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Showing papers in "IEEE Transactions on Magnetics in 1996"


Journal ArticleDOI
TL;DR: In this article, the authors used a combination of molecular dynamics based upon the Landau-Lifshitz-Gilbert equation of motion and a Monte Carlo method for dealing with magnetic viscosity to identify the thermal stability limits on data storage density in longitudinal recording on thin film media.
Abstract: Simulations have been carried out with the purpose of identifying the thermal stability limits on data storage density in longitudinal recording on thin film media. The simulations use a combination of molecular dynamics based upon the Landau-Lifshitz-Gilbert equation of motion and a Monte Carlo method for dealing with magnetic viscosity. Based upon the limits on media coercivity imposed by available heads and SNR considerations, but assuming that sufficient head resolution can be achieved, an upper bound of about 36 Gbit/in./sup 2/ is projected.

508 citations


Journal ArticleDOI
Jacques C. S. Kools1
TL;DR: An overview of the material properties of exchange-biased spin-valves is given in this paper, where the microstructure and magnetic properties of these materials are discussed as relevant for industrial application in magnetoresistive read heads for rigid disk and tape recording and Magnetic Random Access Memory (MRAM) devices.
Abstract: An overview is given of the material properties of exchange-biased spin-valves. More specifically, we discuss the microstructure and magnetic properties of these materials as relevant for (future) industrial application in magnetoresistive read heads for rigid disk and tape recording and Magnetic Random Access Memory (MRAM) devices.

411 citations


Journal ArticleDOI
TL;DR: In this paper, the growth and characterization of superlattice nanowires are discussed, which are ideal for measurements of GMR in the current perpendicular to plane (CPP) geometry and are an example of a structure which can only be produced by electrodeposition.
Abstract: Electrodeposition is one of the simpler and cheaper processes available for the fabrication of thin metal films. Recent developments have made it possible to electrodeposit a wide range of nanostructured materials, including many that exhibit giant magnetoresistance (GMR). We review progress in the growth and characterization of such films, starting with electrodeposited ferromagnetic metal/non-magnetic metal superlattices in which the individual layers can be as thin as 10 /spl Aring/ or less and for which several workers have reported significant GMR at room temperature. Next we describe a method which can be used to produce superlattices having a thickness of several /spl mu/m and an area of less than 1 /spl mu/m/sup 2/. These "superlattice nanowires" are ideal for measurements of GMR in the current perpendicular to plane (CPP) geometry and are an example of a structure which at present can only be produced by electrodeposition. Finally, we consider the electrodeposition of heterogeneous alloy films showing GMR.

244 citations


Journal ArticleDOI
TL;DR: A new code is presented which improves the minimum distance properties of sequence detectors operating at high linear densities, and possesses the similar distance-gaining property of the (1,k) code, but can be implemented with considerably higher rates.
Abstract: A new code is presented which improves the minimum distance properties of sequence detectors operating at high linear densities. This code, which is called the maximum transition run code, eliminates data patterns producing three or more consecutive transitions while imposing the usual k-constraint necessary for timing recovery. The code possesses the similar distance-gaining property of the (1,k) code, but can be implemented with considerably higher rates. Bit error rate simulations on fixed delay tree search with decision feedback and high order partial response maximum likelihood detectors confirm large coding gains over the conventional (0,k) code.

239 citations


Journal ArticleDOI
TL;DR: In this article, a new type of micro swimming mechanism was proposed for microrobots working in water, which is composed of a small magnet attached to a spiral wire, and an external alternating magnetic field causes the magnet to rotate due to magnetic torque.
Abstract: A new type of micro swimming mechanism is proposed for microrobots working in water. It is composed of a small magnet attached to a spiral wire. An external alternating magnetic field causes the magnet to rotate due to magnetic torque. As a result, the mechanism can swim propelled by waves traveling along the spiral. The swimming velocity increases linearly with increasing excitation frequency, and the increasing rate depends on the shape of the spiral. The experimental velocity agrees with the calculation result based upon Lighthill's theory (1975, 1976).

