Perpendicular magnetic recording medium | Patent Application Number 10141446

The present invention provides a perpendicular magnetic recording medium 11 having a perpendicular magnetization film 22 formed on a substrate 20, wherein a high perpendicular orientation film 24 having higher perpendicular orientation than that of the perpendicular magnetization film 22 is formed over or/and under the perpendicular magnetization film 22.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of application Ser. No. 09/366,251, filed Aug. 3, 1999 now U.S. Pat. No. 6,426,157.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a perpendicular magnetic recording medium used as a magnetic disc.

2. Description of the Related Art

Recently, with progress of personal computers and work stations, the hard disc has been required to have a large capacity and small size, i.e., a high density. However, in order to realize a high recording density in the conventional longitudinal direction recording method, there are various problems. For example, if the recording bit is made smaller, there arises a problem of thermal fluctuation of recording magnetization and a problem of high coercive force which may exceed the recording capability of the recording head. To cope with this, a perpendicular magnetic recording method has been studied as means to significantly increase the recording density.

FIG. 156

However, in such a conventional perpendicular magnetic recording medium, there has been a problem that medium noise characteristic is very bad in a low recording density region. This is because the perpendicular magnetization film 54 is magnetized perpendicularly, and a demagnetizing field caused by the magnetic poles generated on the medium surface generates a reversed-magnetic domain. The lower is the recording density, the more the reversed-magnetic domains are generated. This has been the main cause to deteriorate the medium noise characteristic in the low recording density region. This medium noise increase in the low recording density region becomes a big trouble when forming a high-density information recording apparatus.

In order to reduce the effect of the demagnetizing field generated by the magnetic pole generated on the medium surface, there has been suggested to provide a soft magnetic layer under the perpendicular magnetization film so as to reduce the magnetic poles generated at the boundary between the perpendicular magnetization film and the soft magnetic layer (Japanese Patent Publication (examined) B58-91). This is generally known as a perpendicular two-layered magnetic recording medium.

However, in this two-layered perpendicular magnetic recording medium, if a perpendicular magnetization film is provided on a soft magnetic layer such as NiFe (Permalloy), there arises a problem that the soft magnetic layer generates a spike-shaped noise, disabling to obtain a preferable medium S/N ratio.

To cope with this, Japanese Patent Publication (unexamined) A59-127235, Japanese Patent Publication (unexamined) A59-191130, Japanese Patent Publication (unexamined) A60-239916, Japanese Patent Publication (unexamined) A61-8719, and Japanese Patent Publication (unexamined) A1-173312 suggest use of a perpendicular magnetization film on a backing layer made from Co or a Co alloy which is more advantageous than use of the permalloy soft magnetic layer.

However, the inventor of the present invention has found that when these soft magnetic films are used, these films easily absorb an external magnetic field generated by a magnetic disc rotation spindle motor. This results in concentration of the magnetic flux in a magnetic head and losing of recording signals. That is, the perpendicular magnetic recording medium of the two-layered film configuration can reduce the effect of the demagnetizing field caused by the magnetic poles generated on the medium surface, but this cannot be a solution for medium noise reduction.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a perpendicular magnetic recording medium having a reduced effect of the demagnetizing field caused by a magnetic poles generated on a perpendicular magnetization film surface and having a preferable medium noise characteristic in a low recording density region.

The perpendicular magnetic recording medium according to the present invention has a perpendicular magnetization film formed on a substrate, wherein a high perpendicular orientation film having higher perpendicular orientation than the perpendicular magnetization film is formed over or/and under the perpendicular magnetization film.

A backing soft magnetic film may be formed under the high perpendicular orientation film, or under the perpendicular magnetic film if there is no high perpendicular orientation film under the perpendicular magnetization film.

It is preferable that the high perpendicular orientation film have a perpendicular magnetic anisotropic energy Ku [erg/cc] and a saturation magnetization Ms [emu/cc] which are in the relationship R defined as 2 Ku/4Ï€Ms² equal to or greater than (≧) 1.4.

Moreover, it is preferable that the high perpendicular orientation film have a greater perpendicular magnetic anisotropic energy than that of the perpendicular magnetization film. The perpendicular magnetic anisotropic energy of the high perpendicular orientation film is preferably equal to or greater than 1×10⁶ [erg/cc], and more preferably equal to or greater than 2×10⁷ [erg/cc]. The high perpendicular orientation film preferably has a thickness equal to or greater than 50 [nm]

The high perpendicular orientation film is preferably made from: a CoCrM alloy (wherein M represent three elements selected from a group consisting of Pt, Ta, La, Lu, Pr, and Sr); an alloy containing RCo₅ (R=Y, Ce, Sm, La, Pr) as a main content; an alloy containing R₂Co₁₇ (R=Y, Ce, Sm, La, Pr) as a main content; Ba ferrite (BaFe₁₂O₁₉ BaFe₁₈O₂₇ and the like); Sr ferrite (SrFe₁₂O₁₉, SrFe₁₈O₂₇ and the like), PtCo, and the like.

