bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron swarm properties in CCl2F2 and mixtures with N2 under steady-state conditions
Authors: Fréchette M. F.
Published: July 2002

Spatial growth of ionization currents has been measured in CCl2F2/N2 mixtures by the steady-state Townsend method over the range of reduced fields 80 ≤E/p20≤180 V cm−1 Torr−1. The experimental values obtained differ markedly from those published in the literature. A detailed account of the various hypotheses used in the experiment is presented in the light of correspondence with the electron transport theory and is followed by a comparison of experimental data, i.e., limit fields (E/p20)*, ionization (α), attachment (η), and effective ionization (ᾱ) coefficients, with available theoretical values from Boltzmann-equation analysis of electron swarms in the pure gas and its mixture with N2. Good agreement with the theoretical calculations by J. P. Novak and M. F. Fréchette [J. Appl. Phys. 57, 4368 (1985)] provides further supporting evidence for the applicability of these authors’ proposed set of electron scattering cross sections and, in particular, favors the attachment cross sections reported by E. Illenberger, H.-U. Scheunemann, and H. Baumgärtel [Ber. Bunsenges. Phys. Chem. 82, 1154 (1978); Chem. Phys. 37, 21 (1979)].
Ion beam mixing of metallic and insulating layers on SiC and Si3N4
Authors: Bhattacharya R. S. , Rai A. K. , Pronko P. P.
Published: July 2002

Ion beam mixing of B, ZrO2, and Cr layers with sintered α-SiC, and Y and Cr layers with hot pressed Si3N4 was measured at room temperature. The mixing ion was selected from 1-MeV Ni+, 2-MeV Au+, or 1-MeV O+ ions. The amount of mixing was evaluated from Rutherford backscattering and Auger electron spectroscopies and occasionally from cross-section transmission electron microscopy. It was found that mixing takes place in the B/SiC, Cr/SiC, and Y/Si3N4 systems. No mixing is observed in the ZrO2/SiC and Cr/Si3N4 systems even after high dose ion bombardment. The enthalpy of mixing rule, which states that metals mix with insulators if the reaction enthalpy is negative and do not mix if it is positive, has been examined and found to hold for these systems.
Monte Carlo electron backscattering and transmission coefficients for thin aluminum and gold films
Authors: Williamson W. , Antolak A. J.
Published: July 2002

Monte Carlo calculations have been performed to calculate the electron backscattering and transmission coefficients for thin aluminum and gold films using a revised version of the photon-electron transport code sandyl. The variations in the coefficients were studied as a function of substep size for normal incidence. Backscattering coefficients for normally and obliquely incident electrons with 20-, 40-, and 60-keV energy were compared with experimental data for various film thicknesses. In most cases the agreement between theory and experiment was within 10%. The largest errors were for 20-keV electrons incident on gold where the difference was between 15% and 20%.
O2 chemical potential of nonstoichiometric ceria, CeO2−x, determined by a solid electrochemical method
Authors: Riess I. , Janczikowski H. , Nölting J.
Published: July 2002

The chemical potential of oxygen in nonstoichiometric ceria, CeO2−x, was measured versus composition x (10−4 ≤x ≤10−2) and temperature (823≤T≤1073 K) using a novel solid electrochemical cell, utilizing yttrium stabilized zirconia. The composition of CeO2−x was varied by coulometric titration. The O2 chemical potential was determined from the electromotive force of the cell with air used as the reference gas. With this new experimental setup, it is possible to carry out long coulometric titrations at very low oxygen partial pressures (limited by 10−30 atm at 823 K or by 10−13 atm at 1473 K). For x between 10−4 and 10−2, the O2 partial pressure in equilibrium with CeO2−x was found to change from 10−8 to 10−18 atm at 1073 K and from 10−16 to 10−30 atm at 823 K. The oxygen vacancies in CeO2−x were determined to be V″0 in this (x,T) range. The charge on aliovalent cations impurities was found to dominate the negative (effective) charge concentration for x≲10−3. The oxygen partial molar enthalpy ΔH̄(O2) is 870 kJ/mol (9 eV) for x≳3×10−3 decreasing for smaller x to a value of 670 kJ/mol (7 eV) for x=10−4.
Magnetization reversal in conducting ferromagnets studied by neutron depolarization in nickel
Authors: Stüsser N. , Rekveldt M. Th. , Spruijt T.
Published: July 2002

The magnetization reversal in a picture-frame single crystal of nickel with the legs parallel to the [111] crystallographic axes was studied by the time-dependent neutron depolarization technique. The observed depolarization is consistent with a magnetic reversal starting at the surface and forming a 180° domain wall boundary which moves toward the center of the specimen. From the data analysis, the wall velocity was found to be the same along the entire contour of the domain boundary. The wall velocity measured during the magnetization reversal is compared with a calculation based on eddy-current limited-domain wall motion in a ring-shaped specimen.
Amorphous carbon coating on amorphous silicon photoreceptors
Authors: Kakinuma H. , Fukuda H. , Nishikawa S. , Watanabe T. , Nihei K.
Published: July 2002