218 citations


Journal ArticleDOI
TL;DR: This paper presents a method for automatic design of magnetic devices that can be used to determine both the topology and shape of the required device, as well as the materials to be used.
Abstract: This paper presents a method for automatic design of magnetic devices. The process can be used to determine both the topology and shape of the required device, as well as the materials to be used. Sensitivity information derived directly from Maxwell's equations is used to direct the optimization process. The method is applied to the design of a jumping ring (magnetic bearing).

175 citations


Journal ArticleDOI
TL;DR: An overview of various finite element techniques based on the magnetic vector potential for the solution of three-dimensional magnetostatic problems is presented in this paper, where the vector potential is interpolated with the aid of edge finite elements and no gauge is enforced.
Abstract: An overview of various finite element techniques based on the magnetic vector potential for the solution of three-dimensional magnetostatic problems is presented. If nodal finite elements are used for the approximation of the vector potential, a lack of gauging results in an ill-conditioned system. The implicit enforcement of the Coulomb gauge dramatically improves the numerical stability, but the normal component of the vector potential must be allowed to be discontinuous on iron/air interfaces. If the vector potential is is interpolated with the aid of edge finite elements and no gauge is enforced, a singular system results. It can be solved efficiently by conjugate gradient methods, provided care is taken to ensure that the current density is divergence free. Finally, if a tree-cotree gauging of the vector potential is introduced, the numerical stability depends on how the tree is selected with no obvious optimal choice available.

168 citations


Journal ArticleDOI
C.A. Luongo1
TL;DR: In this article, the authors review the developments in the US SMES program that have taken us to where we are today, briefly review SMES-related activities around the world, and points out trends in applications and development of SMES.
Abstract: The last couple of years have seen an expansion on both applications and market development strategies for SMES (superconducting magnetic energy storage). Although originally envisioned as a large-scale load-leveling device, today's electric utility industry realities point to other applications of SMES. These applications-transmission line stabilization, spinning reserve and voltage control-are likely to open the door to SMES commercialization in the electric utility sector. In the industrial sector, power quality concerns are already driving the development of a market for micro-SMES devices, and load-leveling at an industrial scale is fast becoming a potential application. Work recently completed as part of the US SMES program, as well as ongoing design activities, point to self- (or cold-) supported SMES as the design option in the near-future. This is a major departure from the earth-supported SMES systems first envisioned 25 years ago for utility load-leveling. The path to commercialize SMES is not likely to include a large 'demonstration' unit, or model, but rather follow an evolutionary process in which bigger and better units will be fielded in response to specific applications. This paper reviews the developments in the US SMES program that have taken us to where we are today, briefly reviews SMES-related activities around the world, and points out trends in applications and development of SMES.

163 citations


Journal ArticleDOI
TL;DR: In this article, the effective complex permeability and permittivity spectra in composites with various ferrite volume fractions were calculated using the Bruggeman effective medium theory, and matching conditions for the maximum microwave absorption were determined by substituting the complex porosity and permitivity in the equation for the impedance matching condition.
Abstract: The effective complex permeability and permittivity spectra in composites with various ferrite volume fractions were calculated using the Bruggeman effective medium theory. The matching conditions for the maximum microwave absorption were determined by substituting the complex permeability and permittivity in the equation for the impedance matching condition. The minimum reflection loss increases from -5 to -40 dB as the ferrite volume fraction increases for /spl nu//sub f/<0.26, where single dip of minimum reflection loss was observed. However, two matching conditions were observed for v/sub f//spl ges/0.26, and two minimum reflection losses shown to be about -40 dB. The results indicate that a microwave absorber with reflection loss of about -40 dB can be designed by controlling the ferrite volume fraction in MnZn ferrite-rubber composites in the frequency range 0.8-12 GHz.

144 citations


Journal ArticleDOI
TL;DR: In this paper, the convergence of the non-gauged vector potential formulation (curl curl equation) is studied and an explanation of the convergence behavior is given through the analysis of the matrix structure: under the condition of the compatibility, the CCE is implicitly ganged by an iterative solver.
Abstract: The vector potential formulation is widely used in electromagnetic field computation due to its robustness. Numerical experiences on the convergence behaviour of the non-gauged vector potential formulation (curl curl equation) are reported. The convergence of the system depends on the discretisation of the source variable (the right hand side of the equation). The system converges if the matrix equation is compatible, i.e. if the RHS is in the range of the curl-curl matrix. The compatibility is ensured when the current density is expressed by the curl of a source field (vector potential) and when this source field is projected on the space curl W/sup 1/, where W/sup 1/ is the space of the Whitney edge element. An explanation of the convergence behaviour is given through the analysis of the matrix structure: under the condition of the compatibility, the curl-curl equation is implicitly ganged by an iterative solver.

