bluuebunny/crossref_metadata_2025 huggingface dataset:
Misorientation effect on the monolayer terrace topography of (100) InP substrates annealed under a PH3/H2 ambient and homoepitaxial layers grown by metalorganic chemical vapor deposition
Authors: Merlin V. , Duc Tran Minh , Younes G. , Monteil Y. , Souliere V. , Regreny P.
Published: July 2002

The detailed monolayer terracelike topography of nominal on-axis and misoriented vicinal (100) InP surfaces was systematically investigated by ‘‘ex situ’’ atomic force microscopy. Vicinal (100) InP reconstructs into steps around 550 °C in either argon or phosphine/hydrogen. Widths of observed monoatomic terraces are measured to be in close agreement with misorientation angles. Homoepitaxial growth by metalorganic chemical vapor deposition preserves the terracelike structure. Growth acts through a monoatomic step flow mode following the classical Burton–Cabrera–Frank theory. Surface diffusion length is estimated up to 350 nm in our standard growth conditions at 630 °C and 2.5 μm/h. Spiral growth is also observed and takes its origin from a screw dislocation emerging on the surface of the substrate. The critical misorientation angle below which the spiral growth mechanism occurs and competes with the vicinal steps is in the range of 0.05°–0.1°.
Epitaxial growth of CoSi2 layer on (100)Si and facet formation at the CoSi2/Si interface
Authors: Byun Jeong Soo , Kim Do-Heyoung , Kim Woo Shik , Kim Hyeong Joon
Published: July 2002

The epitaxial nature of the CoSi2 formed on the (100)Si substrate as a result of annealing a Co/Ta bilayer at 500–1000 °C for 20 s in N2 atmosphere is described. At the early stage of annealing, diffusion of Co and Si occurs across the interlayed Ta layer, first forming a CoSi layer on the Si substrate. After that, CoSi2 grains nucleate at the CoSi/Si interface and grow laterally parallel to the surface. Due to a difference in mobility the CoSi2 grains at the interface of the CoSi/Si impede the interface movement, leading the facet formation. Even after annealing below 600 °C, the epitaxial CoSi2 grains are nucleated at the limited area of the nonepitaxial CoSi/Si interface and the faceted corner, and grow laterally along the Si surface. By increasing the annealing temperature, the epitaxiality of CoSi2 improves due to the increased lateral growth rate of the CoSi2. However, annealing above 900 °C impairs the CoSi2 crystallinity because the interlayered Ta loses its function as a diffusion barrier due to the formation of the TaSi2.
Raman spectroscopy and x-ray diffraction of PbTiO3 thin film
Authors: Ching-Prado E. , Reynés-Figueroa A. , Katiyar R. S. , Majumder S. B. , Agrawal D. C.
Published: July 2002

A PbTiO3 thin film prepared on silicon substrate by sol-gel technique has been studied by micro-Raman spectroscopy and x-ray diffraction (XRD). The spectra, in comparison to the single crystal work, show high background in the low frequency region and Raman lines are broader, thus revealing the polycrystalline nature of the film. The frequencies of the Raman bands in the film are clearly shifted to lower frequencies compared to the corresponding ones in the single crystal or powder forms. This phenomenon is similar to the hydrostatic pressure effect on the Raman lines of PbTiO3 single crystal. The film, therefore, has grains under stress. This stress is caused by nonequilibrium defects and diffusion at the interface. Measurements at different film positions showed variations in the frequency and width of the Raman bands which are associated with the stress and grain size inhomogeneities. The measured shift in the Raman frequencies suggests grain sizes ≤1 μm. XRD indicates grain size of around 22 nm and an average stress around 1.3 GPa, which was determined using the measured shift for the c-lattice constant.
Solution of electromagnetic inverse problem using combinational method of Hopfield neural network and genetic algorithm
Authors: Kishimoto M. , Sakasai K. , Ara K.
Published: July 2002

We regard a magnetic inverse problem as a spatial optimum allocation problem of currents and use a Hopfield neural network for solving this optimization problem. Because the Hopfield neural network has an initial state problem that the optimum solution cannot be obtained unless an initial state of network is set up suitably, adoption of a genetic algorithm is proposed for solving this initial state problem of Hopfield neural network. The effectiveness of proposed method is confirmed by computational simulations.
Structure, magnetic properties, and giant magnetoresistance in melt-spun metallic copper–cobalt ribbons
Authors: Yu R. H. , Zhang X. X. , Tejada J. , Zhu J. , Knobel M.
Published: July 2002

We report a comprehensive investigation of structural, magnetic, and transport properties of as-quenched and annealed CoxCu1−x (0≤x≤0.20) granular alloys prepared by melt spinning. Using x-ray diffraction, differential scanning calorimetry measurements, and magnetic characterization, we have uncovered a Co phase separation process which results in the variation of magnetic and transport properties of Co–Cu heterogeneous alloys. In the Co composition range (0≤x≤0.15), the maximum giant magnetoresistance (GMR) was observed for CoCu samples annealed at 450 °C for 30 min, where Co particle diameters are in the range of 3.5–4.5 nm. The variation of magnetic and transport properties with the concentration and size of precipitated Co clusters is discussed, and is consistent with the prediction of the two-channel model, in which spin-dependent scattering is dominated by the cluster-matrix interfaces. The reduction of GMR in high Co concentration is attributed to the appearance of magnetic coupling among magnetic particles. In contrast, very small particles tend to behave superparamagnetically, resulting in the reduction of the ratio of spin-dependent scattering to spin-independent scattering potentials, and thus in the reduction of the GMR effect.
Current blocking in InP/InGaAs double heterostructure bipolar transistors
Authors: McKinnon W. R. , McAlister S. P. , Abid Z. , Guzzo E. E.
Published: July 2002

