JP2006294121A - Magnetic recording medium and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a super high density magnetic recording medium which has excellent magnetic characteristics and thermal demagnetization resistance and wherein an FePt film is made to be a ordered alloy, an axis c to be an easily magnetized axis of an FePt crystal is preferentially oriented in a direction vertical to the surface of the film and the FePt magnetic film is physically separated in a film intra-surface direction. <P>SOLUTION: An underlayer consisting essentially of Fe and O and having a discontinuous form in a film intra-surface direction is provided on a substrate, a layer consisting essentially of Fe and a layer consisting essentially of Pt are layered in this order on the underlayer, then a layered film is heated at a prescribed temperature, alternate diffusion between the layer consisting essentially of Fe and the layer consisting essentially of Pt is made to occur and Fe and Pt are made to be an alloy. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a magnetic recording medium.

Corresponding to the progress of the advanced information society in recent years, the need for larger capacity and higher density of information recording devices is increasing. At present, even in the magnetic recording apparatus that plays the main role of the information recording apparatus, the surface recording density is being improved in response to the increase in capacity. In order to record the recording bit finely, a so-called perpendicular magnetic recording system is known in which the recording magnetization direction is recorded perpendicularly to the film surface. Conventionally, a Co—Cr alloy film has been used as a material for the perpendicular magnetic recording film. However, in order to further increase the surface recording density in the future, it is necessary to make the magnetic particles very fine. However, if it is too fine, the magnetic anisotropy energy of the magnetic particles, that is, the product (KuV) of the magnetic anisotropy constant (Ku) and volume (V) approaches the thermal vibration energy of the magnetic particles, The magnetization state becomes thermally unstable and causes thermal demagnetization. Therefore, in order to obtain a magnetic recording medium capable of recording at a higher density, it is necessary to use a magnetic material having a higher magnetic anisotropy than the CoCr-based alloy for the recording layer.
For example, an Fe—Pt alloy film has been studied as the material (see, for example, Non-Patent Document 1). In case the alloy having regular phase (L1 ₀ phase), having a high magnetic anisotropy order of magnitude or more compared to the Co-Cr based alloy as described above. In order to obtain an ordered Fe—Pt alloy, it is necessary to heat-treat the Fe—Pt alloy at a temperature of about 600 ° C. after forming the Fe—Pt alloy into a thin film by vapor deposition or sputtering. Further, simultaneously with the ordering, in order to apply the Fe—Pt film as a perpendicular magnetic recording medium, the c axis, which is the easy axis of magnetization of the ordered phase alloy crystal, must be preferentially oriented in the direction perpendicular to the film surface.

  On the other hand, as a technique for reducing the problem of thermal demagnetization, a recording medium called a patterned medium, in which a magnetic film is formed by arranging magnetic dots physically separated in the in-plane direction, has been studied. . In a conventional magnetic recording medium, the recording film has a layer structure continuous in the film surface direction, and the minimum unit of recording is usually formed by several tens of magnetic particles. A schematic diagram showing this relationship is shown in FIG. In this case, it is the KuV of each small magnetic particle that bears resistance to thermal demagnetization. On the other hand, in the patterned medium, as shown in FIG. 2, the minimum recording unit is the magnetic dot itself, and it is KuV of the magnetic dot that bears the resistance to thermal demagnetization. Therefore, even with the same Ku, a patterned medium with V being several tens of times larger can improve thermal demagnetization resistance and increase the recording density. As methods for producing magnetic dots on patterned media, lithography, microfabrication, and methods that utilize the self-assembled properties of the materials themselves are being studied, but they are not yet in practical use. .

M.M. Watanabe and M.M. Hamma: Jpn. J. et al. Appl. phys. Vol. 66, p. 1692 (1995)

  In order to obtain an ultra-high density perpendicular magnetic recording medium, it is ideal to produce a patterned medium with a material having a very high magnetic anisotropy such as an Fe—Pt film. The present invention requires ordered Fe—Pt alloying, c-axis vertical orientation, which is the easy axis of magnetization of Fe—Pt crystal, and physical separation of the Fe—Pt magnetic film in the in-plane direction. It is an object of the present invention to provide an ultra-high density magnetic recording medium having excellent magnetic properties and heat resistance.

