Patent Application
20080055777
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 same reference numerals are employed throughout for designating the same or similar features, and wherein the various features are not necessarily drawn to scale but rather are drawn as to best illustrate the pertinent features, wherein:
The present invention addresses and effectively solves, or at least mitigates, drawbacks and disadvantages associated with the use of high performance, high areal density perpendicular magnetic recording media in applications where the media surface is subject to hard particle-induced scratching during use, e.g., as in hard disk drive systems utilizing transducer heads operating at very low flying heights. Specifically, the present inventors have determined that minute particles present in the hard disk drive, especially on the media or head surfaces, may scratch the media surface. Such scratches may result in permanent, i.e., unrecoverable, magnetic signal loss or errors even in instances where the scratch process has not caused physical removal of the magnetic material.
As indicated above, the phenomenon of scratch erasure is especially notable in perpendicular magnetic recording media comprised of magnetic recording layers having perpendicular magnetic anisotropy, which recording layers typically utilize magnetic materials having a hexagonal close packed (hcp) crystal structure and <0001> preferred basal plane crystallographic orientations with the c-axis perpendicular to the film surface. Extensive studies by the present inventors have determined that scratch erasure results from a permanent change or alteration in a magnetic property, e.g., coercivity Hc, of the magnetic recording layer under extreme mechanic stress conditions. The scratch-damaged region(s) of the magnetic recording film or layer is (are) unwritable or unrewritable and therefore unable to serve the intended purpose of magnetic recording.
Briefly stated, the present inventors have determined that thin film perpendicular media with layer stacks including magnetic recording layers with the aforementioned hcp structure and <0001> preferred basal plane crystallographic orientations and provided with at least one low shear modulus layer (i.e., with a shear modulus of about 30 or less) exhibit significantly improved scratch-induced magnetic damage such as data erasure.
In more detail, according to investigations concerning scratch erasure conducted by the instant inventors, after magnetic recording signals were written to the media with wide band signal writers having a track width of 50 μm at a given linear density, e.g., 40 kfci, “Hysitron” technique scratches were made on the recorded regions at several normal loads with a cube-cornered diamond tip. (According to the “Hysitron” technique, a Hysitron system, which is a nano-indentation/nano-scratching apparatus, is utilized for forming a series of nano-scratches on the medium surface under controlled load forces typically ranging from a few tens of micro-Newtons, μN, to a few hundreds of μN. By using an appropriately sized nano-indentor, e.g., with a radius of curvature of a few hundred nm, nano-scratches of depth≧1 nm and width≧100 nm can be formed which effectively replicate actual hard particle-induced scratches during media operation). It was observed that the polarity of the recorded magnetic signal around the center of the scratch was reversed when the applied load was sufficiently great.
Referring to
Adverting to
It has been further determined that poor scratch damage performance, relative to longitudinal magnetic recording media, is not characteristic of all perpendicular media. The perpendicular media illustrated in
While not desirous of being bound by any particular theory, it is nonetheless believed that the increased susceptibility to scratch damage evidenced by perpendicular media with hcp-structured magnetic recording layers arises from the perpendicular c-axis orientation of the hcp Co-alloy crystal lattice. In perpendicular media, the hcp <0001> basal planes are parallel to the media growth plane and more readily experience slip under shear stress, thereby leading to a loss of hcp crystal orientation. The loss of hcp crystal orientation in turn leads to loss of the magneto-crystalline anisotropy with a dramatic reduction in coercivity Hc. By contrast, due to their more favorable crystalline orientation, longitudinal media are more robust than perpendicular media in terms of shear stress-induced loss of hcp crystallinity and Hc degradation. MFM signal reversal in
The present inventors have determined that thin film perpendicular media with layer stacks magnetic recording layers including hcp structure and <0001> preferred basal plane crystallographic orientations and at least one low shear modulus layer (i.e., with a shear modulus of about 30 or less) exhibit significantly improved scratch-induced magnetic damage performance. Referring to Table I below, shown therein are pertinent mechanical properties of two illustrative, but non-limitative, examples of low shear modulus materials, i.e., silver (Ag) and gold (Au), as well as an illustrative, but non-limitative, example of a comparatively higher shear modulus material, i.e., copper (Cu).
By way of illustration only, granular perpendicular media comprising layer stacks including a magnetic recording layer with hcp structure and <0001> preferred basal plane crystallographic orientation and a silver (Ag) layer as a low shear modulus cap layer between the recording layer and the protective overcoat layer were fabricated and evaluated for scratch erasure resistance via the aforementioned Hysitron scratch technique. Table II below presents a comparison of the results of determination of the critical scratch load (in μN) for phase reversal of the magnetic signal as a function of thickness of the Ag cap layer, from which it is clearly evident that the presence of at least one low shear modulus layer in the layer stack of perpendicular media results in a significant improvement in scratch damage performance.
According to the invention, the use of low shear modulus layers for mitigating the performance reduction of perpendicular media arising from scratch damage is not limited to the illustrated case where the low shear modulus layer is present in the layer stack as a cap layer between the recording layer and the protective overcoat layer; rather, the at least one low shear modulus layer may be present at a number of different locations within the layer stack, e.g., between the substrate and the overlying magnetically soft underlayer (SUL), between the SUL and the overlying at least one interlayer, between the at least one interlayer and the overlying magnetic recording layer, etc. The at least one low shear modulus layer may comprise more than one low shear modulus material, e.g., an alloy or other composite or laminate of Ag and Au, and the thickness thereof may range from about 2.5 to about 1000 nm, and is preferably from about 10 to about 20 nm.