Hard hydrogenated amorphous carbon (a-C:H) films were coated on amorphous silicon photoreceptors by the plasma decomposition of acetylene (C2H2). This overlayer proved to be a much better protective layer for the adsorption of external species compared to an a-SiNx or a-Si1−xCx overcoating layer, and the image degradation induced by such adsorption was considerably reduced. The highly protective properties were attributed to the hydrophobic nature of C–Hn (n=1–3) and C–C bonds contained in the a-C:H film. The optical properties of the a-C:H films are also described.
A design criterion to ameliorate ohmic contact to n-GaAs
Authors: Gupta Ram P. , Khokle W. S.
Published: July 2002

A metal n+-n semiconductor structure is ohmic for a n+ region larger than metal semiconductor (M-S) barrier width. However, if the undepleted n+ region is too thick, the electrons tunneling across the M-S junction lose energy during transit and may not retain sufficient energy to surmount the n+-n barrier. The high–low junction thus impedes the carrier motion and adds to the contact resistance of the structure. In the present study, carrier energy loss mechanisms are considered to determine the distance hot electrons travel before losing too much energy to overcome the barrier. The results provide the optimum length of the interfacial n+ layer to ameliorate ohmic contact to n-GaAs.
Drift-diffusion model for absorption and resorption currents in polymers
Authors: Algora del Valle C. , Sancho Ruiz M. , Martínez López G.
Published: July 2002

Considering the lack of explanations for absorption and resorption currents in polymers, we propose to reformulate the latest and most comprehensive model based on surface ohmic conduction. This model, carried out by numerical simulation, contained oversimplifications. We also analyze the diffusion of carriers from the electrode edge. Finally, and in view of the negative results obtained by both models, we propose a new model based on a mechanism of drift diffusion which allows us to explain the characteristics of absorption and resorption currents in polymers. The simulation carried out for the three models is very precise and employs the integral equation method.
Effects of a magnetic field on the thermodynamics of dilute classical spin chains (abstract)
Authors: McGurn Arthur R. , Hu Guo Q.
Published: July 2002

The thermodynamics of a diluted chain of ferromagnetic classical spins in the presence of an external magnetic field is determined in the limit of the continuum model. The magnetization, susceptibility, specific heat, and elastic neutron scattering are determined for both the isotropic Heisenberg and the classical XY models as functions of temperature, magnetic field, and magnetic concentration. Scaling laws for the behavior of the thermodynamic quantities in field, temperature, and magnetic concentration are obtained.
Free energy of weakly dilute Ising models
Authors: Creswick R. J. , Farach H. A. , Poole C. P.
Published: July 2002

The effect of random quenched site dilution on the free energy of nearest-neighbor Ising models is considered. An exact relation between the distribution of local fields and the change in the free energy on dilution is derived. For frustrated systems at low temperatures, dilution leads to a lowering of the entropy, while for well-ordered systems dilution raises the internal energy.
Experiments on muon precession in iron that failed (abstract)
Authors: Arrott A. S.
Published: July 2002

There have been several experiments on the precession of muons in iron where the precession frequency is not understood on the basis of the model of a muon diffusing among the interstitial sites averaging out the dipolar fields that are quite different on the sites, depending on their relation to the magnetization direction. In two new experiments, one at 300 K and one at 1040 K, the absence of the muon precession signal appears difficult to explain. At 300 K a single-crystal plate of iron is placed in a large external field parallel to the polarization and direction of propagation of the muon beam. The crystal is set at angle with respect to the beam in such a way that the component of Bμ, the magnetic induction seen by the muon, along the applied field should vanish, leaving a transverse component about which the muon should precess. The calculation of the fields and angles for this uses the known values of the anisotropy constant, the saturation magnetization, and the hyperfine coupling constant. The purpose of the experiment was to determine the anisotropy of the hyperfine constant by observation of the variation of the minimum precession frequency with angle. The experiment is carried out using a pulsed muon beam in applied longitudinal fields comparable to 4πM. The precession signal is not observed. At 1040 K a polycrystalline iron oblate ellipsoid of revolution is placed in longitudinal and transverse applied fields with the principal axis set at various angles with respect to the muon beam. Though the demagnetizing field of the rotated ellipsoid in the longitudinal field should produce a transverse component of Bμ, the expected precession signal is not observed. The application of a transverse field does produce the expected precession signal. The effects of the applied fields on the muon depolarization due to critical fluctuations are observed.
Hall effect and magnetoresistance in low dimensional magnetic systems
Authors: Ibrahim A. K. , Powers R. , Zimmerman G. O. , Tahar M.
Published: July 2002

We have measured the Hall effect and magnetoresistance of stages 5 and 9 FeCl3-graphite intercalated compounds in a magnetic field up to 20 T and at several temperatures. Our preliminary results indicate that the Hall coefficient (RH) of stage 5 is positive at all field values and has insignificant variation between room and liquid helium temperature. In stage 9, however, RH has a complicated field and temperature dependence. The magnetoresistance of the two stages at all temperature and field values is positive and stage 5 exhibits strong Shubinkov–de Haas oscillations at helium temperature. Fourier transforms of these oscillations are performed and the results indicate that stage 5 has a dominant fundamental frequency which is attributed to the hole carriers, whereas stage 9 exhibits a modulation of several frequencies which are related to different carrier pockets.
Relaxation of photoinduced effect on surface spin-wave modes in H+2 -implanted YIG thin films (abstract)
Authors: Uematsu K. , Sakurai A. , Shin J. S. , Tsuchiya T.
Published: July 2002

