bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanisms of amino acid formation using optical emission spectroscopy
Authors: Miyakawa S. , Sawaoka A. B. , Ushio K. , Kobayashi K.
Published: July 2002

Magnetoplasma dynamic arc jet was characterized by optical emission spectroscopy (OES) in order to study the mechanisms of amino acid formation induced by electric discharge. Nitrogen, oxygen, and hydrogen atoms and CN radicals were produced by instantaneously heating a CO–N2–H2O gas mixture to 10 000 K. These plasma species were rapidly cooled to form an amorphous film containing amino acid precursors by directly colliding against a wall of a glass tube. This is a new method of producing amino acid precursors without involving the reaction among hydrogen cyanide (HCN), formaldehyde (H2CO), and ammonia (NH3); HCN, H2CO, and NH3 are generally considered important intermediates in amino acid formation. Spark discharge (SD), which is a typical electric discharge in amino acid synthesis, was also characterized by OES. Only CN radicals were observed in a CO–N2–H2O mixture plasma. These radicals became more stable molecules by colliding against other molecules, and sufficiently cooled molecules were dissolved in water. Although HCN appeared to have been formed by SD, amino acids were not effectively synthesized. Therefore, the high activation and rapid cooling processes should be important for the amino acid formation from a CO–N2–H2O gas mixture.
Multigrid computation for micromagnetics
Authors: Hirano Satoshi , Hayashi Nobuo
Published: July 2002

A numerical scheme is presented in which a static micromagnetic calculation is performed using one of the multigrid methods, the V-cycle method. An equilibrium equation in which the discretized Laplacian of magnetization is solved is derived from the magnetic energy and relaxed in the V-cycle method based on the weighted Jacobi relaxation. Calculations made for a one-dimension Bloch wall and a flux-closure structure in Permalloy™ films show the validity and the versatility of the new scheme.
Magnetism and magnetostriction in GdFe2 and GdCo2
Authors: Wu Ruqian
Published: July 2002

Using the density functional full potential linearized augmented plane wave method, the magnetism and magnetostriction of the GdFe2 and GdCo2 compounds are investigated. The calculated magnetostrictive constant, λ001, is negative for GdCo2(−327×10−6), but is positive for GdFe2(+44×10−6), mainly due to different numbers of their valence electrons. These results agree well with experimental data, −1200×10−6 for GdCo2 and +39×10−6 for GdFe2, respectively.
Magnetic mesostructure of giant magnetostrictive spring magnet type multilayers
Authors: Chopra Harsh Deep , Ludwig A. , Quandt E. , Hua Susan Z. , Brown H. J. , Swartzendruber L. J. , Wuttig Manfred
Published: July 2002

The magnetic behavior of giant magnetostrictive TbFe/FeCo multilayers show that individual layers of as-deposited multilayers in their demagnetized state are single domain due to stray-field coupling between adjacent layers. Such multilayers do not show a collective behavior during magnetization reversal. In contrast, stress-free films obtained by annealing at 543 K for 1 h subdivide themselves into multiple domains to lower their overall energy, and show a collective magnetization behavior. An interesting observation is the dynamic formation and collapse of magnetoelastically induced domains in TbFe layers in annealed multilayers during reversal.
Preparation of FeRhIr/Ag/Fe multilayer films and their unique magnetic phase transition being applied to a small magnetic field
Authors: Hashi S. , Inoue M. , Arai K. I. , Kim Y. S.
Published: July 2002

Magnetic properties of multilayer films composed of FeRhIr (or FeRh), Ag and Fe layers were investigated in detail. The results showed that the multilayer film with (FeRhIr/Ag/Fe/Ag)×9/FeRhIr/Ag/Fe structure exhibits a very unique magnetic phase transition, where the transition temperature was subject to change from 40 to 170 °C by the application of a magnetic field ranging from 250 to 150 Oe. The change in pinning strength of magnetization in antiferromagnetic and ferromagnetic phases of FeRhIr layers with a magnetic field is considered to be responsible for the unique properties. Associated with the magnetic phase transition of FeRhIr layers, magnetostrictive response of the film was actually obtained by applying a magnetic field up to 100 Oe.
Giant magnetoresistance properties of patterned IrMn exchange biased spin valves
Authors: Mao Sining , Giusti Jim , Amin Nurul , Van ek Johannes , Murdock Ed
Published: July 2002

Giant magnetoresistance (GMR) responses were studied in micron-sized IrMn pinned spin valve stripes. As the stripe height is decreased both the pinning field and free layer bias field increase while the GMR ratio stays almost constant. The free layer coercivity becomes zero for the shortest stripe while the pinned layer coercivity drops slightly at high aspect ratio. The pinned layer switching field is enhanced in the patterned films, indicating a strong magnetostatic coupling between the free and pinned layer that was further simulated micromagnetically.
Ion beam sputtered spin-valve films with improved giant magnetoresistance response
Authors: Mao M. , Miller M. , Johnson P. , Tong H.-C. , Qian C. , Miloslavsky L. , Hung C.-Y. , Wang J. , Hegde H.
Published: July 2002

A large value of giant magnetoresistance ΔR/R=9% with an exchange field Hex=350 Oe has been measured from simple NiFe/CoFe/Cu/CoFe/IrMn top spin-valve films prepared by ion beam deposition (IBD) techniques. The exchange biasing was greatly enhanced when a synthetic pinned layer, CoFe/Ru/CoFe, is used in the spin-valve structures. Apparent exchange field values in excess of 2000 Oe and ΔR/R values above 8% have been obtained in synthetic spin-valve films. These IBD spin-valve films show excellent thermal stability and they are suitable for the applications in high density magnetic recording heads.
Magnetic properties of perovskite-type Fe–Ni nitrides γ′-(Fe1−xNix)4N (0⩽x⩽0.9)
Authors: Diao X. G. , Takeuchi A. Y. , Garcia F. , Scorzelli R. B. , Rechenberg H. R.
Published: July 2002

