JP2005196885A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tape-shaped magnetic recording medium capable of realizing high density recording by applying a recording layer constitution of a hard disk to the tape-shaped magnetic recording medium. <P>SOLUTION: In the magnetic recording medium 10 wherein at least an amorphous layer 3, a seed layer 4, a base layer 5, a magnetic layer 6 and a protective layer 7 are successively formed on a non-magnetic substrate 1 consisting of a long-length polymer film, the seed layer 4 consists of any of Ti, Cr, Mo, W, Zr, a Ti alloy, a Cr alloy and a Zr alloy, the base layer 5 consists of a Ru film and the magnetic layer 6 has a granular structure consisting of crystal grains having ferromagnetism and non-magnetic grain boundary surrounding the grains. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a high-density recording type magnetic recording medium, and in particular, as a reproducing magnetic head, a magnetoresistive effect type magnetic head (MR head) or a giant magnetoresistive effect type magnetic head (GMR head). The present invention also relates to a tape-like magnetic recording medium suitable for a system using a high-sensitivity magnetic head.

  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. Recently, in order to achieve higher density recording, a magnetic head used for reproducing a recording signal is replaced with a highly sensitive magnetoresistive head (MR head) instead of a conventional induction head. The giant magnetoresistive effect type magnetic head (GMR head) has been applied, and is applied not only to hard disks but also to so-called magnetic tapes.

  As the above-described high-density recording type magnetic tape medium, conventionally, a so-called CoO—O vapor-deposited tape in which a magnetic recording layer is formed by a vacuum vapor deposition method is mainly known. In order to meet the demands of magnetic recording media, the magnetic recording medium has been made thinner, and at the same time, research has been carried out to ensure good magnetic properties. I can say that.

  On the other hand, in the field of hard disks having a configuration in which a CoPt-based or CoCr-based metal thin film is formed on a substrate by a sputtering method (see, for example, Patent Documents 1 to 4), dramatic high-density recording is currently progressing. It is out.

JP-A-7-57236 Japanese Patent Laid-Open No. 7-73433 JP-A-9-198641 JP 2003-123240 A

In view of the conventional situation as described above, studies have been made on a technique for applying the recording layer configuration of a hard disk to a recording layer of a magnetic tape.
However, in the manufacturing process of the hard disk, when the recording layer is formed on the substrate by the sputtering method, heat treatment is usually performed at 300 ° C. or higher, and therefore the substrate needs to be made of a material having extremely high heat resistance. Has been.

  That is, considering the application of the recording layer configuration of a conventional hard disk to a tape-like magnetic recording medium, it is necessary to use a material with extremely high heat resistance, such as polyimide, as a material that can withstand the heating temperature. Since a so-called versatile plastic film such as polyethylene terephthalate (PET) cannot be applied, it has been considered practically expensive and impractical.

  Considering the above-described problems, a magnetic tape medium having an elemental magnetic layer mainly composed of Co—Pt—Cr and containing Si oxide, which can be formed at a low temperature of about room temperature without requiring a high-temperature heat treatment step. However, when such a magnetic layer is formed on a plastic film, the crystal orientation is disturbed due to lattice mismatch, and the medium noise is remarkably increased. The problem of being expensive has arisen.

Furthermore, if O ₂ or H ₂ O is adsorbed on the surface of the plastic film as the support of the magnetic tape or is mixed in the plastic film, these disturb the crystal orientation of the magnetic layer, Since this causes an increase in medium noise, improvement of these is also necessary.

  Therefore, in the present invention, various problems for applying the recording layer configuration of the hard disk as described above to the tape-like magnetic recording medium are solved, and the tape-like magnetic that can realize unprecedented high-density recording is achieved. It was decided to provide a recording medium.

  In the present invention, at least an amorphous layer, a seed layer, an underlayer, a magnetic layer, and a protective layer are sequentially formed on a nonmagnetic support made of a long polymer film. , Cr, Mo, W, Zr, Ti alloy, Cr alloy, Zr alloy, the underlayer is made of Ru, and the magnetic layer is composed of crystal grains having ferromagnetism and nonmagnetic grain boundaries surrounding it. A magnetic recording medium having a granular structure is provided.

In the magnetic recording medium of the present invention, a barrier layer having a function of sealing O ₂ or H ₂ O is formed between the nonmagnetic support and the amorphous layer.

  According to the configuration of the present invention, since the amorphous layer is formed on the nonmagnetic support (plastic film), the influence on the seed layer is suppressed with respect to the interstitial mismatch.

