several different devices.

In general, the methods that are used in two dimensions are applicable in three dimensions. These are ususally classified as single- and multiple-solution techniques. Into the first category fall Maxwell stresses and the Coulomb implementation of virtual work; into the second falls the classical virtual work approach. The Maxwell stress approach requires a surface integral of a product of flux density (B) components. In two dimensions this is a relatively simple task; it reduces to defining a line in the plane and computing B as the differential of A (the vector potential). In three dimensions, the definition of a surface may not be simple and, if a scalar potential is used for the solution, the computation of flux density components is far from trivial. When these requirements are compared with the classical virtual work approach, the reduction in computing effort by using a single-solution technique many not seem so significant. A second factor influencing the use of a multiple-solution approach is fundamental to the finite-element method; in general, the method produces accurate values for global quantities such as coenergy, with coarser discretizations than those required for local accuracy. Single-solution methods tend to require high-accuracy local fields and thus require considerably more computer effort per solution. On problems ranging from a disk drive actuator to a permanent magnet generator accuracies within 3% of measured have been computed with virtual work. The equivalent two-dimensional solutions did not do better than 10%.
Spatial patterns of magnetic fields produced by multiple dipoles in an inhomogeneous volume conductor
Authors: Iramina K. , Ueno S.
Published: July 2002

This study is focused on the influence of inhomogeneities in the head upon surface magnetic fields. The effects of combinations of dipoles and an inhomogeneous region on spatial distributions of magnetoencephalograms (MEGs) are investigated. The head is assumed to be a spherical volume conductor, in which there is a small sphere in the frontal region. That is assumed to be a brain lesion such as a brain tumor. Magnetic field components perpendicular to the surface of the sphere are calculated, and spatial distributions of MEGs and EEGs are simulated. Two or four current dipoles are used as electrical sources. Two dipoles are positioned in parallel and in the opposite directions. Four dipoles are positioned to form a closed loop. These types of electrical sources generate very small electric fields on the sphere, whereas the closed current loop and opposing dipoles act as equivalent magnetic dipoles which generate high magnetic fields. When a single dipole is located near a boundary of inhomogeneous region, surface magnetic fields are strongly influenced by volume currents which flow on the inhomogeneous boundary. In contrast, when the opposing or circular current dipoles exist near a boundary of an inhomogeneous region, magnetic fields are not almost affected by the inhomogeneous boundary.
8
9Y nuclear-magnetic-resonance measurements in (DyxY1−x)Fe2 compounds
Authors: Alves K. M. B. , Alves N. , Sampaio L. C. , da Cunha S. F. , Guimarães A. P.
Published: July 2002

In a previous work, 89Y measurements at 4.2 K in (RxY1−x)Fe2 compounds, with R=Tb and Ho and 0.05≤x≤0.20, have shown broad nuclear-magnetic-resonance (NMR) spectra, due to transferred hyperfine interactions. 89Y NMR signals could not be observed with R=Dy in the same composition range. In the present work, compounds were prepared with Dy in the concentration range 0.005≤x≤0.02 to investigate the origin of this anomaly. Compared to the pure YFe2 compound, the observed NMR spectra are broadened and show a shift towards higher frequencies. With increasing Dy concentration, the NMR signals fall very rapidly. Magnetization measurements at 4.2 K were performed in samples with Tb, Ho, and Dy; the results indicate that the behavior of the Dy compounds is qualitatively different in the low-magnetic-field region of the curves, requiring a minimum applied field to start increasing the magnetization. The NMR data and the magnetization results of the Dy compounds can both be explained as arising from a much lower mobility of the domain walls.
Electronic density of states, stability, and coherency effects between resonant states in quasicrystalline Al73.2Mn21Si5.8
Authors: Wang K. , Garoche P. , Calvayrac Y.
Published: July 2002

In quasicrystalline AlMnSi alloys, the spin-glass contribution makes difficult the correct evaluation of the electronic density of states (DOS) at the Fermi level. The present investigation shows that the low temperature specific heat contribution varies as the inverse of the square of the magnetic field, and so enables us to separate the spin-glass contribution from the electronic one. The d DOS at the Fermi level is reduced to about 70% of the value observed in the AlMn solid solution. This reduction can be understood as resulting from a sp-d resonant effect which opens a pseudogap at the center of the virtual bound state. This pseudogap, along with the icosahedral symmetry, can explain the origin of the stability of this phase.
Magnetic separation of fine particle dusts using a superconducting magnet and wire meshes
Authors: Ueno S. , Shimohata K. , Yamada T. , Iwamoto M.
Published: July 2002

