bluuebunny/crossref_metadata_2025 huggingface dataset:
Rugate filter design: An analytical approach using uniform WKB solutions
Authors: Perelman N. , Averbukh I.
Published: July 2002

An analytical approach to the design of rugate filters with a smooth amplitude modulation of the sine-wave index is developed. The approach is based on the uniform WKB solutions (asymptotic expansions) of the coupled-wave equations. A closed-form solution for the inverse problem (finding the refractive index profile for a given reflectance shape inside the stop band) is found.
Two-wave and induced three-wave mixing in thin holograms
Authors: Petrov M. P. , Petrov V. M. , Raptis Y. S. , Xu L. P. , Anastassakis E.
Published: July 2002

The results of investigations of two- and three-wave mixing in thin holograms are presented. A spatial light modulator fabricated from a Bi12SiO20 (or BSO) crystal was used as a photosensitive medium for holographic recording. It was found experimentally that mixing can take place between higher-order diffracted beams, a phenomenon which uniquely characterizes thin holograms. The necessary theoretical analysis underlying the wave mixing for two specific orientations of the BSO crystal has been developed. We have found qualitative agreement between theory and experiments and concluded that the modulator can be used as an efficient medium for adaptive interferometric techniques.
Measurement of rotational and vibrational relaxation in gases by photoacoustic resonance: Application to SF6
Authors: Lei G. , Di Bartolo B.
Published: July 2002

The photoacoustic resonance method has been applied to study molecular relaxation in a cylindrical cavity. The profile of the acoustic resonance, excited by the vibrational mode υ3 of gas sample SF6 with a CO2 laser, was measured as a function of pressure between 1 and 800 Torr. A general theoretical treatment of vibrational and rotational relaxation on the acoustically resonant characteristics, such as the resonant frequency and the broadening of half-width, taking into account the contributions of surface and volume losses, and the nonideality of gas, was worked out in detail and was used to frame the discussion of the relaxation processes following the vibrational excitation. The analysis of the experimental data yields a value of vibrational relaxation time (pτ)V-T=0.21±0.01 μs atm, and a value of (pτ)R-T=0.09±0.06 ns atm for the rotational relaxation time of SF6 at T=295 K.
Determination of Mn composition in Zn1−xMnxSe from Faraday rotation analysis
Authors: Zheng Yu-Xiang , Chen Liang-Yao , Zhou Shi-Ming , Wang Ya-Dong , Wang Yu , Qian You-Hua , Wang Jie , Jin Cai-Xia , Wang Xun
Published: July 2002

In Zn1−xMnxSe, Mn2+ d→d* transitions were found to induce giant Faraday rotation, and peaks of the Faraday rotation spectra were red-shifted linearly with increasing Mn composition. Through studying the magneto-optical transition variation with Mn composition, the Mn composition can be determined. Results from the Faraday rotation analysis were compared with the x-ray diffraction data and were found in good agreement with each other.
Hybrid pole pieces for permanent magnets
Authors: Abele M. G. , Jensen J. H.
Published: July 2002

Highly uniform magnetic fields for nuclear-magnetic-resonance imaging require accurate design of the pole pieces of a permanent magnet structure. We present a mathematical theory of pole pieces viewed as filters that eliminate selected harmonics of an expansion of the field distortion. Previous work has discussed two types of filters: active pole pieces and passive pole pieces. These are reviewed and a third type of filter, the hybrid pole piece, is introduced. The hybrid pole piece provides distinct advantages by combining features of both active and passive pole pieces.
Automized magnetic hysteresis measurement system
Authors: Disselnkötter Rolf
Published: July 2002

Modeling and design of magnetic components require primary data on material hysteresis properties. In this article a flexible and highly automized system is described, which is suited for the characterization of the low frequency soft magnetic behavior (≊5 Hz–2 kHz) of ferromagnetic samples. The apparatus consists of a PC with the control program, a modular data acquisition/signal generation system, and a remotely controllable power amplifier to which the sample is connected. Integration of the secondary output voltage is performed digitally. The system operates in current control mode, and the user can select from a variety of adjustable excitation functions and even complex measurement procedures. It is possible to perform stationary or transient measurements of major and minor loops, initial magnetization and commutation curves, to do automatic demagnetization, and to output specific parameters which are necessary for sample characterization or model calibration. Amplitude selection and autoscaling of the measurement sensitivity can proceed within wide dynamic ranges. Sample, signal parameter, output, and characteristic data can be printed or plotted, edited, saved, reloaded, or changed in format. A number of different options for measurement and postprocessing are available. Instead of B(H) also M(H) or μ (H) curves or time signals can be displayed. Future software versions will also support the voltage control mode (which is already provided in the amplifier), and the measurement of the anhysteretic curve. A selection of example measurements obtained for two samples and with different types of excitation signals indicates the suitability of the system for various applications.
Effect of preparation technique on the structural and magnetic properties of granular Fe-SiO2 (abstract)
Authors: Christodoulides J. A. , Shevchenko N. B. , Murthy A. S. , Hadjipanayis G. C.
Published: July 2002

