bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetostatic mode spectra of uniaxial ferromagnets
Authors: Reimann H. , Hsia L. C. , Wigen P. E.
Published: February 2003

The Damon-Eshbach dispersion relation for magnetostatic modes in a rectangular platelet is expressed in terms of the permeability tensor of the magnetic medium and the consequences of a uniaxial easy-plane anisotropy are investigated. The anisotropy modifies the critical angle between bulk and surface modes which results in the existence of bulk excitations within the series of DE-surface modes. Two systems are analyzed. In the case of a ferromagnetic layer compound, the anisotropy is large compared with the demagnetizing field and the series of surface modes is replaced by a second series of volume modes. Recent measurements are reported on Ca-doped YIG. Several hundred modes of forward and backward volume modes are in good agreement with the calculated dispersion function using the parameters of pure YIG and Hu = −250 Oe. It is suggested that a measured anisotropy profile along the film normal suppresses a few bulk modes within the series of surface modes and accounts for a gap observed on the low field side of the uniform resonance.
Magnetostatic surface modes in nonuniform thin films with in-plane bias fields
Authors: Morgenthaler F. R.
Published: February 2003

We here develop an integral equation approach to the boundary value problem governing three-dimensional magnetostatic modes or waves in a thin film with either circular or rectangular geometry that applies when the dc magnetization M̄ is entirely in the plane of the film and the bias field and/or material parameters of the ferrite vary along M̄. Exchange effects, magnetic anisotropy, and dual dissipation are all neglected. The electromagnetic boundary conditions required at the film surfaces are built directly into these equations. For circular geometries the radial conditions enter through the components of the Polder susceptibility tensor. Nontrivial solutions occur when ω coincides with an eigenfrequency and we discuss a numerical method for solution of the spectra that correspond to one or more concentric rings. We also develop the analogous integral equations based upon cartesian coordinates for film configurations that involve one or more rectangular strips. For a single strip with uniform bias an approximate analytical treatment is presented. The equations govern a very wide range of physical situations. For example, coupling between modes circulating on two or more concentric annular rings spaced by an air gap can be handled as can the analogous problem involving ferrite strips.
Magnetostatic wave oscillator frequencies
Authors: Sethares J. C. , Stiglitz M. R. , Weinberg I. J.
Published: February 2003

The frequencies of magnetostatic wave (MSW) oscillators employing three principal modes of propagation, surface (MSSW), forward (MSFVW), and backward (MSBVW) volume waves, have been investigated. Previous (MSW) oscillator papers dealt with MSSW. Oscillators were fabricated using LPE-YIG MSW delay lines in a feedback loop of a 2–4 GHz amplifier. Wide and narrow band transducers were employed. Oscillator frequency as a function of biasing field is in agreement with a theoretical analysis. The analysis predicts frequency in terms of material parameters, biasing field, and transducer geometry. With wide band transducers a comb of frequencies is generated. Narrow band transducers for MSSW and MSFVW select a single mode; and MSBVW selects two modes. Spurious modes, attributed to instrumentation, are more than 20 dB below the main response, and bandwidths are less than 0.005 percent. No other spurious modes are observed. MSW oscillators produce clean electronically tunable signals and appear attractive in frequency agile systems.
Beams steering and diffraction of magnetostatic backward volume waves
Authors: Parekh J. P. , Tuan H. S.
Published: February 2003

This paper reports theoretical calculations of the beam spreading of magnetostatic backward volume waves (MSBVW’s) arising from the finite length of practical transducers. The calculations include the beam steering effects resulting from the pronounced anisotropy of MSBVW propagation. The predicted beam spreading of MSBVW’s is significantly larger than that of SAW’s on YZ LiNbO3. On the other hand, based on comparison with reported experimental results on the beam spreading of magnetostatic surface waves (MSSW’s), it would appear that MSBVW’s suffer smaller beam spreading than MSSW’s.
Magnetoelastic softening of moduli and determination of magnetic anisotropy in RE-TM compounds
Authors: Hathaway K. , Cullen J.
Published: February 2003

The longitudinal elastic modulus of polycrystalline Tb.3Dy.7Fe2 shows a magnetoelastic contribution which falls between those of the two shear wave moduli reported previously, and has a strong dependence on magnetic field. The temperature dependence of these moduli at finite fields, when compared with a model of linear magnetoelastic response, yields the anisotropy field as a function of temperature in good agreement with single crystal measurements. The longitudinal velocities of GdCo2 by contrst show no dependence on magnetic field beyond 2 KOe.
Theory of light scattering by the spin wave excitations of thin ferromagnetic films
Authors: Rahman Talat S. , Mills D. L. , Camley R. E.
Published: February 2003

We present calculations of the light scattering spectra produced by surface and standing spin wave excitations of a thin ferromagnetic film which has magnetization parallel to the surface. The influence of both exchange and dipolar coupling between the spins is included, along with spin pinning boundary conditions. The calculations provide a good account of the data on Fe80B20 films reported by Grimsditch, Malozemoff and Brunsch.
Magnetic linear dichroism in Sn doped YIG
Authors: Lucari F. , Terrenzio E. , Tomassetti G.
Published: February 2003

