Media requirements and recording physics for high density magneticrecording

Relevant aspects concerning the ultimate achievable recording densities for particulate as well as for thin-film media are discussed. This review covers the entire range starting from micromagnetics of individual single domain particles, moving on to their magnetic behavior in a particle assembly under particular consideration of the structure being actually obtained in the process of manufacturing recording media, and finally embarking on an outline of recording physics. These considerations are not only carried out for longitudinally and perpendicularly oriented recording media but also for media having an arbitrary orientation of the easy axis of magnetization. All aspects are discussed and illustrated for the first commercially available thin-film medium on a flexible substrate, which is the metal evaporated tape, i.e., the obliquely deposited Co-Ni-O layer for the Hi8 video system     

Statistical study of zig-zag transition boundaries in longitudinaldigital magnetic recording

In this paper, we study the statistics of zig-zag transition walls in digital magnetic recording and their relationship to transition noise defining quantities. We provide analytic results that link the statistics of zig-zag transitions to media/recording parameters. The basis of our study is the triangle zig-zag transition (TZ-ZT) model due to its well-defined triangle zig-zag shape and its cross-track stability. The results we derive here, however, are of a general nature, and given the right interpretation, apply to other zig-zag models as well, as we show in the paper. We also provide an interpretation of the cross-track correlation width, linking this quantity to the statistics of magnetized clusters in thin-film magnetic media. The paper concludes by showing how these results can be used in media noise modeling     

Media for high density magnetic recording

Longitudinal recording is limited at high bit densities by recording demagnetization, self-demagnetization, and adjacent-bit demagnetization, which occur during the writing-demagnetization processes. To minimize these adverse effects it becomes necessary to resort to extreme scaling of the media parameters and their thickness, with the consequence of greatly increasing the difficulty of fabrication and the cost of such optimized media. Pure perpendicular recording circumvents these writing and demagnetization problems because of the strong head coupling of a single pole head with a double layer medium, positive interaction between adjacent bits, and low self-demagnetization at high bit densities. Therefore, it does not require any extreme scaling of the media magnetic parameters and their thickness. Of great interest, at least for the next several years, are the quasi-perpendicular particulate media which can support perpendicular magnetization. These include the isotropic, high-squareness media, and oriented perpendicular media employing particles with uniaxial crystalline or shape anisotropies. The attractiveness of these media derives from their excellent recording performance and from the fact that they preserve the existing head/media interface and they utilize existing coating facilities which should reflect favorably on their cost. In this paper the advantages and disadvantages of the various media under development for high density magnetic recording are compared, and predictions are made for their potential application in future systems.     

A new inexpensive method for the preparation of acicular precursors for magnetic recording media

Magnetic materials meant for audio/video recording applications necessitate that polycrystalline materials be in acicular shape. So preparation of acicular precursors for magnetic storage materials assumes significance. The employment of aqueous solutions do not produce needle shape crystallites. Glycerol is one of the complexing media used for the precipitation of ferrous oxalate dihydrate. An inexpensive method using starch for preparation of acicular particles is described. The influence of an additive namely Gd on acicularity is also investigated.     

Magnetic domains in thin-film recording heads as observed in the SEM by a lock-in technique

In a thin-film magnetic recording head, a magnetic circuit made from two Permalloy thin films, one above the other, is magnetized by a spixally plated thin-film copper coil which is located (together with insulating layers) between those two films. The magnetic domains in a thin Permalloy film can be studied by type-2 magnetic constrast using backscattered electrons (BSE) in the scanning electron microscope (SEM) provided that the film has a smooth surface and is deposited on a flat substrate. In practice, the upper Permalloy film follows the contours of the underlying layers. This gives a topographic signal which is large enough to mask the type-2 magnetic contrast signal in its simple form. The domain walls can, however, be seen if the magnetic recording head is excited with a sinusoidal current and if the video waveform is processed with a lock-in amplifier referenced either to the fundamental or to the second harmonic of the excitation frequency. This lock-in image processing technique has now been applied to obtain images of the magnetic domains both from the upper Permalloy film of an incompletely fabricated head and also from the exposed cross sections of the Permalloy films in an operational thin-film head.     

