US20040005480A1 - Magnetic recording medium - Google Patents

Magnetic recording medium Download PDF

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Publication number
US20040005480A1
US20040005480A1 US10/613,371 US61337103A US2004005480A1 US 20040005480 A1 US20040005480 A1 US 20040005480A1 US 61337103 A US61337103 A US 61337103A US 2004005480 A1 US2004005480 A1 US 2004005480A1
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Prior art keywords
magnetic
magnetic layer
angle
recording medium
layer
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US10/613,371
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English (en)
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Kazunari Motohashi
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Sony Corp
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Sony Corp
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Assigned to SONY CORPORATION reassignment SONY CORPORATION ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MOTOHASHI, KAZUNARI
Publication of US20040005480A1 publication Critical patent/US20040005480A1/en
Priority to US12/215,546 priority Critical patent/US7670693B2/en
Abandoned legal-status Critical Current

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    • 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
    • G11B5/68—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent
    • G11B5/70—Record carriers characterised by the selection of the material comprising one or more layers of magnetisable material homogeneously mixed with a bonding agent on a base layer
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T428/00—Stock material or miscellaneous articles
    • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
    • Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree

Definitions

  • the present invention relates to a high-density magnetic recording medium and, more particularly, to a magnetic recording medium, from which signals are reproduced, for use in a system using a magnetoresistive effect magnetic head (MR head) or a giant magnetoresistive effect magnetic head (GMR head).
  • MR head magnetoresistive effect magnetic head
  • GMR head giant magnetoresistive effect magnetic head
  • a metallic thin film magnetic recording medium in which a magnetic layer is formed by coating a nonmagnetic support directly with various kinds of magnetic materials, such as magnetic metallic materials, Co—Ni alloys, Co—Cr alloys, and, metal oxide Co—CoO, through vacuum thin film forming techniques is utilized as a magnetic recording medium in the field of video tape recorders in order to achieve higher picture quality and higher recording density.
  • the metallic thin film magnetic recording media excel in coercive force and in squareness ratio. Because the magnetic layers thereof can be formed in such a way as to be extremely thin, the metallic thin film magnetic recording media excel in electromagnetic conversion characteristics in a short-wavelength region. Demagnetization during recording and thickness loss during reproduction are extremely small.
  • binders which are nonmagnetic materials, are not mixed into the magnetic layers thereof. It differs from what is called a coated magnetic recording medium in which a magnetic layer is formed by applying a magnetic coating, which is obtained by dispersing magnetic powder in the binder, on a nonmagnetic support. Thus the packing density of ferromagnetic metallic materials is increased, so that the metallic thin film magnetic recording media have an advantage in achieving high recording density.
  • Oblique-evaporated magnetic tape is manufactured by performing, for example, a method of making an elongated nonmagnetic support run in the longitudinal direction thereof and depositing a magnetic material on a major surface of the nonmagnetic support while the tape runs, thereby forming a magnetic layer.
  • a method of making an elongated nonmagnetic support run in the longitudinal direction thereof and depositing a magnetic material on a major surface of the nonmagnetic support while the tape runs, thereby forming a magnetic layer.
  • MR head magnetoresistive effect magnetic head
  • the MR head has a detection limit at which the sensitivity thereof against a leakage magnetic flux saturates.
  • the MR head cannot detect a leakage magnetic flux when the leakage magnetic flux is more than a design limit of the MR head. It is, therefore, necessary to optimize the MR head by reducing the film thickness of the magnetic layer of the magnetic recording medium.
  • the magnetic layer is formed by causing the elongated nonmagnetic support to run in the longitudinal direction thereof and depositing magnetic fine particles on a major surface of the nonmagnetic support. At that time, an angle, at which the magnetic particle incidents upon the nonmagnetic support, is optimized.
  • the reduction in the size of the magnetic fine particles is performed by introducing a reactive gas, such as oxygen or nitrogen, into a magnetic layer forming atmosphere. Consequently, the diameter of the magnetic fine particles constituting the magnetic layer ranges from 5nm to 20 nm or so.