Previously Tsuchiya and Uematsu reported their discovery of a photoinduced effect in which the decrease ΔHp of ferromagnetic resonance field of surface spin-wave modes in the H+2 -implanted layer of YIG thin films is observed during light irradiation at 77 K, and etching depth dependence of ΔHp is measured. The decrease ΔHp in as-implanted films is attributed mainly to generation of Fe2+ ions with hydrogen presence. The main hydrogen distribution has been introduced from the study.1 Here the authors describe ΔHp relaxation as the irradiation is turned on and off in the cases of as-implanted films and films covered with a sputtered SiO2 layer, before and after annealing. (111)-oriented YIG films are used. The energy of H+2 implantation is 30 keV and the dose is 1×1016 ions per cm2. The FMR frequencies are 9.2–9.4 GHz. First, an as-implanted film is irradiated for 10 min without applying a magnetic field and then after removing the irradiation ΔHp is able to be observed (class II). Next, ΔHp is measured to increase during irradiation with a field (class I), and then after removing ΔHp decreases to a class II level. Class I and II are explained from ‘‘one-center model’’ and ‘‘two-center model’’ of photoinduced magnetic anisotropy effect,2 respectively. Relaxation of ΔHp mentioned above, as well as that of ΔHp about films covered with SiO2 are measured and their particular properties are discussed.
Magnetism and microstructure of compositionally modulated disordered Fe/Ta films
Authors: Shan Z. S. , Zhao Z. R. , Zhao J. G. , Sellmyer D. J.
Published: July 2002

Results are presented on compositionally modulated disordered magnetic films of the form (XÅFe/YÅTa), as a function of the modulation wavelength λ≡X+Y. Magnetization, ac susceptibility, torque magnetometry, x-ray diffraction, and Mössbauer measurements are used to probe magnetic transitions and microstructure. For X and Y values less than about 12 Å the structure is amorphous within the layers and compositionally modulated in the direction perpendicular to the film. Films with ultrathin individual layers (1–3 atomic diameters) exhibit perpendicular anisotropy while the thicker ones have in-plane magnetization. Spin-glass and ferromagnetic transitions are observed and are associated with specific regions of the multilayered films.
Exploration of rf behavior of YIG film
Authors: Tang Xing-Ye
Published: July 2002

In this paper the author reports an unusual rf behavior of YIG film. The structure used in the experiment differs from the usual structure of YIG-film-tuned filters as follows: the bias magnetic field is parallel to the plane of the film and is oriented along the bisector of the angle between the planes of two coupling rings. The main points of the phenomena observed are as follows: (1) The relative power curves in response to the bias magnetic field are almost the same one with a single peak. (2) The part of the curve is linear in the left-hand side of the peak, and the other part in the right-hand side is exponential. (3) All the field values corresponding to the peak at various frequencies from 5 to 200 MHz are almost identical; they are 55 Oe. The author considers that this behavior is caused by the alternate extension-contraction and swinging movement of magnetization under the united action of the bias and rf fields, and this behavior may be used to make both linear and logarithmic electrically tuned attenuators at a wide frequency band from 5 to 200 MHz.
Conditional replaceability of magnetic surface anisotropies by effective volume anisotropies in the ferromagnetic resonance of ultrathin films
Authors: Rado George T.
Published: July 2002

Specific conditions are proposed for the replaceability of magnetic surface anisotropies by effective volume anisotropies and for the concomitant replaceability of the actual ferromagnetic resonance (FMR) surface mode or spin wave mode by a uniform mode. These conditions are then applied to the parallel and perpendicular FMR configurations in monocrystalline and amorphous ferromagnetic films. The significance and limitations of the results are discussed.
Evaluation of dynamic magnetic stray fields with high spatial and temporal resolution
Authors: Elsbrock J. B. , Nöthen N. , Balk L. J. , Kubalek E.
Published: July 2002

A setup has been realized for determination of magnetic field distributions with 50-nm spatial resolution and temporal resolution of <1 ns. For typical device configurations the system has a sensitivity of about 1 mT. Important system features are use of stroboscopic techniques; sine wave or pulsed operation of the magnetic device from 100 Hz to 60 MHz; precise determination of the distance between measuring position and head surface; and determination of the electron beam waveform by streak-camera technique with a temporal resolution of 50 ps, even for beam currents of <1 fA. This setup has been applied to the examination of thin film magnetic heads with a 0.6-μm gap and a track width of 26 μm.
The spin-glass transition in three dimensions: Is it understood?
Authors: Salamon M. B.
Published: July 2002

The current state of understanding of the spin-glass transition in three-dimensional systems was the topic of a symposium at the 31st Conference on Magnetism and Magnetic Materials. Panelists were A. J. Bray, J. Mydosh, A. Ogielski, J. Souletie, and A. Zippelius. M. B. Salamon moderated and prepared this summary. The consensus is that there is, indeed, a phase transition in three-dimensional Ising spin glasses, that its properties are dominated by strong critical slowing down, and that the scaling behavior of the nonlinear susceptibility provides the best indicator of its presence. The ordered phase is still not understood in the view of the panel, and evidence seems against interpretations based on modifications of mean-field solutions.
Bias scheme analysis of shielded MR heads for rigid disk recording
Authors: Bhattacharyya M. K. , Davidson R. J. , Gill H. S.
Published: July 2002

