In this paper we propose a new method to reproduce signals from high-density recorded patterns irrespective of the resolution of the readout optical system. The basic mechanism of this method, that is, domain wall displacement due to the temperature gradient, was confirmed by direct observation through a polarizing microscope. A clear readout waveform and a CNR of 39.5dB were obtained for a mark length of O.l,um with this method.

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We have developed a new light intensity modulation recording method called domain tail erasing method. This new recording method enables high-density recording far beyond the optical resolution limit with a medium combining the layer structure of domain wall displacement detection (DWDD) with that of light intensity modulation direct overwrite (LIMDOW). A recording performance nearly identical to that using magnetic field modulation (MFM) was confirmed with this method, using conventional optics with a wavelength of 660 nm and NA of 0.60.

High-density recording four times that of a current DVD-RAM has been achieved by applying Domain Wall Displacement Detection (DWDD) technology using a conventional optical head which has the same wavelength of 660 nm and NA of 0.6 as the DVD head. It has been confirmed by using a sampled servo and PRML that a recording density of 15 Gbit/inch2 with a track pitch of 540 nm and bit length of 80 nm has sufficient system margin. This means that a capacity of 3 GB on a two-inch-diameter disk is now available for portable use. If applied to a digital video camera, one hour of MPEG2 video contents can be recorded at a transfer rate of 6 Mbps.

Use of magneto-optical (MO) medium sputtered from an intermetallic compound alloy target has advantages for mass production but may not be suitable for high-density recording due to its poor perpendicular magnetic anisotropy. The relationship between MsHc, the product of saturation magnetization Ms and coercivity Hc, and film microstructure is discussed in this paper; we obtained an MsHc of 1 .3 x 106 erg/cm3 using microcolumnar structure even when the medium was sputtered from an alloy target. By adopting this film for the memory layer in a DWDD system, tiny marks less than 100 nm in size can be reliably written. As a result, high-density recording at 15 Gbit/inch2 is achieved.