In this work, we have succeeded in preparing γ′-(Fe1−xNix)4N powder samples for x up to 0.9 and have undertaken a systematic study of their structural and magnetic properties by x-ray diffraction and vibrating sample magnetometry. The lattice parameters of the nitrides decrease monotonically from 0.3795 to 0.3747 nm with increasing Ni concentration. The saturation magnetization, measured at room temperature and liquid nitrogen, was found to decrease with increasing Ni concentration. The Curie temperature TC also decrease with increasing Ni concentration, as well as with decreasing lattice parameter. Our results show that the lattice parameters, σs and TC behave in contrast with those of the corresponding fcc γ-Fe1−xNix alloys, for which each of these properties exhibits a maximum at some intermediate composition.
Magnetic ordering in Re-doped a-Fe90Zr10
Authors: Ryan D. H. , Tun Zin , Cadogan J. M.
Published: July 2002

The magnetic properties of rhenium-doped a-Fe90Zr10 have been studied by magnetization, susceptibility, neutron depolarization, and Mössbauer spectroscopy and a magnetic phase diagram is presented. Rhenium leads to a very rapid loss of magnetic order and a-Fe90−xRexZr10 is a spin glass beyond a critical composition of xc∼4.5 at. %.
Selective excitation double Mössbauer spectroscopy: In search of magnetic relaxation
Authors: van Lierop J. , Ryan D. H.
Published: July 2002

Selective excitation double Mössbauer (SEDM) spectroscopy has been used to unambiguously separate the influence of chemical disorder from time-dependent effects in two alloys studied at and above room temperature. a-Fe80B20 is a metallic glass with substantial chemical disorder, but no dynamic effects, and the SEDM spectrum can be fitted assuming only disorder broadening. Fe65Ni35 is a disordered alloy which may exhibit magnetic relaxation. The SEDM spectra of Fe65Ni35 are consistent with chemical disorder, and we rule out magnetic relaxation faster than 2.0±1.2 MHz at 496 K (0.99TC).
Origin and thermal stability of HK in FeTaN thin films
Authors: Minor M. K. , Barnard J. A.
Published: July 2002

In this study 2000 Å FeTaN thin films are annealed at 150 °C in both longitudinal and transverse magnetic fields. Both anneals result in a decrease in HK, which is shown to be a result of interstitial N, however, the transverse anneal results in a 90° rotation of HK and a 33% larger decrease in the magnitude of HK as compared to the longitudinal anneal. Subsequent transverse field anneals show that HK is completely reversible in relatively short times at any temperature above 75 °C. Our results are consistent with the diffusion of interstitial N being responsible for the rotatable behavior of HK in FeTaN.
Comparison on the magnetic and structural properties of Sm(Co0.67−xFe0.25Cu0.06Zr0.02Cx)8.0, where x=0–0.15, melt spun ribbons and cast alloys
Authors: Gong Wei , Ma B. M.
Published: July 2002

The effects of C additions on the phase transformation and magnetic properties of Sm(Co0.67−xFe0.25Cu0.06Zr0.02Cx)8.0, where x ranged from 0 to 0.15, melt spun ribbons and cast alloys have been studied by x-ray diffraction (XRD), differential thermal analysis (DTA), and vibrating sample magnetometer. In addition to the Th2Zn17 structure, two additional compounds, namely, the ZrC and SmCoC2, were detected by XRD after a thermal treatment over 700–1160 °C. The as-spun ribbons were highly crystalline at x=0 and became mostly amorphous at x=0.10. An intrinsic coercivity, Hci, of 3.0 kOe was obtained for the as-spun ribbons with x=0.05. After an optimum heat treatment, the Hci of the ribbons with x=0.01 was increased to 8 kOe. Cast alloys of identical chemical compositions were also solution treated and precipitation hardened. At x=0 for the cast alloy, a Br of 10.8 kG, Hci of 24 kOe, Hc of 9.8 kOe, and (BH)max of 27 MGOe, were obtained after an optimum heat treatment.
Structure and magnetic properties of (Nd1−xCex)6Fe13Al compounds
Authors: Wang Jing-yun , Wang Fang-wei , Shen Bao-gen , Yan Qi-wei , Zhan Wen-shan , Lin Chin
Published: July 2002

Samples of (Nd1−xCex)6Fe13Al (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were prepared by arc melting and annealed for 2 weeks at 700 °C. The x-ray diffraction patterns for the (Nd1−xCex)6Fe13Al samples show that all the above-mentioned samples crystallize with the Nd6Fe13Si-type tetragonal phase. The unit-cell volume v increases first and then decreases as the Ce content increases. The Curie temperature and the spontaneous magnetization decrease almost linearly with increasing Ce concentration. All these prove the existence of the mixed valence of Ce3+ and Ce4+. A complicated temperature dependence of magnetization is observed. Although the series is ferromagnetic at high temperature, there is a low-temperature peak in each M–T curve, which is in agreement with spin-glass behavior. This phenomena is reported in 6:13:1-type compounds.
Recombination characteristics of the Nd–Fe(–Co)–B(–Ga–Zr)-type anisotropic hydrogenation, desorption, disproportionation, recombination alloys
Authors: Kwon H. W. , Kang D. I. , Shon S. W. , Kim Yoon B. , Jeung W. Y.
Published: July 2002