Biasing schemes for MR heads for use at high areal densities, O(108 bits/in.2), longitudinal recording, are reviewed. By use of the finite element analysis, a number of important design parameters are examined including the transfer function and the peak shift for each biasing scheme. We show that the roll-off peak shift and linearity characteristics are dependent on the type of bias scheme.
Magnetic polaritons in an anisotropic film on a ferromagnetic substrate
Authors: Caille Alain , Thibaudeau Claude
Published: July 2002

Substituted rare-earth iron garnet thin films grown by liquid-phase epitaxy on rare-earth iron garnet and exhibiting low saturation magnetization with a uniaxial magnetic anisotropy in a direction perpendicular to the film surface have recently been reported. We have obtained the dispersion relations of surface and guided magnetic polaritons in the film-substrate composite system in the Voigt geometry including retardation effect. Two windows were obtained for the magnetic polariton modes, one corresponding to a surface mode and the other to a guided mode in the anisotropic magnetic film. For low value of the external magnetic field, the frequency of the guided mode moves down with increasing magnetic field while the frequency of the surface mode moves up. For a suitable choice of physical parameters now available in substituted iron garnet films, we predict a crossover of these two branches.
Influence of Dzyaloshinsky-Moriya interactions on the critical behavior of metallic spin glasses
Authors: de Courtenay N. , Bouchiat H. , Hurdequint H. , Fert A.
Published: July 2002

We present nonlinear magnetization measurements as a function of field at different temperatures T ≥Tg on CuMn 0.2 at. % and AgMn 0.5 at. % alloys doped with various amounts of gold impurities. We show that one has to consider the anisotropy as a relevant scaling parameter in order to obtain a complete coherent description of the critical behavior.
Anomalous percolation-threshold behavior in the spin-glass-like, heavy fermion system (Ce,Gd)Al3 (abstract)
Authors: Edelstein A. S. , Holtz R. L. , Gillespie D. J. , Fisher R. A. , Phillips Norman E.
Published: July 2002

Low-field susceptibility measurements show that Ce1−xGdxAl3 exhibits spin-glass-like behavior over nearly the entire concentration range. The temperatures of the spin-glass-like transition Tm(x) are surprisingly high [Tm(0.635)=125 K] considering that none of the rare-earth trialuminides order above 25 K. The Ce is necessary for the anomalous behavior since it is absent in (La, Gd)Al3. For x≤0.23, T≤5 K there is an interplay between the heavy-fermion and spin-glass-like behavior. The values of Tm would probably not be so large if the system were not a heavy-fermion system. On the other hand, the spin-glass-like transition appears to modify the heavy-fermion character of the specific heat. The large C/T values at low temperatures (410 mJ/mole K2 for x=0.26) probably would have been still larger if they were not reduced by the effective field of the spin-glass-like state. The low-field susceptibility measurements show spin-glass-like cusp anomalies for x=0.08, 0.15, 0.18, 0.20, 0.23, 0.34, 0.40, 0.635, 0.77, and 0.9. This anomaly in the susceptibility at Tm persists as one increases x through the antiferromagnetic percolation threshold at x≡xc ∼0.5. However, the magnitude of the susceptibility anomaly decreases two orders of magnitude as one increases x from 0.5 to 0.635. The resistivity in most respects resembles that of a dense Kondo system. It differs in that for x>xc there is an additional amomaly in the resistivity at Tm, which is absent for x≤xc. The presence of this anomaly shows that the range of the order below Tm becomes at least as long as the mean free path for x>xc. For x>xc there are two transition observed in the susceptibility, the spin-glass-like transition at Tm and an antiferromagnetic transition at low temperatures. Specific heat measurements also show the antiferromagnetic transition.
Erasure in particulate and thin-film disk media
Authors: Katti Romney R. , Servan-Schreiber F. , Kryder Mark H.
Published: July 2002

Magnetic recording signals have been written, and subjected to erasure by external magnetic fields, on a variety of longitudinally oriented rigid particulate and thin-film disks. In general, plated thin-film disks are easier to erase than particulate disks, and particulate disks are easier to erase than sputtered thin-film disks. Decaying alternating (ac) erase fields induce greater erasure for a given peak field than do single-direction (dc) erase fields. Successive ac erasures, using the same erase field, induce greater erasure than single ac erasures; while successive dc erasures applied in the same direction do not induce greater erasure than a single dc field erasure. Successive dc erasures where the applied field direction is reversed after each erase application induce additional erasure, but are not as effective as the same number of ac erasures. Erase fields in excess of the disk coercivity induce reductions in signal amplitude, which are attributed to a region of irreversible magnetization switching, and to a region of irreversible approach to saturation as the effects of magnetic inhomogeneities are overcome.
Spin polarization of f bands in RCo5, R2Co17, and R6Mn23 compounds
Authors: Ukyo M. , Koizumi K. , Takahashi H. , Ohtsuka S. , Ukai T. , Mori N.
Published: July 2002

The d bands for RCo5, R2Co17, and R6Mn23 compounds are formulated by Deegan’s prescription and the formulas of Slater and Koster. The d-f elements for these energy bands derived by Lendi are taken into account. The spin polarization of the f bands are investigated. The obtained result explains the experimental result by taking into account the feeble exchange splitting in 4f bands. Additionally, the magnetic moment of rare earths is calculated on the basis of the band model and the calculated result is compared with gJ. It is found that in these compounds the spin polarization is saturated and the moments are much the same as gJ.
Initial susceptibility studies of rapidly solidified monel
Authors: Swartzendruber L. J. , Bennett L. H. , Ettedgui H.
Published: July 2002

