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Magnetics, IEEE Transactions on

Issue 6 • Date Nov 2000

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Displaying Results 1 - 25 of 25
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  • Three-dimensional resistance calculation in end ring of induction motor by finite-element method

    Page(s): 3932 - 3938
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    Among the components of induction motors, the end ring is needed to connect rotor bars electrically. Some approaches to calculating its resistance employ equivalent circuit methods, but they are not accurate because they assume ideal sinusoidal current distribution. This paper presents a method to calculate the current distribution in the end ring by the finite-element method (FEM). This paper uses both two-dimensional (2-D) A-Φ FEM analysis and three-dimensional (3-D) T-Ω FEM analysis. The magnetic flux density is obtained from 2-D analysis, and the electric vector potential is obtained from 3-D analysis. With these results, the current distribution in the end ring is calculated and the proper size of the end ring is selected by solving some case problems View full abstract»

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  • Transform method for calculating low-frequency shielding effectiveness of planar linear multilayered shields

    Page(s): 3910 - 3919
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    A two-dimensional analytical solution for quasistatic magnetic field shielding with planar infinite multilayered shields is presented. The magnetic field source is a system of long straight wires parallel to the shield, carrying sinusoidal currents. The analysis assumes that material media can be considered linear under the applied source fields. The spatial Fourier cosine and sine transforms are applied to the analytical expressions of the magnetic field intensity and flux density is obtained by solving the diffusion equation in each layer. Using transfer relations for every layer in terms of transformed variables allows one to obtain the shielded field, and thus the shielding effectiveness, with no need to determine the integration functions explicitly. The results obtained with both this approach and a finite-element computer code are in good agreement. The method seems to be also suited for the analysis of problems with more complex geometries and source distributions View full abstract»

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  • Optimal code rates for concatenated codes on a PR4-equalized magnetic recording channel

    Page(s): 4044 - 4049
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (148 KB)  

    At some nominal recording density, the read signal in digital magnetic recording resembles a Class IV partial response (PR4) signal and, hence, may be equalized to the PR4 shape with relatively little noise enhancement. When coding is added, for a fixed user density, the recording density must increase as a result of coding overhead, and the read signal will resemble PR4 to a lesser extent. Equalization to PR4 in this case will produce excessive noise enhancement. Thus, coding overhead (or rate) must be selected for optimum tradeoff between code strength and noise enhancement. Toward this end, we provide results for high-rate concatenated codes, assuming a Lorentzian recording channel model. In addition to examining optimal code rates, we compare parallel and serial concatenated code performance on the PR4 channel View full abstract»

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  • Effect of secondary gaps in near-saturated metal-in-gap video heads

    Page(s): 3991 - 3996
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (164 KB)  

    Secondary gaps between the ferrite bulk and the Sendust (AlFeSi alloy) shim may occur in metal-in-gap (MIG) heads. Finite-element models are used to explore the effect that these gaps have on the read/write characteristics of single- and double-sided MIG heads. The presence of a secondary gap is shown to cause an additional peak in the writing field and oscillations in the magnitude of the response during replay. The field and response of a double-sided MIG head is affected more than those of the corresponding single-sided MIG head View full abstract»

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  • Fault tolerance of magnetic bearings with material path reluctances and fringing factors

    Page(s): 3939 - 3946
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    An equivalent magnetic circuit of an eight-pole heteropolar magnetic bearing with path reluctances is developed with nondimensional forms of flux, flux density, and magnetic force equations. The results show that fluxes and magnetic forces are considerably reduced for the magnetic circuit with relatively large path reluctances. A Lagrange multiplier optimization method is used to determine current distribution matrices for the magnetic bearing with large path reluctances. A cost function is defined in a manner that represents load capacity in a specific direction. Optimizing this cost function yields distribution matrices calculated for certain combinations of five poles failed out of eight poles. Position stiffnesses and voltage stiffnesses are calculated for the fault-tolerant magnetic bearings. Fault-tolerant control of a horizontal rigid rotor supported on multiple-coil failed magnetic bearings including large path reluctances is simulated to investigate the effect of path reluctances on imbalance response View full abstract»

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  • Effect of substitution of divalent ions on the electrical and magnetic properties of Ni-Zn-Me ferrites

