Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-04-05
2001-02-06
Pianalto, Bernard (Department: 1762)
Stock material or miscellaneous articles
Composite
Of inorganic material
C360S081000, C427S131000, C427S132000, C428S336000, C428S668000, C428S670000, C428S690000, C428S900000, C428S928000
Reexamination Certificate
active
06183893
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a perpendicular magnetic recording medium having a perpendicular magnetic film suitable for high-density magnetic recording, and a magnetic storage apparatus using the same.
2. Description of the Prior Art
In magnetic disk apparatuses that have been made practicable at present, longitudinal magnetic recording is commercialized. In the longitudinal magnetic recording, a technical objective is to form, in a longitudinal magnetic recording medium which is liable to be magnetized in the direction parallel to its disk substrate surface, longitudinal magnetic domains that are parallel to the substrate at high densities. As a method to increase the recording density of this longitudinal magnetic recording medium, there is proposed a method of using keepered media in which a very thin, soot magnetic film is formed on the surface of a recording medium having an axis of easy magnetization in the longitudinal direction.
This technique is described on page 116 (Article No. DQ-13) and page 133 (Article No. EB-12) of collected abstracts published in 41st Annual Conference of Magnetism &Magnetic Materials (Nov. 12-15, 1996), and the like.
It is stated that according to adoption of such a medium structure it is possible to use an inductive type of thin film head for recording and reading so as to improve the areal recording density of magnetic recording greater than 1 Gb/in.
2
In the case of the longitudinal recording system, however, the magnetization directions of adjacent recorded bits are essentially opposite to each other. Thus, even if such a technique is used, magnetization transition areas whose boundary has a certain width are formed, so that it is technically not easy to realize an areal recording density of 10 Gb/in.
2
or more.
On the other hand, the perpendicular magnetic recording is a method to form magnetization perpendicular to the thin film media surface, and is different from conventional longitudinal recording media in recording principles and the mechanisms of medium noises. Since adjacent magnetization directions are not opposite to each other, the perpendicular magnetic recording has attracted attention as a method suitable for high-density magnetic recording. Various structures of perpendicular media are proposed to improve the performance of magnetic recording.
In order to improve perpendicular orientation of a perpendicular magnetic film composed of, for example, Co alloy materials, investigations have been made on methods of forming an underlayer between the perpendicular magnetic film and a substrate. For example, Japanese Unexamined Patent Publication Nos. 58-77025 and 58-141435 disclose methods of forming a Ti film as an underlayer of a Co—Cr magnetic film. Japanese Unexamined Patent Publication No. 60-214417 discloses a method of using a Ge or Si material as an underlayer, and Japanese Unexamined Patent Publication No. 60-064413 discloses underlayer materials of oxides such as CoO and NiO.
Moreover, as a perpendicular magnetic recording medium which is combined with a single pole type recording head for use, investigations have been made on a medium having a soft magnetic thin film such as permalloy between its substrate and its perpendicular magnetic film.
SUMMARY OF THE INVENTION
For a perpendicular magnetic recording medium capable of high-density recording at a level of 10 Gb/in.
2
or more, it is necessary that its linear recording density resolution is large and further medium noises are small.
Reports up to the present state that it is effective to make the thickness of a perpendicular magnetic film small, to introduce a nonmagnetic CoCr underlayer between a perpendicular magnetic film and a substrate, to add a nonmagnetic element such as Ta as an additive element to a Co alloy magnetic film, or to make the grain size of magnetic crystals smaller, as described in the article titled “High S/N single-layered perpendicular magnetic recording disks” on pp. 95-100 of collected conference materials of 5th Perpendicular Magnetic Recording Symposium (Oct. 23-25, 1996).
Such countermeasures make it possible to reduce medium noises considerably. If the noises cain be further reduced, it is possible to increase the recording density of magnetic recording apparatuses with ease.
In consideration of such situations of perpendicular magnetic recording, a first object of the present invention is to provide a perpendicular magnetic recording medium having a low noise property for implementing a high recording density of 10 Gb/in.
2
or more, and a high-density magnetic storage apparatus using the medium.
As described in Japanese Unexamined Patent Publication No.
57-109127
, the Journal of the Japan Applied Magnetism Society Vol. 8, No. 2, pp. 57-60 (1984), or IEEE Trans., MAG-24, No. 6, pp. 2706-2708 (1988), a Co—Cr based alloy films are used as a perpendicular magnetic recording medium, and it appears preferable to segregate nonmagnetic Cr atoms in the grain boundary of fine grains constituting the medium. This is because areas having a high Cr concentration are formed in the surface of the grains to improve corrosion resistance, and further nonmagnetic Cr atoms are segregated in the grain boundary in the same manner as in the longitudinal recording media so that magnetic exchange interaction between the grains is broken off, whereby magnetic domains are made finer to reduce medium noises.
In the combination of a ring type head and a single layer perpendicular magnetic medium, however, even if the medium is manufactured under conditions for promoting segregation of Cr atoms, the resultant medium is not necessarily strong against thermal fluctuation. This does not bring out advantages of perpendicular magnetic recording.
Therefore, a second object of the present invention is to provide a magnetic recording medium having stability against thermal fluctuation, and a high-density magnetic recording apparatus using the same. (1) First, the following inventions will be described: a perpendicular magnetic recording medium having a low noise property for realizing a high recording density, which can attain the first object of the present invention, and a high-density magnetic recording apparatus using the same.
Examination of recorded magnetization of perpendicular magnetic recording media with a magnetic force microscope and a spin polarized scanning electron microscope has proved that most of noises are caused by reversed domains, which are present in the surface of the media and will be described in detail later, and microscopic fluctuation of magnetization.
The microscopic fluctuation of magnetization means that the intensity of the local magnetization fluctuates at intervals of about 0.2-10 &mgr;m from area to area on the medium surface. In order to reduce medium noises, it is essential not only to reduce the reversed domains but also to reduce the microscopic fluctuation of magnetization present in the surface of the media.
From the results of experiments by the inventors et al., it has been made clear that the object can be attained by the following method.
That is, when a perpendicular magnetic film is magnetized perpendicularly to the film plane and in a single direction, an intense demagnetizing field acts on the medium surface. Under the influence of this demagnetizing field, there are formed so-called reversed domains, which are along the direction reverse to the perpendicular magnetization direction. In order to prohibit the forming of these reversed domains, it is necessary to adopt a perpendicular magnetic film having a large magnetic anisotropic energy.
It is desired that the magnetic anisotropic energy is 2.5×10
6
erg/cc or more. The maximum value of the magnetic anisotropic energy of a perpendicular magnetic film using a Co-alloy material, which can easily be handled as a practical medium, is 5×10
6
erg/cc. There exist Co-alloy materials with ordered lattice structure which have a larger magnetic anisotropic energy than the value. However, a process temperatu
Futamoto Masaaki
Hirayama Yoshiyuki
Honda Yukio
Inaba Nobuyuki
Ito Kenya
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Pianalto Bernard
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