We have observed a phenomenon that flow patterns of gases are influenced by a magnetic field. To explain this phenomenon, a model called a ‘‘magnetic curtain’’ has been introduced. In this paper we apply this phenomenon to magnetic separation of fine particle dust in air. We use a superconducting magnet and fine ferromagnetic wires to obtain high magnetic field and high field gradient. Magnetic separation of fine particles is well realized. The efficiency of fine particle filtration increases with increasing magnetic field and also increases with particle size. The percentage of captured particles is 80% for particles larger than 1 μm, 60% for 0.5–1.0 μm, and 35% for 0.3–0.5 μm, respectively, when the field intensity is 4.5 T and the gradient is 1500 T/m.
Studies of Pd-Fe fine particles (abstract)
Authors: Deng X. H. , Hadjipanayis G. C. , Sorensen C. M. , Klabunde K. J.
Published: July 2002

A vapor-deposition technique was used to prepare Pd-Fe fine particles. Since palladium is fairly inert, it is our hope to develop magnetic particles which are stable in air. An as-cast alloy of bulk Pd-Fe was made by an arc-melting method. This as-cast ingot was evaporated from an alumina crucible in argon gas at a pressure of 2.0 Torr. Particles formed in the gas and were then deposited on a water-cooled copper plate by thermophoresis. Chemical analysis, x-ray diffraction and transmission electron microscopy were used to investigate the composition, structure, and morphology of the particles. The as-received fine particles were amorphous. They showed a Curie temperature of 420 °C, which was lower than that of the as-cast ingot (600 °C). Saturation magnetization and coercivity were 53.5 emu/g and 2000 Oe at 10 K as measured by a SQUID magnetometer.
Giant magnetoresistance in sputtered magnetic superlattices (invited) (abstract)
Authors: Parkin S. S. P. , Fan S. , More N. , Roche K. P.
Published: July 2002

Recently, large values of saturation magnetoresistance (SMR) were reported in single-crystal Fe/Cr superlattice structures prepared by molecular-beam-epitaxy (MBE) techniques.1 We have prepared similar polycrystalline superlattice structures by dc magnetron sputtering in a high-vacuum deposition system and find comparably high SMR values of up to 50% for Cr-layer thicknesses of ≂8 Å. Magnetization-versus-field data suggest that successive Fe layers are coupled antiferromagnetically with one another, as for the MBE-grown films. Magnetic fields of up to 20 kOe are required to align Fe layers 20 Å thick, implying substantial exchange-coupling energies between the Fe layers. While the magnetization curves have a weak temperature dependence even for temperatures above the Néel temperature of bulk Cr, the SMR decreases as the temperature is increased. Work on related structures which do and do not show giant SMR effects will be discussed.
Spatially resolved measurement technique of magnetic anisotropy fields using the magneto-optic Kerr effect
Authors: Gudeman C. S. , Mauri D.
Published: July 2002

In this paper a novel method that permits spatially resolved measurements of the anisotropy field and easy axis direction is reported. The technique employs a Kerr based sensor that monitors the direction of magnetization φ of a magnetically soft thin film while an applied field is rotated in the plane of the film. The magnitude of the rotating field is set approximately to twice the anisotropy field (Hk), and thus the film remains saturated at all times and the domain wall artifacts reported previously are eliminated. φ and the direction of applied field β are then independently measured. We show that the amplitude and phase of sin(β−φ) are related to Hk and the easy axis orientation (EAO), respectively. The amplitude and phase information can be easily determined by first normalizing and then applying a fast Fourier transform to the digitally captured Kerr signal. Operationally, computer controlled translation stages are used to scan the sample under the Kerr laser beam, which is fixed with respect to the toroidal electromagnet generating the rotating applied field. Because the sample need never be rotated, ‘‘maps’’ of Hk and EAO covering approximately 100 locations can be generated in less than 10 min by a fully automated instrument employing this technique.
Magnetic clusters in FeAl1−xCux alloys: SANS measurements
Authors: Booth J. G. , Lawson P. K. , de Boer F. R. , Frings P. H.
Published: July 2002

