Satoru Ohnuki

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.

Exchange coupling effect of in-plane magnetized layer capped on TbFeCo

Abstract The mechanism of the capping layer effect of the reduction of switching field by the insertion of a PtCo layer directly coupled to the TbFeCo layer of a MO disk has already been investigated. It is supposed herein that the magnetization of the capping layer easily rotates to the direction of magnetic field, and subsequently helps the transition metal site magnetic moment of TbFeCo align parallel to the field through exchange interaction, while suppressing the nucleation of the microdomains, whose magnetization is anti-parallel to the field, in the interior of the laser-written mark.

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.

New magnetic domain expansion MO phenomena using an in-plane magnetizing layer

For higher density MO recording, a magnetic domain expansion readout method named MAMMOS has been proposed. Herein we report a novel MAMMOS scheme using an in-plane to perpendicular magnetization changing effect. Expansion readout has been achieved by both a magnetic field modulation method and a light intensity modulation method. A clearly amplified readout signal was reproduced from repetition of 0.2 /spl mu/m packed marks.

Write/erase cyclability of TbFeCo for mark edge recording

Domain size changes due to thermal relaxation after high laser power irradiation on amorphous TbFeCo films were studied. In order to achieve mark edge recording for high‐density magneto‐optical memory, accurate domain size recording is required even after a million erase/write cycles. Highly accelerated erase/write test was performed on typical recording media, rare‐earth (RE) ‐rich and transition‐metal (TM) ‐rich disks. The elongation of the domain size written on the TM‐rich film after erase/write cycles was clearly evident; however, the change in the domain size of RE‐rich films was small. The small domain size change of the RE‐rich disk can be explained in terms of the rapid increase in the coercive force with decreasing temperature and the smaller domain‐wall driving force at recording temperature than those for the TM‐rich disk, even though both have the same level of structural relaxation.

Magnetically coupled MO double layer suitable for field modulation overwriting

Exchange coupled MO films like (PtCo/TbFeCo) and TbFeCo/TbFeCo) enable a very small external field of only 50 Oe for erase and write. Those are suitable media for a field modulation overwriting. In plane magnetized PtCo or low perpendicular anisotropy TbFeCo acts as the external field enhancing layer through exchange coupling with the TbFeCo recording layer.

Thermal and magnetic design of 8 MB/s MO disk

A highly power-sensitive and field-sensitive magnetooptic disk has been developed for an 8-MB/s, 3600-rpm, 30-GB, 10-in five-fold stacked disk system. The disk structure is of (Al-alloy/nitride/PtCo/TbFeCo/nitride) on glass-2p substrate. Power sensitivity has been improved by setting the thickness of metal layers thin enough (Al-alloy: 50 nm, TbFeCo: 20 nm) and Curie temperature at 190 degrees C so as to enable the use of a conventional 30-to-40 mW laser. The compensation temperature of TbFeCo is elevated to about 130 degrees C in order to restrict pit size distribution in a narrow range. The thinning of the metal layers also plays a role in precise pit-edge control by restricting written pit expansion to avoid tear-drop-like pit recording. Insertion of a capping layer of PtCo exchange-coupled to TbFeCo on top improves the field sensitivity drastically to obtain a switching field as low as 100 Oe, enabling the reduction of the bias field coil, which is desirable for high-speed devices. >

Media design of iD PHOTO disk with the CAD structure

We have developed a new MO(Magneto-Optical) disk, which is named iD(image/intelligent disk) PHOTO, as a promising candidate for a digital still camera memory. The iD PHOTO disk achieves 730MB/disk in a 50.8mm diameter by adopting some techniques mainly as follows, CAD (center aperture detection) type Magnetic Super Resolution reading, recording both on land and in groove, magnetic field modulation writing with irradiation of a pulsed laser beam, and PR(1,1) code. The iD PHOTO disk is required high performance in various environments, for it is used in a portable drive. As one of the most important factors, we have previously reported a reduction of electric power consumption by reducing the recording magnetic field. Here, we introduce thermal structure design of iD PHOTO disk to be suit for a drive in a digital still camera.