Further, by forming a barrier layer between the nonmagnetic support and the seed layer, O ₂ and H ₂ O from the nonmagnetic support are suppressed.

  According to the present invention, since the amorphous layer is formed on the nonmagnetic support (plastic film), the influence on the seed layer formed on the upper layer is suppressed with respect to the interstitial mismatch, and further formed as the upper layer. As a result, the magnetic orientation of the magnetic layer is improved, and the recording layer configuration of the hard disk is applied to the tape-like magnetic recording medium, and a tape-like magnetic recording medium capable of realizing unprecedented high-density recording is obtained. It was.

In addition, since the barrier layer was formed on the nonmagnetic support, O ₂ and H ₂ O from the nonmagnetic support were suppressed, and a further crystal orientation improvement effect of the magnetic layer was obtained.

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.
FIG. 1 is a schematic sectional view of a magnetic recording medium of the present invention. The magnetic recording medium 10 is a tape having a structure in which a barrier layer 2, an amorphous layer 3, a seed layer 4, an underlayer 5, a magnetic layer 6, and a protective layer 7 are sequentially formed on a long nonmagnetic support 1. It is a magnetic recording medium. Hereinafter, each layer will be described.

As the nonmagnetic support 1, for example, a polymer film made of polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyimide, polyamide, polyimide amide or the like having a thickness of 3 μm to 10 μm can be applied.
The surface roughness (SRa) of the magnetic layer forming surface of the nonmagnetic support 1 is preferably 0.5 to 3.0 nm, more preferably about 0.5 to 1.5 nm. This is because when the surface roughness SRa is less than 0.5 nm, the surface is too smooth and the surface of the magnetic tape is easily scraped when it is brought into contact with the magnetic head. This is because the output decreases due to the spacing loss.

  Examples of the method of adding roughness to the surface include a method of forming irregularities by adding fine particles having a predetermined particle diameter inside or on the surface. Examples of the fine particles include silica, calcium carbonate, titanium dioxide, alumina, kaolin, talc, graphite, feldspar, molybdenum dioxide, carbon black, barium nitrate and other inorganic particles, polystyrene, polymethyl methacrylate, methyl methacrylate copolymer, methyl Examples include cross-linked products of methacrylate copolymers, organic particles such as polytetrafluoroethylene, polyvinyldenfluoride, polyacrylonitrile, and benzoguanamine resins. Is preferred. Alternatively, it may be formed by providing a continuous film mainly composed of a water-soluble polymer and fine particles.

The barrier layer 2 is made of, for example, Ti, Ta, TiW, Al, AlSi, or Al ₂ O ₃ , Si oxide having excellent gas barrier properties. The film thickness of the barrier layer 2 is desirably 10 nm or less so as not to affect the surface roughness of the layer formed thereon.
By forming the barrier layer 2, the gettering effect of O ₂ or H ₂ O adsorbed on the surface of the nonmagnetic support 1 or released from the inside can be obtained, and the crystal orientation of the magnetic layer described later is improved. can do.
The barrier layer 2 can be formed by sputtering using a target corresponding to the film forming material, but is also affected by the gas atmosphere in the sputtering process. For example, when sputtering is performed in a nitrogen gas atmosphere using SiO ₂ as a target, N is contained as a constituent element of the barrier layer.

The amorphous layer 3 can be made of, for example, Cu, Al, Cr, Ta, Zr, Hf, Re, Co, Ni, Ti, rare earth metals, alloys thereof, oxides, C, Si, or the like. However, it is not limited to these. The film thickness is preferably 1 nm to 5 nm in order to maintain an amorphous structure. By forming the amorphous layer 3, the influence on the seed layer 4 to be described later can be suppressed with respect to the interstitial mismatch, and the crystal orientation of the magnetic layer 6 formed as an upper layer is improved.
Further, the amorphous layer 3 has a function similar to that of the barrier layer 2 described above by using a metal material having a gettering effect of O ₂ or H ₂ O or a material having excellent gas barrier properties such as SiON. You may make it let.

