Magnetic Storage System Research Articles

Molecular dynamics simulation of effect of indenter shape on nanoscratch of Ni

Thin films of Ni and Ni alloy have been widely used in microelectromechanical systems (MEMS) and magnetic storage systems. As the dimensions of components in these systems decrease to the micro-scale, even the nano-scale, the interfacial phenomena significantly differ to the counterparts on the macro-scale. A better understanding of micro-/nano-tribology will benefit the fabrication of the small components. In this manuscript parallel molecular dynamics (MD) simulations have been conducted to investigate the nanoscratch behavior of nickel. The simulations are performed for two cases with different indenter shapes. Case I has a sharp indenter, while the indenter in Case II is blunt. It has been found that the indenter shape significantly influences the nanoscratch deformation. The sharp indenter only generates a small deformation area under the indenter, while the blunt one produces more dislocations and larger deformation area in the substrate. The simulation results show that the vertical forces during scratch in Case I are larger than those in Case II, while the scratching forces are similar in both cases during scratch. In addition, the sharp indenter has smaller indentation hardness than the blunt indenter. However, the blunt indenter exhibits smaller scratch hardness and smaller ratio of the scratching force to the vertical force. In order to improve the thermal stability, an algorithm has been proposed to dynamically determine the time-step of MD simulation, by which the system temperature can be maintained within a small range without thermostat layers.

S1603-1-3 液体超薄膜表面に働く繰り返し応力による表面変形解析 : 振動するスライダ下の液膜変形の線形解析(情報機器コンピュータメカニクス)

In recent magnetic storage systems, the spacing between the flying head and the disk has been dramatically decreased to less than 10 nm for realizing ultra-high density recording. Therefore, it is very important to investigate the deformation and flow characteristics of the lubricant on the recording disk, especially the dynamic deformation of the lubricant, which is suffered from the repetitively applied pressure and shear stress by the flying head slider. In this paper, the dynamic behaviors of the ultra-thin liquid (lubricant) surface under vibrating flying head slider were numerically obtained. The dependence of the liquid surface deformation on the frequency of the stresses and the disk speed were clarified.

P-HDI-07 DEFORMATION CHARACTERISTICS OF ULTRA-THIN LIQUID FILM CONSIDERING TEMPERATURE AND FILM THICKNESS DEPENDENCE OF SURFACE TENSION : NUMERICAL ANALYSES BY THE LONG WAVE EQUATION(Head/Disk Interface and Tribology,Technical Program of Poster Session)

In the latest magnetic storage systems, the spacing between the flying head and the disk has been dramatically decreased to less than 10 nm in order to realize ultra-high density recording. When the flying height is of the same order as the lubricant film thickness, lubricant deformation affects the static and dynamic flying characteristics of the slider. Therefore, it is very important to investigate the deformation and flow characteristics of lubricant on the recording disk. In particular, in heat assisted magnetic recording (HAMR), laser heating of the lubricant changes surface tension distribution, which may cause deformation of the lubricant film. In this paper, we first established temperature and film thickness dependence equation for surface tension. The temperature dependence was obtained by measuring the relation between surface tension and temperature by means of a tensiometer, while film thickness dependence was obtained by theoretical consideration of the van der Waals pressure equation for a multilayer system. By using the steady state long wave equation with consideration to temperature and film thickness dependence of the surface tension, we numerically analyzed the liquid film deformation caused by the temperature distribution. The depression of the liquid was quantitatively obtained.

Optimization of hybrid power system composed of SMES and flywheel MG for large pulsed load

A superconducting magnetic storage system (SMES) has some advantages such as rapid large power response and high storage efficiency which are superior to other energy storage systems. A flywheel motor generator (FWMG) has large scaled capacity and high reliability, and hence is broadly utilized for a large pulsed load, while it has comparatively low storage efficiency due to high mechanical loss compared with SMES. A fusion power plant such as International Thermo-Nuclear Experimental Reactor (ITER) requires a large and long pulsed load which causes a frequency deviation in a utility power system. In order to keep the frequency within an allowable deviation, we propose a hybrid power system for the pulsed load, which equips the SMES and the FWMG with the utility power system. We evaluate installation cost and frequency control performance of three power systems combined with energy storage devices; (i) SMES with the utility power, (ii) FWMG with the utility power, (iii) both SMES and FWMG with the utility power. The first power system has excellent frequency power control performance but its installation cost is high. The second system has inferior frequency control performance but its installation cost is the lowest. The third system has good frequency control performance and its installation cost is attained lower than the first power system by adjusting the ratio between SMES and FWMG.