The temperature dependence of the ac susceptibility for a Cu-Ni alloy near the monel composition (28 at. % Cu) has been measured as a function of temperature for melt-spun material, both in the as-spun condition and after various isothermal anneals. The initial susceptibility of the as-spun material, in the form of a thin ribbon, is significantly affected by the small microscopic compositional inhomogeneity and microstructural defects present after the rapid quenching. Using Curie temperatures estimated from magnetization measurements, the results are compared to a simple model for the ac susceptibility.
Magnetic phase diagram of dilute Cr-Al system from electrical resistivity studies on single crystals
Authors: Yakhmi J. V. , Gopalakrishnan I. K. , Iyer R. M. , Stanford J. L.
Published: July 2002

Electrical resistivity (ρ) studies as a function of temperature are reported for the first time, on single-crystal samples of dilute Cr-Al alloys containing 0.23-, 0.52-, 1.02-, 1.41-, 1.91-, 2.99-, and 4.53-at. % Al with a view to resolve the unusual and complex features reported for the magnetic phase diagram of Cr-Al system. ρ(T) anomalies are obtained in the region of TN for all the concentrations, contrary to earlier conclusions based on data on polycrystalline samples, that antiferromagnetism disappears in the concentration c range 2<c<4 at. % Al. The TN vsAl content plot shows a sharp fall initially up to 1.02 at. % beyond which it rises with increase in Al content. A C-I phase boundary region has been identified in the magnetic phase diagram by utilizing the infrared reflectivity data reported earlier on the same samples as complementary evidence.
Random-exchange and random-field x
y chain for s=1/2
Authors: Schneider T. , Politi A.
Published: July 2002

One of the points of interest in the study of random systems is the nature of the eigenstates, i.e., exponentially localized or extended, and the density of states. To identify the disorder-induced effects, we consider the one-dimensional s=1/2 xy models with random exchange, or random field. Using the transformation to spinless fermions, the problem is reduced to a nonlinear map, providing accurate numerical estimates for the integrated density of states and the exponential localization length. The results clearly reveal: (i) appearance of disorder-induced tails in the integrated density of states at the bottom and top of the spectrum, yielding to a characteristic field dependence of magnetization and susceptibility at zero temperature; and (ii) important differences between random-exchange and random-field models. In the random-exchange case, the middle of the band is found to be extended, while in the random-field case, corresponding to the standard Anderson model, all states are exponentially localized. This difference also affects the temperature dependence of zero-field specific heat and susceptibility as T→0.
Use of smoothness criterion in refining meshes in axisymmetric field problems
Authors: Yoganathan Sittampalam , Chari M. V. K. , Hoole S. Ratnajeevan H.
Published: July 2002

Adaptive refinement of finite element meshes has been performed using the bending of electromagnetic fields at element edges as a measure of error, in problems wih translational symmetry. In this paper it is presented how this could be extended to axisymmetric field problems. It is shown that the error estimate given by the inverse tan relationship is the same in electric and magnetic field problems, although in the governing Poisson equation, permittivity appears in the numerator and permeability in the denominator. This allows the same program developed for magnetic field problems to be used with minor modifications for axisymmetric electric field problems.
Surface impedance-BEM technique for nonlinear TM-eddy current problems
Authors: Ali K. F. , Ahmed M. Taher , Burke P. E.
Published: July 2002

The impedance boundary condition (IBC) approximation is used to formulate the problem as an exterior one, in other words, in terms of only the exterior fundamental solution. The first order boundary element technique has been used to represent the boundary integral equation numerically. The Gauss–Seidel iterative procedure was applied. The results obtained with the present approach are in good agreement with those obtained experimentally and theoretically by other authors.
MLS, a magnetic logic simulator for magnetic bubble logic design
Authors: Kinsman Thomas B. , Cendes Zoltan J.
Published: July 2002

A computer program that simulates the logic functions of magnetic bubble devices has been developed. The program uses a color graphics screen to display the locations of bubbles on a chip during operation. It complements the simulator previously developed for modeling bubble devices on the gate level [Smith et al., IEEE Trans. Magn. MAG-19, 1835 (1983); Smith and Kryder, ibid. MAG-21, 1779 (1985)]. This new tool simplifies the design and testing of bubble logic devices, and facilitates the development of complicated LSI bubble circuits. The program operation is demonstrated with the design of an in-stream faulty loop compensator using bubble logic.
Ultrathin particulate magnetic recording media (abstract)
Authors: Homola A. M. , Lorenz M. R. , Sussner H. , Rice S.
Published: July 2002

This paper presents a novel method of producing an ultrathin and highly oriented particulate magnetic recording medium. The process involves the laying down of a monolayer of magnetically aligned particles where the thickness of the layer is limited only by the diameter of the magnetic particles. Thus, using commercially available magnetic particles, a 50–100-nm-thick magnetic layer can be produced. The particle deposition process depends on electrostatic interactions of charged particles with an oppositely charged disk surface in an aqueous medium. In order to reduce the tendency of the magnetic particles to aggregate, the particles are stabilized by adsorbed colloidal silica. Particle volume concentration (PVC) is higher than usually realized with conventional particulate media and it was measured in excess of 50%. A typical particulate monolayer has an Ms of 1.6×10−3 emu/cm2 and the orientation ratio (Mr/Ms) of 4–4.5. Resolution, at 150-nm flying height, was measured at 1200 fc/mm with a high signal-to-noise ratio.
Transmission electron microscopy of Co-Cr films for magnetic recording
Authors: Lee J.-W. , Demczyk B. G. , Mountfield K. R. , Laughlin D. E.
Published: July 2002

