bluuebunny/crossref_metadata_2025 huggingface dataset:
Very thin barium ferrite particles prepared by a novel technique: Ion exchange resin method
Authors: Zhong Wei , Ding Weiping , Jiang Yumei , Wang Liang , Zhang Ning , Zhang Shiyuan , Du Youwei , Yan Qijie
Published: July 2002

Very thin hexagonal barium ferrite particles have been prepared by a new method—ion exchange resin method. The exchanged resin when heated to 850 °C, transformed to the hexagonal ferrite BaFe12O19 as confirmed by x-ray diffraction. These particles show single-domain behavior with average diameter D̄=220 nm, average aspect ratio D̄/t̄=13, specific magnetization σ=71 emu/g and coercivity Hc=3800 Oe.
Visualization and switching of the local insulator–metal transition in Pr0.7Ca0.3MnO3
Authors: Fiebig M. , Miyano K. , Tomioka Y. , Tokura Y.
Published: July 2002

Optical spectroscopy and topography techniques were used to study the photoinduced insulator–metal transition in the “colossal magnetoresistance” compound Pr0.7Ca0.3MnO3. The transition is shown to generate a well-localized conducting path while the bulk of the sample remains insulating. A change of reflectivity with a characteristic spectral dependence allows for its visualization. A two-stage mechanism is proposed for the local phase transition. Switching experiments with two competing paths are discussed.
Concurrent Nd and Mn spin excitations in Nd0.6Sr0.4MnO3
Authors: Kaiser H. , Stumpe L. E. , Rhyne J .J. , Tokura Y. , Kuwahara H.
Published: July 2002

The spin dynamics of Nd0.6Sr0.4MnO3 have been determined along [qqq], [qq0], and [00q] propagation directions using inelastic neutron scattering. At T=13 K, the low-q Mn–Mn mode energies varied quadratically with wave vector q, but exhibited marked softening on approach to the zone boundaries when compared with a Heisenberg nearest-neighbor exchange calculation. At the larger q’s the modes also show evidence of increasing spin wave energy width. The temperature dependence of the spin wave stiffness parameter D was measured up to Tc=273 K and showed conventional behavior. The 0 K value of D=150 meV Å2 yields D(0)/kTc=6.3. No anomalous E=0 central mode intensity was observed on approach to Tc. At low T additional modes were observed and are ascribed to Nd–Mn exchange interactions. These modes have q=0 spin wave gap of 2.1 meV compared to 1.1 meV for the Mn–Mn excitations.
Magnetic properties of bulk Eu2/3Ca1/3MnO3
Authors: Oliver F. W. , Seifu D. , Hoffman E. , Williams C. , Kannan E. , Hallen B. , Hinmon C. , Kebede A. , Kutz M. , Tessema G.
Published: July 2002

The magnetic and structural properties of the bulk manganite Eu2/3Ca1/3MnO3 are characterized using Mössbauer spectroscopy, magnetization measurements, x-ray diffraction, and resistivity measurements. Here it is demonstrated that one can investigate the magnetic properties of manganites using Mössbauer spectroscopy by doping with europium at the rare earth site and using rays from Eu151 as a probe. Mössbauer measurements were performed at several temperatures between 15 and 293 K using a Eu151 source. The spectrum at room temperature is a single line demonstrating paramagnetism with an isomer shift of 0.60±0.02 mm/s. Measurements at room temperature show the Eu to be trivalent and single phase with a linewidth of 2.933±0.004 mm/s, which is comparable to that found for the Mössbauer standard EuF3. Measurements below 100 K show a much broader linewidth which at 15 K is more than twice that found at 293 K and is associated with a magnetic phase transition. Magnetization as a function of magnetic field measurements up to 5 T show the system to be paramagnetic at 300 K and ferromagnetic-like at 50 K. Magnetic susceptibility measurements made between 300 and 4.2 K show the sample to be paramagnetic down to 100 K, where it undergoes a magnetic phase transition. Mössbauer, resistivity, and magnetic measurements all indicate a change in the paramagnetic state around 230 K.
Spin dynamic effects on the resistivity and the magnetoresistance of a La1.85Sr0.15(Cu1−xLix)O4 system with 0.0⩽x⩽0.15
Authors: Garcı́a S. , Musa J. E. , Baggio-Saitovitch E. M.
Published: July 2002

The interplay between hole doping, spin fluctuations, and unusual normal-state properties in layered cuprates is relevant for the physics of high temperature superconductors. For better understanding of the role of magnetic interactions on the conduction mechanism, a systematic study of the normal-state resistivity ρ(x,T) of the La1.85Sr0.15(Cu1−xLix)O4 system with 0.0⩽x⩽0.15 was performed down to 4.2 K. A logarithmic contribution was found to properly describe the ρ(x,T) deviation from linearity as Tc is approached. Scattering of the carriers by spin fluctuations at the Cu–O2 conduction planes is proposed to be the source of the Kondo-like behavior. Negative magnetoresistance measurements up to 8 T, with an increasing intensity with x, confirm the role of spin degrees in the resistivity behavior.
Sound absorption in metallic foams
Authors: Lu T. J. , Hess Audrey , Ashby M. F.
Published: July 2002

