Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-01-16
2004-07-06
Tupper, Robert S. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C428S692100, C428S693100
Reexamination Certificate
active
06760189
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to soft magnetic films used as core materials of thin-film magnetic heads. In particular, the present invention relates to a soft magnetic film which is composed of an FeCo&agr; alloy wherein &agr; represents a noble metal, which has a saturation magnetic flux density Bs of at least 2.0 T, and which exhibits high corrosion resistance. Also, the present invention relates to a thin-film magnetic head including the soft magnetic film, a method for making the soft magnetic film, and a method for making the thin-film magnetic head.
2. Description of the Related Art
For future higher-density recording, for example, a magnetic material having a high saturation magnetic flux density Bs must be used as a core layer of a thin-film magnetic head to increase the recording density by concentrating the magnetic flux to the vicinity of the gap of the core layer.
A traditionally used magnetic material is a NiFe alloy. The NiFe alloy film is formed by electroplating using a continuous DC and exhibits a saturation magnetic flux density Bs of about 1.8 T.
Although future higher-density recording requires a soft magnetic film having a higher saturation magnetic flux density Bs, the NiFe alloy does not sufficiently meet such a requirement.
Another soft magnetic material often used, other than the NiFe alloy, is an FeCo alloy. The FeCo alloy film having an optimized composition has a higher saturation magnetic flux density Bs than that of the NiFe alloy film, and also has the following problem.
In some configurations of thin-film magnetic heads and other magnetic elements, a NiFe alloy film is disposed on the FeCo alloy film by electroplating. Unfortunately, the FeCo alloy film is dissolved and corroded by ionization during the electroplating.
It is likely that a large potential difference (standard electrode potential difference) is generated between the FeCo alloy film and the NiFe alloy film and causes dissolution of the FeCo alloy film by the galvanic effect.
In a single FeCo alloy film configuration, this film must have high corrosion resistance during the manufacturing processes of thin-film magnetic heads and other magnetic elements. For example, the film must have high corrosion resistance during milling steps of sliders and cleaning steps of the elements. Also, the film must have high corrosion resistance in actual operating environments of thin-film magnetic heads.
Accordingly, in the plating of the NiFe alloy on the soft magnetic film, the soft magnetic film must have a high saturation magnetic flux density Bs and high corrosion resistance.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a soft magnetic film comprising an FeCo alloy which contains a noble metal &agr; such as Pd and which has a saturation magnetic flux density Bs of at least 2.0 T and high corrosion resistance.
Another object of the present invention is to provide a thin-film magnetic head including the soft magnetic film, a method for making the soft magnetic film, and a method for making the thin-film magnetic head.
A soft magnetic film according to the present invention has a composition represented by the formula Fe
X
Co
Y
&agr;
Z
wherein &agr; is at least one element selected from the group consisting of Rh, Pd, Pt, Ru, and Ir, wherein the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5, the &agr; content Z is in the range of 0.5 to 18 mass percent, and X+Y+Z=100 mass percent.
The element &agr; is added to enhance corrosion resistance. At an &agr; content of less than 0.5 mass percent, the corrosion resistance is not enhanced. At an &agr; content exceeding 18 mass percent, the saturation magnetic flux density Bs does not reach 2.0 T due to a decreased Fe content in the composition.
When the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5, a saturation magnetic flux density Bs of at least 2.0 T is achieved, as described in experimental results below.
The above soft magnetic film has a saturation magnetic flux density Bs of at least 2.0 T and exhibits higher corrosion resistance than that of an FeCo alloy not containing the element &agr;.
Preferably, the ratio X/Y by mass percent of Fe to Co is in the range of 2.6 to 4.3 and the &agr; content Z is in the range of 3 to 9 mass percent.
A soft magnetic film having such a preferable composition has a saturation magnetic flux density Bs of at least 2.2 T and exhibit higher corrosion resistance than that of an FeCo alloy not containing the element &agr;.
Preferably, the soft magnetic film has a composition represented by the formula Fe
X
Co
Y
&agr;
Z
&bgr;
V
, wherein &bgr; is at least one of Ni and Cr, the ratio X/Y by mass percent of Fe to Co is in the range of 2 to 5 and more preferably in the range of 2.6 to 4.3, the &agr; content Z is in the range of 0.5 to 18 mass percent and more preferably in the range of 3 to 9 mass percent, the &bgr; content V is in the range of 0.5 to 5 mass percent, and X+Y+Z+V=100 mass percent.
A soft magnetic film having such a composition has a saturation magnetic flux density Bs of at least 2.0 T or at least 2.2 T under optimized conditions and exhibits higher corrosion resistance. The element &bgr; contributes to higher corrosion resistance due to the formation of a passivation film. When the element &bgr; is Ni, the film stress is decreased.
In the present invention, the soft magnetic film may be overlaid with a NiFe alloy film which is formed by plating. Thus, the resulting soft magnetic film is referred to as a composite soft magnetic film.
The noble metal element &agr; is barely ionized alone. In the plating process of a NiFe alloy film on a soft magnetic film containing the element &agr;, the FeCo&agr; alloy is prevented from dissolution by ionization. In an FeCo&agr;&bgr; alloy, a passivation film formed on the surface more effectively prevents the dissolution of the alloy by ionization.
In conclusion, the FeCo&agr; alloy film and the composite soft magnetic film of the FeCo&agr;&bgr; film and the NiFe alloy film have a high saturation magnetic flux density Bs and high corrosion resistance.
The soft magnetic film according to the present invention is preferably formed by plating. A soft magnetic film having a desired thickness or a higher thickness than that by sputtering is thereby formed.
The present invention also relates to a thin-film magnetic head comprising a magnetic lower core layer, an upper core layer formed on the magnetic lower core layer with a magnetic gap provided therebetween, a coil layer for applying a recording magnetic field to the lower core layer and the upper core layer, wherein at least one of the lower core layer and the upper core layer comprises the above-described soft magnetic film.
Preferably, the thin-film magnetic head further comprises a lower magnetic pole layer on the lower core layer and at a face opposing a recording medium, wherein the lower magnetic pole layer comprises the soft magnetic film.
The present invention also relates to a thin-film magnetic head comprising a lower core layer; an upper core layer; and a magnetic pole unit provided between the lower core layer and the upper core layer, the length of the magnetic pole unit being shorter than that of the lower core layer and the upper core layer in the track width direction. The magnetic pole unit comprises a lower magnetic pole layer in contact with the lower core layer; an upper magnetic pole layer in contact with the upper core layer; and a gap layer lying between the lower magnetic pole layer and the upper magnetic pole layer, or comprising an upper magnetic pole layer in contact with the upper core layer and a gap layer lying between the upper magnetic pole layer and the lower core layer, wherein at least one of the upper magnetic pole layer and the lower magnetic pole layer comprises the above-described soft magnetic film.
Preferably, the upper magnetic pole layer comprises the above-described soft magnetic film, the upper core layer on the upper magneti
Gotoh Mitsuhiro
Kanada Yoshihiro
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Tupper Robert S.
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