As a result of various investigations to achieve the above object, the present inventors have provided a base film having Fe and O as main components and a discontinuous form in the in-plane direction on the substrate, and Fe as the main component. And a layer containing Pt as a main component are formed in this order, and then the laminated film is heated to a predetermined temperature so that the layer containing Fe and the layer containing Pt as a main component are mutually connected. By causing diffusion and alloying Fe and Pt, the magnetic film is physically separated into discontinuous islands in the in-plane direction, and at the same time, a very high perpendicular magnetic anisotropy It was found that sex was expressed. A schematic cross-sectional view of the magnetic recording medium of the present invention is shown in FIG.
The mechanism by which the Fe—Pt ordered alloy film separated into islands can be obtained by the method of the present invention is considered as follows. When an Fe oxide film made of Fe and O is formed very thin on a substrate, the Fe oxide does not form a continuous layer in the in-plane direction, but is discontinuous in the film surface direction. It becomes the shape of the shape. When an Fe layer and a Pt layer are laminated on each of them to a thickness of several nanometers, they are relatively thick and become a layered film. Next, when this laminated film is heated, atoms in the Fe layer and the Pt layer diffuse to each other in the thickness direction, but at the same time, these atoms try to move in the in-plane direction. At this time, Fe atoms attached on the Fe oxide are difficult to move, and Fe atoms attached to the substrate surface are easy to move. This is because the affinity between Fe and the Fe oxide is high while the affinity between Fe and the substrate surface is low. As a result, Fe and Pt are collected on the island-shaped Fe oxide, and a portion having neither Fe nor Pt is generated on the substrate, and the Fe—Pt alloy film has an island shape. A schematic cross-sectional view showing this formation mechanism is shown in FIG. Further, during this heat diffusion, the crystal orientation of the Fe oxide affects the crystal orientation of Fe and Pt, and the c-axis of the Fe—Pt alloy film is preferentially oriented in the direction perpendicular to the film surface. By such a mechanism, it is considered that the Fe—Pt film of the present invention is physically separated into a discontinuous island shape in the in-plane direction, and at the same time, exhibits a very high perpendicular magnetic anisotropy. .
The average thickness of the film containing Fe and O as main components is preferably less than 2 nm. When the thickness of the film containing Fe and O as a main component becomes thicker than 2 nm, the Fe oxide becomes a layered form and the affinity for Fe in the in-plane direction becomes uniform. This is because the alloy film also becomes a continuous film in the in-plane direction.
Further, as shown in the schematic cross-sectional view shown in FIG. 5, in order to modify the substrate surface and control the affinity with Fe, Si and O as main components are provided under the film containing Fe and O as main components. It is also effective to provide an underlayer.
As the substrate, a substrate made of a substance having a lower affinity for Fe than Fe oxide, such as a glass substrate, can be used. When a base layer made of Si and O is provided, a substrate having high affinity with Fe can also be used.
Example 1
A film made of Fe and O (Fe—O film) was formed on the crystallized glass substrate, an Fe layer was formed thereon, and a Pt layer was further formed thereon. The Fe—O film was formed by DC sputtering of an Fe target in a mixed gas of Ar and O ₂ . The average thickness of the Fe—O layer was 1 nm. The Fe layer and the Pt layer were formed by DC sputtering each of an Fe or Pt target in Ar gas. The thicknesses of the Fe layer and the Pt layer were 3 nm each. The gas pressure during sputtering of the Fe—O film was 1.0 Pa, and the gas pressure during sputtering of the Fe layer and the Pt layer was both 0.5 Pa.
The laminated film thus formed was heat-treated in a vacuum to cause mutual atomic diffusion between the Fe layer and the Pt layer, thereby obtaining an Fe—Pt ordered alloy thin film. An infrared lamp heater was used for the heat treatment, the input power was 1800 W, and the heating time was 30 seconds. The maximum temperature reached by the film during heating was about 650 ° C.
(Example 2)
A Fe—Pt ordered alloy thin film was produced in the same manner as in Example 1 except that the average thickness of the Fe—O film was 1.5 nm.
(Example 3)
An Fe—Pt ordered alloy thin film was produced in the same manner as in Example 1 except that a SiO ₂ layer having a thickness of 10 nm was formed under the Fe-0 film. The SiO ₂ layer was formed by RF sputtering a SiO ₂ target in Ar gas. The gas pressure during sputtering was 0.6 Pa.
(Comparative Example 1)
An Fe—Pt ordered alloy thin film was produced in the same manner as in Example 1 except that the Fe—O film was not provided.
(Comparative Example 2)
An Fe—Pt ordered alloy thin film was produced in the same manner as in Example 1 except that the average thickness of the Fe—O film was 2 nm.
The magnetic properties of the Fe—Pt ordered alloy films prepared in Examples 1 to 3 and Comparative Examples 1 to 2 were measured using a sample resonance magnetometer. The magnetic hysteresis curves in the direction perpendicular to the film surface and the direction in the film surface were measured, and the coercive force (Hc) in each direction was calculated. The higher the Hc in the direction perpendicular to the film surface and the smaller the Hc in the in-plane direction, the better the perpendicular magnetization film. Moreover, the crystal structure of the produced Fe—Pt ordered alloy film was analyzed by measuring a θ-2θ curve using an X-ray diffractometer. When the Fe—Pt crystal is ordered and its c-axis is preferentially oriented in the direction perpendicular to the film surface, only diffraction from the FePt (001) plane and the FePt (002) plane is observed. In addition, the structure of the prepared FePt ordered alloy film within the film surface is observed on a plane using a transmission electron microscope (TEM) to evaluate whether the film has a discontinuous island structure or a continuous layer structure. did.