The sound absorption capacity of one type of aluminum alloy foams—trade name Alporas—is studied experimentally. The foam in its as-received cast form contains closed porosities, and hence does not absorb sound well. To make the foam more transparent to air motion, techniques based on either rolling or hole drilling are used. Under rolling, the faces of some of the cells break to form small sharp-edged cracks as observed from a scanning electronic microscope. These cracks become passage ways for the in-and-out movement of air particles, resulting in sound absorption improvement. The best performance is nevertheless achieved via hole drilling where nearly all of the sound can be absorbed at selected frequencies. Combining rolling with hole drilling does not appear to lend additional benefits for sound absorption. Image analysis is carried out to characterize the changes in cell morphologies due to rolling/compression, and the drop in elastic modulus due to the formation of cracks is recorded. The effects of varying the relative foam density and panel thickness on sound absorption are measured, and optimal relative density and thickness of the panel are identified. Analytical models are used to explain the measured increase in sound absorption due to rolling and/or drilling. Sound absorbed by viscous flow across small cracks appears to dominate over that dissipated via other mechanisms.
Piezoelectric and pyroelectric properties of ferroelectric Langmuir–Blodgett polymer films
Authors: Bune A. V. , Zhu Chuanxing , Ducharme Stephen , Blinov L. M. , Fridkin V. M. , Palto S. P. , Petukhova N. G. , Yudin S. G.
Published: July 2002

The piezoelectric and pyroelectric responses of ferroelectric Langmuir–Blodgett polymer films are less than the largest values measured with bulk films of the same composition. The films of the crystalline copolymer poly(vinylidene fluoride trifluoroethylene) fabricated by the Langmuir–Blodgett technique are 30 ML thick (15 nm) and are highly crystalline and oriented with polarization perpendicular to the film. Both piezoelectric and pyroelectric measurements show reversible ferroelectric switching. The films are suitable for use in pyroelectric infrared imaging and in piezoelectric acoustic transducers.
Excitonic structure and absorption coefficient measurements of ZnO single crystal epitaxial films deposited by pulsed laser deposition
Authors: Muth J. F. , Kolbas R. M. , Sharma A. K. , Oktyabrsky S. , Narayan J.
Published: July 2002

The optical properties of high quality single crystal epitaxial zinc oxide thin films grown by pulsed laser deposition on c-plane sapphire substrates were studied. It was found that annealing the films in oxygen dramatically improved the optical and electrical properties. The absorption coefficient, band gap, and exciton binding energies were determined by transmission measurements and photoluminescence. In both the annealed and the as-deposited films excitonic absorption features were observed at both room temperature and 77 K. In the annealed films the excitonic absorption peaks were substantially sharper and deep level photoluminescence was suppressed.
Flexible boundary condition for a moving dislocation
Authors: Ohsawa K. , Kuramoto E.
Published: July 2002

It is well known that a boundary condition usually affects the result of the computer simulation of defects, especially extended defects like a straight dislocation, where the model size dependence of the result is sometimes observed. In order to solve this problem, a flexible boundary condition is developed for the simulation of a moving dislocation by applying the Lagrange principle in the present study. Under the flexible boundary condition described here, various properties of a screw dislocation, i.e., stable core structure, Peierls stress and glide property, are calculated in a square lattice and the model size dependence of the result is hardly obtained over a wide range. Contrary to the present flexible boundary condition, explicit size dependence is observed in the case of a rigid boundary condition due to a strong image force from the boundary. It is observed, however, that the result tends to approach that obtained in the above flexible boundary model as the size of the model lattice increases. Unfortunately, in the case of a screw dislocation with higher Peierls stress than 10−2G, the flexible boundary condition is not available, because lattice vibrations with a high frequency are emitted from the dislocation line during glide motion and the boundary cannot respond to these waves.
Optical excitation of Er3+ ions in a-SiN alloys
Authors: Bell M. J. V. , Nunes L. A. O. , Zanatta A. R.
Published: July 2002

Photoluminescence excitation spectroscopy was carried out on the I13/24→4I15/2 transition from Er-doped amorphous silicon–nitrogen thin film alloys (a-SiN). The sample was prepared by cosputtering of a Si target partially covered with Er pellets. It is demonstrated that Er3+ ions may be excited by direct sharp-line intra-4f-shell absorption as well as by energy transfer from the a-SiN matrix. The effects of temperature and possible energy transfer mechanisms to Er ions are presented and discussed.
A transient solution of the Boltzmann equation exposes energy overshoot in semiconductor devices
Authors: Lin Chung-Kai , Goldsman Neil , Mayergoyz Isaak D. , Chang Chien-Hwa
Published: July 2002

A method is developed to analyze the transient response of semiconductor devices in phase space. This is achieved by solving the space and time dependent electron Boltzmann transport equation self-consistently with the Poisson and transient hole-current-continuity equation. The result gives the details of the time evolution of the distribution function. The method is applied to analyze a bipolar junction transistor. The model predicts the limits in which the steady-state response approximation can be applied. The model exposes a transient overshoot in the high energy tail of the distribution function.
Resistivity, thermopower and the correlation to infrared active vibrations of Mn1.56Co0.96Ni0.48O4 spinel films sputtered in an oxygen partial pressure series
Authors: Dannenberg Rand , Baliga S. , Gambino R. J. , King A. H. , Doctor A. P.
Published: July 2002

