Sony Corporation

Masaki Takenouchi

Mikio Yoshida

Nobuhiro Saito

An optical disc having a functional film, formed by a thin metal plate, and a protective film, formed on a transparent substrate, is disclosed. The protective film satisfies a condition d.gtoreq.2d.sub.0, where d is a maximum film thickness at an outer periphery of the protective film and d.sub.0 is a mean film thickness at a flat portion on a data area. A magneto-optical disc having a functional film which is a metal thin film having magneto-optical effects is also disclosed, wherein the protective film satisfies a condition that a difference L.sub.1 between a maximum film thickness d at the outer periphery of the protective film and a mean film thickness d.sub.0 at a flat portion of the data area is 40 .mu.m or less and the protective film has a curved surface having a radius of curvature R.sub.1 .gtoreq.12.48 mm at the outer periphery of the protective film. The present invention provides an optical disc having superior recording properties and a sufficient corrosion resistance even when the disc is provided with a highly corrosive thin metal film, such as a rare earth-transition metal amorphous thin film.

Optical disc having a protective layer which is thicker at its outer

Anticorrosion magneto-optical recording medium is disclosed. The magneto-optical recording medium comprises a recording layer formed of an amorphous alloy of transition metal and rare-earth metal such as Tb--Fe or Tb--FeCo. On the recording layer, there are provided a transition metal layer such as FeCoCr alloy layer and a rare-earth metal layer such as Tb, in this order. Selective oxidation of rare-earth metal in the recording layer is effectively avoided by the existance of the layers.

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Miyagi, Japan

Masaki Takenouchi