bluuebunny/crossref_metadata_2025 huggingface dataset:
New models for current distributions and scalar potential formulations of magnetic field problems
Authors: Ciric I. R.
Published: July 2002

Given volume distributions of stationary or quasistationary electric current are replaced by equivalent distributions of fictitious magnetization and, eventually, of surface current, on the basis of the Ampèrian model for magnetized media. The fictitious magnetization is subsequently replaced by the equivalent distribution of fictitious magnetic charge. Consequently, the magnetic field due to given volume currents is determined from that produced by the corresponding charges and surface currents. This modeling method is also presented for generalized distributions of current. A scalar potential is introduced to describe the field in the models constructed. This scalar potential is a single-valued function of position when the current distribution is modeled by using a fictitious magnetization and only an equivalent charge distribution within the region considered. The modeling procedure is flexible and the models proposed yield an easier physical interpretation and a substantially reduced amount of computation with respect to vector or combined vector and scalar potential methods used so far. A few illustrative examples are given. This paper relates to stationary or quasistationary magnetic fields, but the modeling technique and the scalar potential presented are applicable to problems relative to any physical fields governed by the same equations.
Dynamics of patterned laser-induced chemical vapor deposition
Authors: Jelski Daniel A. , George Thomas F.
Published: July 2002

An expression for the grating growth rate in laser-induced chemical vapor deposition is derived which incorporates the contribution from the plasmon field intensity. It is found that the ultimate grating height is independent of laser intensity, while the grating growth rate is linear in intensity. For the shallow grating case the expression reduces to exponential growth. Also discussed are several possible mechanisms which account for the periodic structure.
An analytical model for the inverse narrow-gate effect of a metal-oxide-semiconductor field-effect transistor
Authors: Hong K. M. , Cheng Y. C.
Published: July 2002

A closed-form analytical expression is derived to predict the threshold voltage of a narrow-gate metal-oxide-semiconductor field-effect transistor with a fully recessed field-isolation structure. The calculation is based on a simple conformal transform and a physical model employing the depletion approximation. The physical origin of the inverse narrow-gate effect is mentioned. Threshold-voltage variations under the influence of various physical parameters are discussed, and a comparison with published data shows that the present model is useful.
On the mechanism and frequency limit of double-barrier quantum-well structures
Authors: Pan D. S. , Meng C. C.
Published: July 2002

Two parameters are adopted to characterize the transport process in double-barrier quantum-well (DBQW) structures. It is shown that, in general, both coherent resonant tunneling and incoherent sequential tunneling processes are possible. However, for most high-frequency applications, large current densities (>104 A/cm2) are required and, therefore, the sequential process is unlikely to occur. To determine the high-frequency capability, both the adiabatic limit of the dc current-voltage curve as well as the capacitance charging time in an embedding circuit need to be considered. We confirm that the DBQW structures with barrier thickness of 20 Å or smaller can operate up to about 1 THz.
An x-ray topographic study of β-SiC films on Si substrates
Authors: Fatemi M. , Nordquist P. E. R.
Published: July 2002

Defects in β-SiC films grown on Si substrates by chemical-vapor deposition have been investigated using x-ray double-crystal topography. Varying levels of dislocations are often observed in the form of channels, originating at the SiC/Si interface, which can be detected topographically regardless of the visible roughness in the film surface. It is found that rough surfaces are crystallographically more ‘‘flat,’’ on a macroscopic scale, compared to smooth surfaces which are often curved. Films in the latter group also contain fewer defects than the former, and are characterized mostly by misfit striations along [110] directions. A model for defect propagation is proposed connecting the observed topographic detail to the lattice mismatch, differences in thermal expansion, and the relative thickness of film and substrate.
Effects of field fluctuation on impact ionization rates in semiconductor devices due to the discreteness and distribution of dopants
Authors: Arnold D. , Kim K. , Hess K.
Published: July 2002

Field fluctuations due to dopants in a p+−n junction have been calculated and used to study the effects on the impact ionization rate with a Monte Carlo simulation. Results are plotted along the direction normal to the interface. We report that the field fluctuations have no effect on the ionization rate in the dead space and a small and spatially delayed effect in the region after the dead space even though the field shows large and rapid fluctuations. A similar ‘‘averaged-out’’ effect is also shown for the average electron energy. The enhancement in the ionization rate due to the field fluctuations which Shockley expected in his pioneering research is shown to be negligibly small.
Piezoresistance response of ytterbium foil gauges shocked to 45 kbar in fused silica matrix
Authors: Brar N. S. , Gupta Y. M.
Published: July 2002

Resistance change at peak stress and the residual resistance change of ytterbium foil gauges embedded at different depths in fused silica matrix were determined under shock loading to a stress of 45 kbar. The results show that for a given peak stress, the gauge response was unchanged for an order of magnitude variation (103–104 kbar/μs) in the loading rate. Measured resistance change at peak stress and upon unloading agree very well with the analytic model calculations for stresses up to 30 kbar in the fused silica. Peak resistance change values in the present work have been reconciled with earlier ytterbium data in a polymethylmethacrylate (PMMA) matrix on the basis of differences in longitudinal stress in the gauge foils for the two materials (polymethylmethacrylate and fused silica) and differences in the electromechanical constants of the two sets of foils. Above 30 kbar stress in the fused silica, measured resistance values are lower than the calculated values. This difference is attributed to changes in the ytterbium as a result of the initiation of the fcc to bcc phase transition. The resistance change-time profile from the 45-kbar experiment shows a strongly time-dependent behavior suggesting that a significant fraction of the material has been transformed.
Experimental study on a precession-free rotor suspended by magnets
Authors: Kitano Y. , Ohyama T. , Matsuo T. , Sasaki S.
Published: July 2002