Previous studies have shown that large coercivities, exceeding 2 kOe, can be obtained in Fe-based ceramic granular films. The coercivities were also found to be sensitive to the type of matrix material used, being higher in the SiO2 matrix. In this study the hysteresis behavior of FeX(SiO2)1−X granular films was studied as a function of the preparation technique. The films were prepared by dc magnetron sputtering over the composition range of xv=0.1–0.9 volume fraction of Fe. Tandem deposition both with and without titanium sublimation, and deposition from a composite target were used in preparing the films, which resulted in different oxygen environments. Coercivity measurements were found to be strongly composition dependent, with maximum values up to 700 Oe at xv≊0.5 of Fe, for all sets of samples. Typical granular structure was observed, with grain size in the range of 5–20 nm, with the smaller size obtained from composite targets. X-ray diffraction and selected area diffraction showed a structure of a-Fe (bcc). Thermomagnetic curves showed a peak which can be associated with the onset of superparamagnetism. By varying the deposition method and the oxygen environment, we were able to switch from a relatively magnetically hard sample (Hc∼500 Oe) to a soft sample (Hc∼20 Oe). Mossbauer data are being analyzed to determine the presence of any oxides, their magnetic state and their effect on hysteresis.
Cavity length dependence of the peak conversion efficiency in AlGaAs lasers
Authors: Sánchez M. , Camps I. , González J. C. , Díaz P. , Prutskij T. A.
Published: July 2002

The dependence of the peak power conversion efficiency ηcpeak on the cavity length and lasing wavelength is theoretically and experimentally analyzed for straight separate confinement heterostructures AlGaAs lasers with an active layer thickness of 30 nm. A simple model that considers the dependence on cavity length of different diode parameters was used for theoretical estimations. The internal quantum efficiency is considered cavity-length dependent. It was found that the optimum cavity length which maximizes the power conversion efficiency depends upon the laser emission wavelength.
Radiation from a dielectric disk near a lossy dielectric plane
Authors: McCall S. L. , Lanzerotti L. D. , Yurke B. , Pargellis A. N.
Published: July 2002

We calculate how the radiation pattern, the quality factor Q, and the resonant frequency of a dielectric disk resonator are altered from that of free space when the resonator is brought in close proximity to a lossy dielectric plane. The calculations are compared with measurements performed at frequencies near 10.4 GHz on a sapphire disk resonator that is within a wavelength of a copper backplane. As the resonator approaches the backplane, the resonant frequency increases and the radiated power is suppressed, enhancing the Q of the resonance by a factor Qe. Experimentally, the Q of the resonator is enhanced by an optimum value of 4.5 when the midplane of the disk is about 0.5 cm above the copper backplane. Here the resonant frequency is shifted to 10.45 GHz.
High temperature annealing effects on the electrical characteristics of C implanted Si
Authors: Lombardo S. , Cacciato A. , Larsen K. Kyllesbech , Raineri V. , La Via F. , Privitera V. , Campisano S. U.
Published: July 2002

We have investigated the electrical characteristics of p+–n Si junction diodes implanted with 300 keV C ions at fluences of 0.5 and 1×1015 cm−2 and annealed at 900 or 1100 °C. In all cases cross-sectional transmission electron microscopy shows an excellent crystalline quality, with no extended defects, and the C-rich region is characterized by an n-type doping. In the material annealed at 900 °C the C-rich region shows a low electron mobility and the presence of deep donor levels, and, as a consequence, the diode characteristics are nonideal. These effects can be attributed to the formation of C–Si self-interstitial-type complexes after the 900 °C anneal. At 1100 °C part of the C–Si complexes dissolve and the electrical characteristics of the materials noticeably improve.
High-dose phenomena in zinc-implanted silicon crystals
Authors: Simov S. , Kalitzova M. , Karpuzov D. , Yankov R. , Angelov Ch. , Faure J. , Bonhomme P. , Balossier G.
Published: July 2002

The structure of (100) silicon implanted with Zn+ ions at an energy of 50 keV was studied. The ion doses were varied from 1×1015 to 1×1017 cm−2 and the beam current density was 10 μA cm−2. The analytical techniques employed for sample characterization included cross-sectional transmission electron microscopy and x-ray energy dispersion analysis. The energy deposition of the ion beam was calculated by using computer simulation codes. For the two lower doses of 1×1015 and 1×1016 a crystalline-to-amorphous transformation was observed in the implanted layer and this was correlated with the thermal history of the implants and the attendant changes in morphology. In contrast, an amorphous-to-crystalline transition was found to occur at higher doses, namely 5×1016 and 1×1017, where the formation of a complex, structured layer consisting of an amorphous phase mixed with crystalline grains of Zn and partly recrystallized Si was identified together with other specific structural features. Detailed characterization of the resulting microstructures was carried out taking into account the effects of sample heating, ion-beam-induced amorphization, crystallization, and sputtering.
Phase evolution in low-pressure Se vapor selenization of evaporated Cu/In bilayer precursors
Authors: Lakshmikumar S. T. , Rastogi A. C.
Published: July 2002

Evolution of elemental binaries and single-phase copper indium diselenide, CuInSe2 (CIS) during Se vapor selenization of evaporated Cu/In bilayer metal precursors at pressures of 0.3–10 mbar and temperatures in the range of 260–400 °C has been investigated. At low pressures, the relative kinetics of selenization of Cu and In are changed resulting in the formation of single-phase CIS even at very low temperatures (260 °C). Optical, Auger, and x-ray photoelectron spectroscopy investigations are employed to characterize the chalcopyrite absorber layer. At higher pressures (≊7–10 mbar), simultaneous formation of the equilibrium binaries, CuSe and In2Se3 at low temperatures leads to the formation of CIS through a diffusion limited reaction of the binaries at higher temperatures. The availability of Se reacting species varies significantly in the pressure regime. At low reactor pressures and Se availability, the reaction CuSe+In(l)+Se→CIS, proceeds to completion even at low temperatures. The detailed study of the phase evolution is made by x-ray diffraction and scanning electron microscopy investigations and correlated with the Se availability in the reactor.
Excess carrier lifetime and ambipolar diffusion anisotropy in a nipi-doped In0.2Ga0.8As/GaAs multiple-quantum-well structure
Authors: Lin H. T. , Rich D. H. , Larsson A.
Published: July 2002

