WO2004068390A2 - Magnetic recording medium, production process thereof, and magnetic recording and reproducing apparatus - Google Patents

Magnetic recording medium, production process thereof, and magnetic recording and reproducing apparatus Download PDF

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Publication number
WO2004068390A2
WO2004068390A2 PCT/JP2004/000806 JP2004000806W WO2004068390A2 WO 2004068390 A2 WO2004068390 A2 WO 2004068390A2 JP 2004000806 W JP2004000806 W JP 2004000806W WO 2004068390 A2 WO2004068390 A2 WO 2004068390A2
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WO
WIPO (PCT)
Prior art keywords
magnetic
recording medium
layer
based alloy
magnetic recording
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PCT/JP2004/000806
Other languages
French (fr)
Other versions
WO2004068390A3 (en
Inventor
Hiroshi Osawa
Original Assignee
Showa Denko K.K.
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Publication date
Priority claimed from JP2003025211A external-priority patent/JP2004265462A/en
Application filed by Showa Denko K.K. filed Critical Showa Denko K.K.
Publication of WO2004068390A2 publication Critical patent/WO2004068390A2/en
Publication of WO2004068390A3 publication Critical patent/WO2004068390A3/en

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Classifications

    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/84—Processes or apparatus specially adapted for manufacturing record carriers
    • G11B5/8404—Processes or apparatus specially adapted for manufacturing record carriers manufacturing base layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/7368—Non-polymeric layer under the lowermost magnetic recording layer
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/7368—Non-polymeric layer under the lowermost magnetic recording layer
    • G11B5/7369—Two or more non-magnetic underlayers, e.g. seed layers or barrier layers
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73911—Inorganic substrates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73911—Inorganic substrates
    • G11B5/73913—Composites or coated substrates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73911—Inorganic substrates
    • G11B5/73917—Metallic substrates, i.e. elemental metal or metal alloy substrates
    • G11B5/73919—Aluminium or titanium elemental or alloy substrates
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
    • G11B5/62—Record carriers characterised by the selection of the material
    • G11B5/73—Base layers, i.e. all non-magnetic layers lying under a lowermost magnetic recording layer, e.g. including any non-magnetic layer in between a first magnetic recording layer and either an underlying substrate or a soft magnetic underlayer
    • G11B5/739—Magnetic recording media substrates
    • G11B5/73911—Inorganic substrates
    • G11B5/73921—Glass or ceramic substrates

Definitions

  • the present invention relates to a magnetic recording medium for use in a hard disk drive or a similar apparatus, to a method for producing the magnetic recording medium, and to a magnetic recording and reproducing apparatus.
  • HDD hard disk drive
  • Such a magnetic recording medium must have an increased recording density, and therefore, the recording medium is required to have enhanced coercive force and reduced noise.
  • a mainstream magnetic recording medium employed in a hard disk drive has a structure in which a metallic film is stacked on a magnetic recording medium substrate through sputtering.
  • Substrates employed as magnetic recording medium substrates includes an aluminum substrate and a glass substrate, which are widely used.
  • a typically employed aluminum substrate is produced by forming Ni-P-based alloy film having a thickness of about 10 ⁇ m on a mirror-polished Al-Mg alloy substrate through electroless plating, and mirror-polishing the surface.
  • the glass substrate an amorphous glass substrate and a glass-ceramic substrate are employed. Either type of glass substrate is mirror-polished prior to use.
  • magnetic recording media which are generally used in a hard disk drive have a structure in which a non-magnetic undercoat layer (e.g., Ni-Al-based alloy, Cr, or Cr alloy), a non-magnetic intermediate layer (e.g., Co-Cr or Co-Cr-Ta-based alloy), a magnetic layer (e.g., Co-Cr-Pt-Ta-based alloy or Co-Cr-Pt-B-based alloy), and a protective layer (e.g., carbon) are sequentially formed on a non-magnetic substrate, the protective layer being coated with a lubricant layer formed from a liquid lubricant.
  • a non-magnetic undercoat layer e.g., Ni-Al-based alloy, Cr, or Cr alloy
  • a non-magnetic intermediate layer e.g., Co-Cr or Co-Cr-Ta-based alloy
  • a magnetic layer e.g., Co-Cr-Pt-Ta-based
  • Alloys such as Co-Cr-Pt-Ta-based alloy and Co-Cr-Pt-B-based alloy employable in the magnetic layer predominantly contain Co.
  • Co alloys have a hexagonal closest packed structure (hep structure) in which the C axis serves as an easy-magnetization axis.
  • Recording types of magnetic recording media include longitudinal recording and perpendicular recording, and a magnetic layer thereof generally employs Co alloy.
  • the C axis of the Co alloy In a longitudinal magnetic recording medium, the C axis of the Co alloy is oriented parallel to the non-magnetic substrate, whereas in a perpendicular magnetic recording medium, the C axis of the Co alloy is oriented perpendicular to the non-magnetic substrate. Therefore, in the case of longitudinal recording, the Co alloy layer preferably assumes the (10 ) or (11 -0) crystal plane at the surface thereof.
  • the symbol " • " in each pair of parentheses representing the crystal plane denotes the abbreviation of a Miller-Bravais index showing a crystal plane.
  • the crystal planes of a hexagonal system such as Co are generally represented by four index elements; i.e., (hkil).
  • index elements i.e., (hkil).
  • the notation (hikl) is represented by (hk-1) through abbreviation of the "i.”
  • the Co alloy magnetic layer preferably assumes the (00T) crystal plane at the surface thereof.
  • the presence of the (10-1) and (00-1) crystal planes of the Co alloy, which contain a perpendicular component, in the magnetic layer is not preferred, since magnetization in the longitudinal direction tends to decrease.
  • an undercoat layer made of Cr alloy having a body-centered cubic structure (bcc structure) is generally employed.
  • the (11 ) plane of the Co alloy tends to be present on the (100) plane of the Cr alloy, and the (10-0) plane of the Co alloy tends to be present on the (112) plane of the Cr alloy.
  • an undercoat layer made of Cr alloy is formed on the alloy plating film, whereby the (100) crystal plane of the Cr alloy tends to be present on the undercoat layer.
  • a magnetic layer made of Co alloy is epitaxially grown on the Cr alloy layer, the Co alloy magnetic layer assumes the (11 -0) crystal plane.
  • the crystal plane Since the C axis serving as an easy-magnetization axis present in the (10-1) crystal plane of the Co alloy has both longitudinal and perpendicular vector components, the crystal plane is not suited for longitudinal recording and perpendicular recording.
  • the magnetic recording medium disclosed in European Patent Application EP 0704839 Al has an undercoat layer formed of an Al alloy of B2 structure (Al-Ni-based alloy, Al-Co-based alloy, Al-Fe-based alloy, etc.).
  • the magnetic layer of the recording medium has a crystal grain size reduced by virtue of Al-Ni-based alloy, Al-Co-based alloy, etc., and noise reduction has been confirmed.
  • Al alloys the Al-Ni-based alloy is employed in practice in a non-magnetic undercoat layer.
  • the crystal lattice of the (112) plane of the Al-Ni-based alloy and that of the (10-0) crystal plane of the Co alloy forming the magnetic layer are highly matched with each other, whereby the (10-0) crystal plane of the Co alloy is epitaxially grown on the (112) plane of the Al-Ni-based alloy.
  • the Co alloy magnetic layer assumes the (10 ) crystal plane, thereby attaining high coercive force.
  • Japanese Patent No. 3217012 has proposed a technique for promoting epitaxial growth of the (11*0) crystal plane of a Co alloy forming the magnetic layer, the technique including forming an undercoat layer predominantly containing Co under the Cr alloy layer so as to grow the (100) plane of the Cr alloy layer.
  • Japanese Patent Application Laid-Open (kokai) No. 2000-113443 does not particularly mention the crystal plane of the layer surface, it has proposed a technique for enhancing SNR (signal to noise ratio) characteristics of a magnetic recording medium by forming a Cr-based layer formed of a Cr-P-based alloy or a Cr-Mo-P-based alloy between the non-magnetic substrate (e.g., glass, carbon, or silicon) and the Cr-based non-magnetic undercoat layer.
  • the non-magnetic substrate e.g., glass, carbon, or silicon
  • the technique including employment of an Al alloy of B2 structure Al-Ni-based alloy, Al-Co-based alloy, Al-Fe-based alloy, etc.
  • the (112) peak attributed to the Al-Ni-based alloy is weak, . and the surface of the alloy layer might not sufficiently assume the (112) plane.
  • the thickness of the Al-Ni-based alloy layer must be increased in order to assume the (112) plane of the Al-Ni-based alloy. Therefore, the Al-Ni-based alloy has an increased grain size, which is problematic.
  • the Cr alloy layer assumes the (100) plane, and epitaxial growth of the (11-0) plane of the Co alloy forming the magnetic layer is observed on the (100) plane.
  • the Cr alloy layer has an unsatisfactorily reduced grain size, and a certain limit is imposed on reduction of media noise.
  • the present invention has been accomplished in view of the foregoing, and an object of the present invention is to provide a magnetic recording medium which can enhance magnetic anisotropy and has excellent magnetic characteristics and read- write performance. Another object of the invention is to provide a method for producing the magnetic recording medium. Still another object of the invention is to provide a magnetic recording and reproducing apparatus.
  • DISCLOSURE OF INVENTION The present inventor has conducted extensive studies in an attempt to solve the aforementioned problems, and has found that the characteristics of a magnetic recording medium can be enhanced by employing a non-magnetic undercoat layer formed of an Mo-P-based alloy containing Mo and P. The present invention has been accomplished on the basis of this finding. Accordingly, the present invention is directed to the following.
  • a magnetic recording medium including at least a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in this order, on a non-magnetic substrate, characterized in that the non-magnetic undercoat layer contains an Mo-P-based alloy.