The one-flux analysis of double-heterostructure bipolar transistors with composite collectors in the preceding article W. R. McKinnon, J. Appl. Phys. 79, 2762 (1996) is compared to drift-diffusion calculations and to measurements on InP/InGaAs/InP/composite collectors-double heterostructure bipolar transistors. For quantitative agreement we include the effects of ionized impurities in the space-charge regions, and an approximate treatment of Fermi–Dirac statistics.
Magnetic properties of exchange-coupled Fe/FeO bilayers
Authors: Dimitrov D. V. , Murthy A. S. , Hadjipanayis G. C. , Swann C. P.
Published: July 2002

The magnetic, structural and microstructural properties of sputtered Fe thin films and Fe\Fe–O bilayers were studied as a function of the Fe layer thickness, the type of the Fe oxide and the substrate used. Two different ways to prepare the oxide layers were used; postdeposition oxidation and reactive sputtering. Postdeposition oxidation produced films with mixed Fe–oxides (FeO, Fe3O4, Fe2O3); however reactive sputtering led to bilayers with controlled stoichiometry, Fe\FeO, Fe\Fe3O4, and Fe\FE2O3, respectively. The coercivity of both the Fe films and fE\Fe–O bilayers, deposited on substrates with or without Cr buffer layer, was found to increase with decreasing Fe film thickness. The coercivity of the samples deposited on a Ag buffer layer was much lower and did not change substantially with the Fe film thickness. The presence of the Fe–oxide layer led to a large increase of coercivity. This is attributed to the higher anisotropy of the oxide and to exchange coupling of Fe–oxide with the softer Fe layer.
Study of photoconductivity in AlxGa1−xAs/GaAs modulation-doped heterostructures
Authors: Peng Zhongling , Saku Tadashi , Horikoshi Yoshiji
Published: July 2002

Temperature-dependent Hall effect measurements under different illumination conditions are performed on AlxGa1−xAs/GaAs heterostructures doped with both Si and Sn. For a Sn-doped AlxGa1−xAs/GaAs heterostructure with x=0.35, two distinct DX center levels are observed directly without exposure to light. The two-dimensional electron gas concentration measured under illumination decreases from the value due to persistent photoconductivity to a value less than that measured in the dark when the excitation photon energy is larger than the band gap of the AlGaAs barrier. This decrease occurs only at temperatures below 90 K. This negative photoconductivity is explained by taking into account the partial freeze-out of electrons into the shallow DX centers and the transfer of holes photogenerated in the barrier into the channel region. No such phenomena are observed in Sn-doped heterostructures with x <0.35 or in the Si-doped heterostructures. The reasons for this are also investigated.
Study of local stress, morphology, and liquid-crystal alignment on buffed polyimide surfaces
Authors: Kikuchi Hirotsugu , Logan J. A. , Yoon Do Y.
Published: July 2002

The magnitude of local stress applied to a polymer surface in the buffing process, which is a critical method to uniformly align liquid crystals for displays, has been evaluated from the polarizing optical microscopic investigation of nematic liquid crystals in contact with polyimide surfaces which were suitably buffed in order to visualize the individual tracks of the buffing rayon fibers. The estimated magnitude of local stress is most likely to be far greater than the yield stress of the polymer film, thereby causing permanent molecular orientation along the buffing direction. The surfaces of poly(amic acid) and cured polyimide films, subjected to different buffing and cure profiles, have been examined by atomic force microscopy. The ability of these buffed polymer surfaces to align nematic and chiral smectic C (ferroelectric) liquid crystals were also investigated. These studies show that the presence of microgrooves on buffed polymer surfaces is not necessary for alignment of liquid crystals. The contribution of polymer molecules from the buffing fibers, deposited and oriented on the polyimide surfaces during buffing, can also be ruled out. Rather, it is concluded that the liquid-crystal alignment is mainly caused by the anisotropic interactions between liquid-crystal molecules and the polymer segments oriented through plastic deformation, with little contribution from frictional heating. For the alignment of smectics, both the degree of order and mechanical properties of polyimide films are found to be important factors.
Magnetic exchange and charge transfer in mixed-valence manganites and cuprates
Authors: Dionne Gerald F.
Published: July 2002

Metallic resistivity occurs at cryogenic temperatures in insulators with small carrier trap energies, e.g., superconducting cuprates. A similar metallic regime has been reported for the lanthanide (RE) manganites (RE3+1−xA2+x)MnO3. To interpret the anomalous resistivity ρ as a function of temperature and magnetic field in these compounds, a model constructed from the relation for mobility activated semiconduction and the Brillouin–Weiss theory of ferromagnetism has been developed. The resistivity maximum occurs at the susceptibility peak slightly above the Curie temperature TC and its magnitude is related to the hopping electron trap energy Ehop by exp(Ehop/kTC). Where T<TC, ρ is metallic because Ehop is small due to the collinear polarization of spins. For T≥TC, Ehop increases to a value ∼0.1 eV equal to the decrease in stabilization energy of the transfer electrons caused by the transition from spin alignment to disorder. The magnetoresistance sensitivity dρ/dH at T=TC is controlled by TC through (1/TC)exp(Ehop/kTC). The relative sensitivity (1/ρ)dρ/dH, however, is proportional to 1/T2C. These results also reinforce the concept that metallic resistivity in the superconducting cuprates occurs because of the frustration of antiferromagnetism.
Magnetic interactions in nanocrystalline SmFeCo
Authors: Cornejo D. R. , Missell F. P. , González J. M.
Published: July 2002