The effects of strain-induced structural defects in a nipi-doped In0.2Ga0.8As/GaAs multiple-quantum well sample were studied with time-resolved electron-beam-induced absorption modulation, in which carrier recombination lifetimes and ambipolar diffusion constants are measured with high spatial, spectral, and temporal resolution. Based on a phenomenological model, carrier lifetimes in the limit of weak excitation at room temperature were determined. The lifetime is found to be reduced by a factor of ∼1013 compared to a theoretically calculated value, owing to the presence of strain-induced defects and alternate recombination channels. By using a two-dimensional diffusion model, the ambipolar diffusion coefficients Da along high-symmetry [110], [11̄0], and [100] directions were determined and resulted in an anisotropic behavior such that D[110]a≳D[11̄0]a ≳D[100]a. The anisotropy in diffusion is attributed to corresponding asymmetries in the misfit dislocation density.
Crystallization of sputtered amorphous oxide films
Authors: Gu B. X. , Zhang S. Y. , Zhang H. Y. , Zhu X. B. , Zhai H. R.
Published: July 2002

Amorphous oxide films with a composition of Bi2DyFe5O12 have been prepared by rf sputtering technique. The crystallization process was investigated using x-ray diffraction, differential thermal analysis, magnetic properties, magnetic resonance spectra, magneto-optical Faraday spectra, Raman spectra, and infrared reflection spectra. Amorphous oxide films exhibit very small magnetization and Faraday rotation at room temperature. At about 600 °C amorphous films crystallize to a garnet phase. With crystallization the magnetization and Faraday rotation increase rapidly. Raman and infrared spectra studies show the presence of tetrahedral sites in the amorphous films. As the annealing temperature increases, the peaks corresponding to octahedral and dodecahedral sites occur successively. It is of interest to note that amorphous oxide films containing Fe3+ ions show no magnetic resonance spectra at 71 and 300 K. The films annealed above crystallization temperature show a normal resonance spectrum. With increasing annealing temperature the linewidth decreases rapidly and the effective magnetization and anisotropy constant increase.
The vector magnetic field dependence of the magnetic moment of particulate recording media
Authors: Hsu Shau-Wei
Published: July 2002

The magnetic moment for a γ-Fe2O3:Co recording media was measured as functions of strength and direction of applied field. Fourier expansions on the component of magnetic moment along the applied field direction (mx) to the rotation angle (θ) show that the zeroth, first, and second order coefficients are related to the reversible part, remanent part, and irreversible susceptibility, respectively. The calculated effective angle between the magnetic moment and the applied field (α) consistently equals zero at θ≂134° and θ≂304° for the decreasing- and increasing-field measurements, respectively. The (θ-α) vs θ curves correspond to those predicted by the texture model.
Wannier–Stark localization in a strained-layer InxGa1−xAs/InyGa1−yP superlattice
Authors: Kim J. W. , Lee Y. J. , Vogt T. J. , Patrizi G. A. , Robinson G. Y. , Lile D. L.
Published: July 2002

We present an observation of the Wannier–Stark effect in a strained InGaAs/InGaP superlattice grown on a GaAs substrate. A blueshift of the effective absorption edge is observed in room and low-temperature photocurrent and transmission measurements. A ∼2000 cm−1 absorption change due to the transition of the absorption edge from a broad to a sharp quantum well-like excitonic shape was obtained for as little as a 2 V change in bias voltage.
Fe adsorption and film growth on GaAs(001) (2×4)-As (abstract)
Authors: Kneedler E. , Thibado P. M. , Jonker B. T. , Bennett B. R. , Whitman L. J. , Shanabrook B. V. , Krebs J. J.
Published: July 2002

We have examined the initial interface formation and subsequent film growth for Fe films on the As-terminated (2×4) reconstructed surface of GaAs(001) in an effort to correlate the initial adsorption sites and film growth with the magnetic anisotropy. The growth and surface studies were performed in a four chamber ultrahigh vacuum system which incorporates UHV sample transfer between the chambers for III–V semiconductor growth, metal growth, photoelectron diffraction (PED), and scanning tunneling microscopy (STM). After coating with a thin film of Au (40 Å) at room temperature, the samples were removed from the system for postgrowth characterization, which included ferromagnetic resonance and magnetometry. The GaAs(001) surface was prepared via homoepitaxial growth by MBE, with the growth terminated in a manner which resulted in a well-ordered As-dimer terminated (2×4) reconstructed surface as revealed by reflection high energy electron diffraction and STM. Fe deposition was performed in a second MBE chamber for coverages which ranged from 0.1 ML to several tens of monolayers at a substrate temperature of 175 °C.

