Vertical recording medium with thin soft magnetic film

A vertical magnetic recording medium includes a soft magnetic film formed on a substrate, and a vertical magnetization film formed on the soft magnetic film. &mgr;&middot;&dgr;b&gE;1000, when &mgr; is a permeability of the soft magnetic film, and &dgr;b [nm] is a film thickness of the soft magnetic film. The permeability &mgr; of the soft magnetic film is 5&lE;&mgr;&lE;200, and the film thickness &dgr;b of the soft magnetic film is equal to or less than 500 nm. Also, vertical magnetic anisotropy energy Ku [erg/cc] of the vertical magnetization film is 1&times;107&lE;Ku&lE;7&times;108, and coercive force Hc [kOe] of the vertical magnetization film in the vertical direction to a surface of the vertical magnetization film is 5&lE;Hc&lE;10.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a vertical magnetic recording medium suitable for a magnetic disk.

2. Description of the Related Art

In recent years, a much larger capacity and a much smaller size have been required for had disk drives, as information devices such as personal computers and work stations have progressed. In magnetic disks, much higher density is also required.

However, in a longitudinal magnetic recording method which has been being widely used, problems arise in that miniaturization of recording bits incurs heat fluctuation in recording magnetization and that a higher coercive force which may exceed the recording ability of a recording head is required, when realizing a high recording density. Hence, a vertical magnetic recording method has been discussed as a magnetic recording method capable of greatly improving the recording density while solving the problems described above. As a kind of vertical magnetic recording medium which realizes this method, there is a vertical magnetic recording medium having a two-layer structure which is composed of a soft magnetic film with a high magnetic permeability and a vertical magnetization film with a high vertical anisotropy.

FIG. 1 is a schematic cross sectional view showing an example of a conventional vertical magnetic recording medium. The vertical magnetic recording medium 21 is composed of a lower soft magnetic film 23 and a vertical magnetization film 24 which are laminated in an order on a substrate 22 made of non-magnetic material. For example, a NiFe film is used as the lower soft magnetic film 23 , and CoCr-based alloy is used for the vertical magnetization film 24 (Nippon-Ouyou-Jiki-Gakkai-Shi, Vol. 8, No. 1, 1984, pp. 17-22).

This vertical magnetic recording medium 21 achieves recording more easily than a conventional longitudinal magnetic recording method because of existence of the lower soft magnetic film 23 . That is, this vertical magnetic recording medium 21 can easily perform recording since it has much greater vertical magnetic anisotropic energy than the magnetic anisotropic energy of a conventional longitudinal magnetic recording medium in the longitudinal direction and also has much greater coercive force in the direction vertical to the film surface than a conventional longitudinal magnetic recording medium. Therefore, the vertical magnetic recording medium 21 can be stronger against heat fluctuation than a medium according to the longitudinal magnetic recording method. To deal with the problem of the heat fluctuation, it tends to use a film having high vertical magnetic anisotropic energy and coercive force in the direction vertical to the film surface greater than those of a CoCr-based film which has been the main trend of vertical magnetic films.

Meanwhile, in the conventional vertical magnetic recording medium using a vertical magnetization film which has great vertical magnetic anisotropic energy and large coercive force in the direction vertical to the film surface, the magnetic permeability and film thickness b of the lower soft magnetic film must be set to greater values in order to maintain a recording sensitivity, than in the case of using a conventional vertical magnetization film.

Where a practical medium manufacturing process is considered, the lower soft magnetic film should be thinner as much as possible. This is because a manufacturing process of the vertical magnetization film formed on the lower soft magnetic film becomes easier. The vertical magnetization film determines the recording/reproducing ability at a high recording density, when the lower soft magnetic film is thinned.

In conjunction with the above description, a vertical magnetic recording medium is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 4-283413). In this reference, a lower soft magnetic lining layer ( 12 ) and a vertical magnetization film ( 13 ) are formed in order on a non-magnetic material substrate ( 11 ). After a magnetic polar surface layer of the lower soft magnetic layer ( 12 ) is removed by an ion etching method or an inverse sputtering method, the vertical magnetization film ( 13 ) is formed thereon. The coercive force of the vertical magnetization film ( 13 ) becomes gradually smaller into a direction of the phase boundary with the lower soft magnetic layer ( 12 ) from the surface of the vertical magnetization film ( 13 ). Also, the saturation magnetization becomes gradually larger into a direction of the phase boundary with the lower soft magnetic layer ( 12 ) from the surface of the vertical magnetization film ( 13 ).

Also, a vertical magnetic recording medium is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 6-139542). In this reference, a lower soft magnetic layer ( 12 ) and a vertical magnetization film ( 13 ) are formed in order on a non-magnetic material substrate ( 11 ). The lower soft magnetic layer ( 12 ) has the relative permeability in a range of 20 to 1000 and the saturation magnetic flux density of 10 kG or more.

Also, a vertical magnetic recording medium is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-149628). In this reference, the vertical magnetic recording medium ( 20 ) is composed of a substrate ( 22 ), a lower soft magnetic film ( 24 ) formed on the substrate ( 22 ), and a vertical magnetization film 28 formed on the lower soft magnetic film ( 24 ). The lower soft magnetic film ( 24 ) is provided not to have a non-magnetic wall structure. The coercive force of the lower soft magnetic film ( 24 ) is equal to or less than 300 Oe.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a vertical magnetic recording medium which can comply with thinning of the lower soft magnetic film.

Another object of the present invention is to provide a vertical magnetic recording medium which has large vertical magnetic anisotropic energy and large coercive force in the direction vertical to the film surface.

Still another object of the present invention is to provide a vertical magnetic recording medium which can eliminate the problem of heat fluctuation.