  • a magnetic recording medium characterized in that the recording medium is produced through a method for producing a magnetic recording medium as recited in (12) or (13).
  • a magnetic recording and reproducing apparatus having a magnetic recording medium as recited in any one of (1) to (10) and (14), and a magnetic head for recording information in the magnetic recording medium and reproducing information from the magnetic recording medium.
  • 1 Oe is approximately 79 A/m.
  • the term "-based” refers to the case in which a substance may contain a component other than the literally described component.
  • the "Mo-P-based alloy” may contain a component other than Mo and P.
  • FIG. 1 is a cross-section of a first embodiment of the magnetic recording medium of the present invention.
  • FIG. 2 is a cross-section of a second embodiment of the magnetic recording medium of the present invention.
  • FIG. 3 is a cross-section of a third embodiment of the magnetic recording medium of the present invention.
  • FIG. 4 is a schematic view of an exemplary magnetic recording and reproducing apparatus according to the present invention.
  • FIG. 1 schematically shows a first embodiment of the magnetic recording medium of the present invention.
  • a non-magnetic undercoat layer 2 In the magnetic recording medium as shown in FIG. 1, a non-magnetic undercoat layer 2, a magnetic layer 5, and a protective layer 6 are sequentially stacked in this order on a non-magnetic substrate 1.
  • the non-magnetic substrate 1 is preferably a glass substrate which is generally employed as a substrate for a magnetic recording medium or is preferably an aluminum alloy substrate having an Ni-P-based alloy plating film thereon (hereinafter referred to as an Ni-P-plated Al substrate).
  • non-magnetic substrate further include substrates formed of a non-metallic material such as ceramics, silicon, silicon carbide, carbon, or resin.
  • a substrate formed of such a nonmetallic material and coated with anNiP film or an Ni-P-based alloy film may also be used.
  • the non-magnetic substrate 1 desirably has enhanced surface flatness. Specifically, the non-magnetic substrate 1 desirably has a surface roughness (Ra) of 2 nm or less, preferably 1 nm or less.
  • the non-magnetic substrate 1 preferably has a surface micro-waviness (Wa) of 0.3 mn or less (more preferably 0.25 nm or less), because the flying height of the magnetic head during recording and reproducing can be reduced, which is suited for high-density recording.
  • the micro-waviness (Wa) can be determined by means of, for example, a surface roughness meter (P-12, product of KLa-Tencor) as an average surface roughness value as measured in a range of 80 ⁇ m.
  • At least one of a ch-tmfer section of the end surface and a side surface of the non-magnetic substrate preferably has a surface roughness (Ra) of 10 nm or less (more preferably 9.5 nm or less), from the viewpoint of flying stability of a magnetic head.
  • the non-magnetic substrate 1 is preferably a glass substrate, from the viewpoints of cost and durability.
  • a glass substrate or a silicon substrate are preferably used, from the viewpoint of surface flatness.
  • the non-magnetic substrate 1 may be formed of aluminum or silicon.
  • a substrate formed of aluminum or silicon which is plated with an Ni-P-based alloy film can also be employed.
  • glass materials which can be employed as the substrate include glass ceramics and amorphous glass.
  • amorphous glass which can be used include generally used soda-lime glass, aluminoborosilicate glass, and aluminosilicate glass.
  • glass ceramics which can be used include lithium-containing glass ceramics.
  • groove lines are formed on a surface of the non-magnetic substrate 1.
  • formation of groove lines is particularly preferred.
  • magnetic characteristics e.g., coercive force
  • read-write performance e.g., SNR (signal to noise ratio), PW50
  • the groove lines are preferably formed in a generally circumferential direction of the substrate 1, from the viewpoint of enhancement of magnetic anisotropy in a circumferential direction of the magnetic recording medium.
  • the groove lines are preferably formed such that the processed surface has a surface roughness — average level gap between the ' top level and the bottom level as viewed in the cross-section in the radial direction — of 0.02 nm to 20 nm (more preferably 0.05 nm to 10 nm).
  • the line density of the groove lines is preferably 7,500 lines/mm or more (preferably 20,000 lines/mm or more).
  • the groove lines can be formed through, for example, mechanical texturing by use of a lapping tape employing fixed abrasive grains, or by use of free abrasive grains.
  • the ceramic substrate examples include a sintered product predominantly containing generally used alumina, silicon nitride, or a similar compound, and a fiber-reinforced product thereof.
  • the non-magnetic undercoat layer 2 has a stacked structure containing a first undercoat layer 3 formed close to the non-magnetic substrate 1, and a second undercoat layer 4 formed on the first undercoat layer 3.
  • the first undercoat layer 3 disposed close to the non-magnetic substrate 1 is an Mo-P-based alloy layer formed of an Mo-P-based alloy.
  • the non-magnetic undercoat layer may have a single-layer structure or a stacked structure having three or more layers.
  • the non-magnetic undercoat layer is provided so as to contain an Mo-P-based alloy
  • the stacked structure having two or more layers is employed, at least one layer among the plurality of layers (preferably the layer disposed most close to the non-magnetic substrate) is provided so as to contain an Mo-P-based alloy.
  • the Mo-P-based alloy forming the first undercoat layer 3 preferably has an Mo content falling within a range of 30 to 90 at.%, a P content falling within a range of 10 to 60 at.%, and a total content of Mo and P falling within a range of 60 to 100 at.%.
  • the layer disposed directly on the first undercoat layer i.e., second undercoat layer 4
  • the layer disposed directly on the first undercoat layer has a large crystal grain size, thereby deteriorating SNR characteristics.
  • the Mo-P-based alloy forming the non-magnetic undercoat layer 2 may contain an additional element having an auxiliary effect (e.g., enhancing orientation, grain-size reduction, or similar effect on the second undercoat layer 4 and the magnetic layer 5).
  • additional element include one or more species selected from among Ti, V, Cr, Mn, Zr, Hf, Ru, B, Al, Si, and W.
  • the total content of the additional elements is preferably 40 at.% or less. When the total content is in excess of 40 at.%, the aforementioned effect (enhancing orientation or grain-size-reduction) is reduced. Thus, the total content is preferably controlled to 0.1 at.% or more. When the content is less than 0.1 at.%, the aforementioned effect is reduced.
  • the first undercoat layer 3 can be formed through DC or RF magnetron sputtering using a sputtering target.
  • Ar gas is generally employed as a sputtering gas for discharge.
  • the pressure of the sputtering gas is preferably 0.1 Pa to 5 Pa.
  • the second undercoat layer 4 may be a Cr layer formed of Cr.
  • the layer 4 may be a Cr alloy layer formed of a Cr alloy containing Cr and one or more species selected from among Ti, Mo, Al, Ta, W, Ni, B, Si, and V.
  • Cr alloys a Cr-Mo-based alloy, a Cr-W-based alloy, a Cr-V-based alloy, and a Cr-Ti-based alloy are particularly preferred.
  • the lattice constant of the second undercoat layer 4 can be regulated to a value proximate to that of the magnetic layer 5, as compared with the second undercoat layer formed fiom a Cr layer.
  • the degree of lattice matching between the second undercoat layer 4 and the magnetic layer 5 can be enhanced, thereby enhancing SNR characteristics.
  • the second undercoat layer 4 preferably assumes, as a preferential crystal plane, the (100) plane at the surface layer 4.
  • the Co alloy magnetic layer 5 assumes the (11-0) plane more preferentially, thereby enhancing magnetic characteristics (e.g., coercive force (He)) and recording-reproducing characteristics (e.g., SNR).
  • the magnetic layer 5 is preferably formed from a Co alloy predominantly containing Co, the alloy being a material which attains high lattice matching with a crystal plane present in the non-magnetic undercoat layer 2; e.g., the (100) plane, and which has an hep structure.
  • the magnetic layer preferably contains one or more species selected from among a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-based alloy, and a Co-Cr-Pt-B-X-based alloy (wherein X is Ta or Cu).
  • the magnetic layer contain one or more species selected from among a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-Ta-based alloy, and a Co-Cr-Pt-B-Cu-based alloy being particularly preferred.
  • a Cr content of 5 at.% to 25 at.% and a Ta content of 1 at.% to 10 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
  • a Cr content of 10 at.% to 25 at.% and a Pt content of 8 at.% to 16 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
  • a Cr content of 10 at.% to 25 at.%, a Pt content of 8 at.% to 16 at.%, and a B content of 1 at.% to 20 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
  • a Cr content of 10 at.% to 25 at.%, a Pt content of 8 at.% to 16 at.%, a B content of 1 at.% to 20 at.%, and a Ta content of 1 at.% to 4 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
  • the B content more preferably falls within a range of 2 at.% to 20 at.%.
  • a Cr content of 10 at.% to 25 at.%, a Pt content of 8 at.% to 16 at.%, a B content of 2 at.% to 20 at.%, and a Cu content of 1 at.% to 4 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
  • the magnetic layer 5 preferably have a thickness of 10 nm or more (preferably 15 nm or more) from the viewpoint of thermal stability characteristics. From the viewpoint of high recording density, the thickness is preferably 40 nm or less. This is because, when the thickness is in excess of 40 nm, the magnetic layer 5 has a large grain size, thereby failing to attain favorable recording and reproducing characteristics.
  • the magnetic layer 5 may have a single-layer structure or a multi-layer structure.
  • the aforementioned materials a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-based alloy, and a Co-Cr-Pt-B-X-based alloy ) for forming each layer can also be used.
  • a component layer which is in direct contact with the non-magnetic undercoat layer 2 is preferably formed of a Co-Cr-Pt-B-Ta-based alloy, a Co-Cr-Pt-B-Cu-based alloy, or a Co-Cr-Pt-B-based alloy, from the viewpoint of improvement of recording and reproducing characteristics (particularly SNR characteristics).