  • magnetic fine particles start growing at an angle close to parallel with respect to the longitudinal direction of the nonmagnetic support at an initial growth portion of the magnetic layer. Growth direction of the particles gradually and upwardly changes with respect to the longitudinal direction of the nonmagnetic support, so that a growth angle increases.
  • the entire magnetic layer has a columnar structure in which the growth direction of the magnetic fine particles is curved.
  • FIGS. 1A and 2A are schematic views each illustrating the deposited state of the magnetic fine particles 3 a in the magnetic layer 3 of the magnetic tape to be used as digital video tape, and also illustrating the growth direction thereof indicated by arrows.
  • FIGS. 1B and 2B are graphs respectively illustrating the growth directions of the magnetic fine particles, which correspond to FIGS. 1A and 2A and are indicated by arrows, which emanate from a reference point of the coordinate system, for facilitating the understanding of the change in the growth direction.
  • FIGS. 1A and 1B are schematic views illustrating the magnetic tape in which the film thickness of the magnetic layer 3 is set to be 200 nm or so.
  • FIGS. 2A and 2B are schematic views illustrating the magnetic tape in which the film thickness of the magnetic layer 3 is set to be about 55 nm or less.
  • the magnetic fine particles 3 a contained therein are relatively and sufficiently small.
  • the entire arranging direction of the magnetic fine particles 3 a contained in the curved-column structure can be regarded as being continuous.
  • the invention is created to provide a high-recording-density-capable magnetic recording medium.
  • a magnetic recording medium that excels in electromagnetic conversion characteristics.
  • the magnetic recording medium has a 55 nm or less thickness magnetic layer formed on a major surface of an elongated nonmagnetic support by performing a vacuum thin film forming technique, the magnetic recording medium being slid over a magnetoresistive effect magnetic head or a giant magnetoresistive effect head to reproduce a signal, wherein an angle ⁇ which is formed by a growth direction of magnetic particles in a columnar structure in a longitudinal cross-section of the magnetic layer and a normal to a longitudinal direction of the nonmagnetic support, satisfies the following relation:
  • ⁇ i is an angle of ⁇ in an initial growth portion of the magnetic layer
  • ⁇ f is an angle of ⁇ in a final growth portion of the magnetic layer
  • the orientation of the magnetic fine particles constituting the magnetic layer of the magnetic recording medium is improved by focusing attention to an angle in the growth direction of the magnetic fine particles.
  • the improvement of the electromagnetic conversion characteristics is achieved. Consequently, the present invention provides high-recording-density magnetic recording media applicable to various magnetic recording tape systems, for instance, tape streamers.
  • the orientation of the magnetic fine particles constituting the magnetic layer is improved.
  • the electromagnetic conversion properties are enhanced. Consequently, the magnetic recording media according to the present invention are extremely advantageous in effectively utilizing high reproduction sensitivity of the MR head or the GMR head.
  • FIG. 1A is a schematic view illustrating a columnar structure of magnetic fine particulars in a longitudinal section of a magnetic layer
  • FIG. 1B is a view schematically illustrating change in the growth direction of the magnetic fine particles in the direction of thickness of the magnetic layer
  • FIG. 2A is a schematic view illustrating a columnar structure of magnetic fine particulars in the longitudinal section of a magnetic layer
  • FIG. 2B is a view schematically illustrating change in the growth direction of magnetic fine particles in the direction of thickness of the magnetic layer
  • FIG. 3 is a schematic view illustrating the constitution of a magnetic recording medium
  • FIG. 4 is a schematic view illustrating the configuration of a vacuum evaporator for forming a magnetic layer
  • FIG. 5 is a schematic view illustrating an angle ⁇ i at an initial growth portion of a magnetic layer, and an angle ⁇ f at a final growth portion of the magnetic layer;
  • FIG. 6 is a graph illustrating the relation between a tangent of the difference of an angle ⁇ i at an initial growth portion of a magnetic layer and an angle ⁇ f in a final growth portion of the magnetic layer and a relative value of an electromagnetic conversion characteristic (that is, CNR).
