JP2005085325A - Magnetic recording medium and manufacturing method of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a magnetic tape medium having excellent electromagnetic transducing characteristics and archive properties and high reliability at a low cost. <P>SOLUTION: A high density magnetic recording medium 10 is provided, having a magnetic layer 2 consisting of a Co containing maghemite thin film having 10 to 15 wt.% Co content on a long-length substrate 1 consisting of any one of polyethylene terephthalate, polyethylene naphthalate and aramid. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a high-density type magnetic recording medium and a method for manufacturing the same, and particularly in a system using a magnetoresistive head (MR head) or a giant magnetoresistive head (GMR head). It is an object of the present invention to provide a magnetic recording medium in which density recording is realized and excellent in storage stability and a method for manufacturing the same.
It is.

  In recent years, in magnetic recording media, in order to handle a large amount of data, there is an increasing demand for higher density recording. In particular, recently, in order to achieve higher density recording, a magnetic head used for reproducing a recording signal is replaced with a magnetoresistive head (MR head) or a giant magnetoresistive instead of a conventional induction head. High-sensitivity magnetic heads such as effect type magnetic heads (GMR heads) have been applied, and are applied not only to hard disks but also to so-called magnetic tapes.

  As such a high-density type magnetic recording medium, a metal thin film type magnetic recording medium in which a magnetic layer is formed by a so-called sputtering method or vacuum deposition method has been conventionally used. In order to improve the recording density using a thin film, it is required to make the magnetic layer thin to further increase the coercive force and reduce the noise. In addition to the high density recording, there is an increasing demand for so-called archiving that can be stored for a long time without causing deterioration of signal quality.

In order to satisfy various requirements for the magnetic recording medium as described above, a perpendicular recording medium for a hard disk having a structure in which a magnetic layer of a cobalt-containing maghemite thin film is formed by a sputtering method has been proposed (for example, Patent Document 1, 2).
Such cobalt-containing maghemite thin films have excellent storage stability, high film hardness and durability compared to metal thin film magnetic layers, and have a fine particle size because they are formed by sputtering. As compared with the conventional vapor deposition type magnetic tape, there is an advantage that noise can be further reduced.

  On the other hand, with regard to magnetic tape, for example, a metal thin film type magnetic tape has been put into practical use as a next-generation high-density type magnetic recording medium, but the corrosion resistance is inferior to that of a coating type magnetic tape. However, there is still a problem to be solved with respect to the characteristic (archive property) of storing data over a long period of time.

  In addition, when reproducing signals with an MR head or GMR head, it is necessary to make the magnetic layer thinner in order to avoid saturation of the magnetic head, but the coercive force is reduced, and a cobalt-based vapor deposition type magnetic tape. However, there is a problem that stable signal recording becomes difficult.

  In addition, as the magnetic head becomes more sensitive, it is important to further reduce noise caused by the medium side. However, there is a limitation in the manufacturing process for miniaturization of magnetic particles constituting the magnetic layer. It can be said that there is still a problem in reducing noise.

JP 11-328651 A Japanese Patent Laid-Open No. 11-328652

In order to solve the problems of archiving, recording signal stability, noise reduction, etc., which have been problems with magnetic tapes having a magnetic layer mainly composed of cobalt, a magnetic layer comprising a cobalt-containing maghemite thin film is used as a tape medium. Application to is being studied.
However, in order to obtain a high coercive force, the conventional cobalt-containing maghemite thin film requires a heat treatment of about 200 to 300 ° C. at the time of film formation. There is a problem that the coercive force is restricted by the material.

  Therefore, in the present invention, in view of the above-described problems, the coercive force Hc (2000 to 3000 Oe) enables high-density recording even at a heating temperature of about room temperature to 200 ° C., regardless of the material of the substrate (base film). ) Can be obtained, and a method for manufacturing the same.

  In the present invention, the magnetic recording medium is a tape-like magnetic recording medium used in a sliding state with respect to a magnetoresistive magnetic head or a giant magnetoresistive magnetic head, from any of polyethylene terephthalate, polyethylene naphthalate, and aramid. Provided is a magnetic recording medium having a magnetic layer made of a cobalt-containing maghemite thin film having a cobalt content of 10 to 15% by weight on a long substrate.

