JP2005056504A - Information recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an information recording medium which is excellent in storage stability and on which high-density recording is possible in an optical assistant magnetic recording or a surface recording type magnetic field modulation magneto-optical recording. <P>SOLUTION: This information recording medium 1 is characterized by forming a reflective layer 3, an interference layer 4, a base layer 5, a perpendicular magnetic recording layer 6 consisting of cobalt/palladium multilayered film and a protective layer 7 in this order at least one surface of a non-magnetic support body 2. It is desirable that this medium is used in an optical information recording medium which performs the recording and/or the reproducing of information by making light to be incident on the magnetic recording layer 6 through the protective layer 7 of this medium 1 or an optical assist magnetic recording. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an information recording medium, and more particularly to an information recording medium capable of magneto-optical recording and optical-assisted magnetic recording.

  In recent years, with the spread of the Internet, the use form of computers has changed, such as processing of large-capacity moving image information and audio information using a personal computer. Accordingly, the storage capacity required for magnetic recording media such as hard disks is also increasing.

  Currently, the magnetic recording method employed in commercially available hard disk devices is a longitudinal magnetic recording method in which magnetization is performed in the running direction of the recording medium, but due to “thermal fluctuation” in which magnetization information recorded on the medium is lost by heat. It is said that there is a limit to increasing the density. On the other hand, a perpendicular magnetic recording method that performs magnetization perpendicular to the disk surface of the recording medium is expected as a next-generation magnetic recording method that realizes high density, and as a magnetic material for perpendicular magnetic recording, Cobalt-chromium alloys (Co-Cr) have been considered promising.

  However, when high-density recording exceeding 100 Gbit / inch 2 is to be performed, the influence of thermal fluctuation becomes strong even in the perpendicular magnetic recording system. Therefore, as a perpendicular magnetic recording material, a rare earth transition metal alloy such as TbFeCo, which has a high perpendicular magnetic anisotropy Ku as compared with a CoCr alloy and is thermally stable, and a transition metal / noble metal multilayer such as Co / Pd and Co / Pt Films, rare earth noble metal alloys such as FePt, and the like are attracting attention.

  These high Ku materials have strong magnetic coupling in the in-plane direction and tend to be domain wall motion recording. When recording a very small recording signal with such a recording material, the written recording signal is disturbed or lost due to the movement of the domain wall, so that it is noisy and used as a magnetic recording medium material. Is difficult. For this reason, recently, optically assisted magnetic recording, in which laser light is irradiated near the head to be recorded on the medium, heated, and the temperature is increased and the coercive force is decreased, is focused. Has been. The optically assisted magnetic recording has a feature that a small recording mark can be clearly recorded even on a recording material having high coercive force Hc and high Ku at room temperature and strong in-plane exchange coupling.

  Since the recording process of the optically assisted magnetic recording is almost the same as that of the magnetic field modulation magneto-optical recording MO, the same recording material as that of the conventional magnetic field modulation MO is arranged in the vicinity of the magnetic head, that is, substantially the same structure as the magnetic disk. A recording medium can be produced. However, since the TbFeCo alloy used as a conventional magnetic field modulation MO recording material contains Tb that is very easily oxidized, it is easily oxidized only by an extremely thin protective layer such as a conventional magnetic disk, which is sufficient. There is a problem that it is difficult to ensure reliability.

Therefore, when an attempt is made to use a transition metal / noble metal multilayer film material such as a Co / Pd multilayer film or a Co / Pt multilayer film excellent in corrosion resistance as a recording material (see, for example, Patent Document 1), Hc is not obtained in these multilayer films alone. If it is too low to be used and an undercoat layer is applied to increase Hc, there is a problem that the heat diffusion rate increases and heating with a laser cannot be performed sufficiently.
JP-A-1-251356

  The present invention has been made in view of the above-described problems of the prior art, and is intended to provide an information recording medium that is excellent in storage stability and capable of high-density recording in optically assisted magnetic recording or surface recording type magnetic field modulation MO recording. To do.