The backing soft magnetic film is preferably made from FeSiAl, FesiAl alloy, FeTaN, FeTaN alloy, and the like.

In the perpendicular magnetic recording medium according to the present invention, the perpendicular magnetization film on its upper surface or lower surface a high perpendicular orientation film having a higher perpendicular orientation than that of the perpendicular magnetization film. Accordingly, it is possible to significantly suppress generation of a reversed magnetic domain in the vicinity of the surface of the perpendicular magnetization film.

When the high perpendicular orientation film is made from a CoCr alloy, it is preferable that the perpendicular magnetic anisotropic energy Ku [erg/cc] and the saturation magnetization Ms [emu/cc] be in the relationship as R=2 Ku/4Ï€Ms² wherein R≧1.4.

On the other hand, when the high perpendicular orientation film is made from a SmCo alloy (i.e., a material other than the CoCr alloy), it is preferable that the high perpendicular orientation film have a perpendicular magnetic anisotropic energy Ku greater than that of the perpendicular magnetization film. This enables to reduce generation of reversed magnetic domain in the vicinity of the surface of the perpendicular magnetization film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1

FIG. 6

FIG. 1

FIG. 2

FIG. 3

FIG. 4

FIG. 5

FIG. 6

The high perpendicular orientation film 24 has a higher perpendicular orientation characteristic than the perpendicular magnetization film 22. The high perpendicular orientation film 24 may be made from: CoCrM alloys wherein M represents any three elements selected from a group consisting of Pt, Ta, La, Lu, Pr, and Sr; RCo₅ wherein R represents any one of Y, Ce, Sm, La, and Pr; R₂Co₁₇ wherein R represents any one of Y, Ce, Sm, La, and Pr; Ba ferrite, Sr ferrite, PtCo, and the like.

The high perpendicular orientation film 24 made from the aforementioned materials is provided at least over or under the perpendicular magnetization film 22. This reduces effects of the demagnetizing field generated by the magnetic pole on the surface of the perpendicular magnetization film 22. Accordingly, it is possible to obtain a perpendicular magnetic recording medium having a preferable noise characteristic even in the low recording density region.

EXAMPLE 1

Using a 6-inch Co₈₀Cr₁₇Ta₃ (%) target for sputtering, a perpendicular magnetization film Co₈₀Cr₁₇Ta₃ was formed to have a thickness of 100 nm on a 2.5-inch substrate at 400 degrees centigrade. The film formation conditions were as follows: initial vacuum degree 5×10^−7 [mTorr]; electric power 0.5 [kw]; argon gas pressure 4 [mTorr]; film formation speed 3 [nm/sec].

After this, the film was covered by the high perpendicular orientation film of 5 to 55 [nm] thickness formed by using: a Co₇₄Cr₂₂Pt₂TaLa target, a Co₇₅Cr₂₁Pt₂TaLa target, a Co₇₆Cr₂₀Pt₂TaLa target, a Co₇₇Cr₁₉Pt₂TaLa target, and a Co₇₈Cr₁₈Pt₂TaLa target.

After this, a C (carbon) protection film 10 [nm] was formed to cover the high perpendicular orientation film.

The medium having the high perpendicular orientation film of Co₇₆Cr₂₀Pt₂TaLa of 50 [nm] thickness will be referred to as medium AAA2 of the present invention. On the other hand, the medium having only the perpendicular magnetization film Co₈₀Cr₁₇Ta₃without forming the high perpendicular orientation film of Co₇₆Cr₂₀Pt₂TaLa will be referred to as a conventional medium (comparative example) D1.

It should be noted we also prepared a medium having the Co₇₆Cr₂₀Pt₂TaLa film and the Co₈₀Cr₁₇Ta₃ film in the reversed order. That is, firstly, Co₇₅Cr₂₀Pt₂TaLa film was formed on the substrate, and then the Co₈₀Cr₁₇Ta₃ film was formed on the Co₇₆Cr₂₀Pt₂TaLa film.