A high-speed rotor which is characterized by a mechanical precession eliminator and by a magnetic suspension has been constructed. In this instrument, a cylindrical rotor 2 cm (0.02 m) in diameter and 20 cm (0.2 m) long was made of aluminum. The moment of inertia of this rotor was approximately 86 g cm2 (8.6×10−6 kg m2) about the long axis. A stable rotation of 120 000 rpm was obtained in air as well as in vacuum. The rotor was suspended vertically by a set of suspension magnets at the top of the rotor and a set at the bottom. In addition, the bottom of the rotor is flexibly supported by a ruby bearing which moves smoothly on a plate but is constrained by friction. When precession of the rotor begins, the frictional force eliminates the precession intrinsically. Measurements of slowing rate for the revolution were made at several different air pressures. There is good agreement with the theory.
A simple formula for the dielectric constant of a solution
Authors: Becker Roger J.
Published: July 2002

A formula is derived for the dielectric constant of a single-phase solution which has the virtue of being simple in form but more accurate than the formulas commonly used in predicting the dielectric properties of solid-state solutions. If a solid solution is made up of materials with similar molecular structure and polarizability tensors, then the formula collapses to a simple weighted average. This formula is used to estimate the relative contributions to scattering losses from various defects in a solid solution. It is found that voids and vacancies cause proportionally greater scattering than local departures in stoichiometry.
Coumarin-4 laser efficiency up to 0.14% under coaxial flash-lamp pumping
Authors: Zhang Fu Geng , Yu Chuang Lian
Published: July 2002

Under coaxial flash lamp pumping the laser efficiency of coumarin-4 in slightly basic ethyl alcohol solution as an active medium has reached a value of 0.14%. That is three times higher than that in the basic aqueous solution. Its tunable wavelength range of laser output has extended from 440 to 510 nm with the maximum at 460 nm.
Self-aligned contacts in silicon by nitrogen implantation
Authors: Theimer J. , Maby E. W. , Lieb S. , MacCrone R. K.
Published: July 2002

A process is described for the formation of self-aligned contacts to the source and drain regions of a silicon insulated-gate field-effect transistor by means of nitrogen implantation. It is shown that the nitrogen induces an oxidation delay period during which no oxide growth is observed in the contact regions, but oxidation is not suppressed over the polycrystalline silicon gate if it has been protected from the nitrogen implant. If the contact regions are not covered by silicon dioxide during nitrogen implantation, metallization can be performed immediately after gate oxidation, and the contacts thus formed appear to have good electrical character. However, the thickness of silicon dioxide which can be grown over the gate is limited.
A new method for measurement of coercive force in bubble garnets using microwave absorption
Authors: Hosoe Y. , Ikeda T. , Ohta N. , Sugita Y.
Published: July 2002

A new method has been developed for measurement of coercive force in bubble garnets using microwave absorption. The inflection point was observed in the derivative absorption signal when the measurement was carried out, changing the modulation field in a garnet film supporting magnetic bubbles. This inflection is related to the domain-wall absorption and the modulation field at the inflection point gives the coercive force in the garnet film. Using this method the coercive force can be determined even if the bubbles can hardly be observed. The coercive force of garnet films supporting submicron (0.3–1 μm diam) bubbles has been measured.
Radiation damage of GaAs thin-film solar cells on Si substrates
Authors: Itoh Yoshio , Yamaguchi Masafumi , Nishioka Takashi , Yamamoto Akio
Published: July 2002

1-MeV electron irradiation damages in GaAs thin-film solar cells on Si substrates are examined for the first time. Damage constant for minority-carrier diffusion length in GaAs heteroepitaxial films on Si substrates is found to be the same as that in GaAs homoepitaxial films on GaAs substrates. This agreement suggests that GaAs/Si has the same defect introduction rate with radiation as GaAs/GaAs. The degradation of GaAs solar cells on Si with electron irradiation is less than that of GaAs solar cells on GaAs, because in the present, GaAs films on Si substrates have lower minority-carrier diffusion length compared to GaAs films on GaAs and these films are insensitive to radiation. The p+-p+-n AlGaAs-GaAs heteroface solar cell with junction depth of about 0.3 μm is concluded to be useful for a high-efficiency and radiation-resistant solar cell fabricated on a Si substrate.
Feasibility of tunable infrared detectors using metal-insulator-metal structures
Authors: Schwartz Carey
Published: July 2002

It is suggested that metal-insulator-metal (MIM) structures under bias can be used as voltage-controlled tunable detectors. Theoretical results are based upon adapting a theory of photostimulated field emission to the MIM geometry. It is shown that tunneling resonances, which exist both below and above the tunneling-barrier maximum, provide a mechanism by which the biased MIM junction detects photons within a tunable wavelength band. It is also suggested that exploitation of these tunneling resonances can improve the sensitivity of the scanning tunneling microscope.
3d and 4f magnetism in Nd2Fe14−xCoxB and Y2Fe14−xCoxB compounds
Authors: Bolzoni F. , Leccabue F. , Moze O. , Pareti L. , Solzi M. , Deriu A.
Published: July 2002