  Further, the method for producing a magnetic recording medium of the present invention comprises forming a cobalt-containing magnetite thin film by sputtering on a long substrate made of any of polyethylene terephthalate, polyethylene naphthalate, and aramid, Cooling and heat-treating the Co-containing magnetite thin film while heating the cobalt-containing magnetite thin film to form a magnetic layer made of a cobalt-containing maghemite thin film having a cobalt content of 10 to 15% by weight. Shall.

  According to the present invention, it is possible to form a cobalt-containing maghemite thin film having a practically sufficient coercive force Hc on a substrate made of a general-purpose plastic by numerically specifying the cobalt content in the magnetic layer. Become.

  According to the present invention, by specifying the cobalt content of the cobalt-containing maghemite thin film constituting the magnetic layer as 10 to 15% by weight, the cobalt-containing maghemite is suppressed to a temperature applicable to general-purpose plastics in the heating oxidation process. It became possible to form a thin film. As a result, the magnetic recording medium having excellent corrosion resistance at low cost, improved electromagnetic conversion characteristics and archiving properties, and high reliability were obtained.

Moreover, excellent electromagnetic conversion characteristics are obtained by forming minute projections having a height of 5 to 30 nm on the magnetic layer forming surface side at a rate of 0.5 × 10 ^{8 to} 5.0 × 10 ⁸ pieces / mm ^2. Thus, good running stability and running durability were obtained, and a decrease in output due to wear with the magnetic head could be effectively avoided.

Specific embodiments of the magnetic recording medium of the present invention will be described, but the present invention is not limited to the following examples.
A schematic sectional view of an example of the magnetic recording medium 10 of the present invention is shown in FIG. In the magnetic recording medium 10, a magnetic layer 2 is directly formed on one main surface of a long and nonmagnetic substrate 1, and a protective layer 3 and a lubricant layer 4 are sequentially formed on the magnetic layer 2. It has the structure which was made.

The substrate 1 is made of any one of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and aramid (aromatic polyamide).
On the magnetic layer forming surface side of the substrate 1, it is desirable that 5 to 30 nm high protrusions are formed at a rate of 5 × 10 ^{6 to} 3 × 10 ⁷ pieces / mm ² .
This is because if the height of the protrusion is less than 5 nm, sufficient running durability due to sliding with the magnetic head cannot be ensured, and if it exceeds 30 nm, the output decreases due to spacing and causes noise.
Further, if the number of protrusions is less than 5 × 10 ⁶ pieces / mm ² , sufficient running durability cannot be obtained, and if it exceeds 3 × 10 ⁷ pieces / mm ² , the surface becomes too rough, causing noise.

The magnetic layer 2 is made of a cobalt-containing maghemite thin film (Co—γFe ₂ O ₃ ), and the cobalt content is 10 to 15% by weight.
If it is assumed that the cobalt content is less than 10% by weight, for example, a PET film is applied as the substrate 1, it is necessary to select a heating temperature of about 60 to 70 ° C. during the heat oxidation treatment in the magnetic layer forming step. For this reason, a practically sufficient coercive force Hc cannot be secured. On the other hand, when the cobalt content exceeds 15% by weight, rust is generated when stored for a long time in a high-temperature and high-humidity environment, resulting in a decrease in corrosion resistance.

  The magnetic layer 2 is an in-plane alignment film of a cobalt-containing maghemite thin film, and the coercive force Hc in the in-plane direction needs to be maintained at 2000 Oe (159 kA / m) or more in order to realize low noise and high resolution. There is. However, if it exceeds 3000 Oe (239 kA / m), the signal cannot be recorded sufficiently and the reproduction output is lowered.

The product Mr · t of the remanent magnetization Mr of the cobalt-containing maghemite thin film constituting the magnetic layer 2 and the magnetic layer thickness t is preferably 0.2 to ² memu / cm ² .
If Mr · t is less than 0.2 memu / cm ² , sufficient reproduction output cannot be obtained, and if it exceeds ² memu / cm ² , the reproduction GMR head is saturated and distortion occurs in the reproduction output. is there.

In addition, the film thickness t of the magnetic layer 2 is desirably a thin layer in order to reduce the cupping of the finally obtained magnetic tape. However, if the film thickness of the magnetic layer is less than 10 nm, it is sufficient for practical use. There is a problem that it is difficult to obtain the magnetic force Hc.
On the other hand, when the film thickness t is thick, the coercive force Hc tends to increase. However, when a high-sensitivity magnetic head such as a GMR head is applied, the magnetic particles constituting the magnetic layer 2 when the magnetic layer is thicker than 50 nm. Increases the noise. Further, the effect on the running durability of the surface protrusion formed on the substrate 1 cannot be sufficiently obtained.
From the above, the thickness t of the magnetic layer 2 is preferably 10 to 50 nm.

