Conventional Magnetic Recording Research Articles

The feasibility of magnetic recording at 1 Terabit per square inch

This paper explores the feasibility of implementing conventional magnetic recording technology at densities up to one Terabit per square inch. The key limiting physical factor is the superparamagnetic effect (thermal stability) in the recording medium. Ambient thermal energy can cause the magnetic signals to decay. The requirement for thermal stability over periods of years dictates a lower limit to the size of magnetic grains (switching units) in the recording medium. To achieve the highest areal densities, it will be necessary to use a magnetic recording configuration capable of writing and storing data on very small magnetic grains together with a signal processing system capable of recovering data reliably when each bit is recorded on very few such grains. In addition to these physical effects, there are a number of practical engineering factors that must be considered: tolerances on the head geometry, reliability of head-disk interface, track-following accuracy. In an example system, we use a perpendicular recording configuration since it appears to offer some advantage in terms of maximizing the number of stable magnetic grains per unit area. The readback signals are processed by equalization to a simple binary eye followed by soft detection of a low-rate simple parity check code. The example system approaches a density of 1 Terabit per square inch and allows 3 dB of margin against thermal decay, adjacent track interference, etc.

Output Enhancement Effect of Magnetic Underlayer in High-Density Magnetic Recording

A double-layered tape with a metal particulate (MP) upper layer and a metal-evaporated (ME) underlayer is fabricated. Output properties were enhanced over the single-layered MP tape in high-density recording. This effect cannot be explained by conventional magnetic recording mechanisms, and a new model of magneto-static interaction is proposed. This model is supported by a preliminary computer simulation.

Exchange-Coupled Magnetic Bilayer Media for Thermomagnetic Writing and Flux Detection

We have newly developed a perpendicular thermomagnetic recording coupled with magnetic flux detection. Conventional magneto-optical thin films with TbFeCo compensation compositions are advantageous for thermomagnetic writing, but insufficient for magnetic flux detection due to low flux density at room temperature. We therefore designed magnetically exchange-coupled bilayer media suitable for flux detection by adding a magnetic layer with high flux density to a conventional TbFeCo magnetic recording layer.

Sensing position and speed by recording magnetization transitions on mechanically functional machine members

A means for sensing relative position and speed of mechanically functional machine members having accessible ferromagnetic portions is described. The method is based on creating, sensing, and annihilating local transitions in the polarity of remanent magnetization in surface regions of such parts while in motion, in analogous fashion to conventional magnetic recording. The presence and location of a transition, sensible by its associated external field, constitutes stored information carried by the member. Bias and “erasure” are provided by a permanent magnet; transitions are “written” by pulsed currents through a coil on a gapped core and “read” by Hall-effect field sensors located at purposeful distances downstream. Transition position is determinable within ±0.1 mm. Velocity is determined by the elapsed time between a recording pulse and its detection. Experimental data from a polyurethane timing belt reinforced with cabled steel wires demonstrates system operation.

Investigation of High Density Magnetic Recording with Single-layer Perpendicular Media

This paper describes the recent research results on magnetic recording with single-layer perpendicular recording media. This includes the thermal stability of recorded information, the linear recording density resolution, the recorded track edge profile, the media noise, the nonlinear transition shifts, the signal decay due to demagnetizing field, etc. The combination of Co-alloy single-layer perpendicular media with high perpendicular magnetic anisotropies (Mr/Ms>0.95) and ring-head writing has a high potential to increase the attainable areal density beyond 10 Gb/in2 while avoiding or reducing the difficulties which are feared to face with the conventional longitudinal magnetic recording.

Photorefractive polymers for digital holographic optical storage

Holographic data recording appears to have several advantages over conventional optical and magnetic recording methods [1].[2] A high read/write rate can be achieved by utilizing massively parallel reading and writing schemes. High storage density can be obtained by multiplexing many holograms within the same volume. Photorefractive materials are promising candidates for reversible holographic optical storage applications[3]. The photorefractive effect has been studied for years in inorganic crystals[4][5] and has quite recently been observed in thin polymer films[6][7]. Gray scale imaging has been observed in both inorganic[8] and polymeric[9] photorefractive materials. A meaningful assessment of a material’s potential for digital data storage requires experiments involving practical data storage schemes. In this paper, we describe the development of a new class of highly efficient photorefractive materials based on organic glasses and the testing of these materials using a sophisticated holographic data storage test stand built specifically for this purposef[10].

High-density magnetic tape recording by non-tracking method

Conventional helical-scan magnetic recording requires precise head tracking, precise tape path and accurate servo control. We have developed a magnetic tape recording system based on a new concept, the ‘non-tracking method’, which requires less accuracy. By combining double density track scanning and data rearrangement through a memory device, all data can be reproduced in correct order without precise head tracking. When the track pitch is 9.8 μm, the non-tracking method expands the tolerance on head tracking to ±100 μm, while the head tracking tolerance of ±5 μm is needed in conventional recording. Using the non-tracking method, a newly developed rotary head drum loading system called ‘non-loading’ and also a newly developed metal-evaporated tape, we have developed an extremely high density digital audio tape recording system, including a stamp-sized tape cassette and a miniature digital audio recorder. Two hours stereo digital recording is achieved with the small cassette.

