bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of amorphous hydrogenated carbon nitride films in radio-frequency plasma
Authors: Zhang Mei , Nakayama Yoshikazu , Miyazaki Tsutomu , Kume Masato
Published: July 2002

Amorphous hydrogenated carbon nitride films are deposited both on the cathode and anode in N2–CH4 atmosphere by radiofrequency plasma chemical vapor deposition. The species of the plasma are detected by optical emission spectroscopy and ionization-threshold mass spectroscopy. The effects of varying the N2 partial pressure on plasma states and film properties have been investigated. The results of plasma diagnosis indicate that reactive nitrogen radicals are more easily generated than methane-derived radicals and they increase as the N2 partial pressure in plasma. The films grown on the cathode and anode definitely show different properties. It seems that CN and CNH species in plasma do not contribute to film growth directly. The efficient bombardment of nitrogen ions on growing surface leads to the formation of the film which has lower hydrogen content and more CN bond constructions.
Transmission electron microscopy of silicides nucleated in Y–Si reaction system
Authors: Noya Atsushi , Takeyama Mayumi B. , Sasaki Katsutaka , Aoyagi Eiji , Hiraga Kenji
Published: July 2002

The nucleation of silicides was examined by transmission electron microscopy in a Y–Si reaction system, in which the Y layer was deposited on the Si substrate at 330 °C. It was revealed that the amorphization due to alloying took place and the concentration gradient was formed over the alloying layer during deposition. A hexagonal YSi2 phase and a cubic Y5Si3 metastable phase were observed at the layer adjoining the Si substrate and at the midmost region of the alloying layer, respectively. This result was interpreted in the light of the proposed phenomenological theory that the silicide phases were nucleated from the amorphous alloys with suitable compositions within the formed concentration gradient.
Finite-element modeling of nanoindentation
Authors: Knapp J. A. , Follstaedt D. M. , Myers S. M. , Barbour J. C. , Friedmann T. A.
Published: July 2002

Procedures have been developed based on finite-element modeling of nanoindentation data to obtain the mechanical properties of thin films and ion-beam-modified layers independently of the properties of the underlying substrates. These procedures accurately deduce the yield strength, Young’s elastic modulus, and layer hardness from indentations as deep as 50% of the layer thickness or more. We have used these procedures to evaluate materials ranging from ion implanted metals to deposited, diamond-like carbon layers. The technique increases the applicability of indentation testing to very thin layers, composite layers, and modulated compositions. This article presents an overview of the procedures involved and illustrates them with selected examples.
E-field induced phase transition in 〈001〉-oriented rhombohedral 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 crystals
Authors: Paik Dong-Soo , Park Seung-Eek , Wada Satoshi , Liu Shi-Fang , Shrout Thomas R.
Published: July 2002

E-field induced phase transformation and associated changes in dielectric/piezoelectric properties of 〈001〉-oriented rhombohedral 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 crystals were investigated. The longitudinal strain level was found to abruptly increase at 20 kV/cm, corresponding to that where an induced phase appears within a multidomain matrix. Decreases in the dielectric constant (K3T∼4000 to 500), transverse coupling (k31∼70% to 50%) and transverse piezoelectric coefficient (d31∼−1100 to −200 pC/N) associated with the induced phase were the result of increased crystal anisotropy. By contrast, the thickness coupling (kT) increased from 53% at 0 kV/cm to 64% at 45 kV/cm, associated with this phase transition. The measured dielectric and piezoelectric properties found for the induced phase state were nearly identical to those of 〈001〉 poled tetragonal (1−x)PZN−xPT (x>0.1) crystals. Based on these results, it is evident that the symmetry of induced phase is tetragonal, 4 mm.
Structure and magnetization of MnSb thin films deposited at different substrate temperatures
Authors: Low B. L. , Ong C. K. , Lin J. , Huan A. C. H. , Gong H. , Liew T. Y. F.
Published: July 2002

The influence of substrate temperatures on the structure, morphology, magnetic properties, and surface composition of MnSb films prepared by hot-wall epitaxy are analyzed. All the films are found to be single phase with nickel arsenide (NiAs) crystal structure. X-ray photoelectron spectroscopy study on the core levels reveals that the surface oxidation of the films is not very much enhanced with increasing substrate temperature except for a variation in the concentration of Sb2O3 and MnO2 near the surface-air interface. The decrease in saturation magnetization for the films is attributed to an increase in the manganese oxide content as substrate temperature increases. It is also observed that preferential Mn segregation from the grains to the grain boundaries will reduce the magnetic coupling between grains and thus increase coercivity and decrease coercivity squareness.
Electrostatic adhesion testing of thin metallic layers
Authors: Dubec M. , Brotzen F. R. , Dunn C. F.
Published: July 2002

Testing of the adhesion strength of various metallizations on Si was carried out by a novel electrostatic technique. This technique made possible the evaluation of the characteristic adhesion stress and of the Weibull modulus, the latter being a measure of the distribution of weak adhesion spots. Adhesion characteristics of various metallic films (Cu, Ti–W, Al–Cu) were determined, and the effect of substrate treatments on these characteristics was analyzed.
Energy and momentum relaxation of two-dimensional electron gas due to near-surface deformation scattering
Authors: Pipa V. I. , Vasko F. T. , Mitin V. V.
Published: July 2002