The seed layer 4 is made of any one of Ti, Cr, Mo, W, Zr, Ti alloy, Cr alloy, and Zr alloy. By forming the seed layer 4, the crystal orientation of the underlayer 5 described later can be improved. In order to obtain an in-plane medium using CoPtCr—SiO ₂ as the magnetic layer 6 described later, the seed layer 4 is preferably made of a TiW nonmagnetic alloy film.
The film thickness of the seed 4 is preferably 5 nm to 100 nm, and more preferably 5 nm to 50 nm.
If the film thickness of the seed layer 4 is less than 5 nm, the crystal orientation of the underlayer 5 described later cannot be sufficiently improved, and the coercive force Hc and C / N characteristics of the finally obtained magnetic recording medium 10 deteriorate. To do. On the other hand, if it exceeds 100 nm, crystal growth becomes excessive, and the surface roughness SRa of the magnetic layer 6 described later becomes too large, causing noise.

The underlayer 5 is made of a Ru film.
Ru has the same hexagonal close-packed structure as Co, which is a main component of the magnetic layer 6 described later, and is almost the same as Co except that the a axis is about 8% and the c axis is only about 5%. It becomes a crystal structure.
Therefore, the base layer 5 made of a Ru film is formed as a lower layer of the magnetic layer 6 and the c-axis is oriented in the plane, preferably (100) orientation or (110) orientation. The in-plane orientation of the magnetic layer 6 is improved, and good magnetic characteristics and electromagnetic conversion characteristics can be obtained in the finally obtained magnetic recording medium.
The thickness of the underlayer 5 is preferably 10 nm to 100 nm, and particularly preferably 15 nm to 50 nm. When the thickness of the underlayer 5 is less than 10 nm, good orientation cannot be obtained, and the coercive force Hc and C / N of the magnetic recording medium are significantly deteriorated. On the other hand, if the film thickness exceeds 100 nm, crystal growth becomes excessive, the surface roughness becomes too high, and noise increases.

  The magnetic layer 6 is assumed to have a granular structure composed of ferromagnetic crystal grains mainly composed of Co and nonmagnetic grain boundaries surrounding the ferromagnetic crystal grains. For example, between the crystal grains of Co—Pt—Cr, Si oxide is dispersed in islands. As a result, it is possible to reduce the noise caused by the variation in the magnetization of the magnetization transition portion. At the same time, each crystal grain is magnetically isolated so that the rotation of the magnetization becomes a simultaneous rotation type and the coercive force Hc is reduced. growing.

When the magnetic layer 6 has a granular structure in which Si oxides are dispersed in an island shape between Co—Pt—Cr crystal grains, the content of Si oxides is converted to Si atoms in the Co. It is preferable that the content be 8 atomic% or more and 20 atomic% or less with respect to —Pt—Cr.
When the content of Si atoms is less than 8 atomic%, the effect of surrounding and isolating the Co—Pt—Cr crystal grains becomes insufficient, and the effects of low noise and high coercive force cannot be obtained. On the other hand, when the content exceeds 20 atomic%, the Co—Pt—Cr content in the magnetic layer 6 is relatively reduced, resulting in higher noise and lower coercivity.

  Further, when the total of Co—Pt—Cr constituting the magnetic layer 6 and Si atoms of the Si oxide is 100 atomic%, the Pt content is 12 atomic% or more and 20 atomic% or less, and the Cr content is It is preferable that the content is 10 atomic% or less and the balance is Co. Thereby, high coercive force and low noise can be achieved.

  The magnetic layer 6 can be formed by a conventionally known sputtering method using, for example, a material obtained by adding a Si oxide to a Co—Pt—Cr alloy.

The protective layer 7 can be formed of, for example, diamond-like carbon (DLC), graphite-like carbon, amorphous carbon, CN, BN, WC, WMoC, ZrNbN, B ₄ C, SiO ₂ , ZrO ₂ or the like. Carbon is particularly preferable and can be formed by a conventionally known CVD method, PVD method, or the like.
The thickness of the protective layer 7 is preferably 2 nm to 30 nm, and more preferably 5 nm to 10 nm. If the thickness of the protective layer 7 is less than 2 nm, a sufficient surface protection function cannot be obtained. On the other hand, if it exceeds 20 nm, the output is reduced due to spacing loss.

On the protective layer 7, for example, a hydrocarbon-based or fluorine-based lubricant may be applied to form a lubricant layer (not shown), thereby improving running performance.
Further, a back layer (not shown) may be provided on the surface opposite to the magnetic layer forming surface. The back layer can be composed mainly of carbon, for example, and may be formed by any conventionally known wet process or dry process.

  The magnetic recording medium 10 of the present invention is particularly suitable as a magnetic recording medium for a magnetic recording tape system equipped with a high-sensitivity reproducing magnetic head such as an MR head or a GMR head.

