As magnetic discs such as floppy discs and hard discs, a blend obtained by kneading a magnetic powder such as .gamma.-Fe.sub.2 O.sub.3 or Fe and a synthetic resin binder is used to be coated on a non-magnetic substrate. In the magnetic layer of the magnetic disc of the type, however, since the proportion of the magnetic powder therein is small to be from 30 to 40% by volume, the saturated magnetic flux density is insufficient for a magnetic recording medium, which is therefore a bar to attainment of high density recording in the magnetic disc.
As opposed to the coated-type magnetic recording media of the said kind, magnetic recording media of a different kind, which have a thin magnetic metal film as formed on a non-magnetic substrate and which have a possibility of high density recording in the magnetic film, have been developed.
As means of forming the thin metal film-type magnetic recording medium of the said kind, (1) a chemical plating method as a wet-type method and (2) a sputtering method, an ion plating method or a vacuum evaporation plating method as a dry-type method have been employed. Regarding the chemical plating method (1), for example, a thin metal film medium such as Co-P or Co-Ni-P has been proposed. However, the method has various problems in the complication of the laminated structure of the films formed, the crush-resistance to head, the reliability such as error-characteristic and the stability in the formation of films. On the other hand, the dry-type method (2) has been proposed to overcome the said problems, and, for example, Co or Co-Ni has been investigated. However, when the film formed has hcp structure, the c-axis of the hcp structure, which is an easy magnetization axis, is apt to be oriented vertically to the film plane and the film is not suitable for an in-plane magnetic recording medium. In order to weaken the orientating property of the c-axis, addition of another element, for example, nitrogen (N) (JP-A-57-72307, the term "JP-A" as used herein means an "unexamined published Japanese patent application"), oxygen (O) (JP-A-60-163225), chromium (Cr) (Previous Papers for Applied Physics Associated Lecture, 1985, page 29, G-1 to 4, by Ishikawa, Tani, et al., Japan), tungusten (W) (R. D. Fisher, et al,; IEEE Trans. Magn., MAG-17, 3190 (1981)) or platinum (Pt) (J. A. Aboaf, et al.; IEEE Trans. Magn, MAG-19, 1514 (1983)), or formation of a laminated structure of CoNi/Cr or CoNiCr/Cr (Previous Papers for Applied Physics Associated Lecture, 1985, page 29, G-1 to 4, by Ishikawa, Tani, et al., Japan) has been proposed.
These magnetic recording media are extremely excellent in the magnetic characteristics such as saturated magnetic flux density, coercive force and squareness ratio.
However, in order to maintain the excellent coercive force of these media, the thickness of the Cr-layer of the said first layer is required to be increased. Therefore, a longer time is required for film formation and the producability is low. In addition, the surface property is worsened to cause deterioration of error characteristic and the like, and the reliability is often lowered. Moreover, these media have other problems that these are poor in the corrosion-resistance and the error characteristic thereof is often worsened.
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USPTO Backgrounds