  Further, in order to enhance the in-plane orientation of the magnetic layer 2 and promote the refinement of crystal grains, and to suppress the deformation of the substrate 1, any material such as an oxidation material may be interposed between the substrate 1 and the magnetic layer 2. An underlayer (not shown) made of a material film or a nonmagnetic metal film may be formed.

A protective layer 3 such as hard carbon is formed on the magnetic layer in order to improve durability and weather resistance.
The thickness of the protective layer 3 is preferably 1 to 10 nm.
If the protective layer 3 is less than 1 nm, sufficient durability cannot be obtained, and if the protective layer 3 is formed thicker than 10 nm, the spacing increases and there is a possibility that sufficient output cannot be obtained when performing short wavelength recording.
Any protective layer 3 may be used as long as it is used as a protective layer for a conventionally known metal magnetic thin film type magnetic recording medium. In particular, in order to reduce the wear of the magnetic head, a DLC (diamond-like carbon) thin film formed by plasma CVD is suitable. _{Other, CrO 2, Al 2 O 3} , BN, Co _{oxide, MgO, SiO 2, Si 3} O 4, SiN, SiC, SiN x -SiO 2, ZrO 2, TiO 2, TiC , and the like.

Furthermore, it is desirable to improve the runnability of the magnetic recording medium by forming the lubricant layer 4 on the outermost surface on the magnetic layer forming surface side.
Further, a back layer may be provided on the surface of the substrate 1 opposite to the magnetic layer forming surface. Examples of the back layer include those containing carbon as a main component.

Next, a method for manufacturing the magnetic recording medium of the present invention will be described.
First, a substrate 1 made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), or aramid (aromatic polyamide) is prepared.
Next, a cobalt-containing magnetite thin film is formed on one main surface of the substrate 1 by a sputtering method.
Specifically, a cobalt-containing magnetite film is formed on the substrate 1 by carrying out reactive sputtering while introducing oxygen using a cobalt-containing iron alloy target on a substrate (plastic film) that is continuously conveyed. The cobalt-containing magnetite film is oxidized to form a cobalt-containing maghemite film.

The cobalt content in the iron-cobalt alloy used for the target is 10 to 15% by weight, and the magnetic layer 2 finally obtained is a cobalt-containing maghemite thin film having a cobalt content of 10 to 15% by weight.
When the cobalt content is increased, the coercive force Hc can be increased, and in order to obtain a practically sufficient coercive force Hc, the cobalt content in the magnetic layer 2 needs to be 10% by weight or more. . In particular, in order to obtain high Hc while lowering the heating temperature during the oxidation treatment described later as much as possible, it is desirable that the cobalt content is large, but if it exceeds 15% by weight, the stability over time of the magnetic tape decreases. Therefore, the cobalt content is specified as 10 to 15% by weight.

  The sputtering method is not particularly limited, and any method such as an RF magnetron sputtering method, an ECR sputtering method, or an opposed target sputtering method can be applied. In these sputtering methods, a cobalt-containing magnetite film is formed while arbitrarily controlling the oxygen flow rate, gas pressure, and input power.

In the cobalt-containing magnetite thin film forming step by the sputtering method, the temperature of the substrate 1 is about room temperature (20 to 50 ° C.).
In the conventionally known process for forming a cobalt-containing maghemite thin film in a hard disk manufacturing process, it was necessary to heat the substrate to about 200 ° C. in order to form an in-plane alignment film. In consideration of the application, it is not desirable to heat the substrate 1 to a high temperature. Further, the substrate may be deformed due to a temperature rise due to exposure to sputtering plasma or the like. Therefore, in the cobalt-containing magnetite thin film forming step, for example, it is desirable to form a sputter film while cooling the substrate 1, for example, the magnetic layer is formed by running on the peripheral surface of a can (cooling can) having a cooling mechanism inside. It is desirable to perform sputtering film formation while cooling the surface opposite to the surface.

Next, the cobalt-containing magnetite thin film is oxidized to form a cobalt-containing maghemite thin film.
As the maghemite thin film forming step, a method of contacting and transporting a can kept at a high temperature in the atmosphere (annealing in the atmosphere) is generally known. In this case, the temperature of the substrate 1 is set to 200 ° C. to 300 ° C. Since it is heated for a long time while being held at a certain level, a general-purpose plastic film such as PET or PEN cannot be used as a substrate. Therefore, in the case of annealing in the air, it is necessary to apply aramid (aromatic polyamide) having heat resistance as the substrate 1. Also in this case, it is desirable that the running surface of the substrate 1 is cooled by a cooling can and the magnetic layer side is heated by a heating means such as a halogen lamp.