Interaction of Focused Radiation with Magneto-optical Discs

Abstract Direct access storage devices are widely used in computers to store and manage data. In conventional magnetic recording, a magnetic head flying very close to the disc surface alters the polarization of the magnetic field at the disc surface to write and/or erase information on the disc. An optical disc is a multilayered medium consisting of a thick glass substrate on which many layers of different materials are sputtered. Only one of these layers serves as a recording medium and it is initially magnetized uniformly in one direction. To write on this disc, the initial magnetic field is altered by focusing light from a laser source with high numerical aperture (NA) lens to heat the magnetic medium beyond its Curie point, the temperature at which the magnetic medium loses its magnetization. This domain with zero magnetization is subsequently magnetized in the reversed direction by using an induction magnet. All these processes take place while the disc is rotating at a very high speed with respect t...

High Density Magnetic Tape Recording by Non-Tracking Method

Conventional helical-scan magnetic recording requires precise head tracking, precise tape path and accurate servo control for them. We have developed a magnetic tape recording system based on a new concept, "Non-tracking Method" which requires less accuracy of them. By combining double track scanning and data rearrangement through a memory divice, all data can be reproduced in correct order without precise head tracking. When track pitch is 9.8μm, the non-tracking method expands the tolerance on head tracking to plus and minus 100μm, while the head tracking tolerance of plus and minus 5μm is needed in conventional recording. Using the non-tracking method, a newly developed rotary head drum loading system which is called "non-tape-loading" and also a newly developed metal-evaporated tape, we have developed a extremely high density digital audio tape recording system, including a stamp-sized tape cassette and a tiny digital audio recorder. Two hours stereo digital recording is realized with the tiny cassette.

Laser-Induced Heating of a Multilayered Medium Resting on a Half-Space: Part II—Moving Source

Direct access storage devices (DASDs) are widely used in the computer industry to store and manage data. In conventional magnetic recording, an induction head flying very close to the disk surface alters the polarization of the magnetic field of the disk surface to erase and/or write the information on the disk. However, a new technology known as magneto-optical recording or optical recording has considerable promise to increase data densities and reliability of data storage. In magneto-optical storage, magnetic fields are altered by a laser source, which heats the magnetic medium beyond its Curie point, a temperature at which the magnetic medium loses its magnetization. This domain with zero magnetization is subsequently reversed by using an induction magnet. All these processes take place when the disk is rotating at a very high speed with respect to the laser source. An optical disk is a multilayered medium consisting of a thick glass disk on which many layers of different materials are sputtered, only one layer of which serves as a magnetic medium. Therefore, in this paper, a problem of laser-induced heating of a multilayered medium resting on a half-space is considered when the laser is translating with respect to it. The transient heat conduction equation is solved by employing the Laplace transform in the time domain and the Fourier Transform in the x, y dimensions. The resulting ordinary differential equation is solved and the inversion of the Laplace transform is obtained by a technique developed by Crump. The Fourier inversion is obtained by using a Fast Fourier Transform. The technique developed here is then applied to calculate domain size for recorded bits for a given disk, laser power, source characteristics, and rotational velocity.

Edge detection for magnetooptical data storage

The polarization sensitive optical heterodyne methods used to detect polarization rotations in conventional magnetooptic data storage systems can be altered to produce nonzero electronic signals only when the polarization rotation changes. Such systems detect the edges of the magnetic domains optically and produce signals similar to conventional inductive magnetic recording channels. Both theoretical and experimental results indicate that optimized edge detection systems can have a performance comparable with present level detection systems but with less complexity. The maximum carrier-to-noise ratio (CNR) occurs for domains 1.3 microm in length when edge detection is used, and the CNR found experimentally at this maximum is 47 dB, comparable to level detection for this size domain.

Recent advances in thin films for magneto-optic recording

Magneto-optic storage technology based on amorphous rare-earth transition metal alloys has recently been introduced on the market and is viewed as a competitor for conventional magnetic recording. We will review the preparation, microstructure, magnetic and magneto-optic properties of amorphous rare-earth transition-metal films. Their advances with respect to thermo-magnetic switching and magneto-optic recording as well as their improved long term stability are discussed. Two new classes of materials, oxides and, recently, metallic multilayers, are at the focus of research for magneto-optic recording, promising advantages over the rare-earth transition-metal alloys. Their properties and possible advantages with respect to future issues of magneto-optic recording are discussed.

