Magnetic Memory Disk Research Articles

Ultrafast precessional magnetization reversal by picosecond magnetic field pulse shaping.

Since the invention of the first magnetic memory disk in 1954, much effort has been put into enhancing the speed, bit density and reliability of magnetic memory devices. In the case of magnetic random access memory (MRAM) devices, fast coherent magnetization rotation by precession of the entire memory cell is desired, because reversal by domain-wall motion is much too slow. In principle, the fundamental limit of the switching speed via precession is given by half of the precession period. However, under-critically damped systems exhibit severe ringing and simulations show that, as a consequence, undesired back-switching of magnetic elements of an MRAM can easily be initiated by subsequent write pulses, threatening data integrity. We present a method to reverse the magnetization in under-critically damped systems by coherent rotation of the magnetization while avoiding any ringing. This is achieved by applying specifically shaped magnetic field pulses that match the intrinsic properties of the magnetic elements. We demonstrate, by probing all three magnetization components, that reliable precessional reversal in lithographically structured micrometre-sized elliptical permalloy elements is possible at switching times of about 200 ps, which is ten times faster than the natural damping time constant.

Preparation of Ba-ferrite containing glass-ceramics in BaO–Fe 2O 3–SiO 2

Ba-ferrite (BaFe 12O 19) containing glass-ceramics have been prepared from the glass in BaO–Fe 2O 3–SiO 2 through a novel 2 step crystallization method in order to manufacture the magnetic memory disk without deformation. It is revealed that the glass pre-crystallized prior to secondary crystallization shows no shape deformation during heat-treatment and also exhibits better magnetic properties compared with the conventional 1 step crystallized glass.

Controlled crystallization and characterization of cordierite glass-ceramics for magnetic memory disk substrate

Glass-ceramics containing cordierite (2MgO-2Al2O3-5SiO2) as a crystal phase based on the glasses in the system MgO-Al2O3-SiO2 were investigated for the application to magnetic disk substrate for higher storage capacity. Parent glasses were prepared with CeO2 addition as a flux and were crystallized by a controlled 2-step heat treatment The maximum nucleation and crystal growth rates were 2.4 × 109/mm3 · hr at 800 °C and 0.3 μm/hr at 915°C respectively. Only α- cordierite was precipitated after heat-treatment. After nucleation at 800 °C for 5 hours prior to crystallization at 915 °C for 1 hour, the resulting crystal volume fraction and crystal size were 17.6% and 0.3 μm, respectively. Heat-treated specimens through the above condition showed the optimum properties for magnetic memory disk substrates as follows.; Bending strength of 192 MPa, Vickers hardness of 642.1 kg/mm2, thermal expansion coefficient of 39 × 10−7/K and surface roughness of 27 A.

Influence of the short-range order parameter on the optical properties of amorphous nickel-phosphorus alloy

The influence of the short-range order of amorphous nickel-phosphorus alloy on the IR absorption is studied. The relation between the optical properties and the microstructure of amorphous nickel-phosphorus alloys obtained by various technological methods is considered. It is shown that a coating of amorphous Ni−P alloy obtained by electrolytic deposition has the most homogeneous structure; this permits the use of such coatings as protective layers for optical and magnetic memory disks. Optical methods permitting the estimation of the dimensions of the microcrystalline regions in an amorphous matrix are outlined.

Unstable Vibration Characteristics of a Flexible Disk Rotating in a Confined Fluid. 2nd Report, The Influence of Gap Width.

A rotating disp is utilized in many industrial flelds, such as a magnetic memory disk and a rotational mixer, and higher rotational speed is needed to achieve high performance. However it is well known that a flexible disk rotating in a confined fluid undergoes unstable vibration when the rotational speed exceeds a critical one, and that the unstable vibration occurs due to the interaction between the flexible rotating disk and the swirling fluid flow around it. Up to now, I have studied experimentally the characteristics of unstable vibrations induced in a single flexible disk rotating in a confined fluid, and found that the unstable vibration exhibits different mode shapes depending on the rotational speed, and visualized the unstable vibration mode shapes. This paper deals with detailed experimental investigation of the influence of the gap width between the rotating flexible disk and the side-shroud wall on the unstable vibration characteristics of a flexible disk rotating in a confined fluid. It was found that the gap width is an important parameter for the unstable vibration characteristics.

