Magnetic disc comprising a substrate of an amorphous glass continuous

Abstract

A substrate for a magnetic disc, which comprises a crystallized glass consisting essentially of an amorphous glass continuous phase and crystal particles dispersed in the continuous phase, the substrate having fine projections of the crystal particles on the surface thereof, a method of producing the substrate, the magnetic disc using the substrate, and a method of producing the magnetic disc are provided. The crystallized glass is made from a glass material of a Li.sub.2 O-SiO.sub.2, Li.sub.2 O-Al.sub.2 O.sub.3 -SiO.sub.2, Li.sub.2 O-MgO-Al.sub.2 O.sub.3 -SiO.sub.2, MgO-Al.sub.2 O.sub.3 -SiO.sub.2, Na.sub.2 O-Al.sub.2 O.sub.3 -SiO.sub.2 or BaO-Al.sub.2 O.sub.3 -SiO.sub.2 system, and the crystal particles have one or more compositions selected from Li.sub.2 O.multidot.SiO.sub.2, Li.sub.2 O.multidot.2SiO.sub.2, Li.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.2SiO.sub.2, Li.sub.2 O.multidot.Al.sub.2 O.sub.3 .multidot.4SiO.sub.2, SiO.sub.2 and 2MgO.multidot.2Al.sub.2 O.sub.3 .multidot.5SiO.sub.2, and an average particle size of 0.01 to 3.0 .mu.m, and are projected at a density of 10.sup.2 to 10.sup.6 /mm.sup.2 and at an average height of 0.005 to 0.2 .mu.m on the surface of the substrate, the total surface area of the projections of crystal particles occupying at most 30% of the unit surface area of the substrate. The projections are made by chemical etching with an aqueous solution of hydrofluoric acid, physical etching with sputtering under vacuum or ion-milling, or mechanical etching with sand blasting. The magnetic disc comprises the crystallized glass substrate, a chromium or chromium alloy undercoat film, thin magnetic film, protective carbon film and lubricant film.