The recombination characteristics of the Nd–Fe–B-type isotropic and anisotropic hydrogenation, desorption, disproportionation, recombination (HDDR) alloys were investigated using three types of alloys: alloy A (Nd12.6Fe81.4B6), alloy B (Nd12.6Fe81.3B6Zr0.1), and alloy C (Nd12.6Fe68.8Co11.5B6Ga1.0Zr0.1). Alloy A is featured with the isotropic HDDR character, while alloys B and C are featured with the anisotropic HDDR character. Recombination characteristics of the alloys were examined by observing the coercivity variation as a function of recombination time. Microstructural development during the HDDR was examined by means of transmission electron microscopy, and it was correlated with the coercivity variation. The present study revealed that the intrinsic coercivities of the recombined materials rapidly increased with increasing the recombination time and then showed a peak, after which the coercivities decreased gradually as usual. However, it has been found that the degraded coercivity was recovered significantly on prolonged recombination. Compared with the isotropic HDDR alloy A, the anisotropic HDDR alloys B and C are notable for their greater recovery of coercivity. The significant recovery of coercivity was accounted for in terms of the development of a well-defined smooth grain boundary between the recombined grains on prolonged recombination.
Magnetic properties, magnetoresistance, and electronic structure of cubic DyCu5
Authors: Idzikowski B. , Jezierski A. , Nenkov K.
Published: July 2002

The magnetic properties, magnetoresistance (MR), and electronic structure of the cubic phase (structure-type AuBe5, space group F-43m) of melt-spun DyCu5 have been investigated. In ac-susceptibility and magnetization measurements it has been found that below a critical temperature Tm=7.5 K this phase is metamagnetic. αDyCu5 samples show a negative magnetoresistance ratio MR(H)=[R(H)−R(0)]/R(0) of about −27% at 10 K and 5 T. This effect has similar behavior in transverse and perpendicular current-field directions. The electronic structure of αDyCu5 was calculated by the ab initio self-consistent spin-polarized tight-binding linear muffin tin orbital method in the atomic sphere approximation for the experimental value of lattice parameter a=0.7027 nm. The Fermi-level EF is located at the minority 4f Dy band. The main contribution to the density of states at the EF comes from 4f states of Dy and 3d states of copper atoms in one of two nonequivalent positions in a crystallographic cell.
Effect of write field rise times on the switching thresholds of pseudo spin valve memory cells
Authors: Pohm A. V. , Anderson J. M. , Beech R. S. , Daughton J. M.
Published: July 2002

A number of experiments were performed on submicron, giant magnetoresistance, pseudospin valve, memory elements which showed that the write thresholds are significantly reduced if the rise time of the word write pulses are less than 2 ns and the elements are in the proper initial states. Tested elements had cell widths of 0.3 and 0.17 μm and total lengths of about 1.8 μm. The active lengths were 1.0 to 1.2 μm. Rise times used in the tests were 1.25, 2, and 4 ns.
Integration of spin valves and GaAs diodes in magnetoresistive random access memory cells
Authors: Boeve H. , Das J. , Bruynseraede C. , De Boeck J. , Borghs G.
Published: July 2002

A magnetoresistive random access memory, based on a dynamic random access memory-like floor plan, is demonstrated for an array of magnetic memory cells. Each memory cell consists of a giant magnetoresistive spin-valve structure in series with a GaAs diode. Any single bit in the matrix can be addressed using a coincident current scheme, both for write and read operations. The integration of a series diode in the memory cell yields, for this first demonstrator, read signals of approximately 10 mV.
Microstructural and micromagnetic characterization of thin film magnetic tunnel junctions
Authors: Dunin-Borkowski R. E. , McCartney M. R. , Smith David J. , Gider S. , Runge B.-U. , Parkin S. S. P.
Published: July 2002

High-resolution electron microscopy, Lorentz microscopy, and off-axis electron holography have been used to characterize magnetic tunnel junctions. Observations in cross section show that the tunnel barriers are slightly narrower and smoother after annealing at temperatures up to 350 °C. The demagnetization of a magnetically hard CoPtCr reference layer through repeated magnetization reversal of a soft layer of either Co or Ni40Fe60 is likely to originate from magnetic fringing fields at Néel walls, which form in the soft layers close to the coercive field.
Determination of barrier oxidation states in spin dependent tunneling structures
Authors: Sharma Manish , Wang Shan X. , Nickel Janice H.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) was used to characterize spin dependent tunneling (SDT) structures using plasma oxidized Ta as the insulating barrier. We are able to determine the relative proportion of the different oxidation states of the insulating barrier material. Information available from this technique includes barrier oxidation states, thickness, and completeness of oxidation. Information on the electrodes is also obtained: specifically, Ta is found to diffuse into NiFe, and oxidation of Ni is observed. XPS is shown to be a powerful tool in characterizing the materials sets that comprise SDT devices.
Growth and measurements of ferroelectric lead zirconate titanate on diamond by pulsed laser deposition
Authors: Du H. , Johnson D. W. , Zhu W. , Graebner J. E. , Kammlott G. W. , Jin S. , Rogers J. , Willett R. , Fleming R. M.
Published: July 2002