136 citations


Journal ArticleDOI
TL;DR: In this article, a magnetoresistive GMR-sensor scheme is demonstrated and analyzed in which the hard magnetic layers are replaced by Artificial Antiferromagnetic Subsystems (AAF's), which consist of ferromagnetic layers antiferromagnetically coupled via interlayers.
Abstract: A magnetoresistive GMR-sensor scheme is demonstrated and analyzed in which the hard magnetic layers are replaced by Artificial Antiferromagnetic Subsystems (AAF's). These consist of ferromagnetic layers antiferromagnetically coupled via interlayers. The magnetic rigidity of this AAF is improved by an order of magnitude compared to the individual magnetic layers. Operational field windows for 360/spl deg/-angle detectors 20 kA/m have been realized. The sensor signal /spl Delta//spl rho///spl rho/ is 6%. The temperature-operation range extends itself up to 150/spl deg/C. The angle resolution is 1/spl deg/.

Journal ArticleDOI
TL;DR: The coil current-to-force relationship is developed for this type of machine, and several optimal solutions for realizing an arbitrary static force are presented for various constraints on the orientation of the implanted permanent magnet.
Abstract: Very small implanted permanent magnets guided by large electromagnetic coils have been proposed previously as a method for delivering hyperthermia to or guiding catheters through brain tissue. This procedure is termed "magnetic stereotaxis". Early efforts employed a single coil on a movable boom, a design that proved logistically difficult to use on human patients. The present work deals instead with a design where several stationary coils are employed to develop a force on the implanted magnet. The coil current-to-force relationship is developed for this type of machine, and several optimal solutions for realizing an arbitrary static force are presented for various constraints on the orientation of the implanted permanent magnet. Costs of the different solutions are compared in several examples using a mathematical model based on the Magnetic Stereotaxis System (MSS) developed by Stereotaxis, Inc., the University of Virginia, and Wang NMR.

Journal ArticleDOI
TL;DR: A vector generalization of the Jiles-Atherton model of ferromagnetic hysteresis is proposed in this article, which gives a differential equation relating vector magnetization to vector magnetic field and essentially retains the simplicity of the original scalar model.
Abstract: A vector generalization of the Jiles-Atherton model (1986) of ferromagnetic hysteresis is proposed. It gives a differential equation relating vector magnetization to vector magnetic field and essentially retains the simplicity of the original scalar model. The model can handle both the isotropic and anisotropic case and is equivalent to the scalar model for unidirectional fields. It exhibits major features of vector hysteresis such as rotational hysteresis and DC magnetization.

Journal ArticleDOI
TL;DR: In this paper, the authors present results on magneto-impedance (MI) in a NiFe/Co/NiFe sandwich film of 0.2 /spl mu/m thickness, which exhibits the impedance change up to 8% for a field of 4 Oe at a frequency of 400 MHz.
Abstract: This paper presents results on magneto-impedance (MI) in a NiFe/Co/NiFe sandwich film of 0.2 /spl mu/m thickness, which exhibits the impedance change up to 8% for a field of 4 Oe at a frequency of 400 MHz. The effect of voltage change with the field can be especially large (/spl sim/200% for 5 Oe) if the sandwich film is incorporated in a self oscillation circuit which can be directly used for magnetic sensor head applications. The comparative analysis of MI in a sandwich film and a single magnetic layer is given, demonstrating that the sandwich structure can show an increase in MI of about a factor of 6 over a single magnetic layer and the maximum MI effect occurs at frequencies of an order of magnitude lower.