Other methods for forming a cobalt-containing maghemite thin film include a method of irradiating plasma activated oxygen ions for several seconds (plasma oxidation method) that can be oxidized at a low temperature of 150 ° C. or lower, and an oxygen-containing gas atmosphere. And UV ozone treatment method of irradiating with ultraviolet rays.
In these cases, in-line processing can be performed for a relatively short time, and a PET film, a PEN film, or the like can be applied to the substrate 1.
Even in the case of these methods, it is desirable that the substrate 1 side is cooled by a cooling can and the magnetic layer side is heated by a heating means such as a halogen lamp.

Next, the protective layer 3 is formed on the magnetic layer 2. The protective layer 3 can be formed by a sputtering method, a CVD (Chemical Vapor Deposition) method, or the like. In particular, in order to reduce wear of the magnetic head, a DLC (diamond-like carbon) formed by a plasma CVD method is used. A thin film is preferred. Examples of the carbon compound of the film forming material in this case include conventionally known materials such as hydrocarbons, ketones, and alcohols. Further, at the time of plasma generation, argon, hydrogen or the like may be introduced as a gas for promoting the decomposition of the carbon compound.
Protective layer 3, _{other, CrO 2, Al 2 O 3} , BN, Co _{oxide, MgO, SiO 2, Si 3} O 4, SiN, SiC, from _{SiN x -SiO 2, ZrO 2,} TiO 2, TiC or the like It is good also as a thin film. The thickness of the protective layer 3 is preferably 1 to 10 nm. If the protective layer 3 is less than 1 nm, sufficient durability cannot be obtained. If the protective layer 3 is formed thicker than 10 nm, the spacing may increase, and sufficient output may not be obtained when performing short wavelength recording.

Further, the lubricant layer 4 is formed on the outermost surface on the magnetic layer forming surface side.
Further, a back layer may be provided on the surface of the substrate 1 opposite to the magnetic layer forming surface. The back layer can be formed by a conventionally known method such as a wet process or a dry process.

Hereinafter, the present invention will be described with specific examples.
[Example 1]
A polyamide film having a thickness of 4.5 μm was prepared as the substrate 1.
Next, using a counter target sputtering apparatus, the distance between the substrate 1 and the target is set to 150 mm by a reactive sputtering method, and the substrate 1 is conveyed at a feed rate of 10 m / min at room temperature (30 ° C.). A Fe + 10 wt% Co metal alloy target was sputtered at a total pressure of 0.30 Pa, argon of 20 sccm, and oxygen of 30 sccm to form a Co-containing magnetite thin film with a thickness of 30 nm.
Further, plasma oxidation treatment was performed by continuously setting the temperature of the substrate 1 to be about 200 ° C. to form a magnetic layer 2 made of a Co-containing maghemite thin film.
Next, the substrate 1 was conveyed at a feed rate of 5 m / min, argon 20 sccm, total pressure 0.20 Pa, and a protective layer 3 made of a carbon film was formed to a thickness of 5 nm by sputtering.
Thereafter, a perfluoropolyether is applied on the protective layer 3 to form the lubricant layer 4, and carbon black, calcium carbonate, polyester resin, nitrocellulose resin is formed on the surface opposite to the magnetic layer forming surface. A back layer was formed by applying a paint mainly composed of. Thereafter, a sample magnetic tape was prepared by slitting to a width of 8 mm.

[Examples 2 to 5], [Comparative Examples 1 to 3]
Sample magnetic tapes were produced by controlling the material of the substrate (plastic film), the Co content of the magnetic layer, and the set temperature of the substrate during the heat treatment in the Co-containing maghemite thin film forming step. Other manufacturing conditions are the same as those in the first embodiment.

The coercive force Hc of each sample magnetic tape produced as described above was measured using a “vibrating sample magnetometer VSM”. At this time, the maximum applied magnetic field was 15 kOe.
Note that the practically sufficient coercive force Hc was evaluated to be 2000 Oe (159 kA / m) or more.
Regarding the magnetostatic characteristics and cupping, it was confirmed that each magnetic tape was within a practically specified range.