Mn 1.56 Co 0.96 Ni 0.48 O 4 spinel was sputter deposited using a series of oxygen partial pressures. Electrical resistivity versus temperature and thermopower versus temperature measurements at each oxygen partial pressure were made. The variations of the thermopower and resistivity with oxygen partial pressure are consistent with a change in the ratio of Mn3+to Mn4+ cations, which occurs due to changes of oxygen content of the material. The weak temperature dependence of the thermopower indicates small polaron hopping is the charge transport mechanism. Combining the models of Mott and Schnakenberg to analyze the transport data, we find that the Debye temperature (or frequency) is an increasing function of the oxygen partial pressure used during sputtering. The calculated shift in the Debye frequency from the resistivity is consistent with the observed shift in the fundamental infrared active lattice vibrations from Fourier transform infrared spectroscopy and Raman spectroscopy.
Electrical response during indentation of a 1-3 piezoelectric ceramic-polymer composite
Authors: Saigal A. , Giannakopoulos A. E. , Pettermann H. E. , Suresh S.
Published: July 2002

The electrical response during indentation of a piezoelectric ceramic-polymer 1-3 composite has been investigated. The current (quasistatic charge increment) induced in the indentor due to the polarized layer on the contact surface increases with load as the contact area increases. Good agreement was found between the measured currents as a function of load with those predicted using an analytical model. In addition, the current increases with increasing indentation velocity and indentor diameter. It uses known analytical results to develop a new tool for characterizing the electrical response of piezoelectric composites. As such, linear elastic indentation with simultaneous measurement of load and electric current is shown to be a new, fast, and nondestructive technique that can be used for quality assurance and to study the effect of aging and development/presence of damage/microcracking in monolithic piezoelectric and 1-3 piezoelectric composites.
Elimination of hillock formation in Al interconnects using Ni or Co
Authors: Saha S. K. , Howell R. S. , Hatalis M. K.
Published: July 2002

The effect of using bilayer Ni/Al-1%Cu or Co/Al-1%Cu metallization stacks with regard to hillock formation is investigated in this study and compared to hillock suppression capabilities of Al-1%Si and Al-1%Cu single layer films and Ti/Al-1%Cu bilayer metallization stacks. Various heat treatments during and immediately after depositions were used to study the resistances of different metallization stack specimens to hillock formation. The densities and sizes of hillocks were characterized using scanning electron microscopy and atomic force microscopy, while interfacial reactions between the transition metal layer and Al-1%Cu in the metallization stack were examined using glancing angle x-ray diffraction. Resistivities of the bilayer metallization stacks were characterized using conventional four-point probe measurements. Our studies indicate that metallization processes involving bilayer metallization stacks of nickel and cobalt with Al-1%Cu are more robust compared to those involving titanium with Al-1%Cu. The mechanism of hillock formation is analyzed in light of intermetallic compound formation and stress-strain considerations.
Ferroelectric state induced by the quasiparticle injection into a cuprate superconductor
Authors: Shafranjuk S. E.
Published: July 2002

We present a model of the N-I-S tunneling device where the frequency of the Josephson plasma mode (JPM) in the cuprate superconducting electrode S is regulated between zero and several THz by the quasiparticle injection from the normal electrode N through the barrier I. We calculate the shift δΩpl of the transverse JPM Ωpl versus the dc bias current and find the conditions when the resonance vanishes. That causes the nonequilibrium instability in respect to the transition into an electronic ferroelectric state in S.
Evidence for the stable existence of the Fe2Nd phase in the Fe–Nd system
Authors: Santos I. A. , Gama S.
Published: July 2002

We did directional solidification experiments on Fe20Nd80 alloys at several low cooling rates in order to observe the solidification sequence, displayed along the length of the sample. We also took measurements of the transition temperatures around the eutectic temperature using a Calvet type calorimeter. Our results show that the formation of the eutectic L↔(Nd)+Fe17Nd2 occurs first, and is followed by the eutectic L↔(Nd)+Fe2Nd. The calorimetric measurements give the temperature of the first eutectic to be 688 °C, the temperature of the peritectic formation of the phase Fe2Nd to be 682 °C and the temperature of its eutectoid decomposition as 659 °C. Thermomagnetic measurements give the Curie temperature of the Fe2Nd phase as 250 °C. A new phase diagram for this system is proposed.
Degradation of InGaAsP/InP-based multiquantum-well lasers
Authors: Kallstenius Thomas , Bäckström Jakob , Smith Ulf , Stoltz Björn
Published: July 2002

The formation of dark-area defects (DADs) along the active stripe in InGaAsP/InP-based buried-heterostructure multiquantum-well (BH-MQW) lasers, observed in electroluminescence and photoluminescence (PL) after degradation, is found to be related to dislocations along [011]. The fact that DADs only occurred in lasers showing an increase in threshold current of more than 30% indicates that the [011] dislocations are a consequence rather than the actual origin of the degradation. Observed jogs along a [011] dislocation imply the presence of point defects in the active stripe. The nature of these point defects is not clear, but a comparison of the results for lasers with p/n and semi-insulating current blocking singles out Zn as being a possible candidate. An observed direct proportionality between the increase in threshold current and the reduction in PL intensity is interpreted as being due to a reduction in carrier lifetime due to enhanced nonradiative recombination. A dependence of the distribution of threshold-current increase on current density during aging is explained in terms of a model, in which nonradiative defects are generated during current injection. A comparison of the degradation in MQW and in bulk lasers without an MQW structure shows the degradation characteristics to be different, although the BH structure is the same. The presence of a strained structure and/or a confinement of point defects within the MQW structure therefore seems to have a decisive influence on device reliability.
The effects of KrF pulsed laser and thermal annealing on the crystallinity and surface morphology of radiofrequency magnetron sputtered ZnS:Mn thin films deposited on Si
Authors: Mastio E. A. , Craven M. R. , Cranton W. M. , Thomas C. B. , Robino M. , Fogarassy E.
Published: July 2002

