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Magnetics, IEEE Transactions on

Issue 6 • Date Nov 1991

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Displaying Results 1 - 25 of 319
  • Comparison of computationally efficient forms of FDTS/DF against PR4-ML

    Publication Year: 1991 , Page(s): 4567 - 4572
    Cited by:  Papers (7)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (480 KB)  

    The authors compare the error-rate performance and circuit complexity of fixed-delay tree search with decision-feedback (FDTS/DF) to that of Class IV partial response equalization followed by Viterbi detection (PR4-ML). The impact of realistic impulse responses, misequalization, phase errors, and offtrack interference on both detection strategies is explored. Two computationally efficient methods for implementing FDTS/DF are presented. These FDTS/DF architectures avoid explicit multiplication-one uses a RAM-based table lookup and the other uses binary equalization over the tree-depth View full abstract»

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  • A switched reluctance motor model with mutual coupling and multi-phase excitation

    Publication Year: 1991 , Page(s): 5423 - 5425
    Cited by:  Papers (23)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    A novel switched reluctance motor (SRM) magnetic equivalent circuit model with mutual coupling and multiphase excitation is presented which successfully predicts the magnetic behavior of an SRM with multiple phase at a time excitation. The model is new in that it spreads the saturable elements throughout the machine rather than at the tooth tips. This allows the dominant mutual coupling effect, core saturation during multi-phase excitation, to be modeled. The authors describe methods for calculating or functionally representing values for the circuit elements given the machine geometry and a minimum number of finite-element models, a method for modeling saturable materials, and a method for solving the resulting mesh for flux values given excitation levels. The model results are compared with intermediate finite-element results View full abstract»

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  • Nonlinear effects of transition broadening

    Publication Year: 1991 , Page(s): 4831 - 4833
    Cited by:  Papers (16)  |  Patents (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Nonlinear broadening of closely spaced transitions has been studied using micromagnetics simulations. Results show a large increase in the width of a transition due to the demagnetizing field effect of earlier transitions. Based on this observation, a simple recording channel model is developed to investigate the effects of nonlinear transition broadening on detection performance. This analysis shows that the conventional peak detector is much less sensitive to the detrimental effects of nonlinearity than the more advanced partial response maximum likelihood (PRML) scheme, mainly due to the extra transition spacing provided by the minimum run-length-limited constraint. This result suggests that in order to preserve the improved signal detection capability of advanced signal processing schemes like PRML, reduction of nonlinearity is essential in the media design View full abstract»

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  • Effects on magnetic toners in AC and DC magnetic fields

    Publication Year: 1991 , Page(s): 5426 - 5428
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (276 KB)  

    Magnetic forces acting on moving magnetic toners have been investigated by dropping the toners through DC and AC magnetic fields. A CCD (charge coupled device) camera system was used to observe the effects on magnetic toners in the magnetic fields, The distribution of toner chains in a DC magnetic field depends on the distribution of applied DC magnetic force. After applying an AC magnetic field greater than the coercivity of the toners, the length of toner chains was reduced and the sliding velocity of the toner chains was increased as the applied AC magnetic field was increased. The effects on magnetic toners by applying an AC magnetic field can be considered as an AC demagnetizing effect View full abstract»

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  • Magnetic recording channel model with intertrack interference

    Publication Year: 1991 , Page(s): 4834 - 4836
    Cited by:  Papers (13)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    The authors propose a multichannel model for saturation recording which includes interference from adjacent tracks. In saturation recording, the signal is recorded as a series of flux reversals on the medium. Each track is a pulse amplitude modulated (PAM) signal, where the pulse shape is the system response to a flux reversal. The old information (OI) in each guard band is also modeled as a single PAM signal. The side reading properties of the head are modeled using the reciprocity integral to compute flux transition response. Using a result of D.A. Lindholm (1977) to represent the field of an inductive head, the authors compute specific channel models for various values of misregistration. They determine the pulse shape as a function of the head-to-track registration for each adjacent track and OI track View full abstract»

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  • A stress-dependent magnetic Preisach hysteresis model

    Publication Year: 1991 , Page(s): 4796 - 4798
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    The authors present a generalization of the classical Preisach model which handles coupled magnetic and mechanical hysteresis. Magnetostrictive materials are known to have hysteresis with respect to both magnetic field H and mechanical stress λ. To test the validity of the model, experiments where the two components H and λ have been verified in many different ways have been performed on Terfenol-D and compared to results computed from the model. Some of these results are presented. This stress-dependent model is found to have an accuracy comparable to that of the classical Preisach model View full abstract»

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  • Small magnetic patterns written with a scanning tunneling microscope

