Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1999-05-11
2002-04-16
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S065100, C428S065100, C428S065100
Reexamination Certificate
active
06372367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic recording medium having a large information recording capacity and a magnetic recording apparatus using such a magnetic recording medium. Particularly, the invention relates to a magnetic recording medium adapted for high-density magnetic recording, a method for producing such a magnetic recording medium, and a small-sized large-capacity magnetic recording apparatus using such a magnetic recording medium.
2. Description of Related Art
The demand for increase in the capacity of a magnetic recording apparatus has become higher and higher. An electromagnetic inductive magnetic head utilizing the voltage change caused by a flux change with the passage of time has been used as a related-art magnetic head. This head has an advantage that both recording and reproducing can be performed by one head. On the other hand, recently, a combination type head in which a recording head and a reproducing head are provided separately so that use of a more highly sensitive magneto-resistance effect type head for reproduction has been progressed rapidly. In order to improve the sensitivity of a magneto-resistance effect type head utilizing the change of electric resistance of a head device caused by the change of magnetic flux leaked from a medium, a still more highly sensitive head utilizing a very large change of magnetic resistance (a giant magneto-resistance effect or a spin valve effect) generated in magnetic layers of the type having a plurality of magnetic layers laminated through a non-magnetic layer has been put into practical use. This head utilizes a phenomenon in which the direction of relative magnetization of magnetic layers having the non-magnetic layer therebetween is changed in accordance with the magnetic field leaked from the medium to change magnetic resistance.
On the other hand, factors necessary for increasing the density of the magnetic recording medium are (1) establishing both surface flatness required by low floating of the magnetic head and avoidance of a head sticking phenomenon at the time of stopping the magnetic head, with greater improvement of durability against frictional motion, (2) low noise characteristics and (3) achievement of stable magnetic characteristics with a large process margin.
First, as a countermeasure to the head sticking phenomenon, Japanese Patent No. 2064981 (JP-B-4-62413) discloses a magnetic recording medium having an underlayer, a magnetic layer and a protective layer formed successively on a non-magnetic support, wherein: a landing zone is provided in the magnetic recording medium; a roughness forming layer for forming roughness on a surface of the protective film layer in the landing zone toward the magnetic layer is provided between the non-magnetic support and the underlayer in the landing zone; and the roughness forming layer has larger surface roughness than that of a main surface of the non-magnetic support and has a grain boundary of a film material. That is, the Japanese Patent No. 2064981 discloses a configuration in which a rough layer due to the grain boundary generated at the time of formation of a thin film of aluminum, or the like, is provided under the magnetic film to thereby give roughness to the surface of the protective film.
Further, JP-B-2547651 discloses a magnetic recording medium having a magnetic layer interposed between a protective layer and a surface of a non-magnetic support coated with a roughness-forming substance for forming roughness on the surface of the support, wherein: the roughness-forming substance is a single metal or an alloy having a melting point not higher than 1,100° C.; a structure of a large number of islands discontinuous in the plane direction of the surface of the non-magnetic support is formed on the surface of the non-magnetic support by the roughness-forming substance; an underlayer for the magnetic layer is provided between the non-magnetic support and the magnetic layer; and an oxygen trap layer is provided between the non-magnetic support and the underlayer. That is, the above JP-B-2547651 discloses a configuration in which a roughness-forming layer having a discontinuous island structure of aluminum, or the like, is provided. The above JP-B-2547651 further describes that the oxygen trap layer prevents the rise of oxygen from the nonmagnetic support to thereby improve the crystallinity of the undercoat film and improve the magnetic characteristic on page 3, left column, lines 26-28. That is, the oxygen trap layer is provided between the non-magnetic support and the underlayer in order to improve the magnetic characteristic of the magnetic film.
As disclosed in PCT Patent Application PCT/JP96/02720 (WO 98/12698), the inventors of the present invention have found that it is easy and controllable, for forming a roughness-forming layer, to use a method of forming discontinuous island-like protrusions of an intermetallic compound by sputtering by use of a target of a peritectic alloy type composition having an intermetallic compound phase of aluminum and chrome, or the like.
Further, as described in JP-A-10-74314, it has been found that not only can the magnetic characteristic of the magnetic film be improved, but also medium noise, which is a problem particularly in a magneto-resistance effect type head, can be reduced if a non-magnetic alloy layer containing Co as a main component is provided under the underlayer. It has been further found that the non-magnetic alloy layer containing Co as a main component is excellent also in adhesion to a glass substrate which has been often used as a countermeasure to a shock on the magnetic disk device in recent years.
SUMMARY OF THE INVENTION
In order to improve the characteristic of the aforementioned magnetic recording medium, the inventors of the present invention have made experiments. As a result, it has been found that medium noise can be reduced more stably if a non-magnetic alloy layer containing Co as a main component is impregnated with Cr or Zr having a high tendency to be oxidized, and the surface of the non-magnetic alloy layer is exposed to an oxygen atmosphere to be slightly oxidized, as described in Japanese Patent Application 8-292451 (JP-A-10-143865). All the contents of this document are incorporated here by reference.
A magnetic disk was produced by the aforementioned technique as follows. A Co—Cr—Zr alloy layer was provided as a first underlayer. A rough layer of an intermetallic compound was provided, as a second underlayer on the first underlayer, by sputtering a target of an Al—Cr composition. A Co—Cr—Zr alloy layer was provided as a third underlayer on the second underlayer. After the surface of the third underlayer was slightly oxidized, a fourth undercoat film and a magnetic film were formed to produce a magnetic disk. As a result, it was however found that crashing (a phenomenon that the magnetic layer is worn out) occurred in a friction durability test under a severe condition that dust was introduced. The terminology “friction durability test under the condition that dust is introduced” (hereinafter referred to as “dust introduction test”) means a test for measuring the number of seeking times to cause crashing when a seeking operation of the magnetic head is repeated after about 0.1 g of alumina particles each having a size of about 2 &mgr;m is sprinkled onto the magnetic disk surface in the magnetic disk device.
To improve the aforementioned problem, a first object of the present invention is to provide a magnetic recording medium in which, while the low noise characteristic which is important for achieving high recording density is kept, high reliability of frictional durability can be secured even in the aforementioned severe friction durability test.
A second object of the present invention is to provide a method for producing such a magnetic recording medium.
To attain the foregoing objects, the inventors of the present invention have tested various materials for forming first, second and third underlayers. As a resu
Funamoto Susumu
Hosoe Yuzuru
Kato Akira
Matsuda Yoshibumi
Ogawa Yoko
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Rickman Holly C.
Thibodeau Paul
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