bluuebunny/crossref_metadata_2025 huggingface dataset:
Ab initio, VTST, and QCT study of the 1 2A″ potential energy surface of the N(2D)+O2(X 3Σg−)→O(3P)+NO(X 2Π) reaction
Authors: González Miguel , Miquel Irene , Sayós R.
Published: July 2002

An ab initio study based on the CASSCF (Complete Active Space Self-Consistent Field) and CASPT2 (Second-Order Perturbation Theory on a CASSCF wave function) methods has been carried out on the ground A″2 potential energy surface (PES) involved in the relevant atmospheric reaction between N(2D) and O2 to produce O(3P) and NO. Also, some intersections between PES have been studied. The stationary points have been characterized and a grid of more than 800 points have been fitted to an analytical function. This analytical representation of the PES has been used to obtain kinetic and dynamic properties of the reaction. The rate constant of this reaction has been calculated at different levels of theory [variational transition state theory (VTST) and quasiclassical trajectory (QCT) methods] and has been compared with the experimental values (overall rate constant including physical electronic quenching) obtaining a good agreement. The QCT method has also been employed to study the properties of products from both the abstraction and insertion microscopic mechanisms. The vibrational distribution of NO arising from the reaction at 100 K has also been calculated and compared with the experimental ones. In this case, the agreement between the theoretical and the experimental results is not so good, the experimental vibrational distribution being less excited. Future work is necessary to determine the origin of this difference.
Similarity modeling on an expanded mesh applied to rotating turbulence
Authors: Domaradzki J. Andrzej , Horiuti Kiyosi
Published: July 2002

Because of the reduction in the turbulent kinetic energy decay rates rotating turbulence presents a significant challenge for turbulence models developed for nonrotating cases. We show that the modeling difficulties are removed if the generalized similarity methods are implemented on an expanded mesh.
In situ
magnetization measurements of Cu/Co multilayers during the process of electrodeposition
Authors: Gündel A. , Chassaing E. , Schmidt J. E.
Published: July 2002

The electrocrystallization of Cu–Co multilayers has been investigated by means of in situ magnetization measurements, during the electrodeposition, using an electrochemical alternating gradient magnetometer. The hysteresis loops were also recorded in situ. This allowed us to measure a magnetization efficiency, ratio of the magnetization increase to the electrical charge used. This efficiency tends to decrease as the number of bilayers increases, probably as a result of the increase in the roughness of the surface. It exhibits the same dependency on cobalt plating time as the Faradaic efficiency, which confirms that at the beginning of cobalt deposition, hydrogen evolution is the main reaction. The multilayers exhibit a typical ferromagnetic behavior. The magnetization increases and the coercive field decreases when the number of bilayers and/or the thickness of the cobalt layer increase.
Formation of Sm–Co nanoparticles in a W matrix using multilayered precursors
Authors: Farber P. , Okumura H. , Zhang Y. , Christodoulides J. , Yoon S. , Hadjipanayis G. C.
Published: July 2002

Sm–Co particles have been produced in a W matrix by annealing sputtered Sm–Co/W multilayers with layer thicknesses of 5–28 nm at temperatures of 600–850 °C. The Sm–Co particles had the intermetallic 1:7 and 2:17 structures with sizes below 10 nm and coercivities in the range of 2–10 kOe. A reduction of magnetization with prolonged annealing has been observed and attributed to alloying of Co with both W and Si by interdiffusion through the W layer.
The temperature-jump problem for a variable collision frequency model
Authors: Barichello L. B. , Bartz A. C. R. , Camargo M. , Siewert C. E.
Published: July 2002

An analytical version of the discrete-ordinates method is used here in the field of rarefied-gas dynamics to solve a version of the temperature-jump problem that is based on a linearized, variable collision frequency model of the Boltzmann equation. In addition to a complete development of the discrete-ordinates method for the application considered, the computational algorithm is implemented to yield accurate numerical results for three specific cases: the classical BGK model, the Williams model (the collision frequency is proportional to the magnitude of the velocity), and the rigid-sphere model.
One-dimensional electromagnetic solitons in a hot electron-positron plasma
Authors: Lontano Maurizio , Bulanov Sergei , Koga James
Published: July 2002

The set of relativistic hydrodynamic equations for a two-species plasma is derived with the aim to investigate the interaction between arbitrary amplitude electromagnetic (EM) fields and hot plasmas. The equations are then specialized in order to study the existence of solitonlike EM distributions in a one-dimensional electron-positron plasma. It is found that: (i) a nonzero temperature makes possible the existence of nondrifting soliton-like solutions, otherwise impossible in a strictly cold plasma; (ii) in an ultrarelativistic plasma, extremely large concentrations of EM energy densities can be achieved; (iii) correspondingly, the temperature profile of the background plasma develops strong nonuniformities.
Gain limiting processes in Er-doped Si nanocrystal waveguides in SiO2
Authors: Kik P. G. , Polman A.
Published: July 2002

Erbium-doped Si nanocrystal based optical waveguides were formed by Er and Si ion implantation into SiO2. Optical images of the waveguide output facet show a single, well-confined optical mode. Transmission measurements reveal a clear Er related absorption of 2.7 dB/cm at 1.532 μm, corresponding to a cross section of 8×10−20 cm2. The Si nanocrystals act as sensitizers for Er but under high doping conditions (∼50 Er ions per nanocrystals) no pump-induced change in the Er related absorption is observed under optical pumping (λ=458 nm), which is ascribed to an Auger quenching effect. For very high pump powers, a broad absorption feature is observed, attributed to free carrier absorption.
On a general link between anomalous diffusion and nonextensivity
Authors: Frank T. D.
Published: July 2002