    Publication Year: 1991 , Page(s): 5289 - 5291
    Cited by:  Papers (4)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    The authors present a technique for writing submicron magnetic bit patterns on double-layered perpendicular recording media by using a scanning tunneling microscope (STM) with an amorphous magnetic tip and observing them with a magnetic force microscope (MFM). The proposed technique provides a very small tip-to-medium spacing on the order of angstroms. It is shown that the magnetization of the extremity of an amorphous tip can be reversed by switching the external field. The possibility of writing magnetic bit patterns in double-layered perpendicular media at a high areal density equivalent to 1 Gb/in2 or more by means of this technology is demonstrated View full abstract»

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  • Matched filter limits and code performance in digital magnetic recording

    Publication Year: 1991 , Page(s): 4594 - 4599
    Cited by:  Papers (6)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    Presents a method for evaluating the performance of recording channels and codes for systems with additive spectral Gaussian noise. Starting with a noise-whitened isolated pulse, matched filters are calculated for the amplitude and timing channels which have the maximum signal-to-noise ratio (SNR) and minimum jitter, respectively. In high-density recording systems, the pulse slimming equalization required to control intersymbol interference degrades the SNR and jitter. For the timing channel, a detector SNR is defined whose error statistics are nearly identical to the amplitude channel SNR. Procedures for calculating losses relative to the matched filter SNR are developed that facilitate performance comparisons of both channels. A series of runs for the Lorentzian input pulse and cosn equalized output pulses compares the performance of several modulation codes and detection techniques. Write equalization and partial response type four equalization are examined View full abstract»

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  • Magnetic recording channel front-ends

    Publication Year: 1991 , Page(s): 4503 - 4508
    Cited by:  Papers (8)  |  Patents (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Readback front-end electronics for both inductive and magnetic recording (MR) heads are investigated. For inductive front-ends, it is shown that the channel bandwidth is determined by the transfer of the induced head voltage to the front-end input terminals. The parameters limiting this bandwidth are calculated. A noise analysis shows that the signal-to-noise ratio can be optimized and gives the parameter values for which this happens. The effect of noise matching of the head to the front-end is demonstrated. For MR front-ends the principles of auto bias and relative resistance sensing are presented. Front-end configurations producing voltage biasing and current biasing are discussed. Two examples of signal conditioning in MR front-ends are given: an on-the-chip equalizer compensating the frequency roll-off introduced by the head cable inductance, and a signal-adaptive circuit for removing thermal asperities View full abstract»

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  • A Terfenol based magnetostrictive diode laser magnetometer

    Publication Year: 1991 , Page(s): 5358 - 5360
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (196 KB)  

    A simple, rugged Terfenol-based magnetostrictive magnetometer prototype has been developed. Experiments were performed to determine the optimum operating point for the transducer and to study the characteristic of the diode laser sensor. A laboratory prototype has been constructed and evaluated under different field strengths and frequencies. Nonlinear responses were observed and their origin examined. The origin of the nonlinearity was interpreted as a result of running the diode laser sensor at an improper operating point. The device has an ultimate sensitivity of 160×10-6 A/m (=2 μ-Oe) View full abstract»

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  • Performance evaluation of a new coding scheme for the peak detecting magnetic recording channel

    Publication Year: 1991 , Page(s): 4804 - 4806
    Cited by:  Papers (3)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    A code designed for the magnetic recording channel with peak detection is compared with the industry standard (1,7) code. The coding technique produces two different peaks in the readback waveform which differ in both amplitude and phase. The detector for the code must distinguish between two different types of peaks in addition to determining the existence of these peaks. Using a simple linear model, results indicate that the code outperforms a (1,7) coded system for density ratios above a certain critical value. For a Lorentzian transition response and for the measured transition responses from both helical scan tape recorder and a thin film disk system this critical density ratio is approximately 1.5 View full abstract»

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  • Measurement of anisotropy in obliquely oriented media

    Publication Year: 1991 , Page(s): 4864 - 4866
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    The uniaxial anisotropy energy Ku and angle of the intrinsic easy axis to the perpendicular direction, α, which does not include the effect of the shape anisotropy of the film, of an obliquely oriented medium were analyzed, based on magnetic torque analysis method (β is the angle of the easy axis to the perpendicular direction, which includes the effect of the shape anisotropy of the film) to determine Ku and α in obliquely oriented media on the basis of a non-approximated theoretical calculation. It is pointed out that the β+45° torque analysis method is also applicable to media with an easy axis in the oblique direction View full abstract»

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  • A high resolution flying magnetic disc recording system with zero reproduce spacing loss

    Publication Year: 1991 , Page(s): 4549 - 4554
    Cited by:  Papers (16)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (452 KB)  

