Patent Application
20080085425
The following detailed description of the embodiments of the present invention can best be understood when read in conjunction with the following drawings, in which the features are not necessarily drawn to scale but rather are drawn as to best illustrate the pertinent features and the same reference numerals are employed throughout for designating similar features, wherein:
The present invention addresses and solves the above-described drawbacks and disadvantages associated with conventionally structured bit patterned magnetic recording media, wherein the coercivity field Hc of each magnetic element depends upon the magnetic state of the neighboring magnetic elements due to magnetostatic mutual interaction(s), including disadvantageous creation of a coercivity field distribution which causes deterioration of the magnetic performance characteristics, lowered thermal stability, and increased bit error rate (BER), while maintaining full compatibility with all aspects of conventional manufacturing technology and methodology for bit patterned media.
Briefly stated, the present inventors have determined that improved bit patterned magnetic recording media are obtainable by providing such media with a layer of a ferromagnetic material for regulating magnetic exchange coupling between the magnetic elements. The layer comprises a ferromagnetic material having a saturation magnetization Ms ranging from about 1 to about 2,000 emu/cm3 and is selected for reducing coercivity field distribution of the magnetic elements, partially shunting magnetostatic interaction therebetween, and reducing demagnetization fields and bit error rate (BER). Preferably, the ferromagnetic material has a saturation magnetization Ms below about 400 emu/cm3, more preferably below about 200 emu/cm3. The inventors have further determined that the inventive methodology is versatile, i.e., the layer of ferromagnetic material may be provided above, below, or between each of the plurality of discrete magnetic elements of such media, and each of the magnetic elements may comprise a conventional structure selected from the group consisting of longitudinal, perpendicular, laminated, anti-ferromagnetically coupled (AFC), granular, and superlattice media designs.
It has been further determined that the inventive methodology affords a significant improvement, i.e., reduction, in the demagnetization field of bit patterned magnetic media, e.g., on the order of about 25% relative to conventionally structured bit patterned media without the coupling layer. In addition, BERw is increased by about 1 dB for a 1 Tbit design.
Referring to
As illustrated in
As described in more detail below, in medium 60 shown in
According to the invention, layer 3 of a ferromagnetic material has a selected saturation magnetization Ms ranging from about 1 to about 2,000 emu/cm3 for reducing the coercivity distribution of the magnetic elements 1, partially shunting magnetostatic interaction therebetween, and reducing demagnetization fields and bit error rate (BER). Preferably, the ferromagnetic material has a saturation magnetization Ms below about 400 emu/cm3, more preferably below about 200 emu/cm3. The thickness of layer 3 is depends on the saturation magnetization Ms of the material of the layer. If Ms is large, layer 3 is thinner than when Ms is small. For example, if Ms of layer 3 is greater than about 1,000 emu/cm3, the thickness thereof will generally be less than about 5 nm, but when Ms of layer 3 is about 200 emu/cm3, the thickness is generally less than about 25 nm. The ferromagnetic material of layer 3 comprises an alloy or combination of at least one ferromagnetic element and at least one additional element, preferably comprising at least one ferromagnetic element selected from the group consisting of Fe, Co, and Ni and at least one additional element selected from the group consisting of Al, Si, Ti, V, Cr, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Hf, Ta, W, Re, Ir, Pt, and Au.
The non-magnetic substrate 2 may be comprised of a non-magnetic material selected from the group consisting of: Al, Al—Mg alloys, other Al-based alloys, NiP-plated Al or Al-based alloys, glass, ceramics, glass-ceramics, polymeric materials, and composites or laminates of these materials. The thickness of substrate 2 is not critical; however, in the case of magnetic recording media for use in hard disk applications, substrate 2 must be of a thickness sufficient to provide the necessary rigidity.
