JPH01173313A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To provide a magnetic recording medium which exhibits high coercive force, high squareness ratio and high residual magnetization by laminating two-layered structures each combined with a magnetic layer consisting of a Co-Ni alloy having 20-500Angstrom thickness and an underlying layer consisting of Cr thicker than said magnetic layer 2-50 times on a nonmagnetic substrate. CONSTITUTION:The two-layered structures each combined with the magnetic layer having 20-500Angstrom thickness and the underlying layer thicker than said magnetic layer are laminated 2-50 times on the nonmagnetic substrate of the magnetic recording medium which is formed with the underlying layers consisting of the Cr and the magnetic layers consisting of the Co-Ni alloy on said substrate. The coercive force of the magnetic layers consisting of the Co-Ni alloy is generally larger as the thickness thereof is smaller. The magnetic layers are, thereupon, divided to the thin layers and the Cr layers which are the underlying layers are interposed between the respective magnetic layers to increase the coercive force as the recording medium. However, the saturation magnetization and eventually the residual magnetization are extremely degraded if the thickness of the magnetic layers is below 20Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film magnetic recording medium used for magnetic disks, magnetic drums, etc.

[Conventional technology]

In recent years, with the demand for higher density magnetic recording, development of metal thin film type magnetic recording media using sputtering, vacuum deposition, etc. has been progressing in place of the conventional coated type magnetic recording media. Compared to iron oxide, which has been mainly used in coated media, metal thin film media have much greater spontaneous magnetization and intrinsic coercivity, so it is possible to reduce the thickness of the recording layer.
It is believed that this makes it possible to shorten the recording wavelength, resulting in dramatically higher recording densities.

Among the materials currently being considered as candidates for the magnetic recording layer of thin-film magnetic recording media manufactured by sputtering, Co containing 15 to 40% Ni in atomic ratio has been used.
-Ni alloys or Co--Ni alloys to which some amounts of Cr, W, rare earth metals, etc. are added are considered the most promising because they have an excellent balance between magnetic properties and material cost.

By the way, conventional magnetic recording media, such as magnetic disks, are made by recording C on a non-magnetic substrate made of a plated AfL alloy.
It has a structure in which a base layer made of R or the like and a magnetic layer made of the Co--Ni alloy mentioned above are formed, and a protective layer is further provided to provide corrosion resistance, lubricity, etc. during use.

[Problem that the invention seeks to solve]

However, in the conventional Ii1 recording medium having the above-described structure, when trying to obtain excellent magnetic properties suitable for high-density recording, various problems such as those described below have occurred.

■ In order to obtain a high coercive force, a Cr underlayer that is 3 to 5 times thicker than the magnetic layer is required, but if the Cr underlayer becomes too thick, the squareness ratio (= residual magnetization/saturation magnetization).

(2) In order to obtain high reproduction output, it is necessary to increase the thickness of the magnetic layer and increase the value of residual magnetization, but as the thickness of the magnetic layer increases, the coercive force decreases.

(2) The lower the Ar pressure during sputtering, the better quality thin film is formed with fewer defects such as protrusions and pinholes, and the value of residual magnetization increases, but as the Ar pressure decreases, the coercive force decreases.

An object of the present invention is to solve the above-mentioned problems and provide a magnetic recording medium that exhibits high coercive force, high squareness ratio, and high residual magnetization, and has a large latitude in film formation conditions.

[Means and effects for solving the problems] The magnetic recording medium of the present invention has an underlayer made of Cr and a Co-layer on a non-magnetic substrate.
In a magnetic recording medium formed with a magnetic layer made of a Ni-based alloy and further provided with a protective layer, a two-layer structure combining a magnetic layer with a thickness of 20 to 500 nm and an underlayer thicker than the magnetic layer, It is characterized by being laminated 2 to 50 times.

In the present invention, regarding the Co-Ni alloy magnetic layer,
Generally, the smaller the thickness, the larger the coercive force. Therefore, by dividing the magnetic layer into thinner layers than before and stacking them with a Cr layer as an underlayer interposed between each magnetic layer, the high coercive force of each magnetic layer can be maintained throughout the entire recording layer. Therefore, it is considered that the coercive force as a recording medium increases compared to the case where the magnetic layer is a single layer. In this case, as mentioned above, the coercive force of the Co-Ni alloy is Cr
Go-N exhibits a high value that can be applied to recording media only when there is an underlayer, so a Cr underlayer must be interposed between each magnetic layer.In other words, Go-N
The coercive force can be increased most effectively when a two-layer structure is laminated, which is a combination of an i-based alloy magnetic layer and a Cr underlayer. However, unless the thickness of the Cr underlayer exceeds the thickness of the Co--Ni alloy magnetic layer, it is not possible to obtain a higher coercive force than in the past.