Stochastic processes of systems with composable entropy measures are studied. The processes are described by Fokker–Planck equations which are nonlinear with respect to their probability densities and whose diffusion coefficients are derived from the entropy measures in questions. In nonextensive (extensive) systems anomalous (normal) diffusion is found.
Atomic scale measurements of the interfacial electronic structure and chemistry of zirconium silicate gate dielectrics
Authors: Muller David A. , Wilk Glen D.
Published: July 2002

We have examined the interfaces in Zr-silicate gate dielectrics grown on Si substrates using electron energy loss spectroscopy. The Zr-silicate interface is found to be stable with the Si substrate and the polycrystalline silicon (poly-Si) electrode under annealing to 1050 °C. At this interface, a 0.35 nm wide Zr-free interface region is observed in the as-deposited film, and does not change on annealing. The Zr-free region is too thin to take on the bulk SiO2 electronic structure, and thus is unlikely to compromise the dielectric properties of the device. For films with an Al electrode, a 2 nm reaction layer forms at the Zr-silicate interface.
Interdiffusion in antiferromagnetic/ferromagnetic exchange coupled NiFe/IrMn/CoFe multilayer
Authors: Lee J. H. , Jeong H. D. , Yoon C. S. , Kim C. K. , Park B. G. , Lee T. D.
Published: July 2002

Auger electron spectroscopy (AES) and Rutherford backscattering spectroscopy (RBS) analysis were carried out in order to study the extent of interdiffusion during thermal treatment of the pinned electrode (Ta/NiFe/Cu/NiFe/IrMn/CoFe) of the magnetic tunneling junction. From the concentration profile results from RBS and AES, a significant amount of Mn–CoFe interdiffusion was observed when the sample was annealed at 200 °C–400 °C under vacuum. The multilayer was completely intermixed at 400 °C, losing the exchange bias interaction between the IrMn and CoFe layers. It was demonstrated that the migration of Mn was enhanced by the preferential oxidation of Mn on the surface. In fact, when a thin layer of Ta for oxidation protection was deposited on top of the electrode, the Mn diffusion was minimal up to 300 °C. Our experiment suggests that in actual magnetic tunneling junctions, the Mn diffusion to the insulation layer could be enhanced by the presence of the free oxygen radicals in the insulation layer produced during the plasma oxidation of the Al layer.
Ab initio potential energy surfaces of the propane dimer
Authors: Jalkanen Jukka-Pekka , Mahlanen Riina , Pakkanen Tapani A. , Rowley Richard L.
Published: July 2002

The potential energy surface of a model propane dimer was systematically mapped with quantum chemical calculations. The calculations included approximately 12 separation distances between the monomers for each of 121 different relative geometries, or 1487 different configurations. The generated potential energy map reveals that the most attractive interactions are those having a maximum number of close contacts between carbon and hydrogen. The potential well depth of the most attractive orientation found was −1.625 kcal mol−1. The complete ab initio energy surface was fitted to a simple model consisting of pairwise-additive interatomic potentials, each modeled with a modified Morse function of interatomic distance. The resultant model accurately represents the entire propane dimer ab initio energy surface. The efficacy of the generated parameter set was tested with previously published ethane dimer energies and propane routes not included in fitting. The new parameter set is consistent with these results indicating a high level of transferability for the interatomic C–H, C–C, and H–H potentials obtained.
Use of crystal polymorphs for resolving an equilibrium liquid’s state on supercooling to 0 K
Authors: Johari G. P.
Published: July 2002

There are two ways by which an equilibrium liquid’s heat capacity, Cp,liq, is seen to decrease to zero on cooling to 0 K: (i) decrease abruptly first to the Cp of its ordered crystal at T>0 K, and thereafter the crystal’s Cp decrease to zero at 0 K, and (ii) decrease continuously to zero at 0 K. The prohibitively long time needed for Cp measurements at sufficiently low temperatures has prevented one from determining the relative merits of these two inferences. Here, we propose a method for doing so by a comparative analysis of the Cp data of an equilibrium liquid and of its two crystalline forms, one of which is orientationally disordered. The method is then used to test these merits with the available Cp and entropy data of ethanol. The results support the inference of a continuous decrease in Cp to zero at 0 K, but not that of an abrupt decrease.
Observation of laser oscillation in aggregates of ultrasmall silicon nanoparticles
Authors: Nayfeh M. H. , Rao S. , Barry N. , Therrien J. , Belomoin G. , Smith A. , Chaieb S.
Published: July 2002

We report laser oscillation at ∼610 nm in aggregates of ultrasmall elemental Si nanoparticles. The particles are ultrabright red emitting, dispersed from bulk Si by electrochemistry. The aggregates are excited by radiation at 550–570 nm from a mercury lamp. Intense directed Gaussian beams, with a threshold, manifest the emission. We observe line narrowing, and speckle patterns, indicating spatial coherence. This microlasing constitutes an important step towards the realization of a laser on a chip, hence optoelectronics integration and optical interconnects.
One-electron pseudopotential calculations of excited states of LiAr, NaAr, and KAr
Authors: Rhouma M. B. El Hadj , Berriche H. , Lakhdar Z. B. , Spiegelman F.
Published: July 2002

