JP2008091026A - Magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic recording medium maintaining a high squareness ratio and high coercive force, capable of reducing inclination of a hysteresis loop on which intensity of exchange interaction reflects in the vicinity of the coercive force and having excellent noise characteristics and a structure wherein an underlayer has thin film thickness. <P>SOLUTION: The magnetic recording medium is so constituted that a silicon underlayer including silicon and having ≥1 nm and <10 nm thickness is provided on a substrate, a palladium intermediate layer film-deposited by a sputtering method under an N<SB>2</SB>additive atmosphere having 1 to 10% partial pressure of N<SB>2</SB>and subjected to heat treatment at 200 to 400°C for 10 to 30 min is provided on the silicon underlayer and a perpendicularly magnetized film which is formed by alternately film-depositing Co and Pd over a plurality of times and whose magnetization easy axis is oriented vertically to the substrate is provided on the palladium intermediate layer. As a result, satisfactory recording and reproducing characteristics can be obtained even when the silicon underlayer is thinner than 10 nm. The underlayer constituted of the silicon underlayer and the palladium intermediate layer is useful as an intermediate layer in a perpendicular two-layer recording medium wherein a soft magnetic film adopted as a lowermost layer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic recording medium having a perpendicular magnetization film whose easy axis is oriented perpendicularly to a substrate.

  Most commercially available magnetic recording media are in-plane magnetic recording media in which the easy axis of magnetization in the magnetic film is oriented horizontally with respect to the substrate.

  In order to achieve high density in the in-plane magnetic recording medium, which is a conventional technique, it is necessary to reduce noise by reducing the thickness of the magnetic layer and miniaturizing the magnetic particles. However, if the particle size of the magnetic particles is made too small, the volume of the magnetic particles decreases, so that the recording magnetization becomes unstable due to the thermal fluctuation effect and the recorded information may be lost. Further, when the recording density is increased, the medium noise may increase due to the influence of the demagnetizing field at the recording bit boundary.

In contrast, the so-called perpendicular magnetic recording medium in which the easy axis in the magnetic film is oriented perpendicularly to the substrate is less affected by the demagnetizing field at the bit boundary even when the density is increased, and the boundary is clearly recorded. Since magnetization is formed, noise can be reduced.
Further, since the perpendicular magnetic recording medium does not need to be made as thin as an in-plane recording medium in order to achieve a high recording density, the volume of the magnetic particles can be kept large, and thus the thermal fluctuation resistance can be increased. In recent years it has attracted a lot of attention.

For example, Japanese Patent Application Laid-Open No. 60-214417 discloses a perpendicular magnetic recording medium using Ge or Si as a material for a base film of a perpendicular magnetization film made of a Co alloy.
Japanese Patent Laid-Open No. 63-21111 discloses a perpendicular magnetic recording medium in which a carbon-containing material film having a thickness of 1 to 100 mm is formed as a base film of a perpendicular magnetization film made of a Co alloy.

However, in these conventional magnetic recording media, it is difficult to increase the squareness ratio, and there is a problem that the reverse domain nucleation magnetic field −H _n becomes small. Sufficient squareness ratio, and -H _n not only is not the medium noise resulting increases, it becomes thermal stability characteristics are low.

In contrast, the squareness ratio, the magnetic recording medium capable of improving the -H _n, transition metals (e.g. Co) and precious metal (e.g. Pd) and the proposed magnetic recording medium having a multi-layer film laminated on the multilayer is (JP-A-6-111403, US Pat. No. 5,660,930).
In recent years, a further increase in recording density of magnetic recording media has been demanded, and accordingly, improvement in noise characteristics has been demanded.

  However, the above conventional magnetic recording medium (with a transition metal / noble metal multilayer film) has a large exchange interaction acting in the in-plane direction of the film, so it is not satisfactory in terms of noise characteristics, and more noise characteristics. An excellent magnetic recording medium has been demanded. In consideration of application to a perpendicular double-layer film medium excellent in recording and reproduction, a magnetic recording medium having a thin structure immediately below the recording layer is desired.

The present invention has been made in view of the above circumstances, and maintains the high squareness ratio, −H _n and coercive force H _c , and the slope α in the vicinity of the coercive force of the hysteresis loop reflecting the strength of the exchange interaction. An object of the present invention is to propose a magnetic recording medium that can be reduced, has excellent noise characteristics, and has a thin base film thickness.

As a result of intensive studies to achieve the above object, the present inventor formed a silicon underlayer on the substrate, and alternately formed Co and Pd on the substrate several times, thereby forming a perpendicular magnetization film. Is formed, a silicon underlayer is formed to a thickness of 1 nm or more and less than 10 nm, a palladium intermediate layer is formed thereon by sputtering in an N ₂ addition atmosphere, and then heat treatment is performed. Can reduce the hysteresis loop slope α (increase the squareness ratio and −H _n ) and improve the noise characteristics and the heat-resistant fluctuation characteristics. In this case, the silicon underlayer and the perpendicular magnetization film It was discovered that a high S / N ratio and high thermal stability can be achieved by forming a palladium intermediate layer in between, and the present invention has been made.