Comparing the results of Magnetic Circular Dichroism (MCD) measurements on Sn and Zr doped Yttrium Iron Garnets with those of Si doped YIG (1), some interesting differences can be observed. In fact, here, transitions at 1.65, 2.00 and 2.15 μm of wavelength are present other than the one at 1.20 μm characteristic of YIG(Si). We try to explain this difference on the basis of a computation of the electrostatic energy between the dopant and the Fe2+ ions and by considering the electron band scheme of pure YIG. So it is possible to hypothesize the presence, in our samples, of Fe2+ ions localized in both octahedral and tetrahedral sites, in contrast to what is observed in YIG(Si). To check this hypothesis, measurements of Magnetic Linear Dichroism (MLD) at room temperature are performed on a sample of YIG(Sn) (110). The results of the MLD versus the angle between the inducing magnetic field and the [100] crystal direction are presented; the measurements are made at different wavelengths in the interval 1–2.7 μm. The angular behavior of the MLD is in general similar to that expected by the theory for the octahedral centers, but strong contributions by centers with different symmetry appear to be superimposed, especially at low wavelength.
Spin-polarized atomic hydrogen: A magnetic gas (invited)
Authors: Silvera Isaac F. , Walraven J. T. M.
Published: February 2003

Atomic hydrogen (H) has recently been created in a long-lived state referred to as spin-polarized atomic hydrogen (H↓). A moderate density gas (n≃1017 atoms/ cc) has been produced at temperatures T≃400 mK. H↓ is predicted to be the only atomic substance that remains gaseous to T = 0 K; current experiments are consistent with this picture. Since the H↓ atoms behave as composite bosons the gas is expected to have a Bose-Einstein condensation (BEC) and related superfluidity at a sufficiently high density or low temperature. H↓ is expected to display spectacular static and dynamic properties. Since the gas is polarized, the dominant electronic magnetization, M⃗e, is proportional to the atomic density. In an inhomogeneous magnetic field M⃗e will also be highly inhomogeneous. BEC will be spatially localized and the static M⃗e should be an identifying feature of this state. The low-lying excitation spectrum should not only feature electronic and nuclear spin-transitions, but should also have magnetic translational modes of the gas. The experimental technique for stabilization of H↓ as well as many of the predicted magnetic properties are discussed.
Magnetic studies and removal of non-stoichiometry in MnO and CoO
Authors: Jagadeesh M. S. , Silinsky P. , Seehra M. S.
Published: February 2003

A major impediment in accurately determining the magnetic properties of the transition-metal oxides (MnO, CoO, NiO, FeO) has been the presence of non-stoichiometry (NS) in the available crystals. From studies in crystals of MnO and CoO, we report two important developments: First, the temperature-dependent magnetic susceptibility (χ) provides an excellent probe for detecting NS and second, a method has been developed to remove NS. From these studies, the presence of Mn3O4 in MnO and that of cation vacanies in CoO is inferred. In MnO and CoO, NS has been removed to undetectable levels by annealing the single crystals in the presence of Mn and Co atmospheres, respectively, at 1300 K for about 200 hours. Possible applications of these techniques to other systems are also discussed.
Influence of Ru3+ ions on anisotropy of PbFe12O19 single crystals
Authors: Zhai H. R. , Liu J. Z. , Lu M.
Published: February 2003

A remarkable influence of Ru3+ ions on the anisotropy of single crystals of PbFe12O19 was found. Single crystals of PbFe12−xRuxO19 were grown by flux method. For small addition of Ru ions, the uniaxial anisotropy constant K1 increases sharply, and reaches a maximum at x = 0.05. Then, the K1 tends to decrease with further increasing x. A maximum relative increment of 27% in K1 was obtained at 273°K. Also, the variation of K1 and Ha with T in a range of 100–273°K was investigated. For the crystals with x = 0.35, the phenomenon of spin reorientation was observed with the change of easy direction from c axis to basal plane at the temperature around 200°K. Below 200°K, K1 becomes negative. In addition, K2 increases monotonously with decreasing temperature.
LPE of LuLaSmGaFe garnet from a PbO-V2O5 flux
Authors: Berkstresser G. W. , Blank S. L.
Published: February 2003

A flux for garnet systems prepared from a PbO and V2O5 mixture has been found advantageous for thin film growth by LPE. There is reduced garnet solubility which leads to slower growth rates. A study of growth kinetics which are interpreted in terms of published models indicates a reduced kinetic constant. Melt equilibrium of the LuLaSmGaFe garnet in the PbO-V2O5 flux system was extensively examined over a wide temperature range. Relationships between film and melt compositions are interpreted in the context of an ideal solution theory for liquid and solid. The relationship between La and Ga interaction in this melt system is examined to reveal effects of growth temperature. Suggested modes for empirical adjustment of the equilibrium model to encompass growth rate effects are briefly discussed.
Influence of flux composition and growth temperature on the octahedral incorporation of rare-earth cations in rare-earth iron garnet
Authors: Gualtieri D. M. , Tumelty P. F. , Gilleo M. A.
Published: February 2003

Epitaxial films of RE3Fe5O12, where RE is Y or Ho, or the combination of Y or Ho with another rare-earth, were grown on (111) Gd3Ga5O12 substrates at nearly identical temperature from melts for which R3 = PbO/2B2O3 = 31.2, 7.4, or 5.0. The octahedral substitution for Fe was calculated from the Curie temperature and lattice constant. B2O3 was found to inhibit the octahedral substitution of rare-earth cations. In the case of RE = Y or Ho, this substitution was RE0.055 in the formula unit at R3 = 31.2, and approximately RE0.040 at R3 = 5.0. Lu was found to have a five-fold greater preference for octahedral substitution than Y or Ho. Octahedral preference was found to correlate well with ionic radius. Boron incorporation was small. Growth rate has a negligible effect on octahedral substitution, but reducing the growth temperature increases the octahedral substitution of rare-earth by about one-third percent per °C.
Domain wall resonance in magnetic bubble films
Authors: Parker A. A. , Parker M. A. , Wigen P. E.
Published: February 2003

