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Magnetics, IEEE Transactions on

Issue 5 • Date September 1985

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Displaying Results 1 - 25 of 235
  • [Front cover and table of contents]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • Conference organization

    Publication Year: 1985 , Page(s): 1325 - 1326
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    Freely Available from IEEE
  • Industrial contributors

    Publication Year: 1985 , Page(s): 1327
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    Freely Available from IEEE
  • Chairman's preface

    Publication Year: 1985 , Page(s): 1328
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  • Conference highlights

    Publication Year: 1985 , Page(s): 1329 - 1331
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    First Page of the Article
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  • Laser doppler interferometry on magnetic recording systems

    Publication Year: 1985 , Page(s): 1332 - 1337
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Laser Doppler interferometry is used to determine the six components of velocity of read/write heads in magnetic disk files. These measurements are made on production drives in which the only alteration is the installation of a window so that the laser beams can be directed onto any of the four corners of the slider. A laser Doppler vibrometer (LDV) is used to measure the out-of-plane velocity of the four corners from which we calculate the out-of-plane velocity of the geometric center as well as the pitch and roll of the slider. A laser Doppler anemometer (LDA) measures the in-plane velocity of the four corners, which gives the radial and tangential velocity of the geometric center and the yaw of the slider. We are also using the LDV for the measurement of disk runout and surface topography as well as suspension and actuator vibration. These measurements allow us to determine the natural frequencies of the slider bearing, the rotating disk, the actuator, and the suspension arm. In this paper we summarize some of the results we have obtained using this method on various 5-1/4" and 8" rigid disk drives that employ "Winchester" and "mini-Winchester" sliders together with stepper motor and servo controlled actuators of both the linear and swing arm designs. View full abstract»

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  • Review of head-media coupling in magnetic recording

    Publication Year: 1985 , Page(s): 1338 - 1343
    Cited by:  Papers (4)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    Recent advance of magnetic recording technology has resulted in tremendous increase in area densities. Several new components were developed: Thin film media, and thin film head in longitudinal recording; Single-layer media, double-layer media, and probe head in perpendicular recording. A variety of head and media combinations become possible, and each has a different degree of head-media coupling. The soft magnetic underlayer in double-layer perpendicular media has such a strong coupling with the head that the head and media must be treated as a single entity in the analysis. The evaluation of only a head or a medium without knowing its counterpart could be quite misleading. Optimization of head-media coupling to select the most suitable combination becomes a key factor in designing a high density recording system. We will review the recording and reproducing processes from both the theoretical and experimental aspects for all the head-media structures which have some practical interest. View full abstract»

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  • Recording codes for digital magnetic storage

    Publication Year: 1985 , Page(s): 1344 - 1349
    Cited by:  Papers (108)  |  Patents (28)
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    This paper provides a tutorial introduction to recording codes for magnetic disk storage devices and a review of progress in code construction algorithms. Topics covered include: a brief description of typical magnetic recording channels; motivation for use of recording codes; methods of selecting codes to maximize data density and reliability; and techniques for code design and implementation. View full abstract»

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  • Noise in high performance thin-film longitudinal magnetic recording media

    Publication Year: 1985 , Page(s): 1350 - 1355
    Cited by:  Papers (76)  |  Patents (2)
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    The problem of noise in thin-film longitudinal media is analyzed experimentally and theoretically. The physical mechanism for the noise is shown to be fluctuations in the geometry of the zig-zag transitions separating bit cells. The shifted-transition noise model is introduced as a means of quantifying the noise processes. Spatial, spectral, and autocorrelation properties are introduced. A calculation of the RMS noise voltage yields the characteristic noise versus density curves found experimentally, and clarifies their interpretation with respect to the signal-to-noise ratio. The corresponding experimental data for several plated and sputtered media are presented and analyzed in the light of the model predictions. View full abstract»

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  • The synthesis of magnetic recording trellis codes with good hamming distance properties

    Publication Year: 1985 , Page(s): 1356 - 1358
    Cited by:  Papers (13)
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    In this paper we present, by means of an example, a systematic procedure to synthesize combined modulation/error correcting trellis codes, suitable for Viterbi decoding. This synthesis is based on firstly selecting a suitable linear convolutional code, secondly by analysing the state system of this code to determine the important Hamming distance building properties, and finally by mapping a code with the desired restrictions on its sequences onto this state system. As an example we develop a R = 3/6 dc free (b,l,c) = (0,3,2) code with d_{\min} = 4 . This code improves on the best codes in [1]. Codes having b \geq 1 , and which will thus be more suitable for magnetic recording, can also be synthesized following the proposed procedure. View full abstract»

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  • Transitions on perpendicular rigid disks in quasi-contact

