JPH04248115A - Magnetic recording medium and its production - Google Patents

Abstract

PURPOSE:To improve reproducibility and to increase intrasurface anisotropy of the medium by providing a base layer comprising iron or iron-cobalt alloy between a substrate and a magnetic film comprising a partial oxide of cobalt. CONSTITUTION:The magnetic film of this invention is obtained by reactive sputtering with using metal cobalt as a target in an oxygen atmosphere or by sputtering with using a mixture of metal cobalt Co and cobalt oxide CoO as a target. By providing a base layer comprising iron or iron-cobalt alloy, the magnetic film comprising a partial oxide of cobalt has >=500 intrasurface coercive force, and moreover, >=500 intrasurface coercive force and >=0.6 squareness ratio with large energy product. The intrasurface coercive force Hc (represents intrasurface direction) of the magnetic film is larger than the perpendicular coercive force Hcrt. angle, and the squareness ratio is larger than (perpendicular residual magnetization Mrrt. angle/saturation magnetization Ms). This indicates that the film is an intrasurface anisotropic film.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium capable of high-density recording. More specifically, the present invention relates to a magnetic recording medium suitable for flexible disks, magnetic tapes, and hard disks, and a method for manufacturing the same. [0002] Conventionally, Co--Cr alloy thin films, Co partial oxide thin films, Fe-Co alloy partial oxide thin films, etc. have been proposed as perpendicular magnetic recording media capable of high-density magnetic recording. . These partial oxide thin films have large perpendicular magnetic anisotropy, enable high-density recording, and are hard because they are composed of oxides, exhibiting excellent wear resistance against head sliding. These partial oxide thin films can be produced by vacuum evaporation in an oxygen atmosphere or reactive sputtering in an oxygen atmosphere. By the way, even in the conventional longitudinal recording method, it is possible to increase the recording density by increasing the coercive force. In a cobalt partial oxide film, the anisotropy direction can be made vertical or in-plane by selecting the formation conditions. A cobalt partial oxide film having anisotropy in the in-plane direction has conventionally been produced by an oblique evaporation method. However, since the obtained cobalt partial oxide film had in-plane uniaxial anisotropy, it could not be used for disk-shaped magnetic recording media. Therefore, the present inventors proposed a sputtering method in which the argon gas pressure is lowered as a method for forming a cobalt partial oxide film that is easily magnetized in-plane by perpendicular incidence. Although this method has made it possible to obtain a magnetic film with an in-plane coercive force of 1000 Oe or more, there is a problem in so-called reproducibility, in which the coercive force decreases in some cases. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording medium with good reproducibility and large in-plane anisotropy. [Means for Solving the Problems] In view of the above-mentioned circumstances, the present inventors have conducted intensive research and found that the above-mentioned problems can be solved by providing a base layer made of iron or an iron-cobalt alloy. This has led to the present invention. That is,
A first aspect of the present invention provides a magnetic recording medium characterized in that an underlayer made of iron or an iron-cobalt alloy is provided between a substrate and a magnetic film made of a partial oxide of cobalt. The second describes a method for producing a magnetic recording medium, which is characterized by depositing an underlayer made of iron or an iron-cobalt alloy and a magnetic film made of a cobalt partial oxide on a substrate in that order by sputtering. That is. The substrate used in the present invention has a thickness of 1
A plate, sheet or film made of an organic polymer such as polyester or polyimide, a metal plate such as aluminum or stainless steel, or a glass plate having a size of 0 μm to several mm can be used. The magnetic film made of cobalt partial oxide in the present invention can be obtained by reactive sputtering in an oxygen atmosphere using metallic cobalt as a target, or by sputtering using a mixture of metallic cobalt Co and cobalt oxide CoO as a target. Practical sputtering methods include DC magnetron sputtering and high frequency magnetron sputtering. The magnetic film of the present invention made of a cobalt partial oxide having a large in-plane coercive force, that is, a magnetic film having a large in-plane coercive force and in-plane squareness ratio, can be suitably obtained by a high-frequency sputtering method. Furthermore, the lower the sputtering gas pressure, the greater the in-plane coercive force that can be obtained. Therefore, a magnetic film with a large in-plane coercive force can be obtained especially by low argon gas pressure and high frequency magnetron sputtering method. When the sputtering gas pressure is high or the direct current method is used, the perpendicular magnetic anisotropy increases and the in-plane coercive force tends to decrease. Although the substrate temperature is not particularly limited, it is rather a feature of the present invention that a magnetic film having a high in-plane coercive force can be obtained at room temperature. [0009]Also, substantially the same in-plane anisotropy can be obtained by either the reactive sputtering method in oxygen or the sputtering method using a partial oxide target. Saturation magnetization is also an important parameter and can be controlled by the degree of oxidation. The larger the saturation magnetization, the higher the low-density reproduction output, but the recording density tends to decrease and noise also increases. Also, the saturation magnetization should be set to an appropriate value. Appropriate saturation magnetization is 300-700