In order to achieve the above object, the present invention is as follows.
(1) An information recording medium comprising a reflecting layer, an interference layer, an underlayer, a perpendicular magnetic recording layer made of a cobalt / palladium multilayer film, and a protective layer formed in this order on at least one surface of a nonmagnetic support. .
(2) The optical recording medium for recording information and / or reproducing information by making light incident on the recording layer through the protective layer of the information recording medium, or used for optically assisted magnetic recording (1) Information recording media.

  The information recording medium of the present invention uses a Co / Pd multilayer film as a recording material and does not contain an easily oxidizable element such as a rare earth element, and therefore has excellent corrosion resistance and storage stability. In addition, in order to improve thermal conductivity, the laser power can be reduced by providing each layer in an appropriate layer configuration and order, such as a reflective layer that easily diffuses heat, an interference layer that hardly diffuses heat, and an underlayer that easily diffuses heat. Effectively used, optical assist or surface recording MO recording becomes possible.

  Further, the information recording medium of the present invention uses a Co / Pd multilayer film having a large Kerr rotation angle of light in a short wavelength region of wavelength 660 nm or less as a recording film, and further, each layer such as a reflective layer and a protective layer is an appropriate layer. Since the Kerr effect can be enhanced by setting the configuration and order, it is promising as a surface recording type MO medium using a short wavelength laser.

Hereinafter, the present invention will be described in detail with reference to FIG.
A non-magnetic support (hereinafter also simply referred to as a support or a substrate) 2 used in the information recording medium 1 of the present invention is a glass substrate processed into a disk shape, an aluminum substrate, silicon when used in the form of a hard disk. A substrate, a carbon substrate, a polycarbonate substrate, or the like can be used. The disk size is not particularly limited, and a general disk-shaped substrate of 1.0 inch to 5.25 inch can be used. The thickness is not particularly limited, and a thickness of 0.1 to 2.0 mm can be used. In addition, in the hard disk, since the recording and reproduction is performed while the magnetic head is moved slightly floating, the surface roughness of the substrate is preferably smooth. For this reason, the substrate surface is polished physically or chemically, Mirror finish is preferred. In the present invention, a perpendicular magnetic recording layer (hereinafter also referred to as “magnetic recording layer” or “magnetic layer”) 6 comprising a cobalt / palladium multilayer film is used. This magnetic layer is formed at room temperature without heating the substrate. However, since sufficient magnetic properties can be obtained, the substrate heating required when using a CoCr-based alloy is unnecessary, and it is excellent in productivity and at the same time difficult to use with a CoCr-based alloy. Substrates can also be used.

  In addition, when used in the form of a flexible disk, a flexible polymer material can be used. Flexible polymer materials include aromatic polyimide, aromatic polyamide, aromatic polyamideimide, polyether ketone, polyethersulfone, polyetherimide, polysulfone, polyphenylene sulfide, polyethylene naphthalate, polyethylene terephthalate, polycarbonate, triacetate A resin film composed of cellulose, fluororesin, or the like can be used.

  The resin film may be laminated with the same resin film or another resin film. By laminating the resin film, warpage and undulation caused by the support itself can be reduced. As a result, it is possible to reduce the surface blurring during the rotation of the disk, the collision frequency and the collision strength between the head and the disk can be reduced, and the scratch resistance of the magnetic recording layer can be remarkably improved. In addition, since the magnetic recording layer can be handled in a state where it is formed on one side at the time of manufacture, the surface is less likely to be scratched and defects due to film meandering are less likely to occur than when the magnetic recording layer is formed on both sides of the support.

  As a laminating method, roll laminating using a heat roller, laminating using a flat plate heat press, or the like can be used. Examples of the method for applying the adhesive include a method of applying and laminating an adhesive on the adhesive surface, a method of using an adhesive sheet in which an adhesive is previously applied to a release paper, and the like. The type of the adhesive is not particularly limited, and a general hot melt adhesive, thermosetting adhesive, UV curable adhesive, EB curable adhesive, pressure-sensitive adhesive sheet, anaerobic adhesive, or the like may be used. Yes.