Ordered magnetic nanohole and antidot arrays prepared through replication from anodic alumina templates

Highly ordered arrays of Ni nanoholes and Fe 20Ni 80 antidots have been prepared, respectively, by replica/antireplica processing and sputtering techniques using nanoporous alumina membranes as templates. Geometrical characteristics as nanohole/antidot diameter, interpore distance and the overall hexagonal symmetry of arrays are controlled through the original templates. Experimental data on their hysteresis and magnetic domain structure have been taken by vibrating sample magnetometry and magnetic force microscopy, respectively. An analysis of the magnetization process, resulting magnetic anisotropy and magnetic domain structure is summarized considering the influence of those geometry aspects. In particular, the hexagonal symmetry and the density of nanohole/antidots determine the overall magnetic behavior, which is of interest in future high-density magnetic storage systems.

Maximum a Posteriori Estimation With Vector Autoregressive Models for Digital Magnetic Recording Channels

In recent signal processing schemes of various high density digital magnetic storage systems, it needs to detect signal sequences with signal-dependent media noise and colored Gaussian noise, and so on. The more the areal recording density of storage systems gets increasingly, the more it seems increasingly difficult for any signal processing system to reduce or cancel the effects caused by noise and interference because total noise for which several different distributions are mixed occurs frequently in recording channels. High areal density recording needs not only the severe demand for signal detection, but also comes in predisposed to trend for recording by a large-sector size instead of a single sector which consists of 512 information 8-bit bytes. From this trend, nonbinary low-density parity check (LDPC) codes will be important for future recording systems. For these future problems, this paper proposes the signal estimation method based on statistical inference for such a finite mixture model with known number of noise components. Our signal detection scheme with vector (multivariate) autoregressive (AR) models for total noise is applied to maximum a posteriori probability sequence detection. Furthermore, burst error correcting nonbinary low-density generator matrix (LDGM) codes are used for an error correcting code which satisfies the specific run-length limited condition in the proposed signal processing system. We show that the scheme of these error correcting and signal detection methods are effective to estimate signal sequences degraded by a mixture of noise and improve the error rate performances with respect to the conventional scheme using binary LDGM codes and univariate AR models.

Determination of effective anisotropy in a modern particulate magnetic recording media

The dramatic increases achieved in the areal density of magnetic data storage systems depend crucially upon a commensurate reduction in the size of the particles that comprise modern recording media. When modelling the characteristics and performance during the continuing development of such high-performance media, it is essential that the effects of reduced magnetic particle dimensions be fully taken into account. An analytic technique is presented that facilitates determination of the effective anisotropy of the particulate media under investigation. The procedure is demonstrated using experimental data obtained from a series of mono-layer samples composed of single-domain cobalt nano-particles, in which the particle volumes and packing fractions are varied throughout the series. The particles, with diameters in the size range 6.2–9 nm, are determined to possess an effective anisotropy ≈7.9×10 6 erg/cm 3 and a CoO outer shell of thickness 1.1 nm. When these values are utilised to construct a model describing the physical and magnetic properties of the samples, as a function of deposited Co volume thickness, then close correspondence is obtained between predicted and experimentally measured model descriptors.

Long range ordering in self-assembled Ni arrays on patterned Si

We have succeeded in aligning self-assembled structures by using a lithographically defined stripe. The 140 nm wide by 100 nm high SiO 2 strip is shown to guide the assembly of 500 nm latex spheres so that spheres are aligned along the strip and are in registration on either side of the strip. This method can be used to increase long-range ordering in magnetic storage systems without compromising the density. Inverse sphere Ni arrays were made by electrodeposition through the latex template. We also show that the hexagonal symmetry of the resulting inverse sphere Ni arrays can be simulated using the approach presented below.

Frequency domain subspace identification of a tape servo system

As capacity demands for magnetic tape storage systems grow, servo actuator design for tracking data on high density tape media presents new modeling and control design challenges. In this paper a frequency weighted subspace identification algorithm is presented for control relevant model estimation of a tape servo actuator. Common to other subspace identification methods, the proposed algorithm is based on linear algebra techniques providing means for model order selection and model computation. The proposed subspace identification also allows for frequency dependent weightings to emphasize frequency data around the cross-over frequency to find models relevant for control design. The algorithm is applied to data obtained from a tape storage device, demonstrating model order selection and the estimation of servo actuator dynamics with control relevant model fit criteria.