    Page(s): 3962 - 3967
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    The effect of Cu2+, Cd2+, Co2+, Ca2+, Mn2+, and Mg2+ ions on the physical properties of stoichiometric Ni0.5Zn0.5Fe 2O4 ferrite is investigated. The specimen is prepared by the conventional manufacturing method without atmosphere control. The divalent ions replace one-half the Ni2+ ion molar content. We found that the magnetic and electrical properties of Ni-Zn ferrite changes considerably with the substituent species. Copper ions play an important role in lowering the sintering temperature and increasing density. Manganese and cobalt ions increase electrical resistivity by about two orders of magnitude, while the Ca and Mn ions improve thermal stability of the initial permeability. We also discuss our investigation of the physical properties of the Ni-Zn-Me ferrites on the basis of site occupation of the cation species in the spinel structure View full abstract»

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  • Noise due to particle distributions in metal-particle media

    Page(s): 4005 - 4010
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    Noise is a concern when it comes to storing data because noise can cause a corrupted signal and, therefore, lost data. Micromagnetic simulation was used to gain insight and understanding of particulate media noise due to nonuniform particle distribution. These distributions result in a spatial fluctuation of the anisotropy field and orientation of the particles, which introduces randomness into the recording process. The effect of the randomness (i.e., noise) on the recording process was studied, as were effects of reduced media thickness and improved particle alignment on the noise level and record nonlinearity. Effect of the noise on write-equalized recordings was also investigated. The focus of the paper is on thin metal-particle media View full abstract»

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  • Magnetic ground state of a thin-film element

    Page(s): 3886 - 3899
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    By means of three-dimensional numerical calculations we studied possible micromagnetic configurations in a rectangular Permalloy-like thin-film element. The parameters were chosen to be compatible with the so-called micromagnetic standard problem 1. We demonstrate that for these parameters a diamond domain pattern is the lowest energy state that replaces cross-tie patterns favorable in larger elements. Only at smaller sizes does the originally envisaged Landau pattern form the ground state. The transition to high-remanence structures (or what would be comparable to a “single-domain” state) is found for lateral sizes that are an order of magnitude smaller than the benchmark parameters. The transitions among the different domain patterns become plausible in view of the energy of symmetric Neel walls in extended thin films. The features of the high-remanence structures can be derived from the principle of uniform charge distribution View full abstract»

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  • Low magnetic field measurement with a reversed-field electron-spin-resonance magnetometer

    Page(s): 3953 - 3956
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    An effective method of measuring low magnetic fields is presented. In this method, the magnetic field direction is reversed periodically so that the effects of external magnetic fields, such as the earth's magnetism, are removed. The usefulness of the method is investigated by using a split coil magnetic field source and an electron-spin-resonance magnetometer. A magnetic field of 10 mT can be measured with an uncertainty of less than 0.2 μT, i.e., 20 ppm View full abstract»

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  • New two-dimensional model for inhomogeneous permanent magnets

    Page(s): 3926 - 3931
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    Existing solutions of the nucleation fields in inhomogeneous ferromagnets, based on the minimization of the energy equation of a soft magnetic inclusion implanted in a hard magnetic matrix, are reviewed and compared. A macroscopic two-dimensional (2-D) model based on the Preisach formalism is proposed. The properties of the model and the effect of the identification parameters on the major loop characteristics are investigated. The simulated results include major and minor loops and the rotational hysteresis loss calculation View full abstract»

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  • Anhysteretic magnetization and demagnetization factor in Preisach models

    Page(s): 3900 - 3909
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    The anhysteretic magnetization Man depends on the internal field after degaussing Han and, possibly, on the demagnetization factor N. Neel's theory of the N dependence is criticized. Classes of Preisach models are identified for which Man (Han) does not depend on N. A numerical method is presented to determine Man (Han, N) from a Preisach model. The zero-field anhysteretic permeability is expressed in terms of the Preisach distribution up to first order in N-k, where k is the parameter of the moving Preisach model View full abstract»

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  • Analysis of a biphase-based servo format for hard-disk drives

    Page(s): 4019 - 4027
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB)  

    Biphase modulation in an embedded-servo format for hard-disk drives is investigated. It is shown that for biphase, at the low linear densities typical of servo information, near-maximum-likelihood performance can be attained by a simple bit detector consisting of a full-response linear equalizer and a binary slicer. Compared to the commonly used method of dibit coding, a signal-to-noise ratio gain of some 4 dB is achieved. The same equalizer may be used as the basis for near-maximum-likelihood position error signal amplitude estimation and timing recovery. Simulations of a practical servo demodulator based on a fifth-order analog filter show that at typical linear densities, this ideal performance is closely approached. The equalizer has a band-pass character and yields excellent suppression of the effects of thermal asperities and magneto-resistive head asymmetry View full abstract»