  The thickness of the flexible polymer support is 10 μm to 200 μm, preferably 20 μm to 150 μm, and more preferably 25 μm to 80 μm. When the thickness of the support 2 is 10 μm or more, stability during high-speed rotation is improved, and surface blurring is reduced. On the other hand, when the thickness of the support 2 is 200 μm or less, the rigidity at the time of rotation becomes low, it becomes easy to avoid the impact at the time of contact, and the jump of the magnetic head is prevented.

The waist strength of the support 2 represented by the following formula is preferably such that the value at b = 10 mm is in the range of 4.9 to 19.6 MPa (0.5 to 2.0 kgf / mm ² ), 6.86-14.76 MPa (0.7-1.5 kgf / mm < ² >) is more preferable.

The waist of the strength of the support = Ebd ^3/12

  In this equation, E represents Young's modulus, b represents film width, and d represents film thickness.

  The surface of the flexible polymer support is preferably as smooth as possible in order to perform recording with a magnetic head. Unevenness on the surface of the support significantly reduces the signal recording / reproducing characteristics. Specifically, in the case of using an undercoat layer to be described later, the surface roughness measured by an optical surface roughness meter is 5 nm or less, preferably 2 nm or less, and stylus type surface roughness as the center plane average roughness SRa. The protrusion height measured by the meter is within 1 μm, preferably within 0.1 μm. In the case where an undercoat film is not used, the surface roughness measured with an optical surface roughness meter is within 3 nm, preferably within 1 nm, as the center plane average roughness SRa, and the protrusion measured with a stylus type surface roughness meter The height is within 0.1 μm, preferably within 0.06 μm.

  An undercoat layer is preferably provided on the surface of the support on the side where the magnetic recording layer is provided for the purpose of improving planarity. Since the magnetic recording layer is formed by sputtering or the like, the undercoat layer is preferably excellent in heat resistance. As the material of the undercoat layer, for example, a polyimide resin, a polyamideimide resin, a silicon resin, a fluorine resin, or the like can be used. it can. Thermosetting polyimide resins and thermosetting silicone resins are particularly preferred because they have a high smoothing effect. The thickness of the undercoat layer is preferably 0.1 μm to 3.0 μm. When another resin film is laminated on the support 2, an undercoat layer may be formed before laminating, or an undercoat layer may be formed after laminating.

  As the thermosetting polyimide resin, for example, polyimide obtained by thermal polymerization of an imide monomer having two or more terminal unsaturated groups in the molecule, such as bisallyl nadiimide “BANI” manufactured by Maruzen Petrochemical Co., Ltd. Resins are preferably used. Since this imide monomer can be thermally polymerized at a relatively low temperature after being applied to the surface of the support in the monomer state, the monomer as a raw material can be directly applied to the support and cured. In addition, this imide monomer can be used by being dissolved in a general-purpose solvent. It has excellent productivity and workability, has a low molecular weight, and its solution viscosity is low. Is expensive.

  As the thermosetting silicon resin, a silicon resin polymerized by a sol-gel method using a silicon compound having an organic group introduced as a raw material is preferably used. This silicon resin has a structure in which a part of the silicon dioxide bond is substituted with an organic group, and has a heat resistance significantly higher than that of silicon rubber, and also has a flexibility higher than that of a silicon dioxide film, and thus a flexible film. Even if a resin film is formed on the support, cracks and peeling are unlikely to occur. Moreover, since the monomer used as a raw material can be directly applied and cured on the support, a general-purpose solvent can be used, the wrapping around the unevenness is good, and the smoothing effect is high. Furthermore, since the condensation polymerization reaction proceeds from a relatively low temperature by adding a catalyst such as an acid or a chelating agent, it can be cured in a short time, and a resin film can be formed using a general-purpose coating apparatus.