The microstructure of Co-Cr thin films for perpendicular magnetic recording has been examined by transmission electron microscopy in both conventional (bright field/dark field and selected area diffraction) and convergent beam electron diffraction modes. Results of as-deposited samples indicate that the films consist of well-oriented c axis structures. A range of microstructures (columnar morphology, transition layers, twins, etc.) have been observed. These and other results will be presented.
The effect of crystal structure of very thin hcp Co-Ni films on the initial magnetization curves and hysteresis loops
Authors: Baral D. , Lee H.
Published: July 2002

Magnetic properties of thin films are strongly influenced by the orientation of the film. In this paper, thin (800 Å) hexagonal Co-Ni films with different textures were studied to understand the effect of film structure on the initial magnetization curves and hysteresis loops. It was found that films with [0002] texture had lower coercivity (∼100–250 Oe depending on grain size) and the energy required to saturate such samples was ∼2–4×106 ergs/cm3. Whereas films with [101̄1] texture had a coercivity of ∼700 Oe and energy required for saturation was ∼107 ergs/cm3. The hysteresis loss (energy of hysteresis) from these samples ranged from 0.6 to 3.5×107 ergs/cm3. It was found that the coercivity and hysteresis loss increases linearly with the magnetization energy. These results were consistent with the measurements on bulk single crystals where the energy required for saturation is smallest for basal plane samples.
High magnetic moment Fe-Co-Al sputtered films
Authors: Cadieu F. J. , Pirich R. G. , DeCarlo J. , Russak M. A.
Published: July 2002

The magnetic properties of transition-metal–rich Fe-Co-Al films prepared by sputtering from a hollow cathode ring segmented target have been studied as a function of transition-metal composition as well as differing sputtering parameters such as substrate temperature. The major new results observed are high values of the saturation moment for series of samples with (Fe79Co21)100−xAlx for x=0–25. The saturation magnetization 4πMs observed at x=0 is 29.2±2.6 kG. This measured value was in agreement with extrapolations based on data for x=10–25.
Effect of magnetic anisotropy of Ba-ferrite particles on squareness of perpendicular recording media
Authors: Kishimoto M. , Kitahata S. , Amemiya M.
Published: July 2002

Magnetic anisotropy constants of Ba-ferrite platelet particles are measured by means of a torque magnetometer, and the magnetic easy direction of the particles is calculated from the anisotropy constants. The squareness in the perpendicular direction of tapes depends on the magnetic easy direction of the particles, and decreases as the magnetic easy direction inclines from the direction perpendicular to the platelet plane to the direction parallel to the platelet plane.
Field ion microscopy (FIM) and atom probe (AP) investigations of FeNdB and related permanent magnets
Authors: Hütten A. , Haasen P.
Published: July 2002

A field ion microscope combined with an atom probe was used to study the local chemical compositions of rapidly solidified FeNdB magnets. For specimens with compositions Fe74,6Nd15,3B10,1 and Fe77Nd15Al2B6, concentration waves resembling known phases were observed although the measured coercivity was still very low. For a specimen (Fe70Co30)77Nd15B8 there were no phases observed, though fluctuations in the B concentration were found.
Activated dynamic scaling in disordered systems (invited)
Authors: Fisher Daniel S.
Published: July 2002

The long time dynamics of various random systems is discussed in terms of a general activated dynamic scaling Ansatz. The natural dynamic scaling variable is (ln t)/ξψ where t is the time and ξ a correlation length. Applications include the critical behavior of random field Ising magnets, the ordered phase of spin glasses, and approach to equilibrium in the ordered phases of these and other random systems.
Free electronlike Stoner excitations in Fe
Authors: Penn David R.
Published: July 2002

Methods have recently developed to probe the Stoner excitation spectrum which has not been amenable to study by neutron diffraction. The experiments have utilized energy loss spectroscopy combined with spin polarization of the incident electron beam or with spin polarization detection of the scattered beam, or both beam spin polarization and polarization detection [J. Kirschner, D. Rebenstorff, and M. Iback, Phys. Rev. Lett. 53, 698 (1984) (denoted by I)]. Due to the many possible scattering processes the experiments do not measure the Stoner excitation cross section directly but rather measure the magnitudes of combination of scattering amplitudes. To draw even semiquantitative conclusions regarding the Stoner spectrum requires theoretical analysis. Because Glazer and Tosatti [Solid State Commun. 52, 905 (1984)] give more complete information than previous experiments it is possible for the first time to carry out a detailed theoretical analysis. The analysis concludes that free electronlike Stoner excitations (FESE) make a much larger contribution to the scattering than d electron Stoner excitations (DESE), the usual type.
Electronic structure of Nd2Fe14B
Authors: Ching W. Y. , Gu Zong-Quan
Published: July 2002