Journal ArticleDOI
Jaquelin K. Spong1, Speriosu, Robert E. Fontana1, Moris Dovek1, T.L. Hylton1 
TL;DR: In this article, the authors describe the design, fabrication, and performance of a spin valve magnetic field sensor based on the giant magnetoresistive effect, which is a balanced, four resistor, fully biased, Wheatstone bridge network with bipolar output.
Abstract: We describe the design, fabrication, and performance of a "spin valve" magnetic field sensor based on the giant magnetoresistive effect. The sensor is a balanced, four resistor, fully biased, Wheatstone bridge network with bipolar output. The devices described here show magnetoresistance ratios /spl Delta/V/V=/spl Delta/R/R=6%, saturation fields of 25 Oe, and a Johnson limited noise floor of 2.6 /spl mu/Oe/(Hz)/sup 1/2/. The linearity of the device is +/-2% of the full scale amplitude, with a hysteresis of 1% over the linear range. Fabrication of this device requires a novel approach to setting the directions of the antiferromagnetic exchange layers that bias the sensor. As compared to bridges based on the anisotropic magnetoresistance effect, these devices offer superior signal amplitude and linearity. To our knowledge this is the first report of such a device.

Journal ArticleDOI
TL;DR: In this article, the authors developed a new permeance meter in the 1 MHz-1.5 GHz range using either a microstrip pickup coil or a shielded loop pickup coil.
Abstract: We have developed a new permeance meter in the 1 MHz-1.5 GHz range using either a microstrip pickup coil or a shielded loop pickup coil. Both pickup coils and the driving plates are free from LC resonance due to impedance matching. In the MHz range we must consider signal-to-noise ratio of the pickup coil. In the GHz range we must eliminate the voltage induced by the electric field, and an electromagnetic higher order mode in the driving plates.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the effect of CoSiB/SiO/sub 2/CoSiB films with line structures on the impedance change ratio, where easy axes have been induced in a perpendicular direction to the driving current.
Abstract: Giant Magneto-Impedance (MI) effect of CoSiB/SiO/sub 2//Cu/SiO/sub 2//CoSiB films with line structures have been studied. Easy axes have been induced in perpendicular direction to the driving current, and the insulating SiO/sub 2/ layers have prevented the driving current from penetrating into the CoSiB layers. This structure has enabled the effective occurrence of resistance change at a frequency as low as several MHz. As a result, impedance change ratios /spl Delta/Z/Z/sub 0/=(Z/sub maximum/-Z(H/sub ext/=0))/Z(H/sub ext/=0) are much higher than that of any other layered film without insulating layers. The /spl Delta/Z/Z/sub 0/ at 20 MHz is as high as 700% at 11 Oe, and the maximum slope is 300%/Oe.

Journal ArticleDOI
TL;DR: This paper examines an axial-field permanent-magnet synchronous wind power generator, mainly from the magnetic viewpoint, as well as some primary test results concerning model generators having nominal power of 5 and 10 kW.
Abstract: In order to achieve the gearless construction of a wind energy conversion system (WECS), a low-speed (i.e. multipole) generator is required. This paper examines an axial-field permanent-magnet synchronous wind power generator, mainly from the magnetic viewpoint. Both mechanical and electromagnetic designs are described as well as some primary test results concerning model generators having nominal power of 5 and 10 kW.

Journal ArticleDOI
TL;DR: In this article, a solenoidal superconducting magnetic energy storage with active and passive shielding has been optimized by means of different optimization procedures based on the global search algorithm, evolution strategies, simulated annealing and conjugate gradient method, all coupled to integral or finite element codes.
Abstract: A proposal for benchmark problems to test electromagnetic optimization methods, relevant to multiobjective optimization of a solenoidal superconducting magnetic energy storage with active and passive shielding is presented. The system has been optimized by means of different optimization procedures based on the global search algorithm, evolution strategies, simulated annealing and the conjugate gradient method, all coupled to integral or finite element codes. A comparison of results is performed and the features of the problem as a test of optimization procedures are discussed.

Journal ArticleDOI
Leonid Grcev, F.E. Menter1
TL;DR: In this paper, a procedure for computation of transient fields near large earthing systems, as a response to a typical lightning current impulse, based on computational methodology developed in the field of antennas, is presented.
Abstract: Electromagnetic compatibility studies require knowledge of transient voltages that may be developed near earthing systems during lightning discharge, since such voltages may be coupled to sensitive electronic circuits. For such purpose, accurate evaluation of the transient electric field near to and/or at the surface of the grounding conductors is necessary. In this paper, a procedure for computation of transient fields near large earthing systems, as a response to a typical lightning current impulse, based on computational methodology developed in the field of antennas, is presented. Computed results are favorably compared with published measurement results. The model is applied to check the common assumption that the soil ionization can be neglected in case of large earthing systems. Presented results show that the soil ionization threshold is met and exceeded during typical lightning discharge in a large earthing system.