  • the uppermost layer is preferably formed of a Co-Cr-Pt-B-Cu-based alloy or a Co-Cr-Pt-B-based alloy from the viewpoint of improvement of recording and reproducing characteristics (particularly SNR characteristics).
  • the protective layer 6 can be formed from conventionally known materials predominantly containing, for example, carbon or SiC.
  • the protective layer 6 preferably has a thickness of 1 nm to 10 nm from the viewpoint of spacing loss upon use for recording and reproducing and durability of the medium.
  • a lubrication layer formed of a fluorine-containing lubricant such as perfluoropolyether may be provided in accordance with needs.
  • Groove lines are preferably formed on a surface of the non-magnetic substrate 1.
  • the groove lines are preferably formed through, for example, mechanical texturing by use of a lapping tape employing fixed abrasive grains or by use of free abrasive grains.
  • a surface of the substrate 1 is brought into contact with an abrasive tape and pressed against the tape.
  • An abrasive slurry containing abrasive grains is fed to a sliding contact surface of the substrate 1 and the abrasive tape.
  • the substrate 1 is rotated, and the abrasive tape is moved on the substrate 1.
  • the texturing can be performed along with oscillation.
  • oscillation refers to an operation of oscillating an abrasive tape in a radial direction of the substrate 1 while the abrasive tape is moved on the substrate 1 in a circumferential direction.
  • the oscillation speed is preferably 60 cycles/min to 1,200 cycles/minute, since the surface of the substrate is uniformly polished in amount through texturing.
  • a texturing method employing immobilized abrasives there may be employed a texturing method employing immobilized abrasives, a texturing method employing an immobilized grinding wheel, a laser processing, etc.
  • the non-magnetic substrate 1 is placed in a chamber of a film formation apparatus (sputtering apparatus).
  • the non-magnetic substrate 1 is heated to 100°C to 400°C in accordance with needs.
  • a first undercoat layer 3, a second undercoat layer 4, and a magnetic layer 5 are formed on the non-magnetic substrate 1.
  • the chamber can be evacuated to 1 x 10 " Pa to 1 x 10 " Pa.
  • Ar can be used as a sputtering gas.
  • the electric power supplied is preferably 0.2 kW to 2.0 kW. By controlling the discharge time and the supplied electric power, the thickness of the formed film can be adjusted.
  • Each layer can be formed by use of a sputtering target having a composition identical to that of the material of each layer.
  • the surface of the undercoat layer 3 is preferably exposed to an oxygen-containing gas.
  • the oxygen-containing gas preferably has an oxygen partial pressure 5 x 10 "4 Pa or higher, preferably 5 x 10 "3 Pa to 5 x 10 "2 Pa.
  • air is preferred.
  • a water-containing gas may also be employed as the oxygen-containing gas.
  • the exposure time preferably falls within a range of 0.5 seconds to 15 seconds.
  • the exposure treatment may be performed through a method including removing the substrate 1 on which the first undercoat layer 3 has been formed from the chamber and exposing the substrate to air or an oxygen-containing gas.
  • the treatment may also be preformed without removing the substrate 1 from the chamber and by feeding an oxygen-containing gas (e.g., air) into the chamber.
  • the method including exposing the first undercoat layer 3 to an oxygen-containing gas in the chamber effectively produces the magnetic recording medium, since removal of the substrate 1 from the chamber can be omitted.
  • an oxygen-containing gas having an oxygen partial pressure of 5 x 10 "4 Pa or higher is preferably used in the chamber under a vacuum lower than 1 x 10 "5 Pa.
  • the oxygen partial pressure of the oxygen-containing gas during exposure treatment is preferably controlled to 5 x 10 " Pa or lower.
  • the magnetic layer 5 formed from a B-containing alloy e.g., Co-Cr-Pt-B-based alloy or Co-Cr-Pt-B-X-based alloy
  • the magnetic layer 5 is preferably formed such that the Cr content of a region having a B content of 1 at.% or more is controlled to be 40 at.% or less, in the vicinity of the interface between the non-magnetic undercoat layer 2 and the magnetic layer 5.
  • a protective layer 6 is formed through a conventionally known method such as sputtering, plasma CVD, or a combination thereof.
  • a lubrication layer can be formed through a conventionally known method such as spin coating or dipping.
  • the magnetic layer 5 can be imparted with high magnetic anisotropy.
  • magnetic characteristics e.g., coercive force
  • read-write performance e.g., SNR (signal to noise ratio), PW50
  • SNR signal to noise ratio
  • FIG. 2 shows a second embodiment of the magnetic recording medium of the present invention.
  • a non-magnetic intermediate layer 7 is provided between a non-magnetic undercoat layer 2 and a magnetic layer 5, in order to promote epitaxial growth of a Co alloy forming the magnetic layer 5.
  • the non-magnetic intermediate layer 7 preferably contains Co and Cr; comprises a Co-Cr-based alloy.
  • the Cr content preferably falls within a range of 25 at.% to 45 at.% from the viewpoint of enhancement of SNR.
  • the non-magnetic intermediate layer 7 preferably has a thickness falling within a range of 0.5 nm to 3 nm from the viewpoint of enhancement of SNR.
  • the magnetic recording medium exhibits improved magnetic characteristics (e.g., coercive force) and improved recording-reproducing characteristics (e.g., SNR).
  • improved magnetic characteristics e.g., coercive force
  • improved recording-reproducing characteristics e.g., SNR
  • FIG. 3 shows a third embodiment of the magnetic recording medium of the present invention.
  • an anti-ferromagnetic coupling layer 8 is provided between a non-magnetic undercoat layer 2 and a magnetic layer 5, in order to improve thermal decay.
  • the anti-ferromagnetic coupling layer 8 may be formed of a non-magnetic coupling layer 10 provided on a stabilizing layer 9.
  • the stabilizing layer 9 can be formed from a magnetic material such as a Co-Ru-based alloy, a Co-Cr-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-B-based alloy, or a Co-Cr-Ta-based alloy.
  • the non-magnetic coupling layer 10 is preferably formed from Ru.
  • the thickness of the non-magnetic coupling layer 10 is preferably about 0.8 nm (e.g., 0.6 nm to 1.0 nm), so as to attain the maximum value of anti-ferromagnetic coupling.
  • the magnetic recording medium includes an anti-ferromagnetic coupling layer 8 Since the magnetic recording medium includes an anti-ferromagnetic coupling layer 8, excellent thermal stability is attained.
  • FIG. 4 shows an exemplary magnetic recording and reproducing apparatus employing the aforementioned magnetic recording medium.
  • the magnetic recording and reproducing apparatus as shown in FIG. 4 includes a magnetic recording medium 20 as described in any of the aforementioned embodiments, a medium-driving member 21 for rotating the magnetic recording medium 20, a magnetic head 22 for recording information in and reproducing information from the magnetic recording medium 20, a head-driving member 23 for moving the magnetic head 22 relative to the magnetic recording medium 20, and a record reproduction signal processing system 24.
  • the record reproduction signal processing system 24 is provided such that data input from the outside is processed to transmit a record signal to the magnetic head 22 and that a reproduction signal obtained from the magnetic head 22 is processed to transmit data to the outside.
  • Examples of elements which can be used to serve as the magnetic head 22 include elements having, as a reproduction element, a magnetoresistance (MR) element based on anisotropic magnetoresistance (AMR) or a giant magnetoresistance (GMR) element based on giant magnetoresistance (GMR). Recording density can be increased through employment of a GMR element.
  • MR magnetoresistance
  • AMR anisotropic magnetoresistance
  • GMR giant magnetoresistance
  • GMR giant magnetoresistance
  • the magnetic layer 5 included in the recording medium can be imparted with high magnetic anisotropy, and thus excellent magnetic characteristics and read-write performance can be attained, thereby enhancing recording density.
  • a magnetic recording medium having a structure shown in FIG. 2 was fabricated.
  • a glass substrate (amorphous glass GD-7, product of NIPPON SHEET GLASS) was employed as the non-magnetic substrate 1.
  • the substrate 1 had the following dimensions: outer diameter of 65 mm, inner diameter of 20 mm, and thickness of 0.635 mm.
  • the substrate 1 was subjected to mechanical texturing under the following conditions.
  • Abrasive grains contained in an abrasive slurry employed were diamond abrasive grains having a D90 (grain size value when the cumulative mass percent is 90 mass%) of 0.15 ⁇ m.
  • the slurry was added dropwise at 50 mL/minute for two seconds before the start of texturing.
  • the substrate 1 was rotated, and an abrasive tape made of polyester fabric was moved on the substrate 1.
  • the abrasive tape was fed at 75 mm/niinute, and the substrate 1 was rotated at 600 rpm.
  • the oscillation speed was 120 cycles/min.
  • the pressure of the tape was 2.0 kgf (19.6 N).
  • the texturing time was 10 seconds.
  • the substrate 1 was placed in a DC magnetron sputtering apparatus (C3010, product of ANELVA (Japan)), and the chamber was evacuated to 2 x 10 "7 Torr (2.7 x 10 "5 Pa). Subsequently, by use of an Mo-P alloy (Mo: 90 at.% and P: 10 at.%) target, a first undercoat layer 3 (thickness: 5 nm) formed of the Mo-P alloy was formed at room temperature.
  • a DC magnetron sputtering apparatus C3010, product of ANELVA (Japan)
  • the substrate 1 was heated to 250°C, and the first undercoat layer 3 was exposed to oxygen gas which was fed into the chamber.
  • the oxygen partial pressure and the exposure time were controlled to 0.05 Pa and 5 seconds, respectively.
  • a second undercoat layer 4 (thickness: 8 nm) was formed by use of a target formed of a Cr-Ti-B alloy (Cr: 83 at.%, Ti: 15 at.%, and B 2 at.%).