In order to achieve an aspect of the present invention, a vertical magnetic recording medium includes a soft magnetic film formed on a substrate, and a vertical magnetization film formed on the soft magnetic film, b 1000, when is a permeability of the soft magnetic film, and b nm is a film thickness of the soft magnetic film.

Here, it is desirable that the permeability of the soft magnetic film is 5 200. Also, it is desirable that the film thickness b of the soft magnetic film is equal to or less than 500 nm.

Also, it is desirable that vertical magnetic anisotropy energy Ku erg/cc of the vertical magnetization film is 1 10 7 Ku 7 10 8 . Also, it is desirable that coercive force Hc kOe of the vertical magnetization film in the vertical direction to a surface of the vertical magnetization film is 5 Hc 10.

Also, the vertical magnetization film may include FePt alloy. In this case, it is desirable that the vertical magnetization film comprises x at %Fe-(100-x) at %Pt alloy, where 40 x 60. It is more desirable that the vertical magnetization film comprises 50at %Fe-50at %Pt alloy, where x 50 at %.

Also, the vertical magnetization film may include RCo alloy, where R is one or more selected from the group consisting of Y, Ce, Sm, La and Pr. In this case, the vertical magnetization film may include RCo 5 alloy, where R is one or more selected from the group consisting of Y, Ce and Sm. Alternatively, the vertical magnetization film may include R 2 Co 17 alloy, where R is one or more selected from the group consisting of Y, Ce, Sm, La and Pr.

Also, the soft magnetic film may include FeSiAl alloy. In this case, it is desirable that the vertical magnetization film comprises 84.9wt %Fe-xwt %Si-(15.1-x)wt %Al alloy, where 8.0 x 12.0. It is more desirable that the vertical magnetization film may include 84.9wt %Fe-9.6wt %Si-5.5wt %Al.

Also, the soft magnetic film may include CoNiFe alloy. Especially, it is desirable that the soft magnetic film may include 62at %Co-12at %Ni-26at %Fe alloy.

In order to achieve another aspect of the present invention, a vertical magnetic recording medium includes a soft magnetic film formed on a substrate, and a vertical magnetization film formed on the soft magnetic film, and b 1000 when is a permeability of the soft magnetic film, and b nm is a film thickness of the soft magnetic film. In addition, the permeability of the soft magnetic film is 5 200, and the film thickness b of the soft magnetic film is equal to or less than 500 nm.

Here, it is desirable that the vertical magnetization film may include FePt alloy or RCo alloy, where R is one or more selected from the group consisting of Y, Ce, Sm, La and Pr.

Also, it is desirable that the soft magnetic film may include FeSiAl alloy or CoNiFe alloy.

Also, it is desirable that vertical magnetic anisotropy energy Ku erg/cc of the vertical magnetization film is 1 10 7 Ku 7 10 8 , and coercive force Hc kOe of the vertical magnetization film in the vertical direction to a surface of the vertical magnetization film is 5 Hc 10.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a vertical magnetic recording medium according to the present invention will now be described below in detail with reference to the attached drawings.

FIG. 2 is a cross sectional view showing a vertical magnetic recording medium according to the present invention. The vertical magnetic recording medium 1 is composed of a lower soft magnetic film 3 with a magnetic permeability and a film thickness b , and a vertical magnetization film 4 which are laminated on a substrate 2 made of non-magnetic material.

It is preferable that the magnetic permeability of the lower soft magnetic film 3 satisfies 5 200, and the film thickness b thereof is 500 nm or less. For example, alloys such as FeSiAl alloy and CoNiFe alloy are used for the lower soft magnetic film 3 . It is preferable that as the FeSiAl alloy is used is 84.9wt %Fe-Xwt %Si-(15.1-X)wt %Al alloy (hereinafter, to be referred to as Fe 84.9 -Si X Al 15.1-X alloy) where 8.0 X 12.0 is satisfied, for example. More preferably, the composition of the FeSiAl alloy is 84.9wt %Fe-9.6wt %Si-5.4wt %Al. Also, it is preferable that 62at %Co-12at %Ni-26at %Fe is used as the CoNiFe alloy, for example.

It is preferable that the vertical magnetization film 4 has the vertical magnetic anisotropic energy Ku erg/cc in a range of 1 10 7 Ku 7 10 8 , and the coercive force Hc kOe in the direction vertical to its film surface in a range of 5 Hc 10. For example, FePt alloy or RCo alloy (where R is one or more selected from the group consisting of Y, Ce, Sm, La, and Pr) is used for the vertical magnetization film 4 . It is preferable that as the FePt alloy is used X at %Fe-(100-X)at %Pt alloy (hereinafter, to be referred to as Fe x -Pt 100-x ) where 40 X 60 is satisfied, for example. It is more preferable that composition of the FePt alloy is 50at %Fe-50at %Pt. Also, it is preferable that as the Rco alloy is Rco 5 alloy (where R is one or more selected from the group consisting of Y, Ce, and Sm), R 2 Co 17 alloy (where R is one or more selected from the group consisting of Y, Ce, Sm, La, and Pr). In the vertical magnetic recording medium 1 , a condition of b 1000 is satisfied where the magnetic permeability of the lower soft magnetic film 3 is and the thickness thereof is b nm . Therefore, sufficient reproduction sensitivity can be maintained even if the lower soft magnetic film 3 is thinned.

FIG. 3 is a cross sectional view showing a specific example of a vertical magnetic recording medium according to the first embodiment. The vertical magnetic recording medium 11 is composed of a 84.9wt %Fe-9.6wt %Si-5.5wt %Al film 13 (hereinafter to be referred to as a Fe 84.9 Si 9.6 Al 5.5 film 13 ) as a lower soft magnetic film with a magnetic permeability and a film thickness b , and a 50at %Fe-50at %Pt film 14 (hereinafter to be referred to as a Fe 50 Pt 50 film 14 ) as a vertical magnetization film 4 , which are laminated on a substrate 2 made of non-magnetic material.