Several samples of enhanced-remanence nanocrystalline Sm15Fe19Co66 were prepared by mechanical alloying of the elementary powders followed by heat treatments. Sample A had a remanence ratio η=σr/σs=0.68 and Hc=7.1 kOe, while, for B, η=0.58 and Hc=10.4 kOe, and, for C, η=0.57 and Hc=12.6 kOe. The isothermal remanent magnetization Mr(H), obtained for different initial demagnetized states (ac, dc+, dc−), and the demagnetization remanence Md(−H), obtained for an initially saturated state, were determined. The ac-demagnetization Henkel plot showed both magnetizing and demagnetizing interactions as observed in other nanocrystalline magnets. A comparison with the moving Preisach model indicates the importance of both mean-field and random interactions.
Magnetic circular dichroism at the K and L edges of Co and Cu in Co/Cu(001)
Authors: Wu Ruqian , Freeman A. J.
Published: July 2002

The fcc Co/Cu(001) system is investigated using the full potential linearized augmented plane wave method. Through the atomic force approach, large multilayer relaxations (6.5%, 5.3%, and 2.8%) are found between the adjacent Cu layers, which reduces the total energy by 128 meV. The spin and orbital magnetic moments for Co atoms are 1.79 and 0.12 μB, respectively. At the interfacial Cu site, we found a sizable induced magnetic moment, 0.05 μB, which can be split into d (0.074 μB) and s,p(0.024 μB) contributions. Interestingly, the spin polarization of d and s,p states can be detected separately through the magnetic circular dichroism at the L and K edges, for which the calculated results agree very well with experiments.
Anomolous ΔE effects in TbDyZn alloys
Authors: Cullen J. R. , Wun-Fogle M. , Restorff J. B. , Teter J. P. , Clark A. E.
Published: July 2002

The temperature dependence of Young’s modulus has been measured for a series of Tb1−xDyxZn pseudobinary compounds with x ranging from 0 to 1. From the sharp dips in the modulus vs temperature data, the reorientation transition temperatures have been determined, and the magnetic phase diagram deduced. Magnetization measurements taken on the same samples show less pronounced features at the corresponding temperatures.
Observation of independent iron and rare-earth ordering in RFe6Ge6 (R=Y, Gd–Lu) compounds
Authors: Ryan D. H. , Cadogan J. M.
Published: July 2002

Mössbauer and magnetization measurements have been used to study magnetic ordering in RFe6Ge6 alloys. The iron sublattice orders antiferromagnetically and TN remains essentially constant across the series at ∼480 K with no evidence of a net magnetization in any of the alloys. For R=Gd−Er, the rare-earth sublattice orders ferromagnetically with Tc’s that descend from 30 K at Gd to 3 K at Er. This order is established without affecting the order on the iron sublattice. The large difference in ordering temperatures and the unrelated magnetic structures adopted by the two sublattices indicate that the iron and rare-earth moments are effectively isolated from each other and that they order independently.
Pole tip recession studies of hard carbon-coated thin-film tape heads
Authors: Bhushan Bharat , Patton Steven T. , Sundaram Ramesh , Dey Subrata
Published: July 2002

Hard carbon coatings were deposited by cathodic arc and direct ion beam deposition techniques on thin-film Al2O3–TiC heads and by the latter technique on thin-film Ni–Zn ferrite heads. Functional accelerated tests were conducted against metal particle tapes in a linear tape drive. Ion beam carbon coatings on Ni–Zn ferrite and Al2O3–TiC heads substantially reduced the pole tip recession observed with uncoated heads. Cathodic arc carbon coated Al2O3–TiC heads performed better than uncoated heads, but were less effective than the ion beam coating. Pole tip recession increased only if carbon was removed from the pole tip. This suggests that coating effectiveness is determined by its adherence to the pole tip. In two-wide pole tip heads, wear of the pole adjacent to the substrate was less than that of the other pole. Coatings withstood accelerated tests and may meet life time requirements of future heads.
Large shielding factor obtained by a multiple-shell magnetic shield having separate magnetic shaking
Authors: Sasada I. , Yamamoto T. , Yamauchi T.
Published: July 2002

Large shielding factors obtained by magnetic shaking techniques are reported. A cylindrical magnetic shield with both ends open (length=120 cm, inner diameter=52 cm) was constructed as a one-half model of an actual size. Metglas 2705M amorphous tapes of 5 cm in width and about 22 μm in thickness were wound helically on the outer surface of a tube (outer diameter=52 cm) to form a thin multiple-shell structure of five shells. The outer three shells, each made of 4 layers of tapes, were subjected to a common magnetic shaking (200 Hz). The fourth shell made of 8 layers was subjected to a different magnetic shaking (536 Hz). The innermost one was a passive shell. The shielding factor in the center of the shield measured for a transversely applied magnetic field (100 mG) showed 1/f-like behavior and extremely large values of 90 900 at 1 Hz and 21 000 at 10 Hz when the opening compensation was on. The shielding factor was much lower and constant at the level of 7000 at frequencies of less than 10 Hz when opening compensation was off. The residual dc magnetic field at the center was as small as 5 μG. It is shown by the experiments that a multiple-shell structure with even narrow spacings exhibits large shielding factors when a magnetic shaking technique is applied. It is also shown that the opening compensation technique is a key to building an open-structure magnetic shield with a large shielding factor.
An experimental investigation on the effective magnetic anisotropy of nanocrystalline Fe89Zr7B4 soft magnetic alloys
Authors: Zhou F. , He K. Y.
Published: July 2002

