Kenji Torazawa

Magnetic domain expansion readout for amplification of an ultra high density magneto‐optical recording signal

An amplified magneto‐optical signal readout by using a dynamic domain expansion effect has been proposed and experimentally confirmed. Small domains of around 0.3 μm in diameter were expanded by a pulsed external field on the readout layer copied from the recording layer. An amplified readout signal up to three times larger than that of the original one has been achieved.

Magnetic expansion read-out of MSR disk with double in-plane magnetic layers

Magnetically induced super resolution (MSR) is a useful technique for high density magneto-optical storage. The magnetic domain expansion disk with double in-plane layers was prepared and its magnetic domain expansion read-out characteristics were measured. The film mainly consists of GdFeCo read-out layer, GdFeCo intermediate layer and TbFeCo memory layer. Given a difference in content of the GdFeCo readout and intermediate layers, it is clearly observed that there exists a threshold read-out laser power. When 0.6 /spl mu/m continuous domains were recorded on the magnetic expansion disk, the read-out signal level became about 2 times higher than that of a conventional CAD (Center Aperture Detection) disk without an external magnetic field.

Magnetic Domain Expansion Readout For An Ultra High Density MO Recording

An advanced readout technique using a dynamic domain expansion phenomenon has been proposed and investigated. Very small domains of 0.08 /spl mu/m which achieve an areal density of 20 Gb/in/sup 2/ (CD single side 30 GB with 680 nm laser) expand during readout, causing the readout signal to increase to the same level as for a 0.6 /spl mu/m domain.

Key Technologies to Realize Magneto-Optical Storage of Over 7 Gbytes in CD-Sized Disk.

Many types of recording technologies have been reported for future magneto-optical (MO) storage. However, they have not been well discussed from the viewpoint of total recording technology including the recording and readout methods, the pick-up technology and the signal processing technology. We propose key technologies for realizing MO storage of over 7 Gbytes in a CD-sized disk using a red laser, and describe the analytical and experimental results pertaining to each key technology.

High density recording on magnetically induced super resolution disk with magnetic field modulation and pulsed laser irradiation

The magnetically induced super resolution disk with an in-plane magnetized layer (CAD-MSR) is one of the most useful candidates for high density recording because of its simple structure and no initializing fields. This paper describes an evaluation of a CAD-MSR disk using magnetic field modulation with a pulsed laser, which is also useful for high density recording. We obtained a jitter of less than 10% at a bit density of 0.3 /spl mu/m/bit (2 T=0.4 /spl mu/m in (1,7) RLL code). The real density corresponds to an unformatted capacity of more than 5 Gbytes on a /spl phi/ 120 mm disk.

Thermal stability of Pt/Co multilayered films

The thermal stability of Pt/Co multilayered films with various underlayers has been studied by annealing up to 400 °C. In Pt/Co films sputtered on glass or amorphous AlN underlayers, their coercivity and the squareness of magnetic hysteresis loops are degraded by annealing above 300 °C. In contrast, in films sputtered on ZnO or Pt underlayers, the coercivity is remarkably increased by annealing at 300 °C. The film with the ZnO underlayer shows a hysteresis loop with perfect squareness even after annealing at 400 °C. The results of x‐ray diffraction indicate that the ZnO underlayer not only enhances the fcc Pt/Co(111) orientation but also prevents the decay of the multilayered structure during annealing. The results of laser microannealing using a conventional disk drive system also indicate that the Pt/Co films with ZnO underlayers have superior resistance to laser damage.

Erasable digital audio disk system.

Following the popularization of the compact disc, much attention has been paid to development of an erasable optical disk. A magnetooptical disk has proved the most useful in our development of a digital audio disk system which cannot only play and record but also has erase and rewrite disks. This system using MO disks is capable of playing 45-min PCM sound on a CD format which makes high-fidelity sound with a low word error rate of 10−9 (after error correction). This system can also be used for the compact disk playback.

Magnetic AMplifying Magneto-Optical System (MAMMOS) for ultra high density MO recording

A readout method to amplify the MO signal by using a magnetic domain expansion phenomenon has been proposed and results shown. It was found that the small MO signal reproduced from the small recorded domain was amplified. This novel magnetic domain expansion read out technique shows high promise for future data storage technology.

Microstructures of Pt/Co Films Deposited on Sputter-Etched Underlayers

Pt/Co multilayered films deposited on a sputter-etched SiN underlayer show larger magnetic anisotropy (1×106 erg/cm3) and better squareness(=1) than those on nonetched underlayers. The results of small-angle X-ray diffraction indicate the improvement of the multilayer structural order due to the etching. According to the transmission electron microscopy observation and the electrical resistivity measurement, the etching of underlayers transforms the Pt/Co films from island structure to continuous structure in an early stage of film growth. The scanning tunneling microscopy observation suggests that the sputter etching flattens the surface of the underlayer.

High density magneto-optical disk technologies

Many types of high density recording technologies have been proposed in the field of magneto-optical recording to satisfy demands of storing a large amount of digital information. Magnetically induced super resolution (MSR) is one of the most hopeful technology. However, trials of using the MSR technology in a realistic magneto-optical system were not fully investigated. Previously, we reported the concept and fundamental results of experiments and calculations of a high density magneto-optical recording system using a combination of a center-aperture-detection type of MSR (CAD-MSR) disk and other technologies. In this study, we have improved each of the technology discussed in our previous report. Moreover, we have evaluated the feasibility of magneto-optical disk systems which have a 4 Gbit/in/sup 2/ density with taking account of the margins.