Stock material or miscellaneous articles – All metal or with adjacent metals – Composite; i.e. – plural – adjacent – spatially distinct metal...
Reexamination Certificate
2001-03-12
2003-04-29
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
All metal or with adjacent metals
Composite; i.e., plural, adjacent, spatially distinct metal...
C428S212000, C428S332000, C428S336000, C428S457000, C428S469000, C428S472000, C428S670000, C428S692100, C428S690000, C428S690000, C428S690000
Reexamination Certificate
active
06555252
ABSTRACT:
TECHNICAL FIELD
The present invention relates to magnetic recording media, and more particularly is a modulated grain-composition magnetic media system with up to terabit areal density recording capacity which, in preferred practice is produced by sequential multiple layer vacuum deposition, and subsequent annealing, procedures that allow selective fabrication of magnetic recording materials with intended grain size and coercivity, with longitudinal or perpendicular magnetic particle “c-axis” orientation.
BACKGROUND
As reported in an article by Wood, titled “The Feasibility of Magnetic Recording at 1 Terabit Per Square Inch”, IEEE Transactions of Magnetics, Vol. 36, No. 1, (January 2000), areal density, (ie. bits per square inch), in magnetic recording products has grown at a rate approaching 100% per annum, (with practical systems now operating at an areal density of 10
10
bits per square inch). Said article, which is incorporated by reference hereinto, also projects that in view of ultimate practical limitations in realizable magnetic read-write system heads, an ultimate-utility providing magnetic recording material can be described as one which presents with a maximum Coercivity (Hc) of approximately twelve Kilo-Oersteds (12K-Oe) based on perpendicularly oriented magnetic particles which have an associated minimum grain size diameter of just under ten (10 nm) nanometers, (ie. minimum stable grain size volume of six-hundred (600) cubic nanometers). Said paper further makes clear that while magnetic media with smaller grain size and larger Coercivities (Hc) are very achievable, thermal stability and practical ultimate magnetic head writing capability provide the recited grain size and Coercivity (Hc) values as representing theoretically “optimum” in unpatterned magnetic recording media.
In view of the fact that presently marketed magnetic recording system technology typically utilizes longitudinally “c-axis” oriented magnetic particle containing materials which demonstrate maximum Coercivities (Hc) on the order of three (3K-Oe) to four (4K-Oe) Kilo-Oersteds, it can be concluded that a magnetic recording material which would provide a minimum grain size of around ten (10) nanometers and a maximum Coercivity (Hc) of approximately twelve (12K-Oe), but which would allow adjustment of maximum Coercivity (Hc) downward by controllable and known fabrication parameters, and which magnetic recording material could be fabricated to demonstrate either longitudinal or perpendicular magnetic particle “c-axis” orientation therewithin, again by control of known fabrication parameters, would provide not only immediate utility, but utility projected into the far foreseeable future when practical fabricated magnetic recording system write head system capabilities approach upper theoretical limitations.
The inventors of the present invention have identified several nanocomposite material containing films with potential for application in extremely high-density magnetic recording materials, including CoPr, CoPt, CoSm, SmFeSiC SmFeAlC and FePt. (See “Nanoscale Design of Films for Extremely High Density Magnetic Recording”, Sellmyer, Yu, Thomas, Liu & Kirby, Phys. Low-Dim. Struct., ½155, (1998)).
The present inventors have also observed that various materials demonstrate relaxed viscosity at temperatures of, for instance:
1446 K for SiO
2
;
820 K for GeO
2
;
526 K for B
2
O
3
;
186 K for Glycerol;
(see for instance “Dynamics of Strong and Fragile Glass Formers: Differences and Correlation with Low-Temperature Properties”, Sokolov et al., Phys. Rev. Lett, Vol. 71, No. 13, p. 2062, (1993)).
The conceptual insight leading to the present invention, was that magnetic recording material systems which combine alternating layers of appropriate thicknesses of:
nanocomposite material containing films; and
films of materials which demonstrate relaxed viscosity at desirable anneal temperatures;
might allow fabrication of magnetic recording materials which demonstrate predictable magnetic material grain size, predictable maximum coercivity (Hc) and magnetic particle “c-axis” orientation, (ie. longitudinal or perpendicular to a resulting magnetic recording material film), by a relatively simple multi-layer vacuum deposition, (and subsequent anneal), procedure onto even non-lattice matched substrates.
