Fumio Kugiya

Investigation of 2 Gb/in/sup 2/ magnetic recording at a track density of 17 kTPI

Developments of magnetic head, recording medium, positioning, and signal processing technologies made it possible to perform magnetic recording at an areal density of 2 Gb/in/sup 2/ on a prototype 3.5-in diameter hard disk drive. A track density of 17 kTPI, which is comparable to or even greater than that used in optical storage systems, is used to minimize the reduction in the physical clearance between the medium and the head. The authors outline the system and its component technologies. The read/write characteristics of the 3.5-in prototype disk system are also reported. >

Simulation of perpendicular recording on Co‐Cr media with a thin Permalloy film‐ferrite composite head

Numerical analyses of thin film head‐medium system for perpendicular recording are performed using a two‐dimensional model. The formulation is based on Poisson’s equation for magnetic vector potential in the head‐medium system. The following conclusions are drawn: (1) Magneto‐motive force needed for producing a sufficient perpendicular field in the medium is about 1/10 that of the SPT (single pole type) head proposed by Iwaski et al. (2) There is an optimum spacing between the magnetic layer and the ferrite of the head that lies 5–20 times the distance between the main pole and the underlayer. (3) The conductor should be placed in the very tip portion of the magnetic layer. (4) Simulation confirms that recording of densities as high as 100 kBPI is possible using a thin film head‐Co‐Cr medium system.

Sensitivity‐enhanced electron holography and its application to magnetic recording investigations

The sensitivity for electron‐phase measurement in electron holography has been improved to better than 2π/100 by the application of digital interferometry at the optical reconstruction stage. This enables quantitative measurement of magnetic flux as small as (1/100)(h/e)(=4.1×10−17 Wb), hitherto undetectable, with high spatial resolution. With this technique, we have observed the distribution of leakage magnetic field from a thin cross section of a perpendicularly magnetized recording film (cobalt‐chromium) with a recording density as high as 300 kFCI (85 nm bit length), the highest density ever directly observed.

Studies of spacing loss in longitudinal and perpendicular recording

The effect of head‐to‐medium spacing on longitudinal and perpendicular magnetic recording with ring heads has been clarified. Media tested are a γ‐Fe2O3 particulate disk and a Co–Ni–P plated disk for longitudinal recording, and single and double layer of Co–Cr sputtered disks for perpendicular recording. Experiments are performed utilizing Mn–Zn ferrite ring heads with 0.30, 0.56, and 0.78‐μm gap lengths. In addition, self‐consistent calculations by finite element method, which takes into consideration head‐to‐medium interaction, are applied to clarify the mechanism of read spacing loss.

Precise Mark Shape Control in Mark Length Recording on Magnetooptical Disk

To realize higher storage density on a magnetooptical disk, we proposed the write control method, which controls shapes of recorded mark in marks length recording. In this paper, the analysis of this write control method is reported. Based on the model of the recording process, we discuss the necessary condition of the recording pulse waveform for the control of the recorded mark shape on magnetooptical recording media which have large heat conductivity. The write control method is examined under the condition of 880 Mb/in2 recording density. The precise control of the recording mark shape is confirmed through the experiment. From the result of the computer simulation, it is proven that this method satisfies the necessary condition, which clarified the effect of this method theoretically.

Measurement of intensity of recorded magnetization on Co-Cr film by electron holography

Electron holography has excellent features that permit the direct observation of magnetic flux in micro regions and the quantitative measurement of the flux intensity. Using this method, the intensity of recorded magnetization on a Co-cr single layer medium is measured. As a result, it is revealed that the demagnetization factor, which is determined by the aspect ratio of the recorded bit cell, dominates the magnetization recorded in contact with a head. It is also learned that the spacing loss in the recording process is -160d/λ[dB).

Influence of initial growth layer and Ti underlayer on magnetic properties and recording characteristics of very thin films of evaporated Co-Cr media

A Co-Cr film deposited directly on a substrate has an initial growth layer with low coercivity. However, the existence of a Ti underlayer prevents the formation of such a layer. As a result, Co-Cr film deposited on a Ti underlayer has high perpendicular anisotropy and coercivity even in cases of extremely thin film thickness (200 AA). As for the read-write characteristics of Co-Cr thin-film media, the existence of such an initial growth layer greatly improves the reproduced output level. The cause for this is considered to be that the free charges which appear on the back surface of the perpendicular recording layer are reduced and the demagnetization field acting on the recorded magnetization subsequently decreases due to the existence of the initial growth layer. >

5.25 inch floppy disk drive using perpendicular magnetic recording

5.25 inch high density perpendicular magnetic recording floppy disk drive has beer developed by employing new types of high saturation magnetization ring head, Co-Cr single layer medium with Ge underlayer, head slider with ellipsoidal surface configuration to assure intimate head to medium contact, and signal equalization. By these combination, recording density D50 of 145 kFCI, peakshift of 28 % at 100 kFCI, signal to noise ratio of 40.4 dB for cut-off frequency 4.25 MHz, overwrite signal to noise ratio of 27 dB, measured by writing signals at 48 kFCI over previously written 100 kFCI signals were obtained as typical recording characteristics. These results would indicate that floppy disk drive with 100 kFCI recording density has enough system margin by above-mentioned combination. In this paper, design and performance of newly developed floppy disk drive are described.

A study of magnetization model for particulate media

The leakage magnetic field of a single gamma -Fe/sub 2/O/sub 3/ particle is observed by electron holography to be approximately single domain and uniaxial. On the basis of this result, a vector magnetization model is introduced in which curling and rotation in unison modes for a prolate take place. Using this model and the particle size and orientation distributions in gamma -Fe/sub 2/O/sub 3/ particulate media observed by high-resolution scanning electron microscopy, M-H loops and H/sub c/- Omega characteristics of the film are calculated. Moreover, read/write simulations of the isolated pulses are performed using the finite element method. These calculated results agree fairly well with measurements. >

Observation of Magnetization Structure on Co-Cr Perpendicular Magnetic Recording Media by Bitter and Electron Holography Methods

The magnetization structure of single-layer Co-Cr media recorded with a ring head at 20 and 100 kFCI is investigated along with the microstructure of Co-Cr film prepared by vacuum deposition. A stronger magnetization as well as a deeper penetration of perpendicular magnetization have been realized with the highly-oriented Co-Cr films consisting of pillar-like c-axis-oriented Co-Cr columns. This magnetic behavior is considered necessary to achieve a high-density and high-output perpendicular magnetic recording when the medium is combined with a ring head.