Thin films of ZnS:Mn (800 nm) have been deposited by rf magnetron sputtering onto 100 mm diam n-type single-crystal (100) Si wafers. Specifically for use as active layers in thin film electroluminescent devices, the films need a postdeposition annealing treatment to enhance their luminescent properties. Inherent to the later process step are structural modifications of the phosphor layer which form the basis of this study. Both pulsed laser and thermal postannealing techniques have been investigated. Reported are the induced crystalline and surface morphology modifications via x-ray diffraction and atomic force microscopy analysis. As-grown and thermally treated films were cubic in nature and no significant grain growth or reorientation occurred while heating up to 700 °C. Pulsed (∼ 20 ns duration) KrF laser treated samples were annealed at power densities from 10.76 to 24.27 MW/cm2 under 10.34 bar of argon pressure. Beam quality and diagnostics were emphasized during laser irradiation with particular attention brought to energy and pulse duration measurements. It has been demonstrated that at the power densities used, a gradual phase transition from cubic to hexagonal is occurring while the average crystallite size remains constant. Surface analysis highlights concomitance between the phase transition and the smoothening of the irradiated surface. A one dimensional thermal model of the pulsed laser annealing process shows that a surface temperature for crystalline ZnS equating to the transition temperature should be reached at 17 MW/cm2, significantly below the numerically evaluated melting threshold of 30.5 MW/cm2. Combining experimental and theoretical results, it is concluded that the phase transition occurs in the solid state.
Near-field optical properties of localized plasmons around lithographically designed nanostructures
Authors: Weeber Jean-Claude , Girard Christian , Krenn Joachim R. , Dereux Alain , Goudonnet Jean-Pierre
Published: July 2002

This article presents a theoretical study of the near-field optical properties of subwavelength resonant metallic particles deposited on a surface. Using the Green’s dyadic method, we derive stable solutions for both electric and magnetic fields inside and outside metallic particles of arbitrary shape. To assess the reliability of the computational scheme applied to resonant particles, we compare our data with those produced by other models. Since the Green’s dyadic method allows us to cope with particles exhibiting sharp edges such as lithographically designed nanostructures, we explore mesoscopic optical effects which are out of reach of standard computational methods.
Highly sensitive quantum well infrared photodetectors
Authors: Cwik Tom , Yeh C.
Published: July 2002

A fundamentally new method for light coupling in quantum well infrared photodetectors that provides a ten-fold improvement over an optimized grating coupler is presented. It is based on the prism-film coupler concept developed earlier for selective mode coupling into integrated optical circuits. In this article this concept is specifically used to turn the incident electric field from one that is polarized parallel to the quantum well layer to one that is mostly perpendicular to the layer, thereby increasing dramatically the sensitivity of the quantum well infrared photodetector. Detailed sample design and its computer simulation results are given and discussed.
Amorphous and microcrystalline silicon films grown at low temperatures by radio-frequency and hot-wire chemical vapor deposition
Authors: Alpuim P. , Chu V. , Conde J. P.
Published: July 2002

The effect of hydrogen dilution on the optical, transport, and structural properties of amorphous and microcrystalline silicon thin films deposited by hot-wire (HW) chemical vapor deposition and radio-frequency (rf) plasma-enhanced chemical vapor deposition using substrate temperatures (Tsub) of 100 and 25 °C is reported. Microcrystalline silicon (μc-Si:H) is obtained using HW with a large crystalline fraction and a crystallite size of ∼30 nm for hydrogen dilutions above 85% independently of Tsub. The deposition of μc-Si:H by rf, with a crystallite size of ∼8 nm, requires increasing the hydrogen dilution and shows decreasing crystalline fraction as Tsub is decreased. The photoconductivity, defect density, and structure factor of the amorphous silicon films (a-Si:H) are strongly improved by the use of hydrogen dilution in the Tsub range studied. a-Si:H films with a photoconductivity-to-dark conductivity ratio above 105, a deep defect density below 1017 cm−3, an Urbach energy below 60 meV and a structure factor below 0.1 were obtained for rf films down to 25 °C (at growth rates ∼0.1–0.4 Å/s) and for HW films down to 100 °C (at growth rates ∼10 Å/s), using the appropriate hydrogen dilution. In the low Tsub range studied, the growth mechanism, film properties, and the amorphous to microcrystalline silicon transition depend on the flux of atomic hydrogen available. The properties of the films are compared to those of samples produced at 175 and 250 °C in the same reactors.
Carrier mobility and density contributions to photoconductivity transients in polycrystalline ZnO films
Authors: Studenikin S. A. , Golego Nickolay , Cocivera Michael
Published: July 2002

Slow photoconductivity transients were comprehensively studied in ZnO films prepared by spray pyrolysis of the zinc-nitrate solution. Surface charge controlled the film conductivity, and it was possible to reversibly change the conductivity by many orders of magnitude using short-term annealing in hydrogen and oxygen. Under illumination, the conductivity of as-grown films may increase by several orders of magnitude, depending on the dark conductivity. Photoconductivity was due to the capture of nonequilibrium holes at surface oxygen states to produce an equivalent number of excess electrons in the conduction band. Reverse process of the photoconductivity relaxation is determined by an electron tunneling mechanism to the surface oxygen states.
Metal-organic chemical vapor deposition of single domain GaAs on Ge/GexSi1−x/Si and Ge substrates
Authors: Ting S. M. , Fitzgerald E. A.
Published: July 2002