  • FIG. 3 is a schematically sectional view illustrating a magnetic recording medium 10 that is an embodiment of the present invention.
  • the magnetic recording medium 10 has a structure in which an underlying layer 2 , a magnetic layer 3 , and a protective layer 4 are sequentially formed on an elongated nonmagnetic support 1 in this order.
  • a lubricant layer 5 may be formed on the protective layer 4 from a predetermined lubricant.
  • a backcoating layer may be formed on the opposite side to a side on which the magnetic layer 3 is formed.
  • Nonmagnetic support 1 Known materials used in the related art magnetic tape may be employed as the material of the nonmagnetic support 1 .
  • polyester group including polyethylene terephthalate (PET) and polyethylene naphthalate (PEN); polyolefins group, such as polyethylene and polypropylene; cellulose derivatives, such as cellulose acetate; and plastics, such as polycarbonate, polyimide, polyamide and polyamideimide are cited.
  • the underlying layer 2 may be formed from a coating material containing binder resins, fillers, and surface active agents. Then, minute irregularities may be added to the surface of the underlying layer 2 . The mechanical strength thereof may be enhanced.
  • Binder resins constituting this underlying layer 2 are, for instance, water-soluble polyester resins, water-based acryl resins, and water-soluble polyurethane.
  • the fillers are particles made of heat-resisting polymers or particles made of silicon dioxide or calcium carbonate. It is preferable that the average of the particle diameter of the filler constituting the lying layer 2 ranges 5 nm to 30 nm, and that the density of surface projections formed from the filler is 50 ⁇ 10 4 per mm 2 to 3000 ⁇ 10 4 per mm 2 or so. This enables the finally obtained magnetic recording medium 10 to realize more favorable running durability and electromagnetic conversion characteristics.
  • Minute projections may be formed on the nonmagnetic support 1 by using a method of artificially forming irregularities thereon through a lithography technique, or using a method of forming an island-like structure of metal, inorganic compound or organic polymer through a plating technique or vacuum thin film forming technique, in addition to the above-described methods.
  • the magnetic layer 3 is formed by performing a vacuum evaporation method according to which ferromagnetic metallic materials are heat-evaporated, and then made to adhere to the underlying layer 2 under vacuum.
  • the oblique evaporation manufacturing method has the steps of making the elongated nonmagnetic support 1 run in the longitudinal direction thereof and depositing a magnetic material on a major surface of the nonmagnetic support while the tape runs thereby to form a magnetic layer.
  • This oblique evaporation manufacturing method has advantages in favorable film-formability, high productivity, and easy-operability.
  • a continuously winding type vacuum evaporator 40 illustrated in FIG. 4 can be applied as a vacuum evaporator for forming the magnetic layer 3 .
  • This vacuum evaporator 40 is configured specifically for what is called the oblique evaporation.
  • a cooling can 42 In the vacuum chamber 41 evacuated to about 1 ⁇ 10 ⁇ 3 Pa, a cooling can 42 , which is adapted to be cooled to a temperature of, for example, ⁇ 20° C. or so and to be rotated in a direction indicated by arrow A in this figure, and an evaporation source 43 for ferromagnetic metallic thin film are disposed in such a way as to face each other.
  • a supply roll 44 and a take-up roll 45 are disposed in the vacuum chamber 41 , as shown in this figure.
  • the nonmagnetic support 1 is fed from the supply roll 44 in the direction indicated by arrow B in this figure. Then, the nonmagnetic support 1 runs along the circumferential surface of the cooling can 42 . Thereafter, the nonmagnetic support 1 is taken up by the take-up roll 45 .
  • guide rollers 47 and 48 are placed between the supply roll 44 and the cooling can 42 and between the cooling can 42 and the take-up roll 48 , respectively.
  • the roller 47 applies a predetermined tension onto the nonmagnetic support 1 running in a range between the supply roller 44 and the cooling can 42 .
  • the roller 48 applies the predetermined tension onto the support 1 running in a range between the supply roller 44 and the cooling can 42 .