Although the annealed equiatomic alloy FeAl is paramagnetic, the series of alloys represented by the formula FeAl1−xCux becomes ferromagnetic for x≥0.27, beyond which the Curie temperature rises rapidly. It is thought that the magnetization in high fields arises from saturated clusters in an itinerant matrix. Five of these alloys (having x=0.25, 0.28, 0.30, 0.325, and 0.35) have been examined in powder form over the range 4–300 K using SANS at ILL, Grenoble. The paramagnetic alloy with x=0.25 shows a featureless, temperature-independent scattering pattern with some forward peaking which may arise primarily from surface scattering. In contrast, the results for the ferromagnetic alloys show marked features which can be linked to the magnetic properties; that for the alloy with x=0.325 is especially remarkable in that very weak critical scattering is seen near the Curie temperature with a much larger Q-dependent peak at about 50 K. These features are very similar in form to those reported for the alloy Fe70Al30 in which the ferromagnetism is thought to be broken up at low temperatures by random fields arising from dynamic magnetic clusters, leading to a reentrant (super)paramagnetism that freezes at lower temperatures into a cluster glass state. The correspondence between the two systems seems substantial.
Random-field mechanism in random-bond multicritical systems (abstract)
Authors: Hui Kenneth , Berker A. Nihat
Published: July 2002

It is argued on general grounds that bond randomness drastically alters multicritical phase diagrams via a random-field mechanism. For example, tricritical points and critical endpoints are entirely eliminated (in spatial dimension d≤2) or depressed in temperature (d>2). These predictions are confirmed by a renormalization-group calculation.1 Another consequence of this phenomenon is that, under bond randomness, the phase transitions of q-state Potts models are second order for all q at dimensionality d≤2.
Bimetallic derivatives of the [M(en)3]3+ ion (M=Cr and Co): A series of compounds with unusual magnetic and structural properties (abstract)
Authors: Palacio Fernando , Morón M. Carmen , Pons J. , Casabó J. , Solans X. , Merabet K. E. , Huang D. , Shi X. , Teo Boon K. , Carlin Richard L.
Published: July 2002

The crystal structure and magnetic susceptibility of a series of [M(en)3]3+ (M=Cr or Co) derivatives are described. In particular, the crystalline structures of (1) [Cr(en)3]3[FeCl6]Cl6⋅H2O, (2) [Co(en)3]3[FeCl6]Cl6⋅H2O, and (3) [Cr(en)3][FeCl6]⋅11H2O are reported. Structural data, in Å, for these compounds are as follows: (1) space group R3, a=15.447(4), c=21.060(6), Z=3; (2) space group R3, a=15.346(3), c=20.880(5), Z=3; (3) space group P3c1, a=11.654(3), c=15.508(4), Z=2. The main structural feature of the first two isomorphous materials is that they consist of a three-dimensional network of triangular antiprisms formed by the [M(en)3]3+ (M=Cr or Co) ions and connected with each other by sharing corners. An [FeCl6]3− ion is placed at the center of each antiprism. Compound (3) contains a sc arrangement of [Cr(en)3]3+ and [FeCl6]3− octahedra. In addition, the magnetic susceptibilities of the above-mentioned isomorphous compounds and of [M(en)3][FeCl6] (M=Cr and Co) and [Cr(en)3][InCl6] are reported. While [Cr(en)3]3[FeCl6]Cl6⋅H2O orders as a ferrimagnet at 0.91 K, [Cr(en)3][FeCl6] exhibits antiferromagnetic properties with Tc=2.26 K, a temperature rather similar to the antiferromagnetic ordering temperature of [Co(en)3][FeCl6].
Magnetic properties of FeAlMnC steels
Authors: Jen S. U. , Yao Y. D. , Huang P. L. , Lee C. C. , Chang S. C.
Published: July 2002

