M. Yoshihiro

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.

Magnetic expansion readout of 0.2 μm packed domains on a magneto-optical disk with an in-plane magnetized readout layer

We have investigated an in-plane magnetized readout-layer-based magnetic domain expansion phenomenon in a magneto-optical (MO) medium. Very high-density 0.2 μm packed domains are expanded up to three times the readout signal level in comparison with the conventional approach of applying alternative external field in the readout process. This result suggests that more than 10 Gbits/in.Reference 2 MO recording density may be achieved by implementing the domain expansion technique, using even the currently available 680 nm laser and numerical aperture of 0.55.

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. >

Magnetic parameter control for high‐density quadrivalued MO recording (invited) (abstract)

To increase recording density of MO media, several schemes have been proposed. Among them, magnetic multivalued (MMV) recording is one of the most promising methods. We have first realized the quadrivalued MMV media using a field modulation method. Such media is composed of an exchange coupled TbFeCo/PtCo bilayer. By switching the external field in four levels, the separated signal corresponding to the each field is obtained as a four leveled output. For the acutal device application for high‐density and high‐speed recording, it is necessary to reduce the external field as small as possible. In the previous experiment, about ±900 Oe was necessary to record the whole levels. For such MMV media, the quadrivalued signal response depends on the magnetic characteristics of the TbFeCo/PtCo bilayer, which is so called dual write state. The higher field level on the MMV media is defined by the threshold field of the dual write state. It is found that the threshold field is controllable to tune the magnetic parame...