As indicated above, the nature of the magnetic elements 1 is not critical for practice of the present invention and obtainment of the several advantages afforded thereby. Specifically, each of the magnetic elements 1 may comprise conventional magnetic recording media structures or designs in the form of thin film layer stacks, selected from the group consisting of longitudinal, perpendicular, laminated, anti-ferromagnetically coupled (AFC), granular, and superlattice media. It should be noted, however, that ferromagnetic layer 3 according to the present invention is distinct from any ferromagnetic layer(s) forming part of the layer stacks of the magnetic elements 1 (e.g., a soft magnetic underlayer, SUL, of perpendicular media), and is not to be equated therewith for any purpose. Further, in the embodiments shown in
According to the invention, each layer of the layer stacks comprising the magnetic elements 1, as well as ferromagnetic layer 3 of selected saturation magnetization Ms for regulating magnetic exchange coupling between the discrete magnetic recording elements 1 and the protective overcoat layer may be deposited or otherwise formed by any suitable technique utilized for formation of thin film layers, e.g., any suitable physical vapor deposition (“PVD”) technique, including, but not limited to, sputtering, vacuum evaporation, ion plating, cathodic arc deposition (“CAD”), etc., or by any combination of various PVD techniques. The lubricant topcoat layer may be provided over the upper surface of the protective overcoat layer in any convenient manner, e.g., as by dipping the thus-formed medium into a liquid bath containing a solution of the lubricant compound.
Further according to the invention, the discrete magnetic elements 1 may be formed in any conventional manner, e.g., as by initial deposition of a layer stack of desired structure or design for a selected media type which continuously extends over the surface of substrate 2, followed by patterning by according to conventional techniques, including, for example, physical and/or chemical deposition and materials removal methodologies including photolithographic masking, etching, etc., or by photolithographic masking followed by selective deposition of materials comprising the layer stack through apertures formed in the masking layer. In addition, it should be noted that the present invention is not limited to formation of circular, columnar-shaped discrete magnetic elements arrayed in a hexagonal close packed pattern as in
According to certain embodiments of the present invention, each of the layer stacks comprises a non-magnetic interlayer between the substrate and the at least one magnetic recording layer for controlling the crystallographic structure/orientation of the at least one magnetic recording layer. More specifically, according to preferred embodiments of the invention, a non-magnetic interlayer is provided beneath the ferromagnetic layer for forming magnetic elements with recording layers having hcp crystal structure with <0002> orientation perpendicular to the film plane. In such instances, the non-magnetic interlayer comprises an amorphous layer and a layer with a fcc or hcp crystallographic structure. When the layer has a fcc structure, it grows with <111> orientation perpendicular to the film plane and when it has a hcp structure, it grows with <0002> orientation perpendicular to the film plane.
When the layer of ferromagnetic material is formed between a non-magnetic interlayer and magnetic recording layer of the magnetic elements, it should have fcc or hcp crystallographic structure/orientation. When the layer of ferromagnetic material has a fcc crystallographic structure, it should grow with <111> orientation perpendicular to the film plane and when the layer of ferromagnetic material has a hcp crystallographic structure, it should grow with <0002> orientation perpendicular to the film plane.
According to further embodiments of the invention, step (b) comprises forming each of the layer stacks as comprising a soft magnetic underlayer (SUL) between the substrate and the non-magnetic interlayer, in which case the material of the SUL is preferably amorphous.
Thus, the present invention advantageously provides improved performance, high areal density, bit patterned magnetic media which media afford substantially improved demagnetization fields and bit error rate BERw by virtue of the presence of the ferromagnetic coupling layer. The media of the present invention enjoy particular utility in high recording density systems for computer-related applications. In addition, the inventive media can be fabricated by means of conventional media manufacturing technologies, as indicated above.
In the previous description, numerous specific details are set forth, such as specific materials, structures, processes, etc., in order to provide a better understanding of the present invention. However, the present invention can be practiced without resorting to the details specifically set forth. In other instances, well-known processing materials and techniques have not been described in detail in order not to unnecessarily obscure the present invention.
Only the preferred embodiments of the present invention and but a few examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is susceptible of changes and/or modifications within the scope of the inventive concept as expressed herein.