A series of high yielding strength (90–180 ksi) and high-elongation (30%–45%) FeAlMnC steels have been made. The magnetic, microstructural, and thermal expansion properties of these steels have been studied. Basically, their magnetic transitions on cooling can be classified into three groups according to their microstructures: (i) For fully austenitic (γ) steels, the transition is from paramagnetic to antiferromagnetic. TN is lowered with the addition of Al; (ii) for α+γ phase steel (volume fraction of α≤0.3%), the transition is from superparamagnetic to antiferromagnetic, and (iii) for the mixed phase steel, whose α phase has percolated, it is ferromagnetic with TC≂200 C. The susceptibility of austenitic steels is low. Their nonmagnetic properties are comparable to commercial 304 or 25/12 stainless steel. An Invar-like property in the thermal expansion was observed around TN. Their volume magnetostriction values are in the range of 10−6–10−5.
Longitudinal jumps in Kondo systems
Authors: Zhang Shufeng , Levy Peter M.
Published: July 2002

The side jump is known to make important contributions to the extraordinary Hall effect in Kondo systems. We show that as a corollary to this, the longitudinal jump also makes important contributions to the resistivity.
Two-dimensional magnetic order of Er in ErBa2Cu3O7
Authors: Lynn J. W. , Clinton T. W. , Li W-H. , Erwin R. W. , Liu J. Z. , Shelton R. N. , Klavins P.
Published: July 2002

Neutron diffraction has been used to study the magnetic order of the Er ions in superconducting ErBa2Cu3O7. Above the three-dimensional (3D) Néel temperature (TN=0.618 K) a rod of scattering characteristic of two-dimensional (2D) behavior is unambiguously observed, showing that the magnetic interactions of the rare earth ions are highly anisotropic, while there are no significant correlations observed between the sheets of Er spins. The system orders two dimensionally, and as a necessary consequence 3D order also sets in at the same temperature. The order parameter is found to obey the exact Onsager solution for a S= (1)/(2) , 2D Ising antiferromagnet. At low T, two separate types of simple 3D antiferromagnetic structures are found, one characterized by a wave vector of ( (1)/(2) , 0,0), and the other by ( (1)/(2) ,0, (1)/(2) ).
Structural and magnetic studies of Fe/Ni multilayers (abstract)
Authors: Kim C. , Qadri S. B. , Maruyama B. , Kim K. H. , Edelstein A. S.
Published: July 2002

Compositionally modulated multilayer samples of Fe/Ni have been prepared in a dual-ion-beam sputtering system in which one beam is used to deposit the film and the other is directed at the substrate to increase the surface mobility of the arriving atoms. The multilayers had equal thicknesses of Fe and Ni, and wavelengths λ varying between 15 and 120 Å. The composition modulation was investigated by measuring the satellite intensities. The phases present have been studied by x-ray diffraction and extended x-ray-absorption fine-structure measurements. The x-ray investigations included Read photographs. The Ni layers have fcc structure. For λ=120 Å the Fe layers primarily have the usual structure of Fe, namely bcc. For λ<40 Å the Fe layers have fcc structure. For λ=50 Å the Fe layers are a mixture of fcc and bcc phases. The magnetic properties have been investigated by vibrating-sample-magnetometer measurements. For λ=35 Å, T=298 K, and the magnetic field parallel to the substrate, the coercive force is only a few gauss and, of more importance, the saturation magnetization is approximately the sum of the magnetization expected for bcc Fe and fcc Ni. For λ=35 Å, T=298 K, and the magnetic field perpendicular to the substrate, a field of 20 kOe is required to achieve saturation.
Structure and magnetic properties of Mn-Al multilayered films
Authors: Takeuchi T. , Hirayama Y. , Futamoto M.
Published: July 2002

Correlation between the structure and the magnetic properties of Mn-Al multilayered films prepared by vacuum evaporation have been investigated. Films on MgO(100) substrates with layer thicknesses of 100 Å or more were found to have structures with flat layers and (100) orientation of α-Mn, while a film on a glass substrate and a film with a layer thickness of 50 Å on a MgO(100) substrate were seen to have variations in layer thicknesses and no crystal orientation of α-Mn. Saturation magnetizations for the former two films are more than several times greater than those for the latter two films. From these properties, it is judged that stacking of α-Mn layers with (100) surfaces and Al layers is an important factor for the evolution of ferromagnetic properties in Mn-Al multilayered films.
Critical behavior of amorphous Fe80−xMxB14Si6 alloys with M=Mo, V, Mn, and 2≤x≤14
Authors: Jen S. U. , Lee C. C. , Huang P. L. , Lin S. T.
Published: July 2002