In the present invention, the thickness of the magnetic layer is defined as 20 to 500 for the following reason. That is, Co-N
Since the i-based alloy and Cr diffuse into each other near the interface to form a nonmagnetic layer, if the thickness of the magnetic layer is too thin, such as less than 20 mm, the saturation magnetization and thus the residual magnetization will significantly decrease. °On the other hand, the thicker each magnetic layer is, the larger the residual magnetization will be. However, if the thickness of the magnetic layer becomes thicker than 500, the thickness of the entire recording medium will increase, and the original thickness will increase. This makes it unsuitable for the purpose of high-density magnetic recording.

In the present invention, the number of laminations of the two-layer structure of the magnetic layer and the underlayer is set to 2 to 50 times for the following reasons.

First, because of the repeated lamination structure, the number of laminations must be two or more times, but in fact, even with just two laminations, the effect of increasing coercive force can be obtained. On the other hand, on the premise that it is not appropriate to increase the overall thickness of the recording medium too much, the thickness of the Co-Ni alloy magnetic layer and the Cr underlayer will inevitably decrease as the number of layers increases. become. In particular, when the thickness of the Cr underlayer becomes thinner, magnetic coupling occurs between the upper and lower magnetic layers, and the coercive force decreases. Although it depends on the pressure during sputtering, if the number of laminations exceeds 50, it will not be possible to obtain a coercive force that exceeds that of conventional magnetic recording media.The above has only discussed the increase in coercive force. However, when the number of laminations is in the range of 2 to 20 times, the squareness ratio can also be improved compared to conventional magnetic recording media.

As described above, according to the magnetic recording medium of the present invention, it is possible to provide a magnetic recording medium exhibiting high coercive force, high squareness ratio, and high residual magnetization, and it is possible to obtain such a good balance of magnetic properties. The range of possible sputtering conditions is wider than before.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

First, the DC magnetron sputtering apparatus shown in FIG. 3 used for forming the magnetic layer and the underlayer will be described. Third
In the figure, a substrate holder 2 is rotatably supported within a vacuum chamber 1 . This substrate holder 2 is connected to a motor 5 via a gear 3.4, and the rotation of the motor 5 is controlled by a substrate holder rotation control section 6. A substrate 7 is held in a part of this substrate holder 2. Also, in the vacuum chamber 1, two googets 8.9 (C
o-Ni alloy and Cr), and these targets 8.9 are each connected to a DC power source 1O111. Further, a shutter 12 is rotatably provided between the substrate holder 2 and the targets 8 and 9.
is driven by the shutter drive section 13. The DC power supply 10.11 and the shutter drive section 12 are controlled by a switching control section 14.

Using a DC magnetron sputtering apparatus with such a configuration, the substrate 7 is mounted on the substrate holder 2, the vacuum chamber 1 is made into a sputtering gas (for example, Ar) atmosphere at a predetermined pressure, and the switching control is performed while continuously rotating the substrate holder 2. The unit 14 controls the DC power supply 10.11 to generate two targets 8.9.
sputter discharge is caused alternately, and in conjunction with this, one target that is not being discharged is shielded with a shutter 12,
A two-layer structure consisting of a Co--Ni alloy magnetic layer and a Cr underlayer is laminated on the substrate 7.

Example 1 Using the apparatus shown in FIG. 3, Corning 705 was used as the substrate.
8 glass, Cr and 70% C as targets.

- 30% Ni alloy, Cr underlayer and 70% Co
-The total film thickness of the 70% Go-30% Ni alloy magnetic layer was laminated by varying the thickness ratio with the 30% Ni alloy magnetic layer and the number of laminations of this two-layer structure. For example, 70%Co-30%Ni
/ To explain the case where the film thickness ratio of Cr is 1 = 5 and the number of laminations is 10 times, the film thickness is 100 people Noah 0% Go - 30% N
This means that the two-layer structure in which the i-alloy magnetic layer is laminated 100 times on the Cr underlayer with a thickness of 500 mm is 70 times.
The total thickness of the %Co-30%Ni alloy magnetic layer is 1000 mm, and the total thickness of the Cr underlayer is 5000 mm.

Moreover, the main sputtering conditions are as follows.

Sputtering gas: Ar, Ar pressure crab 1 to 7 x 1O-3Torr, substrate temperature: water cooling, substrate rotation speed: 40 rp11 sputtering current:
0.5 A The magnetic properties of all the thin films produced were measured using a vibrating sample magnetometer, and the number of laminations, coercive force Hc, and saturation magnetization Ms δ (δ
is the total thickness of the magnetic layer) and the squareness ratio S is shown in Figs. 1 and 2. Fig. 1 shows the relationship between the total thickness of the magnetic layer
In the case of -3 Torr, Figure 2 shows the Ar pressure cuff X 10=
Torn) case.

As is clear from Figures 1 and 2, there are some differences in behavior depending on the Ar pressure, but in both cases the thickness of the Cr underlayer exceeds the thickness of the 70%Co-30%Ni alloy magnetic layer. An increase in coercive force due to lamination is observed only in cases where

Moreover, when compared with the case where the 70% Co-30% Ni alloy magnetic layer and the Cr underlayer are laminated once (Comparative Example 1), the first
In the figure, the coercive force increases in the range of 2 to 50 laminations, and in FIG. 2, the coercive force increases in the range of 2 to 20 laminations.