Domain wall resonance frequency has been measured as a function of the magnitude and direction of an applied in-plane magnetic field. The effective wall mass determined from this data does not agree with the mass predicted by the usual Bloch wall model for the wall mass. A model that calculates the effect of magnetic surface charges on the mass is found to agree with the data for low fields. A model proposed by Morkowski is found to agree with the data for large values of the in-plane field. The angle dependence of the mass is found to be of the form 1/m = a0+a1 cos (2Θ) where Θ is the angle between the applied in-plane field and the plane of the domain wall.
Analysis of dynamic diffuse wall based on two-dimensional twist wall
Authors: Fujii T. , Kumosaki K. , Inoue M.
Published: February 2003

The mechanism and the dynamic properties of the dynamic diffuse wall observed in Garnet bubbles have been analyzed based on two dimensional twist wall with a finite film thickness. The analysis reveals that during wall motion, 360 °-spin twist nucleates inside the wall and propagates along the film thickness. The wall distortion takes place where the 360 °-twist appears. Annihilation and/or accumulation of the 360 °-twist occurs at the film surface. The number of the 360 °-twists contained in a wall increases with increasing drive and in-plane fields, which leads to an increase of the apparent wall width obtained by domain walls observed by transmitted light (Faraday effect). Most of the experimental results may be well interpreted by the present analysis.
FMR study of neon implanted LPE grown garnet layers
Authors: Algra H. A. , de Roode W. , Henskens R. A. , Robertson J. M.
Published: February 2003

The results of a study on the effects of neon implantation into bubble films are presented. Epitaxial films of composition La, Ga:YIG and Tm, Ca, Ge:YIG were implanted with 300 keV, 1014 Ne+ ions/cm2. The films were studied by ferromagnetic resonance (FMR) and by double crystal X-ray diffraction. The FMR spectra of the ion-implanted films exhibit an additional set of clearly observable spin wave resonances. Numerical calculations for the La, Ga:YIG film yield an anisotropy profile in the implanted layer, while moreover a decrease in the exchange constant was found. These findings were confirmed by an etching experiment. A good agreement between the maximum of the strain profile, as deduced from double crystal X-ray measurements, and the estimated anisotropy profile was found.
Critical curves for implanted garnet films in the presence of a demagnetizing field
Authors: Best J. S.
Published: February 2003

Demagnetizing fields near implanted/non-implanted boundaries have a significant effect upon the magnetization directions in contiguous disk devices. A new critical curve for the stable magnetization directions in an implanted garnet film is derived, including the effect of a uniform demagnetizing field. The magnitude of the in-plane field on the critical curve boundary is increased by the presence of the demagnetizing field. For a long, narrow implanted region, aligned along one three-fold easy axis, the magnitude of the in-plane field on the curve along the other two easy axes is ≊Hk1/3+HD/2. Approximating the implanted region between minor loops by a long ellipsoid, the minimum drive field for reliable propagation is predicted to be ≊Hk1/3+HD/2, in reasonable agreement with experiment.
1-μm bubble permalloy ’’contiguous-disk’’ devices
Authors: Sanders I. L. , Kane S. M. , Cohen M. S.
Published: February 2003

Gapless bubble propagation circuits based on a complementary permalloy contiguous-disk structure present an interesting alternative to the ion-implanted bubble devices currently being developed. This new approach combines the attractive lithographic tolerances inherent in the ion-implanted structure with the better established permalloy fabrication techniques. Successful propagation of 1 μm diameter bubbles has been demonstrated over bias field margins greater than 10% in circuits with a cell size of 15 μm2. The stepped structure was formed using an SiO2 lift-off method. The minimum lithographic feature was 1 μm and the operating drive field was approximately 50 Oe. Device tolerance to processing variations in terms of the required spacer thicknesses is shown to be adequate.
Bubble rectifiers and reverse rotation transfer gates based on gaps in ion implanted propagation patterns
Authors: Wolfe R. , Muehlner D. J. , Nelson T. J.
Published: February 2003

Gaps between unimplanted disks in ion implanted propagation patterns (I2P2’s) can allow bubbles to pass through in one direction and not in the opposite direction. These ’’bubble rectifiers’’ have been shown to perform a merge function. In a major-minor I2P2 bubble memory, a horizontal major line with a gap for each minor loop has been designed. Bubbles transferred out of minor loops down to this major line pass through the gaps and then propagate on the lower side past all the gaps to a detector, preserving the order of data tranferred in at the upper ends of the minor loops. For propagation on these multi-gapped lines, good bias field margins, somewhat lower than those for minor loop propagation, have been achieved with 2 μm gaps in 8 μm patterns and 1 μm gaps in 4 μm patterns. Using appropriately oriented gaps, bubbles can be transferred from one propagation track to another by temporary reversal of the drive field rotation direction. A family of reverse rotation transfer gates has been designed which provide selective transfer in or out of either end of the minor loops, depending on the starting phase and the number of reverse rotations, without disrupting adjacent data. The major advantage of these transfer gates is the absence of conductors.
Effects of conductor passivation on bubble propagation in contiguous disk devices
Authors: Horng C. T. , Schwenker R. O.
Published: February 2003

