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  Method of producing a magnetic recording medium and a magnetic recording medium formed therebyUSPTO Application #: 20070009654Title: Method of producing a magnetic recording medium and a magnetic recording medium formed thereby Abstract: A perpendicular magnetic recording medium has a magnetic recording layer with ferromagnetic crystalline grains and nonmagnetic and nonmetallic grain boundary region surrounding the grains. The surface of its underlayer, before forming the magnetic recording layer, is exposed to an O2 or N2 atmosphere or an atmosphere of rare gas and O2 or N2, to attach the O2 or N2 as nucleation sites for promoting growth of the nonmagnetic and nonmetallic region. By forming the magnetic recording layer thereafter, both ferromagnetic crystalline grains and the nonmagnetic and nonmetallic grain boundary region are formed from the initial stage of the growth of the magnetic recording layer. Thus, a magnetic recording layer having excellent segregation structure can be formed. (end of abstract) Agent: Rossi, Kimms & Mcdowell LLP. - Ashburn, VA, US Inventors: Sadayuki Watanabe, Yasushi Sakai USPTO Applicaton #: 20070009654 - Class: 427126300 (USPTO) Related Patent Categories: Coating Processes, Electrical Product Produced, Metallic Compound Coating, Metal Oxide, Peroxide, Or Hydroxide Coating The Patent Description & Claims data below is from USPTO Patent Application 20070009654. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This is a continuation of application Ser. No. 10/390,332, filed Mar. 17, 2003. BACKGROUND [0002] A perpendicular magnetic recording system with recording magnetization perpendicular to the medium surface has been contemplated as an alternative to a conventional longitudinal magnetic recording system, to attain higher recording density. A perpendicular magnetic recording medium is principally composed of a magnetic recording layer of a hard magnetic material, an underlayer for aligning the magnetic recording layer to an aimed direction, a protective layer for protecting the surface of the magnetic recording layer, and an underlayer of a soft magnetic material having a function to converge a magnetic flux that is generated by a magnetic head for recording in the magnetic layer. [0003] The soft magnetic underlayer can be omitted since recording is possible without it, although it can improve media performance. A medium without the soft magnetic underlayer is called a single-layered perpendicular magnetic recording medium, and a medium having the soft magnetic underlayer is called a double-layered perpendicular magnetic recording medium. A perpendicular magnetic recording medium, as well as a longitudinal magnetic recording medium, must perform high thermal stability compatible with low media noise in order to achieve high recording density. [0004] In conventional longitudinal magnetic recording media, various compositions and structures of a magnetic recording layer and materials for a nonmagnetic underlayer have been proposed. Practical magnetic recording layers use an alloy of Co and Cr (hereinafter referred to as CoCr) and obtain magnetically isolated magnetic grains by segregating the chromium at the grain boundary. Another type of a magnetic recording layer, called a granular magnetic recording layer that uses nonmagnetic and nonmetallic substance, such as oxide or nitride, has been proposed. [0005] In a magnetic recording layer of the CoCr, the substrate must be heated to a temperature higher than 200.degree. C. during the deposition of the layer to sufficiently segregate the chromium. On the other hand, the granular magnetic recording layer has a feature where the nonmagnetic and nonmetallic substance segregates even if the substrate heating is omitted. The magnetic recording layer of CoCr and the granular magnetic recording layer can be applied to a perpendicular magnetic recording medium as well, establishing perpendicular anisotropy by controlling crystal alignment in the recording layer with the aid of an underlayer, for example. [0006] In a perpendicular magnetic recording medium, however, it is equally difficult to segrate chromium in the magnetic recording layer using CoCr as in a longitudinal magnetic recording medium. On the hand, a perpendicular magnetic recording layer employing a granular magnetic layer makes chromium separation easier than in the CoCr recording layer. As a result, magnetic interaction between the grains can be suppressed, leading to low media noise. However, the granular magnetic recording layer in a thin film thickness of about 10 nm or less does not give sufficient segregation structure, resulting in poor isolation between grains, and causing media noise. [0007] Because recording in a perpendicular magnetic recording medium is ideally done with a sharp perpendicular magnetic field induced by a magnetic recording head, it is desirable to form the magnetic recording layer as thin as possible. If an initial growth layer with such insufficient segregation is formed, it is difficult to obtain a useful thin magnetic recording layer. Consequently, lower noise and higher recording density have not been attained with granular magnetic recording layers. [0008] Accordingly, there is a need to develop a perpendicular magnetic recording medium that exhibits low noise and high recording density by