The potential curves and spectroscopic constants of the excited states of alkali–argon diatomics MRg (M=Li, Na and K, Rg=Ar) are calculated using usual semilocal single valence electron pseudopotentials on alkali atoms [M+]-core pseudopotentials), semilocal pseudopotentials replac(ing all the electrons of argon ([Ar]-core pseudopotentials), and core polarization pseudopotentials on both centers. All states dissociating into Li(2s, 2p, 3s, 3p, 3d, 4s, and 4p), Na(3s, 3p, 3d, 4s, 4p, 4d, 5p) and K(4s, 4p, 5s, 3d, 5p, 4d, 6s, 4f, 6p, 5d, 7s, 5f) are considered. The core–core interactions for Li+Ar and Na+Ar are included using the accurate ab initio potentials of Ahmadi et al. [G. R. Ahmadi, J. Almlöf, and I. Roeggen, Chem. Phys. 199, 33 (1995); G. R. Ahmadi and I. Roeggen, J. Phys. B 27, 5603 (1994)] while the K+Ar ion data are determined by MP2 all-electron calculations.
Monte Carlo simulations of star-branched polymers confined between two walls
Authors: Romiszowski Piotr , Sikorski Andrzej
Published: July 2002

The properties of simplified lattice models of confined branched polymers were studied by the Monte Carlo method. Model chains were located between two parallel impenetrable surfaces. The distance between surfaces, as well as the chain length, were varied. The model chains consisted of f=3 branches of equal length (star-branched polymers) and were based on a simple cubic lattice. The model was athermal and the excluded volume was introduced. Monte Carlo sampling algorithm using local chain micromodifications was applied. Both static and dynamic properties of the system were investigated. The differences between star-branched chains and linear ones which were trapped between walls were discussed. The behavior of static properties made it possible to construct a universal curve presenting the effect of surface-to-surface distance on chain dimensions. The possible explanation of the shape of this curve was given. The changes of dynamic properties were discussed in the context of possible chain’s mechanism of motion.
Mechanisms of molecular electronic rectification through electronic levels with strong vibrational coupling
Authors: Kuznetsov Alexander M. , Ulstrup Jens
Published: July 2002

We present a new view and an analytical formalism of electron flow through a donor–acceptor molecule inserted between a pair of metal electrodes. The donor and acceptor levels are strongly coupled to an environmental nuclear continuum. The formalism applies to molecular donor–acceptor systems both in vacuum or air, and in aqueous solution under electrochemical potential control. Multifarious patterns of rectified electron flow from the negatively to the positively biased electrode arise. The electronic interaction between the donor and acceptor fragments, mutually and with the electrodes, can be weak, corresponding to the fully diabatic limit. The rectification process then reduces to a sequence of vibrationally relaxed single-electron transfer steps. In the limits where the interactions are strong, denoted as the partially and fully adiabatic limits, the character of the rectification process is different, and electron flow proceeds coherently, without vibrational relaxation. In still another class of mechanisms the electronic level broadening of either donor or acceptor from the adjacent electrode is so strong that it is comparable to the vibrational broadening. The process then reduces to a three-level transition similar to STM of large redox molecules. Recent data for rectification in hexadecyl-quinolinium tricyanodimethanide monolayers by Metzger and co-workers [J. Am. Chem. Soc. 119, 10455 (1997); Acc. Chem. Res. 32, 950 (1999)], are discussed in terms of the reported views and formalism.
A high performance digital receiver for home-built nuclear magnetic resonance spectrometers
Authors: Michal Carl A. , Broughton Kesten , Hansen Elsa
Published: July 2002

The design and construction of a high-performance, low-cost, and easy to assemble quadrature digital receiver for a home-built nuclear magnetic resonance (NMR) spectrometer is described. Critical synchronization and timing issues are considered and solutions are discussed. The performance of the receiver is compared to that of a modern commercial NMR spectrometer. Advantages of this system include excellent passband flatness and delay flatness, very sharp filter cutoff, high dynamic range, bandwidths up to 30 MHz, and perfect balance between the quadrature channels with no component matching or adjustment.
Effect of reactive ion etching on the exchange coupling between IrMn and NiFe
Authors: Seigler Michael A.
Published: July 2002

The effect of reactive ion etching on the exchange coupling between an antiferromagnetic material (IrMn) and a ferromagnetic material (NiFe) was investigated. Although IrMn is not reactively etched using oxygen or fluorine based chemistries, these chemistries are shown to reduce the exchange coupling between the IrMn and NiFe films by altering the IrMn film composition. These chemistries also have the effect of increasing the resistivity of the IrMn from ∼200 μohm-cm to >1000 μohm-cm. Reactive ion etching is shown to be a good process for reducing the coupling between IrMn–NiFe bilayers used as freelayers in sheet film spinvalves due to its material selectivity and etch stop capability. This process could be used in the processing of exchange-tab-type readback sensors used for magnetic recording.
Light-emitting electrochemical cells using a molten delocalized salt
Authors: Panozzo S. , Armand M. , Stéphan O.
Published: July 2002

The device performances of light-emitting electrochemical cells are improved by adding a room-temperature molten salt (tetrahexylammonium-bis-trifluoro-methyl-sulfonyl imide) directly into the light-emitting layer. For poly(9,9-dihexyl-fluorene-2,7-diyl) with an indium-tin-oxide anode and an aluminum cathode, the power efficiency can be increased by more than one order of magnitude. An even more pronounced effect is observed for poly [2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene]. Equally important for both luminescent polymers, the operating voltage is drastically reduced.
Prototype spin-dependent tunneling isolators integrated with integrated circuit electronics
Authors: Wang Dexin , Tondra Mark , Nordman Cathy , Qian Zhenghong , Daughton James M. , Lange Erik , Brownell David , Tran Loc , Schuetz James
Published: July 2002