We model the influence of a cap layer with a fixed thickness placed on top of a semi-infinite heterostructure on the energy and momentum relaxation rates for two-dimensional electrons localized in the lowest subband of a quantum well, and interacting with the acoustic phonon via the deformation potential. The relaxation rates are derived from the corresponding balance equations for a small deviation from the thermodynamic equilibrium. Our results indicate that at low temperatures the efficiency of the scattering is changed substantially depending on the mechanical conditions at the surface; the cases of free and rigid surfaces are considered. The dependencies of the electron energy and momentum rates on the distance from the electron layer to the surface, on the temperature and electron concentration are analyzed. It is shown that the efficiencies of relaxation are changed substantially (up to two times for standard parameters of GaAs or InAs based quantum wells) depending nonmonotonically on the distance of the 2D layer to the surface and on the electron temperature.
Oxidation of silicon nitride films in an oxygen plasma
Authors: Kennedy G. P. , Buiu O. , Taylor S.
Published: July 2002

The fabrication of oxynitrides using low thermal budget process technology is a key component in the production of advanced devices. This work focuses on the use of plasma anodization of low-pressure chemical vapor deposition (LPCVD) silicon nitride films to produce silicon oxynitride films, which are characterized structurally and electrically. The oxynitride dielectric films have a three layer structure, with “SiO2”-like layers at the surface and near the interface, and a “Si3N4”-like layer between them. Hence, nitrogen atoms are replaced by oxygen atoms at the surface of the film and near the Si/dielectric interface. The conductivity of the silicon nitride film was found to be higher than the silicon oxynitride film, whereas the conductivity of the oxynitride and, therefore, its trapping characteristics are more temperature dependent. Furthermore, the activation energy required to release an electron from a trap in the silicon oxynitride film (0.218 eV) is 1.7× that of the silicon nitride film (0.130 eV). Although oxidation of the LPCVD silicon nitride film did not reduce the interface trap density (≅1012 cm−2 eV−1 for both Si3N4 and SiON films), the density of traps, which are thought to be silicon dangling bonds in the form of an sp3 state near midgap, have reduced. A model to explain the conduction properties of the silicon oxynitride film—based on the Fowler–Nordheim conduction mechanism—was developed. Moreover, this model takes into account the trapping dynamics of the film. It was found that the best theoretical fit to the experimental current density data was obtained by assuming that the areal trap density, No,=5×1012 cm−2 and the trap capture cross section, σ=1×10−16 cm2.
Numerical investigation of monolithic heterojunction and buried layer GaAs lateral p-i-n photodetectors
Authors: Haralson J. N. , Brennan K. F.
Published: July 2002

This paper presents a numerical study of two planar photodetector device designs, a heterojunction lateral p-i-n and a buried layer lateral p-i-n. The devices are planar structures comprised of interdigitated p+ and n+ wells containing either a heterojunction or buried charge sheet. Numerical simulation reveals that when pulsed with an 827 nm optical source at 0.68 mW/cm2, these two devices exhibited vastly superior frequency performance and responsivity compared to a heterostructure metal–semiconductor–metal photodetector formed with identical finger spacing and geometry. The calculated dark currents are similar in magnitude while the capacitances vary among the devices.
Magnetoresistance, micromagnetism, and domain wall effects in epitaxial Fe and Co structures with stripe domains (invited)
Authors: Kent Andrew D. , Rüdiger Ulrich , Yu Jun , Thomas Luc , Parkin Stuart S. P.
Published: July 2002

We review our recent magnetotransport and micromagnetic studies of lithographically defined epitaxial thin film structures of body-centered-cubic Fe and hexagonal-closed-packed (hcp) Co with stripe domains. Micromagnetic structure and resistivity anisotropy are shown to be the predominant sources of low field magnetoresistance (MR) in these microstructures, with domain wall (DW) effects smaller but observable (DW-MR≲1%). In Fe, at low temperature, in a regime in which fields have a significant effect on electron trajectories, a novel negative DW contribution to the resistivity is observed. In hcp Co microstructures, temperature dependent transport measurements for current perpendicular and parallel to walls show that any additional resistivity due to DW scattering is very small.
Ion energy distributions and sheath voltages in a radio-frequency-biased, inductively coupled, high-density plasma reactor
Authors: Sobolewski Mark A. , Olthoff James K. , Wang Yicheng
Published: July 2002

Ion energy distributions were measured at a grounded surface in an inductively coupled, high-density plasma reactor for pure argon, argon–helium, and argon–xenon discharges at 1.33 Pa (10 mTorr), as a function of radio-frequency (rf) bias amplitude, rf bias frequency, radial position, inductive source power, and ion mass. The ground sheath voltage which accelerates the ions was also determined using capacitive probe measurements and Langmuir probe data. Together, the measurements provide a complete characterization of ion dynamics in the sheath, allowing ion transit time effects to be distinguished from sheath impedance effects. Models are presented which describe both effects and explain why they are observed in the same range of rf bias frequency.
Electron-phonon relaxation rates in InGaAs–InP and HgCdTe–CdTe quantum wells
Authors: Alcalde Augusto M. , Weber Gerald
Published: July 2002

We calculate electron-LO-confined and interface-phonon scattering rates in In1−xGaxAs–InP and Hg1−xCdxTe–CdTe quantum wells considering the influence of nonparabolicity on the energy subbands. A simple k⋅p model is used to take into account this nonparabolicity and a reformulated dielectric continuum slab model is employed to describe the confined phonon modes. We find that the subband nonparabolicity increases the scattering rates significantly for all transitions and that this effect is more pronounced as transitions from higher subbands are involved. We show that this behavior can be understood in terms of the phonon wave vector, the density of final states and the electron-phonon overlap.
Simulations of self-organized filaments in a dielectric barrier glow discharge plasma
Authors: Brauer I. , Punset C. , Purwins H.-G. , Boeuf J. P.
Published: July 2002

