Jiro Hokkyo

Reproducing characteristics of perpendicular magnetic recording

The effects of magnetic properties and thickness of single-layer Co-Cr film media on perpendicular recording with a ring head are investigated. The effects of the reproducing head gap length and the reproducing head-to-medium spacing on reproduction are also discussed. Experiments are performed using ring heads for recording and reproducing and using single layer Co-Cr film media whose effective perpendicular anisotropy field Hk,eff from the in-plane hysteresis curve is greater than 5 kOe. The following results are obtained: (I) The reproduced voltage Ep at long wavelength is nearly proportional to the thickness δ of the medium and to the coercive force H_{c}(\perp) in the normal direction of the film. (2) E p is independent of the saturation magnetization M s . (3) The -6dB wavelength λ 50 is independent of δ. (4) λ 50 gradually increases as H_{c}(\perp) or M s increases. These results are well explained by a model of perpendicularly-recorded magnetization which assumes zero transition width and self-demagnetization in the medium. Calculations based on our model predict that the wavelength response of the reproduced voltage strongly depends on the reproducing head gap length and the reproducing head-to-medium spacing rather than on H_{c}(\perp) , M s and δ. An excellent high recording density (λ 50 of 0.45 μm or 113 kBPI) can be obtained by a medium and a head-to-medium interface suitable for high-density recording.

A new W-shaped single-pole head and a high density flexible disk perpendicular magnetic recording system

A new single-pole head with no auxiliary pole was developed for perpendicular magnetic recording. The head is called WSP head (W-shaped Single Pole head) because the head has a W-shaped side core which contributes to increase the recording and reproducing sensitivitiy. The head field of the new head has the same distribusion as that of an auxiliary pole head[1]. The recording and reproducing sensitivity of the head is equal to or higher than that of a ring-type video head. The head eliminates mechanical problems which prevent its application in perpendicular magnetic recording because we can locate the head on one side of the recording medium. As a possible application of the WSP head, a 3 1/2-inch flexible disk recording system was constructed. A linear recording density of the flexible disk system was 65.5 kbits/inch. This density is equivalent to 8 times that of the existing high-density 3 1/2-inch micro-floppy and 11 times that of a 5 1/4-inch floppy disk. In termes of information storage, this density gives a 4 megabyte unformated capacity on one side of a 3 1/2-inch flexible disk. The overwrite signal-to-noise ratio was greater than 30 dB and the peakshift displacement was less than 10 % at the linear dinsity of 65.5 kbits/inch.

Noise characteristics of Co‐Ni obliquely evaporated tape

In Co‐Ni obliquely evaporated tape, the magnetic properties and the microstructure are greatly affected by the oxygen gas introduced during the evaporation phase. When the oxygen flow rate is low, the dc‐erased noise which is caused by the inhomogeneous structure of the magnetic layer, is greater than the ac‐erased noise. The modulation noise level is also high and increases as the carrier frequency increases, as in longitudinal thin‐film media having zig‐zag transitions. As the oxygen flow rate increases, the signal output level increases to a maximum and the ac‐erased, dc‐erased, and modulation noise levels decrease. Tape prepared using the optimum oxygen flow rate does not show any increase in the modulation noise as carrier frequency is increased. Analysis of the three noises in the normal and reverse head transport directions made it clear that the ac‐erased noise can be affected by the inhomogeneousness of the microstructure in the column, the modulation noise by the irregularity of the magnetic transition region which includes the microstructure, and the dc‐erased noise not only by the inhomogeneousness of the microstructure but also by the partial switching caused by the magnetic field of the trailing edge of the Sm‐Co magnet. Co‐Ni obliquely evaporated tape prepared using the optimum oxygen flow rate is a particlelike medium with a high signal output level and low‐noise characteristics.In Co‐Ni obliquely evaporated tape, the magnetic properties and the microstructure are greatly affected by the oxygen gas introduced during the evaporation phase. When the oxygen flow rate is low, the dc‐erased noise which is caused by the inhomogeneous structure of the magnetic layer, is greater than the ac‐erased noise. The modulation noise level is also high and increases as the carrier frequency increases, as in longitudinal thin‐film media having zig‐zag transitions. As the oxygen flow rate increases, the signal output level increases to a maximum and the ac‐erased, dc‐erased, and modulation noise levels decrease. Tape prepared using the optimum oxygen flow rate does not show any increase in the modulation noise as carrier frequency is increased. Analysis of the three noises in the normal and reverse head transport directions made it clear that the ac‐erased noise can be affected by the inhomogeneousness of the microstructure in the column, the modulation noise by the irregularity of the magnetic tra...

Perpendicular magnetic anisotropy and microstructure of sputter-deposited Co-Cr film

Abstract The Ar pressure dependence of both the microstructure and the magnetic properties of sputter-deposited Co-Cr film is investigated. As the Ar pressure decreases, the structural binding between columns in the film becomes denser and stronger. The columnar structure has no relation to the crystal orientation. A domain structure change is suggested.

Interaction between head and recording medium in perpendicular recording

A simple model for a perpendicular magnetic recording head of magnetic thin film is proposed. The interrelation between the recording field and the magnetization in the head pole, and the interaction between the head and the recording medium, especially the high permeability layer in a double-layered medium, are explained in terms of the model. The paper indicates that the recording field distribution is little affected by magnetic saturation in the head pole, and that the interaction between the head and the medium greatly increases the effective component of the recording field, narrows the distribution of this component, and increases the ratio of the effective component to the ineffective component.

Co-Ni obliquely evaporated tape and its magnetic and recording characteristics

Abstract This paper describes technology for a Co-Ni evaporated tape, a metal evaporated, or ME tape fabricated by a vacuum evaporation method, focusing on magnetic properties, microstructure, recording characteristics and noise prosperties. The high reproduced signal output, low noise and high resolution of ME tape obtained by using a ring head are attributed to oblique anisotropy and a particle-like structure. A breakthrough in improving the durability of ME tape has been achieved by technological improvements in tribology.

Peakshift characteristics of perpendicular magnetic recording

The characteristics of the peakshift for two Head/Medium combinations of a perpendicular magnetic recording are studied in this paper. One is a combination of a ring head and a single-layer medium, and another is that of a single-pole head and a double-layered medium. Dps20 is defined as the linear density at which the peakshift reaches 20 %, and D50 is defined as the linear density at which the readback voltage is 6 dB below the readback voltage at 1 kBPI. It is shown theoretically that the relation between Dps20 and D50 for these two combinations becomes the same when the phase of the readback voltage for a combination of a ringhead and a single-layer medium is equalized by the Hilbert transformation to that of a combination of a single-pole head and a double-layered medium. This means that about the relation between Dps20 and D50 there is no difference between these two Head/Medium combinations when only the readback from the complete perpendicular recorded magnetization is considered. It is also indicated experimentally that a simple highpass filter is very useful to improve the peakshift without worsening signal-to-noise ratio for the combination of a ring head and a single-layer medium.

Magnetic Property Change of High Permeable Layer in Double Layered Perpendicular Media

Introduction Putting a high permeability layer beneath the Co-Cr layer of double-layer perpendicular magnetic recording film media can make the single-pole head recording/reproducing sensitivity substantially higher for Co-Cr single-layer film media [1]. We will report the effects of the Co-Cr layer on the magnetic characteristics of Permalloy underlayer film. The research group headed by Mr. Sugita has made reports on evaporated film lately [2].