Future Memory Storage Technology: Protein-Based Memory Devices May Facilitate Surpassing Moore's Law

Storage media based on biomolecules may provide a commercially viable alternative to current magnetic and optical storage systems. Our research is aimed at developing the storage media systems based on newly designed thermostable bacteriorhodopsin (bR) mutants and exploring limits of high-density optical recording using far-field and near-field approach

Adaptive Decomposition of Noise Sources in Digital Recording Systems With Media Noise

In digital recording systems, the total amount of data-dependent media noise increases considerably as recording densities increase. A proper noise characterization is crucial for the design of receivers for high-density storage systems. This characterization involves the selection of a proper noise model and subsequently the accurate estimation of the parameters of the selected model. The estimation algorithm proposed in this paper jointly estimates the parameters of both media and additive noise with a high accuracy. The proposed algorithm makes use of the data dependency of the media noise to distinguish between the different noise sources. The algorithm is simple and as a result can be implemented in recording systems, with only a limited amount of complexity, as an easy add-on to read-channel ICs. From the simulation results and the analytical derivation of the estimation algorithm, we can clearly indicate which data patterns yield near-optimal estimation performance. These patterns are the ideal test patterns in experimental systems. We propose and discuss test patterns for magnetic and optical storage systems

Universal Access to All Knowledge

like the idea that there's a God somewhere looking after us. But sometimes I think it's a wrathful God. Who are the right gods? Janus sounds nice, but the idea of Sisyphus having to roll a rock continuously up a hill strikes me as more appropriate. When tending files on spinning magnetic storage systems and trying to preserve them for centuries, I think of Damocles' sword hanging over us. One major slip and it could be a very, very bad day at the Archive. I thought I'd go over some of the Internet Archive's experience working with digital materials in large numbers from an archival point of view. What are the technological issues? What are the access and use issues? What are the institutional problems and issues? What are the copyright issues? How should this all work?

Nanomechanical Property and Nanowear Measurements for Sub-10-nm Thick Films in Magnetic Storage

In the magnetic storage industry, thin film carbon overcoats play a critical role in reducing magnetic and physical spacing between the recording slider and the rotating disk so that the information stored per unit area is maximized. Thin film carbon overcoats have been improved such that they exhibit higher hardness with lower thickness of few nanometers and still being able to perform reliably. In this paper, nanoindentation and nanoscratch techniques to measure nanomechanical properties, namely hardness, elastic modulus and shear strength of thin solid films were presented along with a recently developed high resolution force transducer. Nanowear behavior characterization techniques were also examined and were applied to commercially available magnetic disks to characterize their wear behavior. It was shown that the properties and wear behavior of sub-10-nm thick film carbon overcoats were reliably measured. These techniques could be applied to different thin solid films on substrates, and they are not restricted to magnetic storage systems.

Shear strength determination using the nanoscratch technique and its application to thin solid films

Reliable measurement of mechanical properties of thin solid films has been challenging, despite widespread usage of thin films in applications such as semiconductor, magnetic storage, and microelectromechanical systems. Some of the challenges include instrument limitations and inadequacy of theoretical models to obtain quantitative prediction of thin film properties. In this article, we propose a technique to extract the shear strength of thin films from nanoscratch experiments using a contact mechanics analysis of a sliding sphere. Based on the stress field analysis by Hamilton, the stress status around the contact point is obtained at the initiation of yield, and is used to establish a direct correlation between contact pressure/surface traction and shear strength. Nanoscratch experiments were also performed on an extremely thin diamond carbon overcoat used in supersmooth magnetic storage disks, and the shear strength was successfully obtained using the proposed technique. These results were comparable with hardness values reported in the literature, assuming Tabor’s empirical relation (hardness ≈ 3*yield strength) and Tresca yield criterion. Finally, a finite element model was developed to simulate a rigid sphere sliding over a deformable solid to further verify the validit yo f the proposed model. The finite element analysis confirmed that the calculation results from the proposed relation are in good agreement with experimentally measured bulk property values of shear strength.

Electrodeposition and Nanobiosystems

As seen elsewhere in this section on electrodeposition, electrodeposition is a key method for making the materials used in computer chips and magnetic data storage systems; every day it helps lower the cost and improve the performance of our information society.

