JP4583345B2 - Perpendicular magnetic recording medium - Google Patents

Description

  The present invention relates to a perpendicular magnetic recording medium, and more particularly to a perpendicular magnetic recording medium mounted on various magnetic recording devices including an external storage device of a computer.

  As a technique for realizing a high density magnetic recording, a perpendicular magnetic recording system is drawing attention in place of the conventional longitudinal magnetic recording system.

  As a material for a magnetic recording layer for a perpendicular magnetic recording medium, a CoCr-based alloy crystalline film is currently being studied, and the c-axis of a CoCr-based alloy having an hcp structure is used as a film surface for use in perpendicular magnetic recording. The crystal orientation is controlled to be perpendicular to (the c-plane is parallel to the film surface). In order to further increase the density in the future, attempts have been made to refine the CoCr crystal grains, reduce the variation in grain size, reduce the magnetic interaction between crystal grains, and the like.

  On the other hand, as a method of controlling the magnetic layer structure for increasing the density of the longitudinal recording medium, a magnetic crystal grain, generally called a granular magnetic layer, is surrounded by a nonmagnetic nonmetallic material such as an oxide or nitride. A magnetic layer having a structure has been proposed in, for example, USP 5,679,473. In such a granular magnetic film, the nonmagnetic nonmetallic grain boundary phase separates the magnetic particles, thereby reducing the magnetic interaction between the magnetic particles and suppressing the formation of zigzag domain walls that occur in the transition region of the recording bit. Therefore, it is considered that low noise characteristics can be obtained.

  Under these circumstances, it has been proposed to use a granular magnetic layer as a recording layer of a perpendicular magnetic recording medium. For example, IEEE Trans., Magn., Vol. 36, 2393 (2000) describes a perpendicular recording medium having Ru as an underlayer and a CoPtCrO alloy having a granular structure as a magnetic layer. However, here, by increasing the film thickness of the Ru layer, which is the underlying layer of the granular magnetic layer, the crystallinity of the Ru layer and its c-axis orientation are improved, resulting in excellent magnetic properties and electromagnetic conversion properties. Has been obtained. In the example given here, a magnetic film having a granular structure is formed by reactive sputtering in an oxygen-containing atmosphere using a CoPtCr target. However, in film formation using reactive sputtering, the amount of oxide produced is very sensitive to the amount of oxygen in the sputtering atmosphere, so it is difficult to control the amount of oxide surrounding the magnetic crystal grains, and the magnetic crystal Since the grains are also easily oxidized and it is very difficult to separate the constituent materials of the magnetic crystal grains and the oxide grain boundaries, improvement is necessary.

  That is, in the granular magnetic layer containing oxide and metal, in order to control the crystal grains and the segregation structure thereof in order to ensure low noise characteristics, the amount of oxide contained in the magnetic layer is appropriately controlled. This is very important. In addition, it is necessary to prevent the magnetic crystal grains from containing oxides in order to obtain excellent magnetic properties.

  In a perpendicular magnetic recording medium using a granular magnetic layer, the amount of oxide contained in the magnetic layer and a method for appropriately separating the oxide into grain boundaries have been intensively studied. As a result, the granular magnetic layer, i.e., the magnetic layer becomes ferromagnetic. It has been found that the following configuration and manufacturing method are suitable for using as a perpendicular magnetic recording medium a magnetic layer composed of non-magnetic grain boundaries mainly composed of crystal grains and oxides surrounding them.

That is, the present onset Ming, at least the seed layer on the non-magnetic substrate, a non-magnetic undercoat layer, a magnetic layer, a protective layer a perpendicular magnetic recording medium which are sequentially stacked, wherein the seed layer is a face-centered cubic (fcc ), The nonmagnetic underlayer is a metal or alloy having a hexagonal close-packed (hcp) crystal structure, and the magnetic layer surrounds the crystal grains having ferromagnetism and the surroundings. The non-magnetic grain boundary mainly composed of oxide is an alloy in which the ferromagnetic crystal grains contain at least Co and Pt, and the volume of the non-magnetic grain boundary mainly composed of the oxide is that of the entire magnetic layer. Ri 40% der than 15% or more by volume, the thickness of the magnetic layer is characterized in der Rukoto than 20nm or less 5 nm.