  • the nonmagnetic support 1 is enabled to smoothly run in these regions.
  • the evaporation source 43 is a crucible containing a ferromagnetic metallic material, such as Co.
  • a ferromagnetic metallic material such as Co.
  • an electron beam source 49 for heating and evaporating the ferromagnetic metallic material of the evaporation source 43 is disposed. That is, an electron beam 50 is irradiated from the electron beam source 49 onto the ferromagnetic metallic material of the evaporation source 43 by being accelerated. As indicated by arrow C in this figure, this ferromagnetic metallic material is heated and evaporated. Then, the ferromagnetic metallic material adheres onto the nonmagnetic support 1 that runs along the circumferential surface of the cooling can 42 facing the evaporation source 43 . Thus, the ferromagnetic metallic thin film is formed.
  • a first shutter 51 and a second shutter 52 are provided between the evaporation source 43 and the cooling can 42 .
  • the nonmagnetic support 1 runs through the first shutter 51 at the earlier stage and then through the second shutter 52 at the later stage.
  • the first shutter 51 and the second shutter 52 outwardly expose only a predetermined region of the nonmagnetic support 1 .
  • oxygen gas is supplied to the neighborhood of the surface of the nonmagnetic support 1 through an oxygen gas inlet (not shown) to thereby enhance the magnetic properties, the durability, and the weatherability of the ferromagnetic metallic thin film.
  • known means such as resistance heating means, high-frequency heating means, and laser heating means, may be used, in addition to the heating means using electron beams.
  • the ferromagnetic metallic material is vaporized from the evaporation source 43 .
  • the nonmagnetic support 1 is made to run along the circumferential surface of the cooling can 42 .
  • the vaporized ferromagnetic metallic material is deposited only on the portion outwardly exposed from between the first shutter 51 and the second shutter 52 .
  • the first shutter 51 is disposed at the earlier running stage of the nonmagnetic support 1 and determines a maximum incidence angle ⁇ i of the evaporated metallic magnetic material.
  • the second shutter 52 is disposed at the later running stage of the nonmagnetic support 1 and determines a minimum incidence angle ⁇ f of the evaporated metallic magnetic material.
  • the “incidence angle” is defined here in as an angle formed by a direction, in which the vaporized ferromagnetic metallic material incidents upon the nonmagnetic support 1 , and a normal direction to the nonmagnetic support at a place upon which the vaporized ferromagnetic metallic material incidents.
  • the nonmagnetic support 1 runs from the first shutter 51 toward the second shutter 52 , so that the evaporated ferromagnetic metallic material is first deposited on a part of the nonmagnetic support 1 , which is at the side of the first shutter 51 . Then, as the nonmagnetic support 1 runs from the first shutter 51 toward the second shutter 52 , the remaining parts of the vaporized ferromagnetic metallic material are sequentially deposited thereon. Therefore, the ferromagnetic metallic material is first deposited on the nonmagnetic support 1 at the maximum incidence angle. Finally, the deposition of the ferromagnetic metallic material is finished at the minimum incidence angle.
  • the magnetic fine particles grow in a direction determined according to what is called a “tangent rule” relating to the incidence angle in a columnar structure in a longitudinal section of the magnetic layer 3 formed by limiting the incidence angle of the magnetic fine particles through the above-mentioned evaporation method. It is also known that although an actual angle, at which the growth of the column occurs, differs from the incidence angle of the magnetic fine particles, the range of the angle at which the growth of the column is not larger than the difference between the maximum incidence angle ⁇ i and the minimum incidence angle ⁇ f.
  • a deposition range should be restricted so that at least, the maximum incidence angle ⁇ i and the minimum incidence angle ⁇ f meet the following relation:
  • the magnetic recording media according to the present invention is applied to recording/reproducing apparatus having MR head or GMR head. It is preferable for reducing noises and enhancing C/N that the magnetic layer 3 should be formed in such a way as to be extremely thin.