Low power, fast speed, small size, wide temperature range, and common-mode-noise-rejection capability are some of the attributes of magnetoresistive devices for galvanic isolation over conventional devices such as optical and capacitive devices. We have fabricated prototype galvanic isolators using spin-dependent tunneling materials. The tunnel junctions have been deposited by rf diode sputtering and the Al2O3 barriers are formed by depositing a thin layer of Al, then oxidizing it with oxygen contained plasma. The junctions are then patterned using photolithography techniques to define the pinned and free layers separately. A series of tunnel junctions are connected in a Wheatstone bridge form and are fabricated directly on top of the integrated circuit (IC) electronics that are used to process the signals from the bridge. In its core magnetics design, this digital device simply employs a one-bit memory cell capable of operating at 5 V. The functions of the devices are tested using a function generator, an IC driver chip, a probe station, two dc power supplies, and a high-speed network analyzer. The power consumption for the isolator is <1 mW when operating at 2 MHz, a factor of 10 lower than the giant magnetoresistance product of similar functions. The operating speed of this device reaches 60 MHz, limited by the design of the electronics.
Ultrahigh vacuum scanning tunneling microscopy/magnetic force microscopy study of ultrathin iron films grown on polycrystalline nickel oxide films
Authors: Dreyer M. , Hwang D. G. , Gomez R. D.
Published: July 2002

The thickness dependence of the topographic and magnetic structure of ultrathin Fe films grown on polycrystalline NiO films under ultrahigh vacuum (UHV) conditions was studied to investigate the growth mechanism of the ferromagnetic film and the corresponding magnetic interaction with the antiferromagnetic substrate. Externally prepared NiO films of 60 nm thickness were cleaned by heating in UHV. Ultrathin layers of Fe in the range of 1–27 nm were deposited on top of the NiO film and were analyzed at specific coverages. Iron grows as a polycrystalline film with the grains increasing in size with the thickness. The contours of the underlying NiO crystallites were evident at low coverages but gradually disappeared as the Fe grains coalesced at thicker coverages. Magnetic force microscopy images of the 1 nm thick film show randomly oriented magnetic grains with an average domain size of 30 nm. With an increase in film thickness the size of the domains grows to about 200 nm at 15 nm of iron. At a film thickness of 19 nm cross-tie domain walls become visible, indicating the crossover of some parts of the film from random magnetic grains into continuous domains with in-plane magnetization. A further increase in the film thickness leads to larger in-plane domains, while there are some areas with localized grains on the surface.
Micromagnetic simulation for tunnel junctions with synthetic antiferromagnetic pinned layers annealed at different external fields
Authors: Liu Yaowen , Zhang Zongzhi , Zhang Zhengang , Freitas P. P. , Martins J. L.
Published: July 2002

Bottom-pinned tunnel junctions with synthetic antiferromagnetic (SAF) pinned layers require an annealing step near the blocking temperature under an applied magnetic field to set the exchange direction. Experimental results (anneal at 270 °C, for a MnIr/SAF structure) show that the tunnel magnetoresistance signal is strongly reduced (3%) for anneals under an applied field of 2000 Oe, when compared with large tunnel magnetoresistance signals (>20%) obtained for samples annealed either at low (250 Oe) or high (5000 Oe) fields. To clearly understand this behavior, a micromagnetic simulation was performed to demonstrate the magnetization evolution of the SAF layer during the different field anneals. The simulated magnetization configurations indicate that the SAF layer net moment aligns parallel to the applied field (high field anneal) or antiparallel to the applied field (low field anneal), leading in both cases to high TMR signal. After annealing at intermediate field, the SAF net moment rotates almost orthogonal to the annealing field direction, resulting in the measured low TMR signal.
Write field analysis in perpendicular recording using three-dimensional micromagnetic simulation
Authors: Gao K. , Bertram H. N.
Published: July 2002

A three-dimensional micromagnetic perpendicular recording model is developed to study the effect of magnetic properties and head geometry on the write head field. For parameters characteristic of 200 Gbit/in.2, the maximum write field is about 0.73 Bs. Thirty percent of this field is due to neck saturation. Calculated head field gradients at track center agree well with the theoretical Westmijze field. The maximum write field is independent of the SUL thickness for thicknesses greater than the track width. At an SUL thickness of half the track width, the field decreases by 10%, and thereafter decreases rapidly.
Magneto-optical effects calculated for granular composites with magnetized nano-onions dispersed in matrixes
Authors: Abe M. , Kuroda J.
Published: July 2002

For granular composite having nano-onions (nanosized, multicore-shell structured particles) dispersed in a matrix we derived an effective dielectric permittivity tensor including off-diagonal terms, based on the Maxwell Garnett effective field approximation. The magneto-optical Kerr effect was calculated from the effective permittivity tensor for the composite containing nano-onions with Au (core)/Fe (inner shell)/Au (outer shell) structure. The off-diagonal term, 〈εxy〉=〈εxy′〉+i〈εxy″〉, of the effective permittivity tensor and Kerr effect derived from it exhibit a dispersion relation, 〈εxy′〉 making a peak and 〈εxy″〉 crossing zero, at a wavelength around 630 nm. The dispersion may be ascribed to the plasma resonance of Au, because similar peak was found in the Kerr rotation spectra for compositionally modulated multilayered Au/Fe films due to the plasma resonance of Au.
Magnetovolume effects of Y–Fe–Co–Ti intermetallics
Authors: Wang J. L. , Ibarra M. R. , Marquina C. , Garcı́a-Landa B. , Tegus O. , Xiao Q. F. , Brück E. , Yang F. M. , Wu G. H.
Published: July 2002