The current work investigates the sublattice orientation of GaAs on (001) Ge/GexSi1−x/Si and Ge substrates offcut 6° to [110] as a function of atmospheric pressure metal-organic chemical vapor deposition (MOCVD) nucleation conditions. Anisotropic sidewall etching of the GaAs films and differential interference contrast microscopy of the GaAs film surface reveal a 90° sublattice rotation between the two possible GaAs phases. One sublattice orientation dominates at film nucleation temperatures >600 °C, another dominates at nucleation temperatures <500 °C. Incomplete transition between the two sublattice orientations during pregrowth thermal cycling accounts for the appearance of localized bands and clouded regions of antiphase disorder, marking a shift in the polarity of the GaAs film. We have concluded that the observed domain rotation results from a temperature-dependent surface transition prior to actual GaAs nucleation. In particular it is suspected that background arsenic levels in the MOCVD system induce the observed transition. We propose that localized antiphase disorder reflects kinetically limited arsenic dimer orientation on the prenucleation germanium surface. Conditions for the complete suppression of antiphase disorder under optimized growth conditions are described and demonstrated by transmission electron microscopy.
Role of the rare-earth on the electrical and magnetic properties of cobalt perovskites
Authors: Fondado A. , Mira J. , Rivas J. , Rey C. , Breijo M. P. , Señarı́s-Rodrı́guez M. A.
Published: July 2002

The magnetic and electrical properties of R1−xSrxCoO3 materials (R=La, Pr, Nd, Gd) (0⩽x⩽0.50) are studied. Rare-earths with angular momentum L≠0 enhance coercive field values. They are maximum for R=Nd (the highest L) and much smaller for Gd and La (L=0). The result is interpreted as the contribution of the L–S coupling in the rare-earth to the magnetic anisotropy of the system. Electrical conductivity is improved with Sr doping, but increases of rare-earth atomic number lead to decreases of conductivity. This is attributed to the increase of lattice distortions, due to the smaller R3+ ionic size, and to the effect of the rare-earth on the spin state of cobalt ions.
Pseudodipolar anisotropy in the square rotator model
Authors: Rastelli E. , Carbognani A. , Regina S. , Tassi A.
Published: July 2002

The effect of pseudodipolar anisotropic interactions in a square planar rotator model is investigated. The pseudodipolar anisotropy ranges from the pure dipole spin–spin interaction (η=1) that supports long range order, to the isotropic antiferromagnetic interaction (η=0) decaying as 1/r3 where r is the spin–spin distance for which no long range order exists. At zero temperature a continuous manifold of spin configurations that minimize the energy of the model is found for any η. This implies absence of long range order in the linear spin wave approximation. However order by thermal disorder is restored except for η=0 when thermal fluctuations are accounted for. A rich scenario of configurations is found at low temperature performing both analytic calculations and Monte Carlo simulations.
Magnetic orientation of collagen and bone mixture
Authors: Kotani Hiroko , Iwasaka Masakazu , Ueno Shoogo , Curtis Adam
Published: July 2002

There are no reported studies on the effects of magnetic fields on osteoblast collagen secretory processes during osteoblast differentiation. It is important to understand the effect of magnetic-field exposure on osteoblast collagen secretory processes since bone is remodeled continuously by bone-forming osteoblasts and bone-resorbing osteoclasts. We hypothesized that a mixture of collagen and osteoblasts, an adherent cell, would orient perpendicular to a magnetic field since collagen fibers are known to orient perpendicular to magnetic fields. As the osteoblasts proliferate along the collagen fibers, the magnetic orientation of the osteoblasts will change to a perpendicular direction as well. We tested this hypothesis by comparing the magnetic orientation of osteoblasts and the magnetic orientation of an osteoblast and collagen mixture after exposure to 8 T magnetic fields, which were produced by a superconducting magnet, or without exposure to magnetic fields (control). We succeeded in producing the magnetic orientation of osteoblasts without collagen after long-term exposure to magnetic fields. We observed that osteoblasts oriented parallel to the magnetic fields, but a mixture of osteoblasts and collagen oriented perpendicular to the magnetic fields. The magnetic control of osteoblast orientation will help to clarify the underlying mechanisms of osteoblast differentiation, which is important for the development of potential medical and engineering applications such as tissue repair, artificial bone development, etc.
Si
29
nuclear magnetic resonance spectra and relaxation in ε-FeSi
Authors: Corti M. , Fanciulli M. , Tabak F.
Published: July 2002

The magnetic properties of ε-FeSi are studied by Si29 nuclear magnetic resonance spectra and spin-lattice relaxation, at different magnetic fields, up to 15 T. For T⩾200 K, an asymmetric central line with a satellite-like structure is observed, having a width linearly increasing with the field and a shift proportional to the magnetic susceptibility. Below 200 K, a progressive broadening of the central line is detected on cooling, indicating an inhomogeneous distribution of local magnetization. The spin-lattice relaxation, measured across the spectrum follows a law of the form T1−1∝K2T, with K corresponding to the shift of the different isocromates. The results are discussed in the light of the spin-fluctuations theory for exchange-enhanced semiconductors.
Structure and magnetic properties of melt-spinning Pr(Fe0.6Co0.4)2 alloys
Authors: Tang S. L. , Wang D. H. , Cao Q. Q. , Jin Z. Q. , Zhang J. R. , Zhang S. Y. , Du Y. W.
Published: July 2002