A systematic study of the effects of Co substitution on the crystal structure and magnetic anisotropy of Y2Fe14−xCoxB and Nd2Fe14−xCoxB has been carried out in order to clarify the different roles and contributions to the anisotropy of both rare earth and transition metals. The substitution of Co leads to an enhancement of the Curie temperature in both series of compounds. The Co has been found to provide a planar anisotropy which is larger than that of the axial anisotropy of Fe. A marked site preference has been observed. Two distinct contributions of the Co to the anisotropy have been observed.
Aging and its circumvention in rf-plasma oxidized Pb-alloy Josephson junctions
Authors: Wada Masato , Nakano Jun’ichi
Published: July 2002

The aging phenomenon of Pb-alloy Josephson junctions is investigated and an effective method of circumventing it is presented. Junctions consist of Pb-alloy electrodes and a tunneling barrier formed by rf-plasma oxidation of the Pb-alloy. First, aging and annealing-driven change in normal tunneling resistance are compared to verify the usage of annealing as an experimental method for simulation and acceleration of aging. Next, process variables affecting the annealing change in junction characteristics are examined and their influence is described. The importance of the oxide-base electrode interface is confirmed and that of the counterelectrode-oxide interface is experimentally shown. Furthermore, possible changes in the oxide itself are discussed. Finally, on the basis of these studies, rf-plasma oxidation in a CO2 atmosphere is employed and proven to be an effective method for circumventing the annealing change in the junction characteristics.
Measurements of transverse-gain profiles in rf- and dc-excited CO2 gain cavities
Authors: Sharp Richard C.
Published: July 2002

Spatially resolved transverse-gain profile measurements have been made in rf- and dc-excited waveguidelike cavities for CO2 laser gas mixtures. Both current density and gas temperature impact the CO2 gain profile. As measured, transversely rf-excited cavities show higher CO2 gain near the wall boundaries when compared to longitudinally dc-excited cavities. We propose that transverse-rf excitation may be inherently better than dc-longitudinal excitation in producing a higher average spatial gain, owing to more uniform current density pumping.
Silicon loss during TiSi2 formation
Authors: Cohen C. , Nipoti R. , Siejka J. , Bentini G. G. , Berti M. , Drigo A. V.
Published: July 2002

When Ti-Si diffusion couples are annealed in vacuum to form TiSi2, most of the oxygen contamination in the as-deposited metal film is lost. An experiment demonstrating that a Si loss also takes place is presented, thus confirming that the oxygen loss occurs by SiO sublimation.
Reply to ‘‘Comment on ‘Particle-size distribution effects on sintering rates’ [J. Appl. Phys. 6
0, 383 (1986)]’’
Authors: Ring Terry A. , Chappel J. S. , Birchall J. D.
Published: July 2002

A closed form solution to our numerical results is noted.
Superconducting AgMo6S8 thin films prepared by reactive sputtering
Authors: Hertel G. B. , Orlando T. P. , Tarascon J. M.
Published: July 2002

Preferentially oriented thin films of the Chevrel-phase superconductor AgMo6S8 were prepared by reactive sputtering. Ag and Mo were simultaneously sputtered from separate guns onto sapphire substrates held at about 850 °C with H2S gas injected near the substrate. The films have superconducting critical temperatures up to 9.2 K and narrow-phase transitions. The reactive sputtering process chosen for the preparation of our films makes it possible to change the superconducting properties and the microstructure of the samples in a systematic way by changing individual preparation parameters and to study which of the preparation conditions are the most crucial for the formation of the Chevrel phase. We find that the superconducting transition temperature of the Chevrel phase is very sensitive to both substrate temperature and to the flow of H2S but insensitive to the background pressure in the chamber before deposition. The microstructure can be changed by controlling the H2S pressure. X-ray measurements show that the films are preferentially oriented with the rhombohedral 001 planes parallel to the surface of the substrate.
The effects of Cr2O3 and Fe2O3 additions on the thermal conductivity of Al2O3
Authors: Williams R. K. , Graves R. S. , Janney M. A. , Tiegs T. N. , Yarbrough D. W.
Published: July 2002

Thermal conductivity data for a series of Al2O3, Al2O3-Cr2O3, Al2O3-Fe2O3, and Al2O3-Cr2O3-Fe2O3 samples are reported. The results, which span the temperature range 300–360 K, show that grain size has an important effect on the thermal conductivity of Al2O3, and this effect is larger than would be anticipated from standard theories. Results for seven Al2O3-based solid solutions were examined in terms of a Callaway formula, and it was found that the point defect relaxation times were principally dependent on solute content and the mass difference between the solute and solvent. The data support a theory that suggests that a heavy atom in a light matrix scatters less effectively than a light atom in a heavy matrix. The data do not show that isolated point defects are more effective phonon scatterers than point defects in a concentrated solution.
Theory of saturation photocurrent and photovoltage in p-n junction solar cells
Authors: Mohammad S. Noor , Abidi S. T. H.
Published: July 2002