  • the thickness of the magnetic layer ranges from 5 nm to 55 nm. In the case that the magnetic layer has a thickness that is less than 5 nm, a sufficient reproduction output sometimes cannot be obtained even when, for example, high-sensitivity GMR head is used. Conversely, in the case that the magnetic layer 3 is formed in such a way as to be thicker than 55 nm, a desired recording density sometimes cannot be achieved when MR head or GMR head is employed.
  • ferromagnetic metallic material constituting the magnetic layer 3 Various kinds of materials, for example, ferromagnetic metals such as Co and Ni, Co—Ni alloy, Co—Fe alloy, Co—Ni—Fe alloy, Co—Cr alloy, Co—Pt alloy, Co—Pt—B alloy, Co—Cr—Ta alloy, and Co—Cr—Pt—Ta alloy, or materials such as those obtained by performing the deposition thereof in oxygen environment so that oxygen is contained in resultant film, or materials made to contain one or more other kinds of elements into the above mentioned materials may be applied as the ferromagnetic metallic material constituting the magnetic layer 3 .
  • ferromagnetic metals such as Co and Ni, Co—Ni alloy, Co—Fe alloy, Co—Ni—Fe alloy, Co—Cr alloy, Co—Pt alloy, Co—Pt—B alloy, Co—Cr—Ta alloy, and Co—Cr—Pt—Ta alloy, or materials such as those obtained by performing the deposition thereof in oxygen environment so
  • an intermediate layer (not shown) may be formed between the magnetic layer 3 and the nonmagnetic support 1 , in addition to the underlying layer 2 , by using the vacuum thin film forming technique so as to miniature crystal particles constituting the magnetic layer 3 and to improve the orientation thereof.
  • the vacuum thin film forming techniques are, for instance, a vacuum evaporation method of heating and evaporating a predetermined material under vacuum conditions and causing the evaporated material to adhere to a target to be processed, an ion-plating method of evaporating a predetermined material during electric discharge, and what are called physical vapor deposition (PVD) methods, such as a sputtering method of causing glow discharge in atmosphere, whose primary ingredient is argon, and impacting and ejecting atoms of a surface of a target with generated argon ions.
  • PVD physical vapor deposition
  • the materials constituting the intermediate layer are metallic materials, such as Co, Cu, Ni, Fe, Zr, Pt, Au, Ta, W, Ag, Al, Mn, Cr, Ti, V, Nb, Mo, and Ru, alloys each obtained by combination of given two or more kinds of such materials, or compounds of these metallic materials, and oxygen or nitrogen, compounds of silicon dioxide, silicon nitride, ITO (Indium Tin Oxide), In 2 O 3 , and Zr, carbon, and diamond-like carbon.
  • metallic materials such as Co, Cu, Ni, Fe, Zr, Pt, Au, Ta, W, Ag, Al, Mn, Cr, Ti, V, Nb, Mo, and Ru, alloys each obtained by combination of given two or more kinds of such materials, or compounds of these metallic materials, and oxygen or nitrogen, compounds of silicon dioxide, silicon nitride, ITO (Indium Tin Oxide), In 2 O 3 , and Zr, carbon, and diamond-like carbon.
  • the protective layer 4 made of diamond-like carbon is formed on the magnetic layer 3 so as to ensure favorable running durability and corrosion resistance.
  • the protective layer 4 may be formed by CVD (Chemical Vapor Deposition) method using, for example, a plasma CVD continuous-film-formation apparatus.
  • CVD methods such as a mesh-electrode DC plasma method, an electron-beam-excited plasma source method, a cold cathode ion source method, an ionized evaporation method, and a catalytic CVD method, may be used.
  • Known materials, such as hydrocarbon compounds, ketonic compounds, and alcohol compounds may be used as carbon compounds used for the CVD method.
  • Ar gas or H 2 gas may be introduced thereinto as a gas for accelerating the decomposition of carbon compounds.
  • a lubricant layer 5 may be formed by applying, for instance, an arbitrary perfluoropolyether lubricant thereto so as to improve the running performance.
  • a backcoating layer 6 is formed with the intention of improving the running performance and preventing electrostatics.