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  • Numerical method for eddy-current computation in a nonsimply connected thin conducting shell

    Page(s): 3920 - 3925
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    This paper describes a numerical method for eddy-current computation in a nonsimply connected thin conducting shell. The model uses a finite-element method coupled with a boundary integral method. We introduce a virtual current equal to the overall current in the shell and we consider the electric field as a variable. For a collar meshing, numerical and analytical solutions are compared with different values of the skin depth. Eddy-current distributions are shown for the case of a thin cylindrical shell View full abstract»

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  • Magneto-optical garnet films made by reactive sputtering

    Page(s): 3957 - 3961
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    Reactive radio frequency (RF) sputtering was used to grow cerium-doped yttrium iron garnet (YIG) films on magnesium oxide substrates. Magnesium oxide has been proven to be a good buffer material for semiconducting substrates. Reactive sputtering was not effective for cerium doping because the cerium target reacted with the oxygen in the sputtering gas. The films were amorphous as deposited. Stoichiometric compositions yielded smooth, polycrystalline garnet films on annealing. The effects of fluctuations in the yttrium-to-iron ratio were studied. Separate iron and yttrium targets were cosputtered in order to tailor the composition systematically along the iron-yttrium binary phase diagram. Oxygen content was found to be important in the formation of garnet and in the prevention of secondary phases. The garnet films had strong in-plane magnetizations and small coercive fields, which have promise for waveguide and switch devices, respectively View full abstract»

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  • Thermal proximity imaging of hard-disk substrates

    Page(s): 3997 - 4004
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    We discuss a new measurement technique called thermal proximity sensing (TPS) and its application to the inspection of magnetic hard-disk surfaces. This method uses the magneto-resistive (MR) readback element of a hard-disk file in a novel thermally sensitive mode to actively sense the air-bearing gap spacing while the disk spins under the slider. We present model calculations that describe the origin of the thermal sensitivity and its range of applicability. By collecting height information as a function of position, we have obtained high-resolution images of disk topography with sensitivity in the subnanometer range. Initial results of the technique, obtained on a test stand, showed an exceptional imaging ability for surface features. We have also obtained useful surface structure data from in situ measurements of disk surface defects in an operating hard-disk file View full abstract»

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  • Coded modulation for E2PR4 and ME2PR4 channels

    Page(s): 4036 - 4043
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    We consider a multilevel modulation scheme based on: 1) a structured set partition (SSP) of partial-response (PR) channel output words; 2) a set of conventional block codes with different error-correcting capabilities; and 3) a Viterbi detector searching for the two best paths on the channel trellis. For the classic and modified target polynomials, examples of SSPs with the good spectra of minimum Euclidean distances are given. Bit error rates (BERs) of the proposed scheme are investigated for the conventional (E2PR4) and modified (ME2PR4) channels with the target polynomials 1+2D-2D3-D4 and 5+4D-3D2-4D3-2D4, respectively. Results of simulations show that a gain of 3.4 dB can be achieved for linear densities of 2.5 to 3.0 and BER of 10-6 without using any additional distance enhancing constraints [such as d=1, maximum transition run (MTR), or quasi-MTR] View full abstract»

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  • Magnetic percolation phenomenon in high-field high-gradient separators

    Page(s): 3947 - 3952
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    This paper deals with the modeling of paramagnetic particle capture in high-gradient magnetic separators. The model allows the simulation of the progressive saturation of the collectors of the extraction matrix. The results show that magnetic separation is a complex process to model. Yet several elementary phenomena such as magnetic percolation and effects of slight changes of geometrical conditions are pointed out. The evolution of a matrix efficiency as a function of its saturation degree is also given View full abstract»

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  • Magnetic anisotropies in single and multilayered thin films grown by bowed-substrate sputtering