A theory of saturation photocurrent and photovoltage has been developed for p-n junction solar cells. The theory is based on ambipolar transport equations for electrons and holes near the junction, and on empirical models for band-gap narrowing and Fermi–Dirac integrals. It is applicable to solar cells made of nondegenerate or lowly degenerate semiconductors with position dependent band structures. Interestingly, it includes provision of both short-circuit and open-circuit configurations and involves the use of boundary conditions valid at the junction for all levels of injection. The boundary conditions automatically reduce to those of Dhariwal et al. for nondegenerate semiconductors with uniform doping. The empirical models for band-gap narrowing and Fermi-Dirac integrals are found to be significantly accurate when compared with available experiments or with exact results. Numerical calculations have been carried out for a number of silicon solar cells possessing varied doping levels, and the results have been found to be in good agreement with available experiments. The analysis shows that the saturation photovoltage developed by a p+n solar cell is higher than that developed by an equivalent n+p solar cell, and that the photovoltage is lower than the diffusion potential of the corresponding solar cell.
An efficient magnetic flux integration method for bounded current sources
Authors: Ioannides A. A. , Swithenby S. J.
Published: July 2002

The magnetic flux threading a general pickup coil system is expressed as a power series expansion in which the source and detector dependencies are separated. Specific expressions are developed for the commonest coil system—a single circular coil. For a given configuration, the maximum error is simply related to the number of terms retained in the expansion. Actual computations show that, for a single circular coil, and for configurations typically encountered in biomagnetic studies, the power series expansion method is about 20 times faster than direct integration of the vector potential over the coil perimeter.
Evidence for 2D X
Y Kosterlitz-Thouless transitions in magnetic graphite intercalation compounds
Authors: Dresselhaus G. , Nicholls J. T. , Chen S. T. , Dresselhaus M. S.
Published: July 2002

Magnetic graphite intercalation compounds (GIC’s) allow a controlled separation of atomically abrupt magnetic layers by variation of the stage of the sample. Thus very small J′/J values (∼10−4) and quasi-two-dimensional behavior can be achieved where J′ and J are, respectively, the interplanar and intraplanar exchange constants. The applicability of a 2D XY model is established by a comparison of the high-temperature susceptibility with the high-temperature series expansions for the various 2D and 3D models. Low-temperature studies provide values for magnetic interactions pertinent to the most interesting intermediate temperature range, where a 2D XY bound vortex phase may occur.
Magnetic properties of multilayered Fe/Cu film deposited by facing targets sputtering (abstract)
Authors: Fukizawa A. , Naoe M.
Published: July 2002

Iron and copper both form solid solutions with only a few atomic percent in ultimate concentration. Thus, multilayered films of ferromagnetic Fe and diamagnetic Cu provide unique means for investing the magnetic interaction among Fe thin layers distinctly separated by Cu layers and the role of Fe/Cu interface. Facing targets sputtering (FTS) apparatus has been developed for preparing multilayered films composed of very thin continuous layers of different metals with high mobility adatoms and low energy bombarding particles. Multilayered Fe/Cu films have been prepared on glass slide substrates by depositing alternatively Fe and Cu layers with 99.99% in purity using FTS apparatus. The thickness of individual Fe and Cu layers is in the range of 5–70 Å. Small-angle x-ray diffractometry indicates that the multilayered structure is formed even for each layer as thin as 5 Å. Saturation magnetization 4πMs of the Fe layer as thin as about 7 Å is comparable to that of bulk Fe. However, 4πMs of the films with an Fe layer thinner than 7 Å is remarkably small than that of the films with the thicker Fe layer. Coercivity Hc monotonously decreases with decreasing thicknesses of Fe and Cu layers from 70 Å to about 10 Å. The hysteresis M-H loop of the multilayered films with Fe layers thinner than 10 Å shows rotatable anisotropy, impling perpendicular anisotropy. When the thickness of the Fe layer is fixed at 13 Å, perpendicular anisotropy increases with decreasing the thickness of the Cu layer in the range below 13 Å. Heat treatments of the multilayered films up to 300 °C resulted in a change of layer structure and also magnetic properties. Dependence in magnetic properties and multilayered structures on annealing temperature will be discussed in detail.
Magnetic ordering in dimorphic phases of FeF3⋅3H2O: Magnetic and Mössbauer studies
Authors: Dézsi I. , Pannaparayil T. , Mulay L. N.
Published: July 2002

The two crystallographic modifications of ferric fluoride trihydrate (α- and β-FeF3⋅3H2O) were synthesized and studied by magnetic and Mössbauer techniques. The two forms could be distinguished by their different Mössbauer parameters. The magnetic susceptibility versus temperature curves also showed distinct differences. The susceptibility decreased monotonically with increasing temperature for the α form. For the β form, however, the susceptibility decreased initially and then went through a broad maximum around 130 K. The α form was found to convert to the β form after a year. The broad maximum in the susceptibility versus temperature curve observed for β-FeF3⋅3H2O is explained in terms of cooperative interaction involving relatively small number of Fe3+ ions. Postulates concerning the nature of the short-range antiferromagnetic ordering within ‘‘clusters’’ of Fe3+ ions are presented.
Nonlocal magnetic susceptibility tensor and spin-wave resonance of the ferromagnetic film (abstract)
Authors: Shi Long-pei
Published: July 2002