achieving excellent segregation structure in the magnetic layer. The present invention addresses this need. SUMMARY OF THE INVENTION [0009] The present invention relates to a method of producing a perpendicular magnetic recording medium and to a perpendicular magnetic recording medium produced thereby. Such a perpendicular magnetic recording medium is suitable for mounting on a variety of magnetic recording devices. [0010] One aspect of the present invention is a method of producing a perpendicular magnetic recording medium comprising the steps of sequentially laminating an underlayer, a magnetic recording layer, a protective layer, and a liquid lubricant layer on a nonmagnetic substrate. The magnetic recording layer comprises ferromagnetic crystalline grains and nonmagnetic grain boundary region comprised mainly of oxide or nitride surrounding the crystalline grains. The laminated underlayer is exposed to an atmosphere containing O.sub.2 or N.sub.2 before laminating the magnetic recording layer. The atmosphere can contain rare gas. [0011] The underlayer can be composed of Ru or an alloy of Ru, which can be RuW, RuCu, RuC, RuB, or RuCoCr. A seed layer can be laminated before laminating the underlayer. The seed layer can be composed of a Ni-base alloy, which can be NiFe, NiFeNb, NiFeB, NiFeSi, or NiFeCr. If a seed layer is used, a soft magnetic underlayer can be laminated before the seed layer. The soft magnetic underlayer can be composed of crystalline materials of a NiFe alloy and a Sendust alloy (FeSiAl), fine crystalline materials of FeTaC and CoTaZr, or an amorphous cobalt alloy of CoZrNb. [0012] Another aspect of the present invention is a perpendicular magnetic recording medium produced by the method above. BRIEF DESCRIPTION OF THE DRAWINGS [0013] FIG. 1 is a schematic cross-sectional view illustrating an example of embodiment of a perpendicular magnetic recording medium according to the present invention. [0014] FIG. 2 is a chart showing dependence of magnetic cluster size on the magnetic recording layer thickness obtained from MFM evaluation for Examples 1 and 2 and Comparative Examples 1 and 2. [0015] FIG. 3 is a chart showing dependence of standard deviation of magnetic cluster size on the magnetic recording layer thickness obtained from MFM evaluation for Examples 1 and 2 and Comparative Examples 1 and 2. [0016] FIG. 4 is a chart showing dependence of the normalized media noise in the case of the magnetic recording layer thickness of 15 nm on linear recording density obtained from the evaluation of magnetic parametric performance for Examples 1 and 2 and Comparative Examples 1 and 2. DETAILED DESCRIPTION [0017] Both the magnetic portion and the nonmagnetic and nonmetallic grain boundary region can be simultaneously formed from the initial stage of the recording layer formation, and the ferromagnetic crystalline grains can be magnetically separated. Specifically, an oxide or a nitride can form a nonmagnetic and nonmetallic underlayer. The underlayer is exposed to an atmosphere containing O.sub.2 or N.sub.2 before depositing the granular magnetic recording layer onto the underlayer. The O.sub.2 or N.sub.2 attached on the substrate surface with the underlayer can act as nucleation sites to grow the nonmagnetic and nonmetallic region causing separation of ferromagnetic crystalline grains from the initial growth layer of the magnetic recording layer. [0018] Some aspects of preferred embodiments of the present invention will be described with reference to the accompanied drawings in the following. FIG. 1 is a schematic cross-sectional view illustrating an example of embodiment of a perpendicular magnetic recording medium according to the present invention. The perpendicular magnetic recording medium has a structure comprising at least an underlayer 2, a magnetic layer 3, and a protective layer 4 sequentially formed on a nonmagnetic substrate 1. A liquid lubricant layer 5 is further formed on the layers. [0019] The nonmagnetic substrate 1 can be composed of a NiP-plated aluminum alloy, strengthened glass, or crystallized glass, which are currently being used in a conventional magnetic recording medium. A plastic substrate made of a resin, such as polycarbonate, polyolefin, or the like, also can be used when a temperature of substrate heating is held under about 100.degree. C. [0020] The underlayer 2 is preferably composed of a metal with a hexagonal closest packed (hcp) structure or an alloy of such a metal, or a metal with a face centered cubic (fcc) structure or an alloy of such a metal. The metal with the hcp structure includes Ti, Zr, Ru, Zn, Tc, and Re. The metal with the fcc structure includes Cu, Rh, Pd, Ag, Ir, Pt, Au, Ni, and Co. Of the materials exemplified above, Ru or Ru alloy exhibits excellent effect because of weak reactivity when exposed to O.sub.2 or N.sub.2. Although a thin film is desirable, a thickness at least 3 nm is preferable, which thickness of crystal growth provides acceptable mass or structure. Continue reading... Full patent description for Method of producing a magnetic recording medium and a magnetic recording medium formed thereby Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Method of producing a magnetic recording medium and a magnetic recording medium formed thereby patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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