That is, the present inventor is a magnetic recording medium in which a silicon base film containing silicon is first provided on a substrate, and a perpendicular magnetization film having an easy axis of magnetization oriented perpendicular to the substrate is provided thereon, There has been proposed a magnetic recording medium characterized in that the perpendicular magnetization film is formed by alternately depositing Co and Pd a plurality of times (Japanese Patent Application No. 2001-286455). In this case, in this proposal, the silicon base film is preferably 10 nm or more in thickness from the viewpoint of coercive force and noise characteristics. However, the characteristics of the cobalt / palladium perpendicular magnetic layer are improved even when the silicon underlayer is as thin as 10 nm or less by forming a palladium intermediate layer on the silicon underlayer in an atmosphere containing N ₂ and further heat-treating it. It has been found that this can be done, and the present invention has been made.

Accordingly, the present invention provides: (1) A silicon base film having a thickness of 1 nm or more and less than 10 nm including silicon is provided on a substrate, and the N ₂ partial pressure is 1 to 10% in an N ₂ addition atmosphere on the silicon base film. A palladium intermediate layer formed by sputtering and heat-treated at 200 to 400 ° C. for 10 to 30 minutes is provided, and Co and Pd are alternately formed multiple times on this palladium intermediate layer. A magnetic recording medium comprising a perpendicularly magnetized film having an easy axis of magnetization formed perpendicularly to a substrate;
(2) The magnetic recording medium according to (1), wherein the palladium intermediate layer has a thickness of 1 to 10 nm,
(3) The magnetic recording medium according to (1) or (2), wherein the Pd layer is formed to have a thickness of 0.4 to 1.4 nm.
(4) The magnetic recording medium according to any one of (1) to (3), wherein the Co layer is formed to have a thickness of 0.1 to 0.6 nm. To do.

  According to the present invention, the recording / reproducing characteristics are good even when the silicon underlayer is thinner than 10 nm. In addition, the base film composed of the silicon base film and the palladium intermediate layer according to the present invention is useful as an intermediate layer in a perpendicular double-layer recording medium having a soft magnetic film as the bottom layer.

Hereinafter, the present invention will be described in more detail.
In the magnetic recording medium of the present invention, a silicon base film containing silicon is provided on a substrate, a palladium intermediate layer is provided thereon, and a perpendicular magnetization film having an easy axis of magnetization oriented perpendicular to the substrate is provided thereon. The perpendicular magnetization film is formed by alternately depositing Co and Pd a plurality of times.

  FIG. 1 shows an embodiment of the magnetic recording medium of the present invention. In the magnetic recording medium shown here, a silicon underlayer 2 is provided on a substrate 1, and a palladium intermediate layer 3 is provided thereon, Further, a perpendicular magnetization film 4 having an easy axis oriented perpendicular to the substrate is provided thereon, and a protective film 5 and a lubricating film 6 are provided thereon.

  Here, as the substrate 1, an aluminum alloy substrate (hereinafter referred to as “NiP plated Al substrate”) on which a NiP plating film generally used as a substrate for a magnetic recording medium is formed, a glass substrate, a carbon substrate, a flexible resin substrate. Alternatively, a substrate in which a NiP film is formed on these substrates by a dry plating method such as a plating method or a sputtering method can be used.

  The silicon base film 2 is made of a material containing silicon, and is particularly preferably silicon. The thickness of the silicon base film 2 is in the range of 1 nm or more and less than 10 nm, and is particularly preferably 5 nm. The silicon base film can be formed by a sputtering method.

  In the present invention, the palladium intermediate layer 3 is formed on the silicon base film 2. This palladium intermediate layer is made of a material containing palladium, and is particularly preferably palladium.

In this case, the palladium intermediate layer is formed by a sputtering method using palladium as a target in an N ₂ addition atmosphere. The sputtering method can be performed in a conventional manner under an inert gas such as Ar, and the conditions thereof can also be normal conditions. However, as described above, the atmosphere is an N ₂ gas addition atmosphere. . In order to achieve the object of the present invention, the N ₂ partial pressure is preferably 1 to 10%, particularly 4 to 6%.

  The thickness of the palladium intermediate layer is preferably 1 to 10 nm, particularly 1 to 5 nm, particularly 3 to 5 nm. If the palladium intermediate layer is too thin, there is a possibility that the loop inclination α will increase and the medium noise will increase. If it is too thick, the total film thickness of the silicon underlayer and the palladium intermediate layer will increase, resulting in a vertical bilayer film. There is a possibility that a problem that application to a medium becomes difficult may occur.