The magnetic susceptibility and spin-wave resonance is studied by the method of Green’s function based upon the Heisenberg model with the surface magnetic anisotropy. It is proved that the ferromagnetic film which loses translational invariance in one direction has a nonlocal magnetic susceptibility tensor. Applying the method of nonlocal magnetic susceptibility formulation, which results in self-coherence of magnetization in the film, the relation between the surface magnetic anisotropy of film and the modes of spin wave exited by the uniform microwave field is derived, and the expressions of position and intensity of resonance peaks are given. According to the nonzero condition of self-coherence of magnetization in the film, three cases have been shown that the uniform microwave field should be able to excite spin wave: (1) Free surface boundary condition (D=0): Only the uniform mode (K=0) should be excited. (2) Symmetrical surface anisotropy boundary condition: For the strong surface anisotropy (D=J), the nz=1,3,5,... odd modes [k=nzπ/(n+1)] should be excited. For the weak surface anisotropy (D≪J), the nz=(2εn)1/2/π, 2,4,6,... even modes (k=nzπ/n) should be excited. (3) Asymmetrical surface anisotropy boundary condition: In general, all the modes should be excited. There is no k=0 spin wave in both cases (3) and (2).
Magneto-optical Kerr effect of Fe/Cu compositionally modulated multilayered films
Authors: Katayama T. , Nishihara Y. , Awano H.
Published: July 2002

The wavelength dependence of polar magneto-optical Kerr rotation (θK) and the structure of Fe/Cu compositionally modulated multilayered films with the modulation length (D) up to ∼95 Å were investigated. It has been found that values of θK are low and Kerr rotation spectra are simple in wavelength region between 250 and 800 nm for the films with relatively small D. However, a new peak of θK appears at around 560 nm, corresponding to the absorption edge of Cu metal, and becomes large with the increase of D. The new peak moves towards the longer wavelength side with the increase of thickness ratio (Fe/Cu) of Fe to Cu layers.
Design of high recording density thin-film heads for particulate rigid disks
Authors: Ohura M. , Tsuji Y. , Kuwatsuka S. , Hanazono M. , Kawakami K. , Saitoh M.
Published: July 2002

Thin-film heads for 8.8-in.-diam particulate media rigid disks having a recording density of 20 kBPI were designed utilizing numerical analysis techniques and experimental results. The heads having a total thickness of 3.5 μm (outer edge to edge length in media movement direction) and gap depth of less than 1.5 μm provide satisfactory reproducing and recording characteristics. A novel head structure was developed for which the magnetic path is closed at the front end of the gap film to simplify detection of the end point in the polishing process in order to achieve the desired gap depth. The head is fabricated by adding two steps to the conventional process before the top magnetic film is deposited. These steps are (1) removing a part of the gap film, masking by the top organic insulating film, by using carbon tetrafluoride ion and (2) etching back the organic film so as to expose the gap film from the edge of the organic film that determine the cardinal point of the head gap.
Soft polycrystalline magnetization curves
Authors: Arrott A. S.
Published: July 2002

The magnetization curve for polycrystalline soft magnetic materials are calculated using an approximate model. The dependence of Ms/M on H/HK depends upon a parameter 〈D〉 that relates the demagnetizing field in a given grain to the difference between a particular component of the magnetization in that grain and the ensemble average over all grain orientations of the component. For 〈D〉=1 a component of the magnetic induction B is constant from grain to grain. The calculation of the field dependence of the magnetization is complicated, involving the solution of nonlinear integral equations by computer, except in the simple limits 〈D〉=0, which is the constant H model and 〈D〉=∞ which is the constant M model. For 4πMs ≫HK the constant M model gives results that are very little different than the constant B model. The constant H model gives quite different results that are unrealistic. Calculation of the magnetization with the constant M model, including coercivity, is quite simple and realistic. The calculation is applicable to the treatment of the depolarization of polarized neutron beams passing through polycrystalline ferromagnetic materials.
Atomic and magnetic structure of Er(Fe1−xNix)3 intermetallic compounds
Authors: Tharp Dwayne E. , Yang Ying-chang , James William J. , Yelon W. B. , Xie Decai , Yang Jilian
Published: July 2002

Neutron diffraction studies have been made on the intermetallic compounds, ErFe2Ni, ErFe1.5Ni1.5, and ErFeNi2, to determine the effect of the nonmagnetic Ni atoms on the three magnetic phases of ErFe3. Diffraction patterns above the Curie temperature show that Ni atoms almost exclusively occupy the h1 sites. At room temperature, a nearly basal plane ferrimagnetic arrangement of magnetic moments results whereas at 4.2 K, a noncollinear structure is observed, in contrast to the uniaxial collinear structure obtained for ErFe3. The results are explained on the basis of the competitive local anisotropies and the change in exchange interactions of Er-Fe upon substitution of Ni.
A rigorous analysis of a magnetic thin-film layered structure with a sinusoidal surface corrugation
Authors: Chang N. S. , Erkin S.
Published: July 2002