AM 2001 lubricant film on canasite glass-ceramic magnetic memory disk

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAM 2001 lubricant film on canasite glass-ceramic magnetic memory diskEmmanuel C. OnyiriukaCite this: Chem. Mater. 1993, 5, 6, 798–801Publication Date (Print):June 1, 1993Publication History Published online1 May 2002Published inissue 1 June 1993https://doi.org/10.1021/cm00030a014RIGHTS & PERMISSIONSArticle Views76Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (511 KB) Get e-Alerts Get e-Alerts

A Fluorescence Technique for Measuring Lubricant Thickness on Hard Magnetic Disks

A fluorescence technique for detecting thin lubricant films on hard magnetic memory disks has been investigated. A lubricant with a small amount of dissolved fluorescent dye was applied to disks. Illuminated by an ultraviolet light source, the fluorescent material emitted visible light which was detected by photographic film in a camera. From the photograph, two-dimensional lubricant distribution over the disk surface was easily obtained, since a thicker lubricant resulted in a greater increase in the blackening of the photographic film. With this technique, lubricant film displacement from the wear track during sliding, as well as recovery by later lubricant migration from adjacent areas, was easily observed. The half-life of this recovery was found to be approximately one day. The effect of humidity on lubricant displacement was also examined, and it was observed that higher humidity resulted in a greater rate of displacement. Moisture adsorption on thin film disks and humidity effects on the friction c...

散乱理論を用いた微小傷の測定評価に関する研究 ＩＩ 傷の深さと幅の定量的評価について

In this paper, the optical measuring method of fine scratches on mirror surfaces, such as the magnetic memory disk and the block gauge is investigated. The theoretical background of this method is based on Beckmann's Kirchhoff Approximation which is the theory of scattering of electromagnetic waves. Emphasis is on quantitative measuring method of fine scratches by the non-contact method. The results obtained are summarized as follows : First, the profile of fine scratch can be approximated to the triangle scratch, because experimental results from the various profiles of scratches are in close agreement with those in computer simulations for triangle scratches of the same depth and width. Secondly, typical factors related to size of scratch are found by the zero-and first order scattering intensities and the scattering angle, which are obtained from scattering intensity distributions. And then the depth and width of a scratch is simultaneously estimated by them. Finally, the range to be measured by this method is from 0.05 to 0.4 μm deep, from 10 to 80 μm wide for the scratches resulting spontaneously on block gauge and the scratches fabricated by diamond cutting tools.

散乱理論を用いた微小傷の測定評価に関する研究 Ｉ 三角形傷の散乱光強度分布の特性

The purpose of this research is to estimate quantitatively the depth of fine scratches in mirror surfaces, such as the surfaces of magnetic memory disks and laser mirrors. Bechmann's Kirchhoff Approximation, namely the theory of the scattering of electromagnetic waves, is adopted for measuring the depth of scratch. It is estimated by the linear relationships between the scratch depth and intensity-related factors representing the typical characteristics of the scattering intensity distribution obtained by computer simulation. The results obtained are summarized as follows. Firstly, the computer simulations and the experiments show that the depth of fine scratch can be estimated by introducing Bechmann's Kirchhoff Approximation. Secondly, when we approximate the scratch profile to a triangle profile, the depth of scratch is larger than 0.25 μm if the two peak intensities of the scattering distribution, which are seen in almost symmetrical location to the direction of specular reflection, are larger than the intensity of a 45 deg scattering angle. On the other hand, the depth of scratch is smaller than 0.25 μm if they are smaller than the intensity of a 45 deg scattering angle. Finally, it is verified experimentally that the depth of scratch from 0.1 to 1.3 μm can be measured within an error range of about 30% by this method.