The spontaneous filamentation of a dielectric barrier glow discharge plasma (Townsend, not streamer breakdown), i.e., an instability of the homogeneous state has been simulated and understood with the help of a self-consistent two-dimensional fluid model of the discharge. The formation of self-organized or solitary filaments observed experimentally and described in previous papers can be explained in terms of electron and ion transport coefficients only, without including gas heating, plasma chemistry or surface effects. The conditions favoring the plasma filamentation are discussed.
Sputtered Sm–Co films: Microstructure and magnetic properties
Authors: Neu V. , Shaheen S. A.
Published: July 2002

Films of Sm–Co have been sputtered on heated polycrystalline Al2O3 substrates. The effect of variations of the Sm content on microstructure and hard magnetic properties was studied for otherwise constant process parameters. As generally observed, the samples possess a magnetic texture where the easy magnetization directions of the grains lay preferably in the film plane. For a lower Sm content the TbCu7-type structure is stabilized and for a higher Sm content the CaCu5-type structure is stabilized. The crossover occurs for a Sm content of around 17 at. %. Consistent with the changes in the intrinsic properties, coercivity increases and remanence decreases with increasing the Sm content. The grain size increases with increasing the Sm content and is attributed to a higher surface mobility during crystallization and grain growth. This behavior is also assumed to cause the improvement in the in-plane texture with increasing the Sm content, that had been quantified by magnetic and crystallographic investigations.
Thin-film friction and adhesion studies using atomic force microscopy
Authors: Bhushan Bharat , Dandavate Chetan
Published: July 2002

An atomic force microscope is used to study the effect of tip radius and humidity on the adhesive force and coefficient of friction. Samples studied are Si (100), 2 nm thick bonded perfluoropolyether lubricant (Z-DOL) coated Si (100), 20 nm thick diamond-like carbon (DLC) coated Si (100) and plasma etched DLC coated Si (100). Tip diameters ranged from 100 nm to 14.5 μm. It is observed that both adhesive force and coefficient of friction are strongly dependent on the tip radius and humidity. The change is caused by the formation of meniscus bridges from capillary condensation of water vapor. DLC coated surface is rather insensitive to the changes in the radius and humidity because of its passivated surface. Etching of DLC activates the surface and makes it sensitive to the environment. In addition, a technique is developed to get adhesive force maps of surfaces, which can be used to obtain an estimate of film thickness only a couple of monolayers thick. Examples and applications of this technique are presented.
Blue shift in ultraviolet absorption spectra of monodisperse CeO2−x nanoparticles
Authors: Tsunekawa S. , Fukuda T. , Kasuya A.
Published: July 2002

Blue shifts corresponding to the absorption edge in the UV-A (310–400 nm) range are obtained from ultraviolet (UV) absorption spectra of monodisperse CeO2−x (0<x<0.5) nanoparticles, which are produced as toluene suspensions by a successive microemulsification method. The blue shift of the nanoparticles is inversely proportional to the 2.2 power of the particle size for a direct transition, but no relation is found for an indirect transition. In contrast, the shift for thin films of 100–200 nm thickness exhibits a relation nearly inverse proportional to the square root of the thickness for the direct transition. These relations are different from that for the quantum size effect, though the difference is small for the nanoparticles. A possible explanation for the blue shift is a valence change of the Ce ions.
Micromagnetic analysis of anisotropy orientation in high density longitudinal magnetic recording
Authors: Zhou Hong , Bertram H. Neal , Doerner Mary F. , Mirzamaani Mohammad
Published: July 2002

Micromagnetic simulations have been performed to compare the recording performance of oriented media (Mr=1.50) with planar isotropic media in longitudinal recording. With no exchange, oriented medium exhibits substantially less dc noise power thus larger signal-to-noise ratio (SNR). But with increasing linear density, the oriented medium shows larger nonlinear amplitude reduction, larger nonlinear transition shift, and less SNR advantage. At finite exchange, there is no substantial SNR difference between oriented and isotropic medium.
Magnetostatic coupling in spin valves: Revisiting Néel’s formula
Authors: Schulthess T. C. , Butler W. H.
Published: July 2002

We use a numerical, atomistic approach to calculate the magnetostatic coupling in spin valves. In addition to the numerical treatment, the coupling energy is evaluated analytically and it is shown that Néel’s formula is accurate to first order in the ratio of roughness amplitude to grain size. We also generalize the formula so that it can be applied to systems such as Py/Co/Cu/Co/Py spin valves that have complex ferromagnetic layers.
Observation of the structural phase transition in manganite films by magneto-optical imaging
Authors: Vlasko-Vlasov V. K. , Lin Y. , Welp U. , Crabtree G. W. , Miller D. J. , Nikitenko V. I.
Published: July 2002

A high-resolution magneto-optical imaging technique is used to reveal the formation of twins occurring during a martensitic phase transition at ∼105 K in La2/3Ca1/3MnO3 (LCMO) films grown on SrTiO3 (STO) substrates. The magnetic contrast arises due to the magneto-elastic tilts of the Mn- magnetic moments in the twins. Different magnetic structures are found in LCMO films grown on MgO, NGO, and LAO substrates showing the importance of the substrate material for the manganite film properties.
Effect of magnetic anisotropy on the current capability of thin film inductor
Authors: Shin Dong-hoon , Kim Choong-sik , Jeong Jong-han , Bae Seok , Nam Seoung-eui , Kim Hyoung-june
Published: July 2002