The microwave filter characteristics of a magnetostatic surface wave in a magnetic layered structure with sinusoidal corrugation on one layer and noncorrugated on the other are described. A rejection filter properties having a high Q value are numerically evaluated by solving the dispersion relation derived from Floquet theory. Also, high Q characteristics obtained in our model are satisfactorily confirmed in comparison with results which were analyzed based on perturbation theory with a multiple space scale method. It is found that the high Q property of the filter in our model can be easily obtained by adjusting the saturation magnetization of the noncorrugated layer.
Ferromagnetic resonance calculations in multilayers of iron and its alloys (abstract)
Authors: Lin T. S. , Vittoria C.
Published: July 2002

We have extended previous1 calculations of ferromagnetic resonance (FMR) in magnetic alternating layered structures by including the effects of exchange coupling between layers. Whereas in previous calculations the magnetic layers were separated by a nonmagnetic layer, in this calculation all the layers are magnetic. In particular we consider the problem in which successive iron layers in the layered structure are separated by an iron alloy layer. The magnetic properties of the alloy are purposely chosen so that the ferromagnetic resonance field in the absence of any external fields due to exchange coupling between layers is close to (∼600 Oe) the iron FMR line. We find that the separation in FMR fields corresponding to the two types of layers is strongly affected by exchange coupling A12. For A12=−0.1 ergs/cm2 the separation between the lines is 384 Oe in comparison to 604 Oe for A12=0. However, for A12=0.1 ergs/cm2 both lines are shifted dramatically from the Kittel resonance conditions. This implies that FMR should be a useful technique in measuring exchange effects in multilayers structures. The calculation will be discussed in terms of recent experimental results.2
Brillouin light scattering on MSW excitations in device structures (invited) (abstract)
Authors: Patton Carl E.
Published: July 2002

Magnetostatic wave (MSW) propagation in planar magnetic samples has formed the physical basis for most of the MSW device structures which have been developed in recent years. The properties of these waves, however, were accessible only by indirect means, usually in the form of the final device operating characteristics. With the technique of Brillouin light scattering (BLS), it is now possible to measure the dispersion properties and energy flow profiles of MSW excitations in situ in actual device configurations. The technique requires an incident low-power laser beam focused on the surface of the magnetic layer, some collection optics to sample the scattered light, and a sensitive, high-contrast Fabry-Perot interferometer for frequency analysis. In simple terms, one needs simply to ‘‘bounce’’ a laser beam off the active magnetic layer in the device in order to probe directly the excitations which make the device work. The technique is noninvasive and independent of any device function which the MSW signals serve. The BLS technique should prove to be a powerful diagnostic tool in the developing technology of MSW devices. The technique is broadband, and is capable of device diagnostics from the low GHz range up to frequencies in the THz regime.
Use of magnetic materials in microwave and millimeter wave monolithic integrated circuits (invited) (abstract)
Authors: Schloemann Ernst
Published: July 2002

This talk will review the requirements for ferrite devices in microwave and millimeter wave monolithic integrated circuits (MMICs). Future radar and communications systems will make extensive use of MMICs for realizing the desired circuit functions, such as low-noise amplification, power-amplification, switching, and phase shifting. Ferrite devices can perform many useful functions in this emerging technology serving as circulators, isolators, switches, phase shifters, tunable filters, and delay lines. The technical approaches that hold promise for realizing the benefits of low cost and high reliability generally associated with integrated circuit techniques will be discussed.
Two-dimensional neutron diffraction of YFe2O4 and CoCr2O4
Authors: Funahashi S. , Morii Y. , Child H. R.
Published: July 2002

A new wide-angle neutron diffraction instrument has been used to study CoCr2O4 and YFe2O4. The instrument is capable of measuring the scattered intensity over a wide region of reciprocal space in a short time, and this feature was used to measure the magnetic diffraction pattern of these materials at temperatures below the magnetic ordering temperature.
Dimensional effects in Ni-Cr multilayered thin films
Authors: Stearns M. B. , Lee C. H.
Published: July 2002

The dimensionality of Ni-Cr multilayered structures (MLS) was studied from the variation of the temperature dependence of the saturation magnetization Ms with the Ni layer thickness. Since NiCr alloys containing more than 12% Cr are nonmagnetic the thickness of the interfaces and pure Ni regions can be obtained from the measured value of Ms by modeling the MLS and determining the thickness of the pure Ni regions. Assuming that the pure Ni regions are isolated sufficiently to behave independently, comparison was made with several theories. It was found that the observed behavior is similar to that described by the theory of Davis and Keffer with a surface anisotropy energy of about 0.1 that of the exchange energy. This theory uses nonperiodic boundary conditions and assumes a surface anisotropy field which causes the partial pinning of the surface spins. The magnetization decrease calculated with this theory falls off less rapidly with film thickness than other theories. At high fields the magnetization and Curie temperatures of the MLS having 20 Å or less of Ni is found to be field dependent. This is indicative that a considerable amount of the magnetic moments arise from itinerant d electrons.
Evidence for the d’Almeida–Thouless transition line in a dilute metallic spin glass from time response measurements near T
g
Authors: Bontemps N. , Hoogerbeets R. , Luo Wei-li , Orbach R.
Published: July 2002