    A novel method has been developed for reducing the reproduce spacing loss and thereby potentially allowing increased linear densities on a disc media while maintaining a reasonable flying height. A laminated magnetic recording media is composed of a high coercivity layer in which the data signals are stored, and a thin, low coercivity, high permeability overlayer called a keeper layer. A small DC bias applied to the head saturates a section of the keeper layer, forming a virtual gap that is in direct contact with the high coercivity storage layer. This virtual gap functions as a transducing zone that enables a signal flux to be transferred from unsaturated keeper regions to the pole pieces of the flying head. Experimental results show that a considerable reduction, if not elimination, of the reproduce spacing loss is achieved using the keepered disc. Additionally the keepered disc virtual gap was found to be about 10% smaller than the physical gap in the flying head that induced it. A series of simulations were conducted using finite difference models which confirmed the trends observed in the experimental data View full abstract»

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  • Modeling of electromagnetic systems

    Publication Year: 1991 , Page(s): 4509 - 4515
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB)  

    Modeling techniques are presented for simulation of hybrid (partly electrical, partly magnetic) networks on electrical network simulators. The frequency dependence of the permeability is modeled by a relaxation description, which leads to frequency-independent component values in the network model. The hybrid models can be used for analyses in both the time and frequency domain and for noise analyses. The modeling techniques are applied to a ferrite ring and a ferrite head View full abstract»

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  • Gradient coils and reciprocity

    Publication Year: 1991 , Page(s): 4398 - 4399
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB)  

    It is observed that the problem of optimizing the design of gradient coils is identical to the problem of optimizing the design of vibrating sample magnetometer (VSM) pick-up coils. The problem of optimizing the design of the gradient coils is that of maximizing the appropriate field gradient at the position of the magnetic sample depending on the design of the alternating gradient magnetometer (AGM). The equivalence of the two problems may be proved directly by reciprocity. In the AGM case, electric current is supplied to the coil system, and it produces, with a certain coefficient of coupling, a mechanical force on the magnetic sample. In the VSM case, mechanical displacement is supplied to the magnetic sample, and it produces, with a certain coefficient of coupling, an electric voltage in the coil system. Since electrical voltage and current and mechanical force and displacement are the conjugate variables of electrical and mechanical systems, respectively, the theorem of reciprocity asserts that the two coupling coefficients must be identical View full abstract»

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  • Thermal effects in shielded MR heads for tape applications

    Publication Year: 1991 , Page(s): 4704 - 4706
    Cited by:  Papers (9)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    The authors discuss some factors that limit the permissible input power in multi-track magnetoresistive (MR) tape heads. The possible consequences of increasing the power dissipation in MR heads as a means of increasing readback signal amplitude are discussed. A simple model to describe the temperature rise of a shielded MR element is given. Evidence for exceeding the Curie point of ferrite used in shielded MR heads is seen with element temperatures in excess of 340°C recorded prior to element burnout View full abstract»

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  • MR/inductive head for hard disk drive

    Publication Year: 1991 , Page(s): 4684 - 4686
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    A SAL (soft adjacent layer) bias piggy back type magnetoresistive (MR)/inductive head was examined. On measuring the transconducting characteristics of the tested MR/inductive head, the following conclusions were reached: (1) Absolute output of 600 μVp-p was obtained, when the read track width was 4.0 μm, the medium speed was 6.4 m/s and the flying height was 0.15 μm. Thus, the superiority of this head compared with an ordinary inductive head was confirmed. (2) Although the MR element did not have a center tap, it was found that with a second harmonic distortion of under -26 dBm the head was suited for practical use. (3) The error rate curve of a worst-case pattern had 40% phase margin of 1172 fc/mm data window at error rate 10-12. These results mean it can be used practically. This head is suitable for small-diameter high-capacity hard disk drives with 136 track/mm and 212 kB/mm2 areal density corresponding to 100 MB in a 2.5-inch disk or 40 MB in a 1.8-inch disk View full abstract»

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  • Dynamic spatial variations of the `unconverted' exit beam in the magnetostatic wave-optical interaction

    Publication Year: 1991 , Page(s): 5486 - 5488
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    The authors have observed in YIG (yttrium-iron-garnet) an effect apart from the anisotropic MSW (magnetostatic wave) optical collinear interaction which has a much wider bandwidth than the latter: about 500 MHz vs 10 MHz at MSW frequencies between 6 and 7 GHz. A slit placed in front of the detector profiles the film parallel to its width. It is found that the beam has a non-Gaussian component synchronous with the MSW modulation. The shape of this component depends on kMSW, but there is usually one negative and one positive peak, as if light were being deflected from one part of the beam to another. When the whole beam is focused on the detector, these wideband features cancel, leaving the expected narrow peak associated with the anisotropic interaction. Changes in the profile shape are small as the input MSW power is varied between 2 and 20 dBm. This wideband effect may be due to isotropic MSW-optical interactions, but this is in doubt because the peak spreading does not appear to change with k MSW in the unconverted exit beam View full abstract»

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  • Deposition of Sn hydrosols on Co-γ-Fe2O3 magnetic particles

