Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2000-07-26
2001-07-17
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06262867
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a disk storage system, a thin film magnetic head therefor and a fabrication method thereof.
The present invention relates to a magnetic core for a magnetic head, and more particularly to a recording head for a dual element head for a disk system having a high recording density.
In recent years, the recording density of a disk storage system has become higher and the magnetic coercive force of recording medium has increased; accordingly, there is a need for a thin film magnetic head which is capable of sufficiently recording on a recording medium having a high magnetic coercive force.
In order to realize this, it is necessary to use a material having a high saturation magnetic flux density (B
S
) as a core material of the magnetic head. In the past, a 80Ni—Fe alloy film of 3 &mgr;m thickness has been used for the core material.
However, since the resistivity of the 80Ni—Fe alloy film is as low as 16 to 20 &mgr;&OHgr;·cm, the eddy current loss becomes large in the high frequency bands. Therefore, the strength of the recording magnetic field of the magnetic head in a high frequency band is decreased, and accordingly the recording frequency is limited to about 30 MHz at maximum.
As an alternative material, Co system amorphous materials and a Fe—Al—Si sendust alloy thin film are proposed. However, these materials are not in practical use as yet because the former is thermally unstable, since the material is amorphous, and the latter has a disadvantage in the fabrication process as the magnetic core material for the inductive head, since it requires a high temperature heat treatment at nearly 500° C.
In recent years, three-element group materials of Co—Ni—Fe have been proposed (Japanese Patent Application Laid-Open No. Sho 60-82,638, Japanese Patent Application Laid-Open No. Sho 61-76,642, Japanese Patent Application Laid-Open No. Sho 64-8,605, Japanese Patent Application Laid-Open No. Hei 2-68,906, Japanese Patent Application Laid-Open No. Hei 2-290,995).
Although the saturation magnetic flux density (B
S
) of these three-element system materials is as high as 1.5 T, the resistivity is not large and the crystal grain size is not small in the 80Ni—Fe alloy; and, in addition to this, there is a disadvantage in the high frequency characteristic as in the 80Ni—Fe alloy.
On the other hand, the memory capacity of the disk storage system has been steadily growing year by year, and areal density of a 3.5-inch type disk in production now has been increased up to 350 MB/in
2
.
In this case, the data recording frequency is nearly 27 MHz, which is near the performance limit of a magnetic head using the 80Ni—Fe alloy film or the Co—Ni—Fe alloy film.
Although there is proposed in Japanese Patent Application Laid-Open No. 3-68,744 a magnetic film for high frequency use formed by adding Nb, Ta, Cr, Mo to (40-50) Ni—Fe through a sputtering method, it is difficult to magnetically form a thick film using a sputtering method because the material has a large magnetocrystalline anisotropy.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a disk storage system, a thin film magnetic head therefor and a fabrication method thereof wherein there is provided a disk storage system with a magnetic head for high density recording in a high frequency band.
Another object of the present invention is to provide a magnetic head for high density recording in a high frequency band, that is, a magnetic head which is capable of performing high speed access and has a high transfer rate.
The present invention has been developed for solving the above problems, and involves a thin film magnetic head that is mounted on a disk storage system having a high transfer rate and high recording density, in which there is a magnetic disk rotated above 4000 rpm when the disk storage system is recording or reproducing, and in which the recording frequency is not higher than 45 MHz.
It is required that the magnetic core of the write head be made of a material having a large saturation magnetic flux density (B
S
), a small magnetic coercive force in the hard axis direction and a large resistivity.
In other words, the range of composition obtainable for a large resistivity and high saturation magnetic flux density is a range containing Ni of 38 to 60 wt % for Ni—Fe alloy.
However, when a magnetic film having a thickness of above 2 &mgr;m is usually applied to a thin film magnetic head or the like fabricated through a sputtering method, the crystal grain size of the film becomes large, the magnetic coercive force in the hard axis direction is large and the uniaxial magnetic anisotropy is hardly induced, since this composition region is in a range where magnetocrystalline anisotropy is largest.
Therefore, a plating method has been employed in order to suppress the crystal grain size to a small value, and it has been proposed to add a third element, such as Co, Mn, Cr, Pd, B, In and the like, to a base of 38 to 60 wt % Ni—Fe two-element alloy.
The results were found to be a composition range and a fabrication method of an outstanding thin film having a saturation magnetic flux density (B
S
) larger than 1.5 T, a magnetic coercive force in the hard axis direction (H
CH
) smaller than 1.0 Oe and a resistivity larger than 40 &mgr;&OHgr;·cm, while keeping the film thickness of 2 to 5 &mgr;m which is required for the recording magnetic field.
By using this material for a thin film magnetic head, it is possible to provide a high performance disk storage system having areal density of 500 MB/in
2
, a recording frequency of 45 MHz and a transmission speed of above 15 MB/s.
The present invention is characterized by a disk storage system comprising a thin film magnetic disk for recording information, rotating means for the thin film magnetic disk, a thin film magnetic head for performing writing and reading of information and provided in a floating type slider, transfer means for supporting the floating type slider and for making access to the thin film magnetic disk.
The present invention is characterized by a disk storage system wherein at least one of an upper magnetic core and a lower magnetic core the write head is made of a metallic magnetic material having an average crystal grain size smaller than 500 Å, a resistivity at room temperature larger than 40 &mgr;&OHgr;·cm and a magnetic coercive force in the hard axis direction smaller than 1.0 Oe.
The present invention is characterized by the fact that, in a disk storage system, at least one of an upper magnetic core and a lower magnetic core of the writing magnetic core of the write head is an electroplated thin film made of a Ni—Fe group alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt %.
Further, the present invention is characterized by a disk storage system comprising a magnetic disk having a transfer rate larger than 15 mega-bytes per second, areal density of recording data larger than 500 mega-bits per square inch and a diameter smaller than 3.5 inches.
The present invention is characterized by a disk storage system wherein the magnetic disk rotates faster than 4000 rpm during recording and reproducing, the recording frequency is larger than 45 MHz, and at least an upper magnetic core of a thin film magnetic head for performing the recording is made of a Ni—Fe alloy having Ni of 38 to 60 wt % and Fe of 40 to 62 wt % and having a film thickness of 1 to 5 &mgr;m, an average crystal grain size smaller than 500 Å, a resistivity of 40 to 60 &mgr;&OHgr;·cm and magnetic coercive force in the hard axis direction smaller than 1.0 Oe, the recording magnetomotive force of the write head being larger than 0.5 ampere-turns.
The magnetic core in a disk storage system according to the present invention contains a substance composed of at least one kind of one of Co less than 15 wt % and Mo, Cr, Pd, B, In less than 3 wt % in the total weight.
Further, the present invention is characterized by a disk storage system comprising a thin film magnetic disk for recording information, rotating means for the th
Fuyama Moriaki
Kawabe Takashi
Kita Yoshiaki
Masuda Kenzo
Narumi Shun-ichi
Antonelli Terry Stout & Kraus LLP
Hitachi Ltd
Renner Craig A.
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