The sample was then transferred under UHV to either the PED or STM chamber to determine the initial adsorption sites, growth mode, and evolution of film structure with increasing coverage. For the lowest coverages studied (0.1 ML), we obtain evidence for preferential adsorption at As-dimer sites. At a coverage of 1 ML, two-dimensional islands form approximately 20 Å in size, but elongated along the missing dimer rows with an aspect ratio of 2:1. At high coverages (≳40 Å), we observe three-dimensional mounds or clusters with an average in-plane diameter of approximately 100 Å and a narrow size distribution. Even at this coverage, the monolayer terraces of the GaAs substrate are clearly visible in the STM image, with the Fe film uniformly growing on each terrace. Photoelectron diffraction in the forward scattering regime (high electron kinetic energy) is utilized to determined the growth mode. At low kinetic energy, information on the adsorption site is obtained from Auger electron diffraction and compared with the results of the real space STM images.
Magnetic properties and Pd–H miscibility gap in Ni/Pd composite fine particles
Authors: Manago Takashi , Otani Yoshichika , Miyajima Hideki , Akiba Etsuo
Published: July 2002

The magnetic and structural properties of Ni fine particles coated with Pd were investigated in hydrogen atmospheres by means of in situ magnetometry and in situ x-ray diffractometry. The x-ray diffraction patterns in hydrogen atmospheres show that the width of the plateau in the Pd–H phase boundary (miscibility gap) narrows with decreasing Pd thickness, which is reminiscent of nano-crystalline Pd. At room temperature, the magnetization in hydrogen atmospheres shows a steep saturation and a small decrease in the residual magnetization, indicating that the interface magnetic anisotropy is reduced by the hydrogenation.
High field irreversibility in NiFe2O4 nanoparticles (abstract)
Authors: Kodama R. H. , Berkowitz A. E. , McNiff E. J. , Foner S.
Published: July 2002

Several anomalous magnetic properties of organic coated NiFe2O4 nanoparticles have been reported previously by Berkowitz et al. These properties included low magnetization with a large differential susceptibility at high fields, shifted hysteresis loops after field cooling below 50 K, and Mössbauer spectra indicating a fraction of the material being magnetically ordered but not responsive to applied fields. It was suggested that a ‘‘strongly anisotropic phase’’ was present on the particles surface, and that the organic coating was responsible for producing high local anisotropy fields on the surface atoms. The present study extends the original work in several ways. We find that the lack of saturation in high fields is accompanied by irreversibility up to 20 T, in some cases. We have confirmed the previously reported behavior, in addition to observing similar behavior in samples prepared without the organic surfactant. This implies that we are observing a finite size effect. We have recently reported time dependence of the remanent magnetization which persists down to 0.4 K and does not appear to follow a thermally activated law. Instead, the viscosity becomes temperature independent below 2 K. The model we propose for the high field irreversibility as well as the previously reported behaviors, is that there is a layer of spins at the surface which are spin glass-like, and that these spins can be reoriented irreversibly by a field or by thermal activation. The effect of surface spin interactions on magnetization relaxation will be discussed.
Structural and magnetocrystalline anisotropy contributions to the blocking temperatures of NixCo(1−x)O exchange couples (abstract)
Authors: Takano Kentaro , Berkowitz Ami E. , Cao Wei , Thomas Gareth
Published: July 2002

The simple spin and crystal structure of the antiferromagnetic (AF) monoxide NixCo1−xO facilitates structural characterization and modeling of its magnetic properties NixCo1−xO is also receiving technological attention for biasing magnetoresistive sensors as a robust alternative to FeMn. In this work, we studied the thickness dependence of the AF layer on the exchange field created through interfacial exchange coupling between NixCo1−xO and Ni81Fe19 films. The NixCo(1−x)O films were reactively sputtered on silicon substrates and capped with a 300 Å Ni81Fe19 layer. An additional silver layer was deposited as an oxidation barrier. An exchange field was observed on all the exchange couples with the NixCo(1−x)O thickness ranging from 25 to 1000 Å. The exchange couples were characterized using transmission electron microscopy (TEM) to yield information on the orientation, structure, and size of the crystallites. The films were polycrystalline with columnar grains. For oxide thicknesses below 300 Å, the film was randomly oriented but developed a texture with a preferred orientation for thicker films. We found that the blocking temperature, at which the exchange field goes to zero, decreases with decreasing oxide thickness. The blocking temperature is relatively thickness independent for higher thicknesses but decreases rapdily below a certain thickness. The decrease in the blocking temperature does not appear to be consistent with a finite size scaling law. Instead we modeled this behavior to take into account the temperature dependence associated with the changing microstructure of the AF layer with thickness, in particular the size of the crystallites.

In thick oxide films, the blocking temperature corresponds to the AF ordering temperature, the Néel temperature. The decrease of the blocking temperature below the Néel temperature suggests at the competing magnetic and thermal energies necessary for exhibiting unidirectional anisotropy. The thickness sensitivity of the blocking temperatures of the AF monoxides are found to be strongly dependent on their magnetocrystalline anisotropy.
Thickness dependence of effective magnetic anisotropy
Authors: Chang Ching-Ray
Published: July 2002

Taking into account the occurrence probability of holes and imperfections we derive the nonlinear thickness dependence of the product Kt in very thin films. We predict both the usual 1/t and the recently observed 1/t2 dependence of the effective magnetic anisotropy K from the stochastic model. Agreement between theory and published experimental data is very good.
Magneto-optical investigation of the fcc–bcc phase transition of Fe wedges sandwiched between CuNi alloys (abstract)
Authors: Theuss H. , Weller D. , Carl A.
Published: July 2002