One aspect of the present invention is characterized in that, in the perpendicular magnetic recording medium, the nonmagnetic substrate is a plastic resin.

  As described above, according to the present invention, a granular magnetic layer, that is, a magnetic layer composed of nonmagnetic grain boundaries mainly composed of crystal grains having ferromagnetism and surrounding oxides, and hexagonal close-packed packing (hcp ) In a perpendicular magnetic recording medium having a non-magnetic underlayer that is a metal or alloy having a crystal structure of (2), the ferromagnetic crystal grains are an alloy containing at least Co and Pt, By setting the volume of the magnetic grain boundary to 15% or more and 40% or less of the entire volume of the magnetic layer, crystal grains and grain boundary segregation are preferably controlled, and excellent magnetic characteristics and low noise characteristics can be realized.

  Furthermore, by setting the film thickness of the magnetic layer to 5 nm or more and 20 nm or less, it is possible to obtain a necessary and sufficient reproduction output during recording and reproduction, and to prevent deterioration of crystal orientation and coarsening of the crystal grain size.

  Furthermore, as a method of manufacturing such a perpendicular magnetic recording medium, the magnetic layer is formed by RF magnetron sputtering using a composite target containing a ferromagnetic alloy and an oxide, and When the volume of the oxide contained is 20% or more and 35% or less of the total volume of the target, the oxide incorporated in the crystal grains having ferromagnetism can be reduced, and the oxide is contained in the magnetic layer. The amount of oxide mainly forming grain boundaries can be controlled within a preferred range.

  By adopting such a medium configuration and manufacturing method, an excellent perpendicular magnetic recording medium can be easily obtained. Therefore, it is not necessary to heat the substrate when forming the medium of the present invention, and the manufacturing process is simplified. At the same time, the cost can be reduced, and at the same time, it is possible to use an inexpensive plastic as the substrate in addition to the conventional Al or glass substrate.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic cross-sectional view for explaining the structure of one embodiment of the perpendicular magnetic recording medium of the present invention. The perpendicular magnetic recording medium has at least a nonmagnetic underlayer 2 and a magnetic layer 3 on a nonmagnetic substrate 1. And a protective film 4 are formed in order, and a liquid lubricant layer 5 is further formed thereon. Even if the seed layer 11 is provided between the nonmagnetic underlayer 2 and the nonmagnetic substrate 1 for the purpose of controlling the crystal orientation and crystal grain size of the nonmagnetic underlayer 2, the effect of the present invention is not changed. It is demonstrated all the time. Further, even when a relatively thick (several hundred nm) soft magnetic layer for improving the recording / reproducing sensitivity, which is generally called a backing layer, is provided between the nonmagnetic underlayer 2 and the nonmagnetic substrate 1. It is.

  As the nonmagnetic substrate 1, it is possible to use an Al alloy plated with NiP, tempered glass, crystallized glass, or the like used for a normal magnetic recording medium. Substrates produced by injection molding of polyolefin or other plastic resins can also be used.

  The nonmagnetic underlayer 2 needs to be a metal or alloy having a hexagonal close-packed (hcp) crystal structure. The material is not particularly limited, and among these, the use of a metal of any one of Ti, Re, Ru, and Os, or an alloy containing at least one of Ti, Re, Ru, and Os can cause the crystal orientation of the granular magnetic layer. It is desirable to control the above. The film thickness is not particularly limited, but is preferably about 5 nm to 30 nm.