The present work investigated the impact of conductor passivation on 1 μm bubble propagation in contiguous disk devices. Without conductor passivation, devices with overlying AlCu stripes showed good propagation margins. When the devices were passivated with a thick layer of SiO2, the elastically ’’hard’’ dielectric material imposes a constraint to AlCu deformation and increases the conductor edge force. Furthermore, the edge force of the SiO2 passivation at the conductor edges, being in the same sign as that of the AlCu stripe, contributes to the total force acting on the underlying garnet. This intensifies the lcoal stress fields in the magnetic devices and seriously reduces the bubble propagation margin. To alleviate this passivation-enhanced stress problem, contiguous disk devices were passivated by elastically ’’soft’’ polyimide instead of sputtered SiO2.
Minimum drive fields in contiguous-disk bubble devices
Authors: Calhoun B. A. , Sanders I. L.
Published: February 2003

The shape anisotropy resulting from the elongated, parallel arrangement of the propagation tracks in contiguous-disk bubble devices makes a significant contribution to the minimum drive field of these devices. A simple model relates this contribution to the minimum drive field with the demagnetizing field of the ion-planted region between adjacent propagation tracks. There is good agreement between the prediction of the model and published results on eleven different contiguous-disk bubble devices. The implications on drive field requirements as contiguous-disk devices are scaled to high storage density are briefly considered.
A novel probe tester for the characterization of 1 Mbit/cm2 bubble memory devices
Authors: Chen C. T. , Benglas E. M. , Singh S. K. , Bullock D. C. , Whitinger B.
Published: February 2003

At Texas Instruments, we have developed a new bubble memory probe tester which is capable of generating an arbitrary drive field waveform having a peak amplitude of 90 Oe. It has the provision of noise injection to maximize the S/N ratio. In addition, a dc holding field can be superimposed on the in-plane rotating field to achieve stop/start bubble operation. For the megabit bubble memory devices fabricated by the planar process1 at Texas Instruments, comparable operation margins can be obtained with 50 Oe peak sinusoidal or trapezoidal drive or with 65 Oe peak triangular drive.
Megabit bubble memory process using a new type resin and TaMo alloy-Au conductor
Authors: Majima T. , Hirano A. , Orihara S.
Published: February 2003

A newly developed heat resistant resin, ladder type organosiloxane polymer, is applied to 8 μm period 1 megabit bubble memory devices. Propagation bias margin and reliability are discussed, comparing with the conventional SiO lift-off planar process. TaMo alloy-Au system is also introduced for the conductor. Interdiffusion, electromigration, and corrosion resistance of Au and refractory metals are studied.
Design and characterization of a 1 megabit bubble memory device with relaxed function designs
Authors: Yanase T. , Inoue H. , Iwasa S. , Orihara S. , Matsuyama S.
Published: February 2003

A low drive field 1 megabit bubble memory device has been developed with relaxed function designs and a planar process using a new type of Siloxane resin. The 1 megabit device uses a block replicate/swap organization based upon 1.9 μm diameter bubbles. The basic cell size is 7 μm×8 μm while the minimum feature size has a value of 1 μm. The chip size is 9.1 mm × 9.9 mm. Fabricated 1 megabit chips have been characterized over a drive field range of 45 to 65 Oe (peak field of 100 kHz triangular wave drive), and over a temperature range of 0 to 90°C. The results obtained in the characterization for the 1 megabit chips are good enough to guarantee the same drive field and sense requirements for packaged 1 megabit devices as those for 3 μm bubble 256 kbit devices.
The shape of propagating stripe domains
Authors: Muller M. W. , Weng R.
Published: February 2003

Straight isolated stripe domains pinned at both ends are stable in a range of bias field from bubble stripout threshold to 4πMs, exceeding the bubble stability range at the high-field end. This makes it possible to use such domains in the guiding structures of self-structured multilayered bubble domain devices. When such domains are propagated by translating their pinned ends, they assume a curved shape determined by the balance of the domain walls’ surface tension and the viscous and inertial forces due to coercivity, dynamic damping, and effective wall mass. The wall curvature restricts the ’’track width’’ of self-structured devices using guiding stripe domains. This bound has been estimated, assuming circular deformation, in the quasi-static limit where coercivity is dominant. We have calculated the shape of a uniformly propagating stripe domain as a function of bias field, propagation velocity, coercivity, and damping parameter. The results of the calculation can be used to estimate maximum device track width for desired operating speed and dimensional tolerance, and to measure the coercivity and the damping parameter.
Simulation of flexible magnetic bubbles in device environments
Authors: Blake T. G. W. , Shir C. C.
Published: February 2003

A numerical model for the simulation of the dynamics and deformations of thin film magnetic domains in magnetic bubble devices is described. The motions of the domain wall are calculated from the total effective magnetic field acting on them; the total field includes the equivalent field of the wall energy, the demagnetizing fields, the bias field, and the nonuniform fields from conductors or other sources. The numerical scheme of time integration of the wall motion is described; the simulation time step is adaptively optimized in the presence of incipient numerical instabilities, which are monitored by means of Fourier transformations. The model was used to investigate collapse and run-out of free bubbles and stripe-out and replication of domains under permalloy and current-carrying conductors. The results presented show agreement with experimental data.
Rotating field coil design method for magnetic bubble memory
Authors: Takahara M. , Izumi K. , Takaba T.
Published: February 2003

