Overwrite characteristics of magneto-optical disks by exchange-coupled RE-TM quadrilayered films

The direct overwrite characteristics by light power modulation on a magnetooptical disk with exchange coupled rare-earth-transition-metal (RE-TM) quadrilayers film are described. In this system, it is important to investigate the relationship between the laser power and the bias field margins. These margins are defined by the Curie temperature and the temperature dependence of the reversal field of each layer. Good recording characteristics were obtained, such as a carrier-to-noise ratio >49 dB on a bit length of 0.76 μm. A fairly wide power margin of ±20% was obtained, and a wide tolerance on the bias magnet construction was allowed. For achieving a read cycle of more than 10⁸, it was necessary to keep the read power smaller than 1.5 mW at 2400 rpm