Amorphous Fe80−xMxB14Si6 alloys with M=Mo, V, Mn, and 2≤x≤14 have been made by the rapid quenching method. The critical exponents β, γ, δ, and Tc were determined by two independent methods: the method of Kouvel-Fisher and the scaling plot. With the addition of M, β, and γ deviate more from the values predicted by the three-dimensional Heisenberg model, and are closer to the values proposed by Sobotta and Wagner. δ remains less changed. The magnetic inhomogeneity of these alloys is evidenced by the specific heat, the forced magnetoresistance, and the Mössbauer measurements. By increasing x, the peak of specific heat becomes smeared and less divergent, and forced magnetoresistance changes from negative to positive around Tc.
Magnetic fluctuations and short-range order in strongly frustrated SrCr8−xGa4+xO19 (abstract)
Authors: Broholm C. , Espinosa G. P. , Cooper A. S. , Aeppli G.
Published: July 2002

In SrCr8−xGa4+xO19 antiferromagnetically interacting (θCW≊−500 K; θCW is the Curie–Weiss temperature) Cr ions occupy a two-dimensional Kagomé lattice. The ground state of Ising spins on this lattice is known to be disordered and to have a higher ground-state entropy than the triangular lattice. We have studied the magnetic fluctuations and short-range order in this highly correlated but disordered system by magnetic neutron scattering. We find (3)1/2×(3)1/2 short-range order (ξ≊6 Å) in the instantaneous correlations for T≲50 K. The magnetic fluctuation rate decreases with temperature and static correlations develop below Tg =8 K. The ground state, however, remains strongly fluctuating.
Magnetic separations for biological molecules (abstract)
Authors: Chagnon Mark , Hamilton Tracy
Published: July 2002

Magnetic separations in biological systems have been used as alternative to gravitational or centrifugal separations. There are several advantages to using magnetically separable particles as supports for biological molecules such as enzymes, antibodies, and other bioaffinity adsorbents. For example, when magnetic particles are used as solid-phase supports in immobilized enzyme systems, the enzyme can be selectively recovered from the media, including media containing suspended solids, allowing recycling in enzyme reactors. The practical development of magnetic separations has been hindered by several critical properties of the magnetic particles developed thus far. For example, large magnetic particles (e.g., having a mean diameter in solution greater then 10 μm) respond to weak magnetic fields and magnetic field gradients; however, they tend to settle rapidly, limiting their usefulness for reactions requiring homogeneous conditions. Superparamagnetic particles coated with polymers capable of binding bioaffinity adsorbents have been prepared. Their used in the separation of biological molecules from, or directed movement of the molecules in, the surrounding medium is discussed and separation times and efficiency is compared to conventional protein processing methods.
CoNbZrN alloy films with soft magnetic properties
Authors: Sakai Ryo , Shimada Yutaka
Published: July 2002

CoNbZrN amorphous films were found to exhibit soft magnetic properties when deposited by ion beam sputtering or dc magnetron sputtering. In contrast to CoNbZr films they crystallize into a microcrystalline phase. Good magnetic softness is maintained during heat treatments up to 700 °C. It was found that the crystalline phase includes Co and NbN fine grains. The results of magnetostriction and electrical resistivity measurements suggest that an initial stage of crystallization starts at relatively low temperatures.
Transport mechanisms in ZnO/CdS/CuInSe2 solar cells
Authors: Yoo Ji-Beom , Fahrenbruch Alan L. , Bube R. H.
Published: July 2002

The transport mechanisms in ZnO/CdS/CuInSe2 solar cells prepared by ARCO (now Siemens) Solar Inc. have been analyzed by measurements of current versus voltage at different temperatures in the dark, short-circuit current versus open-circuit voltage at different temperatures in the light, spectral response of quantum efficiency, and junction capacitance. In the dark, recombination in the depletion region and/or thermally assisted tunneling are the dominant transport mechanisms. The observation of a smaller open-circuit voltage than would be predicted from the dark transport parameters is the result of a small change in the transport parameters under illumination, probably without a change in transport mechanism.
Current and thermal noise in mixed Na/Ag β″ alumina
Authors: Brophy James J.
Published: July 2002