  The surface of the undercoat layer is preferably provided with minute protrusions (textures) for the purpose of reducing the true contact area between the magnetic head and the magnetic disk and improving the sliding characteristics. Moreover, the handling property of the support is improved by providing the fine protrusions. As a method for forming the fine protrusions, a method of applying spherical silica particles, a method of forming an organic protrusion by applying an emulsion, and the like can be used. However, in order to ensure the heat resistance of the undercoat layer, the spherical silica particles are applied. Thus, it is preferable to form minute protrusions.

The height of the microprojections is preferably 5 nm to 60 nm, and more preferably 10 nm to 30 mm. When the height of the minute protrusions is 60 nm or less, there is no spacing loss between the recording / reproducing head and the medium, and the signal recording / reproducing characteristics are not deteriorated. Further, when the height of the fine protrusion is 5 nm or more, the effect of improving the sliding characteristics is further enhanced. The density of minute projections is preferably from 0.1 to 100 pieces / [mu] m ^2, more preferably 1 to 10 / [mu] m ^2. When the density of the fine protrusions is 0.1 piece / μm ² or more, the effect of improving the sliding characteristics becomes higher. When the density is 100 pieces / μm ² or less, the aggregated particles do not increase and the high protrusions do not increase. Reproduction characteristics do not deteriorate.

  In addition, the fine protrusions can be fixed to the support surface using a resin as a binder. As the binder, it is preferable to use a resin having sufficient heat resistance, and it is particularly preferable to use a thermosetting polyimide resin or a thermosetting silicone resin as the resin having heat resistance.

  In the present invention, between the nonmagnetic support 2 and the magnetic recording layer 6, in order to control the diffusion rate of heat and to enhance the Kerr rotation angle, a reflection layer (similar to a general magneto-optical disk) Membrane) 3 is provided. For the reflective film, a light reflective material having a high reflectivity with respect to laser light is used. Examples of such a light reflective material include Al, Al—Cu, Al—Ti, Al—In, Al—Nb, Al—Ta, Ag, Ag—Cu, Ag—Pd, Ag—Pd—Cu, and Au. And metals such as Cu and semi-metals. These substances may be used alone or in combination of two or more. This reflective film can be formed by sputtering or electron beam vacuum deposition of the light reflective material on a nonmagnetic support. The thickness of the reflective film is preferably 10 nm to 200 nm. The thicker the reflective film, the faster the heat diffusion rate and the higher the light reflectance. On the other hand, the thinner the reflective film, the slower the heat diffusion rate and the lower the light reflectance.

In the present invention, the interference layer 4 is provided on the reflective film 3. This interference layer is preferably silicon nitride SiN _x used as a protective layer for the MO medium, but other than this, it is transparent and does not affect the properties of the underlayer 5 and magnetic layer described later, has a high refractive index, and is made of a transparent material. If available, it can be used. For example, oxides such as silica and alumina (Si-O, Al-O), nitrides such as aluminum nitride (Si-N, Al-N), sulfides such as zinc sulfide (Zn-S), diamond-like carbon And the like. Moreover, the mixture of these materials may be sufficient. This interference layer can be formed by sputtering, vacuum deposition, chemical vapor reaction (CVD), or the like. The thickness of the interference layer is determined in consideration of the thermal conductivity and the enhancement effect of the Kerr effect. The thicker the interference layer, the lower the heat diffusion rate, and the thinner, the faster the heat diffusion rate. Since the enhancement of the Kerr effect uses multiple reflections between the reflective film and the magnetic layer, there is an optimum point in the thickness of the interference layer depending on the wavelength used, the type of reflective layer material, the thickness of the underlayer, and the thickness of the Co / Pd magnetic layer. . For example, the wavelength of incident light is 660 nm, the reflective layer is an AgCu alloy, the thickness is 50 nm, the thickness of the underlayer is 2 nm, the thickness of the Co / Pd magnetic layer is 15 nm, and the later-described protective layer 7 on the magnetic layer has a refraction of 2.0. a SiN _x, when the interference layer material is SiN _x having a refractive index of 2.0, the Kerr effect is maximized in thickness 80nm~90nm interference layer. When used as an MO medium, in the Kerr effect enhancement using such multiple reflection, the MO output is proportional to the product of the Kerr rotation angle and the square root of the reflectivity, so that the reflectivity decreases. However, it is better to design the car rotation angle to be large.