High-energy Co-Cr thin films sputtered on glass disks forperpendicular recording

The authors have developed high-energy Co-Cr thin-film perpendicular recording media for rigid disks. They obtained high perpendicular coercivity (Hc⊥) exceeding 2000 Oe with Co-Cr films sputtered on glass disks. They examined recording characteristics obtained with double-layered media and single-pole heads. Readout voltages were proportional to Hc⊥ up to 2000 Oe and not dependent on saturation magnetization. The authors explain the experimental results using the hysteresis curve of the Co-Cr film and the permeance factor determined by the magnetic reluctance of the head and medium. Using a magnetic circuit model, they clarify the effect of the difference in the operating point on the hysteresis curves of rigid- and flexible-disk systems     

Three-dimensional magnetic field measurement of a modifiedthin-film magnetic head for vertical recording by means ofLorentz-tomography

The method of Lorentz tomography with an electron beam as a microprobe, combined with an analytical reconstruction procedure, has been successfully adapted to thin-film heads for vertical recording. It is noted that the measured results can be used as a basis for adjusting the magnetic parameters of the thin-film head to achieve good agreement with corresponding FEM or BEM (finite element or boundary element method) calculations. It is concluded that Lorentz tomography can be used as an important tool in the design of thin-film magnetic heads     

Co-modified pigments in magnetic recording

This paper surveys the physical properties and storage performance of the class of 650 Oe pigments, which are presently mainly being used for home video, high-quality audio and will in the future be intended for high-density digital storage applications. The temperature dependence of coercivity, the change of coercivity by annealing of a sample in a magnetic field and various aspects of the switching field distribution are shown up in detail. The different data are discussed within a newly developed comprehensive model of Co-modified particles. The model correlates morphological and chemical data with physical properties and storage performance, especially print-through data and erasability effects.     

Patterning of FePt for magnetic recording

Higher areal density for magnetic recording is needed to provide larger storage capacities on harddisk drives. However, as the recording bit size of traditional magnetic recording materials (such as Co/Cr) approaches 10 nm, the magnetic direction of each recording bit would become unstable at room temperature due to thermal fluctuation. To solve this problem, efforts have been made using two methods: one method is to replace the disk media with new materials possessing higher magnetic anisotropy which would lead to better thermal stability; and the second one is to employ different configurations for the recording layer. FePt with patterned media configuration is a combination of these two methods. In this paper we review some novel and interesting methods of patterning FePt for magnetic recording, including thermal patterning, self-assembly patterning, and lithography patterning.     

Comparison of the magnetic recording performance of medium-scale ring, double-sided pole, metal-in-gap heads on high-coercivity longitudinal media

The magnetic recording performance of medium-scale ring, double-sided pole, and metal-in-gap (MIG) heads were investigated on standard longitudinal high-coercivity floppy, video tape, and isotropic floppy media using a stretched-surface multi-head magnetic recording tester. The isolated pulses for the ring and MIG heads exhibited sharp peaks near tbe edges of the gap for a head-medium separation of less than 0.1 um. Low density maximum output voltage was independent of the type of the write head. The largest output voltage was achieved from the MIG head. The isolated outputs on video media agreed with calculated values for the ring head efficiency set to 52% and the pole head efficiency set to 33% using the Karlqvist head field approximation.     

Fabrication of magnetic nanodot arrays for patterned magnetic recording media

Fabrication processes of arrayed magnetic nanodots for the use of patterned magnetic recording media were reviewed. One candidate for the patterned media is ordered assemble of magnetic nanoparticles, and the other is patterned magnetic thin films fabricated using various micro/nano scale machining processes. For the formation of patterned masks and molds, lithography processes as well as self-organized pattern formation are utilized. For the deposition processes of magnetic dots, electrochemical deposition processes were widely used. These fabrication processes are reviewed mainly from recent reports. The recording systems for the patterned media including probe-type-recording are also overviewed.     