  The silicon underlayer and palladium intermediate layer form the underlayer of the perpendicular magnetization film of the present invention. The total thickness of the silicon underlayer and palladium intermediate layer is 2 to 20 nm, particularly 5 to 10 nm. It is preferable. If it is too thin, there is a possibility that the loop inclination α will increase and the medium noise will increase, and if it is too thick, the total film thickness of the silicon underlayer and palladium intermediate layer will increase, and it will be applied to vertical bilayer media. This may cause a problem that it becomes difficult.

In the present invention, as described above, after the palladium intermediate layer is formed, heat treatment is performed. In this case, the heat treatment conditions are preferably 10 to 30 minutes, particularly 15 to 25 minutes at a substrate temperature of 200 to 400 ° C., particularly 250 to 300 ° C., and the heat treatment atmosphere is 2 × 10 ⁻⁷ Torr or less. The reduced pressure state is preferable.

By performing the heat treatment in this manner, even if the silicon underlayer is thin, the hysteresis loop slope α of the cobalt / palladium laminated perpendicular magnetization film can be reduced and the coercive force can be increased. Here, α reflects the strength of the interaction acting in the in-plane direction of the perpendicular magnetization film, and the smaller the value, the less the interaction between the magnetic particles constituting the perpendicular magnetization film. However, in order to reduce the noise of the recording medium, it is effective to reduce this interaction, that is, to reduce α. From this point of view, the palladium / silicon base film subjected to N ₂ addition and heat treatment is an effective base film for reducing noise in the recording medium.

In the present invention, the perpendicular magnetization film 4 is formed on the palladium intermediate layer.
The perpendicular magnetization film 4 is formed by alternately forming Co and Pd a plurality of times, and it is preferable to form the film by sputtering. The thickness of each Pd layer is preferably 0.4 to 1.4 nm (4 to 14 mm), more preferably 0.6 to 1.0 nm. The thickness of each Co layer is preferably 0.1 to 0.6 nm (1 to 6 mm), more preferably 0.1 to 0.4 nm. When this thickness is out of the above range, the coercive force and the reverse domain nucleation magnetic field −H _n are lowered. In addition, noise characteristics are likely to deteriorate. The total thickness of the perpendicular magnetization film is preferably 5 to 50 nm, particularly 10 to 30 nm, and the Co layer and the Pd layer are laminated in a total of 10 to 60 layers, particularly 10 to 40 layers. Preferred to achieve.

The perpendicular magnetic film 4 is preferably formed by a sputtering method, but at this time, an atmosphere to which N ₂ is added is preferable. In this case, the N ₂ partial pressure when forming the perpendicular magnetization film 4 is preferably 0.1 to 0.3%. When the partial pressure exceeds the above range, H _c, -H _n is reduced, the noise characteristic may be deteriorated. Further, if the partial pressure is less than the above range, the effect of adding N ₂ may not be sufficiently exhibited.

The protective film 5 is for preventing corrosion of the perpendicular magnetization film 4, preventing damage to the surface of the medium when the head contacts the medium, and ensuring lubrication characteristics between the head and the medium. A material can be used, for example, a single composition of C, SiO ₂ , ZrO ₂ , or a material containing these as a main component and containing other elements can be used.
The thickness of the protective film 5 is desirably 1 to 10 nm (10 to 100 mm).
Lubricant such as perfluoropolyether, fluorinated alcohol, fluorinated carboxylic acid or the like can be used for the lubricating film 6.

In order to manufacture the magnetic recording medium having the above-described configuration, the silicon base film 2 is formed on the substrate 1 by sputtering or the like, the palladium intermediate layer 3 is further formed as described above, and then the perpendicular magnetization film 4 is formed by sputtering. It is preferable to form. In order to form the perpendicular magnetization film 4 by sputtering, the perpendicular magnetization film 4 is formed by alternately forming a film using a Co target and a Pd target. Sputtering can be performed by a conventional method, and the conditions can be set to normal conditions. However, α can be reduced by adding N ₂ gas when forming the perpendicular magnetization film 4. Next, the protective film 5 is formed by a plasma CVD method, an ion beam method, a sputtering method or the like. Further, the lubricating film 6 is formed by dipping method, spin coating method or the like.

In the magnetic recording medium of the above structure, the perpendicular magnetization film 4, by the one formed by sputtering Co and Pd multiple times, it is possible to improve the squareness ratio and -H _n . Furthermore, α can be reduced by adding N ₂ gas. Thereby, medium noise can be reduced and noise characteristics can be improved.