Next, a vertical magnetic recording medium according to the present invention will be described more specifically.

The First Embodiment

Samples were formed to have Fe 84.9 Si 9.6 Al 5.5 films 13 which were formed on substrates 12 of a 2.5-inch size at the substrate temperature of 400 C. by a sputtering method by use of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets of a 6-inch size. The samples had ten different thicknesses of 2, 5, 10, 20, 50, 100, 200, 250, 500, and 750 nm. The film forming condition was set in such a manner that the supplied electric power was 0.5 kw, the argon gas pressure was 4 mTorr (5.31 10 1 Pa), and the film forming rate was 3 nm/sec at the initial vacuum degree of 5 10 7 mTorr (6.65 10 8 Pa) to 7 mTorr (9.31 10 1 Pa).

The ten types of samples were heated with a lamp in a sputter chamber. The heating time was changed so as to prepare the ten samples with Fe 84.9 Si 9.6 Al 5.5 films 13 having different magnetic permeabilities . The magnetic permeabilities were changed in a range of seven types of 2, 5, 10, 20, 50, 100, and 200. In other words, mediums respectively having seven types of magnetic permeabilities were prepared for each of ten types of different film thicknesses b . Thus, total seventy different types mediums with Fe 84.9 Si 9.6 Al 5.5 films 13 were prepared. The mediums with the Fe 84.9 Si 9.6 Al 5.5 films 13 having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums A 1 to A 6 in the first embodiment.

Also, Fe 50 Pt 50 films 14 were respectively formed on Fe 84.9 Si 9.6 Al 5.5 films 13 by 50 nm at the substrate temperature of 450 C. by use of a target of 50at %Fe-50at %Pt, for the purpose of measurement of magnetic permeabilities. Further, a C protection film was formed by 5 nm on each of the Fe 50 Pt 50 films 14 .

Also, as comparison examples, mediums with Fe 84.9 Si 9.6 Al 5.5 films 13 having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparative mediums AA 1 to AA 4 . In addition, a medium with Fe 84.9 Si 9.6 Al 5.5 films 13 having combinations of a permeability and a film thickness b nm that satisfy b 400, e.g., ( , b ) (20, 20) was named a comparison medium AA 5 . Further, mediums with Fe 84.9 Si 9.6 Al 5.5 films 13 having combinations of permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums AA 6 to AA 12 .

Further, samples were formed on substrates of a 12-inch size at the substrate temperature of 400 C. by a sputtering method by use of 21.5wt %Ni-78.5wt %Fe target of a 6-inch size, to have five different thicknesses of 5, 10, 50, 100, and 200 nm. The film forming condition was set in such a manner that the supplied electric power was 0.5 KW, the argon gas pressure was 4 mTorr (5.31 10 1 Pa), and the film forming speed was 3 nm/sec, at the initial vacuum degree of 5 10 7 mTorr (6.65 10 8 Pa) to 7 mTorr (9.31 10 1 Pa). The samples with the Ni 21.5 Fe 78.5 films having different film thicknesses were heated with a lamp in a sputter chamber. The heating time was changed so as to prepare Ni 21.5 Fe 78.5 films having different magnetic permeabilities . The magnetic permeabilities were changed in a range of seven kinds of 2, 5, 10, 20, 50, 100, and 200. In other words, mediums with the Ni 21.5 Fe 78.5 films respectively having seven magnetic permeabilities were prepared for every one of five different film thicknesses b . Thus, total thirty-five different kinds of samples with Ni 21.5 Fe 78.5 films were prepared.

Samples with Fe 50 Pt 50 films were respectively formed on the Ni 21.5 Fe 78.5 films by 50 nm by use of 50at %Fe-50at %Pt targets for the purpose of measurement of magnetic permeability. Further, a C protection film was formed by 5 nm on each of the samples. At this time, mediums with the Ni 21.5 Fe 78.5 films having combinations of a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10) were respectively named conventional mediums AB 1 to AB 4 . In addition, mediums with the Ni 21.5 Fe 78.5 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named conventional comparison mediums AC 1 to AC 6 . It should be noted that the Ni 21.5 Fe 78.5 film was generally used for a lower soft magnetic film conventionally.

Then, the vertical magnetic anisotropic energy Ku of each Fe 50 Pt 50 film was measured by a magnetic torque meter to find Ku 7 10 7 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 5.5 kOe .

Recording/reproducing tests were carried out to total seventy kinds of vertical magnetic recording mediums having seven kinds of permeabilities for each of ten different film thicknesses of Fe 84.9 Si 9.6 Al 5.5 films 13 , by use of a monopolar head and a MR head respectively used as a recording head and a reproducing head. The MR head had a reproduction track width of 1 m and a reproduction gap length of 0.1 m. The monopolar head has a track width of 1.5 m. Evaluations were carried out under the condition that the recording current was 10 mAop, the sense current was 12 mA, the circumferential speed was 12.7 m/s, and the floating amount was 45 nm. A signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured.

Table 1 shows reproduced outputs ( V) of the seventy kinds of samples with Fe 84.9 Si 9.6 Al 5.5 films 13 . This table shows the mediums according to the first embodiment and the mediums of comparison examples clearly separated.

TABLE 1 Reproduced output *values of comparison mediums in solid line block *values of mediums in the first embodiment in dotted line block As can be seen from the table 1, the reproduced outputs were sufficiently secured in the region lower than the mediums A 1 to A 6 in the first embodiment, (i.e., in the region of the present embodiment). On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums AA 6 to AA 12 , (i.e., in the region of the conventional samples).