Current noise in mixed-ion Na/Ag β″ alumina ceramics is characteristic of conductivity fluctuations due to diffusion noise of the mobile ions as previously observed in Na, Ag, and Pb β″ alumina single-ion conductors and for mixed-ion Na/Ca β″ alumina. The measured diffusion noise levels are greater for current injection of Ag ions from AgNO3 solution electrodes. Room-temperature conductivities calculated from thermal noise measurements are the same for both Na and Ag electrodes and show a strong mixed alkali effect. Correlation effects between the mobile ions are the same for both Na and Ag ion injection and are strongest near the 50/50 concentration ratio.
Green functions for heterostructures in an electric field
Authors: Glasser M. L. , García-Moliner F. , Velasco V. R.
Published: July 2002

We point out that the Green function for an electron in an infinitely extended electric field is not unique. We describe the mathematical basis underlying this observation and discuss the choice of Green function appropriate for various situations including ‘‘matching’’ calculations.
Measurements of domain-wall energy density for amorphous rare earth–transition metal thin films
Authors: Hajjar R. A. , Shieh H-P. D.
Published: July 2002

The value of domain-wall energy density (σw) has been most often assumed to be proportional to (AxKu)1/2, where exchange stiffness (Ax) is usually calculated from the mean-field theory. We report a simple method to derive σw from the difference between the onset of expanding and collapsing fields (ΔH) for circular domains. A micro-Kerr hysteresis-loop tracer with submicrometer resolution is used to measure the destabilizing field of domains written thermomagnetically in TbFeCo and GdTbFeCo films.
High spatial resolution photoluminescence studies of dislocations in Si-doped, liquid-encapsulated Czochralski GaAs
Authors: Visser E. P. , van der Wel P. J. , Weyher J. L. , Giling L. J.
Published: July 2002

High spatial resolution photoluminescence experiments were performed on Si-doped, liquid-encapsulated Czochralski-grown GaAs. Typical defects investigated were grown-in dislocations surrounded by impurity atmospheres (G) and grown-in dislocations moved by thermal stresses during the post-growth cooling period leaving behind a glide trace (GS). Diluted Sirtl-like etching with the use of light was performed to localize the defects, which showed up as hillocks with a small summit at the dislocation outcrop. The luminescence experiments were carried out in a helium bath cryostat at 4.2 K using a newly developed focusing and translation mechanism, mounted inside the cryostat. A spatial resolution of ≊1 μm could thus be obtained. Grown-in dislocations, starting and ending points of GS dislocations, as well as their glide traces were all found to yield lower luminescence intensities than the crystal matrix. Moreover, a relative enhancement of the (D0,h) transitions with SiGa as a donor compared to the (e,A0) transitions with SiAs as an acceptor was observed at isolated grown-in dislocations and starting points of GS dislocations. Glide traces and ending points of GS dislocations, however, at which the photoluminescence intensity was also significantly lower than at the crystal matrix, did not show this enhancement. The results are explained on the base of a relatively high concentration of nonradiative deep centers at all of the above-mentioned defects, and a high concentration of shallow donors at grown-in dislocations and starting points of GS dislocations. The distinction found between different defects with regard to the impurity incorporation is explained in terms of the thermal history of the crystal.
Magneto-resonant tunneling from a lightly doped contact region interacting with quasi-two-dimensional states in an accumulation layer
Authors: Buchanan M. , Liu H. C. , Powell T. G. , Wasilewski Z. R.
Published: July 2002

We have studied the magnetic field dependence of the tunneling current in GaAs/AlAs double barrier structures. We report new results, periodic with the inverse of the magnetic field, on a weak feature on the rising side of the main resonant tunneling peak. This feature is attributed to resonant tunneling from a lightly doped contact region interacting with the quasi-two-dimensional state in the accumulation layer. A qualitative interpretation is given.
High-laser-damage-threshold potassium dihydrogen phosphate crystals
Authors: Montgomery Ken E. , Milanovich Fred P.
Published: July 2002