  • the film thickness of the backcoating layer 6 is about 0.2 to 0.7 ⁇ m.
  • the backcoating layer 6 is formed by dispersing solid particles of inorganic pigments into the binder and then performing kneading thereof together with an organic solvent selected according to the kind of the binder to thereby prepare a coating material for a backcoating layer, and subsequently applying this coating material on the back surface of the nonmagnetic support 1 . It is desirable that a predetermined lubricant is applied onto the surface of the backcoating 6 .
  • the magnetic recording medium of the present invention manufactured in the above-described manner is suitable for use in a helical-scan magnetic recording system using MR head.
  • MR head is a reproduction-only magnetic head adapted to detect signals sent from a magnetic recording medium by utilizing the magnetoresistive effect.
  • the MR heads are higher in sensitivity and larger in reproduction output than inductive magnetic heads, which perform recording/reproducing by utilizing electromagnetic induction. Therefore, the MR heads are suitable for use with a high-recording-density magnetic recording medium.
  • the MR head has a substantially rectangular MR-device portion held between a pair of magnetic shields, which are made of a soft magnetic material, such as Ni—Zn polycrystalline ferrite through an insulator. Paired terminals are drawn out of both ends of the MR device portion. Sense current is supplied through these terminals to the MR-device portion.
  • the MR-device portion When signals sent from the magnetic recording medium are reproduced by using the MR head, the MR-device portion is slid on the magnetic recording medium. During this state, a sense current is supplied to the MR-device portion through the terminals connected to both ends of the MR-device portion that detects change in the voltage level of this sense current.
  • a sense current is supplied to the MR-device portion during the MR-device portion is slid on the magnetic recording medium, the magnetization direction of the MR-device portion changes according to a magnetic field generated from the magnetic recording medium. The relative angle between the magnetization direction of the MR-device portion and the direction of the sense current supplied to the MR-device changes.
  • a resistance value changes depending upon the relative angle between the magnetization direction of the MR-device portion and the direction of the sense current.
  • a change in the voltage level of the sense current is caused by maintaining the value of the sense current, which is supplied to the MR-device portion, at a constant value.
  • a magnetic field generated by the signal sent from the magnetic recording medium is detected by detecting the change in the voltage level of the sense current. Consequently, the signal recorded on the magnetic recording medium is reproduced.
  • a giant magnetoresistive effect magnetic head may be applied as a reproducing magnetic head.
  • Various techniques for applying a bias magnetic field to the MR-device for instance, a permanent-magnet biasing method, a shunt current biasing method, a self-biasing method, an exchange biasing method, a barber pole method, a divided device method or a servo-biasing method, are applicable, in addition to SAL biasing method.
  • the giant magnetoresistive effect device and various kinds of bias methods are described in detail in, for instance, “MAGNETORESISTIVE HEADS—Fundamentals and Applications” translated by Kazuhiko Hayashi and published by Maruzen Co. LTD.
  • a polyethylene terephthalate (PET)film which is 6.3 ⁇ m in film thickness and 150 mm in width, was prepared as a nonmagnetic support 1 .
  • PET polyethylene terephthalate
  • the underlying layer 2 was formed by applying a coating, which was obtained by dispersing 10 nm diameter silica particles in a water-soluble latex whose main ingredient was an acrylic ester, onto the nonmagnetic support 1 so that the density was 1 ⁇ 10 7 per mm 2 .
  • an intermediate layer made of diamond-like carbons was formed on the underlying layer 2 by the plasma CVD method so that the film thickness of the underlying layer 2 was 3 nm.
  • a magnetic layer 3 was formed by using the vacuum evaporator 40 illustrated in FIG. 4.
  • the material of the magnetic layer 3 was Co. From an oxygen gas introducing pipe, 6 ⁇ 10 ⁇ 4 m 3 /min of oxygen was introduced thereinto. Electron beams 50 were irradiated from the electron beam source 49 onto the material thereby to heat the material.