We investigated the effects of magnetic anisotropy and anisotropy alignment to the coil geometry on the performance of a thin film inductor. For this, Ti/FeTaN bilayer films with large Hk(∼10 Oe) were used as a magnetic layer. We also fabricated a double rectangular spiral inductor which gives a uniaxial coil magnetic flux. When the hard axis of magnetic film is aligned to the magnetic field direction, highest inductance values as well as best frequency response can be obtained. As misalignment angle from the hard axis alignment increases, high-frequency characteristics are substantially degraded, especially at the misalignment angle higher than 45°. Current capability of inductor is found to depend on both Hk and hard axis alignment. The hard axis alignment, in conjunction with large Hk, increases the current capability of inductor significantly.
High resistivity nanocrystalline FeRhN films
Authors: Chen Yingjian , Qian Chester , Hung Chin-Ya , Miller Mark
Published: July 2002

Sputter deposited FeRhN films with unique microstructural characteristics are presented. They consist of fine α-Fe and γ-Fe4N grains with slightly expanded lattice parameters, which result in soft magnetic properties of the film. The significant amount of face-centered-cubic Fe4N phase gives rise to higher resistivity and therefore improved high frequency permeability than conventional FeRhN films.
Magnetic order and weak ferromagnetic transition in Gd2CuO4
Authors: Mira J. , Rivas J. , Butera A. , Steren L. B. , Garcı́a-Beneytez J. M. , Vázquez M.
Published: July 2002

The weak ferromagnetic transition of T′-phase Gd2CuO4 single crystals has been studied by dc-magnetization measurements. Weak ferromagnetism is generated in this material by a very slight canting of the Cu moments from a perfect antiferromagnetic structure. This canting enables the inspection of the magnetic state of the Cu sublattice by pure magnetic methods. The critical exponents of the transition are calculated, γ=1.32(2), β=0.34(1). Nevertheless, a rapid evolution of β to a 2D XY behavior is observed below the critical temperature. It is interpreted as evidence of a transition in the 2D system, namely CuO2 planes, that behave as 3D at the critical point due to the effect of the interlayer interaction along the c-axis.
Spin-glass-like static and dynamic properties of mechanically alloyed Fe–Re–Cr
Authors: De Toro J. A. , López de la Torre M. A. , Arranz M. A. , Riveiro J. M. , Martı́nez J. L.
Published: July 2002

We report the observation of spin-glass-like features in a Fe61Re30Cr9 sample obtained after high energy milling for 460 h. X-ray diffraction showed a broad nanocrystalline peak. The zero-field-cooled and field-cooled magnetization curves exhibited a clear irreversibility, the former showing a relatively sharp maximum for low fields at Tmax≈60 K. In addition, the temperature dependence of the magnetic AC susceptibility (χac) also showed a peak at approximately the same temperature. The frequency sensitivity of such maximum (p=ΔTmax/TmaxΔ log w≈0.02) is small compared to that of typical superparamagnets. However, we discuss the insufficiency of this set of phenomena to assert the existence of a true spin-glass transition and propose the blocking of interacting ferromagnetic nanoparticles as the origin of the observed behavior. The effect of annealing, rendered into nanocrystallite growth, on the χac maximum is studied in an attempt to test this explanation.
Comparison of two and three-dimensional finite element models of large air-gap open-concept magnetic resonance imaging magnet
Authors: Sharifi Masoud , Lavers J. D.
Published: July 2002

Large air-gap C magnets have been proposed for open-concept magnetic resonance imaging (MRI) purposes. The analysis and design of such systems usually involves the use of a finite element model. However, the development of a three-dimensional (3D) model of even this simple structure is time consuming, both in terms of human effort as well as computational resources. An attractive alternative is to use a suitably designed two-dimensional (2D) model with the caveat that it does not simplify the basic problem out of existence. The purpose of this article is to compare 2D (approximate) and 3D (exact) models of a MRI magnet system with a view of developing a method that simplifies the analysis without sacrificing the integrity of the results thus obtained. The 2D approximate models are particularly useful when determining global system characteristics, e.g., the ampere-turn required for a given air-gap flux.
3D-simulations of magnetic structures in af-coupled multilayers with pinholes
Authors: Schepper W. , Diplas K. , Reiss G.
Published: July 2002

For antiferromagnetically (af) coupled Py (Ni81Fe19|Cu)-multilayers lattice calculations have been used already for the investigation of pinholes in GMR elements. The very thin spacer layer (<10 Å) is sensitive against pinholes as a link between the magnetic layers. Additional coupling through the pinhole modifies drastically the af-coupling between the magnetic layers and leads to strong changes in the M(H) and ΔR/R(H) curves. Improved lattice calculations with large grids offer the opportunity, to study effects of geometry in layers structured laterally.
Size effect and temperature dependence of spin conduction in Gd/SiN ultrathin film
Authors: Horiguchi Atushi , Matsuda Tomokazu , Watanabe Yukio
Published: July 2002

