Patent Application
20060082035
1. Field of the Invention
The present invention relates to a magnetic annealing device for inserting a recording medium provided with an axial hole at a center thereof and having a disk shape into a chamber and applying a heat treatment to the recording medium in a magnetic field.
2. Description of the Related Art
As a method of recording data on a recording medium, such as a hard disk, is known a vertical magnetic recording method. The vertical magnetic recording method has a potential of remarkably increasing a recording density in comparison to a longitudinal-direction recording method and, therefore, is a technology attracting an attention.
In the recording medium used in the vertical magnetic recording method, a magnetic anisotropy in a direction vertical to a main surface of the recording medium (magnetization direction) is demanded in the magnetic film 1a, while a magnetic anisotropy in a direction along the main surface of the recording medium is demanded in the soft magnetic film 1b. Because of that, a heat treatment is applied to the recording medium in a magnetic filed.
In
As described, the magnetic anisotropy in the vertical direction and the magnetic anisotropy in the horizontal direction are respectively demanded in the magnetic film and the soft magnetic film. Accordingly, in the case of the magnetic field formed in the chamber, the direction of the magnetic field at a central position thereof, where the recording medium 1 is disposed, is desirably as horizontal as possible.
However, in the constitution of the device shown in
As an alternative constitution in order to solve the foregoing problems, which is shown in
Yet, the constitution of the magnetic circuit shown in
The present invention has been implemented to deal with the foregoing problems. A main object thereof is to provide a magnetic annealing device effectuating an improved horizontal precision of the direction of the magnetic field at the position where the recording medium is disposed when the recording medium having the magnetic film and the soft magnetic film is subjected to the in-magnetic-field heat treatment.
In order to solve the foregoing problems, the present invention provides the following magnetic annealing device. A magnetic annealing device for inserting a recording medium provided with an axial hole formed at a center thereof and having a disk shape into a chamber and applying a heat treatment to the recording medium in a magnetic field is characterized in comprising a magnetic circuit for forming a magnetic field in the chamber,
the magnetic circuit comprising a pair of magnets disposed with a distance therebetween along an axial direction of the axial hole and respectively having magnetic fields directionally opposed to each other and a first ferromagnetic substance disposed between the pair of magnets, and that
the recording medium as a subject of the heat treatment is adapted to be disposed at an intermediate position between the pair of magnets facing each other in the state in which the first ferromagnetic substance is inserted into the axial hole.
An operation and effect of by the magnetic annealing device according to the foregoing constitution are as follows. First, the pair of magnets as components constituting the magnetic circuit are disposed in the chamber so as to render their directions of magnetic fields opposed to each other. The first ferromagnetic substance is disposed between the pair of magnets. The recording medium is provided with the axial hole at the center thereof and has the disk shape. The in-magnetic-field heat treatment is applied to the recording medium in the state in which the first ferromagnetic substance is inserted into the axial hole. Because lines of magnetic forces induced from the pair of magnets repel each other, the directions of the magnetic fields (lines of magnetic forces) at the intermediate position between the pair of magnets facing each other are made to be horizontal. The presence of the first ferromagnetic substance therebetween guides many of the lines of the magnetic forces induced from the pair of magnets in a direction where they pass through inside of the first ferromagnetic substance. Therefore, a magnetization direction at the intermediate position is made further horizontal. As a result, when the recording medium having the magnetic film and the soft magnetic film is heat-treated in the magnetic field, the magnetic annealing device effectuating an improved horizontal precision of the direction of the magnetic field at the position where the recording medium is disposed can be provided.
In the foregoing constitution, a second ferromagnetic substance having a ring shape is further preferably disposed in an outer periphery of the disposed recording medium.
When the second ferromagnetic substance is provided, the horizontal property of the magnetization direction can be further improved.
The magnet preferably includes Fe, Ni, Co, Al and Ti in its composition. The chamber is exposed to a high temperature when the heat treatment is performed, however, the magnet including the foregoing materials can maintain its magnetic characteristic in such a high-temperature atmosphere.
In the fist ferromagnetic substance, a saturation magnetization is preferably at least 1.5 T (tesla) and at most 2.4 T. Then, the horizontal property of the magnetization direction can be improved. At anything below 1.5 T, the demanded magnetic anisotropy cannot be obtained.
The second ferromagnetic substance is preferably an anisotropic magnet when the before-mentioned member having the ring shape is formed.
When the permanent magnet is used, the horizontal element of the magnetization direction can be further increased. As the permanent magnet is preferably used an Alnico magnet in terms of its characteristic.