Next, frequency characteristics (f characteristics) were measured using a drum tester.
A thin film head with a track width of 20 μm was used for recording, and an MR head with a track width of 7 μm (a commercially available playback head for MicroMV) was used for reproduction.
The rotation speed of the drum was controlled so that the relative speed between the magnetic tape and the magnetic head was 6.8 m / s.
The frequency characteristic (f characteristic) was recorded in the recording frequency range of 1 to 30 MHz, and the linear recording density reduced by 6 dB from the output peak was evaluated as D50. D50 allowed 150 kFCI or more.

Moreover, the storage durability of each sample magnetic tape produced as described above was evaluated.
After storing the magnetic tape in an environment of 65 ° C. and 90% RH for 8 weeks, the product Mrt of the remanent magnetization Mr and the magnetic layer thickness t is measured, and if the reduction rate of Mrt before and after storage is 10% or less When the reduction rate of Mrt exceeded 10%, it was evaluated as practically inappropriate (x).

  Table 1 shows the evaluation results of the magnetic tape production conditions, coercive force Hc, frequency characteristics, and storage durability.

As shown in Table 1, in the magnetic tapes of Examples 1 to 5 in which the Co content of the maghemite thin film constituting the magnetic layer was set to 10 to 15% by weight, a practically sufficient coercive force Hc was obtained. Good evaluation was also obtained for frequency characteristics and storage durability.
In particular, in Examples 3 to 5, a practically sufficient coercive force Hc was obtained even when the set temperature was set to 60 ° C. to 100 ° C. during the heat oxidation treatment in the maghemite thin film forming step, and the conventional hard disk recording layer formation was achieved. Although the temperature was lower than the temperature applied in the process, a practically sufficient coercive force Hc could be realized. That is, according to the present invention, it became clear that a versatile plastic film such as PET or PEN can be applied as a substrate.

  On the other hand, in Comparative Example 1, the Co content in the magnetic layer was small, and a practically sufficient coercive force Hc could not be obtained. In order to obtain a sufficient coercive force Hc when the Co content is less than 10% by weight, the substrate 1 may be set to a high temperature during the heat oxidation treatment in the maghemite thin film forming step, but the substrate 1 is thermally deformed. When Examples 1 and 2 are compared with Comparative Example 1, it is necessary to set the Co content to 10% by weight or more in order to perform heat oxidation at about 200 ° C. and obtain a sufficient coercive force Hc. It became clear that there was.

  In Comparative Example 2, the Co content in the maghemite thin film was too high, and rust was generated in a high-temperature and high-humidity environment, so that good evaluation for storage durability could not be obtained.

  In Comparative Example 3, since a PET film was applied as the substrate, the set temperature during the heat oxidation treatment in the maghemite thin film forming step was set to 60 ° C. However, since the Co content was too small, a practically sufficient coercive force Hc was obtained. In addition, the evaluation of the frequency characteristics deteriorated.

  As is clear from the above, by specifying the cobalt content of the cobalt-containing maghemite thin film constituting the magnetic layer to be 10 to 15% by weight, it is suppressed to a temperature applicable to general-purpose plastics in the heating oxidation process. Cobalt-containing maghemite thin films can be formed.

1 is a schematic sectional view of a magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Base | substrate, 2 ... Magnetic layer, 3 ... Protective layer, 4 ... Lubricant layer, 10 ... Magnetic recording medium

Claims (3)

A magnetic recording medium applied to a magnetoresistive head or a giant magnetoresistive head,
On a long substrate made of either polyethylene terephthalate, polyethylene naphthalate or aramid,
A magnetic recording medium comprising a magnetic layer comprising a cobalt-containing maghemite thin film having a cobalt content of 10 to 15% by weight. Fine protrusions having a height of 5 to 30 nm are formed on the magnetic layer forming surface side of the substrate at a rate of 5 × 10 ^{6 to} 3 × 10 ⁷ pieces / mm ² .
The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of 10 to 50 nm. A magnetic recording medium manufacturing method applied to a magnetoresistive head or a giant magnetoresistive head,
A step of forming a cobalt-containing magnetite thin film by sputtering on a long substrate made of polyethylene terephthalate, polyethylene naphthalate, or aramid;
Cooling the substrate side and heating the cobalt-containing magnetite thin film to oxidize the cobalt-containing magnetite thin film to form a magnetic layer comprising a cobalt-containing maghemite thin film having a cobalt content of 10 to 15% by weight; A method for producing a magnetic recording medium, comprising:

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