Junsaku Nakajima

Improvement of readout resolution with an in-plane magnetization film for a magneto-optical disk

For high density recording of magneto-optical disks, we have developed a new method that improves the apparent optical resolution using a medium that consists of a GdFeCo readout layer and a DyFeCo recording layer. The magnetization of the readout layer is designed to be in-plane at room temperature and to become perpendicularly oriented at high temperatures. Therefore, this medium shows polar Kerr effect only at areas heated up by a readout beam whereas the other areas of the medium are masked by an in-plane magnetization. Using this medium, a small bit at the center of the readout beam spot can be detected without cross talk from the neighborhood. The function of the above high resolution readout method was calculated and confirmed through the study of magneto-optical properties. >

New magnetically induced super resolution disk by using exchange-coupled magnetic layers

Readout process of a new type of magnetically induced super resolution (MSR) disk was analyzed by calculating a domain shape in exchange-coupled ferrimagnetic layers. Analysis revealed that a suitable wall energy density at an interface between the layers existed for improving readout characteristics. This result obtained from calculation was confirmed by experiments. An areal recording density of 2.4 Gb/in/sup 2/ was achieved by using an 830 nm wavelength laser.

Improvement of magneto‐optical properties of Co/Pt multilayers prepared by sputtering in Ar

We investigated methods for increasing the coercive force and the Kerr rotation angle and for reducing the Curie temperature of Co/Pt multilayers to make them suitable as magneto‐optical recording media. The multilayers were prepared by magnetron sputtering using Ar gas. It was found that the coercive force increased with the magnetic flux density above the magnetron target and such an increase did not degrade the crystalline quality nor make less rectangular the Kerr hysteresis loops. The Kerr rotation angle increased when the number of layers per unit thickness was increased without changing the total Co content. The Curie temperature increased with Co content but was not affected by the number of layers. Therefore, Co content and number of layers per unit thickness were optimized in order to obtain a large Kerr rotation angle and a low Curie temperature. Moreover, read/write characteristics of a magneto‐optical disk using the Co/Pt multilayer were examined: a carrier‐to‐noise ratio of 45 dB was obtaine...

Readout of Optical Disk Recorded by Pit Edge and Depth Modulation

We report a Read-only (ROM) disc which is recorded by pit edge and depth modulation (PEDM). The information recorded by pit edge modulation is read out through an RF signal channel, and that recorded by pit depth modulation is read out through a tangential push-pull signal channel by detecting signal polarity at the pit edge. Each signal is sliced with a single level and is combined with another signal so that a multi-value recording is realized without multiple level slicing. The information recorded and read out using tangential push-pull signal polarity can never be copied onto recordable discs. Thus, not only a larger recording density and a higher transfer rate but also secure information storage are achieved with no change of the current optical and mechanical systems.

CHARACTERISTICS OF A SUPER RESOLUTION MAGNETO-OPTICAL DISK USING AN IN-PLANE MAGNETIZATION FILM

A super resolution magneto - optical (MO) disk with the medium of a GdFeCo readout layer and a DyFeCo recordingla yer was in vestigated. The readout la yer wasdesig nedsoas to show in - plane magnetization at room temperature and perpendicular magnetization above lOOV for high readout resolution. Readout signal quality was measuredatseverallinearvelocities. The ve-lo city dependence was little in the range from 5 to l0m/s; the maximum car-rier to noise ratio (CNR) at each velocitiesisnearlyequal. The per-formance of high densityrecording was studied with a 680nm wavelength optical head. The CNR and thecrosstalk were 45dB and -40dB respectively at 0.55dm mark leng th and 0.8um track pitch.