  When the seed layer 11 is provided for the purpose of controlling the crystal orientation and grain size of the nonmagnetic underlayer 2, the seed layer is a metal or alloy having a face-centered cubic (fcc) crystal structure. Among them, among them, any metal of Cu, Au, Pd, Pt, Ir, an alloy containing at least one of Cu, Au, Pd, Pt, Ir, or an alloy containing at least Ni and Fe It is desirable that

  Further, for example, a thin film mainly composed of carbon is used as the protective film 4. The liquid lubricant layer 5 may be a perfluoropolyether lubricant, for example.

  The magnetic layer 3 is a so-called granular magnetic layer composed of crystal grains having ferromagnetism and nonmagnetic grain boundaries surrounding the crystal grains, and the nonmagnetic grain boundaries are composed of a metal oxide. The ferromagnetic crystal grains are preferably an alloy containing at least Co and Pt. Further, addition of Cr, Ta, B, Cu or the like to the CoPt alloy is also suitable for controlling magnetic characteristics and obtaining low noise characteristics.

  The crystal grains having ferromagnetism must have a structure in which the c-axis of the crystal lattice is preferentially oriented perpendicular to the film surface.

  Here, the volume of the nonmagnetic grain boundary mainly composed of oxide needs to be 15% or more and 40% or less of the entire volume of the magnetic layer. In the case of 15% or less, a sufficient grain boundary cannot exist between the crystal grains, and the magnetic interaction between the grains cannot be effectively reduced, so that the medium noise increases. . On the other hand, when it is 40% or more, the crystal orientation of the crystal grains deteriorates.

  Note that the oxide forming the grain boundary is not particularly limited as long as it is physically and chemically stable, and oxides such as Mg, Cr, Ti, Zr, and Si can be used.

  Furthermore, the thickness of the magnetic layer 3 is preferably 5 nm or more and 20 nm or less. If it is 5 nm or less, a sufficient signal cannot be obtained at the time of recording and reproduction, which is inappropriate. On the other hand, if it is 20 nm or more, it is not desirable because the crystal grain size tends to increase and the crystal orientation tends to be disturbed.

  Regarding the manufacture of the magnetic recording medium shown in FIG. 1 having the layer structure as described above, it is desirable to take the following manufacturing method when forming the magnetic layer 3.

  First, the magnetic layer is preferably formed by RF magnetron sputtering using a composite target containing a ferromagnetic alloy and an oxide. By adopting such a manufacturing method, the separation of crystal grains and non-magnetic grain boundaries can be advanced and a preferable granular structure can be obtained as compared with the case of reactive sputtering of an oxide-free target in an oxygen-containing atmosphere. .

  Further, the volume of the oxide contained in the composite target to be used is 20% or more and 35% or less of the total volume of the target. Necessary to control the area.

  On the other hand, in the production of the perpendicular magnetic recording medium in the present invention, it is possible to obtain an excellent perpendicular magnetic recording medium even if the substrate heating step as in the conventional magnetic recording medium is omitted, which simplifies the production process. The accompanying manufacturing cost can also be reduced. Further, since there is no need to heat the substrate, it is possible to use a non-magnetic substrate made of a plastic resin such as polycarbonate or polyolefin.

  Specific examples of the present invention will be described below, but these examples are illustrative of the present invention, and are not intended to limit the present invention.

[Example 1]
A polycarbonate substrate (3.5 "disk shape) injection-molded as a non-magnetic substrate is used. After cleaning, this is introduced into a sputtering apparatus, and a seed layer of 5 nm of Pt is formed under an Ar gas pressure of 5 mTorr. A nonmagnetic underlayer made of Ru having a thickness changed from 0 to 20 nm was formed under an Ar gas pressure of 5 mTorr, and subsequently, a CoCr ₁₀ Pr ₁₅ target containing SiO ₂ was used and an Ar gas pressure of 5 mTorr was formed by RF magnetron sputtering. A granular magnetic layer having a thickness of 20 nm was formed below, a carbon protective layer having a thickness of 10 nm was stacked, and then taken out from the vacuum. Thereafter, a liquid lubricant of 1.5 nm was applied to prepare a magnetic recording medium having a structure as shown in FIG. Substrate heating prior to film formation is not performed.