We report a systematic investigation of the fcc–bcc structural phase transition of thin Fe films sandwiched between CuNi alloys. The structures were of the type substrate/20 nm Pt/10 nm CuNi/0–2 nm Fe wedge/1 nm CuNi/2 nm Pt. All films were deposited in high vacuum by electron beam evaporation at temperatures ranging from 400 °C (Pt seed layer) to 100 °C (CuNi alloy layers and Fe wedge) to 20 °C (Pt cap layer). The CuNi composition ratio was varied in 10 at. % steps in order to vary its lattice constant from a=0.3607 nm (Cu) to 0.3517 (Ni) nm, which encompasses the value of gamma Fe (fcc low spin state). X-ray diffraction measurements reveal strong (111) texturing with an alignment of the Pt 〈111〉 axis better than 5 deg (rocking curve width) of the completed structures. Kerr loops in fields ±18 kOe were recorded as function of the Fe-wedge position with a spatial resolution of about 0.8 mm, corresponding to 0.1 nm Fe thickness resolution. These hysteresis loops reveal the saturation Kerr angle (0.1 mdeg resolution), the saturation field (anisotropy field) and a paramagnetic slope, which are all analyzed as function of the Fe thickness and the CuNi composition. Clear evidence for the formation of paramagnetic Fe is found for Cu-rich CuNi alloys, where a Kerr rotation below the resolution limit of our apparatus extends up to ≳2 nm Fe thickness. The transition thickness from fcc to bcc Fe, as characterized by the onset of a linear uptake of the Kerr rotation, shows a pronounced maximum near about 25 at. % Ni, indicating that a small compression of the Fe lattice constant (about −2%) leads to the nonferromagnetic fcc Fe state. A similar study, using CuAu alloys with the aim of characterizing the high spin ferromagnetic fcc Fe phase, is in progress.
On the conduction band polarization in metallic systems with a periodic array of localized magnetic moments
Authors: Hernando A. , Rojo J. M. , Gómez Sal J. C. , Novo J. M.
Published: July 2002

It is shown that the indirect exchange between magnetic moments distributed in a periodic array and carried out through the conduction band results from the balance of a ferromagnetic component, static effect, and an antiferromagnetic one, polarization effect. The sign of the coupling mainly depends on the density of states at the Fermi level. For filled bands only the antiferromagnetic component exists (metallic superexchange) and, in particular, only for free electrons both components exactly compensate to each other, remaining the typical Ruderman–Kittel–Kasuya–Yosida ripple due to the oscillating character of the polarization.
Goldstone modes of incommensurate chromium alloys
Authors: Fishman R. S. , Liu S. H.
Published: July 2002

The spin excitations about the two incommensurate wavevectors of the spin-density-wave (SDW) state in Cr are studied for the first time within the random-phase approximation. Transverse spin-wave (SW) modes and longitudinal phason modes are associated with the rotational and translational symmetries of Cr. While both mode frequencies vanish at the SDW ordering wavevectors, only the SW mode with linear dispersion and mode velocity c=vF/√3 is undamped for nonzero frequencies. As in a local-moment system, the SW mode corresponds to the rigid rotation of the local magnetic moments. The phason modes have a nearly linear dispersion at low frequencies with velocity cph<c. As T approaches TN, cph approaches c. Phason modes have been observed in the longitudinally polarized SDW state below 120 K in pure Cr and are responsible for a 60 meV peak in the cross sections midway between the satellites.
Formation of Nd(Fe1−yCoy)2 in rapidly quenched Nd13.75(Fe1−xCox)80.25B6 (x=0−0.5) alloys
Authors: Girt Er. , Koknaeva M. , Altounian Z.
Published: July 2002

X-ray diffraction patterns of overquenched Nd13.75(Fe1−xCox)80.25B6 (x=0−0.5) ribbons show fine grains of the 2–14–1 phase in an amorphous matrix. The ribbons, subsequently annealed at 975 K for 5 min, were investigated using quantitative x-ray structural analysis. The results indicate that in addition to the main 2–14–1 phase, all the samples have approximately 1 vol % of the γ-Nd phase. The existence of the Nd(Fe1−yCoy)2 phase is established for x≥0.25 and its amount reaches up to 5.4 vol % for higher Co concentrations. From an interpolation of the measured lattice parameters of the 1–2 phase, the Co content is estimated to vary from y=0.38 to y=0.58 for this series of alloys. Using differential scanning calorimetry (DSC) the enthalpy of formation of the 1–2 phase in overquenched Nd13.75(Fe0.7Co0.3)80.25B6 ribbons is found to be about 3 kJ/mol. The activation energy necessary for the formation of the 1–2 phase, for the same composition, as determined from the Kissinger relation is 2.2±0.1 eV.
Hard and soft magnetic properties of nanocrystalline Fe–Nd–Zr–B alloys containing intergranular amorphous phase (abstract)
Authors: Inoue A. , Kojima A. , Takeuchi A. , Masumoto T. , Makino A.
Published: July 2002

The nanoscale crystalline and amorphous phases obtained by partial crystallization of an amorphous phase in rapidly solidified Fe90Nd7−xZrxB3 alloys were found to exhibit rather good hard magnetic properties in the composition range below 3 at. % Zr and good soft magnetic properties in the range above 4 at. % Zr. The hard magnetic alloys consist of nanoscale bcc–Fe and bct–Fe14Nd2B particles surrounded by the remaining amorphous phase, while the soft magnetic alloys are composed of bcc–Fe and remaining amorphous phases. The particle size is measured to be about 20 nm for the bcc–Fe phase and 15 nm for the Fe14Nd2B phase for a the former alloys and about 10 nm for the bcc–Fe phase for the latter alloys. The volume fraction of the remaining amorphous phase is evaluated to be about 20 to 30 at. % and the Nd and Zr contents are much higher than the nominal concentrations for the hard and soft magnetic alloys from the high-resolution TEM images and nanobeam compositional analyses. The remanence (Br), intrinsic coercivity (iHc), and maximum energy product are 1.24 T, 200 kA/m, and 88 kJ/m3, respectively, for the nanocrystalline Fe90Nd5Zr2B3 alloy annealed for 180 s at 1023 K, while the saturation magnetization (Bs), coercivity (Hc), and permeability at 1 kHz are 1.63 T, 16 A/m, and 7000, respectively, for the nanocrystalline Fe90Nd2Zr5B3 alloy annealed for 180 s at 923 K.

The high Br and Bs values are presumably due to the magnetic coupling between bcc–Fe particles via the ferromagnetic intergranular amorphous phase and the large iHc for the alloy containing more than 4 at. % Nd is due to the exchange magnetic interaction betweeen Fe14Nd2B particles via ferromagnetic bcc–Fe and amorphous phases. The appearance of the rather good hard and soft magnetic properties for the same alloy series containing the high Fe content is extremely important for future development of manocrystalline hard and soft magnetic materials.
A metallurgical approach toward alloying in rare earth permanent magnet systems (abstract)
Authors: Branagan D. J. , Dennis K. W. , Kramer M. J. , McCallum R. W.
Published: July 2002

In bulk permanent magnets, the extrinsic properties relating to the microstructure determined the level of hard magnetic properties that is actually achieved. Many researchers have worked on the microstructure property relationships in the Nd2Fe14B (2-14-1) system but, in general, the approach has been to analyze the microstructure of materials which have been shown to have good magnetic properties rather than to study the effect of alloy additions on the metallurgical properties of the system. The microstructure which is obtained under a given set of processing conditions is highly dependent on the solidification behavior of the alloy, as well as grain growth phenomena. Alloy additions which effect the solidification behavior of the melt and then form precipitates which pin grain boundaries, and therefore control grain size, should be valuable in producing the uniform microstructure required for good magnetic properties. A number of refractory metal carbides perform both of these functions. The carbides have a reasonable degree of solubility in the 2-14-1 melt and, under conditions of reasonable rapid solidification, a degree of metastable solubility in the 2-14-1 phase. However, there is very limited equilibrium solid solubility in the 2-14-1 phase so that the intrinsic magnetic properties are not effected. The addition of these materials to 2-14-1 results in a factor or three reduction of the quench rate required to produce amorphous material. In addition, the crystallization temperature of the glass is enhanced leading to enhance nucleation and finer grain size during crystallization. Finally refractory metal carbide precipitates decorate the grain boundaries of the crystallized material inhibiting grain growth. Transition metal carbide formation, solid and liquid solubility, effects on solidification, nucleation, and grain growth will be discussed.
Iron particle surface chemistry and corrosion protection by amine-quinone polyurethanes
Authors: Chacko Antony P. , Nikles David E.
Published: July 2002

The ability of amine-quinone polyurethanes to protect iron particles from corrosion was shown to depend on the polymer composition and on the particle surface chemistry. The amine-quinone polyurethanes were prepared from 2,5-bis(N-2-hydroxyethyl-N-methylamino)-1,4-benzoquinone (AQM-1), tolylene diisocyante and polytetrahydrofuran diol (average molecular weight 650). The AQM-1 content was varied from 20 to 40 wt % (AQPU-15); the polymer with 40 wt % AQM-1 had the highest affinity for the iron surface and showed the best corrosion protection. AQPU-15 had a higher affinity for the commercial iron particle having a aluminum-rich surface, than for a commercial particle having a silicon-rich surface. Tape samples containing AQPU-15 and the particles having the Al-rich surface showed excellent corrosion resistance, maintaining 98% of the initial saturation magnetization after 48 h exposure to pH 2 aqueous buffer. Samples containing AQPU-15 and the particles having the Si-rich surface completely corroded after 2 h exposure. The presence of aluminum on the iron surface served to enhance the adsorption of AQPU-15 and improve the corrosion resistance.
Spin-dependent tunneling effect and GMR in metal–nonmetal granular systems (invited) (abstract)
Authors: Fujimori H. , Mitani S. , Ohnuma S.
Published: July 2002

Giant magnetoresistance (GMR, large negative and isotropic magnetoresistance) arising from a spin-dependent tunneling effect has been found in metal–nonmetal granular systems exhibiting extremely high electrical resistivities. These granular materials are reactively sputtered Co–(Al, Si)–O and Fe–Mg–O thin films, having a two phase nanostructure consisting of the Co (or Fe) rich metallic and magnetic grains and the Al (or Si,Mg) oxide narrow intergrains. These films possess large specific electrical resistivities(ρ0) of 104–106 μΩ cm at room temperature, and show remarkable magnetoresistance (Δρ/ρ0) whose values are about 8% in maximum at room temperature and at about 10 kOe of applied magnetic field. With decreasing temperature, Δρ/ρ0 and ρ0 increase. The temperature dependence of ρ0 can be expressed in terms of log ρ0∝T−1.2, and the electrical current versus applied electrical voltage does not follow the ohmic low. We consider that a spin- dependent tunneling conductance in the path of magnetic grains–nonmetallic intergrains–magnetic grains is responsible for the observed GMRs accompanying high electrical resistivities. The details of these transport properties and the related magnetization and structural properties will be presented.
Magnetization, magnetoresistance, and x-ray diffraction measurements of discontinuous [Ni80Fe20/Ag] multilayers (abstract)
Authors: Lorenz T. , Moske M. , Käufler A. , Geisler H. , Samwer K.
Published: July 2002