In the present invention, in order to improve the recording characteristics of the magnetic recording layer 6, the underlayer 5 is provided as a lower layer of the magnetic layer. Since this underlayer can reduce the initial growth layer of the magnetic layer, a recording medium with high Hc and low noise can be obtained. The thickness of the underlayer is preferably from 0.5 to 10 nm, particularly preferably from 1.0 to 5.0 nm. The underlayer can be produced by a so-called vacuum film forming method such as a sputtering method or a vacuum evaporation method.
Although it does not specifically limit as an element which comprises a base layer, Palladium, platinum, gold | metal | money, silver, copper etc. are mentioned. Among these, palladium is preferable from the viewpoint of ease of formation and cost.

  The Co / Pd multilayer film that becomes the magnetic layer 6 is a multilayer film in which, for example, 10 to several tens of layers of a Co thin film of 0.2 nm and a Pd thin film of 0.8 nm are stacked, and the vertical direction depends on the lattice strain of the Co film in contact with the Pd film. It is thought that magnetic anisotropy appears. The thickness of the cobalt film is preferably 0.10 to 1.00 nm, and more preferably 0.15 to 0.50 nm. If the thickness of the cobalt film is 0.10 nm or more, the recording layer reliably has magnetism, and if it is 1.00 nm or less, the coercive force is improved and noise is reduced. The thickness of the platinum film or palladium film is preferably 0.10 to 2.0 nm, and more preferably 0.40 to 1.20 nm. If the thickness of the platinum film or the palladium film is 0.10 nm or more, the perpendicular magnetic anisotropy is improved, the output is improved or the noise is reduced, and if it is 2.0 nm or less, the magnetization is increased. improves. The thickness of the magnetic layer made of a multilayer film is preferably 5 nm to 50 nm, and particularly preferably 10 to 25 nm. If the thickness of the magnetic layer is 50 nm or less, the light transmission is improved and the heat diffusion rate is lowered. Moreover, if it is 5 nm or more, Hc becomes high and can be suitably used as a high-density recording medium. In order to obtain such a magnetic layer thickness, a necessary amount of the above-described Co or Pd film may be stacked. By controlling these film configurations and film forming conditions described later, the coercive force in the perpendicular direction of the magnetic recording layer can be controlled. The coercive force is preferably in the range of 119.4 to 636.8 kA / m (1500 to 8000 Oe).

  Examples of the method for producing the magnetic recording layer include a physical vapor deposition method (PVD method) such as a vacuum vapor deposition method, a sputtering method, an ion plating method, and an ion implantation method. In terms of easy composition control, A sputtering method is particularly preferred. As a sputtering method, in addition to general DC sputtering and RF sputtering, DC pulse sputtering, RF bias sputtering, reactive sputtering, and the like can be used. At the time of sputtering, cobalt and palladium or platinum as targets, a method of rotating and passing a substrate holding a support on these targets, or conversely, fixing a substrate holding a support, A method of rotating and passing the target can be used. When a recording layer is provided on a web-like support, the required number of targets and cathodes are installed, and the web is transported on the target and sputtered, or cobalt, palladium, or platinum is alternately used as the target in the transport direction. It is possible to use a method in which the webs are stacked so as to become and the web is transported onto the web and sputtered. The perpendicular magnetic recording layer of the present invention can be produced by a sputtering method and can be formed at room temperature. Therefore, even though a flexible nonmagnetic support is used, there is no substrate deformation and excellent flatness. ing.