The possibility of enhancing the resistivity while preserving magnetism is investigated by growing metal/insulator trilayers and superlattices, where the metal is Gd and the insulator is amorphous Si3N4 for the first time. A large size effect on Curie temperature (TC) is found in the susceptibility in contrast with Gd epitaxially grown on metals. TC decreases to 180 K, i.e., 70% of the bulk TC in 10 nm thick Gd film, which is attributed to an electrical isolation and surface states. On the other hand, the susceptibility χ at TC is almost unchanged as in epitaxial Gd on metal. The resistivity R doubled as the Gd layer thickness decreases from 100 to 10 nm, and the TC estimated from R agrees with that from χ. Additionally, a possible interlayer coupling or an effect of surface layers adjacent to Si3N4 was detected in superlattices.
Correlation between lifetime and blocking temperature distribution in spin-valve structures
Authors: Nozières J. P. , Jaren S. , Zhang Y. B. , Pentek K. , Zeltser A. , Wills P. , Speriosu V. S.
Published: July 2002

The blocking temperature distribution Tb(T) and the failure activation energy (as defined by a 10% drop in the magnetoresistance amplitude in a reverse field equivalent to the self-demagnetizing field of a micron size stripe height device) have been determined in spin-valve sheet films with FeMn, IrMn, PtMn, NiMn, and CrPdMn antiferromagnetic exchange biasing layers. We find a clear correlation between the expected lifetime and the fraction of loose (e.g., unblocked) antiferromagnetic grains, which we believe is due to pinned layer rotation being the main failure mechanism in these systems. For CrPdMn structures, a good agreement is found between the stability of sheet films and of finished sliders. From these data, only NiMn and PtMn appear to be suitable for disk-drive applications.
Growth of CoCrTa(112̄0)-oriented thin films on a D03 Mn3Si(002) underlayer
Authors: Hsu Yu-Nu , Laughlin David E. , Lambeth David N.
Published: July 2002

Mn 3 Si possesses a D03 structure, which is a bcc derivative structure with nearly the same atomic spacing as Cr and NiAl which have been commonly used for longitudinal magnetic recording underlayers. AG(30 nm)/CoCrTa(40 nm)/Mn3Si(x, x=100, 200, 400 nm)/Ag(75 nm) thin films were sputter deposited onto hydrofluoric acid (HF)-etched Si:(001) substrates at elevated temperature. Compared to the 100 and 200 nm thick Mn3Si samples, the XRD spectrum of the 400 nm thick Mn3Si sample shows a significant increase in the intensity of the Mn3Si(002) peak. This suggests that a high volume fraction of the D03 phase was formed. The CoCrTa(112̄0) peak intensity has been found to increase with Mn3Si thickness. As a result, the in-plane coercivity increases as the volume fraction of the D03 phase increases.
Magnetic coherence in a (0001) Sm layer studied by x-ray magnetic scattering
Authors: Dufour C. , Dumesnil K. , Stunault A. , Mangin Ph.
Published: July 2002

A 5000 Å thick (0001) Sm film presenting the complex crystal structure of bulk samarium, constituted of a nine hexagonal close-packed planes stacking sequence, has been successfully obtained by molecular-beam epitaxy. Its magnetic behavior has been studied by resonant x-ray magnetic scattering. A long-range antiferromagnetic order of the moments on the hexagonal sites is established below 106 K. The moments on the cubic sites are ordered separately below 12 K. The magnetic coherence length of both magnetic phases has been analyzed. We show that the ordering of the cubic sites has no influence on the magnetic order at the hexagonal sites.
Structure and magnetic properties of the Sm(Co0.68−xFe0.25Cu0.07Zrx)7.7 melt-spun alloys with Zr additions
Authors: Gong Wei
Published: July 2002

The effects of Zr additions on the Sm(Co,Fe,Cu,Zr)z compound have been studied. Melt-spun ribbons with a composition of Sm(Co0.68−xFe0.25Cu0.07Zrx)7.7 (x=0, 0.02, 0.04, 0.07, 0.10, and 0.15) were prepared with a wheel speed of 45 m/s, followed by a vacuum heat treatment in the temperature range of 650–800 °C for 5 min. X-ray diffraction (XRD) results showed that the as-spun ribbons of Sm(Co0.68−xFe0.25Cu0.07Zrx)7.7 have a primary TbCu7-type phase. When the annealing temperature was increased, grain sizes in the ribbons were increased according to reduced XRD peak widths of the TbCu7 phase. A Co23Zr6 compound was observed in the heat-treated ribbons when the Zr content exceeded 0.04. Saturation magnetization of the ribbons was linearly decreased from 95 to 45 emu/g (under a magnetic field H=18 kOe), while the Zr content was increased from 0 to 0.15. However, intrinsic coercivity of the ribbons was significantly dependent on grain size which was associated with both the Zr contents and heat-treatment temperatures. The highest intrinsic coercivity, Hci=13 kOe, was obtained in the ribbons with Zr content of 0.10 and heat treatment at 650 °C. With a maximum energy products up to 9.5 MGOe amd Br of 7.4 kG in the heat-treated ribbons with a suitable Zr addition is considered as promising magnets for high temperature applications.
Structural and magnetic properties of mechanically milled SmCo5:C
Authors: Kirkpatrick E. M. , Leslie-Pelecky Diandra L.
Published: July 2002