    Page(s): 3968 - 3974
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    Thin-film structures composed of nearly nonmagnetostrictive single-layer Co76Fe4B20 or magnetostrictive Fe80B20 and Co75Si15B10 amorphous layers have been deposited on bowed glass substrates using the RF-sputtering technique. The fabrication procedure induces a postdeposition compressive stress in the thin-film structure when the sample is retrieved from an arching device in the sputtering chamber. This results in an induced magneto-elastic anisotropy that governs the magnetic easy axis of the film, depending on the sign of the magnetostriction constant of each layer. Particular attention is paid here to heterogeneous structures made of bi- or multilayers with magnetic easy axis oriented in a different direction in each layer. Bulk magnetic properties were evaluated from hysteresis loops and thermomagnetization measured by vibrating sample magnetometry (VSM) and quantum interference device (SQUID) magnetometry. Magnetic domain walls and out-of-plane magnetized domains were observed by a Kerr imaging system and magnetic force microscopy. The combination of microstructure and strains induced in the layers determines the orientation of the observed magnetic anisotropies, which vary from high in-plane anisotropies up to out-of-plane orientations for selected films. The results, which provide reassurance that effective anisotropies are induced in each of the layers, are discussed in terms of the interactions between magnetic phases with different induced easy magnetization axes View full abstract»

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  • Micromagnetic recording model of pole-tip saturation effects

    Page(s): 3975 - 3983
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    Auxiliary write-head fields, either from simple analytic approximations or from finite-element computations, are used to record transitions on a Landau-Lifschitz-Gilbert model of thin-film recording media. A micromagnetic model of a magnetoresistive element is used to read back the transitions. Focus is on the impact of pole-tip saturation on the quality of the recorded track and subsequent playback. It is shown that with increasing write current, the quality of the recorded transitions degrades much more rapidly than would be expected from the analytical expressions for the write-head field. Specifically, head saturation causes the transition parameter to increase. At high write currents, poor write field gradients at the track edges result in a strong increase in transition parameter with read width percentage of the recorded track View full abstract»

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  • Magnetic analysis of contact head/tape spacing

    Page(s): 3984 - 3990
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    A new magnetic analysis method is used to determine the mean magnetic spacing of a contact head/tape interface. The initial part of the curve of readback signal amplitude versus recording current is measured at a low recording density and is fitted by using theoretical approximations to obtain the head/tape spacing. A tape looper test stand, inductive heads, and various high-density metal particle tapes are used in the recording measurements. The mean head/tape spacing obtained from magnetic analysis agrees well with the results from numerical analysis of mechanical measurements View full abstract»

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  • Simulation of the effect of medium noise on servo position error signal detection in longitudinal recording

    Page(s): 4011 - 4018
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    A medium model with random grain structure and desired grain size distribution is used to study the effect of medium noise on position error signal (PES) signal and sensitivity using 100 Gb/in2 parameters in longitudinal media. Three PES detection schemes are compared: (1) average peak voltage; (2) integration of the absolute playback signal; and (3) maximization of the integration of the product of a phase-adjusted square wave with the playback signal. Scheme III is found to have the best output PES sensitivity for every case. The PES, PES sensitivity, and null point position of the RES signal along with their distributions are studied. It is found that the PES sensitivity has a nearly Gaussian distribution. In most cases, the null point position of the PES has a nonzero average and an asymmetric distribution. Media with different grain sizes and size distributions are investigated and compared. The grain size distribution has a small effect on the PES detection. Increasing the average grain size dramatically increases the standard deviation of the PES sensitivity while slightly decreasing the PES sensitivity. The simulation results also show that increasing the medium grain orientation ratio (OR) improves the PES sensitivity View full abstract»

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  • Performance of random-access-memory-based equalizers in magnetic recording

    Page(s): 4028 - 4035
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    We discuss two algorithms for mitigating the deleterious effects of nonlinear intersymbol interference in PR4- and EPR4-equalized magnetic recording channels. We call these algorithms RAM-Search algorithm because they borrow the idea of employing random-access memory (RAM) from the RAM decision-feedback equalizer (DFE) and because they involve a search. The RAM-Search algorithms have been devised to mitigate the error propagation problem that arises in making feedforward decisions (for precursor terms) in intersymbol interference (ISI) cancellers used in combination with partial-response signaling. We adopt a simple partial-erasure model for the nonlinear write process and a third-order polynomial model for the nonlinear read process, and show that improvements of about 2.5 dB are possible. We also demonstrate the efficacy of the algorithms on captured spinstand signals that suffer from a significant amount of nonlinear ISI View full abstract»

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Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

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Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology