Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Utility Patent
1998-11-10
2001-01-02
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
47, 47, 47, 47
Utility Patent
active
06168861
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic recording medium, such as a thin film magnetic recording disk. The present invention is particularly applicable to high areal density magnetic recording media exhibiting high remanent coercivity and low medium noise.
BACKGROUND ART
The increasing requirements for high areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanence (Mr), coercivity squareness (S*), medium noise or signal-to-noise ratio (SNR) and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particular a high areal density magnetic recording disk medium.
The linear recording density can be increased by increasing the coercivity of the magnetic recording medium. However, this objective can only be accomplished by decreasing the medium noise, as by maintaining very fine magnetically non-coupled grains. Medium noise is a dominant factor restricting increased recording density of magnetic hard disk drives and, hence, has become a barrier to ultra-high areal density recording. Medium noise in thin films is generally attributed primarily to inhomogeneous grain size and intergranular exchange coupling among magnetic grains. Accordingly, considerable effort has been devoted to minimizing medium noise by suitable micro-structure control.
A typical longitudinal magnetic recording medium is depicted in FIG.
1
and comprises a substrate
10
, typically an aluminum (Al) -alloy, such as an aluminum-magnesium (Al—Mg) -alloy, plated with a layer of amorphous nickel-phosphorous (NiP). Alternative substrates include glass, ceramic and glass-ceramic materials, and graphite. Substrate
10
typically contains sequentially deposited on each side thereof a chromium (Cr) or Cr-alloy underlayer
11
,
11
′, a cobalt (Co)-based alloy magnetic layer
12
,
12
′, a protective overcoat
13
,
13
′, typically containing carbon, and a lubricant topcoat
14
,
14
′. Cr underlayer
11
,
11
′ can be applied as a composite comprising a plurality of sub-underlayers
11
A,
11
A′. Cr underlayer
11
,
11
′, Co-base alloy magnetic layer
12
,
12
′ and protective carbon overcoat
13
,
13
′ are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers or stations. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface for polishing to provide a texture, which is substantially reproduced on the disk surface.
Conventional non-magnetic alternative substrate materials include glass, ceramic and glass-ceramic materials, on which seedlayers, such as NiP, have been deposited under the underlayers. In addition, adhesion enhancement layers, such as Cr or Cr alloys, have been deposited between the seedlayers and the substrates.
Kodama et al., Japanese Patent 5-114128, disclose a film structure comprising a substrate, Cr underlayer, and dual magnetic layers, one comprising Co, Cr, tantalum (Ta) and the other comprising Co, Cr and platinum (Pt). However, the coercivity of the medium disclosed by Kodama et al. with such a dual magnetic layer structure is less than that of a medium with a single magnetic layer of Co, Cr and Pt. Thus, the dual magnetic layer structure of Kodama et al. does not satisfy the current demand for higher recording density with higher coercivity and higher SNR.
Lal et al., U.S. Pat. No. 5,432,012, disclose a magnetic thin-film medium comprising a magnetic layer with a compositional gradient, wherein the lowermost stratum is composed of a first alloy having a relatively low noise and low Mr and an uppermost stratum composed of a second alloy having a relatively high noise and high Mr. The disclosed medium is said to exhibit a higher coercivity and less noise than a similar medium composed of either the first or second magnetic alloy layer. The typical values of 4&pgr; Mr of the first stratum of Lal et al., Co, Cr, Ta, and second stratum Co, Ni, Cr, are 6,493 and 11,435 Gauss, respectively, as reported in Table II of Lal et al.
In U.S. Pat. No. 5,763,071, a high areal density magnetic recording medium is disclosed with dual magnetic layers, wherein the first magnetic layer is magnetically anisotropic in the second magnetic layer is magnetical isotropic.
There exist a need for a thin film magnetic recording medium for high areal recording density exhibiting high Hr and high SNR.
DISCLOSURE OF THE INVENTION
An advantage of the present invention is a magnetic recording medium for high areal recording density exhibiting low noise and high remanent coercivity.
Additional advantages and other features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following only to be learned from the practice of the invention. The advantages of the invention may be realized and obtained as particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved, in part or in part by a magnetic recording medium comprising: a non-magnetic substrate; a first magnetic layer; and a second magnetic layer on the first magnetic layer, wherein the first magnetic layer has a higher saturation magnetization (Ms) than that of the second magnetic layer.
Another aspect of the present invention is a magnetic recording medium comprising: a non-magnetic substrate; a first magnetic layer; and a second magnetic layer on the first magnetic layer, wherein the first magnetic layer has a higher Ms than that of the second magnetic layer and each magnetic layer comprises an alloy of cobalt containing platinum, wherein the content, in atomic percentage, of platinum in the second magnetic layer is greater than the content of platinum in the first magnetic layer.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.
REFERENCES:
patent: 5432012 (1995-07-01), Lal et al.
patent: 5432017 (1995-07-01), Lal
patent: 5558945 (1996-09-01), Miyazaki et al.
patent: 5674637 (1997-10-01), Miyazaki
patent: 5763071 (1998-06-01), Chen et al.
patent: 5840394 (1998-11-01), Renjei
patent: 5952097 (1999-09-01), Zhang
patent: 6007924 (1999-12-01), Lal
patent: 5-114128 (1993-05-01), None
Chen Ga-Lane
Chen Qixu
Leu Charles
Ranjan Rajiv Yadau
Song Xing
Kiliman Leszek
McDermott & Will & Emery
Seagate Technology LLC
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