The perpendicular magnetic anisotropic energy Ku of the following seven films were measured using a torque magnetometer; and saturation magnetization Ms of the seven films were measured using a sample vibration type magnetometer (VSM): a Co₇₄Cr₂₂Pt₂TaLa film, a Co₇₅Cr₂₁Pt₂TaLa film, a Co₇₆Cr₂₀Pt₂TaLa film, a Co₇₇Cr₁₉Pt₂TaLa film, a Co₇₈Cr₁₈Pt₂TaLa film, a Co₇₈Cr₁₉Ta₃ film, and a Co₈₀Cr₁₇Ta₃ film. The measurement results are shown in

FIG. 7

In general, a magnetic film can be a perpendicular magnetization film if the perpendicular anisotropy magnetic field Hk is greater than the maximum perpendicular magnetic field 4 pMs (p represents the number π) so as to satisfy the relationship of Hk≧4 pMs. Moreover, the perpendicular anisotropy magnetic field Hk can be expressed by using the perpendicular magnetic anisotropic energy Ku, i.e., Hk=2 Ku/Ms. That is, the quality of the perpendicular orientation of the perpendicular magnetization film can be determined by finding which is greater Hk or 4 pMs. Here, R is assumed to be Hk/4 pMs, and the R values are shown in the table of

FIG. 7

The Co₈₀Cr₁₇Ta₃ film-has R=1.1 whereas the Co₇₆Cr₂₀Pt₂TaLa film has R=1.4. That is the Co₇₆Cr₂₀Pt₂TaLa film has by far better perpendicular magnetic anisotropy than the Co₈₀Cr₁₇Ta₃ film. However, if the percentage content of the Co is 73% or below, the Co alloy does not show the ferromagnetic characteristic. Accordingly, it is impossible to lower the Co content without limit.

On the other hand, by using the ID (inductive)/MR(magneto-resistance effect) composite head, the recording/reproduction characteristics were checked on the medium AAA2 of the present invention and the conventional medium D1. The check conditions were set as follows: ID/MR composite head recording track width 4 [micrometers], the reproduction track width 3 [micrometers], recording gap length 0.4 [micrometers], and reproduction gap length 0.32 [micrometers]. Evaluation of the check was performed under the conditions of: recording current 19 [mAop], sense current 12 [mA], peripheral velocity 12.7 [m/s], floating amount 45 [nm], and noise bandwidth 50 [MHz].

FIG. 8

FIG. 8

Next, the film thickness of the film formed on the perpendicular magnetization film was gradually changed from 5 to 55 [nm] to check the medium noise values at recording density 10 [KFRPI] for all the film types. The results of this check are shown in

FIG. 9

FIG. 13

FIG. 9

FIG. 13

As has been described above, the recording medium AAA2 of the present invention shows a preferable medium noise characteristic even in a low recording density region. That is, by using the AAA2 of the present invention, it is possible to realize suppression of medium noise increase in the low recording region. Moreover, when the Co₇₆Cr₂₀Pt₂TaLa film is provided under or both under and over the perpendicular magnetization film, similar results can be obtained because of the aforementioned reasons. Furthermore, film types other than the Co₇₆Cr₂₀Pt₂TaLa film can also have similar results if the relationship that R is equal to or more than 1.4 is satisfied.

EXAMPLE 2

Media of Example 2 were prepared in the same way as Example 1 except for that the Co_xCr_96−xPt₂TaLa (74≦x≦78) target was replaced by Co_xCr_96−xPt₂TaLu (74≦x≦78) target. The medium examples made from Co₇₆Cr₂₀Pt₂TaLu film having a film thickness of 50 [nm] will be referred to as medium BBB2 of the present invention. Note that we also prepared media having the Co₈₀Cr₁₇Ta₃ film and the Co₇₆Cr₂₀Pt₂TaLu film in the reversed order, i.e., firstly Co₇₆Cr₂₀Pt₂TaLu film was formed on the substrate, and then the Co₈₀Cr₁₇Ta₃ film was formed thereon.

The perpendicular magnetic anisotropic energy Ku of the following six films were measured using a torque magnetometer; and saturation magnetization Ms of these six films were measured using a sample vibration type magnetometer (VSM): a Co₇₄Cr₂₂Pt₂TaLu film, a Co₇₅Cr₂₁Pt₂TaLu film, a Co₇₆Cr₂₀Pt₂TaLu film, a Co₇₇Cr₁₉Pt₂TaLu film, a Co₇₈Cr₁₈Pt₂TaLu film, and a Co₈₀Cr₁₇Ta₃ film. The check results are shown in

FIG. 14

FIG. 7

Here, R is defined as Hk/4 pMs in the same way as in Example 1.

