Stock material or miscellaneous articles – All metal or with adjacent metals – Having magnetic properties – or preformed fiber orientation...
Patent
1997-10-17
2000-01-04
Resan, Steven A.
Stock material or miscellaneous articles
All metal or with adjacent metals
Having magnetic properties, or preformed fiber orientation...
428667, 428694TS, 428900, G11B 05704
Patent
active
060107952
DESCRIPTION:
BRIEF SUMMARY
RELATED APPLICATION
This application relates to PCT International Application Ser. No. PCT/US97/02169 filed Feb. 26, 1997, entitled "THIN FILM MEDIA CONTAINING NICKEL ALUMINUM UNDERLAYER."
TECHNICAL FIELD
This application claims priority from U.S. Provisional Pat. Application Ser. No. 60/028,882, filed Oct. 17, 1996.
The present invention relates to a magnetic recording medium, such as a thin film magnetic recording disk, and to a method of manufacturing the medium. The invention has particular applicability to a magnetic recording medium exhibiting low noise, high coercivity and high recording density.
BACKGROUND ART
The requirements for high areal recording density impose increasingly greater requirements on thin film magnetic recording media in terms of coercivity, remanent squareness, low medium noise and narrow track recording performance. It is extremely difficult to produce a magnetic recording medium satisfying such demanding requirements, particularly a high density magnetic rigid disk medium for longitudinal recording.
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 noncoupled 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. Therefore, 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 typically comprises a non-magnetic substrate 10 having sequentially deposited thereon a plating 11, such as a plating of amorphous nickel-phosphorous (NiP), and underlayer 12, such as chromium (Cr) or a Cr-alloy, a magnetic layer 13, typically comprising a cobalt (Co) alloy, and a protective overcoat 14, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 12, magnetic layer 13 and protective overcoat 14 are typically deposited by sputtering techniques. The Co alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer.
It is recognized that the relevant magnetic properties, such as coercivity (Hc), magnetic remanence (Mr) and coercive squareness (S*), which are critical to the performance of a Co base alloy magnetic thin film, depend primarily on the microstructure of the magnetic layer which, in turn, is influenced by the underlayer on which it is deposited. Conventional underlayers include Cr, molybdenum (Mo), tungsten (W), titanium (Ti), chromium-vanadium (CrV) as well as Cr alloyed with various substitutional elements. It is recognized that underlayers having a fine grain structure are highly desirable, particularly for growing fine grains of hexagonal close packed (HCP) Co 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 producing 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. Such a magnetic recording medium is schematically depicted in FIG. 2 and comprises substrate 20, NiAl underlayer 21 and cobalt alloy magnetic layer 22. However, it was found that the coercivity of a magnetic recording medium comprising an NiAl underlayer, such as that depicted in the FIG. 2, is too low for high density recording, e.g. about 2000 Oersteds.
Lee et al. subsequently reported that the coercivity of a magnetic recording medium compr
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Chang Jyh-Kau
Chen Ga-Lane
Chen Qixu
Leu Charles
Resan Steven A.
Seagate Technology Inc.
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