  • a non-magnetic intermediate layer 7 (thickness: 2 nm) was formed by use of a target formed of a Co-Cr alloy (Co: 65 at.% and Cr: 35 at.%).
  • a magnetic layer 5 (thickness: 20 nm) formed of a CoCrPtB alloy layer was formed by use of a target formed of a Co-Cr-Pt-B alloy (Co: 60 at.%, Cr: 22 at.%, Pt: 12 at.%, and B: 6 at.%).
  • a protective layer 6 (thickness: 5 nm) formed of carbon was formed.
  • Ar was used as a sputtering gas, and the pressure thereof was adjusted to 3 mTorr (0.4 Pa).
  • a lubricant formed of perfluoropolyether was applied through dip coating to the surface of the protective layer so as to form a lubrication layer (thickness: 2 nm), to thereby produce a magnetic recording medium.
  • Example 1 The procedure of Example 1 was repeated, except that the composition and thickness of the first undercoat layer 3 were changed as shown in Table 1, to thereby fabricate magnetic recording media.
  • a magnetic recording medium having a structure shown in FIG. 3 was fabricated.
  • an Mo-P alloy Mo: 70 at.% and P: 30 at.%) target, a first undercoat layer 3 (thickness: 5 nm) was formed at room temperature.
  • an anti-ferromagnetic coupling layer 8 was formed instead of a non-magnetic intermediate layer 7, an anti-ferromagnetic coupling layer 8 was formed.
  • a stabilizing layer 9 (thickness: 2 nm) was formed by use of a Co-Ru alloy (Co: 80 at.% and Ru: 20 at.%) target.
  • a non-magnetic coupling layer 10 (thickness: 0.8 nm) was formed by use of an Ru target. Regarding other conditions, the same conditions as employed in Example 1 were employed.
  • Example 1 The procedure of Example 1 was repeated, except that the glass substrate was not subjected to mechanical texturing, to thereby fabricate a magnetic recording medium.
  • Example 22 The procedure of Example 22 was repeated, except that the composition and thickness of the first undercoat layer 3 were changed as shown in Table 1, to thereby fabricate magnetic recording media.
  • Magnetic recording media were fabricated by changing the first undercoat layer 3 to a Cr-Mo-P-based alloy layer formed of a Cr-Mo-P-based alloy. Regarding other conditions, the same conditions as employed in Example 1 were employed.
  • Example 22 The procedure of Example 22 was repeated, except that the composition and thickness of the Cr-Mo-P-based alloy layer were changed as shown in Table 2, to thereby fabricate a magnetic recording medium.
  • Each of magnetic recording media produced in the above Examples and Comparative Examples was subjected to a glide test by use of a glide tester, with the glide height being adjusted to 0.4 ⁇ inch (1 microinch nearly equal to 25.4 nm).
  • the recording media which had passed the test were further investigated in terms of record reproduction characteristics by use of a read- write analyzer RWA 1632 (product of GUZIK (USA)).
  • the record reproduction characteristics were investigated in terms of read- write performance including read output (TAA), half- width of isolated read pulse power (PW50), SNR, and overwrite (OW).
  • the record reproduction characteristics were evaluated by means of a complex thin-film magnetic recording head having a giant magnetoresistance (GMR) element at a readout portion.
  • GMR giant magnetoresistance
  • Coercive force (He) and squareness ratio (S*) were determined by use of a Kerr effect magnetic characteristics analyzer (RO1900, product of Hitachi Electronics Engineering (Japan)).
  • Magnetic anisotropy index of coercive force (OR) and that of residual magnetization (MrtOR) were determined by use of a VSM (BHV-35, product of (Riken Denshi Co., Ltd. (Japan)).
  • T thickness
  • He coercive force
  • S* squareness ratio
  • T thickness
  • He coercive force
  • S* squareness ratio
  • the test results of magnetic recording media of Examples 1 to 5 revealed that excellent read- write performance was attained when the P content of the first undercoat layer 3 (Mo-P-based alloy layer) was 10 to 50 at.%. When the P content fell within a range of 20 to 40 at.%, more excellent read- write performance was attained.
  • test results of magnetic recording media of Examples 3 and 6 to 10 revealed that excellent magnetic anisotropy in a circumferential direction and read- rite performance were attained when the thickness of the first undercoat layer 3 formed of an Mo-P-based alloy (Mo: 70 at.% and P: 30 at.%) was 2.5 to 30 nm. When the thickness fell within a range of 2.5 to 10 nm, more excellent magnetic anisotropy in a circumferential direction and read- write performance were attained.
  • the test results of magnetic recording media of Examples 11 to 20 revealed that excellent read- write performance was attained when the Mo-P-based alloy contained a third element and the third element was any of Ti, V, Cr, Mn, Zr, Ru, B, Al, Si, and W.
  • the magnetic recording media of Examples 22 to 26 were fabricated without mechanical texturing of the glass substrate 1 , no anisotropy was identified.
  • the magnetic recording media of Examples 22 to 26 exhibited magnetic characteristics inferior to those of the magnetic recording media of Examples 1 to 21, but exhibited excellent read- write performance as compared with the magnetic recording medium of Comparative Example 3 employing a Cr-Mo-P-based alloy.
  • the magnetic recording media of Comparative Examples 1 to 3 employed a Cr-Mo-P-based alloy instead of an Mo-P-based alloy. Even when these recording media were subjected to mechanical texturing of the glass substrate (Comparative Examples 1 and 2) or were not subjected to the texturing (Comparative Example 3), these recording media exhibited magnetic characteristics inferior to those of the magnetic recording media of Examples.
  • the magnetic recording medium according to the present invention has a non-magnetic undercoat layer containing an Mo-P-based alloy.
  • the magnetic layer provided on the non-magnetic undercoat layer can be imparted with high magnetic anisotropy.
  • magnetic characteristics e.g., coercive force
  • read-write performance e.g., SNR and PW50

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Abstract

The object of the present invention is to provide a magnetic recording medium which can enhance magnetic anisotropy and has excellent magnetic characteristics amd read-write performance; a method for producing the magnetic recording medium; and a magnetic recording and reproducing apparatus. In order to achieve the object, the present invention provides a magnetic recording medium including at least a non-magnetic undercoat layer 2, a magnetic layer 5, and a protective layer 6, in this order, on a non-magnetic substrate 1, wherein the non-magnetic undercoat layer 2 contains an Mo-P based alloy.

Description

DESCRIPTION
MAGNETIC RECORDING MEDIUM, PRODUCTION PROCESS THEREOF, AND MAGNETIC RECORDING AND REPRODUCING APPARATUS
CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit pursuant to 35 U.S.C. §119 (e) of U.S. Provisional Application No. 60/445859 filed on February 10, 2003.
TECHNICAL FIELD The present invention relates to a magnetic recording medium for use in a hard disk drive or a similar apparatus, to a method for producing the magnetic recording medium, and to a magnetic recording and reproducing apparatus.
BACKGROUND ART
At present, recording density of a hard disk drive (HDD) — a type of magnetic recording and reproducing apparatus — is increasing at a rate of 60% per year, and this tendency is expected to continue. In this connection, development of a magnetic recording head and a magnetic recording medium suitable for high recording density is under way.
Such a magnetic recording medium must have an increased recording density, and therefore, the recording medium is required to have enhanced coercive force and reduced noise.
A mainstream magnetic recording medium employed in a hard disk drive has a structure in which a metallic film is stacked on a magnetic recording medium substrate through sputtering.
Substrates employed as magnetic recording medium substrates includes an aluminum substrate and a glass substrate, which are widely used. A typically employed aluminum substrate is produced by forming Ni-P-based alloy film having a thickness of about 10 μm on a mirror-polished Al-Mg alloy substrate through electroless plating, and mirror-polishing the surface. Regarding the glass substrate, an amorphous glass substrate and a glass-ceramic substrate are employed. Either type of glass substrate is mirror-polished prior to use. At present, magnetic recording media which are generally used in a hard disk drive have a structure in which a non-magnetic undercoat layer (e.g., Ni-Al-based alloy, Cr, or Cr alloy), a non-magnetic intermediate layer (e.g., Co-Cr or Co-Cr-Ta-based alloy), a magnetic layer (e.g., Co-Cr-Pt-Ta-based alloy or Co-Cr-Pt-B-based alloy), and a protective layer (e.g., carbon) are sequentially formed on a non-magnetic substrate, the protective layer being coated with a lubricant layer formed from a liquid lubricant.
Alloys such as Co-Cr-Pt-Ta-based alloy and Co-Cr-Pt-B-based alloy employable in the magnetic layer predominantly contain Co. Generally, Co alloys have a hexagonal closest packed structure (hep structure) in which the C axis serves as an easy-magnetization axis. Recording types of magnetic recording media include longitudinal recording and perpendicular recording, and a magnetic layer thereof generally employs Co alloy. In a longitudinal magnetic recording medium, the C axis of the Co alloy is oriented parallel to the non-magnetic substrate, whereas in a perpendicular magnetic recording medium, the C axis of the Co alloy is oriented perpendicular to the non-magnetic substrate. Therefore, in the case of longitudinal recording, the Co alloy layer preferably assumes the (10 ) or (11 -0) crystal plane at the surface thereof.
As used herein, the symbol "•" in each pair of parentheses representing the crystal plane denotes the abbreviation of a Miller-Bravais index showing a crystal plane. Specifically, the crystal planes of a hexagonal system such as Co are generally represented by four index elements; i.e., (hkil). Among the elements, "i" is defined as i = -(h + k). Thus, the notation (hikl) is represented by (hk-1) through abbreviation of the "i."