The effective magnetic anisotropy (Keff) of nanocrystalline Fe89Zr7B4 soft magnetic alloys with different bcc Fe grain sizes (D) has been investigated by using the law of approach to saturation. The effective magnetic anisotropy of the alloys is found to be considerably depressed. The values of Keff for the alloys (from 879 to 1038 J/m3) are very close to those of the nanocrystalline Fe73.5Cu1Nb3Si13.5B9 soft magnetic alloys, suggesting that the relatively lower permeability of the alloys is independent of the factor of Keff. With an increase of grain size, Keff is slightly increased. However, the grain size dependence of Keff is obviously deviated from the Keff∝D6 law, which might be mainly attributed to the residual amorphous phase in the alloys.
Structural analysis of AlN and (Ti1−XAlX)N coatings made by plasma enhanced chemical vapor deposition
Authors: Lee Sang-Hyeob , Kim Byoung-June , Kim Hyung-Hwan , Lee Jung-Joong
Published: July 2002

(Ti1−XAlX)N coatings were deposited by plasma enhanced chemical vapor deposition (PECVD) method using a gas mixture of TiCl4, AlCl3, NH3, H2 and Ar. X-ray diffraction and transmission electron microscopy were used to investigate the structure of the deposited (Ti1−XAlX)N coatings. They showed single phase NaCl-structure up to X=0.8, while a mixed phase of NaCl type (Ti0.2Al0.8)N and AlN with würtzite-structure was observed for 0.8<X<1.0. The lattice parameter changed linearly with the function X (d=4.241−0.197 X Å) in the single phase region. Metastable AlN particles with an NaCl structure and a lattice parameter of 4.03 Å were found on AlN coatings produced by PECVD using AlCl3, NH3 and H2. It was assumed that the formation of (Ti1−XAlX)N solid solution in a wide concentration range occurred due to the metastable AlN. When (Ti1−XAlX)N coatings were heat-treated at 1000 °C, AlN with a stable würtzite structure precipitated. However, the broadened x-ray diffraction peak and the diffuse transmission electron microscopy diffraction patterns indicated that the amount of precipitation was not the same for each (Ti1−XAlX)N grain.
Liquid phase epitaxial growth of InGaAs on InP using rare-earth-treated melts
Authors: Gao Wei , Berger Paul R. , Ervin Matthew H. , Pamulapati Jagadeesh , Lareau Richard T. , Schauer Stephen
Published: July 2002

High-quality In0.53Ga0.47As epilayers have been grown on semi-insulating (100) Fe-doped InP substrates. The growths were performed by liquid phase epitaxy (LPE) using rare-earth-doped melts in a graphite boat. The rare-earth elements studied were Yb, Gd and Er which act as gettering agents of impurities. Hall measurements show an elevated electron mobility for rare-earth-treated samples over undoped samples, μe=11 470 cm2/V s at 300 K and reduced carrier concentration (n-type), 9.33×1013 cm−3. The Hall results indicate an improvement in layer quality, but suggests that the treated layers are compensated. Photoluminescence (PL) studies show that the layers grown from rare-earth-doped melts have higher integrated PL efficiency with narrower PL linewidths than the undoped melt growths. The grown materials were fully characterized by Fourier transform infrared spectroscopy, double-crystal x-ray diffraction, energy dispersive spectroscopy, secondary-ion-mass spectroscopy, and deep level transient spectroscopy (DLTS). Compositional measurements reveal no measurable incorporation of rare-earth elements into the grown epilayers. DLTS measurements indicate the creation of two deep levels with rare-earth treatment, which is attributed to either the rare earth elements or impurities from within the rare-earth elements. Subsequent glow discharge mass spectrometry measurements reveal many impurities within the rare-earth elements which preferentially might lead to p-type doping centers and/or deep levels. Thus, rare-earth doping of LPE melts clearly improves epitaxial layer quality, however, the purity of commercially available rare-earth elements hinders optimal results.
Role of optical properties of metallic mirrors in microcavity structures
Authors: Becker H. , Burns S. E. , Tessler N. , Friend R. H.
Published: July 2002

In thin metal films the phase change on reflection of incident light is dependent on the wavelength, the angle of incidence, the type of metal, and the metal thickness. These properties have been exploited to improve the performance of planar metal mirror microcavities. We model substantial alteration of peak emission wavelength and linewidth with mirror thickness. This allows the tuning of the cavity resonance wavelength by variation of metal mirror thickness. The dependence of the phase change on wavelength and angle of incidence can also be used to suppress the angular dependence of the cavity resonance wavelength. These effects are observed in silver-mirrored cavities containing the polymers poly(p-phenylene vinylene), (PPV), and a cyano-substituted derivative of PPV, MEH-CN-PPV.
Optical-absorption spectra associated with shallow donor impurities in spherical infinite-well GaAs quantum dots
Authors: Silva-Valencia J. , Porras-Montenegro N.
Published: July 2002

