Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-11-10
2001-06-05
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S469000, C428S690000, C428S900000, C204S192200, C427S131000
Reexamination Certificate
active
06242086
ABSTRACT:
TECHNICAL FIELD
The present invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The invention has particular applicability to high areal density magnetic recording media exhibiting low noise, high remanent coercivity and high coercivity squareness.
BACKGROUND ART
The requirements for increasingly high areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr or Hcr), magnetic remanance (Mr), coercivity squareness (S*), medium noise, i.e., signal-to-noise ratio (SNR), and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements.
The linear recording density can be increased by increasing the Hr 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 high density magnetic hard disk drives. Medium noise in thin films is attributed primarily to inhomogeneous grain size and intergranular exchange coupling. Accordingly, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
A conventional longitudinal recording disk medium is depicted in FIG.
1
and comprises a substrate
10
, typically an (Al)-alloy, such as an Al-magnesium (AlMg) alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, ceramic and glass-ceramic materials, as well as graphite. There are typically sequentially sputter deposited on each side of substrate
10
, an underlayer
11
,
11
′, such as Cr or a Cr alloy, a magnetic layer
12
,
12
′, such as a cobalt (Co)-based alloy, and a protective overcoat
13
,
13
′, such as a carbon-containing overcoat. Typically, although not shown for illustrative convenience, a lubricant topcoat is applied on the protective overcoat
13
,
13
′.
It is recognized that the magnetic properties, such as Hr, Mr, S* and SNR, which are critical to the performance of a magnetic alloy film, depend primarily upon the microstructure of the magnetic layer which, in turn, is influenced by the underlying layers, such as the underlayer. It is also recognized that underlayers having a fine grain structure are highly desirable, particular for growing fine grains of hexagonal close packed (HCP) Co alloys deposited thereon.
It has been reported that nickel-aluminum (NiAl) films exhibit a grain size which is smaller than similarly deposited Cr films, which are the underlayer of choice in conventional magnetic recording media. Li-Lien Lee et al., “NiAl Underlayers For CoCrTa Magnetic Thin Films”, IEEE Transactions on Magnetics, Vol. 30, No. 6, pp. 3951-3953, 1994. Accordingly, NiAl thin films are potential candidates as underlayers for magnetic recording media for high density longitudinal magnetic recording. However, it was found that the coercivity of a magnetic recording medium comprising an NiAl underlayer is too low for high density recording, e.g. about 2,000 Oersteds (Oe).
Lee et al. subsequently reported that the coercivity of a magnetic recording medium comprising a NiAl underlayer can be significantly enhanced by depositing a plurality of underlayers containing alternative NiAl and Cr layers rather than a single NiAl underlayer. Li-Lien Lee et al., “Effects of Cr Intermediate Layers on CoCrPt Thin Film Media on NiAl Underlayers,” Vol. 31, No. 6, November 1995, pp. 2728-2730.
Li-Lien Lee et al. were able to obtain an underlayer exhibiting a (200)-dominant crystallographic orientation by initially depositing a Cr sub-underlayer directly on the non-magnetic substrate at a high temperature of about 260° C. using radio frequency (RF) sputtering. However, it is very difficult to obtain a Cr (200)-dominant crystallographic orientation, even at elevated temperature such as 260° C., on glass, ceramic and glass ceramic substrates using direct current (DC) magnetron sputtering, which is widely employed in the magnetic recording media industry.
Li-Lien Lee et al. subsequently reported that an underlayer structure exhibiting a (200)-dominant crystallographic orientation was obtained by depositing a magnesium oxide (MgO) seedlayer using radio frequency (RF) sputtering. Li-Lien Lee et al., “Seed layer induced (002) crystallographic texture in NiAl underlayers,” J. Appl. Phys. 79 (8), Apr. 15, 1996, pp. 4902-4904; and David E. Laughlin et al., “The Control and Characterization of the Crystallographic Texture of the Longitudinal Thin Film Recording Media,” IEEE Transactions on Magnetics, Vol. 32, No. 5, September 1996, pp. 3632≧3637. Such a magnetic recording medium, however is not commercially viable from an economic standpoint, because sputtering systems in place throughout the industry making magnetic recording media are based upon direct current (DC) sputtering. Accordingly, RF sputtering an MgO seedlayer is not economically viable. The use of an NiAl underlayer is also disclosed by C. A. Ross et al., “The Role Of An NiAl Underlayers In Longitudinal Thin Film Media” and J. Appl. Phys. 81(a), P.4369, 1996.
Conventional practices in manufacturing magnetic recording media comprise DC magnetron sputtering and high temperatures in order to obtain Cr segregation in Co-alloy grain boundaries to achieve high Hr and high SNR. Conventional practices, therefore, employ a high substrate heating temperature, e.g. above about 200° C., e.g. about 230° C. to about 260+ C., in order to achieve a desirably high Hr. However, such high substrate heating temperatures result in a reduced S* and, hence, increased medium noise.
Accordingly, there exists a need for high density magnetic recording media exhibiting high Hr with high S* and a high SNR. There also exists a need for efficient methodology for producing magnetic recording media exhibiting high Hr, high S* and a high SNR.
DISCLOSURE OF THE INVENTION
An object of the present invention is a magnetic recording medium for high areal recording density exhibiting high Hr and high S*.
Another object of the present invention is a method of manufacturing a magnetic recording medium for high areal recording density exhibiting high Hr and high S*.
Additional objects, advantages and other features of the present invention will be set forth in part in a 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 present invention. The objects and 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 objects are achieved by a magnetic recording medium comprising: a non-magnetic substrate; an underlayer on the substrate; an intermediate layer comprising cobalt, chromium and tantalum and having an oxidized surface, on the underlayer; and a magnetic layer on the intermediate layer.
Another aspect of the present invention is a method of manufacturing a magnetic recording medium, the method comprising: depositing an underlayer on a non-magnetic substrate; depositing an intermediate layer, comprising an alloy of cobalt, chromium and tantalum, on the underlayer; partially oxidizing the surface of the intermediate layer; and depositing a magnetic layer on the oxidized surface of the intermediate layer.
Additional objects and 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 w
Chen Qixu
Leu Charles
Ranjan Rajiv Yadav
Song Xing
McDermott & Will & Emery
Resan Stevan A.
Seagate Technology LLC
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