The electronic structure of Nd2Fe14B has been calculated using the first-principle orthogonalized linear combination of atomic orbitals method. The f electrons in Nd are included in the calculation but are treated as localized states in the determination of the Fermi energy. Results are presented for the total density of states (DOS), orbital-decomposed, and spin-decomposed partial DOS. The calculated spin-magnetic moments on each of the six Fe sites are in good agreement with the values deduced from the neutron scattering experiment. The charge density map and the spin density map on the basal plane of the tetragonal cell show the evidence for covalent bonding between Fe and B atoms and reveal the distortion from the spherically symmetric distribution around the atomic sites.
Electronic structure and magnetic effects at the ideal (110) Fe/Ge interface
Authors: Pickett W. E. , Papaconstantopoulos D. A.
Published: July 2002

Ge and bcc Fe are well lattice matched, and therefore present an excellent prototype system to study magnetic effects at a metal/semiconductor interface. We study the electronic structure of the (110) Fe/Ge interface using a superlattice geometry and a parametrized tight-binding approach. We find that seven layers of Fe and 11 layers of Ge are necessary to identify unambiguously the interface bands in this system. The Fe minority-spin projected band structure has a large gap around the M̄ point (corner of the two-dimensional Brillouin zone) which spans the fundamental gap in Ge. We find four distinct interface bands which lie in this mutual gap and a corresponding large density of states at the Fermi level. For the majority-spin electrons we also find a large density of interface resonances just above the Fermi level which are strongly localized on the Ge atoms at the interface. These results are consistent with the very reactive nature of this interface seen in experimental studies.
A Mössbauer investigation of melt-spun Fe60Al28B12
Authors: McCally R. L. , Moorjani K. , Kistenmacher T. J.
Published: July 2002

Mössbauer studies on two distinct microstructural phases produced in the same batch of melt-spun Fe60Al28B12 reveal distinctly different spectra and hyperfine field distributions. One phase is essentially an amorphous ferromagnet, whereas the other contains a large paramagnetic component together with amorphous ferromagnetic material.
Magnetic properties of amorphous Co-Ti thin films with a perpendicular and an in-plane uniaxial anisotropy
Authors: Suran G. , Ounadjela K. , Machizaud F.
Published: July 2002

The magnetic and related structural properties of CoTi amorphous films are extremely sensitive to the deposition temperature Ts. If Ts is higher than a critical value and is, on film, prepared in the presence of a magnetic field applied parallel to the film plane, one observes the formation of two uniaxial anisotropy fields Hp and Hk, which are, respectively, perpendicular and parallel to the film plane. On films with thicknesses larger than a critical thickness, one observes longitudinal stripe domains which lie parallel to Hk. The corresponding shape of the in-plane B-H loop is characteristic of films with a Hp, but the saturation field Hs is different along the in-plane easy Hes and hard Hhs axis. The as-computed values of Hes and Hhs, using Hk and Hp obtained from ferromagnetic resonance are in good agreement with those deduced from the B-H loop. The physical origin of Hp and Hk are explained by the structural short-range order of CoTi amorphous films.
Magnetization and 31P NMR study of (Zr0.50Ni0.50)100−xPx metallic glasses with 0≤x≤7
Authors: Bakonyi I. , Ebert H. , Voitländer J. , Tompa K. , Lovas A. , Konczos G. , Bánki P. , Schone H. E.
Published: July 2002

The magnetic susceptibility and 31P NMR parameters were studied in amorphous Zr-Ni-P alloys as a function of the P content. The alloy susceptibility showed a slight maximum at around 1 at. % P. The NMR parameters gave further evidence for the dominance of early transition metal atoms at the Fermi level.
Hyperfine and exchange field distributions in amorphous magnetic insulators (abstract)
Authors: Eibschutz M. , Lines M. E.
Published: July 2002

The 57Fe Mössbauer Zeeman spectra of amorphous magnetic ferric insulators, a-Y3Fe5O12 (YIG), a-FeF3, and a-NaFeF4, consist of well-resolved broad experimental lines, which indicate the existence of a distribution of electric field gradients, hyperfine fields, and isomer shifts at the iron sites.1,2 The hyperfine-field distribution in amorphous magnetic insulator is shown to result dominantly from local spin disorder via its supertransferred component HST. Since the same spin disorder determines local exchange fields Hex, the hyperfine-field distribution indirectly contains much information concerning the distribution of exchange, in the spin-glass environment. This work probes the nature of the nearest-neighbor spin correlations in such systems, by analysis of hyperfine field distribution, as measured by 4.2 K Mössbauer spectroscopy. Low-field tails are found in the hyperfine field distribution spectra.3 They indicate the presence of low-energy exchange-field states caused by the cancellation of the nearest-neighbor contributions within the frustrated spin network. The distribution of exchange fields for a-YIG, a-FeF3, and a-NaFeF4 has been determined and, by comparing the results to those expected for a set of randomly oriented spins, the nature of nearest-neighbor spin frustration has been monitored in these amorphous magnetic insulators. The implied spin correlation is one of a quasiconstraint of the nearest neighbors of any given spin which restricts their vector sum to small values.
Crystallization kinetics of an amorphous magnet
Authors: Roig A. , Munoz J. S. , Salamon M. B. , Rao K. V.
Published: July 2002