シリンダ状媒体対応傾斜パッドスライダの浮上安定性に関する検討

We studied a magnetic recording head for a cylindrical perpendicular magnetic storage system with regard to its stability when a slider is flying over a rotating 1-inch-diameter cylindrical medium. We also designed an inclined-pad-type slider for the cylindrical magnetic storage system. This slider has an inclined pad formed on its leading edge and a trailing pad formed on its trailing edge, to generate an air-bearing force. The inclined pad is protruded in the thickness direction of the slider relative to the trailing pad. A waveform of an acoustic-emission (AE) sensor and an envelope of a reproduced signal were obtained from the combination of the cylindrical perpendicular medium and fabricated this slider. These waveforms did not show any large pulse and thermal asperity associated with contact. These results confirm the flying stability of the inclined-pad-type slider.

傾斜パッド型ＳＰＴ浮上ヘッドによるシリンダ状ＣｏＰｔＣｒ‐ＳｉＯ２垂直二層膜媒体のＲ／Ｗ特性

A cylindrical magnetic storage system was investigated and developed, using perpendicular double-layered media with several CoPtCr-SiO2 recording layers and inclined-pad-type heads with a single-pole-type (SPT) writer designed for use with cylindrical media. The fabricated head was capable of stable flight over a rotating cylindrical medium. The inclined-pad-type head had almost the same linear velocity dependence of its flying characteristics as in the theoretical design, and is thought to be a potentially valuable component of cylindrical magnetic storage systems. Composite recording layers of CoPtCr-SiO2/Ru/Pt/Ta deposited on a rotating cylindrical substrate with a soft magnetic underlayer (SUL) had coercivities of 3.9 kOe (medium #A) and 5.9 kOe (medium #B), controlled by varying the SiO2 content, and a squareness ratio of around 1. These properties were almost the same as those of composite recording layers deposited on conventional disk substrates with SULs. The fundamental read/write characteristics of CoPtCr-SiO2/CoZrNb perpendicular double-layered cylindrical media were measured and a D50 value of around 310 kFCI was obtained using medium #B and an SPT writer attached to the inclined-pad-type head. A reduction of the flying height and protective layer thickness is indispensable for further increasing the areal recording density while maintaining sufficient overwrite capability.

Physics of patterned magnetic medium recording: Design considerations

Selected aspects of the recording physics of magnetic data storage systems based on patterned medium are discussed. Considerations for the choice of a recording layer material are outlined. A micromagnetic study of magnetization reversal in patterned magnetic recording medium is presented. The effects of bit geometry, medium thickness, head/medium magnetic spacing, air-bearing surface geometry, write pole material, and write misregistration on magnetization reversal are explored. The influence of a recording layer design on playback resolution is evaluated. The results offer the guidelines for the design and optimization of patterned magnetic recording medium.

Performances of journal bearing with MoS2-shot coating for spindle of magnetic recording storage system

MoS2-shot coating technology is recently focused as one of potential methods of surface modification to realize a low friction state. In this paper, performances of a small-sized journal bearing with MoS2-shot coating, which we aim to apply to a spindle of magnetic recording storage system, are investigated in detail through both of the observation of surface property and experimental approach from the viewpoints of frictional torque, durability against start–stop repetition, and run-out characteristics. In consequence, we can conclude that the MoS2-shot coating spindle is suitable for the application of small-sized journal bearing.

Nanotribology and nanomechanics

The recent emergence and proliferation of proximal probes, in particular scanning probe microscopies (the scanning tunneling microscope and the atomic force microscope), the surface force apparatus, and of computational techniques for simulating tip-surface interactions and interfacial properties, have led to the appearance of the new field of nanotribology, which pertains to experimental and theoretical investigations of interfacial processes on scales ranging from the atomic- and molecular- to the microscope, occurring during adhesion, friction, scratching, wear, indentation, and thin-film lubrication at sliding surfaces. Nanotribological studies are needed to develop fundamental understanding of interfacial phenomena on a small scale and to study interfacial phenomena in micro/nanostructures used in magnetic storage systems, micro/nanoelectromechanical systems (MEMS/NEMS), and other applications. Proximal probes have also been used for nanomechanics and materials characterization studies. In this paper, we present a review of significant aspects of nanotribology, nanomechanics, and materials characterization studies conducted using an atomic force microscope.