FIG. 4 shows the results obtained above in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. As seen from this FIG. 4 , sufficient reproduced outputs can be secured where b 1000 was satisfied.

In case where the magnetic permeability of the lower soft magnetic film is 2, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . Also, in case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and film thickness b of the lower soft magnetic film are lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film was disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed on the lower soft magnetic film is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design, even if the relationship of b 1000 is satisfied. It is necessary to satisfy the relationship of b 1000 and simultaneously to satisfy a relationship of 5 200 and a relationship that b is 500 nm or less.

Similarly, a signal having a recording density of 300 kFRPI was recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs were thereafter measured with a MR head. The measurement values were shown in Table 2.

TABLE 2 Reproduced output Conventional Conventional Conventional Conventional Medium Medium Medium Medium AB1 AB2 AB3 AB4 460 522 516 503 Conven- Conven- Conven- Conven- Conven- Conven- tional tional tional tional tional tional compari compari compari compari compari compari son son son son son son medium medium medium medium medium medium AC1 AC2 AC3 AC4 AC5 AC6 192 142 152 165 174 187 Unit: V As can be seen from the Table 2, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity and the value of b requires at least b 2000 or more, in case of a vertical magnetic recording medium which uses a Ni 21.5 Fe 78.5 film as the lower soft magnetic film. From the above, a vertical magnetic recording medium having a Fe 84.9 Si 9.6 Al 5.5 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical magnetic recording medium having a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is smaller. As a result of this, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 9.6 Al 5.5 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 9.6 Al 5.5 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 9.6 Al 5.5 film is used in place of a Ni 21.5 Fe 78.5 film for a vertical magnetic recording medium, design can be made with a lower value of b . If the relationship of b 1000 is satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Fe 84.9 Si 9.6 Al 5.5 film is and the film thickness thereof is b , the recording/reproducing sensitivity can be sufficiently obtained even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the first embodiment. As a result, by using a Fe 84.9 Si 9.6 Al 5.5 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be more thinned than the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the first embodiment.

The Second Embodiment

Like the first embodiment, total seventy different kinds of samples with Fe84.9Si 9.6 Al 5.5 films were prepared by use of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets, i.e., Fe 84.9 Si 9.6 Al 5.5 films respectively having seven different magnetic permeabilities were prepared for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared by use of 40at %Fe-60at %Pt targets in place of the 50at %Fe-50at %Pt targets in the first embodiment, on Fe 84.9 Si 9.6 Al 5.5 films formed separately from those formed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums B 1 to B 6 according to the second embodiment. In addition, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums BB 1 to BB 4 . Also, a medium having Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium BB 5 . Further, mediums with Fe 84.9 Si 9.6 Al 5.5 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums BB 6 to BB 12 .

Also, in the second embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Fe 40 Pt 60 film was measured by a magnetic torque meter to find Ku 1 10 8 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 7.0 kOe .

Recording/reproducing tests were carried out to total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 3 shows the values of reproduced outputs. This table 3 also shows which values belong to which of the mediums according to the second embodiment and the comparison mediums.

TABLE 3 reproduced output *values of comparison mediums in solid line block *values of mediums in the second embodiment in dotted line block As can be seen from the table 3, the reproduced outputs are sufficiently secured in the region lower than the mediums B 1 to B 6 in the second embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums BB 6 to BB 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. As seen from this FIG. 4 , sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . Also, in case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b are lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed on the lower soft magnetic film is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 is satisfied. It is necessary to satisfy the relationship of b 1000 and simultaneously to satisfy a relationship of 5 200 and a relationship that b is 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI is recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs are thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, it could be understood that a vertical two-layer medium which uses a Fe 84.9 Si 9.6 Al 5.5 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 9.6 Al 5.5 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 9.6 Al 5.5 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 9.6 Al 5.5 film is used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 is satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Fe 84.9 Si 9.6 Al 5.5 film is and the film thickness thereof is b , sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the second embodiment. As a conclusion, by using a Fe 84.9 Si 9.6 Al 5.5 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be made thinner than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the second embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium in which the lower soft magnetic film is made thin and a process of manufacturing a medium is made easier.

The Third Embodiment

Like the first embodiment, total seventy different kinds of samples with Fe 84.9 Si 9.6 Al 5.5 films were prepared by use of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets, i.e., Fe 84.9 Si 9.6 Al 5.5 films respectively having seven different magnetic permeabilities were prepared for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared using 60at %Fe-40at %Pt targets in place of the 50at %Fe-50at %Pt targets in the first embodiment, on Fe 84.9 Si 9.6 Al 5.5 films formed separately from those formed for the purpose of magnetic permeability measurement.

At this time, like the first embodiment, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums C 1 to C 6 according to the third embodiment. In addition, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums CC 1 to CC 4 . Also, a medium having Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium CC 5 . Further, mediums with Fe 84.9 Si 9.6 Al 5.5 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums CC 6 to CC 12 .

Also, in the second embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Fe 60 Pt 40 film was measured by a magnetic torque meter to find Ku 5 10 7 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 5.0 kOe .

Recording/reproducing tests were made to total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 4 shows the values of reproduced outputs. This table 4 also shows which values belong to which of the mediums according to the third embodiment and the comparison mediums.