It is in the emu/cm3 range. The reproduction output is proportional to the thickness, but if it is too thick, the medium becomes too hard and head touch deteriorates, so a thickness of 1000 to 5000 Å is appropriate. However, as mentioned above, the above method has the drawback of poor reproducibility. That is, as sputtering is repeated under the same conditions, the in-plane coercive force gradually decreases, resulting in a perpendicularly magnetized film. This problem can be solved by providing a thin underlayer of iron or iron-cobalt alloy during sputtering. By providing an underlayer made of iron or iron-cobalt alloy, in-plane coercive force of 500 or more, and even in-plane coercive force of 50
With an in-plane squareness ratio of 0 or more and an in-plane squareness ratio of 0.6 or more, a cobalt partial oxide film with a large energy product can be obtained. FIG. 1 shows a magnetization curve of a typical magnetic film obtained by the present invention (an example obtained by Example 1, which will be described later). In-plane coercive force Hc‖ (hereinafter,
The symbol “‖” means in-plane) has a higher vertical coercive force Hc⊥
and the squareness ratio (in-plane residual magnetization Mr‖/saturation magnetization Ms) is larger than (perpendicular residual magnetization Mr⊥/saturation magnetization Ms), indicating that this magnetized film is an in-plane anisotropic film. It shows. The magnetic properties of the cobalt partial oxide film are influenced by the sputtering conditions of the underlying layer. High frequency magnetron sputtering is suitable for obtaining films with large in-plane anisotropy. Furthermore, the argon gas pressure is 0.5-15m.
Torr is suitable. iron or iron. The composition of the cobalt alloy is preferably Fe1-x Cox (0≦x≦0.8), that is, 0 to 80 atomic percent of cobalt. Cobalt alone reduces coercive force. Under these conditions, the thickness of the underlayer is sufficiently effective in the range of 10-500 Å, more preferably in the range of 50-200 Å. 500
When the thickness becomes thicker than Å, the in-plane squareness ratio increases, but the coercive force decreases extremely. [0012] Prior to sputtering, it is very important to bring the inside of the sputtering container to a high vacuum state. If sputtering is performed in a poor vacuum state, vertical anisotropy is likely to occur. Although it is necessary to increase the degree of vacuum in the present invention, when an iron or iron-cobalt alloy underlayer is provided, a magnetic film with large in-plane anisotropy can be stably produced even if the degree of vacuum is slightly poor. It has the characteristic of being obtained. As mentioned above, conventionally, a cobalt partial oxide film with a large in-plane coercive force has been obtained by an oblique evaporation method, which has had the problem of poor adhesion efficiency of evaporated elements, but the method of the present invention substantially improves Since the incidence is perpendicular, these problems are less likely to occur. In addition, the obliquely deposited film has anisotropy in one in-plane direction, and although it may be used for tapes, it cannot be used for floppy disks, etc. However, the magnetic film obtained by the present invention has anisotropy in one in-plane direction It can be used as a rotating medium such as a floppy disk without any problem. The medium of the present invention is a partial oxide, is hard, and has excellent durability against head sliding. However, it is preferable to coat the head with a protective film or lubricant within a range that does not increase the spacing between the head and the medium, since this improves the running performance and durability of the head. [0014] In the medium of the present invention, recording and reproduction are suitably performed using a ring-type head. When recording and reproducing using a ring head, the reproduction output is proportional to the 0.5th power of the product of the coercive force, saturation magnetization, squareness ratio, and thickness of the magnetic film, and the recording density is proportional to the 0.5th power of the coercive force. It is known to do. therefore,
The medium of the present invention provides a medium with high recording density and high reproduction output. Note that N is present in the cobalt partial oxide film.
i, Cr, Al, Nb, Mn, Ta, W, Mo, Zr,
Of course, there are also media with added third elements such as Ti, V, and Si to improve corrosion resistance, and media with Ni etc. added to the iron or iron-cobalt alloy base layer to an extent that does not change the crystal orientation or magnetism. It is within the scope of the present invention. EXAMPLES The present invention will now be explained in more detail with reference to Examples, but the present invention is not limited thereto. Example 1 An iron-cobalt (Fe40Co60) alloy base layer and a cobalt partial oxide film were sputtered in this order by high-frequency magnetron sputtering. The sputtering equipment is
A vacuum chamber equipped with a target of Fe40Co60 having a diameter of 6 inches and a Co:CoO ratio of 6:4 (mole ratio) was used. A polyimide film with a thickness of 30 microns was used as the substrate. The target and substrate holder had the same dimensions and were opposed to each other at a distance of 7 cm. In this apparatus, the sputtered particles were substantially perpendicularly incident. The Fe40Co60 alloy base layer and the Co partial oxide film were sputtered in this order without breaking the vacuum. The degree of vacuum in the sputtering chamber is 1.2 x 10-5 Tor