  The protective layer 7 on the magnetic layer is provided to prevent corrosion of the magnetic recording layer, to prevent wear due to pseudo contact or contact sliding between the magnetic head and the magnetic disk, and to improve running durability and corrosion resistance. . The protective layer may be the same as or different from the interference layer material between the reflective layer and the underlying layer. This protective layer is preferably diamond-like carbon DLC with high hardness in order to enhance the function of protecting the information recording medium from contact with the magnetic head and optical head, but other than this, it is transparent and does not affect the characteristics of the underlayer or magnetic layer. Any transparent material having a high refractive index and a high hardness can be used. For example, oxides such as silica and alumina (Si-O, Al-O), nitrides such as silicon nitride and aluminum nitride (Si-N, Al-N), sulfides such as zinc sulfide (Zn-S), etc. Is mentioned. Moreover, the mixture of these materials may be sufficient. This dielectric layer can be formed by sputtering, vacuum deposition, chemical vapor reaction (CVD), or the like. The film thickness of the dielectric layer is determined in consideration of the amount of magnetic spacing, the protective layer effect, and the Kerr effect enhancement effect. In other words, when the film thickness is thin, the magnetic spacing is reduced, which is advantageous for reading and writing with a magnetic head, but the enhancement of the Kerr effect is reduced, and the recording layer is protected from wear and corrosion as a protective layer. The effect is diminished. The reverse is true when it is thick. Since the optically assisted magnetic recording medium and the surface recording type magnetic field modulation MO medium, which are the objects of the present invention, are premised on reading or writing by a magnetic head, the thickness of this protective film is 1 to 30 nm, preferably 2 to 2 nm. The range is 20 nm.

A lubricating layer (film) 8 is preferably provided on the protective layer 7 in order to improve running durability and corrosion resistance. As the lubricating film, a known lubricant such as a hydrocarbon-based lubricant, a fluorine-based lubricant, or an extreme pressure additive is used.
Hydrocarbon lubricants include carboxylic acids such as stearic acid and oleic acid, esters such as butyl stearate, sulfonic acids such as octadecyl sulfonic acid, phosphate esters such as monooctadecyl phosphate, stearyl alcohol, oleyl alcohol And the like, carboxylic acid amides such as stearamide, and amines such as stearylamine.

Examples of the fluorine-based lubricant include a lubricant in which part or all of the alkyl group of the hydrocarbon-based lubricant is substituted with a fluoroalkyl group or a perfluoropolyether group. Examples of perfluoropolyether groups include perfluoromethylene oxide polymer, perfluoroethylene oxide polymer, perfluoro-n-propylene oxide polymer (CF ₂ CF ₂ CF ₂ O) _n , perfluoroisopropylene oxide polymer (CF (CF ₃ ) CF ₂ O) _n or a copolymer thereof. Specifically, a perfluoromethylene-perfluoroethylene copolymer having a hydroxyl group at the molecular weight terminal (trade name “FOMBLIN Z-DOL” manufactured by Augmont Co., Ltd.) and the like can be mentioned.

Extreme pressure additives include phosphate esters such as trilauryl phosphate, phosphites such as trilauryl phosphite, thiophosphites and thiophosphates such as trilauryl trithiophosphite, dibenzyl disulfide And sulfur-based extreme pressure agents such as
The above lubricants can be used alone or in combination, and a solution in which the lubricant is dissolved in an organic solvent is applied to the protective layer 7 by spin coating, wire bar coating, gravure coating, dip coating or the like. What is necessary is just to apply | coat to the surface or to make it adhere to the surface of the protective layer 7 by a vacuum evaporation method. The coating amount of the lubricant is preferably ^{1~30mg / m 2, 2~20mg / m} 2 is particularly preferred.

Moreover, in order to further improve corrosion resistance, it is preferable to use a rust inhibitor together. Antirust agents include nitrogen-containing heterocycles such as benzotriazole, benzimidazole, purine and pyrimidine, and derivatives in which an alkyl side chain is introduced into the mother nucleus, benzothiazole, 2-mercapton benzothiazole, tetrazaindene Examples thereof include nitrogen- and sulfur-containing heterocycles such as ring compounds and thiouracil compounds and derivatives thereof. These rust preventives may be mixed with a lubricant and applied onto the protective layer 7, or may be applied onto the protective layer 7 before applying the lubricant, and the lubricant may be applied thereon. As an application quantity of a rust preventive agent, 0.1-10 mg / m < ² > is preferable and 0.5-5 mg / m < ² > is especially preferable.