An analysis of measurements of the field (H) and temperature (T) dependence of the time decay of the thermoremanent magnetization of the dilute metallic spin glass, Ag:Mn2.6Sb0.46 (at . %), are presented for temperatures just below the glass temperature (Tg=9.30 K). The thermoremanent magnetization, σTRM(t), is found to decay with time t according to a stretched exponential form: σTRM(t) =σ0 exp[−(t/τp)1−n]. Both the T and H dependence of 1/τp and n can be related using a recent model calculation of the nonequilibrium dynamics of the Parisi quantity x̄ for the infinite range Ising model. Within the context of this model, log10(1/τp) is expected to diverge at Tg. It is shown that the experimental data for 1/τp and n are consistent with this theoretical prediction. Moreover, the H and T dependence of n yields an expression for the AT instability line that is in agreement with both theory and previously reported experimental studies.
Magnetic moments of Co-substituted Y2Fe14B
Authors: Gu Zong-Quan , Ching W. Y.
Published: July 2002

The local spin magnetic moments at each of the six inequivalent Fe sites in Y2Fe14B crystal are studied as the Fe atoms are selectively substituted by Co. First-principles spin-polarized electronic structure calculations are performed by the orthogonalized linear combination of atomic orbitals method and the spin magnetic moments are deduced from the site-projected and spin-projected partial density of states. In general, a Co substituted site has a smaller moment than the same site in Y2Co14B. The unsubstituted Fe sites are almost unchanged. The c, j2, and j1 sites are affected most while the e site is least affected by the Co substitution.
A study of the magnetic properties of cobalt ferrite-coated zinc ferrite particles
Authors: Tang Huan , Du You-wei , Qiu Zi-qiang , Walker J. C.
Published: July 2002

Nearly spherical Zn0.2Fe2.8O4 particles coated with an epitaxial layer of CoFe2O4 ferrites of various thicknesses were studied with Mössbauer spectroscopy. Measurements reveal that the magnetic structures of these particles are different at room temperature and liquid nitrogen or liquid helium temperatures, indicating the existence of a Verwey transition, which occurs between 77 and 119 K. Coating of Co-ferrite has no sizable effect on the transition.
Study of increasing coercivity of nonstoichiometric iron oxide powder caused by aging treatment
Authors: Wei Yu-Nian , Ling Qi-Fen
Published: July 2002

The phenomena of increasing coercivity of nonstoichiometric iron oxide powder (0.66r-Fe2O3⋅0.34Fe3O4) caused by aging treatment was studied. The results of chemical analysis and magnetic measurements at room temperature showed that the ratio of Fe2+/Fe3+ and saturation magnetization before and after aging were almost unchanged, but the coercivity was increased from 377 to 400 Oe. The Mössbauer spectra measured at 300 and 77 K showed the change of the spectra profile before and after aging treatment. The temperature dependence of normalized coercivity measured over the temperature range from 300 to 77 K before and after aging treatment was significantly different. The Hc -T curve after aging had a knee about at 200 K.
Spin-wave resonance in CoCr magnetic thin films
Authors: Cofield M. L. , Glocker D. , Gau J. S.
Published: July 2002

Spin-wave resonance spectra were observed at 9.8 and 35.2 GHz in CoCr thin magnetic films on both silicon and glass substrates. The perpendicular spectra of samples on the glass substrates had both even and odd numbered modes, while the perpendicular spectra of samples on silicon substrates had only odd numbered modes. The films had HKeff =−5.9 to −7.4 kOe and geff =2.12–2.38 for the most intense mode in the perpendicular spectra. The lower values of HKeff were observed for the films on the silicon substrates. Evidence of a surface spin-wave mode was seen in some of the spectra as a less intense mode observed at a higher applied field than the most intense mode in the perpendicular spectra. The resonance fields of the modes with mode number n>4 followed the n2 dispersion relation from which the exchange constant A has been estimated as A=1.0×10−6 erg/cm. The films had other resonances besides the spin-wave modes and the results of VSM studies showed evidence of a transition layer effect in the in-plane hysteresis loop. The results of x-ray diffraction studies show the films have predominate 002 growth axis on both substrates. The SEM cross section did not show any evidence of columnar structure on either of the substrates.
Calculated hysteresis loops and domain structures for CoNi thin films (abstract)
Authors: Victora R. H.
Published: July 2002

Magnetic properties are predicted for several CoNi thin films (∼1500 Å) formed by oblique evaporation.1 Input to the calculation consists of electron micrographs, torque curves, and diffraction data. The calculation includes both magnetostatic and exchange interactions, and consists of numerical integration of the Landau-Lifshitz equations. All reasonable choices of the exchange constant are found to give similar results. All other parameters are fixed from experimental input; thus, there are no free parameters. Domain nucleation is included by switching small segments of the sample and allowing the new domain to grow or decay. It is found that the switching mechanism for nearly perpendicular loops is coherent rotation of the constituent columnarlike grain’s magnetization, while switching for more longitudinal directions occurs by intracolumnar domain nucleation and propagation. Results are in excellent agreement with experimental hysteresis loops, and, in particular, the shifted ‘‘M’’ shape of the coercivity versus applied field-angle graph is reproduced. This work is believed to be the first accurate three-dimensional calculation for transition-metal thin-film hysteresis loops on a first principles basis.
Magnetic viscosity in some alloys and particles (abstract)
Authors: Berkowitz A. E. , Flanders P. J.
Published: July 2002