Further according to the invention, the layer stack may comprise a combination of magnetic recording layer types, e.g., a layer stack including a granular perpendicular magnetic recording layer having hcp structure and <0001> preferred basal plane crystallographic orientation and an overlying multilayer perpendicular magnetic recording layer such as described above, e.g., formed of alternating thin Co or Co-based alloy layers about 3 Å thick and Pd or Pt or Pd- or Pt-based alloy layers up to about 15 Å thick. According to these embodiments, the low shear modulus layer may be placed at any of the aforementioned locations in the layer stack. The combination of granular and multilayer perpendicular magnetic recording layers according to these embodiments affords benefits in both improved scratch damage performance, relative to conventional granular perpendicular magnetic recording media, and improved magnetic recording performance characteristics compared to those of single layer granular media and multilayer media.
Several illustrative, but non-limitative, examples of embodiments of perpendicular media fabricated according to the principles of the present invention will now be described with reference to
Referring to
Yet another example of an embodiment of a scratch damage resistant perpendicular magnetic recording medium 50 is shown, in simplified cross-sectional view, in
Referring now to
With reference to
As has been indicated, media 20-70 according to the present invention generally resemble the conventional perpendicular medium 1 of
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. Substrate 2 typically comprises Al or an Al-based alloy, e.g., an Al—Mg alloy, or glass or glass-ceramics, and, in the case of Al-based substrates, includes a plating layer, typically of NiP, on the surface of substrate 2 (not shown in the figure for illustrative simplicity). An optional adhesion layer 3, typically a less than about 100 Å thick layer of a metal or a metal alloy material, e.g., Ti, a Ti-based alloy, Ta, a Ta-based alloy, Cr, or a Cr-based alloy, may be formed over the surface of substrate surface 2 or the NiP plating layer thereon.
Overlying substrate 2 or optional adhesion layer 3 is a magnetically soft underlayer (SUL) 4 which comprises a layer of a soft, low coercivity magnetic material (or a laminate of layers of a soft material with spacer layers of a non-magnetic material) from about 50 to about 300 nm thick. Suitable magnetically soft, low coercivity materials for use as SUL 4 include, but are not limited to, FeCoB, FeCoCrB, CoZrNb, CoZrTa, FeCoTaZr, FeCoZrNb, and FeTaC.
As in medium 1 shown in
Also as in medium 1, the layer stacks of media 20-70 according to the present invention further comprise an intermediate layer stack 5 between SUL 4 and at least one overlying perpendicular magnetic recording layer 6, which intermediate layer stack 5 is comprised of optional seed layer 5A, and interlayer 5B for facilitating a preferred perpendicular growth orientation and grain size of the overlying at least one perpendicular magnetic recording layer 6, as well as for magnetically decoupling the SUL and magnetic recording layers. Suitable non-magnetic materials for use as interlayer 5B adjacent the magnetically hard perpendicular recording layer 6 include hcp-structured materials, such as Ru, TiCr, CoCr, CoCrRu, Ru/CoCr37Pt6, RuCr/CoCrPt, etc.; suitable materials for use as optional seed layer 5A typically include an fcc material, such as an alloy of Cu, Ag, Pt, or Au, or an amorphous or fine-grained material, such as Ta, TaW, CrTa, Ti, TiN, TiW, or TiCr.
The magnetically hard perpendicular magnetic recording layer 6 is preferably comprised of one or more layers of a Co-based alloy including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, W, Cr, Ru, Ti, Si, O, V, Nb, Ge, B, and Pd. Exemplary alloys include CoCr, CoCrPt, CoCrPtB, CoCrPtSiO2, CoCrPtTiO2, CoCrPtTa2O5, and CoCrPtNb2O5. Preferably, the at least one perpendicular magnetic recording layer 6 comprises an hcp Co-based alloy with a <0001> preferred basal plane and preferred c-axis perpendicular growth orientations; and the interlayer stack 5 comprises an hcp material with a preferred c-axis perpendicular growth orientation. In addition, the at least one perpendicular magnetic recording layer 6 is preferably granular, i.e., comprised of at least partially isolated, uniformly sized and composed, magnetic particles or grains with c-axis growth orientation.
As for medium 60 and 70 shown in
Finally, the layer stack of each of media 20-70 includes a protective overcoat layer 7 above the at least one perpendicular magnetic recording layer 6 and a lubricant topcoat layer 8 over the protective overcoat layer 7. Preferably, the protective overcoat layer 7 comprises a carbon-based material, e.g., diamond-like carbon (“DLC”), and the lubricant topcoat layer 8 comprises a fluoropolymer material, e.g., a perfluoropolyether compound.
According to the invention, each of the layers 3-7, 12, and 13A, 13B 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 8 may be provided over the upper surface of the protective overcoat layer 7 in any convenient manner, e.g., as by dipping the thus-formed medium into a liquid bath containing a solution of the lubricant compound.
Thus, the present invention advantageously provides improved performance, high areal density, magnetic alloy-based perpendicular magnetic media and data/information recording, storage, and retrieval systems, which media afford improved substantially improved scratch damage resistance by virtue of the presence of the at least one low shear modulus layer in the layer stack or by a combination of different types of magnetically hard perpendicular magnetic recording layers. 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, e.g., sputtering.
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.