Development of solid-state laser drivers of higher operating fluence is dependent upon the damage resistance of the frequency conversion crystals. We have demonstrated the correlation between the purity of the crystal growth solution and the laser damage threshold of single-crystal potassium dihydrogen phosphate (KDP). Impurities introduced in the growth process can be atomic species, inorganic or organic compounds (dissolved or particulate), or bacteria. We have developed a purification process for KDP that minimizes contamination: initial recrystallization of bulk KDP followed by ozonation to remove oxidizable material, ultrafiltration to remove nonoxidized particles, and UV-light exposure to suppress bacterial growth. We have also developed a crystal growth method that excludes load-bearing surfaces, which are a potential source of particulate contamination, from the growth environment. The method, which incorporates continuous filtration and continuous flow of the growth solution has yielded crystals with damage thresholds of 28.6 J/cm2 at 355 nm and greater than 64 J/cm2 at 1064 nm (10-ns pulse length).
Oxygen self-diffusion coefficient in the superconductor YBa2Cu3O7−δ from internal friction measurements
Authors: Tallon J. L. , Staines M. P.
Published: July 2002

The internal friction of YBa2Cu3O7−δ is measured at 7.8, 40, and 144 kHz as a function of temperature (from 300 to 1100 K) and oxygen partial pressure. At 40 kHz a marked damping peak occurs at ∼800 K which is attributable to oxygen hopping in the basal plane. The oxygen diffusion coefficient calculated from the hopping relaxation time is in good agreement with other estimates yielding an activation enthalpy, hm=1.07±0.05 eV and D0=1.8×10−4 cm2/s. At a critical value of δ∼0.25 the diffusion coefficient begins to rise rapidly similar to the occurrence of a fast-ion transition.
Ionization coefficients in Ga0.96Al0.04Sb
Authors: Luquet H. , Pérotin M. , Gouskov L. , Llinares C. , Archidi H. , Lahbabi M. , Karim M. , Mbow B.
Published: July 2002

Ionization coefficients of holes and electrons (kp and kn) in Ga0.96Al0.04Sb have been derived from the variations of the photocurrent multiplication as a function of the reverse bias in Be-implanted p+Ga0.96Al0.04Sb/n Ga0.96Al0.04Sb/n+ GaSb mesa diodes. Three wavelength values have been used for the illumination in order to obtain pure hole injection, nearly pure electron injection, and mixed injection. The kp and kn values thus determined for electric fields varying from 18 to 32 V/μm exhibit a high ratio value showing the interest of this material for avalanche photodiodes devices.
A general trend for the Stark widths of single ionized noble gases
Authors: Di Rocco Héctor O.
Published: July 2002

Several papers devoted to the Stark widths of ns-np transitions of the homologous sequence Neii, Arii, Krii and Xeii were published (n=n0+1, where n0 is the principal quantum number of the ground level). From their analysis, a general trend for this sequence is established in function of two relevant atomic parameters for the description of Stark line widths: the atomic number, Z and the upper level ionization potential. The experiments of Vitel et al. shows that, due to a dense plasma effect, a nonlinear dependence between the Stark parameters and the electron density exists: w∝Nγe. From the general trend, the value γ=5/6 is established.
Ion-induced radical production on surfaces during deposition of hydrogenated amorphous carbon
Authors: Yamashita Y. , Katayose K. , Toyoda H. , Sugai H.
Published: July 2002

In a methane/argon discharge used for deposition of hydrogenated amorphous carbon (a-C:H), energetic ion bombardment yields radicals on solid surfaces by two mechanisms: (i)fragmentation of hydrocarbon ions at their impact on the surface and (ii)sputtering of the already deposited a-C:H film. To discriminate between these two mechanisms, the emission intensity of CH(A-X) in the vicinity of a negatively biased electrode was measured as a function of the ion impact energy. The threshold energy for yielding the excited CH radical was found to be ∼2 eV for fragmentation and ∼80 eV for sputtering. The fragmentation yield is much larger on a metal surface than on a-C:H layer. The sputtering yield dominates over the fragmentation yield for the high impact energy(>150 eV).