    Publication Year: 1991 , Page(s): 4642 - 4644
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (220 KB)  

    An improved colloidal solution of tin hydrous oxide has been developed. This solution was found to readily deposit onto the low-wettability surface of Co-γ-Fe2O3 particles to form a uniform layer of irremovable coating. Based upon the chemical characterization of the tin-sol-treated surface, the effectiveness of such treatments on magnetic oxide particles is described in terms of dispersion stability, dispersibility, rheological behavior, and other magnetic tape performance. A significant improvement in wetting, dispersion and flow behavior was observed for the 1% Sn coated magnetic particles upon dispersion in a polyurethane-based formulation. Additional magnetic tape data also revealed that surface treatments on magnetic particles facilitate the particle orientation by exposure to a 2000-Oe external magnetic field before dying, as evidenced by the high values of hysteresis squareness up to 0.8, indicating good dispersion of magnetic particles View full abstract»

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  • A dual-stage magnetic disk drive actuator using a piezoelectric device for a high track density

    Publication Year: 1991 , Page(s): 5298 - 5300
    Cited by:  Papers (81)  |  Patents (64)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (204 KB)  

    A dual-stage actuator has been developed using a piezoelectric device for a magnetic disk drive with a high track density over 15 kTPI. This actuator uses a VCM (voice coil motor) rotary actuator as a coarse actuator and a piezoelectric actuator installed in a head-arm as a fine actuator. The stroke of the fine actuator is 4.6 μm, which is sufficient for a track pitch of 1.5 μm at 17 kTPI. The head position is detected by an optical method using a dot-pattern etched on a disk. The authors describe the design of the dual-stage actuator, including structural analysis, its static and dynamic characteristics, the dual-stage feedback control system. Experimental results of tracking with high accuracy on a 3.5-in disk-drive unit are presented View full abstract»

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  • 3D analysis of MR readback on perpendicular medium

    Publication Year: 1991 , Page(s): 4707 - 4709
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB)  

    A 3-D analysis of magnetoresistive (MR) read on perpendicular media using the reciprocity method is presented. It is shown that the conduction of magnetic flux, obtained from an equivalent reciprocity field, away from the active area is an important phenomenon for this structure, and may introduce error if 2-D analysis is used. The authors examine the effect of shield width and show that when the shield width is equal to the width of the active area of the MR head, 3-D analysis closely resembles the 2-D results. This calculation is extended to a differentially connected dual element MR head for perpendicular recording View full abstract»

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  • On feed-forward and feedback timing recovery for digital magnetic recording systems

    Publication Year: 1991 , Page(s): 4810 - 4812
    Cited by:  Papers (6)  |  Patents (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    Two different timing recovery techniques, namely, feedforward and feedback, for digital magnetic recording systems are compared. The feedforward approach uses nonlinear filtering to derive the timing information, whereas the feedback approach relies on detected symbols from a suitably equalized signal. The steady-state performance of these timing recovery methods is compared under the same operating conditions. It is shown that the feedforward method provides superior performance View full abstract»

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  • A differential equation approach to minor loops in the Jiles-Atherton hysteresis model

    Publication Year: 1991 , Page(s): 4404 - 4406
    Cited by:  Papers (39)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The reason for the failure of the differential equations to yield physical minor loops involved in the magnetization in ferromagnetic materials is explained. A modified solution for minor loops is presented which retains the features of D.C. Jiles and D.L. Atherton's (1983) original motor loops, but only requires knowledge of the initial point on each portion of the loop to obtain the solution. This yields a general differential equation formulation for the Jiles-Atherton theory that can be used with circuit simulations having arbitrary excitations and initial conditions for ferromagnetic components View full abstract»

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  • Decisive factors to performance of ternary recording code

    Publication Year: 1991 , Page(s): 4918 - 4920
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB)  

    The authors investigated the decisive factors affecting the performance of ternary codes in accordance with the NRZL rule, which are associated with the three-level recording waveform. They selected several mBnT codes and evaluated the bit error rate by computer simulation. The results clearly show that a DC-free property guarantees the improvement of the necessary signal-to-noise ratio and that larger code rate provides a greater capacity for noise suppression View full abstract»

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  • Discrete-time modeling of transition noise dominant channels and study of detection performance

    Publication Year: 1991 , Page(s): 4573 - 4578
    Cited by:  Papers (53)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    Discrete-time modeling of transition-noise-dominant channels is considered which facilitates performance analysis of various sample-data detection schemes. Based on the proposed channel description method in the presence of transition noise, expressions for signal-to-total-noise-power ratios associated with a few selected detection schemes are derived. Under the assumption of a Lorentzian step response and perfect equalization, a comparison is made among different detectors based on the signal-to-noise ratio figure-of-merit evaluated as a function of linear density 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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Meet Our Editors

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