Thermal expansion and magnetic properties of the YFe11−xCoxTi compounds have been investigated by various experimental methods. A large magnetovolume effect has been clearly observed below TC for the Fe-rich compounds. When the transition metal concentration changes from Fe to Co rich, the invar-like effect becomes less pronounced and almost disappears close to the pure-Co compound. The dependence of the spontaneous volume magnetostriction on temperature and Co concentration has been estimated from the thermal expansion measurements. It has been found that, for the YFe11−xCoxTi compounds, the largest spontaneous volume magnetostriction (about 2.1%) occurs at x=3, close to the concentration in which a maximum in saturation magnetization was found. The anomalous thermal expansion can be attributed to the volume dependence of the magnetic energy, which is very sensitive to the distance between first-neighbors transition-metal atoms for Fe-rich compounds.
Thermal expansion anomaly of Pr2AlFe13Mn3 compound near its Curie temperature and magnetic properties of Pr2AlFe16−xMnx compounds
Authors: Hao Yanming , Gao Yan , Qu Jingping , Zhan Yong
Published: July 2002

Structure and magnetic properties of Pr2AlFe16−xMnx (x=0–10) compounds have been investigated by means of x-ray diffraction and magnetization measurements. The Pr2AlFe16−xMnx compounds have a rhombohedral Th2Zn17-type structure. Their unit-cell volume increase slowly with increasing x, then rapidly with the further increase of x. This implies a strong positive spontaneous volume magnetostriction exists in the magnetic state for Pr2AlFe16−xMnx compounds. X-ray diffraction of Pr2AlFe13Mn3 compound from 160 to 300 K shows that a negative coefficient of thermal expansion exists, ᾱ≈−3.6×10−4/K, from 180 to 198 K. The Curie temperature and the saturation magnetization of Pr2AlFe16−xMnx compounds show a rapid drop with increasing x.
Temperature dependence of magnetization reversal in TbFeCo films
Authors: Brown S. , Harrell J. W. , Fujiwara H. , Takeuchi T.
Published: July 2002

The magnetization reversal process has been studied in a series of four TbFeCo films over the temperature range 300–460 K. The films were characterized by time decay, dynamic coercivity, Kerr imaging, and torque measurements. For a film with a sputter-etched SiN underlayer, the reversal process at low temperatures was dominated by nucleation followed by rapid domain wall motion. The low temperature relaxation curves for this sample were analyzed using a Fatuzzo model. At high temperatures, the Fatuzzo model did not apply. For the other films, with no etching, relaxation curves were logarithmic at all temperatures. All activation volumes increased with increasing temperature and decreased with increasing sputtering pressure. The magnetic anisotropy direction changed from perpendicular to in-plane as the argon sputtering pressure was increased.
Strong pinning in ternary (Nd–Sm–Gd)Ba2Cu3Oy superconductors
Authors: Muralidhar M. , Nariki S. , Jirsa M. , Wu Y. , Murakami M.
Published: July 2002

We have studied the flux pinning in melt-textured (Nd0.33Sm0.33Gd0.33)Ba2Cu3Oy NSG-123 superconductors with various numbers of Gd2BaCuO5 (Gd-211) particles. Transmission electron microscopy (TEM) showed that submicron Gd-211 particles are uniformly distributed in the superconductive matrix. Dark-field TEM observations further showed that a high density of RE rich RE1+xBa2−xCu3Oy (RE-123ss) clusters 3–10 nm in size were distributed in the NSG-123 matrix. A strongly developed fishtail was observed in the magnetization hysteresis loops of all the samples. A critical current density of 100 kA/cm2 (77 K) was achieved at the secondary peak field of 2 T for the H∥ c axis in the NSG-123 sample with 10 mol % Gd-211. Large grain NSG-123 pellets with 30 mol % Gd-211 and 20 wt % AgO2, 30 mm in diameter and 15 mm in height, exhibited a single-cone profile with a peak value of 1.2 T at 77 K. A higher trapped-field value of 1.5 T was recorded at 2 T, reflecting the secondary peak effect.
Molecular dynamics simulation of a liquid in a complex nano channel flow
Authors: Fan Xi-Jun , Phan-Thien Nhan , Yong Ng Teng , Diao Xu
Published: July 2002

We report some molecular dynamics simulation results for a complex nano channel flow. In certain flow geometry, some of the flow features cannot be predicted by the Navier–Stokes equations with no-slip boundary conditions. The results show a loss of dynamic similarity for flows with similar geometry and global dimensionless flow parameters. Nano-sized vortex flow can be developed at low Reynolds numbers due to near-wall molecules having large enough momenta, resulting in qualitatively different flow field from that predicted by the Navier–Stokes equations.
Local electric field at the emitting surface of a carbon nanotube
Authors: Kokkorakis G. C. , Modinos A. , Xanthakis J. P.
Published: July 2002