Ｆｒａｎｈｏｆｅｒ回折による超精密ダイヤモンド旋削面の粗さ測定

A new measuring method which can estimate quantitatively the periodical fine surface roughness, for example the surface of magnetic memory disk and laser mirror finished by ultraprecision diamond tool machining is presented in this paper. This principle of measurement is based on Fraunhofer diffraction. Relations between the surface roughness and Fraunhofer diffraction patterns of diamond turning surfaces are discussed theoretically and experimentally. The results obtained are summarized as follows: A conventional equation which can accurately estimate the surface roughness of less than 200nm Rmax by measuring the intensity values of 0-3 order diffractions is derived from theoretical analysis based on Fraunhofer diffraction. From the measurements of surface roughness of various workpieces including a magnetic memory disk, it is found that this Fraunhofer diffraction method makes it possible to measure the surface roughness within 10% errors from 1nm to the maximum 200nm.

磁気ディスク用アルミニウム合金の開発の動向とその背景

磁気ディスク用アルミニウム合金の開発の動向とその背景

Studies on fabrication system of ultra-precision metal mirrors. Workpiece fixturing methods for ultra-precision machining.

Ultra-precision machining technology for metal optics has recently become important, in response to demands for high energy laser equipment and magnetic memory disks. In order to realise such precision machining, it is necessary to pay special attention to the workpiece fixture. Conventional fixture techniques, such as vaccum or multi jaw chucks, tend to provide adequate support, but they can also introduce unacceptable levels of partial distortion. In this paper, therefore, distortion-free workpiece techniques for metal mirrors are proposed, simultaneously clarifying both the characteristics and beneficial features.

磁気ディスクの動向とアルミニウム基板への課題

磁気ディスクの動向とアルミニウム基板への課題

Analysis on Simultaneous Double-Sided Grinding Stock Removal Distribution on a Thin Disk

This paper deals with both side grinding on a thin disk used for a magnetic memory disk substrate. A grinding model was set up in which a thin disk was inserted between a pair of grinding wheels and both sides were ground simultaneously. Using this model, an attempt was made to analyze the theoretical stock removal distribution from the thin disk, when changing grinding conditions. In the analysis, a formula on thin disk rotational moment was worked out, and revolutions per minute for the thin disk were calculated using a formula about rotational moment. Calculated stock removal distribution from the thin disk were in agreement with experimental results. This meant that accurate grinding conditions for uniform stock removal could be set up, based on calculation results.

Thin film γ‐Fe2O3 recording disk

AbstractAn α‐Fe2O3 thin film was sputtered onto an Al‐Mg substrate, after which it was transformed to γ‐Fe2O3 by reduction and oxidation and a magnetic memory disk was fabricated. The following results were obtained with regard to these processes: (1) The processing temperature must be below 330°C to maintain the initial surface state of the substrate. (2) If an α‐Fe2O3 film is reduced at 300°C for a few hours and oxidized in air, a homogeneous γ‐Fe2O3 film is obtained. (3) Addition of Ti to the film stabilizes the coercive force and broadens the acceptable conditions for reduction. A γ‐Fe2O3 film, to which Ti and Co have been added, has the following magnetic properties: residual magnetic flux density 2.5 kGs, coercive force 700 Oe, rectangular hysteresis ratio 0.8, coercive squareness 0.76, and film thickness 0.1 ‐ 0.2 μm. (4) Coercive force and demagnetization caused by heating and pressure are as stable as those of an ordinary sprayed magnetic memory medium. A γ‐Fe2O3 thin film disk, processed in the above‐described manner, can have a memory density of 104 − 105 bit/mm2.

高精度の磁気ディスク基板の加工 : 旋削から砥粒加工へ(話題の新加工技術,<特集>加工限界と工程設計)

高精度の磁気ディスク基板の加工 : 旋削から砥粒加工へ(話題の新加工技術,<特集>加工限界と工程設計)

磁気ディスク基板用加工装置の運動解析

Kinematical analysis on lapping a ring shaped plate with a circular tool is carried out and numerical equations on stock removal are obtained, taking into account distributed pressure due to the moment of inertia of the area contacted for both work and tool and due to the eccentric load. A newly designed machine, in which distributed presssure is able to be adjusted with eccentric load due to tool weight, was also built. Experimental stock removal, flatness and parallelism values on 360 mm diameter - 2 mm thick aluminum plates for magnetic memory disk, made by the machine, are in agreement with calculated values. In consequence. procedure deducing the equations is found to be satisfactory. The machine obtained here are not only applied to lapping, but are capable of being applied to mirror-polish the surfaces, plated electroless deposited nickel on an aluminum disk.