Journal ArticleDOI
S. Parhofer1, Joachim Dr. Wecker1, C. Kuhrt1, G. Gieres1, L. Schultz 
TL;DR: In this paper, the authors investigated remanence enhancement due to exchange coupling between the soft and hard-magnetic layers as a function of the Fe-interlayer thickness d, and showed that for decreasing d, the trilayer system is significantly increased.
Abstract: Nd-Fe-B/Fe/Nd-Fe-B trilayers with individual layer thicknesses between 10 and 100 nm have been grown by sputter deposition. The aim of our study is to investigate remanence enhancement due to exchange coupling between the soft- and hard-magnetic layers as a function of the Fe-interlayer thickness d. It is shown that for decreasing d the remanence of the trilayer system is significantly increased due to exchange coupling. The coercivity of the trilayer is also increased for d<40 nm which can be explained with a higher nucleation field for magnetization reversal.

Journal ArticleDOI
TL;DR: In this paper, the resonance frequency and quality factor of closed or aperture coupled cavity resonators with volume and wall losses were calculated by an edge finite element method, and an efficient solver was developed to solve the complex nonlinear eigenvalue problem.
Abstract: The calculation of the resonance frequency and quality factor of closed or aperture coupled cavity resonators with volume and wall losses by an edge finite element method is discussed. An efficient solver is developed to solve the complex nonlinear eigenvalue problem. The effect of the roughness of the walls on the quality factor is taken approximately into account.

Journal ArticleDOI
TL;DR: In this paper, the effect of magnetocrystalline anisotropy on the anhysteretic magnetization has been considered and incorporated into the model of hysteresis.
Abstract: A model of hysteresis has been developed earlier in which the susceptibility depends on the displacement of the prevailing magnetization from the anhysteretic. This model does not take into account the effect of magnetocrystalline anisotropy in a material. In the current work, it has been shown that the effect of anisotropy can be incorporated into this model through its effect on the anhysteretic magnetization.

Journal ArticleDOI
TL;DR: In this paper, a milli-scale piggyback actuator for magnetic disk drives with a high track density was developed, which is comprised of a head suspension assembly supported by a 'flexural' cross-shaped spring, driven in the rotary direction by electromagnetic force.
Abstract: A new milli-scale piggyback actuator for magnetic disk drives with a high track density was developed. The movable part of this actuator is comprised of a head suspension assembly supported by a 'flexural' cross-shaped spring, driven in the rotary direction by electromagnetic force. The advantages are that the actuator moves over a long distance with small power and can be easily manufactured. Our dual-stage actuator system using the flexural milli-actuator can realize 25 kTPI.

Journal ArticleDOI
TL;DR: The rotational symmetric 12-pole 9-tooth (12P9S) motor and the rotational unsymmetric 8-pole nine-to-oth (8P 9S) motors were compared in this article, where the authors investigated the influence of pole-teeth-winding patterns on the performance of two common designs.
Abstract: The pole-teeth-winding configuration in brushless dc motors determines torque and unbalanced magnetic force which are the resultants of the tangential and the normal magnetic force in a small air gap, respectively. This paper calculated torque and unbalanced magnetic force using FEM, Maxwell stress tensor to investigate the influence of pole-teeth-winding patterns on the performance from two common designs, i.e. the rotational symmetric 12-pole 9-tooth (12P9S) motor and the rotational unsymmetric 8-pole 9-tooth (8P9S) motor, and proposed the rotational unsymmetric 10-pole 9-tooth (10P9S) motor which achieves the high average torque of 12P9S motor and the low cogging torque of 8P9S at the same time. The analyses show that 8P9S and 10P9S motor tend to have less cogging torque because their bigger values of the least common multiple of pole and teeth reduce the cogging torque. The torque efficiency depends on pole-teeth-winding configuration. ABC-winding of 12P9S motor and three consecutive teeth winding of 10P9S motor utilize all six energized coil effectively to produce the high average torque. The normal magnetic force in a rotational unsymmetric design is not balanced and results in unbalanced magnetic force.

