Medium with a NiNb sealing layer

Details Medium with a NiNb sealing layer Medium with a NiNb sealing layer

2000-04-27

2004-03-02

Thibodeau, Paul (Department: 1773)

Stock material or miscellaneous articles

All metal or with adjacent metals

Having magnetic properties, or preformed fiber orientation...

C428S663000, C428S668000, C428S333000, C428S690000, C427S129000, C204S192200

Reexamination Certificate

active

06699588

ABSTRACT:

TECHNICAL FIELD
This invention relates to a magnetic medium, such as a thin film magnetic recording medium, and the method of manufacturing the medium. The invention has particular applicability to a magnetic recording medium exhibiting low noise, high coercivity and suitable for high-density longitudinal and perpendicular recording.
BACKGROUND ART
The requirements for high areal density impose increasingly greater requirements on 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 and perpendicular recording. The magnetic anisotropy of longitudinal and perpendicular recording media makes the easily magnetized direction of the media located in the film plane and perpendicular to the film plane, respectively. The remanent magnetic moment of the magnetic media after magnetic recording or writing of longitudinal and perpendicular media is located in the film plane and perpendicular to the film plane, respectively.
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 large grain size and intergranular exchange coupling. Therefore, in order to increase linear density, medium noise must be minimized by suitable microstructure control.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Al—Mg) alloy. Such Al—Mg alloys are typically electrolessly plated with a layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as glass, e.g., an amorphous glass, glass-ceramic material which comprise a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks. The use of glass-based materials, such as glass-ceramic materials, is disclosed by Hoover et al., U.S. Pat. No. 5,273,834.
A conventional longitudinal recording disk medium is depicted in FIG.
1
and typically comprises a non-magnetic substrate
10
having sequentially deposited on each side thereof an underlayer
11
,
11
′, such as chromium (Cr) or Cr-alloy, a magnetic layer
12
,
12
′, typically comprising a cobalt (Co)-base alloy, and a protective overcoat
13
,
13
′, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer
11
,
11
′, magnetic layer
12
,
12
′, and protective overcoat
13
,
13
′, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in
FIG. 1
, but does not comprise Cr-containing underlayers.
Conventional methods for manufacturing longitudinal magnetic recording medium with a glass or glass-ceramic substrate comprise applying a seed layer between the substrate and underlayer. A seed layer seeds the nucleation of a particular crystallographic texture of the underlayer.
Longitudinal magnetic recording media with glass or glass-ceramic substrates are commercially available from different manufacturers with different seed layer materials to reduce the effect of high thermal emissivity of such glass and glass-ceramic substrates, and to influence the crystallographic orientation of subsequently deposited underlayers and magnetic layers. Pre-coat on glass substrates also facilitates laser texturing and mechanical texturing process. Such conventional seed layer materials also include nickel-phosphorous (Ni—P) which is typically sputter deposited on the surface of the glass-ceramic substrate at a thickness of 500 Å. Sputtered NiP films on glass or glass-ceramic substrates were reported in the literature for the control of crystallographic orientation of the longitudinal magnetic media and the enhancement of coercivity (for example, Hsiao-chu Tsai et al., “The Effects of Ni
3
P-sublayer on the Properties of CoNiCr/Cr Media Using Different Substrates,” IEEE Trans. on Magn., Vol. 28, p. 3093, 1992).
Conventional longitudinal magnetic recording media comprising a glass or glass-ceramic substrate having NiP sputtered thereon also comprise, sequentially deposited thereon, a Cr or Cr-alloy underlayer at an appropriate thickness, e.g., about 550 Å, a magnetic layer such as Co—Cr-platinum (Pt)-tantalum (Ta) at an appropriate thickness, e.g., 200 Å, and a protective carbon overcoat at an appropriate thickness, e.g., about 75 Å. Conventional Cr-alloy underlayers comprise vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Other conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr.
The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the glass or glass-ceramic substrate in an inert gas atmosphere, such as an atmosphere of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 Å thick.
Longitudinal magnetic films exhibiting a bicrystal cluster microstructure are expected to exhibit high coercivity, low noise and high remanent squareness. In U.S. Pat. No. 5,830,584, a magnetic medium was disclosed comprising a glass or glass-ceramic substrate and a magnetic layer exhibiting a bicrystal cluster microstructure. The formation of a bicrystal cluster microstructure is induced by oxidizing the surface of a seed layer so that the underlayer subsequently deposited thereon exhibits a (200) crystallographic orientation which, in turn, induces a bicrystal microstructure in a magnetic alloy deposited and epitaxially grown on the underlayer.
U.S. Pat. No. 5,733,370 discloses a method of manufacturing a magnetic recording medium comprising a glass or glass-ceramic substrate and a magnetic layer exhibiting a bicrystal cluster microstructure. The disclosed method comprises sputter depositing a NiP seed layer on a glass or glass-ceramic substrate and subsequently oxidizing the deposited NiP seed layer. The oxidized upper seed layer surface induces the subsequently deposited underlayer to exhibit a (200) crystallographic orientation which, in turn, induces the magnetic alloy layer deposited and epitaxially grown on the underlayer to exhibit a bicrystal cluster microstructure. The magnetic recording media disclosed in U.S. Pat. Nos. 5,733,370 and 5,830,584 exhibit high coercivity, low magnetic remanence (Mr)×thickness (t) and low noise, thereby rendering them particularly suitable for longitudinal recording.
In co-pending application Ser. No. 09/152,324, the adhesion between a seed layer, particularly a NiP seed layer, and a non-conventional substrate, was improved by providing an adhesion enhancement layer, such as Cr or a Cr alloy, between the substrate and the seed layer, with an additional benefit in recording performance obtained by surface oxidizing the seed layer.
Assignee's pending U.S. patent application Ser. No. 09/186,074, entitled “Magnetic thin film medium comprising amorphous sealing layers for reduced lithium migration,” discloses a method which can be used for reducing corrosion of the magnetic re

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