Further, in the above manufacturing method, the perpendicular magnetization film 4 is formed by alternately forming films by sputtering using a Co target and a Pd target. At this time, N ₂ gas is added to the atmosphere when the perpendicular magnetization film 4 is formed. Thus, a magnetic recording medium having excellent noise characteristics can be easily manufactured. As described above, the N ₂ partial pressure is preferably 0.1 to 0.3%. Sputtering can be performed by known methods and conditions except that N ₂ is added to the atmosphere. In this case, the sputtering atmosphere can be performed under an inert gas such as Ar, and it is preferable to add N ₂ to this atmosphere.
In the above-described perpendicular magnetization film, the alternating laminated film of Co and Pd may be Co or Pd in the lowermost layer, but is preferably Pd in the lowermost layer.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated concretely, this invention is not restrict | limited to the following Example.

[Examples and Comparative Examples]
A cleaned glass substrate (made by OHARA, 2.5 inch outer diameter) is housed in the chamber of a DC magnetron sputtering apparatus (manufactured by Anerva, SPC-350S special model), and the vacuum inside the chamber is 2 × 10 ⁻ After evacuating to ⁷ Torr, a silicon base film made of silicon was formed on the substrate using silicon as a target. At this time, the silicon base film thickness was 5 nm.

Next, Pd was used as a target on the silicon base film, and a palladium intermediate layer was formed to 5 nm by sputtering under Ar gas. In this case, as shown in Table 1, N ₂ was added to the sputtering gas at 5 mTorr and the N ₂ partial pressure was 5 vol%, and N ₂ was not added.

  After forming the palladium intermediate layer (note that film formation was performed at room temperature according to a conventional method), as shown in Table 1, a perpendicular magnetization film was formed directly or after heat treatment. In this case, the heat treatment was performed under the conditions of heating from room temperature to a substrate temperature of 260 ° C., finishing heating in 20 minutes from the start of heating, and naturally cooling in vacuum.

In addition, the perpendicular magnetization film was produced by alternately using Co and Pd as targets, respectively, and forming 20 layers of palladium 0.8 nm and cobalt 0.2 nm alternately by sputtering. Sputtering was performed at room temperature under an Ar gas in an atmosphere to which N ₂ was not added.

  A protective film made of carbon (thickness 10 nm (100 mm)) was formed on the perpendicular magnetization film, and a lubricating film made of perfluoropolyether was formed on the protective film by a dipping method.

The magnetostatic characteristics of the magnetic recording media of the above-described examples and comparative examples were measured using a vibrating sample magnetic force type (VSM).
Further, the electromagnetic conversion characteristics of these magnetic recording media were measured using a spin stand LS90-S (manufactured by Kyodo Denshi Co.).
For evaluation of the electromagnetic conversion characteristics, a composite thin film magnetic recording head having a giant magnetoresistive (GMR) element in the reproducing section was used as the magnetic head, and the recording conditions were measured at a linear recording density of 200 kFCI.
The above results are shown in Table 1 and FIG.

As shown in the results of Table 1 and FIG. 2, the hysteresis of the cobalt / palladium laminated perpendicularly magnetized film is obtained by adding N ₂ to the sputtering gas at the time of forming the palladium intermediate layer and further performing heat treatment after the film formation. The loop inclination α can be reduced, the coercive force can be increased, and when a recording / reproducing test is actually performed, a recording / reproducing test is performed by adding an N ₂ to the sputtering gas and applying a heat-treated base film. The S / N ratio was significantly increased.

1 is a partial cross-sectional view showing an embodiment of a magnetic recording medium of the present invention. Pd (5 nm) / Si (5 nm) Pd (5 nm) / Si (5 nm) obtained by forming a Pd (5 nm) / Si (5 nm) base film (a) and a palladium intermediate layer by sputtering in an N ₂ addition atmosphere and further heat-treating It is a magnetization history curve at the time of using a foundation film (b).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Silicon base film 3 Palladium intermediate layer 4 Perpendicular magnetization film 5 Protective film 6 Lubricating film

Claims (4)

Thick containing silicon on a substrate provided with a silicon base film of less than 10nm over 1 nm, N ₂ partial pressure on the silicon underlayer is deposited in 1-10% of N ₂ added atmosphere by a sputtering method, In addition, an easy axis of magnetization formed by providing a palladium intermediate layer that has been heat-treated at 200 to 400 ° C. for 10 to 30 minutes, and alternately forming Co and Pd on the palladium intermediate layer multiple times, respectively. A magnetic recording medium comprising a perpendicular magnetization film oriented perpendicular to a substrate.   The magnetic recording medium according to claim 1, wherein the palladium intermediate layer has a thickness of 1 to 10 nm.   3. The magnetic recording medium according to claim 1, wherein the Pd layer is formed to have a thickness of 0.4 to 1.4 nm.   The magnetic recording medium according to any one of claims 1 to 3, wherein the Co layer is formed to have a thickness of 0.1 to 0.6 nm.

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