An analytical method for optimum design is described on magnetic bubble memory coils. It is remarkably important to design these coils in optimization, satisfying system requirements, bubble chip requirements and package requirements. The design technique in this paper is discussed in relation to coil dimensions, coil characteristics and factors relating to these requirements, in comparing with the calculation and the evaluation result. Practical magnetic bubble memory package examples are also discussed.
The effect of manganese and sulfur on the development of orientation (110) [001]-oriented low-alloy iron
Authors: Thornburg D. R. , Rauch G. C. , Foster K.
Published: February 2003

An investigation was made to determine the role of manganese and sulfur concentration on the development of (110) [001] orientation in low-alloy iron specimens by primary recrystallization and normal grain growth. Fifteen heats, containing nominally 0.8% Si and 0.6% Cr with varying Mn and S contents, were used for the study, with three-stage processing to 0.15 mm thick strip. The manganese content was varied between 0 and 0.15% with nominal sulfur contents of 0.001, 0.006, and 0.012%. Torque and magnetic properties, as well as X-ray pole figures, were used to evaluate the orientation after final annealing. The low-sulfur alloys (0.001% S) did not develop the best (110) [001] orientations. Those specimens containing the higher sulfur concentrations (0.012% were poorly oriented, except for one specimen which contained essentially zero Mn (<0.01%). All the specimens with nominal 0.006% S content developed strong (110) [001] textures with B10 values of up to 1.93 T and 60 Hz core losses at 1.7T as low as 1.5 W/kg.
Mechanism for effects of Al on magnetic properties of grain-oriented 3% Si-Fe
Authors: Luo Y. , Li W. L. , Cheng M. C. , Li Y. F. , Cheng Y. Z.
Published: February 2003

The main purpose of the present work is to study the role of Al in grain-oriented 3% Si-Fe, containing certain N contents (about 0.007%). Based on the experimental results and some thermodynamic considerations about solution-dissolution of AlN and MnS, a mechanism about the effect of Al on the magnetic properties of grain-oriented 3% Si-Fe is proposed, according to which the role of Al is to form AlN, as effective inhibitors.
Frequency dependence of the complex permeability of monocrystalline MnZn ferrous ferrites
Authors: Stoppels D.
Published: February 2003

For recording head applications it is important to know the response of monocrystalline MnZn ferrous ferrites to signals of various frequencies. For this purpose the complex permeability μ̄ = μ′−jμ″ of these materials has been studied using alternating magnetic fields with small amplitude and frequencies up to a few MHz. At 60 kHz, 0.5 MHz and 4.5 MHz the temperature dependence of μ′ and μ″ has been investigated for a wide range of temperatures T, including the temperature where μ′(T) reaches its so-called secondary maximum due to anisotropy compensation by the ferrous ions. An interesting feature found is that when the frequency f is raised this secondary maximum inverts to a minimum. In addition, μ′(f) and μ″(f) have been studied at some selected temperatures. For the case of a [100] preferential direction of the magnetization an empirical expression was obtained for μ′(f).
Compositional and structural studies of a MnZn ferrite under different processing conditions
Authors: Wang F. F. Y. , Krishnan K. M. , Cox D. E. , Reynolds T. G.
Published: February 2003

Among five processing conditions, a three stage vacuum sintering process produced the MnZn ferrite sample with the highest μi. Sintering in air produced samples with larger grain size and high μi values. The process of furnace-cooled overnight oxidized the Fe2+ content and allowed the precipitation of Fe2O3, which, in turn, resulted in sample of small grain size. All five processes produced spinel MnZn ferrite samples with the same unit cell size and the same oxygen parameter.
Recent developments in magnetic recording materials (invited)
Authors: Bate G.
Published: February 2003

Modern recording surfaces call for small, uniform, highly dispersible and orientable particles with high coercivity and an appropriate moment density or, alternatively, thin films having similar properties. Greatly improved particles of all kinds have been introduced in the last few years. The list includes iron oxides with compositions in the range Fe2O3–Fe3O4 (Hc = 250–450 Oe), cobalt-modified iron oxides and chromium dioxide (Hc = 450–700 Oe), and particles of iron, cobalt and their alloys (Hc = 700–1100 Oe). Increasing coercivity corresponds at present to lesser commercial importance and unfortunately, the more attractive magnetic properties seem almost invariably to be associated with thermal, mechanical or chemical instability. Metallic films continue to be attractive because of their thinness, magnetic material undiluted by non-magnetic material, flexibility of magnetic properties and low noise, but their disadvantages include poor reproducibility, poor resistance to wear and propensity to high levels of defects and to corrode. Recent developments of each kind of recording material will be reviewed with particular emphasis being given to unsolved problems.
Influence of particle interaction on coercivity and squareness of thin film recording media
Authors: Soohoo R. F.
Published: February 2003

Digital Recording density in continuous thin films can be significantly larger than in conventional particulate media. For this reason, there is much active research and development in such thin film recording media at present. However, no detailed calculation leading to a satisfactory explanation for the high squareness and an Hc decreasing monotonically with film thickness t has appeared. Using a model of strongly interacting anisotropic grains and neglecting exchange at grain boundaries, we examined here particle interaction and its influence on S and Hc. It is shown that the rather high squareness found in such media (e.g., S?0.8 for films of Co with t≳200Å) is related to strong dipolar interaction between the constituent grains. Although such films are continuous, surface roughness due to microscopic film thickness variation from grain to grain-boundary can be appreciable. Indeed, our calculation shows that these thickness variations can account for Hc and its variation with t experimentally observed.
The origin of Barkhausen noise in small permalloy magnetoresistive sensors
Authors: Tsang C. , Decker S. K.
Published: February 2003