In the case in which a temperature in the heat treatment is approximately 25-300° C., an R-T-B based magnet or a Sm—Co magnet, which are represented by a Nd—Fe—B series, may be used.
The ring-shape member may be formed as a single member, and also may be formed from a plurality of segments disposed in a ring shape for the convenience of an easy manufacturing or the like.
As a preferable method used in disposing the segments in the ring shape, a room for disposing the segments in a vessel having a ring shape and made of a non-magnetic material, such as stainless steel, is prepared and the room in which the segments are disposed is sealed by a non-magnetic member (stainless steel).
Magnetic annealing devices according to preferred embodiments of the present invention are described referring to the drawings.
In
A recording medium 1 to be heat-treated is shown by an imaginary line in
The pair of permanent magnets 4 and 5 is preferably made of a material including Fe, Ni, Co, Al and Ti in its composition. For example, an Alnico magnet can be used. In an in-magnetic-field heat treatment, a temperature in the chamber 10 increases to 25-50° C. depending on a material quality of the magnetic film. A magnetic characteristic of the Alnico magnet is not reduced in the foregoing range of the temperatures. As an alternative option, a samarium cobalt magnet may be also used. When the foregoing magnets are used, the magnets can be disposed in the chamber.
When the temperature in the in-magnetic-field heat treatment is at most 300° C., a R-T-B based magnet represented by a Nd—Fe—B series may be used. The R-T-B based magnet has a high magnetic flux density, which further downsizes the magnetic circuit. Examples of a composition and a manufacturing method relating to a rare-earth magnet of a R—Fe—B series are recited in U.S. Pat. No 4,770,723 and No 4,792,368 of the U.S. patent applications.
The first ferromagnetic substance 6 can employ a material such as SS400 and S15C.
An axial thickness of the first ferromagnetic substance 6 disposed between the pair of permanent magnets 4 and 5 is preferably set to 35-45 times as thick as the magnetic film 1a and the soft magnetic film 1b of the recording medium 1. The first ferromagnetic substance 6 constituted as described can converge a magnetic leakge flux in a predetermined magnetic-field space and thereby increase the horizontal element of the magnetization direction at the intermediate position.
The first ferromagnetic substance 6 having a saturation magnetization of at least 1.5 T and at most 2.4 T is preferably used.
Next, a magnetic annealing device according to a second embodiment of the present invention is described referring to
According to the foregoing constitution, a magnetic anisotropy of the magnetic film 1a formed in the recording medium 1 can be made vertical, while a magnetic anisotropy of the soft magnetic film 1b is made horizontal.
Results obtained from a theoretical calculation of a magnetic field strength relating to each constitution shown in
In the first embodiment, the value of B is larger and the value of Bz is considerably smaller than in the comparison example, from which it is learnt that the horizontal property of the magnetization direction at the intermediate position is increased and that the vertical element Bz at the intermediate position is considerably decreased. In the case of the second embodiment, the foregoing tendency is more remarkable. In other words, it was confirmed that the disposition of the first ferromagnetic substance 6 and the second ferromagnetic substance 7 could lead to the improvement of a magnetic-field characteristic.
<Operation>
A step of manufacturing the recording medium by means of the magnetic annealing device according to the present invention is simply described as follows. The recording medium 1 provided with the magnetic film 1a and the soft magnetic film 1b formed on the substrate 1c is disposed at a predetermined position in the magnetic annealing device. At the center of the recording medium 1 is provided with the axial hole. The magnetic circuit shown in
It was recited in the second embodiment that the same material as in the first ferromagnetic substance 6 was used for the second ferromagnetic substance 7 having the ring shape. The ring-shape member may be formed from a magnet (permanent magnet). When the permanent magnet is used, the horizontal element of the magnetization direction of the soft magnetic film 1b can be increased. The Alnico magnet is preferably used for the permanent magnet. The ring-shape member may be formed, in place of the formation as a single (unit type) member, from a plurality of segments disposed in the ring shape.
Further, when the temperature in-magnetic-field heat treatment is low, a Sm—Co magnet or a Nd—Fe—B based magnet may be used.
In the case in which the ring-shape member is formed from the permanent magnet, magnetic poles of the ring-shape member are formed so that the line of the magnetic force extending from the first ferromagnetic substance 6 to the second ferromagnetic substance 7 can be directed along a direction from the center of the recording medium 1 toward a radial direction thereof.
As a method of disposing the magnets used as the segments in the ring shape, as shown in
In the present embodiment, the N poles of the permanent magnets are opposed to each other. As an alternative arrangement, however, S poles may be opposed to each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2003-040981 | Feb 2003 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP04/01813 | 2/18/2004 | WO | 8/16/2005 |