  • the Co—CoO based magnetic layer was formed by reactive vacuum evaporation in such a way as to be 50 nm in film thickness. At that time, the incident angles of the Co evaporation particles were adjusted as the minimum incidence angle of 45° and as the maximum incidence angle of 70° by the first shutter 51 and the second shutter 52 .
  • a protective layer 4 constituted by a diamond-like carbon was formed on the magnetic layer 3 by the plasma CVD method in such a manner as to have a film thickness of 10 nm.
  • Lubricant layer 5 having a film thickness of 2 nm was formed on the protective layer 4 by applying a perfluoropolyether lubricant thereon.
  • a coating material including carbon particles, whose average diameter was 20 nm, and an urethane resin was applied on a major surface opposite to the surface on which the magnetic layer was form, by using a direct gravure method, so that a 0.5 ⁇ m thick backcoating layer was formed.
  • a raw sheet of an objective magnetic recording medium 10 was obtained.
  • the raw sheet was cut into 8-mm width pieces, so that a sample magnetic tape piece was obtained.
  • sample magnetic tape pieces of Example 2, Example 3, and Comparative Example 1 to Comparative Example 5 were obtained by changing predetermined ones of the conditions as below for manufacturing the magnetic recording medium.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 30 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 40° and 60°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 1.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 40 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 65° and 90°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 1.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 50 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 40° and 70°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 1.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 50 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 45° and 75°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 1.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 30 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 40° and 70°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 2.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 40 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 45° and 90°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 3.
  • Magnetic tape was manufactured by setting the film thickness of the magnetic layer 3 to be 57 nm, and adjusting the minimum incidence angle and the maximum incidence angle of evaporated Co particles to 45° and 70°, respectively, and maintaining the other conditions that were the same as the corresponding conditions in the case of Example 1.
  • MIG Metal-In-Gap
  • MIG Metal-In-Gap
  • Measurement of the electromagnetic conversion characteristic was performed by recording a signal at a recording wavelength of 0.3 ⁇ m with the MIG head and by thereafter reproducing the signal with Ni—Fe MR head whose track width was 5 ⁇ m. Then, the evaluation of the CNR was performed.
  • the relative speed between the sample magnetic tape and the MR head was set to be 7 m/sec.
  • Example 1 to Example 3 meet the conditions that the magnetic tapes has a 55 nm or less thickness magnetic layer formed on the major surface of the elongated nonmagnetic support by performing a vacuum thin film forming technique, and that let ⁇ , ⁇ i, ⁇ f designate an angle which a growth direction of magnetic fine particles in a columnar structure in a longitudinal cross-section of the magnetic layer forms with a normal to the longitudinal direction of the nonmagnetic support, an angle at an initial growth portion of the magnetic layer, and an angle at a final growth portion of the magnetic layer, respectively, and then the angles ⁇ i and ⁇ f have the following relation: ⁇ i ⁇ f ⁇ 25°.
  • a magnetic tape having the magnetic layer 3 whose film thickness was 50 nm, and another magnetic tape having the magnetic layer 3 , whose film thickness was 150 nm, were manufactured by the vacuum evaporator shown in FIG. 4.
  • plural sample tapes were manufactured, among which the difference ( ⁇ i ⁇ f) between the angle ⁇ i at an initial growth portion of the magnetic layer and the angle ⁇ f at the final growth portion thereof was changed by controlling the maximum incidence angle and the minimum incidence angle.
  • the electromagnetic conversion characteristic (CNR) of each of these sample magnetic tapes was measured.
  • FIG. 6 shows the relation between the value of tan ( ⁇ i ⁇ f) and the relative value of the electromagnetic conversion characteristic (CNR).
  • FIG. 6 indicates the presence of the causal relation between the value of tan ( ⁇ i ⁇ f) and the relative value of the electromagnetic conversion characteristic (CNR).
  • the electromagnetic conversion characteristic (CNR) noticeably changed within a range of the value of tan ( ⁇ i ⁇ f) from 0.4 to 0.6.
  • the limit to tolerable degradation of the electromagnetic conversion characteristic was set to ⁇ 0.5 dB, the corresponding value of tan ( ⁇ i ⁇ f) was about 0.47.

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