Wayne Isami Imaino

Self-assembled ferrimagnet--polymer composites for magnetic recording media.

A self-assembled magnetic recording medium was created using colloidal ferrimagnetic building blocks. Monodisperse cobalt ferrite nanoparticles (CoFe(2)O(4)) were synthesized using solution-based methods and then stabilized in solution using the amphiphilic diblock copolymer, poly(acrylic acid)-b-poly(styrene) (PAA-PS). The acid groups of the acrylate block bound the polymer to the nanoparticle surface via multivalent interactions, while the styrene block afforded the magnetic nanoparticle--polymer complex solubility in organic solvents. Moreover, the diblock copolymer improved the colloidal stability of the ferrimagnetic CoFe(2)O(4) nanoparticles by reducing the strong interparticle magnetic interactions, which typically caused the ferrimagnetic nanoparticles to irreversibly aggregate. The nanoparticle--polymer complex was spin-coated onto a silicon substrate to afford self-organized thin film arrays, with the interparticle spacing determined by the molecular weight of the diblock copolymer. The thin film composite was also exposed to an external magnetic field while simultaneously heated above the glass transition temperature of poly(styrene) to allow the nanoparticles to physically rotate to align their easy axes with the direction of the magnetic field. In order to demonstrate that this self-assembled ferrimagnet--polymer composite was suitable as a magnetic recording media, read/write cycles were demonstrated using a contact magnetic tester. This work provides a simple route to synthesizing stabilized ferrimagnetic nanocrystals that are suitable for developing magnetic recording media.

Active damping in HDD actuator

A non-traditional mechanical modification technique to take care of the major servo bandwidth limited resonance mode (butterfly mode) is developed, analyzed, and validated. With an additional sensor on the actuator and an external feedback loop, the butterfly mode can be damped and stiffened such that the gain of the head mechanical transfer function is close to 1/s/sup 2/. Servo improvement is also studied comparing to notch filter approach. It shows that the butterfly mode notch filter can be removed, and the phase margin can be improved by 7 degrees.

Monolayer Assembly of Ferrimagnetic CoxFe3–xO4 Nanocubes for Magnetic Recording

We report a facile synthesis of monodisperse ferrimagnetic Co(x)Fe(3-x)O4 nanocubes (NCs) through thermal decomposition of Fe(acac)3 and Co(acac)2 (acac = acetylacetonate) in the presence of oleic acid and sodium oleate. The sizes of the NCs are tuned from 10 to 60 nm, and their composition is optimized at x = 0.6 to show strong ferrimagnetism with the 20 nm Co0.6Fe2.4O4 NCs showing a room temperature Hc of 1930 Oe. The ferrimagnetic NCs are self-assembled at the water-air interface into a large-area (in square centimeter) monolayer array with a high packing density and (100) texture. The 20 nm NC array can be recorded at linear densities ranging from 254 to 31 kfci (thousand flux changes per inch). The work demonstrates the great potential of solution-phase synthesis and self-assembly of magnetic array for magnetic recording applications.

Scaling tape-recording areal densities to 100 Gb/in 2

We examine the issue of scaling magnetic tape-recording to higher areal densities, focusing on the challenges of achieving 100 Gb/in2 in the linear tape format. The current highest achieved areal density demonstrations of 6.7 Gb/in2 in the linear tape and 23.0 Gb/in2 in the helical scan format provide a reference for this assessment. We argue that controlling the head-tape interaction is key to achieving high linear density, whereas track-following and reel-to-reel servomechanisms as well as transverse dimensional stability are key for achieving high track density. We envision that advancements in media, data-detection techniques, reel-to-reel control, and lateral motion control will enable much higher areal densities. An achievable goal is a linear density of 800 Kb/in and a track pitch of 0.2 µm, resulting in an areal density of 100 Gb/in2.

Six orders of magnitude in linear tape technology: The one-terabyte project

For the last 50 years, tape has persisted as the media of choice when inexpensive data storage is required and speed is not critical. The cost of tape storage normalized per unit capacity (dollars per gigabyte) decreased steadily over this time, driven primarily by advances in areal density and reduction of tape thickness. This paper reports the next advance in tape storage--a demonstration of a tenfold increase in capacity over current-generation Linear Tape-Open® (LTO®) systems. One terabyte (1 TB, or 1000 GB) of uncompressed data was written on half-inch tape using the LTO form factor. This technical breakthrough involves significant advances in nearly every aspect of the recording process: heads, media, channel electronics, and recording platform.

Multilevel volumetric optical storage

Present optical storage devices use two-dimensional recording media which do not take advantage of the ability to focus light to a small spot at a large working distance throughout the volume of a storage media. In this report we propose an approach to volumetric optical storage where the optical had reads from and writes to distinct levels of a multilevel disk structure. This approach has been successfully applied to multilevel ROM and WORM optical disk memories. We detail the physical principles behind this technology, present detailed experimental data on two-level write-once media and briefly describe four-level recording. In companion papers we describe in detail results from four-level recording and readback and multilevel ROM based media and drives.

Multilayer optical recording (MORE)

Extension of optical storage to the third dimension by reading and writing data at distinct levels throughout the volume of optical media will be discussed. An overview of the status, challenges, and limits of this approach will be presented.

Effect of Tape Longitudinal Dynamics on Timing Recovery and Channel Performance

The recording performance is compared for two barium ferrite magnetic recording tapes which differ by a factor of two in friction, but are otherwise very similar. The error rate of the tapes is similar at a tape speed of 4 m/s, but as the read or write speed decreases to 1.16 m/s, the error rate of the smoother, higher friction tape increases by a factor of 100. This effect arises from velocity variations in the tape, which prevent accurate timing recovery and uncertainty in the phase of the recorded waveform. The velocity variation is measured by recording a periodic waveform. Its power spectrum demonstrates the effect of the compressional sound wave resonating between rollers on either side of the recording head.

Photoacoustic-pulse generation and propagation in a metal vapor.

Photoacoustic-pulse generation by breakdown is achieved in dense cesium metal vapors of vapor pressures ranging from 2 to 130 Torr by using a dye laser pulse of energy variable from 10(-6) to 10(-3) J, tuned to the Cs transition at 6010 A. The acoustic-pulse propagation is detected by the transient photorefractive deflection of a cw probe laser beam that is displaced from but parallel to the pulsed laser beam. The temperature-dependent velocity of infinitesimal ultrasonic waves in a corrosive metal vapor is measured for the first time. The supersonic propagation of finite amplitude acoustic pulses (blast waves) obtained with a higher pulse energy is also studied. Our data, with Mach numbers ranging from 2.1 down to below 1.01, agree surprisingly well with the prediction of Vlases and Jones for cylindrical blast waves. This provides a new experimental support for their theoretical trajectory formula for blast waves in the extremely weak amplitude limit.

Decision-Analytic Methodology for Cost-Benefit Evaluation of Diagnostic Testers

Abstract A modular influence diagram model is proposed as a decision-analytic framework for reasoning about diagnostic testing in the manufacture of mechanical products. The influence diagram ties product design, manufacturing, and testing decisions to field quality, costs and risks. The decision-analytic theory of “expected value of information” is used to evaluate the cost-benefit of alternate testing systems. The structure of the model highlights research directions for engineering economics in evaluating cost-benefit tradeoffs in the product cycle from design, to manufacturing, marketing and field service. An implementation in the IDES (Influence Diagram Based Expert System) illustrates the potential of applying such a planning model to real-time diagnostic decisions in the manufacture of mechanical components for high-speed printers.