TABLE 4 Reproduced output *values of comparison mediums in solid line block *values of mediums in the third embodiment in dotted line block As can be seen from the table 4, the reproduced outputs were sufficiently secured in the region lower than the mediums C 1 to C 6 in the third embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums CC 6 to CC 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. From this FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . Also, in case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b of the lower soft magnetic film were lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed thereon is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 is satisfied. But, it is necessary to satisfy the relationship of b 1000 and to satisfy simultaneously a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI was recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs are thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Fe 84.9 Si 9.6 Al 5.5 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 9.6 Al 5.5 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 9.6 Al 5.5 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 9.6 Al 5.5 film is used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 was satisfied and if relationships of 5 200 and b 500 nm are simultaneously satisfied where the magnetic permeability of the Fe 84.9 Si 9.6 Al 5.5 film is and the film thickness thereof is b , a sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the present embodiment. As a result, by using a Fe 84.9 Si 9.6 Al 5.5 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be made thinner than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the present embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium in which the lower soft magnetic film can be made thin and a process of manufacturing a medium can be made easier.

It should be noted that since similar advantages were obtained by using respectively Fe 40 Pt 60 films in the second embodiment, Fe 50 Pt 50 films in the first embodiment, and Fe 60 Pt 40 films in the third embodiment as vertical magnetization films, it is apparent that the vertical magnetic anisotropic energy is distributed within a range of 5 10 7 erg/cc Ku 1 10 8 erg/cc and the coercive force in the direction vertical to the film surface is distributed within a range of 5 kOe Hc 7 kOe as long as a Fe X Pt 100-X film has X which falls in the range of 40 X 60 in X at %Fe-(100-X)at %Pt. Hence, it was also apparent that similar advantages can be obtained as long as a Fe X Pt 100-X film has X which falls in the range of 40 X 60 in X at %Fe-(100-X)at %Pt.

The Fourth Embodiment

In the same manner as in the first embodiment, Fe 84.9 Si 8.0 Al 7.1 films were formed on substrates using 84.9wt %Fe-8.0wt %Si-7.1wt %Al targets in place of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets used in the first embodiment. Like the first embodiment, total seventy different kinds of Fe 84.9 Si 8.0 Al 7.1 films were prepared to have seven different magnetic permeabilities for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared using YCo 5 (at %) targets in place of the 50at %Fe-50at %Pt targets used in the first embodiment, on Fe 84.9 Si 8.0 Al 7.1 films formed separately from those formed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums with Fe 84.9 Si 8.0 Al 7.1 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums D 1 to D 6 according to the fourth embodiment. In addition, mediums with Fe 84.9 Si 8.0 Al 7.1 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums DD 1 to DD 4 . Also, a medium having Fe 84.9 Si 8.0 Al 7.1 films each having a permeability and a film thickness b nm that satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium DD 5 . Further, mediums with Fe 84.9 Si 8.0 Al 7.1 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums DD 6 to DD 12 .

Also, in the fourth embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic films were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each YCO 5 film was measured by a magnetic torque meter to find Ku 1 10 7 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 6.5 kOe .

Recording/reproducing tests were carried out to total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 5 shows the values of reproduced outputs. This table 5 also shows which values belong to which of the mediums according to the present embodiment and the comparison mediums.

TABLE 5 Reproduced output *values of comparison mediums in solid line block *values of mediums in the third embodiment in dotted line block As can be seen from the table 5, the reproduced outputs were sufficiently secured in the region lower than the mediums D 1 to D 6 of the present embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums DD 6 to DD 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. From this FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . In case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b were lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed thereon is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 was satisfied. It is necessary to satisfy the relationship of b 1000 and simultaneously to satisfy a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI is recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs are thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Fe 84.9 Si 8.0 Al 7.1 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 8.0 Al 7.1 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 8.0 Al 7.1 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 8.0 Al 7.1 film was used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 is satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Fe 84.9 Si 8.0 Al 7.1 film is and the film thickness thereof is b , sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the fourth embodiment. As a conclusion, by using a Fe 84.9 Si 8.0 Al 7.1 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be made thinner than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the fourth embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium in which the lower soft magnetic film can be made thin and process of manufacturing a medium can be made easier.

The Fifth Embodiment

In the same manner as in the first embodiment, Fe 84.9 Si 12.0 Al 3.1 films were formed on substrates using 84.9wt %Fe-12.0wt %Si-3.1wt %Al targets in place of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets used in the first embodiment. Like the first embodiment, total seventy different kinds of Fe 84.9 Si 12.0 Al 3.1 films were prepared to have seven different magnetic permeabilities for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared using CeCo 5 (at %) targets in place of the 50at %Fe-50at %Pt targets used in the first embodiment, on Fe 84.9 Si 12.0 Al 3.1 films formed separately from those formed for the purpose of magnetic permeability measurement.

At this time, like the first embodiment, mediums with Fe 84.9 Si 12.0 Al 3.1 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums E 1 to E 6 according to the fifth embodiment. In addition, mediums with Fe 84.9 Si 12.0 Al 3.1 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums EE 1 to EE 4 . Also, a medium having Fe 84.9 Si12.0Al 3.1 films having combinations of a permeability and a film thickness b nm that satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium EE 5 . Further, mediums having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums EE 6 to EE 12 .

Also, in the fifth embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 as the lower soft magnetic films which were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each CeCo 5 film was measured by a magnetic torque meter to find Ku 5.5 10 7 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 6.5 kOe .

Recording/reproducing tests were made to total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 6 shows the values of reproduced outputs. This table 6 also shows which values belong to which of the mediums according to the present embodiment and the comparison mediums.