Domain shapes of field modulation recorded TbFeCo and GbTbFeCo magneto-optical disks (abstract)

Magneto-optical recording by magnetic field modulation is of particular interest, since direct overwriting of information can be performed as in conventional magnetic recording.1,2 We used a floating magnetic head to apply a modulated magnetic field (±100–±600 Oe) at 5 MHz. We report here the shape of the recorded domains by this technique on TbFeCo and GdTbFeCo 5 1/4 in. disks rotating at 1800 rpm. Both TbFeCo and GdTbFeCo films had a Curie temperature of 200 °C and a compensation temperature of 60 °C. The written domains were observed by a polarized microscope. For TbFeCo disks, regular chevron-type domains were formed according to a cooling tail of a continuous laser beam. However, irregular shape domains were observed in GdTbFeCo disks, that is, the outline of a domain was not smooth, which caused a large recording noise and decreased a signal-to-noise ratio. We discuss the relation between domain regularity and magnetic parameters (anisotropy, wall energy, etc.).

An experiment of video recording by perpendicular magnetic flexible disk

Perpendicular magnetic recording has such excellent high-density recordability that its recording characteristics are different from conventional longitudinal magnetic recording characteristics. Some important video-recording characteristics on perpendicular magnetic recording are investigated when a single-pole head and a double-layer medium are used. We found a method for recording of video signals to make the most of the high-density recordability of perpendicular magnetic recording. With this method an experimental video recording system using a perpendicular magnetic flexible disk was produced by way of experiment. The result of this experiment was high-quality video reproduction.

Materials challenges in metallic, reversible, optical recording media: A review

The rate of progress in increasing the data storage density (b/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) in magnetic recording is decreasing principally because of two difficult technical problems. These are: 1) the achievement reliably and repeatably, head-medium spacings of fractions of a micrometer that densities of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\geq 1,000</tex> b/mm require, 2) reduction of track width ∼ bit length. Writing and reading with focussed light beams solves both problems and when combined with magnetic storage of data, the resulting technology has the strengths of optics and magnetics. This is achieved in Thermo-Magnetic Optic (TMO) recording on rare-earth, transition metal alloys on which data can be written, erased and re-written repeatedly at densities <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\sim4.10^{6}</tex> b/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The question is "do these materials match conventional magnetic recording media in the life expectancy of the storage medium?" This calls for accelerated life testing with its inevitable extrapolations. The principal, potential failure mechanisms have been identified as the migration and oxidation of the rare-earth and the relaxation of the perpendicular orientation of the films. The evidence for these mechanisms will be reviewed and the conclusion is reached that films of the correct composition, properly undercoated and overcoated and deposited on the right substrate have a probable life expectancy of at least ten years.

Perpendicular Magnetic Recording Technology

Perpendicular magnetic recording, in which the direction of magnetization is predominantly perpendicular to the plane of the tape or disk, is a relatively new technology that promises information densities significantly higher than those currently used. New recording media and heads are being developed and impressive results can be demonstrated. The head design and the proximity of the head to the recording surface remain, however, factors of critical importance to high-density information storage, just as in conventional magnetic recording.

Overview of requirements for optical storage media

Continuing advances in the technologies supporting wideband communications and information handling are leading to extremely large volume, wide bandwidth digital data systems. Until recently conventional storage techniques, through evolutionary product improvements, have been able to keep pace with the growth. However, a point has been reached where moderate technical improvements are becoming economically impractical. Recognizing these and other problems inherent to this specialized application of wideband, high density recording, RADC has undertaken through its exploratory and advanced development programs to satisfy two specific areas: First, to improve and expand upon the technology base that exists in conventional and nonconventional magnetic recording to overcome several of its deficiencies; second, in those instances where magnetic recording is not feasible due to bandwidth or packing density limitations, RADC has exploited alternative approaches. Techniques ranging from laser and electron beam on film to laser holography and optical digital disk are under investigation or in various stages of development.

Pulse compression using the magnetic-delay-line processor

A new approach to pulse compression in the frequency range below several hundred kilohertz is demonstrated. It uses a wire-electrode pattern to process a signal sensed from a conventional magnetic recording. The experimental results are for a filter to compress a linearly chirped signal.

Magnetooptical beam addressable storage using MnGaGe and GdCo

The discovery of MnGaGe and GdCo, room-temperature magnetooptical materials, and their fabrication in thin-film form has led to experiments on high-areal-density high-data-rate optical storage of digital data. The results of read/write experiments using 77 K GaAs lasers will be presented and briefly discussed. Calculation of the ultimate performance in terms of areal density for a given signal-to-noise ratio as a function of material figure of merit, detector bandwidth, and detector quantum efficiency will be reviewed and discussed giving experimental data for MnGaGe and GdCo. This will be compared with predicted performance for conventional inductive magnetic recording.

Technique for reducing effects of pulse crowding in magnetic recording

The introduction of redundant magnetic transition pairs in data cells, normally encoded with absent transitions, counteracts the effects of pulse crowding. Such pulse crowding is generally encountered in conventional saturation type magnetic recording. The resulting restored waveform is in fair agreement with the synthesized waveform based upon pulse superposition. The technique may be applied to most commonly used recording schemes, thereby realizing increased bit density or greater head-to-medium separation.