1990 International Magnetics Conference. INTERMAG

The following topics are dealt with: recording heads; magnetooptics; hard materials; superconductivity; microwave magnetics; soft films; domains and domain walls; thin-film media; crystalline and amorphous wires; particulate recording media; sensors; soft magnetic devices; biomagnetism; magnetic recording systems; transformers and inductors; multilayers; eddy currents; head-medium interface; solid-state memories; noise in thin-film media; and electromagnetic fields. Abstracts of individual papers can be found under the relevant classification codes in this or other issues     

Iron thin film magnetic recording tape by vacuum deposition

A thin-film video tape was formed by sputtering a protective layer on an iron thin film evaporated at an oblique incident beam angle on a plastic base film. The reproduction characteristics show that this tape is suitable for high density digital recording, with high output at short wavelength and low modulation noise. The area packing density can be raised to more than 130 M bits/in². Since the magnetic layer is easily damaged during tape-transport on VTR equipment, its durability requires improvement for practical comsumer products.     

Thermal stability improvement for longitudinal magnetic recording media

This paper reports and discusses the effects of M/sub r/t cancellation and bottom/top magnetic layer thickness ratio on thermal stability and recording characteristics of low-noise synthetic antiferromagnetic (SAF) longitudinal recording media. It is shown that by proper design and process, SAF media with low M/sub r/t cancellation can deliver excellent overall recording performance with acceptable thermal stability. We present a unique approach to significantly improve the thermal stability of SAF media with low M/sub r/t cancellation by adjusting the bottom/top magnetic layer thickness ratio. Increasing the bottom/top magnetic layer thickness ratio significantly improves amplitude decay rate and media coercivity temperature dependence with little sacrifice in recording performance.     

Preconditioning, write width, and recording properties of Co-Cr-Pt-O perpendicular media with various underlayer designs

The effect of magnetic "preconditioning" on the recording performance of perpendicular media is investigated. Furthermore, the dependence of the magnetic write width (MWW) of shielded-pole heads (SPH) on soft-underlayer (SUL) type and thickness (t/sub SUL/) and the recording performance of perpendicular media with thin SULs are examined. The MWW dependence on SUL structure is influenced by the pole-to-trailing shield spacing. For a wide-gap (/spl sim/80 nm) SPH, thick single-layer, SULs are preferred. For a narrow-gap (/spl sim/50 nm) SPH, MWW is less sensitive to the SUL type. For both narrow and wide-gap SPH and for media with an antiferromagnetically-coupled SUL, MWW is reduced for t/sub SUL/<100 nm. Comparable performance is achieved relative to media with t/sub SUL//spl sim/150 nm.     

The helical-scan magnetic tape recorder as a digital communication channel

The properties of a magnetic tape recorder are viewed in terms of a digital magnetic recording/playback channel which exhibits fading (reduction of playback-signal level) and nonlinear behavior. A method is presented whereby channel nonlinearity may be quantified in a format useful for signal and receiver design. Measurements show this nonlinearity to be relatively small for symmetric two-level signals. Deep fades (dropouts) are the most significant source of errors in digital tape recordings. Fading is considered as multiplicative noise on an essentially linear channel, and measurements are made of the fade probability distribution and an associated additional time dispersion. While the fading process appears to occur relatively slowly (compared with the bit period), neither its probability distribution nor its associated dispersion encourage the use of a receiver which is able to adapt to the changing channel characteristics. Finally an attempt is made to ascribe the fading process to repeatable variations in head-tape separation, and a corresponding probability distribution for this separation is obtained. A helical-scan video recorder was used throughout the measurements because of its low cost and its potential as a high-density storage facility.     

光辅助磁记录-混合记录技术研究进展

混合记录又称为光辅助磁记录，是近年来发展起来的超大容量存储技术，它以激光辅助热磁记录和磁通检测读出为主要特征，具有记录密度潜力大、读出灵敏度和分辨高等优点，是一种很有前途的记录方式。本文较全面地介绍了这种记录方式的基本原理、记录介质及其研究现状，并讨论了其发展前景。     

Properties, preparation, advances and limitations of materials andmedia for perpendicular recording

The trends in perpendicular magnetic recording research are discussed, with emphasis on clarifying the trend of research on recording media, their materials, and head materials. Among numerous proposed perpendicular recording media materials, barium ferrite powder and evaporated Co-Cr films seem to lead in practical applications, since their mass production seems to be very successful. There still exist crucial points in their development. However, improvements are continuously taking place. Other candidate perpendicular recording media for a device which has a ring head are also discussed. It is concluded that, for future high-density magnetic recording, utilizing fully the perpendicular component of media magnetization will furnish the key to success