TABLE 6 Reproduced outputs *values of comparison mediums in solid line block *values of mediums in the fourth embodiment in dotted line block As can be seen from the table 6, the reproduced outputs were sufficiently secured in the region lower than the mediums E 1 to E 6 of the present embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums EE 6 to EE 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. From FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

Also, in case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b , Also, in case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b were lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed on the lower soft magnetic film is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 was satisfied. It is necessary to satisfy the relationship of b 1000 and to satisfy simultaneously a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI is recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs were thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Fe 84.9 Si 12.0 Al 3.1 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 12.0 Al 3.1 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 12.0 Al 3.1 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 12.0 Al 3.1 film was used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 was satisfied and if relationships of 5 200 and b 500 nm were satisfied simultaneously where the magnetic permeability of the Fe 84.9 Si 12.0 Al 3.1 film is and the film thickness thereof is b , sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the present embodiment. As a conclusion, by using a Fe 84.9 Si 12.0 Al 3.1 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be more thinned than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the fifth embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium in which the lower soft magnetic film can be made thinner and a process of manufacturing a medium can be made easier.

It should be noted that since similar advantages are obtained by using respectively Fe 84.9 Si 8.0 Al 7.1 films in the fourth embodiment, Fe 84.9 Si 9.6 Al 5.5 films in the first embodiment, and Fe 84.9 Si 12.0 Al 3.1 films in the fifth embodiment as vertical magnetization films, it is apparent that similar advantages can be obtained as long as a Fe 84.9 -Si X -Al 15.1-X lower soft magnetic film has X which falls in the range of 8.0 X 12.0 (wt %) in Fe 84.9 -Si X -Al 15.1-X .

The Sixth Embodiment

In the same manner as in the first embodiment, Co 62 Ni 12 Fe 26 films were formed on substrates using 62wt %Co-12wt %Ni-26wt %Fe targets in place of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets used in the first embodiment. Like the first embodiment, total seventy different kinds of Co 62 Ni 12 Fe 26 films were prepared to have seven different magnetic permeabilities for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared using SmCo 5 (at %) targets in place of the 50at %Fe-50at %Pt targets used in the first embodiment, on Co 62 Ni 12 Fe 26 films formed separately from those formed for the purpose of magnetic permeability measurement.

At this time, like the first embodiment, mediums having Co 62 Ni 12 Fe 26 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums F 1 to F 6 according to the present embodiment. In addition, mediums having Co 62 Ni 12 Fe 26 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums FF 1 to FF 4 . Also, a medium having Co 62 Ni 12 Fe 26 films having combinations of a permeability and a film thickness b nm that satisfies b 400, e.g., ( , 5b) (20, 20) was named a comparison medium FF 5 . Further, mediums having Co 62 Ni 12 Fe 26 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums FF 6 to FF 12 .

Also, in the fifth embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 as the lower soft magnetic films were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each SmCo 5 film was measured by a magnetic torque meter to find Ku 1 10 8 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 7.0 kOe .

Recording/reproducing tests were made to total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 7 shows the values of reproduced outputs. This table 7 also shows which values belong to which of the mediums according to the present embodiment and the comparison mediums.

TABLE 7 Reproduced output *values of comparison mediums in solid line block *values of mediums in the sixth embodiment in dotted line block As can be seen from the table 7, the reproduced outputs are sufficiently secured in the region lower than the mediums F 1 to F 6 of the present embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums FF 6 to FF 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. From this FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . In case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b were lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed on the lower soft magnetic film is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 is satisfied. It is necessary to satisfy the relationship of b 1000 and simultaneously to satisfy a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI is recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs are thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Co 62 Ni 12 Fe 26 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Co 62 Ni 12 Fe 26 film has greater saturation magnetization than the Ni 21.5 Fe 78.5 film. Therefore, the Co 62 Ni 12 Fe 26 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Co 62 Ni 12 Fe 26 film is used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 is satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Co 62 Ni 12 Fe 26 film is and the film thickness thereof is b , sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the sixth embodiment. As a conclusion, by using a Co 62 Ni 12 Fe 26 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be made thinner than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the present embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium which enables thinning of the lower soft magnetic film and easier process of manufacturing a medium.

The Seventh Embodiment

Like the first embodiment, total seventy different kinds of samples having Fe 84.9 Si 9.6 Al 5.5 films were prepared by use of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets, i.e., Fe 84.9 Si 9.6 Al 5.5 films respectively having seven different magnetic permeabilities were prepared for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared using Y 2 Co 17 (at %) targets in place of the 50at %Fe-50at %Pt targets used in the first embodiment, on Fe 84.9 Si 9.6 Al 5.5 films formed separately from those formed for the purpose of measurement of magnetic permeability. At this time, like the first embodiment, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums G 1 to G 6 according to the seventh embodiment. In addition, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums GG 1 to GG 4 . Also, a medium having Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium GG 5 . Further, mediums with Fe 84.9 Si 9.6 Al 5.5 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums GG 6 to GG 12 .

Also, in the seventh embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 as the lower soft magnetic films were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic film were formed to have a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Y 2 Co 17 film was measured by a magnetic torque meter to find Ku 2 10 8 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 8.0 kOe .

Recording/reproducing tests were made on total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 8 shows the values of reproduced outputs. This table 8 also shows which values belong to which of the mediums according to the seventh embodiment and the comparison mediums.

TABLE 8 Reproduced outputs *values of comparison mediums in solid line block *values of mediums in the seventh embodiment in dotted line block As can be seen from the table 8, the reproduced outputs are sufficiently secured in the region lower than the mediums G 1 to G 6 of the present embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums GG 6 to GG 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b on the lower soft magnetic film. From this FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . Also, in case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b are lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed on the lower soft magnetic film is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 is satisfied. It is necessary to satisfy the relationship of b 1000 and to satisfy simultaneously a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI is recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs are thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Fe84.9Si 9.6 Al 5.5 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 9.6 Al 5.5 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 9.6 Al 5.5 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 9.6 Al 5.5 film was used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 was satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Fe 84.9 Si 9.6 Al 5.5 film is and the film thickness thereof is b , a sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the seventh embodiment. As a conclusion, by using a Fe 84.9 Si 9.6 Al 5.5 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be more thinned than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the present embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium in which the lower soft magnetic film can be made thinner and a process of manufacturing a medium can be made easier.

