Magnetic recording medium and magnetic memory

Details Magnetic recording medium and magnetic memory Magnetic recording medium and magnetic memory

2000-04-14

2001-12-11

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

Circular sheet or circular blank

Recording medium or carrier

C428S216000, C428S408000, C428S690000, C428S900000

Reexamination Certificate

active

06329037

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a magnetic recording medium and a magnetic storage apparatus, and more particularly to a magnetic recording medium which exhibits a high sliding durability, is suitable for high density recording, and stably provides reproducing outputs, and a highly reliable magnetic storage apparatus which is equipped with this magnetic recording medium.
BACKGROUND ART
Magnetic disk apparatus are now indispensable as main storage devices for information related apparatus such as computers and so on, and a higher capacity and faster recording/reproducing are increasingly required therefor as the need for faster processing of a huge amount of data arises for images and audio. For this purpose, faster read/write operations as well as a higher recording density are required. It is essential, as to the recording density, to reduce as much as possible the substantial distance from an element of a recording/reproducing head to a recording film of a magnetic disk serving as a recording medium, and to reduce a track width, and as to the faster operations, to increase the speed of data processing, rotational speed, and seek speed. With these improvements, a magnetic head, which has conventionally operated with a sufficient spacing from a magnetic disk, is forced to operate in a so-called intermittent contact state in which the magnetic head operates nearly in contact with the magnetic disk at a high speed. In addition, for reducing the substantial distance between a magnetic head element and a recording film of a magnetic disk as mentioned above, it is necessary to make a protective layer and a lubricant layer, intervening therebetween, as thin as possible. Specifically, the protective layer should be 10 nm or less; the lubricant layer should be 2 nm or less; and an average spacing between the disk surface and the head should be 30 nm or less, where a contact could occur as the case may be. To realize a magnetic disk which is fit for practical use in such extremely tight conditions, it goes without saying that a key point lies in how to design materials and shapes for the protective layer, the lubricant layer, and a contact portion of the head.
The protective layer and the lubricant layer of the magnetic disk have been conventionally improved from a viewpoint of an increase in abrasion resistance, sliding resistance, corrosion resistance, and soon. The protective layer has been practically made of an amorphous carbon film formed by sputtering graphite in an Ar atmosphere, amorphous hydrogenated carbon film formed likewise by sputtering graphite in an Ar+H2 or Ar+CH4 atmosphere, and so on. In addition to those, a variety of protective films have been under consideration such as those made of diamond-like carbon formed by plasma CVD with a hydrocarbon gas, a carbon film containing a variety of additive elements such as Si, Ti, W, Fe and so on, BN, SiO2, and so forth. Further, JP-A-62-287415 discloses an example which employs a laminate of two types of carbon layers having different hardness, and a soft underlying layer as a buffer layer, particularly with the object of improving a mechanical strength. JP-A-9-91687 also discloses an example which has a protective film having a hardness varying in a film thickness direction. However, either of them is not fit for practical use due to insufficient strength or corrosion resistance when an extremely thin film of 10 nm or less in thickness is concerned.
In respect to the lubricant layer, on the other hand, perfluoropolyether based lubricating oils having absorptive functional groups at terminals are typically used, and a number of lubricants having terminal groups exhibiting an improved integrity with a protective layer have been disclosed.
In conventional use environments, however, considerations on the protective layer and the lubricant layer only have to be made for sliding with a head upon starting and stopping a disk apparatus, i.e., a so-called contact start stop. In actual read and write operations, no problem associated with sliding arises, since the head is spaced from the disk, except for introduction of foreign substances therebetween.
In contrast, a high recording density magnetic disk apparatus for high speed processing, addressed by the present invention, is highly damageable to a contact of a head with a disk rotating at a high speed, or interactions of the two through an air flow or the like, if not contacting, causing damages on a protective layer and resulting damages on the disk itself, so that a need exists for a protective layer which possesses in combination different performance from conventional ones. Thus, any of the above cited techniques is not fit for practical use in an disk apparatus which requires low flotation and extremely thin films, as intended by the present inventors.
It is an object of the present invention to provide a magnetic recording medium which exhibits less damages and a high durability in high speed low flotation sliding, and a highly reliable magnetic storage apparatus by realizing a magnetic recording medium having an extremely thin protective layer having a substantial thickness of 10 nm or less, which can even be used in such severe conditions.
DISCLOSURE OF THE INVENTION
To solve the problems mentioned above, the present invention provides a protective layer made of particular materials. In the following, detailed description thereon will be made.
An exemplary cross-sectional structure of a magnetic recording medium according to the present invention is illustrated in
FIG. 1. A
substrate
1
is a discoidal disk having a hole formed through a central portion thereof, which is typically made of an aluminum-magnesium alloy plated with NiP, or a glass substrate processed to enhance the mechanical strength. In the present invention, though not particularly specified for its materials, the surface of the substrate should be as smooth as possible with a center-line average roughness being equal to or less than several nm, and preferably 1 nm or less. An underlying layer
2
is used to improve the crystallinity of a magnetic layer
3
, and may be made of, for example, Cr or an alloy thereof. Of course, the underlying layer
2
may be in a multilayer structure. The magnetic layer
3
is used to record signals, and is made of, for example, Co-based alloy materials or the like. While ternary alloys such as CoCrTa, CoCrPt, CoCrV, CoNiCr, CoNiV and so on are typically used, a fourth element and/or an oxide may be added to them.
A protective layer
4
is a layer having a particular mechanical strength characteristic which characterizes the present invention. The particular mechanical strength characteristic is specifically expressed by the ratio of a Young's modulus of the protective layer
4
measured in a direction in which a head is pressed against the protective layer
4
to that measured in a direction in which the head runs, at an indentation depth equal to or less than one half of the thickness of the protective layer
4
. Assuming that the Young's modulus in the pressing direction is Ed, and the Young's modulus in the running direction is Ec, the particular mechanical strength characteristic refers to the one having Ec/Ed equal to or less than 0.5. For this measurement, a conical indentator with a distal end having a curvature R of 0.1 microns or less, or a pyramidal indentator, by way of example, is indented to the above-mentioned depth with a microload, and is applied with microvibrations at that position in the head pressing direction or in the head running direction. Then, the Young's modulus may be found from the relationship between the amount of deformation within a range, in which no plastic deformation arises, and a bearing stress.
For largely varying the mechanical characteristic of the protective layer in a direction perpendicular to a substrate surface and in a direction parallel to the same, the protective layer may be formed in a laminate structure having laminated layers of different properties. Particularly, for formi

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