When the temperature reached r, argon gas was introduced at a flow rate of 20 ccm, and the argon gas pressure was set at 2.3 mTorr. Sputtered for 12 seconds with high frequency power of 250W to a thickness of 90Å.
A Fe40Co60 underlayer was obtained. Subsequently, the argon gas flow rate was 20 ccm, and the argon gas pressure was 5 mTorr.
Sputtering was performed for 3 minutes at a high frequency power of 600 W to obtain a cobalt partial oxide film with a thickness of 2740 Å. Saturation magnetization 4
50 emu/cm3, coercive force measured parallel to the plane is 1
000 Oe, and the in-plane squareness ratio was 0.72. The sputtering conditions are shown in Tables 1 and 2, and the magnetic properties are shown in Table 3. Moreover, the magnetization curve is shown in FIG. Example 2-4 A film was prepared in the same manner as in Example 1 except that the sputtering pressure of the Fe40Co60 alloy underlayer was changed. The results are summarized in Table 1, Table 2, and Table 3. From the results in the same table, it can be seen that the influence of argon gas pressure is small. Comparative Example 1, Examples 5 and 6 In sputtering the Fe40Co60 underlayer, the degree of vacuum was 9 x 10-6 Torr, and the argon gas pressure was 1 mT.
orr, change the sputtering time, and Fe40C
It was produced in the same manner as in Example 1 except that the thickness of the O60 alloy base layer was changed. The results are summarized in Table 1, Table 2, and Table 3. From the results in the same table, it can be seen that the appropriate thickness of the Fe40Co60 alloy underlayer is about 100 Å, and that if it is too thick, the coercive force decreases. Comparative Example 2, Examples 7 and 8 The ultimate vacuum level before sputtering was 3×10-6 Torr.
Example 1 was prepared in the same manner as in Example 1, except that Fe60Co40 was used as the base layer alloy and the thickness of the base layer was changed. The results are summarized in Table 1, Table 2, and Table 3. From the results in the same table, it can be seen that the higher the degree of vacuum, the higher the internal anisotropy. Example 9 An iron/cobalt alloy base layer was prepared under the conditions shown in Table 1. Subsequently, a cobalt partial oxide film was formed by reactive sputtering in an oxygen atmosphere. Using cobalt as a target, introduce 20ccm of argon gas and set the temperature to 3mTor.
It was set as r. Furthermore, 8 ccm of oxygen was introduced. 900
Sputtering was performed with W for 1 minute to obtain a cobalt partial oxide film with a thickness of 2240 Å. The magnetic properties are shown in Table 1, Table 2, and Table 3. From the results in the same table, it can be seen that a cobalt partial oxide film can also be suitably obtained by reactive sputtering. Comparative Example 3 Cobalt was used as the underlayer. Argon gas pressure 5m
Sputtering was performed at a power of 500 W for 6 seconds at Torr. Subsequently, a cobalt partial oxide film was obtained by reactive sputtering in the same manner as in Example 9. Table 1 shows its magnetic properties.
, shown in Tables 2 and 3. From the results in the same table, it can be seen that a cobalt partial oxide film with large inner surface anisotropy cannot be obtained with a cobalt underlayer. Example 10 Iron was used as the base layer. Argon gas pressure 5mTor
Sputtering was performed for 6 seconds at a power of 500 W. Subsequently, a cobalt partial oxide film was obtained by reactive sputtering in the same manner as in Example 9. Table 1 shows its magnetic properties.
, shown in Tables 2 and 3. From the results in the same table, it can be seen that a cobalt partial oxide film with large inner surface anisotropy can be obtained even with an iron base layer. [Table 1] [Table 2] [Table 3] [Table 3] [Effect of the invention] When a cobalt partial oxide film is obtained by sputtering method, by providing an iron-cobalt alloy base layer, , a cobalt partial oxide film with large in-plane anisotropy can be stably obtained. The obtained magnetic recording medium has high reproduction output, high recording density, and excellent durability.

[Brief explanation of the drawing]

FIG. 1 is a magnetization curve of the magnetic recording medium obtained in Example 1.

Claims (1)

[Scope of Claims] [Claim 1] A magnetic recording medium characterized in that an underlayer made of iron or an iron-cobalt alloy is provided between a substrate and a magnetic film made of a partial oxide of cobalt. 2. The magnetic recording medium according to claim 1, wherein the underlayer made of iron or iron-cobalt alloy has a thickness of 10 to 500 Å. [Claim 3] The composition of iron or iron-cobalt alloy is F
The magnetic recording medium according to claim 1 or 2, wherein e1-xCox (0≦x≦0.8). 4. The magnetic recording medium according to claim 1, wherein the in-plane coercive force is 500 Oe or more and the in-plane squareness ratio is 0.6 or more. 5. The magnetic recording medium according to claim 1, wherein the magnetic film made of partial oxide of cobalt has a saturation magnetization of 300 to 700 emu/cm 3 . [Claim 6] After depositing a base layer made of iron or an iron-cobalt alloy on the substrate by a sputtering method,
A method for manufacturing a magnetic recording medium, characterized in that a magnetic film made of a partial oxide of cobalt is deposited by a sputtering method with substantially perpendicular incidence.