Mechanically milling SmCo5 powder significantly increases coercivity and remanence ratio by introducing defects; however, these defects can be removed by room-temperature aging, with a resultant decrease in coercivity. A series of (SmCo5)x:C1−x (0.15⩽x⩽1) samples has been fabricated to investigate the effect of C on oxidation protection and magnetic properties. SmCo5 was premilled for 1 h, then added to C powder and milled for times ranging from 15 min to 7 h. X-ray diffraction indicates the presence of crystalline graphite and SmCo5 for milling times ⩽6 h and also shows the presence of fcc Co for milling times >7 h. The magnetic properties are very weakly dependent on milling time after the C addition, which is attributed to the lack of further grain refinement. The saturation magnetization scales linearly with the wt % of SmCo5. Remanence ratios are approximately 0.7 and independent of volume fraction. The maximum coercivity of 16.5 kOe is comparable to the maximum obtained by milling SmCo5 without C. Samples exposed to air for times up to two months show no decrease in coercivity or remanence ratio for x⩽0.70. The addition of C has no detrimental effect on the magnetic properties obtained by milling, except the expected reduction of Ms.
The effects of Fe, Co, and Ni doping on the superconductivity and structure of HfV2
Authors: Lin C. L. , Yuen Tan , Mihalisin T. , Chu F.
Published: July 2002

The temperature dependence of the specific heat has been measured for Fe-, Co-, and Ni-doped HfV2 systems. HfV2 undergoes a structural transformation at TS=116 K and becomes superconducting at TC=9 K. The low temperature specific heat of HfV2 shows an enhanced electronic specific heat coefficient indicating a large density of states at the Fermi level. TC shows nonmonotonic behavior with magnetic ion concentration. It increases initially as one dopes HfV2 with small amounts of Fe, Co, or Ni and reaches a maximum of 9.4 K for about 3.0 to 4.0 at. % doping and then decreases for higher concentrations. On the other hand, the specific heat data at higher temperatures show that both TS and the size of the specific heat anomaly at TS decrease monotonically and dramatically when the concentration of Fe, Co, or Ni is increased. No evidence of a structural transformation is detected for samples with more than 5 at. % Fe, Co, or Ni. The variations of TC and TS can be explained qualitatively by recent theoretical calculations.
Theoretical study of magnetic impurities in small metallic clusters
Authors: Ricardo-Chávez J. L. , Pastor G. M.
Published: July 2002

Magnetic impurities in metallic clusters having N⩽6 atoms are investigated in the framework of the Anderson model by exact diagonalization methods. Parameters representative of the Kondo limit are considered. The spin gap ΔE=E(S=1,3/2)−E(S=0,1/2) shows a remarkable band-filling dependence that can be interpreted in terms of the cluster-specific conduction-electron spectrum. Finite-temperature properties are calculated exactly in the canonical ensemble. The specific heat Cp(T) and the impurity susceptibility χf(T) present characteristic peaks at temperatures of the order of TK≃ΔE/kB [χf(T)∝1/T for T>TK]. This is interpreted as a finite-size equivalent of the Kondo effect. The structural dependence is illustrated.
Magnetism in some UCo1/3T2/3Al solid solutions (T=transition metal)
Authors: Chang S. , Nakotte H. , Andreev A. V. , Bordallo H. N. , Havela L. , Sechovsky V. , Torikachvili M. S.
Published: July 2002

We report on the magnetic properties of UCo1/3T2/3Al (T=Ru, Rh, Pt) solid solutions which form in the hexagonal ZrNiAl structure. We performed neutron diffraction and bulk magnetization studies. All three solid solutions exhibit long-range magnetic order at low temperatures. Bulk magnetization studies indicate a ferromagnetic ground state for UCo1/3Ru2/3Al, UCo1/3Rh2/3Al, and UCo1/3Pt2/3Al below 42, 41, and 27 K, respectively. At 4.2 K, the spontaneous moment ranges from ∼0.15 μB/U-atom (UCo1/3Ru2/3Al) to ∼0.49μB/U-atom (UCo1/3Pt2/3Al). Below TC, we find additional weak magnetic contributions in the neutron diffraction data, and our refinement is consistent with magnetic moments along the c axis. The magnitudes of the moments are in good agreement with the spontaneous moments determined from bulk studies. The results are discussed in terms of f–d hybridization, which is modified by changes in the d band occupation and preferential occupation of the transition metals within the lattice.
Ion beam modified Co/Si multilayers
Authors: Fallon I. M. , Faunce C. A. , Grundy P. J. , Blythe H. J.
Published: July 2002

This article briefly reports microstructural, electrical transport, and magnetic measurements on Co/Si multilayers which are structurally modified by argon ion irradiation during growth. The periodicity and ferromagnetism of the multilayers is retained at ion energies approaching 400 eV. At and above this energy structural modification results in resputtering and thinning of the film, extensive mixing and a destruction of the periodic layered structure with the formation of nonequilibrium microstructures. The measurements show that the modified film is metallic in character, with the presence of low resistance paths and possible spin glass behavior in an amorphous matrix that surrounds a second microstructural component of mainly superparamagnetic nanoclusters.
Perpendicular anisotropy in the amorphous TbCo/Si multilayers
Authors: Chen X. , Wang Y. J. , Liang B. Q. , Tang Y. J. , Zhao H. W. , Xiao J. Q.
Published: July 2002

The TbCo/Si multilayers prepared by the rf magnetron sputtering system with various Si thickness have been investigated. X-ray diffraction, magnetic measurement and Kerr rotation have been performed. No antiferromagnetic coupling was found for the system. With the thickness of Si layer tSi increasing, the perpendicular anisotropy constant Ku, and the saturation magnetization Ms decreased rapidly. It was assumed that Co2Si and Tb had been formed in the interfacial zone between TbCo and Si layers due to the interlayer diffusion. The decreasing of Ms is attributed to the decreasing of the effective thickness of magnetic layer.
Magnetoelastic sensors in combination with nanometer-scale honeycombed thin film ceramic TiO2 for remote query measurement of humidity
Authors: Grimes Craig A. , Kouzoudis Dimitris , Dickey Elizabeth C. , Qian D. , Anderson M. A. , Shahidain Rony , Lindsey Maisha , Green Leonard
Published: July 2002