We present a method for the calculation of the local electric field at the surface of a nanoscopic emitting structure. The method is here applied to carbon nanotubes (NT) where symmetry makes the application of the method easier. The NT is simulated as a cylindrical array of touching spheres, each sphere representing an atom of the tube. The electrostatic potential is written as a linear combination of the potentials produced by each of the spheres. We calculate the local electric field and the corresponding enhancement factor γ for both open and closed nanotubes. For a closed NT we find for γ a simple polynomial expression in terms of the ratio of the height h of the tube to its radius R, which for h/R<40 reduces to a frequently quoted formula of γ. For an open single-wall NT we find that γ is three times greater than that of a single-wall NT of the same h/R. As the thickness of the wall increases this difference diminishes. From these results one may deduce a possible explanation as to why in some experiments a closed NT emits more current than a corresponding open one while in other experiments the opposite holds true.
Polymer stress statistics in the near-wall turbulent flow of a drag-reducing solution
Authors: Sibilla Stefano , Baron Arturo
Published: July 2002

The direct numerical simulation of the turbulent flow of a dilute polymer solution in a plane channel at low-Reynolds number has been performed in order to investigate the reduction in friction drag. The polymer solution has been represented as a continuum fluid whose constitutive equations have been derived on the basis of a modified FENE-P dumbbell model. The mean polymer dynamics in the turbulent flow have been studied through statistical moments of the configuration tensor. The analysis of the results obtained suggests that polymers can be effective in terms of drag reduction only if their relaxation time is comparable to the characteristic time of their convection in the normal-to-the-wall direction within near-wall turbulent structures. The energy budget of the normal components of the Reynolds stress tensor suggests that elongated polymers inhibit turbulence regeneration by opposing pressure redistribution from streamwise to cross-flow velocity fluctuations.
Investigation of magnetic properties and phase evolution of NdxFebal.TiCB10.5 (x=9, 9.5, 10, and 11) melt spun ribbons
Authors: Chang W. C. , Chang J. K. , Chang H. W. , Ma B. M.
Published: July 2002

The magnetic properties and phase evolution of boron enriched NdxFebal.TiCB10.5 (x=9, 9.5, 10, and 11) melt spun ribbons have been investigated. For x=9, 9.5, and 10, the main phases in the ribbons are Nd2Fe14B, Fe3B, and a dilute α-Fe. For x=11, the Fe3B phase is suppressed and only Nd2Fe14B and α-Fe were detected. An increase of rare earth content, from x=9 to x=10, was found to improve not only the intrinsic coercivity (iHc) but also the remanence (Br). The improvement in Br may be ascribed to the grain refinement as evidenced by transmission electron microscopy. A Br=9.2 kG, Hci=12.1 kOe, and (BH)max=16.2 MGOe were obtained on Nd10Febal.TiCB10.5 alloy ribbons quenched at 20 m/s followed with a 675 °C annealing for 10 min. Meanwhile, with an increase in the annealing temperature, the coercivity of the above alloy ribbons could be reduced to 9.8 kOe without sacrificing its Br and (BH)max.
Phase transition and magnetotransport properties of ball-milled half-metallic CrO2
Authors: Wang K.-Y. , Spinu L. , He J. , Zhou W. , Wang W. , Tang J.
Published: July 2002

Small CrO2 particles with mean diameters ranging from 11 to 25 nm have been prepared by ball milling. X-ray diffraction studies show a continuous lattice expansion with increasing milling time. A phase transition to Cr2O3 also occurs with a sudden increase in the amount of Cr2O3 found between 5 and 8 h of milling. The decreases of low-field magnetoresistance with increasing milling time is correlated to the expansion of the lattice parameters of CrO2, which probably leads to the reduction in its spin polarization. High-field magnetoresistance increases with the milling possibly due to the enhanced mixed valence of the chromium, which supports the double exchange model.
Thermal demagnetization of a field-cooled spin glass
Authors: Ryan D. H. , Tun Zin
Published: July 2002

The decay of the field-cooled remanent state in two frustrated alloys has been investigated by magnetization and neutron depolarization. The partially frustrated material undergoes domain formation as the remanence decays, while the fully frustrated sample shows only a uniform fading of the magnetization, consistent with slow paramagnetic dynamics. Domains do not form.
Fast reversal dynamics in perpendicular magnetic recording media with soft underlayer
Authors: Schrefl Thomas , Schabes Manfred E. , Lengsfield Byron
Published: July 2002

Reversal dynamics in perpendicular magnetic recording media is investigated using finite element micromagnetic simulations. The results show that gyromagnetic precession plays an important role during the magnetization reversal of both the soft underlayer and the data layer. Magnetization reversal within the soft underlayer starts at positive applied field due to its low anisotropy and high demagnetization field. The switching of the data layer starts at an applied field of about −0.3 Hk,DL, where Hk,DL is the anisotropy field of the data layer. At finite temperature, thermal activation reduces the dynamic coercivity. However, this effect is smaller than the change of the dynamic coercivity found by varying the Gilbert damping parameter, α. Media dynamic coercivity was found to increase significantly when α was decreased from 0.1 to 0.01.
Magnetic interaction among particles in Co–Cr–Ta media and Co/Pt multilayered media evaluated by anomalous Hall effect
Authors: Das Sarbanoo , Nakagawa Shigeki
Published: July 2002