The crystallization of an amorphous Fe-Ni-P alloy during isothermal annealing has been studied using a method that relies on the magnetism of the crystalline product. By rescaling the time axis for each annealing temperature, the data fall on a universal curve of the Johnson–Mehl–Avrami form, with parameters indicative of linear growth of a fixed number of crystallites. The time scaling parameter can be fitted to a Vogel–Fulcher or a Williams–Landel–Ferry temperature dependence, suggesting that dynamic processes in the glass phase are the rate-limiting steps in crystallization.
5
9Co spin echo NMR in the Co3−xFexB system
Authors: Wójcik M. , Jȩdryka E. , Nesteruk K. , Rosenberg M. , Livingston J. D.
Published: July 2002

5 9Co nuclear magnetic resonance (NMR) was studied by a spin echo technique in a series of Co3−xFexB (0≤x≤1.5) crystalline compounds in zero magnetic field at the temperature of 4.2 K. A revised interpretation of 59Co NMR spectrum in Co3B is given, based on the theory of NMR inside the domain wall. Iron was found to cause reorientation of the easy axis in Co3B.
Anisotropy energies for Y2Fe14B and Nd2Fe14B
Authors: Itoh T. , Hikosaka K. , Takahashi H. , Ukai T. , Mori N.
Published: July 2002

The approximate d bands for Y2Fe14B and Nd2Fe14B are formulated by Deegan’s prescription and the formulas of Slater and Koster. The electronic energies of these crystals with the spin directions [001], [100], [101], and [110] are calculated by Gilat and Raubenheimer’s method. The experimental result of the anisotropy energy for Y2Fe14B is analyzed with use of these calculated results by introducing the differences of the number of d electrons for these four states. In Nd2Fe14B the same differences of the number of d electrons are introduced and the contribution to the anisotropy energy due to 4f electrons is deduced. This contribution is analyzed by the use of the crystalline field potential (the localized model) and the band model with d-f elements derived by Lendi. The obtained results are considered to be reasonable.
Computing transient electromagnetic fields radiated from lightning
Authors: Hoole P. Ratnamahilan P. , Hoole S. Ratnajeevan H.
Published: July 2002

The effect of lightning on airborne electronic equipment and powerlines can be severe and a study requires the solution of electromagnetic fields radiated by the lightning flash. We model the return stroke by simple dipolelike line elements with resident charges prior to the return stroke. The resulting computations are from simple closed-form expressions and permit the modeling of branched lightning. For the first time, computations bear out the observed bipolar electric fields very near the flash.
Magneto-optical properties of Nd-Co and Nd-Fe alloys
Authors: McGuire T. R. , Gambino R. J. , Plaskett T. S. , Reim W.
Published: July 2002

Faraday rotation, as a function of wavelength for amorphous Nd-Co and Nd-Fe films, show the opposite behavior for low concentration Nd. The rotation decreases with increasing λ for Nd-Co and increases for Nd-Fe. This behavior is attributed mainly to the Nd, which has a higher magnetization in the Nd-Co. For Nd alone, a rotation of about 100 deg/cm G is estimated. In Nd-Fe at 50% concentration, the total Faraday rotation is higher than for Nd-Co which may be attributable to the effect of the spontaneous Hall angle.
Spin-polarized photoemission study of epitaxial Fe(001) films on Ag(001) (abstract)
Authors: Jonker B. T. , Prinz G. A. , Kisker E. , Walker K.-H. , Carbone C.
Published: July 2002

The electronic and magnetic character of epitaxial bcc Fe(001) films grown in situ on Ag(001) has been studied as a function of Fe coverage by spin- and angle-resolved photoemission (normal emission).1 The films were characterized with UPS, AES, and LEED, and a layer-by-layer mode of film growth was confirmed for the first 3 ml. We obtain good agreement with the calculated critical point energies2 at Γ for Fe coverages in the monolayer regime; however, we observe no net in-plane spin polarization up to 2.5 ml, even though an exchange-split electronic structure is inferred from the data. Although the initial calculations do not specify a direction for the moment, this is in apparent contrast with the prediction of an enhanced magnetic moment for one or two monolayers.2,3 The absence of polarization indicates that such films cannot be magnetized remanently along the in-plane 〈100〉 axis at room temperature. We conclude that a strong surface/film anisotropy favors the domain moments to lie along the surface normal up to 2.5 ml. Very recent anisotropy calculations for a free-standing Fe monolayer at the Ag lattice indicate that the easy magnetization axis is in fact perpendicular to the surface.4 A significant increase in emission intensity at EF of minority-spin origin accompanied by a net in-plane spin polarization is observed by 5.2 ml (the next coverage studied), suggesting a transition from surface dominated behavior to a bulklike character.
Antiferromagnetic structure of the cubic superconductor ErPd2Sn
Authors: Stanley H. B. , Lynn J. W. , Shelton R. N. , Klavins P.
Published: July 2002

Elastic and inelastic neutron scattering measurements have been made on the cubic Heusler alloy ErPd2Sn, which becomes superconducting at Ts =1.17 K. Antiferromagnetic correlations are found to develop for T>Ts, with an antiferromagnetic transition occurring at T≊1.0 K. The magnetic structure is found to be type II, in which the fcc Er unit cell doubles along all three crystallographic directions. However, there are additional satellites of the allowed reflections which indicate a modulated component of the magnetization density. In addition, the linewidths are broader than instrumental resolution and distinctly non-Gaussian in shape. Inelastic measurements show a broad distribution of scattering extending to energy transfers greater than 1 meV, as well as two distinct crystal field levels at 7.4 and 11.1 meV.