Ribbonlike magnetoelastic sensors can be considered the magnetic analog of an acoustic bell; in response to an externally applied magnetic field impulse the sensors emit magnetic flux with a characteristic resonant frequency. The magnetic flux can be detected external to the test area using a pick-up coil, enabling query remote monitoring of the sensor. The characteristic resonant frequency of a magnetoelastic sensor changes in response to mass loads [L. D. Landau and E. M. Lifshitz, Theory of Elasticity, 3rd ed. (Pergamon, New York, 1986), p. 100]. Therefore, remote query chemical sensors can be fabricated by combining the magnetoelastic sensors with a mass changing, chemically responsive layer. In this work magnetoelastic sensors are coated with humidity-sensitive thin films of ceramic, nanodimensionally porous TiO2 to make remote query humidity sensors.
Infrared diode laser spectroscopy of the NO3 ν3 band
Authors: Ishiwata Takashi , Tanaka Ikuzo , Kawaguchi Kentarou , Hirota Eizi
Published: July 2002

The N–O degenerate stretching band ν3 of the NO3 radical has been studied in the gas phase by infrared tunable diode laser spectroscopy. The NO3 radical was generated by the reaction of NO2 with an excess of O3. Zeeman modulation was employed to observe the paramagnetic absorption lines of 14NO3 and 15NO3 in the wavelength regions 1480–1500 and 1463–1479 cm−1, respectively. Only K′′=3n (n denoting an integer) transitions were observed, and the N′′=even members were missing from the K′′=0 manifold. These observations indicate that the NO3 radical belongs to D3h symmetry in the 2A2′ ground electronic state. The observed spectrum was analyzed using a symmetric-top vibration-rotation Hamiltonian including the spin-rotation interaction. The main parameters thus obtained for 14NO3 are B3=0.455 22(11), C3=0.227 13(6), Cζ3=0.044 79(11), q3=0.001 624(33), t3= 0.000 000 458 0(43), B0=0.457 46(12), C0=B0/2 (fixed), εbb=0.0280(27), and εcc=0.1197(36) for v3=1, εbb=0.0277(28), and εcc=0.1117(34) for v=0, and ν0=1492.3929(9), all in cm−1 with one standard error in parentheses. Although these parameters well reproduced the observed spectrum, the following anomalous features were noted: (1) a large εcc spin-rotation interaction constant was required to explain the spin splittings for both the ν3 and ground states, (2) a higher-order vibration-rotation interaction term having Δk=±4 and Δl=±2 needed to be included, with the corresponding interaction constant t3 larger than that of CHF3, and (3) the centrifugal distortion constants and the first order Coriolis coupling constant which were derived did not agree with those calculated assuming a reasonable force field. These anomalies were ascribed to the interaction with a low-lying excited electronic state and, to some extent, with a combination or overtone state. The N–O bond length was calculated from the B0 rotational constant to be 1.240 Å, in good agreement with an ab initio calculated value.
Calculations of the geometry and binding energy of aromatic dimers: Benzene, toluene, and toluene–benzene
Authors: Schauer Mark , Bernstein E. R.
Published: July 2002

Calculations of the geometries and energies of the benzene, toluene, and toluene–benzene dimers using a combination of atom–atom and multipolar potentials are presented and discussed. An exponential-six atom–atom potential plus a molecular quadrupole–quadrupole interaction term gives the reported parallel displaced C2h benzene dimer geometry. The excited state behavior of the benzene dimer can be qualitatively understood based on this calculation. The toluene–benzene dimer is well modeled by these terms in addition to a dipole–quadrupole interaction term. Both parallel displaced and perpendicular configurations are obtained in agreement with the experimental data. Using exponential-six dipole–dipole, quadrupole–quadrupole, and dipole–quadrupole interactions the toluene dimer can be satisfactorily modeled. The calculations generally suggest that excitation of parallel displaced dimers can lead to rearrangement (and possible excimer formation) in the excited state.
Modifications of the Stokes–Einstein formula
Authors: Zwanzig Robert , Harrison Alan K.
Published: July 2002

Empirically motivated modifications of the Stokes–Einstein formula, in which the diffusion coefficient is inversely proportional to a fractional power of the viscosity, are discussed. We suggest that the results should be analyzed in terms of an effective hydrodynamic radius.
Dissociative attachment reactions of electrons with strong acid molecules
Authors: Adams Nigel G. , Smith David , Viggiano A. A. , Paulson John F. , Henchman Michael J.
Published: July 2002

