In-plane magnetic disc

Abstract: Disclosed are magnetic discs having (A) a Cr-layer, as a lower layer, which has a composition comprising (1) substantially Cr or (2) 10 % by weight or less of one or more selected from Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta, and a balance of being substantially Cr, and (B) a magnetic recording medium layer, as an upper layer, which as a composition comprising (1) substantially Co, (2) 30 % by weight or less of Ni and a balance of being substantially Co, (3) 10 % by weight or less of one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy, and a balance of being substantially Co, (4) 30 % by weight or less of Ni, 10 % by weight or less of one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy, and a balance of being substantially Co, (5) 10% by weight or less of one or more selected from Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W and Ta, and a balance of being substantially Co, (6) 30 % by weight or less of Ni, 10 % by weight or less of one or more selected from Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W and Ta, and a balance of being substantially Co, (7) 10 % by weight or less of one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy, 10 % by weight or less of one or more selected from Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W and Ta, and a balance of being substantially Co, or (8) 30 % by weight or less of Ni, 10 % by weight or less of one or more selected from Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy, 10 % by weight or less of one or more selected from Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W and Ta, and a balance of being substantially Co, both as formed on a non-magnetic substrante, except those where the lower layer has the composition (1) and the upper layer has the composition (1) or (2) as well as those where the lower layer has the composition (1) and the upper layer has the composition (5) or (6) containing only one or more of Cr, Ta and/or W. The magnetic discs have noticeably improved magnetic characteristics and/or corrosion-­ resistance.

Description: The present invention relates to in-plane magnetic discs and, more preferably, to those having noticeably improved magnetic characteristics, especially coercive force. As magnetic discs such as floppy discs and hard discs, a blend obtained by kneading a magnetic powder such as gamma-Fe₂0₃ 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 orienting 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 (0) (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), tungsten (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 in-plane 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 producibility is low. In addition, the surface property is worsened to cause deterioration of error characteristic and the like, and the reliability is often lowered. SUMMARY OF THE INVENTION The object or the present invention in to overcome the said problems in the prior art and to provide in-plane magnetic discs having noticeably improved in-plane magnetic characteristics, as opposed to those formed by the above-mentioned conventional dry-type method. In order to attain the said object, the present invention provides an in-plane magnetic disc comprising (a) a lower layer and (b) a magnetic recording medium film as in upper layer, the upper and lower layers being formed on a non-magnetic substrate, characterised in that the upper layer comprises Co and inevitable impurities and in that the lower layer comprises 10% by weight or less of at least one of Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta, the balance being of Cr and inevitable impurities, provided that the lower layer is not constituted of pure chromium. Preferably, the upper layer comprises 30% by weight or less of Ni. Preferably, the upper layer comprises 10% by weight or less of one or more of Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy and/or 10% by weight or less of one or more of Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W and Ta. DETAILED DESCRIPTION OF THE INVENTION Now, the present invention will be explained in detail hereinafter. As the non-magnetic substrate, Al, Al with Ni-P subbing layer, Al₂0₃, heat-resistant plastics and glass may be used. The Cr-layer to be formed on the non-magnetic substrate as a lower layer has a composition comprising (1) 10 % by weight or less of at least one (M₁) selected from Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta, and a balance being of Cr and inevitable impurities. Because of the addition of M₁, magnetic discs having noticeably improved magnetic characteristics, especially coercive force, can be obtained. If the content of M₁ is more than 10 % by weight, the coercive force of the resulting magnetic discs would lower. The effect could be presumed to be caused by the variation of the lattice constant of the Cr-layer because of the addition of M₁. The magnetic recording medium film to be formed over the said Cr-layer as an upper layer may comprise from 0 to 30 % by weight of Ni, and 10 % by weight or less of one or more (R) selected from Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy and/or 10 % by weight or less of one or more (M₂) selected from Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W, and Ta, and the balance being of Co and inevitable impurities. If the content of Ni is more than 30% by weight, the residual magnetization of the film would noticeably lower so that the electromagnetic transformation characteristic thereof would worsen. The element R is added so as to improve the coercive force of the film. If the content of R is more than 10% by weight, the coercive force and the saturation magnetization of the film would decrease. In addition, the element M₂ is added so as to improve the coercive force of the magnetic recording medium film. This effect could be presumed to be caused by the segregation of M₂ in the grain boundary thereby to isolate the individual crystal grains from one another. If the content of M₂ is more than 10% by weight, the residual magnetization of the magnetic recording medium film would remarkably lower and the electromagnetic transformation characteristic thereof would thereby worsen. Because of the addition of both of these R and M₂, their effects could by synergified, whereby magnetic discs which are extremely excellent in magnetic characteristics can be obtained. The thickness of the said film is desired to be from 0.01 to 0.15 µm. If the thickness is less than 0.01 µm, any sufficient power of reproduction could not be obtained, and if it is more than 0.15 µm, the decrease of the coercive force would be remarkable. In the in-plane magnetic discs of the present invention, a protective film, such as SiO₂ or carbon film, is desired to be formed on the said magnetic recording medium film, so as to improve the abrasion-resistance to head. In accordance with the present invention, the films of the lower layer and the upper layer may be formed by sputtering method, vacuum evaporation plating method or ion plating method. The following examples are intended to illustrate the present invention in more detail but not to limit it in any way. Examples of conventional samples have also been mentioned below, for comparison. EXAMPLES AND COMPARATIVE EXAMPLES A Cr-layer having the composition and thickness as indicated in Tables 1 through 9 below, as a lower layer, and a 500 Å thick magnetic recording medium film having the composition as indicated in the same Tables, as an upper layer, were formed on a 1.5 mm thick aluminium (A1) substrate having a Ni-P subbing layer as coated, by the use of a magnetron sputtering device, whereupon the film formation condition was in every case as mentioned below. Final Vacuum Degree 2 x 10⁻⁵ to 8 x 10⁻⁵ Pa Sputtering Gas (Ar) Pressure 0.4 to 1.2 Pa Sputtering Electric Power 200 to 600 W Target Diameter 15 cm Target-Substrate Distance 100 to 150 mm Each of the thus prepared disc samples was cut and subjected to composition analysis and evaluation of magnetic characteristics. For the composition analysis, both EPMA analysis and chemical analysis were performed, and the magnetic characteristics were measured by the use of a vibrating sample type magnetometer. The results obtained were shown in Tables 1 through 9 below, wherein Tables 1 to 8 indicate the examples of the present invention and Table 9 indicates an example of the conventional sample. As apparent from the previous description, the present invention provides in-plane magnetic discs having noticeably improved magnetic characteristics as opposed to conventional Co-Ni or Co type magnetic discs.