The Eighth Embodiment

Like the first embodiment, total seventy different kinds of Fe 84.9 Si 9.6 Al 5.5 films were prepared by use of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets, i.e., Fe 84.9 Si 9.6 Al 5.5 films respectively having seven different magnetic permeabilities were prepared for every one of ten different film thicknesses b . Also, like the first embodiment, mediums were prepared using CeCo 17 (at %) targets in place of the 50at %Fe-50at %Pt targets used in the first embodiment, on Fe 84.9 Si 9.6 Al 5.5 films formed separately from those formed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums H 1 to H 6 according to the present embodiment. In addition, mediums with Fe 84.9 Si 9.6 Al 5.5 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums HH 1 to HH 4 . Also, a medium having a combination which satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium HH 5 . Further, mediums with Fe 84.9 Si 9.6 Al 5.5 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums HH 6 to HH 12 .

Also, in the eighth embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 as the lower soft magnetic films which were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 as vertical two-layer mediums having Ni 21.5 Fe 78.5 as the lower soft magnetic films were formed to have a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each CeCo 17 film was measured by a magnetic torque meter to find Ku 5 10 8 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 8.5 kOe .

Recording/reproducing tests were made on total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 9 shows the values of reproduced outputs. This table 9 also shows which values belong to which of the mediums according to the present embodiment and the comparison mediums.

TABLE 9 Reproduced Outputs *values of comparison mediums in solid line block *values of mediums in the eighth embodiment in dotted line block As can be seen from the table 9, the reproduced outputs are sufficiently secured in the region lower than the mediums H 1 to H 6 of the eighth embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums HH 6 to HH 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical axis expresses the film thickness b thereof. From this FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . In case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b are lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed on the lower soft magnetic film is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of a b 1000 was satisfied. It is necessary to satisfy the relationship of b 1000 and to satisfy simultaneously a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI was recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs were thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Fe 84.9 Si 9.6 Al 5.5 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Fe 84.9 Si 9.6 Al 5.5 film has smaller anisotropy and is more isotropic than the Ni 21.5 Fe 78.5 film. Therefore, the Fe 84.9 Si 9.6 Al 5.5 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Fe 84.9 Si 9.6 Al 5.5 film was used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of a b 1000 is satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Fe 84.9 Si 9.6 Al 5.5 film was and the film thickness thereof was b , sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the eight embodiment. As a conclusion, by using a Fe 84.9 Si 9.6 Al 5.5 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be made thinner than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the present embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium in which the lower soft magnetic film can be made thinner and a process of manufacturing a medium can be made easier.

The Ninth Embodiment

In the same manner as in the first embodiment, samples were prepared in which Co 62 Ni 12 Fe 26 films were formed on substrates using 62wt %Co-12wt %Ni-26wt %Fe targets were used in place of 84.9wt %Fe-9.6wt %Si-5.5wt %Al targets used in the first embodiment. Like the first embodiment, total seventy different kinds of samples with Co 62 Ni 12 Fe 26 films were prepared. Also, like the first embodiment, mediums were prepared using SmCo 17 (at %) targets in place of the 50at %Fe-50at %Pt targets used in the first embodiment, on Co 62 Ni 12 Fe 26 films formed separately from those formed for the purpose of measurement of magnetic permeability.

At this time, like the first embodiment, mediums having Co 62 Ni 12 Fe 26 films having combinations of a permeability and a film thickness b nm that satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5) were respectively named vertical magnetic recording mediums J 1 to J 6 according to the ninth embodiment. In addition, mediums having Co 62 Ni 12 Fe 26 films having combinations of a permeability and a film thickness b nm that satisfy b 500, e.g., ( , b ) (5, 100), (10, 50), (50, 10), and (100, 5) were respectively named comparison mediums JJ 1 to JJ 4 . Also, a medium having Co 62 Ni 12 Fe 26 films having combinations of a permeability and a film thickness b nm that satisfies b 400, e.g., ( , b ) (20, 20) was named a comparison medium JJ 5 . Further, mediums having Co 62 Ni 12 Fe 26 films each having permeabilities 2 to 200 and a film thickness b 750 nm were respectively named comparison mediums JJ 6 to JJ 12 .

Also, in the ninth embodiment, like the first embodiment, conventional mediums AB 1 to AB 4 as vertical two-layer mediums having Ni 21.5 Fe 78.5 films as the lower soft magnetic films were formed to have a permeability and a film thickness b nm that satisfy b 2000, e.g., ( , b ) (10, 200), (20, 100), (100, 20), and (200, 10). Also, conventional comparison mediums AC 1 to AC 6 were formed to have a permeability and a film thickness b nm satisfy b 1000, e.g., ( , b ) (5, 200), (10, 100), (20, 50), (50, 20), (100, 10), and (200, 5).

Then, the vertical magnetic anisotropic energy Ku of each Sm 2 Co 17 film was measured by a magnetic torque meter to find Ku 7 10 8 erg/cc . In addition, the coercive force in the direction vertical to the film surface was measured by a Kerr rotation angle measurement device to find Hc 10.0 kOe .