Pb(Zr 0.53 Ti 0.47 )O 3 (PZT) on diamond is a potentially robust structure for surface acoustic wave (SAW) device applications. We have studied the growth and physical characteristics of PZT on diamond and other substrates by pulsed laser deposition. Under a broad range of processing conditions we explored, PZT deposited directly on diamond is almost exclusively pyrochlore-type, which is nonferroelectric. Growth of ferroelectric perovskite PZT is promoted via the use of a PbTiO3 buffer layer within a narrow window of processing parameters [i.e., P(O2)=100–200 mTorr, T=550–650 °C, 1–2 J/cm2]. Similar results were also obtained for deposition of PZT on Si, Pt-coated Si, and Pt-coated diamond substrates. The dielectric constants of the perovskite PZT films are 500–650 at 1 V and 100 kHz. The piezoelectric coefficients of these films are in the range of 50×10−12–350×10−12 m/V. The SAW velocity of perovskite PZT films is similar to that of highly oriented sputter deposited ZnO films. The acoustic attenuation in perovskite PZT films is approximately three times higher than that in ZnO, however.
Optical properties of InAlGaAs quantum wells: Influence of segregation and band bowing
Authors: Jensen J. R. , Hvam J. M. , Langbein W.
Published: July 2002

Knowledge of the quaternary InAlGaAs material system is very limited for the composition range relevant for growth on GaAs substrates. We report on the characterization and modeling of InAlGaAs quantum wells with AlGaAs barriers, grown pseudomorphically on a GaAs substrate with molecular beam epitaxy. The quantum wells are characterized with photoluminescence, and the measured transition energies are modeled taking into account the influence of In segregation on the shape of the well potential. From the modeling we deduce a relation for the low temperature band gap of unstrained Inx(AlyGa1−y)1−xAs, for 0⩽x,y⩽0.20. The measured linewidths of the luminescence peaks are in agreement with the broadening expected from random alloy fluctuations and well width fluctuations with an effective interface roughness of 1.1 ML.
Photoluminescence quantum yield of pure and molecularly doped organic solid films
Authors: Mattoussi Hedi , Murata Hideyuki , Merritt Charles D. , Iizumi Yasuhiro , Kido Junji , Kafafi Zakya H.
Published: July 2002

We present measurements of the absolute photoluminescence (PL) quantum yield, φPL, for a wide variety of organic compounds in solid films, pure and molecularly doped with strongly fluorescent materials. The procedure, which uses an integrating sphere, does not entail comparison to other standards, and provides accurate measure of the photoluminescence efficiency for submicron thick films, prepared by high vacuum vapor deposition. Host materials include N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4-4′-diamine (TPD), a common hole transport material for light emitting diodes, tris (8-hydroxyquinolinolato) aluminum (III) (Alq3) and its methyl derivative, Almq3, two aluminum chelates used as electron transport and/or green emitting materials. Dopants include tetraphenylnapthacene (rubrene) and N,N′-diethyl quinacridone (DEQ). Doping results in a substantial increase (∼a factor 2–4) of φPL in comparison with that of the pure host. For instance, measured φPL increases from 0.25 and 0.42 for pure Alq3 and Almq3, respectively, to near unity upon doping with rubrene at a concentration of ∼1 mol %. The above data are discussed within the framework of Förster energy transfer from host to guest.
Electrostatics of the conducting double sphere
Authors: Palaniappan D. , Felderhof B. U.
Published: July 2002

General solutions to the electrostatic problem of a pair of intersecting, conducting spheres of arbitrary radii (a double sphere) placed in an arbitrary potential field are derived. The method is based on Kelvin’s transformation combined with reflection and translation properties for harmonic functions. The basic idea is described in detail for orthogonally intersecting spheres. A theorem is offered for finding the image system for the two-sphere assembly placed in a given electrostatic potential. From the general formula, the image systems for various applied potentials are obtained in a straightforward fashion. The earlier special solutions for equal-sized spheres are recovered from our results. The fundamental quantities of interest in electrostatics such as capacity and polarization (dipole moment) are computed. The polarizability tensor is found to be diagonal with different components for the directions parallel and perpendicular to the line of centers. The general solutions to the problem of a pair of spheres, intersecting at an angle π/n (n an integer), immersed in an arbitrary imposed potential field are also presented.
Uniform surface elemental analysis using sputtering and photoionization mass spectrometry with a 6 ns pulse length Nd:YAG laser
Authors: He Chun , Becker Christopher H.
Published: July 2002

The feasibility of performing a uniform surface elemental analysis was investigated by using high laser power to postionize sputtered neutrals. Model calculations and experiments were performed for situations where a 6 ns high power Nd:YAG laser operating at 532 nm was applied to photoionization. Photoionization mass spectra of Ar+ sputtered alloys containing common metals were measured as a function of laser power density and the relative sensitivity factor of each element was determined. The results show uniform ionization of the elements sputtered from the alloys and, therefore, quantitative measurement of the surface elemental composition at the maximum laser output power. For comparison, the same calculations and experiments were performed using a 35 ps, 532 nm mode-locked, high power Nd:YAG laser. The comparison showed that the 6 ns laser reaches uniform ionization at a lower power density. The capabilities of this technique and its operating parameters relevant to sensitive and quantitative surface analysis are discussed from a practical analysis perspective.
Photoluminescence spectra of undoped and Er3+-doped MgAl2Se4 and CaAl2Se4 single crystals
Authors: Jin Moon-Seog , Park Tae-Young , Kim Hyung-Gon , Choe Sung-Hyu , Song Ho-Jun , Oh Seok-Kyun , Kim Wha-Tek
Published: July 2002