In the case of perpendicular recording, the Co alloy magnetic layer preferably assumes the (00T) crystal plane at the surface thereof. However, in the case of longitudinal recording, the presence of the (10-1) and (00-1) crystal planes of the Co alloy, which contain a perpendicular component, in the magnetic layer is not preferred, since magnetization in the longitudinal direction tends to decrease.
Since a Co alloy magnetic layer assuming the (10-0) and (11-0) crystal planes at the surface thereof is difficult to form, an undercoat layer made of Cr alloy having a body-centered cubic structure (bcc structure) is generally employed. The (11 ) plane of the Co alloy tends to be present on the (100) plane of the Cr alloy, and the (10-0) plane of the Co alloy tends to be present on the (112) plane of the Cr alloy.
After an aluminum substrate electroless-plated with Ni-P-based alloy film has been heated, an undercoat layer made of Cr alloy is formed on the alloy plating film, whereby the (100) crystal plane of the Cr alloy tends to be present on the undercoat layer. When a magnetic layer made of Co alloy is epitaxially grown on the Cr alloy layer, the Co alloy magnetic layer assumes the (11 -0) crystal plane. Thus, a magnetic recording medium having excellent magnetic characteristics can be produced.
In contrast, when a glass substrate is heated and a Cr alloy layer is formed directly on the heated glass substrate, the (110) crystal plane of the Cr alloy tends to be present at the surface of the Cr alloy layer, and the Co alloy layer grown on the Cr alloy layer assumes the (10T) crystal plane.
Since the C axis serving as an easy-magnetization axis present in the (10-1) crystal plane of the Co alloy has both longitudinal and perpendicular vector components, the crystal plane is not suited for longitudinal recording and perpendicular recording.
Therefore, techniques for causing a Cr alloy layer formed on a glass substrate to assume the (100) plane or the (112) plane have been proposed (see, for example, European Patent Application EP 0704839 Al, Japanese Patent No. 3217012, and Japanese Patent Application Laid-Open (kokai) No. 2000- 113443.
The magnetic recording medium disclosed in European Patent Application EP 0704839 Al has an undercoat layer formed of an Al alloy of B2 structure (Al-Ni-based alloy, Al-Co-based alloy, Al-Fe-based alloy, etc.). The magnetic layer of the recording medium has a crystal grain size reduced by virtue of Al-Ni-based alloy, Al-Co-based alloy, etc., and noise reduction has been confirmed. Among such Al alloys, the Al-Ni-based alloy is employed in practice in a non-magnetic undercoat layer.
This is because the crystal lattice of the (112) plane of the Al-Ni-based alloy and that of the (10-0) crystal plane of the Co alloy forming the magnetic layer are highly matched with each other, whereby the (10-0) crystal plane of the Co alloy is epitaxially grown on the (112) plane of the Al-Ni-based alloy. As a result, the Co alloy magnetic layer assumes the (10 ) crystal plane, thereby attaining high coercive force.
Japanese Patent No. 3217012 has proposed a technique for promoting epitaxial growth of the (11*0) crystal plane of a Co alloy forming the magnetic layer, the technique including forming an undercoat layer predominantly containing Co under the Cr alloy layer so as to grow the (100) plane of the Cr alloy layer.
Although Japanese Patent Application Laid-Open (kokai) No. 2000-113443 does not particularly mention the crystal plane of the layer surface, it has proposed a technique for enhancing SNR (signal to noise ratio) characteristics of a magnetic recording medium by forming a Cr-based layer formed of a Cr-P-based alloy or a Cr-Mo-P-based alloy between the non-magnetic substrate (e.g., glass, carbon, or silicon) and the Cr-based non-magnetic undercoat layer.
When the technique including employment of an Al alloy of B2 structure (Al-Ni-based alloy, Al-Co-based alloy, Al-Fe-based alloy, etc.) in the undercoat layer is employed, the technique being proposed in the aforementioned European Patent Application EP 0704839 Al, the (112) peak attributed to the Al-Ni-based alloy is weak, . and the surface of the alloy layer might not sufficiently assume the (112) plane. Thus, as described in the aforementioned patent publication, the thickness of the Al-Ni-based alloy layer must be increased in order to assume the (112) plane of the Al-Ni-based alloy. Therefore, the Al-Ni-based alloy has an increased grain size, which is problematic.
In other words, there are two demands that are contradictory to each other; i.e., a demand that the thickness of the employed Al-Ni-based alloy must be increased in order to enhance coercive force, and a demand that the thickness of the layer must be decreased in order to reduce media noise by decreasing the crystal grain size. Accordingly, the layer configuration for producing suitable magnetic recording media has been difficult to design.
As described in "Examples" of Japanese Patent No. 3217012, when a Co alloy such as Co-30 at.%-Cr-10 at.%-Zr, Co-36 at.%-Mn-10 at.%-Ta, Co-30 at.%-Cr-10 at.%-SiO2, or Co-25 at.%-Cr-12 at.%-W is employed, the Cr alloy layer assumes the (100) plane, and epitaxial growth of the (11-0) plane of the Co alloy forming the magnetic layer is observed on the (100) plane. However, the Cr alloy layer has an unsatisfactorily reduced grain size, and a certain limit is imposed on reduction of media noise.
As described in Japanese Patent Application Laid-Open (kokai) No. 2000-113443, when a Cr-P-based alloy or a Cr-Mo-P-based alloy is employed, the Cr alloy has an unsatisfactorily reduced grain size, and a certain limit is imposed on reduction of media noise.
The present invention has been accomplished in view of the foregoing, and an object of the present invention is to provide a magnetic recording medium which can enhance magnetic anisotropy and has excellent magnetic characteristics and read- write performance. Another object of the invention is to provide a method for producing the magnetic recording medium. Still another object of the invention is to provide a magnetic recording and reproducing apparatus. DISCLOSURE OF INVENTION The present inventor has conducted extensive studies in an attempt to solve the aforementioned problems, and has found that the characteristics of a magnetic recording medium can be enhanced by employing a non-magnetic undercoat layer formed of an Mo-P-based alloy containing Mo and P. The present invention has been accomplished on the basis of this finding. Accordingly, the present invention is directed to the following.
(1) A magnetic recording medium including at least a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in this order, on a non-magnetic substrate, characterized in that the non-magnetic undercoat layer contains an Mo-P-based alloy.
(2) A magnetic recording medium as described in (1), wherein the Mo-P-based alloy has an Mo content falling within a range of 30 to 90 at.%, a P content falling within a range of 10 to 60 at.%, and a total content of Mo and P falling within a range of 60 to 100 at.%.
(3) A magnetic recording medium as described in (1) or (2), wherein the non-magnetic substrate is a glass substrate.
(4) A magnetic recording medium as described in (1) or (2), wherein the non-magnetic substrate is a glass substrate having a groove line on a surface thereof.
(5) A magnetic recording medium as described in any one of (1) to (4), wherein the non-magnetic undercoat layer has a stacked structure including two or more layers.
(6) A magnetic recording medium as described in (5), wherein the non-magnetic undercoat layer has an Mo-P-based alloy layer containing an Mo-P-based alloy, and a Cr layer formed of Cr such that the Mo-P-based alloy is disposed close to the non-magnetic substrate.
(7) A magnetic recording medium as described in (5), wherein the non-magnetic undercoat layer has an Mo-P-based alloy layer containing an Mo-P-based alloy, and a Cr alloy layer containing Cr and one or more species selected from among Ti, Mo, Al, Ta, W, Ni, B, Si, and V such that the Mo-P-based alloy is disposed close to the non-magnetic substrate.
(8) A magnetic recording medium as described in any one of (1) to (7), wherein the non-magnetic substrate is formed of aluminum or silicon.
(9) A magnetic recording medium as described in any one of (1) to (7), wherein the non-magnetic substrate is a substrate having a surface plated with an Ni-P-based alloy.
(10) A magnetic recording medium as described in any one of (1) to (9), wherein the magnetic layer is formed of one or more species selected from among a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-based alloy, and a Co-Cr-Pt-B-X-based alloy (wherein X is Ta or Cu).
(11) A method for producing a magnetic recording medium as recited in any one of (1) to (10), characterized in that the method comprises forming, on a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in this order, and that the non-magnetic undercoat layer contains an Mo-P-based alloy.
(12) A method for producing a magnetic recording medium as described in (11), wherein a surface of the layer containing the Mo-P-based alloy is exposed to an oxygen-containing gas during formation of the non-magnetic undercoat layer.
(13) A method for producing a magnetic recording medium as described in (12), wherein the oxygen-containing gas has an oxygen partial pressure falling within a range of 5 x 10"4 Pato 5 x 10"2 Pa.
(14) A magnetic recording medium characterized in that the recording medium is produced through a method for producing a magnetic recording medium as recited in (12) or (13).
(15) A magnetic recording and reproducing apparatus having a magnetic recording medium as recited in any one of (1) to (10) and (14), and a magnetic head for recording information in the magnetic recording medium and reproducing information from the magnetic recording medium.
Notably, in the present invention, 1 Oe is approximately 79 A/m.
In the present invention, the term "-based" refers to the case in which a substance may contain a component other than the literally described component. For example, the "Mo-P-based alloy" may contain a component other than Mo and P.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section of a first embodiment of the magnetic recording medium of the present invention.
FIG. 2 is a cross-section of a second embodiment of the magnetic recording medium of the present invention.
FIG. 3 is a cross-section of a third embodiment of the magnetic recording medium of the present invention.
FIG. 4 is a schematic view of an exemplary magnetic recording and reproducing apparatus according to the present invention.
MODES FOR CARRYING OUT THE INVENTION
FIG. 1 schematically shows a first embodiment of the magnetic recording medium of the present invention.
In the magnetic recording medium as shown in FIG. 1, a non-magnetic undercoat layer 2, a magnetic layer 5, and a protective layer 6 are sequentially stacked in this order on a non-magnetic substrate 1.
