Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-01-08
2004-03-30
Thibodeau, Paul (Department: 1773)
Dynamic magnetic information storage or retrieval
Head
Core
C428S611000, C428S692100, C428S141000, C428S637000, C428S192000
Reexamination Certificate
active
06714380
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to soft magnetic films which contain a CoFe&agr; alloy (the element &agr; is Ni or the like) used as, for example, core materials of thin-film magnetic heads and which have superior corrosion resistance and a higher saturated magnetic flux density Bs than an NiFe alloy. In addition, the present invention relates to thin-film magnetic heads using the soft magnetic films described above, to methods for manufacturing the soft magnetic films, and to methods for manufacturing the thin-film magnetic heads.
2. Description of the Related Art
In particular, concomitant with the recent trend toward higher recording densities, it has become necessary that, in order to improve a recording density, a magnetic material having a higher saturated magnetic flux density Bs be used for forming a core layer of a thin-film magnetic head so that a magnetic flux is concentrated in the vicinity of the gap of the core layer.
An NiFe alloy has been frequently used for the magnetic material described above. The NiFe alloy described above is formed by an electroplating method using a DC current and is able to have a saturated magnetic flux density Bs of approximately 1.8 T.
In order to further increase the saturated magnetic flux density Bs of the NiFe alloy, for example, an electroplating method using a pulse current is used in place of an electroplating method using a DC current.
According to the method described above, the Bs of the NiFe alloy can be increased; however, the saturated magnetic flux density Bs cannot be increased to 2.0 T or more. In addition, the surface roughness of the film is increased, and hence, there has been a problem in that the NiFe alloy is corroded by various solvents used in a process for forming a thin-film magnetic head.
From the NiFe alloy described above, a soft magnetic film having a high saturated magnetic flux density Bs together with superior corrosion resistance has not been formed.
In addition to the NiFe alloy, as a soft magnetic material which is frequently used, a CoFe alloy film may be mentioned. When the component ratio of Fe is appropriately controlled, the CoFe alloy film may have a higher saturated magnetic flux density Bs than that of an NiFe alloy film; however, it has the following problem.
Depending on the structure of a thin-film magnetic head or another magnetic element, an NiFe alloy may be overlaid on the CoFe alloy in some cases. In the case described above, when the NiFe alloy film is formed on the CoFe alloy film by an electroplating method, the CoFe alloy film may be ionized and dissolved out, and as a result, corrosion occurs.
The reason for this is that a significant potential difference (difference in standard electrode potential) is generated between the CoFe alloy film and the NiFe alloy film, and it is believed that a so-called battery effect is obtained by this potential difference and that the CoFe alloy film is dissolved out.
In addition to the NiFe alloy film and the CoFe alloy film described above, a CoFeNi film is also one of the soft magnetic films which are frequently used. For example, in Table 2 shown in U.S. Pat. No. 6,063,512, four CoFeNi alloy films having different compositions and soft magnetic properties thereof are listed.
However, according to the compositions of the CoFeNi alloy films described in this publication, the saturated magnetic flux densities Bs-thereof are all less than 2.0 T, and compared to a NiFe alloy film, a large saturated magnetic flux density Bs cannot be effectively obtained.
SUMMARY OF THE INVENTION
Accordingly, the present invention was made to solve the conventional problems described above, and an object of the present invention is to provide a soft magnetic film having a higher saturated magnetic flux density Bs than that of an NiFe alloy and superior corrosion resistance, the soft magnetic film containing a CoFe&agr; alloy having appropriate component ratios; a thin-film magnetic head using the soft magnetic film described above; a method for manufacturing the soft magnetic film; and a method for manufacturing the thin-film magnetic head.
In addition, the present invention also provides a soft magnetic film which comprises a CoFe&agr; alloy and which can maintain a high saturated magnetic flux density Bs, in which the CoFe&agr; alloy is prevented from being dissolved out when an NiFe alloy is formed thereon by plating; a thin-film magnetic head using the soft magnetic film described above; a method for manufacturing the soft magnetic film; and a method for manufacturing the thin-film magnetic head.
In accordance with one aspect of the present invention, a soft magnetic film has a composition represented by the formula Co
x
Fe
y
&agr;
z
(the element &agr; is at least one of Ni and Cr), wherein the component ratio X of Co is 8 to 48 mass %, the component ratio Y of Fe is 50 to 90 mass %, the component ratio Z of the element &agr; is 2 to 20 mass %, and the equation X+Y+Z=100 mass % is satisfied.
When a CoFe&agr; alloy has the composition described above, the saturated magnetic flux density Bs thereof can be 2.0 T or more. As described above, in the present invention, a higher saturated magnetic flux density Bs than that of an NiFe alloy can be obtained.
In addition, the formation of coarse crystal grains can be suppressed, dense crystals can be formed, and hence, the surface roughness can be decreased. Accordingly, in the present invention, a soft magnetic film having a high saturated magnetic flux density Bs of 2.0 T or more and, in addition, superior corrosion resistance can be manufactured.
In the present invention, it is preferable that the component ratio X of Co be 23 to 32 mass %, the component ratio Y of Fe be 58 to 71 mass %, the component ratio Z of the element &agr; be 2 to 20 mass %, and the equation X+Y+Z=100 mass % be satisfied.
When a CoFe&agr; alloy has the component ratios in the ranges described above, the saturated magnetic flux density Bs thereof can be 2.15 T or more. In addition, the center line average roughness Ra of the film surface can be 5 nm or less, and the corrosion resistance can be more effectively improved.
In addition, in the present invention, it is more preferable that the component ratio X of Co be 23.3 to 28.3 mass %, the component ratio Y of Fe be 63 to 67.5 mass %, the component ratio Z of the element &agr; be 4.2 to 13.6 mass %, and the equation X+Y+Z=100 mass % be satisfied. Consequently, the saturated magnetic flux density Bs can be 2.2 T or more. In addition, the center line average roughness Ra of the film surface can be 5 nm or less, and the corrosion resistance can be more effectively improved.
Furthermore, in the present invention, it is most preferable that the component ratios, X of Co, Y of Fe, and Z of the element &agr;, be in the area surrounded by three points (X, Y, and Z) of (26.5, 64.6, and 8.9 mass %), (25.5, 63, and 11.5 mass %), and (23.3, 67.5, and 9.2 mass %), and the component ratios satisfy the equation X+Y+Z=100 mass %. Consequently, the saturated magnetic flux density Bs can be more than 2.2 T. In particular, it was confirmed by the experiments described below that the saturated magnetic flux density Bs could be increased up to 2.25 T. In addition, the center line average roughness Ra of the film surface can be 5 nm or less, and the corrosion resistance can be more effectively improved.
In the present invention, a passivation film is preferably formed on a surface of the soft magnetic film. The passivation film is a dense oxide film and is formed by the presence of Ni or Cr in the soft magnetic film.
In the case in which the passivation film is formed on the surface of the soft magnetic film as described above, the CoFe&agr; alloy can be prevented from being ionized and dissolved out even when an NiFe alloy film is formed on the soft magnetic film by plating.
Accordingly, in the present invention, even when an NiFe alloy film is formed on the CoFe&agr; alloy film by plating, a hig
Kanada Yoshihiro
Kawasaki Mitsuo
Alps Electric Co. ,Ltd.
Bernatz Kevin M.
Thibodeau Paul
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