Using the flowing afterglow/Langmuir probe (FALP) technique, we have determined (at variously 300 and 570 K) the dissociative attachment coefficients β for the reactions of electrons with the common acids HNO3 (producing NO−2) and H2SO4 (HSO−4), the superacids FSO3H (FSO−3), CF3SO3H (CF3SO−3), ClSO3H (ClSO−3,Cl−), the acid anhydride (CF3SO2)2O (CF3SO−3), and the halogen halides HBr (Br−) and HI (I−). The anions formed in the reactions are those given in the parentheses. The reactions with HF and HCl were investigated, but did not occur at a measurable rate since they are very endothermic. Dissociative attachment is rapid for the common acids, the superacids, and the anhydride, the measured β being appreciable fractions of the theoretical maximum β for such reactions, βmax. The HI reaction is very fast ( β∼βmax) but the HBr reaction occurs much more slowly because it is significantly endothermic. The data indicate that the extreme acidity of the (Bronsted-type) superacids has its equivalence in the very efficient gas-phase dissociative attachment which these species undergo when reacting with free electrons. The anions of the superacids generated in these reactions, notably FSO−3 and CF3SO−3, are very stable (unreactive) implying exceptionally large electron affinities for the FSO3 and CF3SO3 radicals.
Time reversal and unitarity in the frozen Gaussian approximation for semiclassical scattering
Authors: Herman Michael F.
Published: July 2002

The time reversal and unitarity properties of the semiclassical frozen Gaussian approximation for the propagation of time dependent wave functions are explored. It is found that propagation backwards in time is the adjoint operation to propagation forward in time. This basic property of exact quantum propagation holds exactly in the frozen Gaussian approximation. Unitarity is also demonstrated for frozen Gaussian propagation within the stationary phase approximation. This latter result holds only as long as a prefactor is included in the frozen Gaussian approximation. This point is significant since this prefactor is neglected in many frozen Gaussian variations, and its inclusion can require additional computational effort. The time reversal and unitarity results can be combined to prove the very useful, but nonobvious result that time reversed propagation is the inverse of propagation forward in time in the frozen Gaussian approximation, under the same conditions for which the unitarity property holds.
Second-order susceptibility tensors of partially ordered molecules on surfaces
Authors: Mazely T. L. , Hetherington W. M.
Published: July 2002

The shape of the macroscopic second-order susceptibility tensor of molecules bound to a surface depends upon both the molecular tensor and the distribution of orientations. The details of these dependencies are discussed in general and in the special case of two photon electronic resonance enhancement. Using the results of an orientation averaging procedure, experiments, based upon variation of the angle of incidence, the input polarization, the output polarization, or the frequency, can be devised to determine the shape of a molecular tensor or the orientation distribution. Specific examples are given for interfacial phenol and cinnamic acid.
Electron transmission study of the temporary negative ion states of selected benzenoid and conjugated aromatic hydrocarbons
Authors: Burrow P. D. , Michejda J. A. , Jordan K. D.
Published: July 2002

Electron transmission spectroscopy is utilized to determine the vertical electron affinities and to characterize the temporary anion states of a series of alternant hydrocarbons including benzene, naphthalene, anthracene, tetracene, styrene, and cis- and trans-stilbene. The vibrational structure present in the low lying resonances is interpreted in light of the charge distributions of the temporarily occupied orbitals. The energies of the anion states are compared with the predictions of PPP, PPP-CI, and HAM calculations, the pairing theorem and with the results from optical absorption measurements on the ground state anions in rigid glasses.
Vertical electronic spectrum of NO3: 2A′2, 2E″(2A2,2B1), and 2E′ states
Authors: Kim Bongsoo , Johnston Harold S. , Clabo D. Allen , Schaefer Henry F.
Published: July 2002

A b initio molecular quantum mechanics has been used to study the four lowest electronic states of the nitrate free radical at the D3h geometry deduced from experiment (1985) by Ishiwata, Tanaka, Kawaguchi, and Hirota. Basis sets ranging from double zeta (9s5p/4s2p) to triple zeta plus double polarization quality were used. Both self-consistent-field (SCF) and configuration interaction (CI) wave functions were employed, with molecular orbitals determined for the various electronic states of NO3 and for the ground state NO−3 anion. The CI wave functions included single (S), double (D), and (in some cases) triple (T) excitations. The CISDT wave functions included as many as 511 474 configurations in C2v point group symmetry. The predicted energetic position of the 2E′ state agrees well with the known T0=15 100 cm−1. The 2E″ state, found to be the lowest excited electronic state of NO3, is predicted to lie at a vertical excitation energy of ∼3600 cm−1. The relationship between this prediction and the 1986 experiments by Kawaguchi, Ishiwata, Tanaka, and Hirota suggesting an excited electronic state at 1490 cm−1 is discussed.
Dynamics in low temperature glasses: Theory and experiments on optical dephasing, spectral diffusion, and hydrogen tunneling
Authors: Berg M. , Walsh C. A. , Narasimhan L. R. , Littau K. A. , Fayer M. D.
Published: July 2002

Temperature dependent photon echo (PE) and nonphotochemical hole burning (NPHB) measurements are reported on resorufin in three organic glasses: ethanol (1.5–11 K), glycerol (1.1–25 K), and d-ethanol (1.5–11 K). In all cases, the NPHB results are broadened considerably from the PE results at low temperatures, but the two measurements coalesce at high temperatures. The temperature dependences are found to deviate from the power law dependence expected for two-level system dephasing, and the deviation is attributed to dephasing by a pseudolocal mode. The appropriate correlation functions for PE and hole burning experiments are shown to be different from each other. They also differ from the correlation function for the optical absorption (OA) experiment, which has been the basis for most calculations of optical dephasing in glasses. The broadening of hole widths beyond the PE result is shown to be a measure of the slow spectral diffusion processes in the glass. Other types of dephasing measurement are also analyzed and each measurement is shown to be sensitive to spectral diffusion to a different degree. By making standard assumptions about glass dynamics, the main experimental results can be accounted for. A long range chromophore–glass interaction and a 1/R distribution of relaxation rates R at short times are indicated.