The non-magnetic substrate 1 is preferably a glass substrate which is generally employed as a substrate for a magnetic recording medium or is preferably an aluminum alloy substrate having an Ni-P-based alloy plating film thereon (hereinafter referred to as an Ni-P-plated Al substrate).
Examples of the non-magnetic substrate further include substrates formed of a non-metallic material such as ceramics, silicon, silicon carbide, carbon, or resin. A substrate formed of such a nonmetallic material and coated with anNiP film or an Ni-P-based alloy film may also be used.
In a magnetic recording and reproducing apparatus, the flying height of a magnetic head must be reduced in order to enhance recording density of the apparatus. Thus, the non-magnetic substrate 1 desirably has enhanced surface flatness. Specifically, the non-magnetic substrate 1 desirably has a surface roughness (Ra) of 2 nm or less, preferably 1 nm or less.
The non-magnetic substrate 1 preferably has a surface micro-waviness (Wa) of 0.3 mn or less (more preferably 0.25 nm or less), because the flying height of the magnetic head during recording and reproducing can be reduced, which is suited for high-density recording. The micro-waviness (Wa) can be determined by means of, for example, a surface roughness meter (P-12, product of KLa-Tencor) as an average surface roughness value as measured in a range of 80 μm.
At least one of a ch-tmfer section of the end surface and a side surface of the non-magnetic substrate preferably has a surface roughness (Ra) of 10 nm or less (more preferably 9.5 nm or less), from the viewpoint of flying stability of a magnetic head.
The non-magnetic substrate 1 is preferably a glass substrate, from the viewpoints of cost and durability. A glass substrate or a silicon substrate are preferably used, from the viewpoint of surface flatness.
The non-magnetic substrate 1 may be formed of aluminum or silicon. A substrate formed of aluminum or silicon which is plated with an Ni-P-based alloy film can also be employed.
Examples of glass materials which can be employed as the substrate include glass ceramics and amorphous glass. Examples of the amorphous glass which can be used include generally used soda-lime glass, aluminoborosilicate glass, and aluminosilicate glass. Examples of the glass ceramics which can be used include lithium-containing glass ceramics.
Preferably, groove lines are formed on a surface of the non-magnetic substrate 1. When a glass substrate is employed, formation of groove lines is particularly preferred. Through formation of groove lines, magnetic characteristics (e.g., coercive force) and read-write performance (e.g., SNR (signal to noise ratio), PW50) can be enhanced.
The groove lines are preferably formed in a generally circumferential direction of the substrate 1, from the viewpoint of enhancement of magnetic anisotropy in a circumferential direction of the magnetic recording medium.
The groove lines are preferably formed such that the processed surface has a surface roughness — average level gap between the' top level and the bottom level as viewed in the cross-section in the radial direction — of 0.02 nm to 20 nm (more preferably 0.05 nm to 10 nm). By controlling the shape parameter of groove lines (level gap) to fall within the above range, magnetic characteristics and read- write performance can be enhanced. Groove lines having a level gap in excess of 20 nm tend to result in having non-uniform shapes.
The line density of the groove lines is preferably 7,500 lines/mm or more (preferably 20,000 lines/mm or more).
The groove lines can be formed through, for example, mechanical texturing by use of a lapping tape employing fixed abrasive grains, or by use of free abrasive grains.
Examples of the ceramic substrate include a sintered product predominantly containing generally used alumina, silicon nitride, or a similar compound, and a fiber-reinforced product thereof.
The non-magnetic undercoat layer 2 has a stacked structure containing a first undercoat layer 3 formed close to the non-magnetic substrate 1, and a second undercoat layer 4 formed on the first undercoat layer 3.
Among the first undercoat layer 3 and the second undercoat layer 4 which form the non-magnetic undercoat layer 2, the first undercoat layer 3 disposed close to the non-magnetic substrate 1 is an Mo-P-based alloy layer formed of an Mo-P-based alloy.
Notably, the non-magnetic undercoat layer may have a single-layer structure or a stacked structure having three or more layers. When the single-layer structure is employed, the non-magnetic undercoat layer is provided so as to contain an Mo-P-based alloy, whereas when the stacked structure having two or more layers is employed, at least one layer among the plurality of layers (preferably the layer disposed most close to the non-magnetic substrate) is provided so as to contain an Mo-P-based alloy.
The Mo-P-based alloy forming the first undercoat layer 3 preferably has an Mo content falling within a range of 30 to 90 at.%, a P content falling within a range of 10 to 60 at.%, and a total content of Mo and P falling within a range of 60 to 100 at.%.
When the Mo content or the P content falls outside the corresponding range, the layer disposed directly on the first undercoat layer (i.e., second undercoat layer 4) has a large crystal grain size, thereby deteriorating SNR characteristics.
The Mo-P-based alloy forming the non-magnetic undercoat layer 2 may contain an additional element having an auxiliary effect (e.g., enhancing orientation, grain-size reduction, or similar effect on the second undercoat layer 4 and the magnetic layer 5). Examples of the additional element include one or more species selected from among Ti, V, Cr, Mn, Zr, Hf, Ru, B, Al, Si, and W.
The total content of the additional elements is preferably 40 at.% or less. When the total content is in excess of 40 at.%, the aforementioned effect (enhancing orientation or grain-size-reduction) is reduced. Thus, the total content is preferably controlled to 0.1 at.% or more. When the content is less than 0.1 at.%, the aforementioned effect is reduced.
The first undercoat layer 3 can be formed through DC or RF magnetron sputtering using a sputtering target. When the layer is formed through sputtering, Ar gas is generally employed as a sputtering gas for discharge. The pressure of the sputtering gas is preferably 0.1 Pa to 5 Pa.
The second undercoat layer 4 may be a Cr layer formed of Cr. Alternatively, the layer 4 may be a Cr alloy layer formed of a Cr alloy containing Cr and one or more species selected from among Ti, Mo, Al, Ta, W, Ni, B, Si, and V. Among Cr alloys, a Cr-Mo-based alloy, a Cr-W-based alloy, a Cr-V-based alloy, and a Cr-Ti-based alloy are particularly preferred.
When the second undercoat layer 4 is formed from a Cr alloy layer, the lattice constant of the second undercoat layer 4 can be regulated to a value proximate to that of the magnetic layer 5, as compared with the second undercoat layer formed fiom a Cr layer. Thus, the degree of lattice matching between the second undercoat layer 4 and the magnetic layer 5 can be enhanced, thereby enhancing SNR characteristics.
The second undercoat layer 4 preferably assumes, as a preferential crystal plane, the (100) plane at the surface layer 4. By virtue of the (100) plane, the Co alloy magnetic layer 5 assumes the (11-0) plane more preferentially, thereby enhancing magnetic characteristics (e.g., coercive force (He)) and recording-reproducing characteristics (e.g., SNR).
The magnetic layer 5 is preferably formed from a Co alloy predominantly containing Co, the alloy being a material which attains high lattice matching with a crystal plane present in the non-magnetic undercoat layer 2; e.g., the (100) plane, and which has an hep structure.
For example, the magnetic layer preferably contains one or more species selected from among a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-based alloy, and a Co-Cr-Pt-B-X-based alloy (wherein X is Ta or Cu).
It is particularly preferred that the magnetic layer contain one or more species selected from among a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-Ta-based alloy, and a Co-Cr-Pt-B-Cu-based alloy being particularly preferred.
When a Co-Cr-Ta-based alloy is used, a Cr content of 5 at.% to 25 at.% and a Ta content of 1 at.% to 10 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
When a Co-Cr-Pt-based alloy is used, a Cr content of 10 at.% to 25 at.% and a Pt content of 8 at.% to 16 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
When a Co-Cr-Pt-B-based alloy is used, a Cr content of 10 at.% to 25 at.%, a Pt content of 8 at.% to 16 at.%, and a B content of 1 at.% to 20 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
When a Co-Cr-Pt-B-Ta-based alloy is used, a Cr content of 10 at.% to 25 at.%, a Pt content of 8 at.% to 16 at.%, a B content of 1 at.% to 20 at.%, and a Ta content of 1 at.% to 4 at.% are preferred from the viewpoint of enhancement of SNR characteristics. The B content more preferably falls within a range of 2 at.% to 20 at.%.
When a Co-Cr-Pt-B-Cu-based alloy is used, a Cr content of 10 at.% to 25 at.%, a Pt content of 8 at.% to 16 at.%, a B content of 2 at.% to 20 at.%, and a Cu content of 1 at.% to 4 at.% are preferred from the viewpoint of enhancement of SNR characteristics.
The magnetic layer 5 preferably have a thickness of 10 nm or more (preferably 15 nm or more) from the viewpoint of thermal stability characteristics. From the viewpoint of high recording density, the thickness is preferably 40 nm or less. This is because, when the thickness is in excess of 40 nm, the magnetic layer 5 has a large grain size, thereby failing to attain favorable recording and reproducing characteristics.
The magnetic layer 5 may have a single-layer structure or a multi-layer structure. In this case, the aforementioned materials (a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-based alloy, and a Co-Cr-Pt-B-X-based alloy ) for forming each layer can also be used.
When the magnetic layer 5 has a multi-layer structure, a component layer which is in direct contact with the non-magnetic undercoat layer 2 (i.e., bottommost layer) is preferably formed of a Co-Cr-Pt-B-Ta-based alloy, a Co-Cr-Pt-B-Cu-based alloy, or a Co-Cr-Pt-B-based alloy, from the viewpoint of improvement of recording and reproducing characteristics (particularly SNR characteristics).
The uppermost layer is preferably formed of a Co-Cr-Pt-B-Cu-based alloy or a Co-Cr-Pt-B-based alloy from the viewpoint of improvement of recording and reproducing characteristics (particularly SNR characteristics).