A new method for evaluating magnetic interaction among the particles in perpendicular magnetic recording layers under canted magnetic field has been proposed using anomalous Hall effect (AHE) measurement and vibrating sample magnetometer (VSM) measurement. Initial curves and magnetic hysteresis loops were measured to determine ΔM, an evaluation index to estimate interaction using the relation as ΔM=Minit−0.5×(Mup+Mdown). The degree of interaction ΔM can be determined as a vector by combining the results obtained by VSM and AHE measurements. Distribution of vertices (DOV) of ΔM can be regarded as a degree of interaction in a particular direction. The DOV of ΔM in Co–Cr–Ta thin film extended along the in-plane direction and showed gradual convergence as the applied field direction canted toward the film plane. This can be an indication that the magnetic particles in the Co–Cr–Ta thin film tend to incline to the applied field direction individually. On the other hand, the DOV of ΔM in Co/Pt multilayered thin film extended along the perpendicular direction and the shape of the trajectory of ΔM remained unchanged though the applied field direction deviated widely from the normal direction. This may be due to the strong perpendicular anisotropy in the Co/Pt multilayered thin film.
Visualization of spin waves during switching simulation
Authors: Visscher P. B. , Traistaru O. , Apalkov D. M. , Feng Xuebing
Published: July 2002

We discuss “spin-wave switching,” in which switching is triggered by a spin wave instability rather than a geometric instability mode such as buckling or curling, or end nucleation. This type of switching was reported in a simulation by Safonov and Bertram. We examine the mechanism of spin-wave switching using several visualization methods, and introduce a new method of displaying the spin-wave spectrum. We construct a three dimensional “k-space window” in which the coordinates are the wavevector components kx,ky, and kz. At each allowed k vector in this window we display only the parts of the magnetization attributable to this k vector. Initially we see magnetization only at k=0, and we can visually follow the exponential growth of the unstable Fourier components at the onset of instability.
Transient core modeling using phenomenological eddy currents
Authors: Wolbank Th. M. , Woehrnschimmel R. , Hauser H.
Published: July 2002

The calculation of the static magnetization curve—including hysteresis—has been done with the energetic model (EM). It is based on minimizing the total energy density, consisting of reversible and irreversible contributions and of the energy densities of the applied field H and the demagnetizing field Hd. The main idea of the EM is the interpretation of the magnetization process as a process of order which is determined by an elementary probability function, considering the distribution of magnetic moments on certain (easy) directions [Hauser, J. Appl. Phys. 75, 2584 (1994)]. In this work, the EM is extended to dynamic magnetization based on the well known lag between magnetization and the applied field, described by the phenomenology of an eddy current field. One application of this dynamic model is its integration into a simulation model of an electrical machine. This is described for an induction machine and focus is on its simulation when fed from a voltage source inverter. Evaluating the machine’s response to an excitation with short voltage pulses makes parasitic effects visible which are mainly due to saturation and rotorslotting. These effects can be utilized in sensorless control schemes, where the flux- or rotor-position is determined without a mechanical encoder on the rotor shaft. The obtained complete simulation model correctly describes the transient behavior of a machine that is confirmed by a comparison with measurements. Influences of the machines design parameters on the transient behavior can then be investigated and appropriate optimizations regarding the control schemes are possible.
Ni–Mn–Ga thin films produced by pulsed laser deposition
Authors: Tello P. G. , Castaño F. J. , O’Handley R. C. , Allen S. M. , Esteve M. , Castaño F. , Labarta A. , Batlle X.
Published: July 2002

Polycrystalline Ni–Mn–Ga thin films have been deposited by the pulsed laser deposition (PLD) technique, using slices of a Ni–Mn–Ga single crystal as targets and onto Si (100) substrates at temperatures ranging from 673 K up to 973 K. Off-stoichiometry thin films were deposited at a base pressure of 1×10−6 Torr or in a 5 mTorr Ar atmosphere. Samples deposited in vacuum and temperatures above 823 K are magnetic at room temperature and show the austenitic {220} reflection in their x-ray diffraction patterns. The temperature dependences of both electrical resistance and magnetic susceptibility suggest that these samples exhibit a structural martensitic transition at around 260 K. The magnetoresistance ratio at low temperature can be as high as 1.3%, suggesting the existence of a granular structure in the films.
Temperature dependence of perpendicular magnetic anisotropy for c-plane-oriented MnSb sputtered films
Authors: Ashizawa Yoshito , Saito Shin , Takahashi Migaku
Published: July 2002

The temperature dependence of magnetic anisotropy was investigated for c-plane-oriented MnSb sputtered films. The main results were as follows: (1) A MnSb phase with low Mn contents between 50.1 at. % and 50.8 at. % was formed in c-plane-oriented MnSb films. (2) It was clarified that the perpendicular magnetic anisotropy, which originated from uniaxial magnetocrystalline anisotropy of NiAs-type hexagonal structure, changed from a negative value of −3.99×106 erg/cm3 at room temperature to a positive value of 3.73×105 erg/cm3 at 300 °C. The perpendicular magnetic anisotropy crossed 0 erg/cm3 at about 270 °C. (3) The formation of the MnSb phase with Mn content of about 51.5 at. % was necessary to reduce the transition temperature, where the MnSb film changed its easy axis from the film plane to the film normal direction, to 150–200 °C.
Fabrication and characterization of focused-ion-beam trimmed write heads for perpendicular magnetic recording
Authors: Clinton T. W. , van der Heijden P. A. A. , Karns D. C. , Yu J. , Park C. M. , Batra S.
Published: July 2002