  Hereinafter, the magnetic recording medium of the present invention will be described with specific experimental examples. However, the present invention is not limited to the examples shown below, and is appropriately known in the art without departing from the scope of the present invention. Assume that the configuration can be replaced or added.

[Experimental Example 1]
As the nonmagnetic support 1, a polyethylene terephthalate film having a width of 127 mm, a length of 500 m, and a film thickness of 6.4 μm was prepared.
The surface roughness SRa of the nonmagnetic support 1 (center surface average roughness on the magnetic layer forming surface) was determined by measuring an area of 5 μm × 5 μm using “Nanoscope III” manufactured by Digital Instrumental. However, SRa = 1.0 nm.

  Next, the nonmagnetic support 1 is conveyed at a speed of 5.0 m / min using a known sputtering apparatus, and the barrier layer 2, the amorphous layer 3, the seed layer 4, the underlayer 5, and After the magnetic layer 6 was sequentially formed, the protective layer 7 was similarly formed under the conditions shown below at a conveyance speed of 10 m / min.

(Barrier layer: Ti film)
An input power of 7 W / cm ² was applied to the cathode of the Ti metal target from a direct current sputtering power source to create an argon gas atmosphere and a gas pressure of 4 Pa. Sputter film formation was performed under these conditions to form a barrier layer 2 made of a 5 nm thick Ti film.
(Amorphous layer: C film)
An input power of 10 W / cm ² was applied to the cathode of the C target from a direct current sputtering power source to create an argon gas atmosphere and a gas pressure of 4 Pa. Sputter deposition was performed under these conditions to form an amorphous layer 3 made of a C film having a thickness of 1 nm.
(Seed layer: TiW film)
An input power of 7 W / cm ² was applied from the direct current sputtering power source to the cathode of the alloy target composed of Ti 50 atomic% -W 50 atomic% to create an argon gas atmosphere, and the gas pressure was set to 0.5 Pa. Sputter deposition was performed under these conditions to form a seed layer 3 made of a 10 nm thick TiW film.
(Underlayer: Ru film)
An input power of 10 W / cm ² was applied to the cathode of the Ru metal target from a direct current sputtering power source to form an argon gas atmosphere and a gas pressure of 4 Pa. Sputter film formation was performed under these conditions, and an underlayer 4 made of a Ru film having a thickness of 30 nm was formed.

(Magnetic layer: Co—Pt—Cr (SiO ₂ ))
An input power of 10 W / cm ² is applied from an RF sputtering power source to a cathode of a sintering target composed of Co 60 atomic% -Pt 17 atomic% -Cr 10 atomic% and SiO ₂ -13 atomic%, and an argon gas atmosphere is applied. 1.0 Pa. Sputter film formation was performed under these conditions to form a magnetic layer 5 having a thickness of 13 nm.
(Protective layer: DLC film)
An input power of 10 W / cm ² was applied to the cathode of the C target from a direct current sputtering power source to form an argon gas atmosphere, and the gas pressure was 1.0 Pa. Sputter deposition was performed under these conditions to form a protective layer 7 made of a DLC film having a thickness of 8 nm.
(Back layer)
A coating mainly composed of carbon and urethane resin was applied to the surface opposite to the magnetic layer forming surface to form a back layer having a thickness of 0.6 μm.

Then, it cut | judged to 8 mm width, the perfluoropolyether type lubricant was apply | coated to the magnetic layer formation surface side, the lubricant layer was formed, and the sample magnetic tape was produced.
The magnetic properties of the magnetic tape thus produced were coercive force Hc = 3200 Oe (255 kA / m), product of residual magnetization and magnetic layer thickness Mr · t = 0.5 memu / cm ² (5 mA). It was.

[Experimental Examples 2 to 15]
Various sample magnetic tapes were prepared by changing the constituent materials and contents of the barrier layer 2, the amorphous layer 3, the seed layer 4, the underlayer 5, and the magnetic layer 6, and the film thickness of each layer. These configurations are shown in Table 1 below.

About the sample magnetic tape of the said Experimental Examples 1-15, the frequency characteristic and C / N were measured using the drum tester.
A thin film head having a track width of 20 μm was used for signal recording, and an MR head having a track width of 7 μm (a commercially available reproducing head for MicroMV) was used for reproduction. The relative speed between the magnetic tape and the magnetic head was 6.8 m / s.