MgAl 2 Se 4 ,  MgAl2Se4:Er3+, CaAl2Se4, and CaAl2Se4:Er3+ single crystals were grown by the chemical transport reaction method. The single crystals had the direct energy band gap and their optical energy gaps were 3.286, 2.855, 3.823, and 3.525 eV for the MgAl2Se4, MgAl2Se4:Er3+, CaAl2Se4, and CaAl2Se4:Er3+ single crystals, respectively, at 13 K. Broad photoluminescence spectra peaked at 477 and 672 nm for the MgAl2Se4 single crystal and at 459 and 633 nm for the CaAl2Se4 single crystal were obtained. Sharp emission peaks due to the Er3+ ion in the MgAl2Se4:Er3+ and CaAl2Se4:Er3+ single crystals were observed.
A new mechanism for radiation damage processes in alkali halides
Authors: Dubinko V. I. , Turkin A. A. , Vainshtein D. I. , den Hartog H. W.
Published: July 2002

We present a theory of radiation damage formation in alkali halides based on a new mechanism of dislocation climb, which involves the production of VF centers (self-trapped hole neighboring a cation vacancy) as a result of the absorption of H centers of dislocation lines. We consider the evolution of all experimentally observed extended defects: metal colloids, gas bubbles, and vacancy voids. Voids are shown to arise and grow large due to the reaction between F and VF centers at the surface of halogen bubbles. Voids can ignite a back reaction between the radiolytic products resulting in decomposition of the irradiated material.
Improvement of GaN layer quality by using the bulk-GaN buffer structure grown by metalorganic chemical vapor deposition
Authors: Yang Chien-Cheng , Wu Meng-Chyi , Chi Gou-Chung
Published: July 2002

In this article, we propose a new buffer structure to obtain the high quality GaN epitaxial layers grown on sapphire substrates by a separate-flow reactor of metalorganic chemical vapor deposition (MOCVD). This buffer structure consists of 200–300 Å GaN nucleation layer/6 μm GaN-bulk layer. The bulk-GaN layers have also been prepared by MOCVD. The GaN epitaxial layer grown on this buffer structure exhibits a full width at half maximum (FWHM) of double-crystal x-ray diffraction of 170 arcsec, a FWHM of 300 K photoluminescence of 56 meV, an electron mobility of 400 cm2/V s at 300 K and 815 cm2/V s at 140 K, and a concentration of 3.6×1017 cm−3 at 300 K. The GaN growth with this buffer structure has a wide growth window on the different nucleation-layer thicknesses. A good quality of GaN epitaxial layers can be obtained by using this buffer structure.
Determination of the kinetic parameters by the simultaneous measurements of thermally stimulated conductivity and luminescence
Authors: Opanowicz A.
Published: July 2002

Methods for determination of the recombination coefficient, the relative density of the inactive deep traps, the trap depth, and the frequency factor from the simultaneously measured peaks of thermally stimulated conductivity and luminescence are derived in the case of the temperature-dependent electron recombination lifetime. The derivation of these methods is based on the classical model of an insulator with one kind of active trap, one kind of inactive deep trap, and one kind of recombination center, and the assumption of the quasiequilibrium. Examples of application of the methods are also presented.
Numerical simulation of electron diffraction through a narrow constriction
Authors: Endoh Akira , Sasa Shigehiko , Arimoto Hiroshi , Muto Shunichi
Published: July 2002

We performed time-evolved numerical simulations of a two-dimensional electron wave packet passing through a semicircular constriction (very short quantum wire) by solving the time-dependent Schrödinger equation using the finite difference method to understand the nature of electron diffraction phenomena in semiconductors. By Fourier transformation, we calculated the time-evolved electron wave packet in wave number space, which shows the transition from the Gaussian distribution to the circular distribution having equal energy by entering constriction. The obtained results are compared with the results of our previous simulations of an electron wave packet passing through a rectangular constriction. By analyzing the nature of diffracted subpeaks, the following results were obtained: (1) The intensity of the subpeaks diffracted by a semicircular constriction is higher than that by a rectangular one. (2) The starting point of the diffracted subpeaks is the center position of the narrowest width in a constriction, while that for rectangular ones is the center of the constriction entrance. (3) The lateral wave number of the diffracted subpeak increases with the number n, n being the number counted from the main (0th) peak which propagates straight through, although it deviates negatively from the linear relationship obtained for rectangular ones with an increase in n. (4) There is a time delay in the diffracted subpeaks similar to that for rectangular constrictions. The differences between passing through a semicircular constriction and a rectangular one were interpreted as caused by the reflection on the inside wall of the constriction and the energy spread of each quantum level.
Electron mobility in extremely thin single-gate silicon-on-insulator inversion layers
Authors: Gámiz F. , Roldán J. B. , Cartujo-Cassinello P. , Carceller J. E. , López-Villanueva J. A. , Rodriguez S.
Published: July 2002

Inversion-layer mobility has been investigated in extremely thin silicon-on-insulator metal–oxide–semiconductor field-effect transistors with a silicon film thickness as low as 5 nm. The Poisson and Schrœdinger equations have been self-consistently solved to take into account inversion layer quantization. To evaluate the electron mobility, the Boltzmann transport equation has been solved by the Monte Carlo method, simultaneously taking into account phonon, surface-roughness, and Coulomb scattering. We show that the reduction of the silicon layer has several effects on the electron mobility: (i) a greater confinement of the electrons in the thin silicon film, which implies an increase in the phonon-scattering rate and therefore a mobility decrease; (ii) a reduction in the conduction effective mass and the intervalley-scattering rate due to the redistribution of carriers in the two subband ladders as a consequence of size quantization resulting in a mobility increase; and (iii) an increase in Coulomb scattering because of a greater number of interface traps in the buried Si–SiO2 and to a closer approach of these charged centers to the mobile carriers. The dependence of these effects on the silicon-layer thickness and on the inversion-charge concentration causes the mobility to be a nontrivial function of these variables. A detailed explanation of the mobility behavior is provided. Mobility for samples with silicon thickness below 10 nm is shown to increase in an electric field range that depends on the charged center concentration, while for silicon layers over 10 nm mobility always decreases as the silicon-layer thickness is reduced.
Analysis of the coupling between shear horizontal plate waves and liquids: Application to the measurement of the shear rigidity modulus of glycerol solutions
Authors: Teston F. , Feuillard G. , Tessier L. , Tran Hu Hue L. P. , Lethiecq M.
Published: July 2002

