1. Field of the Invention
The present invention relates to a compound floating magnetic head that writes and reads data to and from a magnetic recording medium such as a magnetic disk, and more particularly to a compound floating magnetic head including sealing glass that is chemically stable even in a highly humid environment.
2. Prior Art
A conventional compound floating magnetic head uses dynamic pressure generated by the travel of a magnetic medium such as a magnetic disk to float the slider of the head with a very small gap between the head and the medium. The ferrite core disposed at the slider section where the gap is the narrowest writes and read data.
The compound floating magnetic head comprises a ferrite core 20 composed of an I-shaped bar 21 and a C-shaped bar 22 shown in FIG. 1 (a), and a non-magnetic slider 10 shown in FIG. 1 (b).
The I-shaped bar 21 and the C-shaped bar 22 are coupled at two positions (front gap FG and back gap BG) and integrated into the ferrite core 20. Front gap FG is positioned on the side of the recording medium (not shown). The length of the gap is determined to a specified width depending on the recording density of the recording medium.
To maintain the gap length at the (specified width), reinforcing bonding glass 23 is formed at the sloped portion on the side of front gap FG.
Furthermore, on the side of front gap FG, the front end of the ferrite core 20 has a step with a specified width that depends on the track width of the recording medium.
The slider 10 is basically a rectangular parallelopiped. To float the slider 10 apart from the recording medium with a specified gap, floating rails 12 and 13 and bleed groove 14 are formed on the surface 11 of the slider 10 that faces the recording medium.
A core accommodation groove (core slit) 16 with a specified depth is formed in the longitudinal direction on the trailing end surface 15 of the floating rail 12.
As shown in FIG. 1 (c), the ferrite core 20 is coupled with a non-magnetic slider 10 in the core slit 16 of the slider 10 by using sealing glass 17. An coupling process is explained below referring to FIG. 1 (d). The ferrite core 20 is temporarily held in the core slit 16 of the slider 10. A bare 18 that is to be melted to form the sealing glass 17 is then placed on the core 20. By heat treatment at a specified temperature, the bar 18 is softened and melted to fill the core slit 16 with the sealing glass 17, thus securing the ferrite core 20 to the slider 10.
In the above-mentioned coupling process, it is important to set heat treatment temperature T1 required to soften and melt the bar 18 to form the sealing glass 17 sufficiently lower than softening temperature T2 of the reinforcing bonding glass 23 of the ferrite core 20 (T1&lt;T2). If heat treatment temperature T1 is set higher than softening temperature T2 of the reinforcing bonding glass 23, the specified electromagnetic conversion characteristics required between the magnetic medium and the ferrite core 20 are deteriorated. For example, the specified gap length on the front gap (FG) side becomes larger.
Conventionally, glass including much lead oxide was used as the sealing glass 17 to obtain a lower softening point. The sealing glass 17 that was used generally comprises 78% PbO by weight, 2.6% SiO.sub.2 by weight and 10% B.sub.2 O.sub.3 by weight. By including much PbO and B.sub.2 O.sub.3 as described above, the sealing glass 17 was easily able to have a low softening point sufficiently lower than softening point T2 of the bonding glass 23. However, when a conventional compound floating magnetic head with this kind of sealing glass 17 was left in a very humid environment, a moisture absorption layer was formed on the sealing glass 17. Chemically, the metal ions included in the sealing glass 17 reacted with hydroxyl groups, weathering and corroding the glass surface. These caused problems: discoloration of the exterior, damage to the recording medium due to dropping of substances precipitated by chemical reaction, and attachment of the magnetic powder of the recording medium to cavity portions from which the precipitated substances were separated.
In any case of the above-mentioned problems, noise was caused during writing and reading data to and from the recording medium, significantly reducing the reliability of the electromagnetic conversion characteristics.