The thicknesses of the SiO 2 layers of the Fe—Pt ordered alloy films prepared in Examples 1 to 3 and Comparative Examples 1 and 2, the average thickness of the Fe—O film, Hc in the vertical direction, Hc, X in the in-plane direction Table 1 shows diffraction peaks observed by line diffraction and the morphology of the Fe—Pt film. The samples of the examples all show large vertical Hc exceeding 10 kOe, while the vertical in-plane Hc is small at less than 3 kOe. Further, in X-ray diffraction, only diffraction from FePt (001) and FePt (002) was observed, and from TEM observation, it was observed that the FePt film was in the form of islands. Therefore, in the example, the Fe—Pt film is ordered alloyed, and the c-axis is preferentially oriented in the direction perpendicular to the film surface, has a high perpendicular magnetic anisotropy, and is not defective in the film surface. It can be seen that a continuous island-shaped magnetic recording medium is formed.
In Comparative Example 1, the difference between Hc in the vertical direction and Hc in the in-plane direction becomes small, and in X-ray diffraction, in addition to FePt (001) and FePt (002), diffraction of FePt (111) is also observed. This indicates that the perpendicular orientation of the c-axis of the FePt film is lowered and the perpendicular magnetic anisotropy is lowered. In Comparative Example 2, FePt is not in the form of islands, but is in the form of layers that are continuous within the film plane.

According to the present invention, FePt having excellent characteristics suitable for an ultra-high density recording medium having a discontinuous island shape physically separated in the in-plane direction and simultaneously having a very high perpendicular magnetic anisotropy. An ordered alloy film is obtained.

The schematic diagram which shows the relationship between the magnetic particle of the conventional recording medium, and the minimum recording unit. The schematic diagram which shows the relationship between the magnetic dot of a patterned medium, and the minimum recording unit. 1 is a schematic cross-sectional view of a magnetic recording medium (Example 1 and Example 2) of the present invention. FIG. 3 is a schematic cross-sectional view showing the formation mechanism of the magnetic recording medium of the present invention. FIG. 3 is a schematic cross-sectional view of a magnetic recording medium (Example 3) of the present invention.

Claims (7)

  On the substrate, a base film mainly composed of Fe and O and an alloy magnetic film mainly composed of Fe and Pt formed thereon are provided, and the magnetic film is in a discontinuous form in the in-plane direction. A magnetic recording medium comprising:   After a base film having Fe and O as main components and a discontinuous form in the film surface direction is provided on a substrate, and a layer containing Fe as a main component and a layer containing Pt as a main component are stacked on the substrate in this order. The laminated film is heated to a predetermined temperature to cause mutual diffusion between the layer containing Fe as a main component and the layer containing Pt as a main component, and Fe and Pt are alloyed. Magnetic recording medium.   After a base film having Fe and O as main components and a discontinuous form in the film surface direction is provided on a substrate, and a layer containing Fe as a main component and a layer containing Pt as a main component are stacked on the substrate in this order. The magnetic film is characterized in that the laminated film is heated to a predetermined temperature to cause mutual diffusion between the layer containing Fe as a main component and the layer containing Pt as a main component so that Fe and Pt are alloyed. A method for manufacturing a recording medium.   3. The magnetic recording medium according to claim 1, wherein the average thickness of the layer mainly composed of Fe and O is less than 2 nm.   4. The method of manufacturing a magnetic recording medium according to claim 3, wherein the average thickness of the layer mainly composed of Fe and O is made thinner than 2 nm.   5. The magnetic recording medium according to claim 1, wherein a layer mainly composed of Si and O is provided under the layer mainly composed of Fe and O. Magnetic recording medium. 6. The method of manufacturing a magnetic recording medium according to claim 3, wherein a layer mainly composed of Si and O is provided below the layer mainly composed of Fe and O. Production method.

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