The protective layer 6 can be formed from conventionally known materials predominantly containing, for example, carbon or SiC.
The protective layer 6 preferably has a thickness of 1 nm to 10 nm from the viewpoint of spacing loss upon use for recording and reproducing and durability of the medium.
On the protective layer 6, a lubrication layer formed of a fluorine-containing lubricant such as perfluoropolyether may be provided in accordance with needs.
Next, an embodiment of the method for producing the aforementioned magnetic recording medium will be described.
Groove lines are preferably formed on a surface of the non-magnetic substrate 1. The groove lines are preferably formed through, for example, mechanical texturing by use of a lapping tape employing fixed abrasive grains or by use of free abrasive grains.
Specifically, the following procedure can be employed. A surface of the substrate 1 is brought into contact with an abrasive tape and pressed against the tape. An abrasive slurry containing abrasive grains is fed to a sliding contact surface of the substrate 1 and the abrasive tape. The substrate 1 is rotated, and the abrasive tape is moved on the substrate 1.
The texturing can be performed along with oscillation. The process "oscillation" refers to an operation of oscillating an abrasive tape in a radial direction of the substrate 1 while the abrasive tape is moved on the substrate 1 in a circumferential direction. The oscillation speed is preferably 60 cycles/min to 1,200 cycles/minute, since the surface of the substrate is uniformly polished in amount through texturing.
Other than the mechanical texturing method employing an abrasive tape, there may be employed a texturing method employing immobilized abrasives, a texturing method employing an immobilized grinding wheel, a laser processing, etc.
After washing is complete, the non-magnetic substrate 1 is placed in a chamber of a film formation apparatus (sputtering apparatus). The non-magnetic substrate 1 is heated to 100°C to 400°C in accordance with needs.
Through DC or RF magnetron sputtering, a first undercoat layer 3, a second undercoat layer 4, and a magnetic layer 5 are formed on the non-magnetic substrate 1.
The following operational conditions of sputtering can be employed for forming the aforementioned layers.
The chamber can be evacuated to 1 x 10" Pa to 1 x 10" Pa. Ar can be used as a sputtering gas. The electric power supplied is preferably 0.2 kW to 2.0 kW. By controlling the discharge time and the supplied electric power, the thickness of the formed film can be adjusted.
Each layer can be formed by use of a sputtering target having a composition identical to that of the material of each layer.
After formation of the first undercoat layer 3, the surface of the undercoat layer 3 is preferably exposed to an oxygen-containing gas. The oxygen-containing gas preferably has an oxygen partial pressure 5 x 10"4 Pa or higher, preferably 5 x 10"3 Pa to 5 x 10"2 Pa. For example, air is preferred. A water-containing gas may also be employed as the oxygen-containing gas. The exposure time preferably falls within a range of 0.5 seconds to 15 seconds.
The exposure treatment may be performed through a method including removing the substrate 1 on which the first undercoat layer 3 has been formed from the chamber and exposing the substrate to air or an oxygen-containing gas. Alternatively, the treatment may also be preformed without removing the substrate 1 from the chamber and by feeding an oxygen-containing gas (e.g., air) into the chamber. The method including exposing the first undercoat layer 3 to an oxygen-containing gas in the chamber effectively produces the magnetic recording medium, since removal of the substrate 1 from the chamber can be omitted. In this case, an oxygen-containing gas having an oxygen partial pressure of 5 x 10"4 Pa or higher is preferably used in the chamber under a vacuum lower than 1 x 10"5 Pa. The oxygen partial pressure of the oxygen-containing gas during exposure treatment is preferably controlled to 5 x 10" Pa or lower.
When the magnetic layer 5 formed from a B-containing alloy (e.g., Co-Cr-Pt-B-based alloy or Co-Cr-Pt-B-X-based alloy) is used, the magnetic layer 5 is preferably formed such that the Cr content of a region having a B content of 1 at.% or more is controlled to be 40 at.% or less, in the vicinity of the interface between the non-magnetic undercoat layer 2 and the magnetic layer 5.
Next, a protective layer 6 is formed through a conventionally known method such as sputtering, plasma CVD, or a combination thereof. On the protective layer 6, a lubrication layer can be formed through a conventionally known method such as spin coating or dipping.
Since the above-mentioned magnetic recording medium has the non-magnetic undercoat layer 2 containing an Mo-P-based alloy, the magnetic layer 5 can be imparted with high magnetic anisotropy.
Thus, magnetic characteristics (e.g., coercive force) and read-write performance (e.g., SNR (signal to noise ratio), PW50) can be enhanced, thereby increasing recording density.
In addition, when a glass substrate, having a flatness higher than that of a metallic substrate, is employed, excellent glide height characteristics can be attained. Thus, error characteristics are not deteriorated, thereby attaining high-density recording.
FIG. 2 shows a second embodiment of the magnetic recording medium of the present invention. In this magnetic recording medium, a non-magnetic intermediate layer 7 is provided between a non-magnetic undercoat layer 2 and a magnetic layer 5, in order to promote epitaxial growth of a Co alloy forming the magnetic layer 5.
The non-magnetic intermediate layer 7 preferably contains Co and Cr; comprises a Co-Cr-based alloy. When the Co-Cr-based alloy is used, the Cr content preferably falls within a range of 25 at.% to 45 at.% from the viewpoint of enhancement of SNR.
The non-magnetic intermediate layer 7 preferably has a thickness falling within a range of 0.5 nm to 3 nm from the viewpoint of enhancement of SNR.
Through provision of the non-magnetic intermediate layer 7, the magnetic recording medium exhibits improved magnetic characteristics (e.g., coercive force) and improved recording-reproducing characteristics (e.g., SNR).
FIG. 3 shows a third embodiment of the magnetic recording medium of the present invention. In this magnetic recording medium, an anti-ferromagnetic coupling layer 8 is provided between a non-magnetic undercoat layer 2 and a magnetic layer 5, in order to improve thermal decay.
The anti-ferromagnetic coupling layer 8 may be formed of a non-magnetic coupling layer 10 provided on a stabilizing layer 9.
The stabilizing layer 9 can be formed from a magnetic material such as a Co-Ru-based alloy, a Co-Cr-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-B-based alloy, or a Co-Cr-Ta-based alloy.
The non-magnetic coupling layer 10 is preferably formed from Ru. The thickness of the non-magnetic coupling layer 10 is preferably about 0.8 nm (e.g., 0.6 nm to 1.0 nm), so as to attain the maximum value of anti-ferromagnetic coupling.
Since the magnetic recording medium includes an anti-ferromagnetic coupling layer 8, excellent thermal stability is attained.
FIG. 4 shows an exemplary magnetic recording and reproducing apparatus employing the aforementioned magnetic recording medium. The magnetic recording and reproducing apparatus as shown in FIG. 4 includes a magnetic recording medium 20 as described in any of the aforementioned embodiments, a medium-driving member 21 for rotating the magnetic recording medium 20, a magnetic head 22 for recording information in and reproducing information from the magnetic recording medium 20, a head-driving member 23 for moving the magnetic head 22 relative to the magnetic recording medium 20, and a record reproduction signal processing system 24. The record reproduction signal processing system 24 is provided such that data input from the outside is processed to transmit a record signal to the magnetic head 22 and that a reproduction signal obtained from the magnetic head 22 is processed to transmit data to the outside. Examples of elements which can be used to serve as the magnetic head 22 include elements having, as a reproduction element, a magnetoresistance (MR) element based on anisotropic magnetoresistance (AMR) or a giant magnetoresistance (GMR) element based on giant magnetoresistance (GMR). Recording density can be increased through employment of a GMR element.
Since the magnetic recording and reproducing apparatus employs the aforementioned magnetic recording medium, the magnetic layer 5 included in the recording medium can be imparted with high magnetic anisotropy, and thus excellent magnetic characteristics and read-write performance can be attained, thereby enhancing recording density.
Examples <Example 1>
A magnetic recording medium having a structure shown in FIG. 2 was fabricated.
A glass substrate (amorphous glass GD-7, product of NIPPON SHEET GLASS) was employed as the non-magnetic substrate 1. The substrate 1 had the following dimensions: outer diameter of 65 mm, inner diameter of 20 mm, and thickness of 0.635 mm.
The substrate 1 was subjected to mechanical texturing under the following conditions. Abrasive grains contained in an abrasive slurry employed were diamond abrasive grains having a D90 (grain size value when the cumulative mass percent is 90 mass%) of 0.15 μm. The slurry was added dropwise at 50 mL/minute for two seconds before the start of texturing. The substrate 1 was rotated, and an abrasive tape made of polyester fabric was moved on the substrate 1. The abrasive tape was fed at 75 mm/niinute, and the substrate 1 was rotated at 600 rpm. The oscillation speed was 120 cycles/min. The pressure of the tape was 2.0 kgf (19.6 N). The texturing time was 10 seconds.
Observation of the surface of the thus-textured substrate 1 under an AFM (product of Digital Instrument) revealed that groove lines having an average surface roughness (Ra) of 0.4 nm and a line density of 25,000 lines/mm were formed in a circumferential direction of the substrate. The average surface roughness (Ra) can be determined in accordance with JIS B 0601-1982 or ISO R 468-1966.
After completion of sufficient washing and drying, the substrate 1 was placed in a DC magnetron sputtering apparatus (C3010, product of ANELVA (Japan)), and the chamber was evacuated to 2 x 10"7 Torr (2.7 x 10"5 Pa). Subsequently, by use of an Mo-P alloy (Mo: 90 at.% and P: 10 at.%) target, a first undercoat layer 3 (thickness: 5 nm) formed of the Mo-P alloy was formed at room temperature.
The substrate 1 was heated to 250°C, and the first undercoat layer 3 was exposed to oxygen gas which was fed into the chamber. The oxygen partial pressure and the exposure time were controlled to 0.05 Pa and 5 seconds, respectively.