The magnetoresistive (MR) response of permalloy sensors is increasingly plagued by jumps or noise of a magnetic origin (so-called Barkhausen noise) as their sizes are reduced to tens of microns. The origin of this noise is not presently understood. In previous work (1) we reported a study of the Barkhausen noise by separately measuring the MR response and the domain processes involved, but detailed correlation between the two was still lacking. In this work, therefore, we performed simultaneous measurements of both the MR response and domain patterns on small MR elements of typically 12μm×24μm, enabling us to analyze the domain processes affecting the MR output. We have identified two classes of domain processes primarily responsible for noise in the MR output, namely, abrupt domain wall population reductions during early stages of demagnetization, and wall state transitions involving nucleation and expansion of N− wall segments around zero field. Additional insight into the N+→N− transitions has been obtained through consideration of the energetics of formation of the N− segment, and the response of such a segment to applied fields.
Applicability of the planar Hall effect
Authors: Fluitman Jan H.
Published: February 2003

The planar Hall effect in ferromagnetic films has been investigated. Particularly the response to inhomogeneous fields has been studied in view of the method of detection of the Hall voltage (’’one-sided’’ or traditional). It is concluded that ’’one-sided’’ detection may be of advantage. The Hall response around the theoretical singularity of the transverse susceptibility has been studied. It is found that a very sensitive device can be designed, based on this effect.
New ductile Fe-Mo-Ni magnet alloys
Authors: Jin S. , Tiefel T. H.
Published: February 2003

New, ductile, and cobalt-free magnet alloys based on the Fe-Mo-Ni system have been developed for potential substitution of some Co-Fe base magnet alloys. The new alloys are very ductile and can be processed into thin tape or fine wire. An Fe-20 Mo-5Ni (wt. %) alloy can be processed to exhibit magnetic properties of Br∼10500 G, Hc∼210 Oe, and (BH)max∼1.1 MGOe which are comparable to those of Vicalloy I (52Co-38Fe-10V). An Fe-7Mo-5Ni alloy exhibits high-remanence, square-loop, anisotropic magnet properties of Br∼19200 G, Hc∼30 Oe, and Br/Bs ∼0.97 which are superior to those of Type 27 Remendur (49Co-48Fe-3V) or Nibcolloy (85Co-12Fe-3V). The new Fe-Mo-Ni alloys consist of abundant elements and could substitute for some of the Co-Fe base magnet alloys which contain large amounts of expensive and strategic cobalt.
Magnetic domains in cobalt and iron borides
Authors: Livingston L. D.
Published: February 2003

Using Kerr and Bitter techniques, magnetic domain patterns have been studied in various cobalt, iron, and cobalt-iron borides prepared by chill casting, directional solidification, and melt-spinning. Magnetic symmetries and metallurgical stability of the phases are discussed.
Low oxygen processing of SmCo5 magnets
Authors: Narasimhan K. S. V. L.
Published: February 2003

A low oxygen processing technique was developed for the manufacture of SmCo5 and temperature compensated magnets. Improvement in the magnetic field orientation monitored by Schulz pole figure technique and the controlled oxygen processing resulted in SmCo5 magnets with energy products of 25–28 MGOe. The temperature dependence of magnetic induction for the Gd, Dy, Ho and Er substituted SmCo5 magnets have been carried out from −50 °C to +200 °C and the results indicate that it is possible to select a composition to tailor fit the temperature characteristics of a device so that a temperature independent magnetic flux can be obtained.
A model on the coercivity of the hardened 2–17 rare earth-cobalt permanent magnets
Authors: Tian-duo Sun
Published: February 2003

A microstructure geometry with cells as rhombic hexahedrons which are separated from each other by a thin layer wall is given. Non-coherent wriggle domain wall displacement mechanism is proposed. An expression for the coercive force Hc = (√3)Δγ/(2Msd) has been derived. The calculated values are fairly in agreement with the measured values either qualitatively or quantitatively.
Low cobalt Cr-Co-Fe permanent magnet alloys (invited)
Authors: Chin G. Y. , Jin S. , Green M. L. , Sherwood R. C. , Wernick J. H.
Published: February 2003

This paper reviews the results of studies in our laboratory in the 2 to 12% Co range of Cr-Co-Fe permanent magnet alloys. Our salient results are as follows: (1) Isotropic ternay alloys, typified by 10.5Co-28Cr-Fe (Chromindur II) with values of Br = 9800, Hc = 400 Oe and (BH)max = 1.8 MGOe. This alloy is now in volume production for telephone receiver applications. (2) Anisotropic ternary alloys prepared by a newly developed ’’deformation-aging’’ process, with values of (BH)max ranging from 2.3 MGOe for a 5Co-33Cr-Fe alloys to 5.5 MGOe for an 11.5Co-33Cr-Fe alloy. Adding 2% Cu raises the value of (BH)max by 0.5–1.0 MGOe. (3) Anisotropic alloys prepared by magnetic-field aging, with values of (BH)max ranging from 4.2 MGOe for a 2.5Co-32Cr-Fe alloy to 6.2 MGOe for a 9Co-27Cr-Fe alloy. (4) Sintered magnets typified by the 5Co-31Cr-Fe alloy with (BH)max∼4.4 MGOe.
Mn-Al-C for permanent magnets (invited)
Authors: Bohlmann M. A. , Koo J. C. , Wise J. H.
Published: February 2003