As a comparative sample of characteristics, a commercially available vapor deposition tape for MicroMV was prepared.
For the frequency characteristics, recording was performed in the range of a recording frequency of 1 to 30 MHz, and the linear recording density decreased by 6 dB from the output peak was evaluated as D50. In addition, it was judged that D50 was a favorable value if it was 180 kfci or more (D50 of the vapor deposition tape for commercially available MicroMV was 160 kfci).
Further, the difference between the output at the recording frequency of 12 MHz and the average value of noise at ± 1 MHz was defined as C / N, and it was judged to be a practically good value if it was −1 dB or more compared to a commercially available MicroMV vapor deposition tape.
Table 2 below shows the measurement results of the coercive force Hc, Mrt, C / N, and D50 of each sample magnetic tape.

  As shown in Table 1 and Table 2, in Experimental Examples 1 to 10, since the amorphous layer was formed on the nonmagnetic support, the influence on the interstitial mismatch between the nonmagnetic support and the film formed on the nonmagnetic support was affected. The crystal orientation of the magnetic layer was improved, a sufficiently high coercive force Hc was obtained in practical use, and practically good values were obtained in both frequency characteristics and C / N characteristics.

In particular, in Experimental Examples 1 and 6 to 9 in which a barrier layer is formed between the nonmagnetic support and the amorphous layer, O ₂ and H ₂ adsorbed on the surface of the nonmagnetic support 1 or released from the inside. Since the gettering effect of O was obtained, the effect of improving the crystal orientation of the magnetic layer was improved, high coercive force Hc was obtained, and practically good values were obtained in both frequency characteristics and C / N characteristics. It was.

  In Experimental Example 11, since the amorphous layer 3 was not formed, the influence on the seed layer 4 with respect to the interstitial mismatch could not be suppressed, the crystal orientation of the magnetic layer 6 was not improved, and the frequency characteristics and C / N characteristics were improved. In any case, a practically good value was not obtained.

  In Experimental Example 12, since the amorphous layer 3 is too thick, it is crystallized, and the effect of improving the crystal orientation of the magnetic layer 6 formed in the upper layer cannot be obtained, and both the frequency characteristics and the C / N characteristics are practical. Good values could not be obtained.

  In Experimental Example 13, since the barrier layer 2 was too thick, the surface roughness SRa of the magnetic layer 6 was increased, noise increased, and C / N deteriorated.

In Experimental Example 14, a SiO ₂ film was formed as an amorphous layer, and this film thickness was too thick, so that it was crystallized, and the effect of improving the crystal orientation of the magnetic layer 6 could not be obtained. No practically good value was obtained in any of the N characteristics.

  In Experimental Example 15, since the Co content in the magnetic layer 6 is too small, a sufficient coercive force cannot be obtained, the output is reduced, and both the frequency characteristic and the C / N characteristic have practically good values. It was not obtained.

1 is a schematic cross-sectional view of an example of a magnetic recording medium of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Nonmagnetic support body, 2 ... Barrier layer, 3 ... Amorphous layer, 4 ... Seed layer, 5 ... Underlayer, 6 ... Magnetic layer, 7 ... Protective layer, 10 ... Magnetic recording medium

Claims (5)

At least an amorphous layer, a seed layer, an underlayer, a magnetic layer, and a protective layer are sequentially formed on a nonmagnetic support made of a long polymer film,
The seed layer is made of any one of Ti, Cr, Mo, W, Zr, Ti alloy, Cr alloy, Zr alloy,
The underlayer is made of Ru,
The magnetic recording medium according to claim 1, wherein the magnetic layer has a granular structure comprising crystal grains having ferromagnetism and nonmagnetic grain boundaries surrounding the crystal grains.   The amorphous layer is made of any one of Cu, Al, Cr, Ta, Zr, Hf, Re, Co, Ni, Ti, rare earth metals, alloys thereof, oxides, C, and Si. 2. The magnetic recording medium according to 1. The magnetic recording medium according to claim 1, wherein a barrier layer for sealing O ₂ or H ₂ O is formed between the nonmagnetic support and the amorphous layer. The magnetic recording medium according to claim 3, wherein the barrier layer is made of any one of Ti, Ta, TiW, Al, AlSi, Al ₂ O ₃ , and Si oxide. The magnetic layer is mainly composed of Co—Pt—Cr and contains Si oxide, and the content of the Si oxide is converted to Si atoms with respect to the Co—Pt—Cr. The magnetic recording medium according to claim 1, wherein the magnetic recording medium is 8 atom% or more and 20 atom% or less.

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