The optical-absorption spectra associated with transitions between the n=1 valence level and the donor-impurity band has been calculated for spherical GaAs quantum dots with infinite potential confinement, using a variational procedure within the effective-mass approximation. We show results either for one impurity and for a homogeneous distribution of impurities inside of the quantum dot. The interaction between the impurities has been neglected. The main features found in the theoretical spectra were an absorption edge associated with transitions involving impurities at the center and a peak related to impurities at the edge of the dot. For all sizes of the quantum dot the peak associated with impurities located next to the edge always governs the total absorption probability. The results are compared with previous results in quantum wells and quantum-well wires of comparable dimensions.
Studies of deposition order anomaly of exchange coupling in bilayers and trilayers of NiFe and CoO
Authors: Ambrose T. , Leifer K. , Hemker K. J. , Chien C. L.
Published: July 2002

The temperature dependence of the exchange field and coercivity and the effect of deposition order have been studied in a series of bilayer (NiFe/CoO and CoO/NiFe) and trilayer (NiFe/CoO/NiFe) films. A profound difference in the exchange field temperature behavior was observed in samples with NiFe deposited on top of CoO compared to samples with CoO deposited on top of NiFe. When CoO is on top of NiFe, the exchange field follows a linear temperature dependence, while for samples with NiFe on top of CoO, the exchange field has a plateau followed by a rapid decrease. These distinct temperature dependences are reproduced in the NiFe/CoO/NiFe trilayer which contains both geometries. Transmission electron microscopy has been employed to study the interface between the NiFe and CoO layers.
Thickness dependence of auto oscillations in circular yttrium-iron-garnet films
Authors: Piskun N. Y. , Peterman D. W. , Wigen P. E.
Published: July 2002

Using high-power ferromagnetic resonance the dependence of the auto-oscillation frequency has been investigated as a function of the thickness of thin circular yttrium-iron-garnet films. For thicknesses over the range from 0.5 to 1.4 μm, the auto-oscillation frequencies are found to be directly proportional to the thickness of the films, even though the linewidth remains nearly unchanged over this range. These results indicate that the auto-oscillation frequency is determined by a magnetostatic mode spacing. The experimental results are compared with numerical calculations, based on a microscopic Hamiltonian and show good agreement (within 10% for first finger) with the experimental data.
Magnetic field dependence of the Curie–Weiss paramagnetism in CrV alloys
Authors: de Oliveira A. J. A. , Ortiz W. A. , Lima O. F. de , Camargo P. C. de
Published: July 2002

The determination of the magnetic properties of antiferromagnetic Cr alloys requires careful consideration of the influence of the applied magnetic field. In this work we show that alloys of Cr-x at. % V present a Curie–Weiss paramagnetism above the Néel temperature, which is suppressed by a characteristic field HL. Samples with x=0.1, 0.2, and 0.4 were investigated through measurements of the magnetic susceptibility as a function of temperature, for different values of the magnetic field. A magnetic phase diagram showing the characteristic line HL vs x at. % V is proposed.
Effects of composition control on crystallographic and magnetic characteristics of Ba ferrite films sputtered with the mixture of Xe, Kr, Ar, and O2 for recording media
Authors: Noma K. , Matsushita N. , Nakagawa S. , Naoe M.
Published: July 2002

Ba ferrite/ZnO bilayered films were deposited by plasma-free sputtering method using the mixture of Xe, Kr, Ar, and O2 as sputtering gas. The discrepancy in the film composition and changes in crystallographic and magnetic characteristics corresponding to the partial gas pressure and gas species were investigated in detail. The plasma diagnosis implied that the severe bombardment of recoiled Ar atoms and energetic sputtered particles to the surface of the film and the selective resputtering of Ba atoms were suppressed by adding Xe into sputtering gas. Ba ferrite films with excellent characteristics were deposited using the mixture of Ar, Xe, and O2 as sputtering gas when the sticking coefficient of Ba atoms on the film surface took the maximum value, while the bombardment to the film surface was negligible and the film composition was almost stoichiometric. On the other hand, although the substitution of Kr for Ar is effective for suppressing the bombardment to the surface, the energy of the arriving Ba and Fe atoms reduced and it caused the smaller sticking coefficient of Ba atom and the worse characteristics.
Effect of neutron irradiation on magnetic properties in the low alloy Ni-Mo steel SA508-3
Authors: Park D. G. , Kim C. G. , Kim H. C. , Hong J. H. , Kim I. S.
Published: July 2002

The B-H hysteresis loop and Barkhausen noise have been measured in the neutron irradiated SA508 steel of 45 μm thickness. The coercive force of B-H loop showed a slow change up to a neutron dose of 1014 n/cm2 and increased by 15.4% for a 1016 n/cm2 dose sample compared with that of the unirradiated one, related to the domain wall motion hindered by the increased defects. However, the amplitude of Barkhausen noise reflecting the wall motion decreased slowly up to 1014 n/cm2 irradiation, followed by a rapid decrease of 37.5% at 1016 n/cm2.
Magnetic structure and superconductivity in (HoxY1−x)Ni2B2C
Authors: Müller K.-H. , Kreyssig A. , Handstein A. , Fuchs G. , Ritter C. , Loewenhaupt M.
Published: July 2002