A second undercoat layer 4 (thickness: 8 nm) was formed by use of a target formed of a Cr-Ti-B alloy (Cr: 83 at.%, Ti: 15 at.%, and B 2 at.%).
A non-magnetic intermediate layer 7 (thickness: 2 nm) was formed by use of a target formed of a Co-Cr alloy (Co: 65 at.% and Cr: 35 at.%).
A magnetic layer 5 (thickness: 20 nm) formed of a CoCrPtB alloy layer was formed by use of a target formed of a Co-Cr-Pt-B alloy (Co: 60 at.%, Cr: 22 at.%, Pt: 12 at.%, and B: 6 at.%).
Subsequently, a protective layer 6 (thickness: 5 nm) formed of carbon was formed.
During formation of each layer, Ar was used as a sputtering gas, and the pressure thereof was adjusted to 3 mTorr (0.4 Pa).
Subsequently, a lubricant formed of perfluoropolyether was applied through dip coating to the surface of the protective layer so as to form a lubrication layer (thickness: 2 nm), to thereby produce a magnetic recording medium.
<Examples 2 to 20>
The procedure of Example 1 was repeated, except that the composition and thickness of the first undercoat layer 3 were changed as shown in Table 1, to thereby fabricate magnetic recording media.
<Example 21>
A magnetic recording medium having a structure shown in FIG. 3 was fabricated. By use of an Mo-P alloy (Mo: 70 at.% and P: 30 at.%) target, a first undercoat layer 3 (thickness: 5 nm) was formed at room temperature.
Instead of a non-magnetic intermediate layer 7, an anti-ferromagnetic coupling layer 8 was formed. A stabilizing layer 9 (thickness: 2 nm) was formed by use of a Co-Ru alloy (Co: 80 at.% and Ru: 20 at.%) target. A non-magnetic coupling layer 10 (thickness: 0.8 nm) was formed by use of an Ru target. Regarding other conditions, the same conditions as employed in Example 1 were employed.
<Example 22>
The procedure of Example 1 was repeated, except that the glass substrate was not subjected to mechanical texturing, to thereby fabricate a magnetic recording medium.
<Examples 23 to 26>
The procedure of Example 22 was repeated, except that the composition and thickness of the first undercoat layer 3 were changed as shown in Table 1, to thereby fabricate magnetic recording media.
<Comparative Examples 1 and 2>
Magnetic recording media were fabricated by changing the first undercoat layer 3 to a Cr-Mo-P-based alloy layer formed of a Cr-Mo-P-based alloy. Regarding other conditions, the same conditions as employed in Example 1 were employed.
<Comparative Example 3>
The procedure of Example 22 was repeated, except that the composition and thickness of the Cr-Mo-P-based alloy layer were changed as shown in Table 2, to thereby fabricate a magnetic recording medium.
Each of magnetic recording media produced in the above Examples and Comparative Examples was subjected to a glide test by use of a glide tester, with the glide height being adjusted to 0.4 μinch (1 microinch nearly equal to 25.4 nm). The recording media which had passed the test were further investigated in terms of record reproduction characteristics by use of a read- write analyzer RWA 1632 (product of GUZIK (USA)).
The record reproduction characteristics were investigated in terms of read- write performance including read output (TAA), half- width of isolated read pulse power (PW50), SNR, and overwrite (OW).
The record reproduction characteristics were evaluated by means of a complex thin-film magnetic recording head having a giant magnetoresistance (GMR) element at a readout portion.
Noise evaluation was performed by measuring the integral noise from 1 MHz to a frequency corresponding to 375 kFCI generated when a pattern signal of 500 kFCI had been written. Read output was measured at 250 kFCI and calculated as SNR = 20 x log(read output/integral noise from 1 MHz to a frequency corresponding to 375 kFCI).
Coercive force (He) and squareness ratio (S*) were determined by use of a Kerr effect magnetic characteristics analyzer (RO1900, product of Hitachi Electronics Engineering (Japan)).
Magnetic anisotropy index of coercive force (OR) and that of residual magnetization (MrtOR) were determined by use of a VSM (BHV-35, product of (Riken Denshi Co., Ltd. (Japan)).
The results are shown in Tables 1 and 2.
Table 1
Figure imgf000020_0001
T: thickness, He: coercive force, S*: squareness ratio
Table 2
Figure imgf000020_0002
T: thickness, He: coercive force, S*: squareness ratio
The test results of magnetic recording media of Examples 1 to 5 revealed that excellent read- write performance was attained when the P content of the first undercoat layer 3 (Mo-P-based alloy layer) was 10 to 50 at.%. When the P content fell within a range of 20 to 40 at.%, more excellent read- write performance was attained.
The test results of magnetic recording media of Examples 3 and 6 to 10 revealed that excellent magnetic anisotropy in a circumferential direction and read- rite performance were attained when the thickness of the first undercoat layer 3 formed of an Mo-P-based alloy (Mo: 70 at.% and P: 30 at.%) was 2.5 to 30 nm. When the thickness fell within a range of 2.5 to 10 nm, more excellent magnetic anisotropy in a circumferential direction and read- write performance were attained.
The test results of magnetic recording media of Examples 11 to 20 revealed that excellent read- write performance was attained when the Mo-P-based alloy contained a third element and the third element was any of Ti, V, Cr, Mn, Zr, Ru, B, Al, Si, and W.
Since the magnetic recording media of Examples 22 to 26 were fabricated without mechanical texturing of the glass substrate 1 , no anisotropy was identified. The magnetic recording media of Examples 22 to 26 exhibited magnetic characteristics inferior to those of the magnetic recording media of Examples 1 to 21, but exhibited excellent read- write performance as compared with the magnetic recording medium of Comparative Example 3 employing a Cr-Mo-P-based alloy.
The magnetic recording media of Comparative Examples 1 to 3 employed a Cr-Mo-P-based alloy instead of an Mo-P-based alloy. Even when these recording media were subjected to mechanical texturing of the glass substrate (Comparative Examples 1 and 2) or were not subjected to the texturing (Comparative Example 3), these recording media exhibited magnetic characteristics inferior to those of the magnetic recording media of Examples.
INDUSTRIAL APPLICABILITY The magnetic recording medium according to the present invention has a non-magnetic undercoat layer containing an Mo-P-based alloy. Thus, the magnetic layer provided on the non-magnetic undercoat layer can be imparted with high magnetic anisotropy.
Therefore, magnetic characteristics (e.g., coercive force) and read-write performance (e.g., SNR and PW50) can be enhanced, thereby increasing recording density.

Claims

1. A magnetic recording medium including at least a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in this order, on a non-magnetic substrate, characterized in that the non-magnetic undercoat layer contains an Mo-P-based alloy.
2. A magnetic recording medium as described in claim 1, wherein the Mo-P-based alloy has an Mo content falling within a range of 30 to 90 at.%, a P content falling within a range of 10 to 60 at.%, and a total content of Mo and P falling within a range of 60 to 100 at.%.
3. A magnetic recording medium as described in claim 1 or 2, wherein the non-magnetic substrate is a glass substrate.
4. A magnetic recording medium as described in claim 1 or 2, wherein the non-magnetic substrate is a glass substrate having a groove line on a surface thereof.
5. A magnetic recording medium as described in any one of claims 1 to 4, wherein the non-magnetic undercoat layer has a stacked structure including two or more layers.
6. A magnetic recording medium as described in claim 5, wherein the non-magnetic undercoat layer has an Mo-P-based alloy layer containing an Mo-P-based alloy, and a Cr layer formed of Cr such that the Mo-P-based alloy is disposed close to the non-magnetic substrate.
7. A magnetic recording medium as described in claim 5, wherein the non-magnetic undercoat layer has an Mo-P-based alloy layer containing an Mo-P-based alloy, and a Cr alloy layer containing Cr and one or more species selected from among Ti, Mo, Al, Ta, W, Ni, B, Si, and V such that the Mo-P-based alloy is disposed close to the non-magnetic substrate.
8. A magnetic recording medium as described in any one of claims 1 to 7, wherein the non-magnetic substrate is formed of aluminum or silicon.
9. A magnetic recording medium as described in any one of claims 1 to 7, wherein the non-magnetic substrate is a substrate having a surface plated with an Ni-P-based alloy.
10. A magnetic recording medium as described in any one of claims 1 to 9, wherein the magnetic layer is formed of one or more species selected from among a Co-Cr-Ta-based alloy, a Co-Cr-Pt-based alloy, a Co-Cr-Pt-Ta-based alloy, a Co-Cr-Pt-B-based alloy, and a Co-Cr-Pt-B-X-based alloy (wherein X is Ta or Cu).
11. A method for producing a magnetic recording medium as recited in any one of claims 1 to 10, characterized in that the method comprises forming, on a non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, and a protective layer, in this order, and that the non-magnetic undercoat layer contains an Mo-P-based alloy.
12. A method for producing a magnetic recording medium as described in claim 11, wherein a surface of the layer containing the Mo-P-based alloy is exposed to an oxygen-containing gas during formation of the non-magnetic undercoat layer.
13. A method for producing a magnetic recording medium as described in claim 12, wherein the oxygen-containing gas has an oxygen partial pressure falling within a range of 5 x lO"4 Pa to 5 x lO"2 Pa.
14. A magnetic recording medium characterized in that the recording medium is produced through a method for producing a magnetic recording medium as recited in claim 12 or 13.
15. A magnetic recording and reproducing apparatus having a magnetic recording medium as recited in any one of claims 1 to 10 and claim 14, and a magnetic head for recording information in the magnetic recording medium and reproducing information from the magnetic recording medium.
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EP0809238A2 (en) * 1996-05-20 1997-11-26 Hitachi, Ltd. Magnetic recording media and magnetic recording system using the same
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