It is noted at this point that other researchers have reported fabrication of FePt films on lattice matched (001) MgO single crystal substrates using Molecular Beam Epitaxy (MBE) systems. Articles describing this are;
“Direct Formation of Ordered CoPt and FePt Compound Thin Films by Sputtering”, Visokay & Sinclair, App. Phys. Lett., 66, (1995);
“Enhanced Magneto-Optical Keer Effect in Spontaneously Ordered FePt Alloys: Quantitative Agreement Between Theory and Experiment”, Cebollada et al., Phys. Rev. B, 50 (1994).
“Control of the Axis of Chemical Ordering and Magnetic Anisotropy in Epitaxial FePt Films”, Farrow et al., J. App. Phys. 79 (1996).
The films achieved present with perpendicularly oriented “c-axis” orientation. Said approach again, however, requires (MBE) capability and use of lattice matching (001) MgO.
Inventors of the presently disclosed invention have investigated fabrication of longitudinally oriented magnetic recording media with a coercivity of 3000 Oe to 6300 Oe, as described in Patent to Sellmyer et al., U.S. Pat. No. 5,824,409. Said 409 Patent describes production of said a magnetic recording media composed of alternating thin film layers of Platinum (Pt) and an element selected from the group consisting of Iron (Fe) and Cobalt (Co), sequentially deposited onto a substrate. To achieve the final system result an anneal of the deposited materials at 300 to 600 degrees Centigrade was performed.
Previous published results by the present Inventors has documented fabrication and investigation of Co:C; CoPt:C, Fe/Pt; FePt:SiO
2
films. Said work is variously described in Scientific Articles:
“Structural and Magnetic Properties of Nanocomposite Co:C Films”, Yu, Liu & Sellmyer, J. App. Phys. Vol. 85, No. 8, (Apr. 15, 1999);
“Nanocomposite CoPt:C Films For Extremely High-Density Recording”, Yu, Liu, Weller & Sellmyer, App. Phys. Lett., Vol. 75, No. 25, (Dec. 20, 1999);
“Magnetic Viscosity and Switching Volumes of Annealed Fe/Pt Multilayers”, Luo, Shan & Sellmyer, J. App. Phys. 79(8), (Apr. 15, 1996);
“Magnetic Properties and Structure of Fe/Pt Thin Films”, Luo & Sellmyer, IEEE Transactions on Magnetics, Vol. 31, No. 6, (November 1995); and
“Structural and Magnetic Properties of FePt:SiO
2
Granular Thin Films”, Luo & Sellmyer, App. Phys. Lett., Vol 75, No. 20, (Nov. 15, 1999).
A further paper by present Inventors is titled “Nanostructured Magnetic Films For Extremely High Density Recording”, Sellmyer, Yu & Kirby, Nanostructured Mat., Vol. 12, (1999). This paper reports that over twenty years coercivity (Hc) in Co-based recording media has increased for approximately 0.3 K-Oe to approximately a present 3K-Oe and that the most advanced media presently are CoCrPtX alloys, where X represents Ta, Nb etc.
A Search of Patents has identified a Patent to Sellmyer et al., U.S. Pat. No. 5,824,409 which focuses on longitudinal high coercivity recording media comprised of alternating layers of Fe and Pt, without mention of intervening Oxide layers therebetween, however.
A recent U.S. Pat. No. 6,183,606 B1 to Kuo et al., describes FePt-Si
3
N
4
composite films. This Patent does not claim perpendicular anisotropy, nor does it describe simultaneously obtaining both high coercivity (eg. 8-11 kOe) and small grain size (eg. 8 nm). Said 606 Patent does provide a thin film for magnetic recording media including particles of about 50 nm diameter, 200 nm thickness, high coercivity, plane-parallel easy axis, FePt at 50/50 proportions, and fcc crystal phase going into fct phase during anneal at near 600 degrees Centigrade. However, the matrix in which the FePt particles reside comprises Si
3
N
4
which is a non-magnetic phase serving the simple role of diluting the magnetism of the material. Other materials are no
Luo Chunping
Sellmyer David J.
Board of Regents of the University of Nebraska
Resan Stevan A.
Uhlir Nikolas J.
Welch James D.
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