Thin films for magnetic sensor application require a high sensitivity at low magnetic fields, for example, realized by Permalloy films. Promising candidates for a further improvement are discontinuous multilayers, first reported by Hylton et al. In our study, we report on [2.5 nm Ni80Fe20/y nm Ag] multilayers with the spacer layer thickness y ranging from 1.2 nm to 6.0 nm. The multilayers were electron beam deposited in UHV at different temperatures. The substrates used are thermally oxidized silicon wafers. The magnetization is obtained using a vibrating sample magnetometer (VSM), the magnetoresistance is measured at room temperature with the Montgomery method. Low and high angle x-ray diffraction measurements are performed in a Siemens D-5000 diffractometer. The samples are annealed ex situ between room temperature and 340 °C. The magnetoresistance is maximal after annealing the samples at a specific temperature, which decreases with increasing Ag-spacer thickness y. Moreover, the GMR decreases if the multilayers are deposited at elevated temperatures (100–200 °C). We also report on the dependence of the GMR on the interface roughness (σ≊0.5 nm rms) which we deduce from the small angle x-ray diffraction measurements. For a characterization of the reliability, we also investigated the dependence of the GMR on aging at 100 °C for several hours.
Spin polarized neutron scattering study of NiCo/Cu multilayers
Authors: Mao Ming , Nguyen S. H. , Gaulin B. D. , Tun Z. , Bian X. , Altounian Z. , Ström-Olsen J. O.
Published: July 2002

Spin polarized neutron reflectometry measurements were performed on Ni80Co20/Cu multilayers with a Cu spacer thickness of 20 Å, corresponding to the second oscillation peak in the magnetoresistance of the NiCo/Cu multilayer system. Measurements in a 15 Oe field indicate a nearly perfect antiferromagnetic stacking of the magnetic moments in successive Ni80Co20 layers. The existence of a small magnetic anisotropy in these magnetically soft multilayers leads to the canting of the magnetic moments at an angle of ∼70° with respect to the neutron spin polarization. This interlayer antiferromagnetic coupling can be suppressed by an applied field of ∼200 Oe.
Structural, field, and temperature dependence of noncollinear magnetic coupling in Fe/Cr(001) superlattices (abstract)
Authors: Ankner J. F. , Kaiser H. , Hamacher K. , Schreyer A. , Zeidler Th. , Zabel H. , Majkrzak C. F. , Schäfer M. , Grünberg P.
Published: July 2002

Utilizing the magneto-optic Kerr effect (MOKE) in conjunction with x-ray and neutron reflectometry (NR) and diffraction, we have studied the magnetic coupling of Fe/Cr(001) superlattices grown at room temperature and 250 °C. Only the samples grown at elevated temperature exhibit noncollinear coupling of 5.0 nm Fe layers across 1.7 nm Cr interlayers. The noncollinear samples feature a less-disordered in-plane interfacial structure than those grown at room temperature. Using x-ray diffuse reflectivity, we have measured a length scale of 10 nm for these in-plane features. We have also observed, via NR, a remanent noncollinear coupling angle of 50° and, via MOKE and NR, a gradual approach to saturation at upwards of 7 kOe. These features can be explained qualitatively by the proximity magnetism model of Slonczewski. We will compare the predictions of both the proximity and bilinear/biquadratic models with our data and present the results of ongoing neutron measurements of the temperature dependence of the coupling.
Propagation and reflection properties of magnetoelastic wave in FeSiB amorphous wire
Authors: Takemura Y. , Masuda S. , Yamada T. , Kakuno K.
Published: July 2002

Propagation and reflection properties of magnetoelastic waves in Fe77.5Si7.5B15 amorphous wires are studied. The attenuation constant increases with increasing the driving frequency of the wave. As the attenuation constant of the wave driving at 500 kHz is quite small (0.18 m−1), the wave is expected to be observed after the propagation of 20 or 30 m. As for the reflection, the magnetoelastic wave is reflected with the efficiency as much as 0.9 at the driving frequency below 2 MHz using a clamp as reflector.
Magnetostriction of a superconductor: Results from the critical-state model
Authors: Koziol Z. , Dunlap R. A.
Published: July 2002

In many cases, the critical-state theory can be treated as a sufficiently accurate approximation for the modeling of the magnetic properties of superconductors. In the present work, the magnetostrictive hysteresis is computed for a quite general case of the modified Kim–Anderson model. The results obtained reproduce many features of the giant magnetostriction (butterfly-shaped curves) reported in the literature for measurements made on single-crystal samples of the high-temperature superconductor Bi2Sr2CaCu2O8. It is shown that the addition of a contribution to the magnetostriction in the superconducting state which is of similar origin as in the normal state, offers a broader phenomenological interpretation of the complex magnetostriction hysteresis found in such heavy-fermion compounds as UPt3, URu2Si2, or UBe13.
Nonlinear flux diffusion and ac susceptibility of superconductors: Exact numerical results
Authors: Koziol/ Z. , Dunlap R. A.
Published: July 2002