A focused ion beam (FIB) has been used to trim write heads for perpendicular magnetic recording using untrimmed HGA-level longitudinal heads. The ion-beam imaging of the write head during FIB processing was minimized to limit exposure of the active magnetic material at the ABS to a 30 keV Ga+ ion dose of less than 1014 Ga+/cm2 (≈10−13 C/μm2) (the GMR reader was never exposed), which is significantly below levels where magnetic properties have been observed to degrade [W. M. Kaminsky et al., Appl. Phys. Lett. 78, 1589 (2001)]. The corresponding recording characteristics and spatial profiles of written tracks have been measured on a spin stand and a magnetic force microscope (MFM). Recording performance, such as SNR, and pulse shape of transitions, for example, as a function of head design and FIB processing is discussed, which compares very favorably to the performance of untrimmed heads. The MFM images reveal curvature in the magnetic transitions (transition smile) when writing with a single-pole writer with a straight trailing edge. Conversely, we demonstrate straight transitions using a single-pole writer with a curved trailing edge. Our results demonstrate the robustness of FIB-trimmed heads down to sub-100-nm length scales.
Numerical modeling of the magnetization of a permanent magnet and its effect on the electromechanical performance of a brushless direct current motor
Authors: Jang G. H. , Chang J. H. , Lee Y. B.
Published: July 2002

This article investigates the electromechanical performance of a brushless dc (BLDC) motor due to the magnetization patterns of a permanent magnet, i.e., rectangular, trapezoidal, and sinusoidal magnetization. A driving circuit equation considering the switching action of the pulse width modulation inverter is coupled with Maxwell’s equation to obtain the nonlinear time-stepping finite element equation for the magnetic field analysis. Newton–Euler’s equations are used to determine the mechanical motion of a rotor due to electromechanical excitation. The results show that rectangular magnetization results in the low phase current for a specified torque. However, sinusoidal magnetization produces the smallest magnetic force and may result in the sound mechanical operation of a BLDC motor.
Passivation-mediated growth of Co on Se, S and O rich GaAs surfaces: A potential approach to control interface crystallinity and magnetic continuity
Authors: Nath Krishna G. , Maeda Fumihiko , Suzuki Satoru , Watanabe Yoshio
Published: July 2002

Passivation-mediated growth was used to control the interface crystalline order and the magnetic continuity in epitaxial Co films on several GaAs(001) surfaces. Using Se, S, and O passivated layers on GaAs before Co deposition, we observed a variety of interface structures depending on the substrate condition. With the help of transmission electron microscopy (TEM) images, we show that a perfect and well-ordered crystalline growth at the initial stage of deposition for Co/Se/GaAs ensures a better growth for thicker film. The magnetic properties of Co overlayers on all the substrates were studied by magnetic linear dichroism in angular distribution (MLDAD) in photoemission and found to be different depending on the film crystallinity. By combining the TEM and MLDAD results, we conclude that Co film on Se/GaAs, which has an ordered interface, is a good candidate for use as a spin filter from the viewpoint of spin-injection mechanism.
Ni–Zn ferrite films with high permeability (μ′=∼30, μ″=∼30) at 1 GHz prepared at 90 °C
Authors: Matsushita N. , Chong C. P. , Mizutani T. , Abe M.
Published: July 2002

Ni–Zn ferrite films were prepared by spin-spray ferrite plating method at 90 °C on glass substrates from a reaction solution of FeCl2(+FeCl3)+NiCl2+ZnCl2 and an oxidizing solution of NaNO2+CH3COONH4. The complex permeability μ=μ′−iμ″ values of the as-plated films were measured at frequencies up to 3 GHz. The Ni0.28Zn0.18Fe2.54O4 film 0.40 μm in thickness plated using the mixture of Fe2+ and Fe3+ as iron ions exhibited a high μ′ of around 42 and a resonance frequency fr of 1.2 GHz. This fr value is about nine times as high as the 130 MHz that was estimated from Snoek’s limit for the Ni–Zn ferrite bulk ceramics. Since μ′ also exhibited a maximum value of about 35, the films prepared in this study will be applicable to both rf inductors and wave absorbers for electromagnetic interference suppression.
Recording, noise, and medium microstructure in perpendicular recording with a soft magnetic underlayer
Authors: Guan Lijie , Zhu Jian-Gang
Published: July 2002

A micromagnetic model for studying recording and noise characteristics in perpendicular media with a soft magnetic underlayer has been developed. The single pole head and soft magnetic underlayer are modeled with two-dimensional meshes and the medium is modeled with a three-dimensional granular structure. Utilizing the model, the dependence of recording characteristics on a medium microstructure, especially the intergranular exchange coupling, and write field is investigated.
Nonlinear optical properties of silicon nanocrystals grown by plasma-enhanced chemical vapor deposition
Authors: Prakash G. Vijaya , Cazzanelli M. , Gaburro Z. , Pavesi L. , Iacona F. , Franzò G. , Priolo F.
Published: July 2002

The real and imaginary parts of third-order nonlinear susceptibility χ(3) have been measured for silicon nanocrystals embedded in SiO2 matrix, formed by high temperature annealing of SiOx films prepared by plasma-enhanced chemical vapor deposition. Measurements have been performed using a femtosecond Ti–sapphire laser at 813 nm using the Z-scan technique with maximum peak intensities up to 2×1010 W/cm2. The real part of χ(3) shows positive nonlinearity for all samples. Intensity-dependent nonlinear absorption is observed and attributed to two-photon absorption processes. The absolute value of χ(3) is on the order of 10−9 esu and shows a systematic increase as the silicon nanocrystalline size decreases. This is due to quantum confinement effects.