Journal ArticleDOI
TL;DR: In this paper, the authors suggest the structure consisting of meander coils (meander type), which has allowances in coil displacement and is easy to be set up, and make a comparison in characteristics between spiral type and meander type.
Abstract: We suggest the contactless power transmission system "Cordless Power Station (CLPS)" that will radiate little noise by making the coil geometry noise-reducible. The system makes use of electromagnetic induction among the coils. So far we have studied the structures of CLPS consisting of some spiral coils, and found out that CLPS could be small-sized and thin. The enough amount of power could be transmitted. In this paper we suggest the structure consisting of meander coils (meander type), which has allowances in coil displacement and is easy to be set up. We studied the power-transmitting characteristics with various magnetic materials and coil misalignment. We also discussed the efficiency improvements in the spiral type. Later we make a comparison in characteristics between spiral type and meander type.

Journal ArticleDOI
TL;DR: A new model for the signal dependent transition noise and partial erasure which occur in the readback signal from thin film recording media is reviewed, which has its basis in physics and can be entirely specified by three parameters of the media.
Abstract: A new model for the signal dependent transition noise and partial erasure which occur in the readback signal from thin film recording media is reviewed. This model, which is referred to as the microtrack model, has its basis in physics and can be entirely specified by three parameters of the media. It is used both as a simulation tool and for analytical calculation. Through simulation, the effect of various amounts of media noise on a PR4 channel is shown. Analytically, the amount of jitter and widening effects of the noise produced by the model are examined. Also, the autocorrelation of this noise and the effect of partial erasure on it is examined.

Journal ArticleDOI
TL;DR: In this article, a new approach to the formulation of a band matrix as a function of rotor position is proposed, which is expressed by a trigonometric interpolating polynomial which is based on the matrices for discrete rotor positions.
Abstract: Methods of movement simulation in the coupled field-circuit analysis of rotating electric machines are considered. Special attention is paid to the application of moving band techniques in the finite element analysis of electromechanical transients. A new approach to the formulation of a band matrix as a function of rotor position is proposed. The matrix of the moving band is expressed by a trigonometric interpolating polynomial which is based on the matrices for discrete rotor positions. The method is verified by comparison of the analytical and numerical results of torque calculation and is applied in the analysis of permanent magnet motor dynamics.

Journal ArticleDOI
TL;DR: In this article, the authors describe studies of elements of micropolycrystalline Permalloy and cobalt whose thicknesses lie in the range 20-30 nm.
Abstract: Two different lithographic techniques have been developed for fabricating magnetic nano-elements on ultra-thin electron-transparent substrates thereby allowing transmission electron microscopy to be used to investigate their properties. Here we describe studies of elements of micropolycrystalline Permalloy and cobalt whose thicknesses lie in the range 20-30 nm. Bright field images show that a high degree of edge acuity is attained and elements with lateral dimensions /spl ap/25 nm have been produced. Lorentz microscopy has provided unique insight into the detailed magnetisation reversal mechanisms in acicular elements with widths in the range 100-300 nm. In cobalt elements a single domain occupies most of the volume with complex domain structures existing very close to the ends; switching fields increase markedly with decreasing element width but are substantially independent of element length. The reversal mechanism is found to involve the propagation of a small "reversing" domain structure along the element length. In Permalloy, extensive domain structures are observed in all but the narrowest elements in the remanent state. The response to applied fields is described.

Journal ArticleDOI
TL;DR: A methodology for the computer aided constrained design of electrical devices is presented and validated through the design of a slotless permanent magnet structure based on the use of the analytical design equations of the device.
Abstract: A methodology for the computer aided constrained design of electrical devices is presented and validated through the design of a slotless permanent magnet structure. It is based on the use of the analytical design equations of the device. Symbolic calculation is widely used to generate an analysis program and a sensitivity computation program. Those programs are linked with an optimisation algorithm that can take constraints into account. The methodology is tested with an experimental software named PASCOSMA.