  The magnetic recording medium manufactured by the above-described manufacturing method may cause aggregation of dust and lubricant adhered in the manufacturing process. For this reason, the produced magnetic recording medium is preferably cleaned by a cleaning process such as heat treatment, wiping, or burnishing.

  In a magnetic disk, tracking servo is used to position the magnetic head and the optical head. The information recording medium of the present invention reads a servo signal on a medium conventionally used in a hard disk and uses a sample servo system in which the head follows in accordance with the signal, and has been conventionally used in an optical disk and an MO disk. Any of the optical servo systems that read the land / groove information of the substrate with light can be used. Furthermore, in the information recording medium of the present invention, the method described later is particularly suitable for recording the tracking information magnetically on the medium and reading it using the Kerr rotation angle of light.

  The method for recording the tracking signal of the magnetic signal on the magnetic disk, that is, the method for preformatting the magnetic recording layer is not particularly limited. For example, the magnetized region may be written by a magnetic head, or the magnetized region may be formed by magnetic transfer. In order to form a magnetized region having a fine pattern in a short time, it is particularly preferable to form the magnetized region by magnetic transfer.

  Magnetic transfer is a method in which a magnetic signal is transferred from a master carrier on which a soft magnetic layer is formed to a slave medium having a magnetic recording layer before being magnetized to form a magnetized region having a predetermined pattern. The master carrier is a convex soft magnetic layer made of a ferromagnetic material such as Co or Fe having a high magnetic flux density formed on a substrate made of a nonmagnetic material such as silicon or aluminum in accordance with the transfer pattern. A conductive layer made of a nonmagnetic metal material such as Cr or Ti can be provided between the substrate and the magnetic layer as necessary. The master carrier can be produced using a stamper used for photofabrication or formation of an optical disk substrate. For example, a master layer can be obtained by forming a magnetic layer on a nickel substrate having a predetermined pattern formed by a stamper. Hereinafter, a method for forming the magnetized region by magnetic transfer will be specifically described.

First, a DC magnetic field in a certain direction is applied to each of both surfaces of the non-magnetic support to the information recording medium of the present invention before being magnetized, thereby exciting the magnetic recording layer of the slave medium in the magnetic field application direction (initial stage). Magnetization). Note that the magnetic recording layer is initially magnetized and becomes the entire magnetized region.
Next, the master carrier is brought into close contact with the initially magnetized slave medium, a DC magnetic field or an AC bias magnetic field in the opposite direction is applied as a transfer magnetic field, and the magnetic layer is excited in this direction. As a result, a magnetic field is applied from the portion where the slave medium and the magnetic layer are in contact to the corresponding portion of the magnetic recording layer, the magnetization direction of that portion is reversed, and a reverse magnetization region is formed in the magnetization region. Is done. As a result, precise pre-formatting of the slave medium is performed.

  The servo signal written by this magnetic transfer method may be read by a magnetic head in the same manner as a normal hard disk, but optical tracking using the following MO principle can also be used.

In other words, in this case, when linearly polarized light is irradiated to the magnetized region magnetized in the direction in which the support side is the S pole and the protective layer is the N pole, the polarization plane of the reflected light is changed from the polarization plane of the incident light by the magnetic Kerr effect. It rotates by a predetermined angle θ (for example, clockwise). On the other hand, when the same linearly polarized light is irradiated to the magnetized region magnetized in the direction in which the support side is the N pole and the protective layer side is the S pole, the polarization plane of the reflected light is a predetermined angle from the polarization plane of the incident light due to the magnetic Kerr effect. Rotate by -θ (for example, counterclockwise).
For this reason, when the tracking laser light is irradiated, the irradiated laser light is reflected by the magnetic disk. The reflected light whose polarization plane has been rotated by a predetermined angle is detected from this reflected light through a polarizing plate, etc., and the tracking servo is performed by detecting the relative deviation between the magnetic head and the track by the intensity of this reflected light. it can. That is, the magnetized region provided concentrically or spirally serves as a tracking guide. As a tracking error detection method, a tracking error detection method used in an optical disc, such as a push-pull method or a three-beam method that obtains a tracking error signal using a two-divided photodetector, can be used.