This article presents an acoustic wave viscometer based on the shear horizontal acoustic plate mode excited by interdigital transducers on a ST-cut quartz substrate. A theoretical model, which is an extension of the plate effective permittivity function taking into account the presence of liquids, is developed in order to predict the phase and attenuation variations versus the viscosity of liquid. These results are discussed and compared to those of models from the literature such as variational or perturbation methods. The measured results for aqueous solutions of glycerol show linear dependence between the phase and attenuation variations and the square root of liquid viscosity, and are consistent with the theoretical results. The device can be used for viscosity measurements up to 1000 mPa s. For higher viscosities, the viscoelastic behavior of the solution appears and the shear rigidity modulus must be taken into account. The value of μ∞=2.5×109 N m2 has been obtained for glycerol by fitting the theoretical curves to the experimental points.
Structural and electrical characterization of microcrystalline silicon films prepared by a layer-by-layer technique with a plasma-enhanced chemical-vapor deposition system
Authors: Hong J. P. , Kim C. O. , Nahm T. U. , Kim C. M.
Published: July 2002

Microcrystalline silicon films have been prepared on indium-coated glass utilizing a layer-by-layer technique with a plasma-enhanced chemical-vapor deposition system. The microcrystalline films were fabricated by varying the number of cycles from 10 to 60 under a fixed H2 time (t2) of 120 s, where the corresponding deposition time (t1) of amorphous silicon thin film was 60 s. Structural properties, such as the crystalline volume fraction (Xc) and grain sizes were analyzed by using Raman spectroscopy and a scanning electron microscopy. The carrier transport was characterized by the temperature dependence of dark conductivity, giving rise to the calculation of activation energy (Ea). Optical energy gaps (Eg) were also investigated using an ultraviolet spectrophotometer. In addition, the process under different hydrogen plasma time (t2) at a fixed number of 20 cycles was extensively carried out to study the dominant role of hydrogen atoms in layer-by-layer deposition. Finally, the correlation between structural and electrical properties has been discussed on the basis of experimental results.
Interdiffusion study of magnesium in magnetite thin films grown on magnesium oxide (001) substrates
Authors: Shaw K. A. , Lochner E. , Lind D. M.
Published: July 2002

Magnetite (Fe3O4) films and multilayers were grown using plasma-assisted molecular beam epitaxy and result in single-phase films grown in registry with a MgO substrate. No evidence of interdiffusion is detected on as-grown films. Both structural and magnetic probes indicate behaviors expected for a magnetite thin film. A thermal stability study of these films was performed by annealing these films under ultrahigh vacuum conditions at temperatures below 900 K. Bulk techniques such as x-ray diffraction, superconducting quantum interference device magnetometry, and energy dispersive spectroscopy confirm that the magnesium interdiffuses throughout the entire film, and surface techniques such as x-ray photoelectron spectroscopy and scanning tunneling microscopy/ion scattering spectroscopy show changes in the surface structure and stoichiometry of the film caused by the magnesium intermixing.
Electronic and structural properties of equiatomic Co–Pt alloy films at low temperature
Authors: Chang G. S. , Whang C. N. , Rhee J. Y. , Lee Y. P.
Published: July 2002

Magneto-optical properties of Co–Pt alloy films were investigated at low and room temperatures. We also investigated atomic and electronic structures of these films. The saturated polar Kerr rotation angles of CoPt and CoPt3 alloy films show different temperature dependence. Synchrotron-radiation photoemission spectroscopy was employed to confirm the correlation between the magneto-optical properties and the electronic structures of these films. Changes of a peak at 4.3 eV relevant to the Pt 5d levels hybridized with Co 3d electrons of the CoPt film and of the valence-band shape upon cooling have the same trend as that of the saturated Kerr rotation angle. A structural phase transition of the CoPt film from the tetragonal L10 to orthorhombic phase upon cooling is suggested by the theoretical calculations using linearized-muffin-tin-orbitals methods within the so-called “LDA+U” scheme as well as the experimental observations. X-ray diffraction patterns before and after cooling also support this structural phase transition.
Characterization of metalorganic decomposition-derived SrBi2Ta2O9 thin films with different thicknesses
Authors: Wu Di , Li Aidong , Ling Huiqin , Yu Tao , Liu Zhiguo , Ming Naiben
Published: July 2002