The superconducting transition and the magnetic structure of polycrystalline (HoxY1−x)Ni2B2C have been investigated for x⩾0.75 by resistivity measurements and neutron diffraction, respectively. For HoNi2B2C, the well known antiferromagnetic structure with c- and a-axis components existing between 4.5 and 6 K has been confirmed. Whereas for all investigated samples the component having the a-axis modulated structure exists in a narrow temperature range only, the intensity connected to the spiral magnetic state along the c-axis increases for x=0.85 and x=0.75 monotonically as the temperature decreases to the lowest measuring temperature of 1.6 K. Our results strongly suggest that the incommensurate modulated structure along the a-axis is responsible for pair breaking in the investigated (HoxY1−x)Ni2B2C samples. On the other hand, the magnetic spiral structure with c-axis wave vector was found to coexist with superconductivity. A linear suppression of the superconducting transition temperature with increasing Ho content was observed which is in agreement with the Abrikosov–Gor’kov theory. We found a linear scaling with the effective de Gennes factors (x DG) (Ho) for both the superconducting transition and the magnetic ordering temperatures.
Fabrication and characterization of Ba1−xKxBiO3/Nb-doped SrTiO3 all-oxide-type Schottky junctions
Authors: Suzuki Seiji , Yamamoto Tetsuya , Suzuki Hiroshi , Kawaguchi Kenichi , Takahashi Kazuhiko , Yoshisato Yorinobu
Published: July 2002

A reproducible process for fabricating Ba1−xKxBiO3/Nb-doped SrTiO3 (BKBO/STNO) all-oxide-type Schottky junctions has been established, and the electrical properties of the junctions have been investigated at room temperature. Improving the STNO surface conditions by high-temperature oxygen-annealing made it possible to fabricate junctions with good rectification properties. The current–voltage characteristics of the junctions were explained by conventional thermionic emission theory. Anomalous capacitance–voltage characteristics of the junctions were observed and were analyzed with a model taking into account the electric-field-dependent permittivity of STNO and the presence of the interfacial layer. The potential barrier profile of the BKBO/STNO interface was calculated and it can be concluded that this model quantitatively explains the capacitance–voltage characteristics.
Specific Fe site moment enhancement in Y2Fe17 upon N insertion
Authors: Zhang Y. D. , Shen N. X. , Budnick J. I. , Hines W. A.
Published: July 2002

In order to gain information concerning the separate effects of lattice expansion and Fe–N chemical bonding on the Fe moment for each individual Fe site in R2Fe17Nx systems (R=rare earth), x-ray diffraction, magnetization, and 57Fe nuclear magnetic resonance experiments were carried out on rhombohedral Y2Fe17Nx with N content 0⩽x⩽2.8. The increase of the average 57Fe hyperfine field (HF) from the unnitrided to the nitrided phase follows the increase in the saturation magnetization, providing evidence that the 57Fe HF does scale with the Fe moment in this system. The changes of the 57Fe HF are not the same for the various Fe sites; e.g., the HF at the 18f site, which has one N atom as a nearest neighbor, has much less enhancement than that at the 9d site, which has no N atoms as a nearest neighbor. More significantly, for the Fe 6c site, the HF does not change at all with nitrogen content. These results are analyzed in conjunction with existing neutron diffraction data regarding the Fe–Fe distance variations upon nitrogenation and yield a very consistent picture.
Nonreciprocal differential detection method for scanning Kerr-effect microscopy
Authors: Silva T. J. , Kos A. B.
Published: July 2002

We describe an optical detection scheme for scanning Kerr-effect microscopy (SKEM) which does not require modification of the magnetic state of a sample for domain observation. The scheme exploits the nonreciprocal nature of the magneto-optic Kerr effect (MOKE) to distinguish polarization rotation due to sample magnetization from other spurious sources, such as sample roughness and birefringence of the microscope optics. We present SKEM images of domain structures in lithographically patterned Ni81Fe19 elements which demonstrate the imaging capabilities of the new detection scheme for materials with typical MOKE magnitudes.
Magnetic properties and giant magnetoresistance of Fe/Au multilayers
Authors: Honda S. , Koguma K. , Nawate M. , Sakamoto I.
Published: July 2002

Magnetic properties and magnetoresistance (MR) are examined for the Fe/Au multilayers (MLs) prepared on glass substrates by electron-beam evaporation techniques as a function of the thicknesses of Fe and Au layers; dFe and dAu. For small dFe, the perpendicular magnetic anisotropy is induced, and in the films of dFe≈5 Å, the stripe magnetic domain patterns are observed. In dFe⩽3 Å, however, a superparamagnetic nature and a granular-type giant magnetoresistance (GMR) appear at room temperature. In a series of [Fe(3 Å)/Au(dAu)]40 MLs, the MR ratio increases with dAu and reaches the first peak at around 10 Å. On the other hand, at 14 K, the ferromagnetic component having a perpendicular anisotropy becomes dominant, and the GMR arises from the random wall alignment due to the antiferromagnetic coupling between the adjacent Fe layers, causing the first MR peak at dAu≈10 Å. The layered structure is obscured and the superparamagnetic Fe grains are created by annealing at 300–350 °C, followed by the crystalline growth upon annealing at temperatures above 350 °C. These variations in the film morphology cause the changes in the saturation magnetization and the MR ratio.
Fracture initiation at sharp notches in single crystal silicon
Authors: Suwito Wan , Dunn Martin L. , Cunningham Shawn J.
Published: July 2002