[Example 1]
A mirror-polished 2.5 inch φ hard disk substrate was placed in a sputtering apparatus, and the substrate was cleaned with Ar ions. Thereafter, argon is introduced to a vacuum degree of 0.133 Pa (1 mTorr), an AgCu reflective layer is formed to a thickness of 50 nm using AgCu (10 at%) as a target by DC magnetron sputtering, and then Si ₃ N ₄ is formed. An interference layer made of SiN _x was formed as a target so as to have a thickness of 80 nm, and then a Pd base layer made of Pd and having a thickness of 2.5 nm was formed using a Pd target. Further on this, the film was rotated on a Co target and a Pd target to form a recording layer composed of a Co / Pd multilayer film. The multilayer film has a thickness of Co of 0.2 nm and Pd of 0.8 nm. By laminating 15 layers, a magnetic layer having a thickness of 15 nm was obtained. Further, a protective layer made of SiN _x was formed thereon so as to have a thickness of 20 nm using Si ₃ N ₄ as a target.

  The manufactured magnetic disk is initialized using a permanent magnet with a magnetic field strength of 1T, and then bonded to a magnetic transfer master unit having a spiral pattern with a groove width of 0.3 μm and a land width of 0.6 μm, and is opposite to the initializing magnetic field. A transfer magnetic field [199 kA / m (2500 Oe)] corresponding to the coercive force was applied to the recording medium to record a spiral servo signal.

  The electromagnetic conversion characteristics of this magnetic disk were evaluated by loading an optical head (wavelength: 660 nm, NA: 0.6) at a radius of 25 mm with a rotation speed of 1000 rpm and applying a tracking servo using the transferred servo signal. In this state, a signal of 2 MHz was recorded by an optical modulation method, and the MO output to signal vicinity noise ratio (CNR) was evaluated. In this apparatus, the tracking error signal is detected by using a special three-beam method in which a sub-beam is provided with a Kerr rotation angle detection mechanism, and the external magnetic field during recording is set to 0.05 T (500 G). The laser power during recording was 5.0 mW, and the laser power during reproduction was 1.5 mW. The CNR results were arranged as relative values based on the results of Example 1. The coercive force in the vertical direction of the manufactured disk and the Kerr rotation angle at a wavelength of 660 nm were determined from a Kerr hysteresis curve using a Kerr effect measuring device (K-250 manufactured by JASCO Corporation).

[Examples 2 to 9, Comparative Examples 1 to 3]
In Example 1, Examples 2 to 9 and Comparative Examples 1 and 2 were produced by replacing the film thickness of the protective layer, the underlayer and the magnetic layer with those shown in Table 1. In Comparative Example 3, a reflective film was not prepared, and a sample was prepared in the same manner as in Example 1 except that.

  The evaluation results of the examples are shown in Table 2 below.

  As can be seen from the above results, the information recording medium to which the present invention is applied can secure a high CNR and is suitable for a high-density medium. In the above embodiment, the form of the front-illuminated light modulation MO is shown. However, the same effect is effective as a front-illuminated magnetic field modulation MO and a light-assisted magnetic recording medium.

Schematic which shows the layer structure of the information recording medium of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Information recording medium 2 Nonmagnetic support body 3 Reflective layer 4 Interference layer 5 Underlayer 6 Magnetic recording layer 7 Protective layer 8 Lubrication layer

Claims (2)

  An information recording medium comprising a reflective layer, an interference layer, an underlayer, a perpendicular magnetic recording layer comprising a cobalt / palladium multilayer film and a protective layer formed in this order on at least one surface of a nonmagnetic support.   The information according to claim 1, wherein the information is used for optical information recording medium or optically assisted magnetic recording for recording and / or reproducing information by inputting light to the recording layer through the protective layer of the information recording medium. recoding media.

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