    Publication Year: 1985 , Page(s): 1359 - 1364
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    Results of quasi-contact recording on rigid perpendicular disks are presented in this paper. Footprints of Various recording heads on different recording media, obtained at quasi-static contact conditions using a high resolution magnetoresistive transducer, provide useful information such as sharpness of the magnetization transition and the effect of the demagnetizing field. Very high density magnetization transitions, up to 12500 fc/mm, on single-layer perpendicular rigid disks were recorded and read back by thin film ring heads at a velocity of 5-8 m/s under quasi-contact conditions. At high linear densities the amplitudes on the experimental density response curve are higher than those obtained by the linear superposition of experimental isolated pulses. View full abstract»

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  • 5.25 inch floppy disk drive using perpendicular magnetic recording

    Publication Year: 1985 , Page(s): 1365 - 1367
    Cited by:  Papers (7)
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    5.25 inch high density perpendicular magnetic recording floppy disk drive has beer developed by employing new types of high saturation magnetization ring head, Co-Cr single layer medium with Ge underlayer, head slider with ellipsoidal surface configuration to assure intimate head to medium contact, and signal equalization. By these combination, recording density D50 of 145 kFCI, peakshift of 28 % at 100 kFCI, signal to noise ratio of 40.4 dB for cut-off frequency 4.25 MHz, overwrite signal to noise ratio of 27 dB, measured by writing signals at 48 kFCI over previously written 100 kFCI signals were obtained as typical recording characteristics. These results would indicate that floppy disk drive with 100 kFCI recording density has enough system margin by above-mentioned combination. In this paper, design and performance of newly developed floppy disk drive are described. View full abstract»

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  • High density recording with perpendicular Co-Cr-Nb media and ring heads

    Publication Year: 1985 , Page(s): 1368 - 1370
    Cited by:  Papers (18)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB)  

    Effective double layer structure was investigated by adding Nb to the sputtering source of Co-Cr thin film perpendicular magnetic recording tapes. The output from the tapes was measured with a ring head through to the short wavelength, λ50=0.19 μm (D50=267KFRPI). View full abstract»

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  • Transversal recording on radially anisotropic disc

    Publication Year: 1985 , Page(s): 1371 - 1373
    Cited by:  Papers (3)
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    Transversal recording has been described in the sixties, as a promising mode to achieve high density magnetic recording [1]. Because of the improvements in longitudinal and vertical recording introduced by thin film technologies for heads and media, research labs took no further interest in this transversal mode, partly due also to the fact that media and heads were not available at that time. However technological advances of recent years such as the attainment of high B(H) loop squareness for amorphous or crystallized magnetic alloys such as CoxSm1-x[2] and the capability of conventional ferrite heads to record vertical bits on a strongly anisotropic medium [3] allow us to assert that transversal magnetic recording (TMR) can be developed today. This paper describes recent studies for a radially anisotropic disc on a new TMR system. Experimental results on Co-Sm are presented, and the complementary features between the transversal mode and both vertical and longitudinal magnetic recording are discussed. View full abstract»

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  • The erasure of high energy tapes

    Publication Year: 1985 , Page(s): 1374 - 1376
    Cited by:  Patents (1)
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    In this paper we describe our studies on the erasure of high energy tape. We have found that the bulk degaussers designed for erasing low coercivity tape cannot adequately erase high energy tape. We also show that increasing the strength of the ac erase field is not a practical solution. We then describe the new techniques we have developed to adequately erase high energy tape. These new techniques employ a combination of dc fields and conventional bulk degaussers. We also show the importance of the direction of the erase fields. Finally, we present an explanation for our findings and show how a bulk degausser can be designed using the results of our studies. View full abstract»

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  • Erasure techniques for high-density recording

    Publication Year: 1985 , Page(s): 1377 - 1379
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    In this study, several erase techniques are examined as to their effect on analog-signal performance in high-density digital magnetic recording. The success of an erasure technique was found to depend on the coercivity of the tape and whether the read-back head senses dφ/dt or flux. View full abstract»

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  • Overwrite as a function of record gap length

    Publication Year: 1985 , Page(s): 1380 - 1382
    Cited by:  Papers (22)
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    In disk recorders, a common head is used for both recording and reproducing. Old data are not erased but are simply recorded over. The partially erased old data signal appears in the new data as error-producing interference. The amount of erasure of the old data signal is called "overwrite", and 30 dB is typically required. To avoid the reproduce gap null, the head gap is usually chosen to be less than half of the 2F (or bandedge) flux change length. To achieve adequate overwrite using a gap this small, it is necessary to use a very thin recording layer. A simple explanation for this, involving greater depth of penetration for low density signals, is at best incomplete. The data below show that the overwrite phenomenon is complex. Overwrite spectra measured using a thick medium show large resonance peaks whose amplitude and position depend on the record gap, record current, and the densities of the overwriting signal and the signal being overwritten. View full abstract»

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  • Roughness and recording properties of particulate tapes: A quantitative study