Pr(Fe 0.6 Co 0.4 ) 2 ribbons were prepared by melt spinning with different wheel speeds from 35 to 45 m/s. Their structure, magnetic properties, and thermal stability are investigated. At a wheel speed of 35 m/s, the ribbon consists of a mixture of Pr(Fe,Co)2 cubic Laves phase and some noncubic phases. An almost Pr(Fe,Co)2 nanocrystalline single phase with a Curie temperature of 305 °C is obtained at a wheel speed of 40 m/s. Except for Pr(FeCo)2 phase a small amount of amorphous phase is observed with increasing wheel speeds to 45 m/s. Pr(Fe,Co)2 phase becomes unstable and decomposes above 770 °C. The resin-bonded Pr(Fe,Co)2 nanocrystalline phase which is obtained at a wheel speed of 40 m/s combines high magnetostriction (λ∥−λ⊥=140 ppm), with significant coercivity, Hci=5 kOe.
Microstructure and magnetostrictive properties of Tb–Dy–Fe (Al) alloys
Authors: Xie J. W. , Fort D. , Bi Y. J. , Abell J. S.
Published: July 2002

Well-aligned pseudosingle crystals of a series of Terfenol-D and Al-substituted alloys have been prepared using the Czochralski method, a route that has the advantage that a grain-aligned rod can be prepared in one relatively speedy operation. The effects of several factors, including pulling rate, heat treatment, and start material purity, on the magnetomechanical coupling coefficients (k33) of the samples have been investigated. The growth rates mainly influence the drive field to reach its maximum k33, while increasing the start material purity gives a 15% improvement of k33 for the Terfenol-D materials. Studies of Al substitution for Fe in Terfenol-D have also been carried out to see whether the substitution would improve the mechanical properties without significantly altering the magnetostrictive properties.
New highly oriented soft magnetic underlayer structures for perpendicular recording
Authors: Gong Heng , Lu Bin , Laughlin David E. , Lambeth David N.
Published: July 2002

Highly oriented soft underlayers with face-centered-cubic (fcc) phase Co, Co alloy, and composite NiFe/Co film structures have been epitaxially grown on single crystal Si wafers by sputter deposition. The epitaxial orientation relationships have been determined by x-ray diffraction and transmission electron microscopy. It was found that the soft underlayer magnetic properties can be modified in a wide range by fine tuning the Co alloy composition or the Co alloy thickness in a NiFe/Co structure. Ti films were sputter deposited on top of the NiFe and Co layers and epitaxial growth in both Ti(0001)/Co(111) and Ti(0001)/NiFe(111) was observed. Through this highly oriented Ti intermediate layer, a Co alloy perpendicular media layer with greatly improved hexagonal-close-packed (0001) orientation can be integrated with the highly (111) textured fcc soft magnetic underlayers.
Improvement of giant magnetoresistance performance of a metal layered structure
Authors: Małkiński Leszek M. , Wang Jian-Qing , Zhou Weilie L. , MacLaren James M. , Ross Caroline A.
Published: July 2002

A metal layered structure consisting of Cr/Cu buffer layer and two Co layers with different thickness, separated by a Cu spacer, was deposited on Si wafers using magnetron sputtering. The influence of the individual layer’s thickness on the magneto transport and magnetic hysteresis was studied. Optimization of the magnetoresistance performance was supported by the current in-plane giant magnetoresistance (GMR) modeling based on the solution to the Boltzmann transport equation. The best structures demonstrated very sharp magnetization reversal of the lower Co layer at about 100 Oe accompanied by resistivity change with a rate of 0.9%/Oe. Maximum GMR effect measured at 5 K was 9.6%. Samples with capping layers exhibited substantially smaller switching fields of the upper Co layer than the uncapped samples with a minute amount of CoO.
Imaging of sub-100-nm magnetic domains in atomically stacked Fe(001)/Au(001) multilayers
Authors: Köhler M. , Schweinböck T. , Schmidt T. , Zweck J. , Bayreuther G. , Fischer P. , Schütz G. , Eimüller T. , Guttmann P. , Schmahl G.
Published: July 2002

In order to study sub-100-nm domains in magnetic multilayers a combination of three high-resolution imaging techniques has been applied to the same samples for the first time: magnetic force microscopy (MFM), Lorentz microscopy with a transmission electron microscope, and magnetic transmission x-ray microscopy (MTXM). The samples—atomically stacked [Fe(001)/Au(001)]n multilayers with an approximate L10-lattice—were prepared by molecular beam epitaxy (MBE) on a GaAs(001) substrate which was then locally removed by laser-induced wet etching to create a window that is transparent for 200 keV electrons and soft x-rays. Magnetization curves with perpendicular and in-plane applied field indicate a spontaneous perpendicular magnetization with an equilibrium domain pattern in small fields and reversible wall motion. About 60 nm wide domains could be observed with MFM and MTXM, respectively. Lorentz images did not show any in-plane magnetic contrast, but the domain pattern appeared when the sample was tilted. This indicates that the magnetization is indeed strictly perpendicular.
New laser illumination method for Kerr microscopy
Authors: Argyle Bernell E. , McCord Jeffery G.
Published: July 2002