In the context of linear anisotropic elasticity, a universal singular stress field may exist in the region surrounding a sharp reentrant corner (notch). In general, both the radial and tangential variation of the stress fields differ for mode I (symmetric) and mode II (antisymmetric) deformations, and for general anisotropy the mode I and II deformations are coupled. A failure criterion based on critical values of the stress intensities may be appropriate in situations where the region around the corner dominated by the singular fields is large compared to the size of intrinsic flaws and any inelastic zones. We determined the mode I stress fields and stress intensities for two sets of notched silicon flexure specimens using a combination of an asymptotic analysis using the Stroh formalism, dimensional considerations, and continuum finite element analysis. We carried out a companion experimental study to assess the suitability of a critical stress intensity failure criterion. Specifically, assuming such a criterion is valid, we extracted critical values of the mode I stress intensities for a series of notched silicon flexure specimens with notch angles of 70.53° and 125.26°. The specimens were fabricated by anisotropic etching of silicon wafers in KOH, resulting in notch angles of 70.53° between (111) and (1̄1̄1) planes and 125.26° between (111) and (100) planes. The data show that good failure correlation is obtained through the use of a single parameter, the critical mode I stress intensity.
Frequency characteristics of the magnetic spatial solitons on the surface of an antiferromagnet
Authors: Wang Qi , Awai Ikuo
Published: July 2002

The frequency characteristics of magnetic spatial solitons on the surface of two-sublattice uniaxial antiferromagnetic crystal have been studied. The distinguishing feature of the solitons is the existence of the frequency passband(s) and stopband(s) that can be switched into each other by varying the power. This is because the nonlinear permeability is not only power dependent but also frequency dependent in infrared frequency region. The passband width may increase sharply with the power when the dielectric constant of the antiferromagnetic crystal is smaller than that of the nonmagnetic substrate. The passband may vary as much as 100 GHz below the infrared resonance frequency of the system.
Diffusion of gold in silicon during rapid thermal annealing: Effectiveness of the surface as a sink for self-interstitials
Authors: Lerch W. , Stolwijk N. A.
Published: July 2002

Rapid thermal annealing was used for short-time diffusion experiments of gold in dislocation-free floating-zone silicon of {100} orientation at 1050 °C and 1119 °C. Concentration-depth profiles measured by the spreading-resistance technique are well described within the framework of the kick-out mechanism involving generation of silicon self-interstitials. More specifically, the gold-incorporation rate appears to be controlled by the outdiffusion of excess self-interstitials towards the surfaces. As a special feature, the measurements reveal a continuous increase of the gold boundary concentration which approaches the pertaining solubility limit only after prolonged annealing. This can be interpreted in terms of a limited effectiveness of gold-alloyed {100} silicon surfaces as sinks for self-interstitials. The validity of this interpretation is supported by computer modeling of the experimental data yielding finite values for the self-interstitial surface-annihilation velocity.
Conduction and low-frequency noise in high temperature processed polycrystalline silicon thin film transistors
Authors: Dimitriadis C. A. , Brini J. , Kamarinos G. , Gueorguiev V. K. , Ivanov Tz. E.
Published: July 2002

The performance of n- and p-channel high-temperature processed polycrystalline silicon thin-film transistors (polysilicon TFTs) has been investigated by conduction and low-frequency noise measurements. The polysilicon films were doped by boron or phosphorus ion implantation at concentrations of about 6×1016 and 3×1017 cm−3, respectively, and hydrogenated by ion implantation of hydrogen. Undoped and nonhydrogenated polysilicon films were also used for comparison. Channel length reduction due to dopant diffusion from the source and drain contacts was found to affect the transistor conduction and its associated noise. Low-frequency noise measurements indicate that the noise power spectral density of the drain current is mainly due to carrier number with correlated mobility fluctuation. The experimental data reveal the presence of exponential band tails in both n- and p-channel hydrogenated undoped polysilicon TFTs. In nonhydrogenated boron doped n-channel devices, high density of band tails and deep levels are present. Hydrogenation removes the deep levels and passivates significantly the band tails. In both hydrogenated and nonhydrogenated phosphorus doped p-channel devices, the density of traps is very high resulting in pinning of the Fermi level. The results indicate the necessity for improvement of the doping technology.
Flexural plate wave resonator excited with Lorentz forces
Authors: Martin S. J. , Butler M. A. , Spates J. J. , Mitchell M. A. , Schubert W. K.
Published: July 2002

A flexural plate wave resonator was constructed by patterning current lines on a silicon nitride membrane suspended on a rectangular silicon frame. Eigenmodes of the rectangular membrane were excited using Lorentz forces generated between alternating surface currents and a static in-plane magnetic field. Preferential coupling to a particular membrane mode was achieved by positioning current lines along longitudinal mode antinodes. An equivalent-circuit model was derived which characterizes the input impedance of a one-port device and the transmission response of a two-port device over a range of frequencies near a single membrane resonance. Experiments were performed to characterize the device’s response to changes in dc magnetic field strength, ambient gas composition, gas pressure, and input power.
Structural and electronic transport properties of polycrystalline p-type CoSb3
Authors: Anno H. , Hatada K. , Shimizu H. , Matsubara K. , Notohara Y. , Sakakibara T. , Tashiro H. , Motoya K.
Published: July 2002