    Publication Year: 1985 , Page(s): 1383 - 1385
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    Recording properties such as modulation noise and output are known to be strongly influenced by the surface roughness of the magnetic coating. On the basis of a simple two-dimensional model for the contact between magnetic head and coating we are able to account for the roughness effects quantitatively. The head-tape distance is used as an intermediate parameter. Our model was successfully tested by experiments on 8 mm metal powder tapes and 1/2-inch video tapes. View full abstract»

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  • Relationship of surface roughness of video tape to its magnetic performance

    Publication Year: 1985 , Page(s): 1386 - 1388
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    The surface roughness, known to influence the recording and play-back properties of magnetic recording media, was interferometrically measured of a series of VHS video tapes. A strong correlation (r>.95) was found between both the signal outputs and noise of these tapes with rms surface roughness. The measured short waveloength rf output was shown to decrease with increasing surface roughness in a manner consistent with three theoretical models. A multiplier of 2.7 times the interferometrically measured rms surface roughness is equal to the calculated head-to-tape spacing of these tapes. View full abstract»

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  • Noise autocorrelation in magnetic recording systems

    Publication Year: 1985 , Page(s): 1389 - 1391
    Cited by:  Papers (15)  |  Patents (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    This paper describes a new technique for measuring the noise autocorrelation in magnetic recording systems. Unlike the spectrum, the autocorrelation function characterizes non-stationary noise as well as stationary noise so it is particularly suitable for signal dependent noise often found in disks. In addition, noise sources can be separated by properly choosing the sample space. Many interesting properties of particulate and metal film disks were found by this technique. View full abstract»

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  • Dropout-error-rate calculations for a maximum-density study

    Publication Year: 1985 , Page(s): 1392 - 1394
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    This paper describes an experimental method for determining the maximum areal density achievable for a given head-to-tape interface (HTI). Using this method, we can calculate amplitude and bit-shift error rates during dropouts for the areal density the HTI is originally designed for, and beyond. First, the read-back waveform is sampled to obtain the amplitude distribution of signal samples below 50% clip level at each areal density. Second, the channel-transfer-function variation is investigated during a dropout to study its effect on the bitshift error rate. Third, empirical relationships between the areal density and an rms-to-rms signal-to-noise ratio (SNR) are obtained. Based on the above information, a theoretical model is presented that predicts the error rate for each areal density after a write skip (defined here as the soft-error rate). The calculated soft-error rate agrees well with its experimental counterpart. The technique presented here is useful in determining the upper limit of the HTI used in the paper. View full abstract»

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  • Interpretation of spectral response in perpendicular recording

    Publication Year: 1985 , Page(s): 1395 - 1397
    Cited by:  Papers (1)
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    A previously published voltage spectrum in perpendicular recording is analyzed here utilizing the exact fields of a probe head and keepered medium. It is concluded that sharp transitions have been written at a negligible spacing. Previous analysis which utilized a duality between a ring head and a probe-keeper head yielded a non-zero spacing or recorded transition length. Measurements of D50for varying record geometries are analyzed in terms of scaling laws. View full abstract»

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  • Analytical modelling of perpendicular recording

    Publication Year: 1985 , Page(s): 1398 - 1400
    Cited by:  Papers (4)
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    An analytical model for perpendicular magnetic recording is presented which is capable of calculating 'ab-initio' the magnetisation distributions written by an 'arbitrary' head field into both single and double layer recording media. Magnetisations are shown to follow the head field distribution existing at the medium's top surface. Application of the theory allows prediction of many of the fundamental features of the perpendicular write/read cycle, e.g. transition widths, replay pulse shapes, D50values etc. View full abstract»

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  • On the transition length in perpendicular recording

    Publication Year: 1985 , Page(s): 1401 - 1403
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    Using the analytical model previously described by the authors [1],[2], magnetization transitions and transition lengths are calculated as a function of relevant physical parameters. When a probe head is used to record on a medium with a permeable under-layer, the readback voltage and the transition length are determined mostly by the head-medium separation. The calculated results agree with experimental observations of the variation of high frequency readback voltage with medium thickness. View full abstract»

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  • A comparison of longitudinal and perpendicular recording based on optimum perpendicular transition

    Publication Year: 1985 , Page(s): 1404 - 1407
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    This paper describes an idealized magnetic transition that results in optimum performance for perpendicular magnetic recording systems. This transition has a step at its center, and its magnetic moment is the maximum allowed when the perpendicular demagnetizing field at the coating surface is limited to Hc. System performance is modelled by the timing margin for a 10-10error rate at the output of a idealized differentiated \cos^{4} read channel [1] in which white gaussian noise has been inserted at the input. This model closely approximates experimental performance measurements. For ring head read, the performance of the optimum and dual arctangent [2] perpendicular transitions is compared with longitudinal recording on thin film media. Since the optimum perpendicular model performs only slightly better than longitudinal recording, and is likely to be superior to real transitions written with a ring head, it would appear that perpendicular recording with ring head read offers little advantage. The performance model has been used to evaluate a recently described perpendicular recording system with single pole read/write on two layer media [3, 4], which shows great promise. 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