Many useful materials such as Permalloy exhibiting a very small magneto-optic Kerr-effect (MOKE), are in a class called weak phase objects (WPOs). Polarized light microscopy converts a WPO’s phase distribution into a viewable and recordable intensity map. Nearly crossing the polars is necessary to convert a WPO to an amplitude image. Therefore, digital image processing procedures are usually necessary to enhance MOKE images. In order to increase efficiency and throughput, three methods to increase light intensity are described and demonstrated. All three methods conduct laser light to the conventional source spot in the microscope by imaging the output face of a multimode optical fiber onto the objective’s rear focal plane. Dithering the fiber or its image more rapidly than video scan rates, average illumination nonuniformities caused by fiber modes and diminishes short-range artifacts due to laser coherence. With a third method the long-range nonuniformity is avoided by dithering the location of the fiber-face image. Time-averaged distributions of fiber-face output and corresponding patterns of illumination on the air bearing surface of a recording head, are presented together with polar Kerr contrast images as evidence of the quality, resolution, and stability of the improved method. A combination of all three methods synchronized at a multiple of the video scan rate, produced the most uniform, steady and incoherent source, making it suitable for efficient, real-time, Kerr-effect video microscopy of magnetic materials and devices.
Domain formation in Fe–N multilayers
Authors: McCord J. , Westwood J.
Published: July 2002

We prepared a series of sputtered FeN single layer films, and bilayer and multilayer films laminated with alumina, in which both the Fe–N thickness and the alumina interlayer thickness varied. The films were characterized by quantitative magneto-optical Kerr-microscopy and inductive measurements. We found a strong influence of interlayer coupling and FeN thickness on the domain formation in these layers. For single layers a transition from cross-tie walls to Bloch-type walls for increasing ferromagnetic layer thickness was observed. The multilayer films displayed a wide range of different types of coupled Neel walls depending on interlayer thickness. These include superimposed, compensated, and 360° walls. The change in domain wall structure strongly influences the coercivity of the thin film systems. The relative coupling strength between the magnetic films is calculated from the domain wall width of the superimposed Neel walls. Magnetic in-plane deviation strongly depends on the sign of magnetostriction. The observed magnetic dispersion leads to an increase in the minimum magnetic switching time. The observed micromagnetic structures result in unwanted irregular domain patterns in structured samples. Both are indicating limitations for applications in thin film recording heads.
High strength and high induction Co27–Fe–Co0.23 soft magnetic alloy for forge application
Authors: Li Lin
Published: July 2002

In magnetic bearing or flywheel technologies, there is a demand for high induction soft magnetic alloys for forged components rotating at high speed (50 000–80 000 rpm). Hiperco® Alloy 27 (Co27–Fe) is ductile and has high magnetic saturation (24 kG) but with low yield stress (35–55 ksi). This work reports a carbon strengthened Co27Fe–C0.23 alloy with high yield stress (75–85 ksi), high induction (B=20 and 21 kG at H=100 and 150 Oe, respectively), and good ductility (1 in. elongation=21%). Postforge annealing is critical to achieve desired combination of high magnetic induction, high yield stress, and good ductility.
Exchange biasing and interface structure in MnNi/Fe(Mo) bilayers
Authors: Cheng Ning , Krishnan Kannan M. , Girt E. , Farrow R. F. C. , Marks R. F. , Kellock A. , Young A. , Huan C. H. A.
Published: July 2002

The role of magnetic, structural, and chemical roughness on the origin of exchange biasing in polycrystalline Mn52Ni48/Fe92(Mo8) bilayers has been investigated by transmission x-ray magnetic circular dichroism (XMCD), vibrating sample magnetometry (VSM), and transmission electron microscopy (TEM). Three bilayer samples of MnNi(22 nm)/Fe(Mo) (6 nm) were grown by molecular beam epitaxy under ultrahigh vacuum conditions with the MnNi layer at temperatures of 200 °C, 250 °C, and 300 °C. The exchange bias, He was observed to be the largest for the 250 °C growth sample. The angular dependence of He can be well modeled in terms of a cosine series with odd terms confirming the unidirectional nature of the anisotropy energy. However, the coefficients are different for the three samples indicating different microscopic magnetic interactions at the interface. XMCD measurements showed no magnetic moment for Mn and Ni but showed systematic variations of the Fe moment, i.e., a decrease in Fe moment with increase in He was observed. We have interpreted this decrease in Fe moment in terms of antiferromagnetic (AF) ordering of Fe at the interface with the extent of the AF ordering being related to the magnitude of the exchange. Thus, for samples grown at 250 °C, it is found that at least about 4 MLs of Fe appear to be AF. Preliminary energy-filtered imaging of cross-section samples shows that the Fe layer is chemically rough suggesting that the decrease in moment may arise from the intermixing of Fe with the MnNi layer.
Improvement of giant magnetoresistance properties of CrMnPt spin valves by dc magnetron sputtering
Authors: Mao Sining , Gao Zheng
Published: July 2002

