Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-01-08
2004-10-05
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S125020, C360S119050
Reexamination Certificate
active
06801392
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic film permitting an increase in the saturation magnetic flux density Bs of a NiFe alloy used as, for example, a core material of a thin film magnetic head, as compared with a conventional value, and having excellent other soft magnetic properties and film properties, and a method of producing the magnetic film. The present invention also relates to a thin film magnetic head using the magnetic film, and a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
In a planar magnetic device such as a thin film magnetic head, a thin film inductor, or the like, a NiFe alloy (Permalloy) is frequently used for a portion made of magnetic a material.
The NiFe alloy has relatively excellent soft magnetic properties, and can easily be plated, and thus the NiFe alloy is one of magnetic materials frequently used.
The NiFe alloy is conventionally plated by electroplating with a DC current. The Fe composition ratio is generally about 45% by mass to 55% by mass. The NiFe alloy having this composition has a saturation magnetic flux density Bs of about 1.5 T (Tesla).
However, in order to improve a recording density in future, it is demanded to further increase the saturation magnetic flux density Bs of the NiFe alloy.
Therefore, the inventors used an electroplating method using a pulsed current in place of a conventional electroplating method using a DC current. As a result, the inventors could increase the Fe composition ratio X of the NiFe alloy as compared with a conventional alloy, and succeeded in increasing the saturation magnetic flux density mainly depending upon the Fe composition ratio X. Specifically, the inventors succeeded in greatly increasing the saturation magnetic flux density Bs to about 1.9 T. A NiFe alloy film formed by an electroplating method using a pulsed current, and a method of producing the same have already been applied for a patent as U.S. patent application Ser. No. 09/599,349.
According to U.S. patent application Ser. No. 09/599,349, a soft magnetic film of an NiFe alloy having a Fe composition ratio X of 60% by mass to 75% by mass, and an average crystal grain diameter of 105 Å or less can be produced by an electroplating method using a pulsed current.
However, the soft magnetic film has the problem in which the saturation magnetic flux density Bs cannot be increased to 1.9 T or more.
The plating bath composition used for producing the soft magnetic film has a Ni ion concentration of about 40 g/l. Although the Fe composition ratio of the NiFe alloy can be possibly increased by increasing the Fe ion concentration of the plating bath, it was found by actual experiment that the Fe composition ratio cannot be increased to 75% by mass or more. Even if the Fe composition ratio can be increased to 75% by mass or more, crystallinity deteriorates to fail to form a dense crystal, thereby failing to improve the saturation magnetic flux density Bs and deteriorating other film properties such as coercive force, surface roughness, etc.
SUMMARY OF THE INVENTION
Accordingly, the present invention has been achieved for solving the above problem of conventional NiFe alloys, and an object of the present invention is to provide a soft magnetic film permitting an increase in the saturation magnetic flux density Bs of a NiFe alloy, and having excellent other soft magnetic properties and film properties.
Another object of the present invention is to provide a thin film magnetic head using a soft magnetic film having a high saturation magnetic flux density Bs of 1.9 T or more so that it can comply with increases in recording density and frequency in future.
A further object of the present invention is to provide a method of manufacturing a thin film magnetic head which is capable of increasing the Fe content in a NiFe alloy by appropriately controlling a plating bath composition, and forming a crystal having a larger crystal grain diameter and higher density than conventional NiFe alloys.
A soft magnetic film of the present invention has a composition represented by the formula Ni
1-X
Fe
X
wherein the Fe composition ratio X is 76% by mass to 90% by mass.
In the present invention, the soft magnetic film preferably has an average crystal grain diameter of 150 Å to 175 Å.
In a NiFe alloy according to a first embodiment of the present invention, only the Fe composition ratio X is defined. The saturation magnetic flux density Bs mainly depends upon the Fe composition ratio X, and increases as the Fe composition ratio X increases. The possible reason for this is that crystallization is appropriately promoted by increasing the Fe composition ratio X to form a dense crystal. However, with the Fe composition ratio X of a certain value or more, crystallization is conversely inhibited to fail to form a dense crystal, possibly decreasing Bs.
A production method of the present invention described below is capable of setting the Fe content of the NiFe alloy to 76% by mass to 90% by mass by appropriately controlling the composition of a plating bath. Therefore, the saturation magnetic flux density Bs of the NiFe alloy can be increased to 1.95 T or more. Also, coercive force Hc can be suppressed to 553 (A/m) or less.
A soft magnetic film of the present invention has a composition represented by the formula Ni
1-X
Fe
X
wherein the average crystal grain diameter is 130 Å to 175 Å, and the Fe composition ratio X is in the range of 70% by mass to 90% by mass.
In a NiFe alloy according to a second embodiment of the present invention, the Fe composition ratio and the average crystal grain diameter of the NiFe alloy are defined.
As described above, the saturation magnetic flux density Bs mainly depends upon the Fe composition ratio X, but a higher saturation magnetic flux density Bs can be stably obtained by further setting the average crystal grain diameter in an appropriate range.
In U.S. patent application Ser. No. 09/599,349, now U.S. Pat. No. 6,449,122, the Fe composition ratio X can be increased to 75% by mass which lies in the range of the Fe composition ratio X of the NiFe alloy according to the second embodiment of the present invention.
Although the range of the Fe composition ratio X of the present invention partially overlaps with that of U.S. patent application Ser. No. 09/599,349, now U.S. Pat. No. 6,449,122, the present invention greatly differs from U.S. patent application Ser. No. 09/599,349, now U.S. Pat. No. 6,449,122, in the crystal grain diameter. Namely, in the present invention, the crystal grain diameter is defined to 130 Å or more, while in U.S. patent application Ser. No. 09/599,349 (U.S. Pat. No. 6,449,122), the crystal grain diameter is defined to 105 Å or less.
In the present invention, crystallization is possibly appropriately promoted to increase the crystal grain diameter, forming a dense crystal, as compared with the NiFe alloy of U.S. patent application Ser. No. 09/599,349 (U.S. Pat. No. 6,449,122). As a result, in the present invention, the saturation magnetic flux density Bs of the NiFe alloy can be increased to 1.9 T or more, succeeding in effectively increasing the saturation magnetic flux density Bs.
In the present invention, coercive force can be suppressed to 553 (A/m) or less. The coercive force Hc possibly increases as the crystal grain diameter increases. However, in the present invention, the coercive force Hc little increases even when the crystal grain diameter increases, and the coercive force Hc of 553 (A/m) or less is a low value sufficiently used, for example, for a core material of a thin film magnetic head.
The possible reason why the coercive force Hc can be kept down even when the crystal grain diameter increases is that a crystal is densely grown. When the crystal is densely formed, the surface roughness of a film plane can be decreased, and in the present invention, the center line average roughness Ra of the film plane can be suppressed to 10 nm or less. In the present invention, the
Kanada Yoshihiro
Kawasaki Mitsuo
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Klimowicz William
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