Mn-Al-C alloy for permanent magnets has merit for several reasons: a) carbon stabilizes the metallurgical phases, deformation temperature is high enough for plastic transformation to produce anisotropic τ-phase efficiently; b) useful magnetic energy exceeds the best hexaferrites; the alloy can be more efficient than Alnico 8 and some other high-cobalt materials; c) Mn sources are more widely distributed and the metal is much less costly to obtain than cobalt. Carbon control and tooling life are key factors to obtain a commercial product. Micrographs illustrate the metallurgical phases. Although Mn-Al-C has a lower temperature coefficient for magnetic flux changes than the hexaferrites, its maximum use will be limited to 100–125 °C. Certain energy-efficient electric motors could be an important application.
A review of coercivity mechanisms (invited)
Authors: Livingston J. D.
Published: February 2003

Mechanisms of magnetization reversal and factors determining coercivity are reviewed for various permanent-magnet materials.
The future of rare earth-transition metal magnets of type RE2TM17 (invited)
Authors: Lee R. W.
Published: February 2003

A brief review of the development of RE2TM17 permanent magnets is followed by a summary of the state-of-the-art. Excellent magnetic properties have been achieved in the laboratory for single-phase 2:17 and two-phase, precipitation hardened magnets of ∼2:15 stoichiometry. Both achieve reduction of cobalt content to ∼50 wt.% by transition metal substitution and the precipitation hardened type exhibit improved temperature characteristics. Recent improvements in coercivity make high volume application practical if the more abundant light rare earths can be successfully substituted for samarium.
Recent developments in the measurement of magnetic fields from isolated nerves and muscles (invited)
Authors: Wikswo J. P.
Published: February 2003

We have developed a Superconducting Quantum Interference Device (SQUID) magnetometer with a miniature, room-temperature toroidal pick-up coil that has sufficient sensitivity and frequency response to measure the magnetic field associated with the action potential of isolated nerves and muscles. A magnetically shielded SQUID operates in a liquid helium storage dewar so that the measurements of the weak magnetic fields can be made in a typical laboratory. The nerve or muscle fiber is immersed by Ringer’s solution and is threaded through the ferrite core of the toroidal pick-up coil so that electrical current within the fiber will thread the toroid but the return current external to the fiber will not. The time-dependent 100 pT magnetic field produced by the cellular action current induces currents in the pick-up coil that are detected by the SQUID with signal-to-noise ratios of 10 to 1 in a 2 kHz bandwidth. In the case of a single large nerve axon, this technique will allow quantitative measurement of the intracellular and transmembrane currents, the effective intracellular axial resistivity, and the time dependence of the transmembrane conductance without puncturing the nerve membrane with a microelectrode. This technique is being extended to study current flow in cardiac muscle.
Efficiency comparison of two preparative mechanisms for magnetic separation of erythrocytes from whole blood
Authors: Graham M. D.
Published: February 2003

Separation efficiencies of erythrocytes, made paramagnetic by oxidation of their cellular oxyhemoglobin to methemoglobin with sodium nitrite, were compared under identical magnetic separation conditions with those of cells whose oxyhemoglobin had been reduced to deoxyhemoglobin through exposure to sodium dithionite, and the percentage of high-spin hemoglobin was estimated spectrophotometrically. Both parallel and transverse flow/matrix filter configurations gave greater average separation efficiencies, with less variability, for erythrocytes containing the dithionite-reduced hemoglobin. These findings are thought to originate in the characteristics of the oxidative reaction, since the spectrophotometric data indicate a similar variability in oxidation of oxyhemoglobin to methemoglobin.
Effects of dislocations on channeling
Authors: Zakowicz W. , Pantell R. H.
Published: February 2003

An analysis is presented for describing dechanneling by a dislocation. Periodicity of the crystal potential is incorporated into the model, and in the region of the distortion particles are allowed to penetrate the atomic planes without dechanneling. Phase space diagrams are used to illustrate the change of state of the channeled particle caused by a distortion. The cross section for dechanneling is found to be proportional to (γ−γ−1)1/2, where γ is the ratio of particle energy to its rest energy.
Infrared reflection studies of γ-ray irradiated NaNO2
Authors: Kim Hyung Kook , Kwun Sook-Il
Published: February 2003

The infrared reflectances of virgin and γ-ray irradiated NaNO2 have been determined from the reflection spectra which have been investigated as functions of temperature (ranging from RT to 180 °C) and crystallographic orientation, and γ-ray irradiation dose (4×107 and 3×108 röntgen.) over a frequency region between 700 and 2000 cm−1. Using the Kramers-Kronig dispersion relation, we have obtained the dielectric function and oscillator parameters from the reflection spectra. These constants are used to explain the ferroelectric properties of NaNO2. In addition the observed differences between the reflection spectra of virgin and those of γ-ray irradiated NaNO2 are explained using a broken-bond model.
Dynamic fracture and spallation in ductile solids
Authors: Johnson J. N.
Published: February 2003