CrMnPt spin valve films with high a giant magnetoresistance (GMR) ratio of 14% were fabricated using dc magnetron sputtering. The switching field is above 700 Oe and the blocking temperature is 320 °C for a 250 Å CrMnPt pinning layer in a simple top spin valve stack. The exchange interfacial coupling constant is of 0.22 erg/cm2 which is much higher than that of the rf sputtered films. The as-made spin valve shows an abnormal resistance transition below the blocking temperature of 150 °C. The results indicate that the deposition method can influence the GMR properties greatly through the modification of the microstructure.
Interface structure and magnetic anisotropy of a Co/Pt multilayer
Authors: Chung I. B. , Koo Y. M. , Lee J. M.
Published: July 2002

A Co/Pt multilayer with strong perpendicular magnetic anisotropy was prepared by electron beam evaporation. Using polarized extended x-ray absorption fine structure (EXAFS) measurements at the Co K edge, the interface structure of the Co/Pt multilayer was investigated. In quantitative analysis, the EXAFS data measured with in-plane polarization showed considerable intermixing at the Co/Pt interfaces, while those measured with out-of-plane polarization indicated an abrupt interface structure. More detailed atomic configurations of the Co/Pt interface were simulated using the measured coordination numbers. The results of the computer simulation showed that the Pt clusters in Co layers and the Co clusters in Pt layers were interfacing. With the obtained structural information and a symmetry-based Néel model, the magnetic anisotropy of the multilayer was estimated. The estimated magnetic anisotropy was consistent with the measured one.
Design tradeoffs for beyond 20 Gb/in.2: Using a merged notched head on advanced low noise media (invited)
Authors: Madison Michael , Arnoldussen Thomas , Pinarbasi Mustafa , Parker Michael , Doerner Mary , Bhatia C. Singh , Call David , Li Jinshan , Dorius Lee , Tang Kai , Ingall Lisa , Lee Ed , Yuan Samuel , Schwenker Robert , Tabib Jila , Lauchlan Laurie , Raniseski John , Smith Robert , Hsiao Wen-Chien , Lin Tsann , Mauri D. , Zolla Howard , Marinero E. , Margulies David , Rubin Kurt , Fullerton Eric , Weller Dieter , Moser Andreas
Published: July 2002

Design considerations for areal densities beyond 20 Gb/in.2 are discussed, and in particular a demonstration at 24.8 Gb/in.2 is shown. The demonstrations used a single combined write and read head (Merge, Notched head). In this article we will discuss the tradeoffs in kilobytes per inch (KBPI) and tracks-per-inch in obtaining areal densities at 25 Gb/in.2 densities. The KBPI is limited by both the total signal-to-noise ratio and the nonlinear-transition shift. Simple estimates of the increase in channel performance from class IV partial response (PR4), extended partial response 4 (EPR4), and modified EEPR4, as well as the addition of codes which eliminate bit shift and tribit errors are discussed as large contributors to the increase in the areal density.
Spin injection and magnetoresistance in ferromagnet– superconductor–ferromagnet tunnel junctions
Authors: Takahashi S. , Imamura H. , Maekawa S.
Published: July 2002

We theoretically study the spin-dependent transport in a ferromagnet–superconductor–ferromagnet double barrier tunnel junction. The spin-polarized tunneling currents give rise to spin imbalance in the superconductor. The resulting nonequilibrium spin density suppresses the superconductivity with increase of the tunneling currents. We focus on the effect of asymmetry in the double tunnel junction, where the barrier height of the tunnel junction and the spin polarization of the ferromagnets are different, on spin injection, and discuss how the superconductivity is suppressed in the asymmetric junction. Our results explain recent experimental results on the critical current suppression in high-Tc superconductors by spin injection.
Dynamic input capacitance of single-electron transistors and the effect on charge-sensitive electrometers
Authors: Zimmerman Neil M. , Keller Mark W.
Published: July 2002

We examine the “input capacitance,” CSETT, of a single-electron tunneling (SET) transistor. We note that this quantity is crucial in quantifying the sensitivity of a SET transistor used as a charge electrometer. Further, we point out that CSETT is not the same as the “gate capacitance,” CG, usually taken to be e/ΔVG, where ΔVG is the period of the oscillation in current versus gate voltage. While CG is indeed the average value of CSETT over one period, CSETT can in fact differ substantially from that value, depending on the applied voltages. This has important consequences for maximizing the sensitivity of SET charge electrometers when a large stray capacitance is present.
Effect of heavy boron doping on the lattice strain around platelet oxide precipitates in Czochralski silicon wafers
Authors: Yonemura Mitsuharu , Sueoka Koji , Kamei Kazuhito
Published: July 2002

The effect of heavy boron doping on local lattice strain around platelet oxide precipitates in Czochralski silicon wafers was investigated quantitatively by convergent beam electron diffraction (CBED). Lightly boron doped (p−) polished wafers, including platelet precipitates with density of about 5×109/cm3 and with an edge length of about 500 nm, were prepared with an isothermal annealing at 800 °C for 700 h. Heavy boron doped (p/p+) epitaxial wafers, including an almost equal precipitate density and length to p− wafers, were also prepared with an isothermal annealing at 800 °C for 200 h. It was found by strain analysis from high-order Laue zone patterns in the CBED disk that (i) the type of lattice strain was coincident in p− and p/p+ wafers: the strain along the normal direction of the platelet precipitate was compressive, while the strain along the parallel direction of the platelet was tensile; (ii) the strain in p/p+ wafers was smaller than that in p− wafers; and (iii) the punched-out dislocations were generated by platelets only in p− wafers. The results of (ii) and (iii) indicate that the strain around the platelets is relaxed due to the heavy boron doping.