1. FIELD OF THE INVENTION
The present invention relates to a perpendicular magnetic recording medium.
2. DESCRIPTION OF THE PRIOR ART
Recently, a perpendicular magnetic recording medium has been developed which forms residual magnetism in a direction perpendicular to the surface of the recording medium. The perpendicular magnetic recording medium ensures high recording density. The conventional perpendicular magnetic recording medium generally includes a film base or an aluminum base, and a Co-Cr film formed on the base by a sputtering method or an electron beam evaporation (E.B. evaporation) method. However, the conventional perpendicular magnetic recording medium does not have a smooth slide against a magnetic head. Thus, the perpendicular magnetic recording medium and/or the magnetic head is damaged during operation, and the conventional perpendicular magnetic recording medium does not have a desirable durability.
In order to protect the Co-Cr metal thin-film from being damaged, (in the conventional perpendicular magnetic recording medium), a protective layer such as a Ni film, Ni-P film, SiO film, SiO.sub.2 film or a noble metal (Au, Rh, Pt, Ag, etc.) film is formed on the Co-Cr metal thin-film through the use of, for example, a plating method, a sputtering method, or an evaporation method. The protective layer can alternatively be an oxide layer or a nitride layer formed on the Co-Cr metal thin-film, or an organic silicon compound film painted on the Co-Cr metal thin-film. However, a suitable thickness of it is difficult to determine in the conventional perpendicular magnetic recording medium. If the protective layer is thick, the protective layer creates a spacing loss which reduces the recording density, and deteriorates the reproduction output. If the protective layer is thin, the recording density can be enhanced, but the perpendicular magnetic recording medium and/or the magnetic head is damaged during operation, and the perpendicular magnetic recording medium does not have a satisfactory durability.