Ferroelectric capacitors having sputtered Pt bottom and top electrodes and metalorganic decomposition derived ferroelectric thin films of SrBi2Ta2O9 (SBT) were prepared. The thickness effects on the structure, surface morphology, and electrical properties of SBT thin films were studied and discussed. Structure and surface morphology were analyzed by x-ray diffraction and atomic force microscope. The electrical properties were characterized by the measurements of hysteresis, capacitance, and pulse switching. The crystalline structure, grain size, and electrical properties do not depend on film thickness when films are less than 440 nm thick. A larger grain size is observed for films thicker than 440 nm, which results in a larger remnant polarization. The thickness dependence of the coercive voltage and reciprocal capacitance can be explained by an interfacial layer model. The thickness-independent coercive field and dielectric constant, calculated from the interfacial layer model, are around 19 kV/cm and 343, respectively. Nonvolatile polarization (Pnv), obtained from pulse-switching measurements, increases with the applied electric field and finally saturates with a slight thickness effect. The relaxation of the remnant polarization that occurs at zero-voltage intervals between the pulses and the thickness-independent behavior of Pnv are explained based on depolarization fields within the ferroelectric due to nonswitching interfacial layers at the film/electrode interfaces.
Nonlinear behavior of magnetic surface waves on the interface between ferromagnet and antiferromagnet
Authors: Wang Qi , Wu Zhong , Li Songmao , Wang Li-qiang
Published: July 2002

In this article the nonlinear frequency characteristics of the transverse magnetic surface waves at microwave frequencies on the interface between a ferromagnet and an antiferromagnet have been studied. The results show that the magnetic surface waves have passband(s) and stopband(s), which are interchangeable through the variation of the wave power. It is shown that the nonlinear surface waves excited on the interface can be backward surface waves with group velocities opposite to their phase velocities in direction. The passband widths of the forward surface waves are about five times larger than those of the backward surface waves in the situation.
Antiparallel pinned NiO spin valve sensor for GMR head application (invited)
Authors: Pinarbasi M. , Metin S. , Gill H. , Parker M. , Gurney B. , Carey M. , Tsang C.
Published: July 2002

NiO antiferromagnetic material possesses certain advantages for spin valve applications and has attracted considerable attention. Some of the key advantages are its insulating properties, very high corrosion resistance, less sensitivity to composition, and its low reset temperature. This material, however, has a low blocking temperature which prevents its application to simple spin valve designs. The use of this material in spin valve structures required significant improvements in thermal stability, blocking temperature, and the spin valve design. In the present study, the blocking temperature and the blocking temperature distribution of the NiO films have been improved by depositing the films reactively using ion beam sputtering. A number of improvements in the processing method and deposition system had to be made to allow full NiO spin valve deposition for mass production. Another critical part was the use of antiparallel pinned design in place of the simple design to improve the thermal stability of the NiO spin valves as read elements at disk drive temperatures. The selection of the ferromagnetic pinned layers and the Ru spacer thickness in AP-pinned spin valves has significant impact on the behavior of the devices. These spin valves are all bottom type, NiO/PL1/Ru/PL2/Cu/Co/NiFe/Ta, where the metallic portion of the spin valve is deposited on top of the NiO AF layer. The PL1 and PL2 are ferromagnetic layers comprising NiFe and Co layers. Read elements have been made using these spin valves that delivered areal densities of 12 Gbit/in. These topics and other improvements which resulted in successful use of NiO spin valves as GMR heads in hard disk drives will be discussed.
Magnetomechanical effects in textured polycrystalline Tb76Dy24
Authors: Graetz J. , Good N. , Fultz B. , Dooley J. , Chave R.
Published: July 2002

Uniaxial stress-strain measurements were performed on polycrystalline Tb76Dy24 alloys which exhibit “giant magnetostriction” at cryogenic temperatures. The Young’s moduli were reduced by up to a factor of five at 77 K, in comparison to their values at 300 K. We attribute this reduction to a mechanical compliance from domain rotation. Large mechanical hysteresis is also found in nominally elastic stress-strain curves measured below the Curie temperature. Hysteretic curves from 0 to 25 MPa demonstrate up to 19% dissipation of the applied mechanical energy. The anisotropy of thermal expansion was also measured and used as a parameter for the degree of crystallographic texture. This anisotropy was correlated to bulk magnetostriction and to mechanical hysteresis.
An evaluation of permeability for striped thin films in the gigahertz range
Authors: Yabukami S. , Takezawa M. , Uo T. , Yamaguchi M. , Arai K. I. , Miyazawa Y. , Watanabe M. , Itagaki A. , Ando H.
Published: July 2002

We developed the fully automatic permeameter which is made of driving plates and shielded loop coil available in 1 MHz–3GHz. We clarified the sensitivity of the permeameter and the sensitivity can be explained by an uncertainty of network analyzer. We evaluate the permeability of striped CoNbZr films (50, 20, 10 μm wide). A reasonable relation between permeability spectrum and domain observations can be demonstrated.
Quantum tunneling of magnetization in Mn12Bz clusters: Evidences of spin parity effect
Authors: Gomes A. M. , Novak M. A. , Wernsdorfer W. , Sessoli R. , Sorace L. , Gatteschi D.
Published: July 2002

We present a comparison of the field dependence of the relaxation times observed for Mn12Bz, (Bz=benzoate) spin cluster, and its derivative containing one extra electron, r-Mn12Bz. At low temperatures Mn12Bz has a total spin S=10, while for the reduced sample r-Mn12Bz the spin of the ground state is S=19/2. Theory predicts that half integer spin should not present quantum tunneling, the so-called spin parity effect. We show evidence from experiments that quantum tunneling is partially inhibited in the reduced species. Low temperature magnetization hysteresis loops of the reduced variety do not show well-defined steps. In addition, the ac susceptibility as a function of the field also does not show a clear resonance at the expected level crossing fields, as seen in the nonreduced sample.
Magnetic properties of the rare-earth silicide Ho5Si3
Authors: Hill P. , Miller Lance L.
Published: July 2002