Figure 2 shows to volume ratio occupied by the non-magnetic grain boundaries of the magnetic layer, the change in the value of the coercive force H _C as measured by a vibrating sample magnetometer while applying a magnetic field in the direction perpendicular to the film plane. It can be seen that the _HC value shows a high value of 3000 Oe or more when the volume ratio of the nonmagnetic grain boundaries in the magnetic layer is 15% or more and 40% or less.

FIG. 3 shows the relationship between the volume ratio of SiO ₂ contained in the target and the volume ratio occupied by nonmagnetic grain boundaries in the magnetic layer. Here, the volume ratio occupied by the nonmagnetic grain boundaries in the magnetic layer was calculated by obtaining the area occupied by the crystal grains and the grain boundaries from a planar image obtained by a transmission electron microscope (TEM). From the figure, it is understood that the volume ratio occupied by the nonmagnetic grain boundaries in the magnetic layer is 15% or more and 40% or less in the region where the amount of SiO ₂ contained in the target is 20% or more and 35% or less.

[Example 2]
The magnetic structure shown in FIG. 1 is the same as in Example 1 except that the amount of SiO ₂ contained in the target is fixed at 25% and the film thickness of the formed magnetic layer is changed from 3 to 50 nm. A recording medium was produced.

FIG. 4 shows the dependence of the _HC value measured in the same manner as shown in FIG. 2 on the thickness of the magnetic layer. H _C value shows a high value of more than 3000Oe following areas 20nm or more thickness 5 nm. Although not intended to be bound by theory, it is considered that Hc is reduced due to the influence of thermal disturbance in the region thinner than 5 nm, while in the region thicker than 20 nm, mainly the crystal grains in the magnetic layer It is considered that _HC was lowered due to disorder of crystal orientation.

It is a cross-sectional schematic diagram which shows the structure of one Example of the perpendicular magnetic recording medium by this invention. It is a figure which shows the change of the value of the coercive force Hc measured with the vibrating sample type magnetometer, applying a magnetic field to the film surface in the direction perpendicular | vertical with respect to the volume ratio which the nonmagnetic grain boundary in a magnetic layer occupies. And SiO ₂ volume ratio in the target is a diagram showing the relationship between the non-magnetic grain boundary occupied volume ratio of the magnetic layer. It is the figure which showed the magnetic layer film thickness dependence of the Hc value measured similarly to having shown in FIG.

Explanation of symbols

1 Nonmagnetic Substrate 11 Seed Layer 2 Nonmagnetic Underlayer 3 Magnetic Layer 4 Protective Layer 5 Liquid Lubricating Layer

Claims (2)

A perpendicular magnetic recording medium in which at least a seed layer, a nonmagnetic underlayer, a magnetic layer, and a protective film are sequentially laminated on a nonmagnetic substrate, wherein the seed layer is a metal having a face-centered cubic (fcc) crystal structure Or an alloy, wherein the non-magnetic underlayer is a metal or alloy having a hexagonal close-packed (hcp) crystal structure, and the magnetic layer is mainly composed of ferromagnetic crystal grains and oxides surrounding them. A crystal grain having a magnetic grain boundary, the crystal grains having ferromagnetism being an alloy containing at least Co and Pt, and the volume of the nonmagnetic grain boundary mainly composed of the oxide is 15% or more and 40% of the total volume of the magnetic layer. hereinafter der is, the perpendicular magnetic recording medium film thickness of the magnetic layer is characterized in der Rukoto than 20nm or less 5 nm. The perpendicular magnetic recording medium according to claim 1, wherein the nonmagnetic substrate is a plastic resin.

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