Magnetic viscosity describes the time-dependent changes in magnetization produced when a system is thermally activated over the energy barriers separating magnetic states. This behavior is usually modeled by calculating the time constants associated with surmounting the set of energy barriers. Néel suggested an alternative approach1 in which the Boltzmann energy kT was used to define a fluctuating internal field Hf, which assisted the crossing of the energy barriers. This fluctuating field has its origin in localized magnetization oscillations (i.e., spin-wave excitations). Some evidence for this model was recently noted2 in that maximum magnetic viscosity scaled with reduced temperature T/Tc for a variety of particulate recording materials. We have measured magnetic viscosity near Hc at 300 K in a number of permanent magnet alloys and recording media particles. All the samples showed a magnetization decay of the form M=Xirr(H0−H)+XirrSν ln t, where Xirr is the irreversible susceptibility, H0 and Sν are constants, and M, H, and t have their usual meanings. The scaling of the magnetic viscosity coefficient Sν with reduced temperature again suggests that Hf contributes to the magnetization change. However, the data also indicate that other parameters, e. g., the volume associated with a reversal event, are important factors in magnetic viscosity.
Rotationally invariant linear magnetoelastic theory (abstract)
Authors: Rinaldi S.
Published: July 2002

The magnetoelastic effects are usually described on the basis of an expression for the magnetoelastic energy which is a function of the symmetric strain εij and of the magnetization direction cosines αi and which has the form Eme=Bijkeεijαkαl, the number of different Bijkl being limited by symmetry. This expression, however, does not satisfy the principle of rotational invariance, i.e., the coupling energy varies when the reference system is rotated; this is equivalent to saying that it does not properly describe the effects of an applied strain containing an antisymmetric component ωij. This problem was previously recognized, studied for special cases, and related effects were observed. However, to our best knowledge, no explicit calculation of rotationally invariant magnetoelastic energy has been previously reported for the general cases of cubic and uniaxial symmetry. We will simply derive these expressions starting from an expansion of the energy of a magnetoelastic system in terms of the particles displacement gradients uij, using the definitions of the symmetric and antisymmetric strain tensors (εij=uij+uji; wij=uij−uji) and

imposing the rotational invariance. It results that, at the lowest order, the rotational invariant expression for the magnetoelastic energy has the form: Eme=Bijklεijαkαl +Pijklwijαkαl +Qijkl(αm)wijεkl +Rijkl(αm)wijwkl; explicit expressions for Pijkl, Qijkl(αm), and Rijkl(αm) will be given for the cases of uniaxial and cubic symmetry. Finally it will be shown how, using a simple transformation, the known theory on the elastic properties of magnetoelastic materials can be used for applied strains having antisymmetric components.
Temperature dependence of the magnetic 1/f noise in Eu0.4Sr0.6S (invited)
Authors: Koch R. H. , Reim W. , Malozemoff A. P. , Ketchen M. B.
Published: July 2002

We analyze in detail a novel integrated SQUID technique for studying magnetic noise and susceptibility. In particular, we show how the susceptibility, π/2 rule and the fluctuation-dissipation theorem (FDT) are affected by large demagnetizing factors and by the geometry of our pickup and field coils. We present data on the spin glass Eu0.4Sr0.6S as a function of temperature. We confirm the FDT and show evidence against the conventional power-law dynamics in the spin-glass phase.
On the static approximation for the Hubbard Hamiltonian
Authors: Lin H. Q. , Hirsch J. E.
Published: July 2002

We study the validity of the static approximation for the Hubbard model. We compare results obtained within the static approximation on two-dimensional finite lattices with results obtained from exact diagonalization and Monte Carlo simulations. We find that the static approximation is quite accurate at high temperatures but breaks down at low temperatures. One reason for its failure is that the static approximation destroys the rotational invariance in spin space.
Mössbauer effect of europium metal under pressure
Authors: Taylor R. D. , Farrell J. N.
Published: July 2002

The pressure dependence of the magnetic hyperfine field and of the isomer shift of 151Eu in europium metal has been studied in a diamond anvil pressure cell at low temperatures. In the pressure range 0–12 GPa at 44 K the magnetic hyperfine field changes from −22 to −8 T while the isomer shift increases from −7.3 to −3.8 mm s−1 relative to a SmF3 source. The changes are interpreted as indicative of a pressure-driven intermediate valence state causing a reduced magnetic moment in Eu. Intermediate valence and magnetic order coexist over the range of pressures studied.
Strings, commensurate and incommensurate vortices in X
Y models (invited) (abstract)
Authors: Lee D. H.
Published: July 2002

A class of simple, translationally invariant, nearest-neighbor, isotropic XY models that possess novel topological defects will be presented.1,2 As the first example, I shall present a model that exhibits, in addition to integer vortices, half-integer-vortex, and ‘‘string’’ excitations. The interaction between the half-integer vortices is a superposition of the usual logarithmic Coulomb potential and a linear potential mediated by the strings. Due to these new excitations the system possesses a rich phase diagram. As the second example, I shall present a model that supports commensurate and incommensurate vortices. Due to a novel ground-state degeneracy, the ‘‘charges’’ of the incommensurate vortices are fixed by their cost in zero-point entropy and are independent of the parameters in the Hamiltonian. Again, as a result of these new defects the model exhibits a very rich phase diagram.