Recording/reproducing tests were made to total seventy kinds of vertical magnetic recording mediums having seven different permeabilities for every one of ten different film thicknesses of lower soft magnetic films, under the same conditions as those of the first embodiment. Specifically, a signal having a recording density of 300 kFRPI was recorded, and thereafter, a reproduced output thereof was measured. Table 10 shows the values of reproduced outputs. This table 10 also shows which values belong to which of the mediums according to the ninth embodiment and the comparison mediums.

TABLE 10 Reproduced outputs *values of comparison mediums in solid line block *values of mediums in the ninth embodiment in dotted line block As can be seen from the table 10, the reproduced outputs are sufficiently secured in the region lower than the mediums J 1 to J 6 of the present embodiment. On the other hand, reproduced outputs can be greatly lowered in the region upper than the comparison mediums JJ 6 to JJ 12 . FIG. 4 also summarizes the results obtained above, in a different manner, where the horizontal axis expresses the magnetic permeability of the lower soft magnetic film and the vertical expresses the film thickness b thereof. From FIG. 4 , it is found that sufficient reproduced outputs can be secured where b 1000 is satisfied.

In case where the magnetic permeability of the lower soft magnetic film is two, sufficient reproduced outputs cannot be secured with respect to any of the film thicknesses b . In case where the film thickness b is 2 nm, sufficient reproduced outputs cannot be secured with respect to any of the permeabilities . This is because the permeability and the film thickness b were lower than required. Further, the reproduced output tends to decrease even when the film thickness b of the lower soft magnetic film exceeds 500 nm. This is because the surface smoothness of the lower soft magnetic film is disturbed since the film thickness b of the lower soft magnetic film is thicker than required. Consequently, the vertical orientation of the vertical magnetization film formed thereon is deteriorated. Hence, it is found that all values of ( , b ) that satisfy the relationship of b 1000 cannot be always used for practical design even if the relationship of b 1000 is satisfied. But, it is necessary to satisfy the relationship of b 1000 and to satisfy simultaneously a relationship of 5 200 and a relationship that b was 500 nm or less.

On the other hand, a signal having a recording density of 300 kFRPI was recorded on the conventional mediums AB 1 to AB 4 and the conventional comparison mediums AC 1 to AC 6 . Reproduced outputs were thereafter measured with a MR head. As shown in the first embodiment, the value of b 1000 is insufficient to obtain securely a recording/reproducing sensitivity but the value of b requires at least b 2000 or more. From this, a vertical two-layer medium which uses a Co 62 Ni 12 Fe 26 film as its lower soft magnetic film can obtain more securely a recording/reproducing sensitivity than a vertical two-layer medium which uses a Ni 21.5 Fe 78.5 film as its lower soft magnetic film, even if the value of b is small. In other words, the lower soft magnetic film can be designed to be thinner. This is because the Co 62 Ni 12 Fe 26 film has greater saturation magnetization than the Ni 21.5 Fe 78.5 film. Therefore, the Co 62 Ni 12 Fe 26 film has a higher sensitivity to the magnetic field generated by the recording head, so that the recording/reproducing sensitivity is improved as a result.

From the above, if a Co 62 Ni 12 Fe 26 film was used in place of a Ni 21.5 Fe 78.5 film for a vertical two-layer medium, design can be made with a lower value of b . If the relationship of b 1000 is satisfied and if relationships of 5 200 and b 500 nm are satisfied simultaneously where the magnetic permeability of the Co 62 Ni 12 Fe 26 film is and the film thickness thereof is b , sufficient recording/reproducing sensitivity can be secured even in case where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional vertical magnetization films, as in the present embodiment. As a conclusion, by using a Co 62 Ni 12 Fe 26 film as a lower soft magnetic film and by satisfying the conditions of b 1000, 5 200, and b 500 nm, the lower soft magnetic film can be more thinned than in the case of using a Ni 21.5 Fe 78.5 film which is often used conventionally as a lower soft magnetic film, even if where the vertical magnetic anisotropic energy Ku and the coercive force Hc in the direction vertical to the film surface are much greater than those of conventional CoCr-based vertical magnetization films (e.g., Ku is about 5 10 6 erg/cc and Hc is about 3 kOe ), as in the case of the material used in the present embodiment. Accordingly, it is possible to obtain a novel vertical two-layer medium which enables thinning of the lower soft magnetic film and easier process of manufacturing a medium.

From the results of the above first to ninth embodiments, it is apparent that the same advantages as obtained in the first to ninth embodiments can be obtained regardless of the material of the vertical magnetization film, if the vertical magnetic anisotropic energy of the vertical magnetization film falls within the range of 1 10 7 erg/cc Ku 7 10 8 erg/cc and if the coercive force in the direction vertical to the film surface of the vertical magnetization film falls within the range of 5 kOe Hc 10 kOe .

Although embodiments of the present invention have been described above on the basis of the drawings, specific structures of the present invention were not limited to those described in the above embodiments but may be variously modified without deviating from the subject of the present invention.

As has been described above, according to the present invention, a vertical magnetic recording medium was composed of layering a lower soft magnetic film and a vertical magnetization film on a substrate made of a non-magnetic material. Here, the lower soft magnetic film is arranged to satisfy a relationship of b 1000 where is the magnetic permeability of the lower soft magnetic film and b is the film thickness thereof. Therefore, even if FePt alloy or RCo alloy (where R Y, Ce, Sm, La, Pr) as a vertical magnetization film has much greater vertical magnetic anisotropic energy Ku and a much greater coercive force Hc in the direction vertical to the film surface than those of a CoCr-based vertical magnetization film which is often used conventionally and generally, the lower soft magnetic film can be more thinned than in the case of using a Ni 21.5 Fe 78.5 film which is often used as the lower soft magnetic film. Accordingly, it is possible to realize a easy process for preparing a medium and to obtain a novel vertical two-layer medium.