In addition, in both Fig. 1 and Fig. 2, the number of laminations is 2 to 20.
While an improvement in the squareness ratio is observed in the range of 200 nm, the saturation magnetization remains at a nearly constant level in this range.

As described above, it can be seen that according to the present invention, a good balance of magnetic properties can be obtained.

Example 2 Using the apparatus shown in FIG. 3, a 1000-thick Cr underlayer and a 200-thick 70% Co-30% Ni alloy were deposited on an aluminum disk substrate plated with N1-P electroless plating. After laminating the two-layer structure with the magnetic layer five times, a 0 layer with a thickness of 500 layers was deposited as a protective film by sputtering to fabricate a magnetic recording medium.

Comparative Example 2 On the same substrate as in Example 2, a 5,000-thick Cr underlayer, a 1,000-thick 70% Co-30% Ni alloy magnetic layer, and a 500-thick zero layer were sequentially laminated by sputtering. We prototyped a magnetic recording medium.

When the magnetic properties of the magnetic recording media of Example 2 and Comparative Example 2 were measured, the results shown in Table 1 were obtained.

Example 3 A 300-thick Cr underlayer and a 75-thick 62.5%Co-30%Ni-7.5%C were formed on the same substrate as in Example 2.
After laminating the two-layer structure with the r-alloy magnetic layer 10 times, a thickness of 5
A magnetic recording medium was prototyped by forming a 0 layer of 0.00 by sputtering.

Comparative Example 3 On the same substrate as in Example 2, a 3000-thick Cr underlayer and a 750-thick 62.5% Co-30% Ni-7,5
A magnetic recording medium was prototyped by sequentially laminating a %Cr alloy magnetic layer and a 0 layer with a thickness of 500 mm by sputtering.

When the magnetic properties of the magnetic recording media of Example 3 and Comparative Example 3 were measured, the results shown in Table 2 were obtained.

Table 1 Table 2 [Effects of the Invention] As detailed above, according to the magnetic recording medium of the present invention, coercive force and squareness ratio can be improved without impairing saturation magnetization. In addition, ■ Even if the total thickness of the Cr underlayer is thicker, the squareness ratio does not decrease and the coercive force increases.■ Even if the total thickness of the Cr underlayer is reduced than before, the coercive force does not decrease.
The squareness ratio improves. ■ Even if the total thickness of the Co-Ni alloy magnetic layer is increased to increase the saturation magnetization, the coercive force does not decrease, and the squareness ratio improves, so the residual magnetization further increases. (2) Even when sputtering is performed at a low Ar pressure that reduces defects in the thin film and increases the value of residual magnetization, a high coercive force can be maintained, improving film quality and yield. It can also be expected to have the effect of allowing a greater margin in manufacturing compared to conventional technologies.

[Brief explanation of the drawing]

Figure 1 shows Ar pressure I x 1O-3Torr tare 0%C
A characteristic diagram showing the relationship between the number of laminations and magnetic properties using the film thickness ratio as a parameter when a two-layer structure of an o-30% Ni alloy magnetic layer and a Cr underlayer is laminated. Figure 2 shows an Ar pressure cuff.
Characteristic diagram 3 showing the relationship between the number of laminations and magnetic properties when a two-layer structure of a 70% Co-30% Ni alloy magnetic layer and a Cr underlayer is laminated at X 1O-3 Torr using the film thickness ratio as a parameter. The figure is a configuration diagram of a DC magnetron sputtering apparatus used in an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Vacuum chamber, 2... Substrate holder, 3.4... Gear, 5... Motor, 6... Substrate holder rotation control unit,
7... Substrate, 8.9... Target, 10.11.
...DC power supply, 12...Shutter, 13...Shutter drive section, 14...Switching control section. Applicant's agent Patent attorney Takehiko Suzue (Itrei LIJ1) 4 collections (r
Pus example 1) Number of layers. Figure 3: Mr. Kunio Ogawa, Commissioner of the Patent Office 1. Indication of the case Japanese Patent Application No. 62-330516 2, Name of the invention Magnetic recording medium 3, Person making the amendment Relationship to the case Patent applicant Co., Ltd. Limes 4, Agent 6, Specification to be amended, Drawings 7, Amendment Contents (1) On page 9, line 12 of the specification, the phrase "r M s・δ" is corrected to "4πMs・δ". (2) Tables 1 and 2 on page 12 of the specification are corrected as follows. Table 1, Table 2 (3) Figures 1 and 2 are corrected as shown in the attached sheet. (k response F111) Sojyo circle Figure 2

Claims (1)

[Claims] In a magnetic recording medium in which an underlayer made of Cr and a magnetic layer made of a Co-Ni alloy are formed on a nonmagnetic substrate, and a protective layer is further provided, a magnetic layer with a thickness of 20 to 500 Å and a magnetic layer made of A two-layer structure combining a thick base layer with a thickness of 2 to 50
A magnetic recording medium characterized by being laminated twice.