Despite their simple chemical formula and hexagonal structure, the magnetic and electrical properties of the family of rare-earth silicides R5Si3 have not been systematically investigated. To begin our systematic study of this system, we have synthesized Ho5Si3 and completed magnetic and resistivity measurements on this sample. AC susceptibility measurements show Ho5Si3 to have μeff=10.5μB/Ho atom and θ=16.5 K. Magnetic measurements indicate that Ho5Si3 undergoes two transitions at low temperatures, the first at 24 K is an antiferromagnetic transition, while the second, at about 8 K, is ferromagnetic. Low temperature measurements as a function of field reveal a metamagnetic transition at Hc=2.2 T. The behavior of this sample is consistent with the complicated low temperature ordering found in other members of this series.
Optical and in situ characterization of plasma oxidized Al for magnetic tunnel junctions
Authors: LeClair P. , Kohlhepp J. T. , Smits A. A. , Swagten H. J. M. , Koopmans B. , de Jonge W. J. M.
Published: July 2002

An optical polarization modulation technique was adapted to provide a simple, fast, and flexible method for studying the kinetics and growth characteristics of thin oxide layers, using Al2O3 as an example. The optical technique allows precise determination of the amount of remaining metallic Al as a function of the initial Al thickness, while scanning a laser spot across the wedge. Optical data suggest that the oxide growth rate for the ultrathin layers may be dependent on the specific microstructure. In situ x-ray photoelectron spectroscopy performed on homogenous samples confirmed the interpretation of the optical results.
Exchange coupling in crystalline/amorphous Nd–Fe–B nanoassemblies
Authors: Shield J. E. , Kappes B. B. , Crew D. C. , Branagan D. J.
Published: July 2002

The demagnetization behavior of nanoassembled crystalline/amorphous microstructures was investigated. The microstructures consisted of isolated Nd2Fe14B crystallites surrounded by regions of remaining amorphous phase. The hard magnetic crystallites interacted with the surrounding amorphous phase over a length scale of approximately 1.5–2 nm. As the extent of the amorphous phase decreased to less than this, interactions between hard magnetic grains were observed.
Production and characterization of asymmetric laser-textured bumps for magnetic media
Authors: Krumbuegel Marco A. , Yang Ming M.
Published: July 2002

Asymmetric “S-shaped” bumps are formed in the presence of a significant temperature gradient on the disk surface during the laser-texture process. The production of S-shaped bumps is of particular interest for low-glide magnetic media, for which the desired high bump densities require the use of high spindle speeds. The formation of S-shaped bumps as a function of laser-pulse energy (0.1–4.5 μJ), pulse width (350–5000 ns), and rotation speed of the spindle (1184–4737 rpm) was investigated. The results show that within the accessible energy range the peak-to-mean bump height increases with the pulse energy. For a constant pulse energy, larger bump heights are obtained for shorter pulse widths. In addition, higher bumps are also obtained for slower spindle speeds if the pulse width is 2000 ns or longer, but this changes as the pulse width is reduced. The full-width-at-half-maximum diameter of the trailing bump cone monotonically increases with the pulse energy for 350–1000 ns pulse width, but shows a local minimum for 2000 and 5000 ns pulse width, which is shifted to smaller pulse energies as the spindle speed is reduced. An investigation of the height shrinkage during the sputter process showed that the shrinkage is larger for 15 nm high bumps textured with 500 ns pulse width and 0.26 μJ pulse energy than for bumps of the about the same height textured with 1000 ns pulse width and 0.40 μJ pulse energy.
The use of organic templates to develop biomimetic chain structures of magnetic nanoparticles
Authors: Li Sichu , John Vijay T. , Irvin Glen C. , Simmons Blake , McPherson Gary L. , Zhou Weilie
Published: July 2002

The double-tailed surfactants AOT (bis 2-ethylexyl sodium sulfosuccinate) and lecithin (phosphatidylcholine) self-assemble in the presence of water and a hydrocarbon to form fluid microstructures. The nanostructure of this gel appears to be made up of bicontinuous networked channels of water and the hydrocarbon phase, α-Fe nanoparticles are synthesized via reducing the ferrous salt in the aqueous microphase of the gel. Transmission electron microscopy of these particles reveals nanospheres with a uniform size distribution ranging from 15 to 18 nm in diameter. An interesting observation is that these nanoparticles appear to be synthesized in the form of entangled chains reminiscent of magnetic nanoparticles in magnetobacteria. Destruction of the gel phase still leaves the aggregation structure largely intact, implying a clear templating role of the surfactant microstructure. Magnetic properties of these particles were characterized using a SQUID susceptometer. The hysteresis loops at ambient temperature reveals a saturation magnetization of 190 emu/g and a coercivity of 240 G, indicating that the nanoparticles are ferromagnetic. The results indicate the possibility of nanoscale engineering of these materials with biomimetic properties.
Sputtered flux distribution on the substrate in electron cyclotron resonance sputtering simulation and experimental study
Authors: Deenamma Vargheese K. , Mohan Rao G.
Published: July 2002

Electron cyclotron resonance plasma based sputtering is characterized by low pressure operation with high ion density. The distribution of sputtered flux on the substrate at different pressures and target–substrate distances has been simulated using Monte Carlo methods and compared with experimental results. It has been shown that due to cylindrical geometry of the target, at low pressures, the variation as a function of distance is different from conventional sputtering. At high pressures, however, the uniformity of sputtered flux increases with the target–substrate distance. Using the simulated data the variation of the thickness with sputtering pressure and target–substrate distance has been studied.