Claims: An in-plane magnetic disc comprising (a) a lower layer and (b) a magnetic recording medium film as an upper layer, the upper and lower layers being formed on a non-magnetic substrate, characterised in that the upper layer comprises Co and inevitable impurities and in that the lower layer comprises 10% by weight or less of at least one of Cu, Nb, Ti, V, Zr, Mo, Zn, W and Ta, the balance being of Cr and inevitable impurities, provided that the lower layer is not exclusively constituted of pure chromium. An in-plane magnetic disc according to claim 1 in which the upper layer comprises 30% by weight or less of Ni. An in-plane magnetic disc according to claim 1 or 2 in which the upper layer comprises 10% by weight or less of one or more of Y, La, Ce, Pr, Nd, Sm, Gd, Tb and Dy and/or 10% by weight or less of one or more of Cu, Nb, Ti, V, Cr, Zr, Mo, Zn, W and Ta.

Inventors: KAWAMOTO ATSUSHI C O CENTRAL R, KUZUO RYUISHI C O CENTRAL RESE, OHMORI KENJI C O CENTRAL RESEA, SEKIYA HIROKO C O CENTRAL RESE, TADA JUNYA C O CENTRAL RESEARC, KAWAMOTO, ATSUSHI C/O CENTRAL RESEARCH LABORATORY, KUZUO, RYUISHI C/O CENTRAL RESEARCH LABORATORY OF, OHMORI, KENJI C/O CENTRAL RESEARCH LABORATORY, SEKIYA, HIROKO C/O CENTRAL RESEARCH LABORATORY, TADA, JUNYA C/O CENTRAL RESEARCH LABORATORY
Applicants: SUMITOMO METAL MINING CO, SUMITOMO METAL MINING COMPANY LIMITED
Application year: 1988
Main classification: G11B5
IPC codes: G11B5