The structural and electronic transport properties of polycrystalline p-type CoSb3 with different grain sizes (about 3 and 3×102 μm) were investigated. The magnetic susceptibility was also measured. Samples were characterized by x-ray diffractometry, electron-probe microanalysis, and optical microscope observation. Samples were found to be stoichiometric and homogeneous. The Hall carrier concentration of the samples is of the order of 1018 cm−3 and weakly dependent on the temperature. The temperature dependence of the Hall mobility suggests that the predominant scattering mechanism drastically changes depending on grain size: for large grain size a combination of the neutral impurity scattering and the acoustic phonon scattering, and for small grain size the ionized impurity scattering. The magnetic susceptibility was found to be essentially diamagnetic independently of grain size, and to vary slightly with temperature. The weak temperature dependence of the susceptibility can be explained by taking into account the three contributions of ion cores, conduction electrons, and trace amounts of magnetic impurities. From the analysis of the susceptibility due to conduction electrons, the band gap energy was determined to be about 70–80 meV, consistent with a recent band structure calculation. Although the effects of nonmagnetic impurity phases segregated (Sb, etc.) on the scattering mechanism are not clear, the grain size is one of the key factors determining the transport properties of polycrystalline CoSb3.
Effect of microstructure on excitonic luminescence of spontaneously ordered Ga0.52In0.48P alloys
Authors: Cheong Hyeonsik M. , Mascarenhas A. , Ahrenkiel S. P. , Jones K. M. , Geisz J. F. , Olson J. M.
Published: July 2002

We compare the results of low-temperature (4.2 K) microphotoluminescence (PL) measurements on cleaved edges of spontaneously ordered GaInP2 alloy samples with the results of cross-section transmission electron microscopy (TEM). The TEM dark-field images show that the size of ordered domains grows as the deposition progresses. The excitonic luminescence peak in the micro-PL spectra of GaInP2 is stronger near the surface of the thin film than near the substrate. From these results, we conclude that there is a direct correlation between the domain size or alternatively, the density of domain boundaries, and the relative strength of the excitonic peak.
Fabrication of YBa2Cu3O7−δ/SrTiO3/La0.7Sr0.3MnO3−δ junctions for the control of supercurrent by spin-polarized quasiparticle current injection
Authors: Stroud R. M. , Kim J. , Eddy C. R. , Chrisey D. B. , Horwitz J. S. , Koller D. , Osofsky M. S. , Soulen R. J. , Auyeung R. C. Y.
Published: July 2002

Supercurrent suppression by the injection of spin-polarized quasiparticle current from a ferromagnet into a superconductor is demonstrated in YBa2Cu3O7−δ/SrTiO3/La0.7Sr0.3MnO3−δ junctions at 77 K. Negative current gains as large as 35 have been observed. The magnitude of the effect depends on the net polarization of the injection current, film resistivities, barrier microstructure, and injection geometry. Fabrication of the junctions is discussed in terms of optimizing these parameters for maximum supercurrent suppression.
Frequency versus Lyapunov exponent map: A new approach to investigate dynamics of nonlinear magnetic systems
Authors: Piskun N. Y. , Wigen P. E.
Published: July 2002

The complex Lyapunov exponent λ plays a vital role in characterizing the dynamics of a physical system. The real part of λ has frequently been related to as just the Lyapunov exponent and has been used for decades to characterize the stability of the system. The imaginary part or the frequency of oscillations can also give valid information about the dynamics of the system, particularly how it behaves near the equilibrium points. In this article we will show that the frequency versus Lyapunov exponent map can give additional information about the very nature of the system and provide background for detailed analysis concerning the applicability of the control technique and its robust nature. As an example of the applicability of the map, an appropriate model to investigate the origin and growth of the auto-oscillations are the circular YIG films. Starting with the low power ferromagnetic resonance spectrum and analyzing the behavior as a function of power the creation and evolution of “shoots” in the map have been demonstrated. The resulting map gives new insights about the relationship between the underlying dynamics of the system and the “growth” of the shoots into auto-oscillation fingers. This approach can explain many features of the auto-oscillation behavior and gives new insights into investigating techniques to control and synchronize chaos as well as to explain desynchronization bursts.
Magnetic force microscopy image restoration technique for removing tip dependence
Authors: Zhu Jian-Gang , Lin Xiangdong , Shi Rick C. , Luo Yansheng
Published: July 2002

Quantitative interpretation of a magnetic force microscopy (MFM) image usually requires detailed knowledge of the magnetization configuration of the sensing tip. Here, we demonstrated a technique that converts the obtained raw MFM image into the magnetic pole density distribution without explicitly knowing the tip magnetization orientation. By creating an approximate point source of magnetic poles in the same sample imaged, the impulse response function of the MFM tip is obtained for deconvolution of a raw image in the Fourier space. Experimental demonstrations with various tip magnetization orientations were performed on recorded magnetic transitions in a thin film longitudinal medium.
Optical properties of PrAg under pressure
Authors: De Molly , Sinharoy P. K. , De S. K.
Published: July 2002

We present interband optical conductivity and oscillator strength calculations of PrAg within the linear muffin-tin orbital formalism in the atomic sphere approximation. We have compared the optical spectra for both the ferromagnetic and paramagnetic phases at normal pressure and found that exchange interaction has considerable influence on its optical properties, thereby ascertaining the ferromagnetic nature of PrAg. The oscillator strength or the transition probability plays a vital role in determining the magnitude and position of the peaks in the optical spectrum. Application of pressure decreases the optical conductivity at 0.4 Ryd but the crucial peak at around 0.04 Ryd is displaced to 0.08 Ryd with reduced magnitude.