A mathematical model of ductile hole growth under the application of a mean tensile stress is developed and applied to the problem of spallation in solids. The object is to describe dynamic ductile fracture under a wide range of tensile loading conditions. The mathematical model presented here describes both plate-impact spallation (as observed by postshot examination and time-resolved pressure measurements) and explosively produced spallation (as observed by dynamic x-radiographic techniques) in copper. It is found to be inapplicable to ductile fracture of expanding rings, even in the absence of possible adiabatic shear banding and classical necking instabilities, because of the fact that the mean tensile stress (void growth) and the deviatoric stress (homogeneous plastic shear strain) are not independent. A phenomenological model of void growth under uniaxial stress conditions is developed independently and applied to the numerical finite-difference solution of fracture in an expanding ring. The initial porosity in a material element is a random variable following Poisson statistics and the assumption that all the void radii are equal. The necessary theoretical generalizations and supporting experimental measurements to improve our understanding of fracture and fragmentation in expanding rings are discussed.
Nonlinear pressure dependence of the elastic moduli of fused quartz up to 3 GPa
Authors: Kondo Ken-ichi , Iio Satoshi , Sawaoka Akira
Published: February 2003

The elastic moduli of fused quartz have been determined by ultrasonic measurements under high hydrostatic compressive stress and showed a nonlinear decrease to a minimum value at 2.1–2.5 GPa, and thereafter an increase with increasing pressure. Changes in the Debye temperature and the Grüneisen constant are determined using the present results. Assuming a contribution of the fourth-order elastic constants to the nonlinear dependence, C1111, C1112, C1122, and C1123 have been tentatively evaluated to be 11.0±1.0, 10.8±3.6, 22.7±11.1, and 8.6±2.0 TPa, respectively. However, the possibilities of a complicated potential curve or a higher-order phase transition are also discussed.
Raman investigation of optical fibers under high tensile stress
Authors: Walrafen G. E. , Krishnan P. N. , Freiman S. W.
Published: February 2003

Raman spectra have been obtained from fused silica optical fibers under tensile stresses from 0 to 3.3 GPa (33 kbars). Reversible intensity increases, relative to the principal Raman maximum at 440 cm−1, were observed for the defect peak at 490 cm−1 and for shoulders near 350–375 and 115 cm−1. Application of tensile stress to fused silica appears to produce changes in the stretched Si—O defect sites, as well as changes in the main network structure.
(p/n) PbTe multiple-layer films prepared by a hot wall technique
Authors: Kinoshita H. , Sakashita T. , Fujiyasu H.
Published: February 2003

The PbTe multiple-layer structures with alternating types of conductivity (p/n) were made by the hot wall technique. The net carrier density of multiple-layer films (obtained by Hall-effect measurements) decreased by an order of magnitude compared to singly doped films. These multiple-layer films indicated sensitive photoconduction and their structures were confirmed by I-V and C-V measurements.
The Lorenz ratio and electron transport properties of NbO
Authors: Hsieh N. , Fine M. E.
Published: February 2003

The thermal and electrical conductives of the same single and polycrystalline samples of NbO were measured over the temperature range 100–660 °K. The Wiedemann-Franz-Lorenz law is rather well obeyed in NbO; however, like Cr, there is a positive deviation from the theoretical Lorenz number. This deviation is a maximum of 30% at approximately 250 °K. Following Cr, this positive deviation is attributed to the multi-energy-band structure of NbO.
Phonon fluctuation model for flicker noise in elemental semiconductors
Authors: Jindal R. P. , Van Der Ziel A.
Published: February 2003

Acoustic mode lattice scattering plays an important role in determining the carrier mobility in elemental semiconductors over a wide range of temperature. For germanium and silicon, over the temperature range of interest, these longitudinal acoustic phonons are primarily scattered by isotopes and chemical impurities. The relaxation time is directly proportional to the fourth power of the phonon wavelength. Hence, for a relatively small phonon wavelength spread of three decades, the phonon relaxation time spans full 12 decades. The number of phonons for a given acoustic mode fluctuates at random. Hence, the phonon population for each mode exhibits a g-r noise spectrum characterized by its relaxation time. Through electron-phonon interaction (assuming elastic scattering), this g-r noise spectrum is transferred to electron mean free path (same holds for hole), where after superposition, it leads to 1/f spectrum. The theoretical results support the experimental findings of several authors.
Reflection of sine-Gordon breathers
Authors: Olsen O. H. , Samuelsen M. R.
Published: February 2003

The influence of a boundary on a breather traveling in a Josephson line cavity is examined by means of numerical computations. For a passive termination the breather is reflected into a breather of less energy; when the characteristic impedance of the line equals the external load resistor the breather is almost annihilated. At an active termination the breather is reflected into a breather of increased energy possibly followed by fluxons, antifluxons, or even breathers.
A method for determining the SQUID parameter β and the coupling coefficient K in a nonhysteretic rf SQUID
Authors: Erné S. N. , Luther H.
Published: February 2003

A method for determining the superconducting-quantum-interference-device (SQUID) parameter β = LsIc/Φo and the coupling coefficient K between the SQUID loop and tank circuit based on the general theory for the nonhysteretic rf SQUID is derived. Analysis of the periodic dependence of the amplitude of the tank-circuit voltage on applied dc flux leads to explicit expressions for β and K. Important advantages of the method are that, during measurements, the SQUID loop has neither to be opened nor decoupled from the tank circuit, and the temperature of the sample does not have to be changed. Measurements with a Nb-point-contact SQUID at 4.2 K to verify the method in practice are reported. Intrinsic errors were estimated to be less than 10%.