FIG. 14

The ID/MR composite head was used to check the recording/reproduction characteristic of the medium BBB2 of the present invention and the conventional medium (comparative example) D1. The head and the recording/reproduction conditions were set in the same way as in Example 1.

FIG. 15

FIG. 15

Next, the film thickness of the film formed on the perpendicular magnetization film was gradually changed from 5 to 55 [nm] to check the medium noise values at recording density 10 [KFRPI] for all the film types. The results of this check are shown in

FIG. 16

FIG. 20

FIG. 16

FIG. 20

As has been described above, the recording medium BBB2 of the present invention shows a preferable medium noise characteristic even in a low recording density region. That is, by using the BBB2 of the present invention, it is possible to realize suppression of medium noise increase in the low recording region. Moreover, when the Co₇₆Cr₂₀Pt₂TaLu film is provided under or both under and over the perpendicular magnetization film, similar results can be obtained because of the aforementioned reasons. Furthermore, film types other than the Co₇₆Cr₂₀Pt₂TaLu film can also have similar results if the relationship that R is equal to or more than 1.4 is satisfied.

EXAMPLE 3

Media of Example 3 were prepared in the same way as Example 1 except for that the Co_xCr_96−xPt₂TaLa (74≦x≦78) target was replaced by Co_xCr_96−xPt₂LaLu (74≦x≦78) target. The medium examples made from Co₇₆Cr₂₀Pt₂LaLu film having a film thickness of 50 [nm] will be referred to as medium CCC2 of the present invention. Note that we also prepared media having the Co₈₀Cr₁₇Ta₃ film and Co₇₆Cr₂₀Pt₂LaLu film in the reversed order, i.e., firstly Co₇₆Cr₂₀Pt₂LaLu film was formed on the substrate, and then the Co₈₀Cr₁₇Ta₃ film was formed thereon.

The perpendicular magnetic anisotropic energy Ku of the following six films were measured using a torque magnetometer; and saturation magnetization Ms of these six films were measured using a sample vibration type magnetometer (VSM): a Co₇₄Cr₂₂Pt₂LaLu film, a Co₇₅Cr₂₁Pt₂LaLu film, a Co₇₆Cr₂₀Pt₂LaLu film, a Co₇₇Cr₁₉Pt₂LaLu film, a Co₇₈Cr₁₈Pt₂LaLu film, and a Co₈₀Cr₁₇Ta₃ film. The check results are shown in

FIG. 21

FIG. 7

Here, R is defined as Hk/4 pMs in the same way as in Example 1.

FIG. 21

The ID/MR composite head was used to check the recording/reproduction characteristic of the medium CCC2 of the present invention and the conventional medium (comparative example) D1. The head and the recording/reproduction conditions were set in the same way as in Example 1.

FIG. 22

FIG. 22

Next, the film thickness of the film formed on the perpendicular magnetization film was gradually changed from 5 to 55 [nm] to check the medium noise values at recording density 10 [KFRPI] for all the film types. The results of this check are shown in

FIG. 23

FIG. 27

FIG. 23

FIG. 27

As has been described above, the recording medium CCC2 of the present invention shows a preferable medium noise characteristic even in a low recording density region. That is, by using the CCC2 of the present invention, it is possible to realize suppression of medium noise increase in the low recording region. Moreover, when the Co₇₆Cr₂₀Pt₂LaLu film is provided under or both under and over the perpendicular magnetization film, similar results can be obtained because of the aforementioned reasons. Furthermore, film types other than the Co₇₆Cr₂₀Pt₂LaLu film can also have similar results if the relationship that R is equal to or more than 1.4 is satisfied.

EXAMPLE 4-1

Media of Example 4-1 were prepared in the same way as Example 1 except for that the Co_xCr_96−xPt₂TaLa (74≦x≦78) target was replaced by Co_xCr_96−xTa₂LaLu (74≦x≦78) target. The medium examples made from Co₇₆Cr₂₀Ta₂LaLu film having a film thickness of 50 [nm] will be referred to as medium DDD2 of the present invention. Note that we also prepared media having the Co₈₀Cr₁₇Ta₃ film and Co₇₆Cr₂₀Ta₂LaLu film in the reversed order, i.e., firstly Co₇₆Cr₂₀Ta₂LaLu film was formed on the substrate, and then the Co₈₀Cr₁₇Ta₃ film was formed thereon.

FIG. 28

FIG. 7

Here, the R is defined in the same way as in Example 1.

FIG. 28