The ac response of a slab of material with electrodynamic characteristics E∼jκ+1, κ≥0, is studied numerically. From the solutions of the nonlinear diffusion equation, the fundamental and higher-order components of the harmonic susceptibility are obtained. A large portion of the data for every κ can be scaled by a single parameter, ξ≡t1/(κ+2). Hκ/(κ+2)0/D, where t is the period of the ac field at the surface, H0 is its amplitude, and D is the slab thickness. This is, however, only an approximate scaling property: The field penetration into a nonlinear medium is a more complex phenomenon than in the linear case. In particular, the susceptibility values are not uniquely defined by a set of only two parameters, such as κ and ξ, while one parameter, i.e., t1/2/D, is sufficient to describe the electrodynamic response of a linear medium.
An application of the wavelets to the magnetic field source searching
Authors: Doi T. , Yoshida S. , Nakaya Y. , Hayano S. , Saito Y.
Published: July 2002

Recently, the wavelet analysis is being applied to the various fields, such as image data compression in informatics and spectrum analysis of the electrocardiogram. In the present article, we propose the two approaches, employing the wavelet analysis for the human heart diagnosis. One is the data base approach, and the other is an inverse approach searching for the magnetic field source of the human heart. The data base approach is an application of the data compression to the magnetocardiogram. Also, the magnetic field source searching is an application of the spectrum analysis to the magnetocardiogram. The results reveal that the data base approach makes it possible to identify the normal or abnormal heart, and the magnetic field source search is capable of estimating the current distribution of a distinct heart.
Anomalous low dimensional system: Study of magnetism and electrical conductivity in Na2Ru4O9−δ
Authors: Cao G. , McCall S. , Freibert F. , Shepard M. , Henning P. , Crow J. E.
Published: July 2002

The magnetic susceptibility χ∥(H∥b), χ⊥(H⊥b) (2≤T≤700 K) and electrical resistivity ρ(T) (2≤T≤300 K) of single crystal Na2Ru4O9−δ (δ≥0) with various oxygen content were measured. The crystal structure of this compound is monoclinic with single, double, and triple chains along the b axis. The most striking feature of this compound is the drastically large anisotropy reflected in the resistivity which exhibits metallic behavior along chains and semiconducting behavior perpendicular to the chains. The resistivity ratio for these two directions (ρ⊥/ρ∥) is larger than 105. This ratio is exceptionally large, indicating that the anisotropy of the bandwidth is substantial. It is remarkable that, after reduction of oxygen content in the system, the magnetic susceptibility undergoes a drastic change, whereas the electrical resistivity along the conducting chains is altered only slightly. It is argued that the different sensitivity to oxygen content reflected in magnetic and transport properties may be attributed to the complexity of the crystal structure. The striking observations presented here may suggest a one-dimensional system that possesses unique physical properties.
Effect of nucleating layers on the soft magnetic properties of multilayer permalloy films
Authors: Grimes Craig A.
Published: July 2002

The effects of different undercoats and silicon nitride nucleating layers on the coercive force, anisotropy field, and 5 to 100 MHz complex permeability spectra of magnetically soft, Ni81Fe19 multilayer thin films sputtered onto flexible, 52-μm-thick polyethylene terephthalate substrate for use as identification markers or electromagnetic interference shields is reported. In comparison to films deposited directly onto the substrate, nonmagnetic undercoat layers, including aluminum, copper, silicon, and silicon nitride, are found to increase the soft magnetic properties of subsequently deposited films. Nucleating layer effects are dependent upon the undercoat/nucleating layer combination.
Optical injection effects and all-optical set-reset operations in two-segment strained multiquantum-well distributed feedback bistable lasers
Authors: Zhou J. , Cada M. , Li G. P. , Makino T.
Published: July 2002

Optical injection effects and all-optical set-reset operations in two-segment strained multiquantum-well (MQW) distributed feedback (DFB) bistable lasers were experimentally investigated. The optical bistable characteristics under detuned optical injection, of strained MQW DFB bistable lasers, show the effect of the residual Fabry–Perot side modes of the DFB structures; optimizing the input wavelength and the input power is suggested for applications. The switching properties of dynamic optical set-reset operations with pulsed optical injection were reported, which appear to be related to the optical bistable characteristics under cw optical injection; however, the switching transients are found to be essential to full understanding of these switching properties.
Ferromagnetism of deuterides YFe2Dx (abstract)
Authors: Kanematsu K. , Ohkubo N. , Itoh K. , Ban S. , Miyajima T. , Yamaguchi Y.
Published: July 2002

Cubic Laves phase alloy YFe2 forms four types of hydrides, YFe2Hx: β1, β2 (hexagonal) of 1.2<x<1.6, γ (hexagonal) of 2.8<x<3.45, and δ (orthorhombic) of 3.7<x. The β1 and β2 hydrides are formed in the hydrogen absorption below and above 500 K. The deuterides YFe2Dx have been prepared by deuterium absorption at various temperatures for YFe2 powders of diameters less than 0.3 mm. The formed samples are mixtures of main and extra deuteride phases. The x-ray and magnetization measurements in a magnetic field of 10.6 kOe showed five types of ferromagnetic deuterides with Curie temperatures of about 100 K (δ1), 300 K (δ2), 380 K (γ), 300–380 K (β1), and 540 K (amorphous). The extrapolated values of magnetization at 0 K are 3.5μB/YFe2Dx. The crystal structures are as follows: δ1, hexagonal, a=0.57 nm, c=2.74 nm; δ2, cubic, a=0.79 nm; γ, hexagonal, a=0.56 nm, c=2.63 nm; and β, hexagonal (a=0.53 nm, c=0.87 nm)–(a=0.51 nm, c=0.82 nm).