1. Field of the Invention
The present invention relates to a composite magnetic head having a servo head, which writes a servo signal on a magnetic tape, provided thereon, and to a process for producing the same, the disclosure of which is based on Japanese Patent Application No. 2003-405513, filed on Dec. 15, 2003.
2. Description of Relate Arts
In recent years, a magnetic tape has became high density for recording, and amongst the magnetic tape, there exists magnetic tapes for backing up a data for a computer has a capacity of approximately several hundreds Gigabits, In order to attain such a capacity, several hundreds of data trucks are formed on the magnetic tape in the width direction thereof. This makes the width of the truck of the magnetic tape very narrow, and a space between neighboring data trucks becomes also narrow. In such a case, in order to trace a recording/playing element possessed by the magnetic head onto the data truck, a servo signal has been previously recorded onto the magnetic tape, and the position of the magnetic tape (the position of the magnetic tape in the width direction) is servo-controlled, while reading the recorded servo signal by the magnetic head (see U.S. Pat. No. 5,689,384 corresponding to Japanese Patent Laid-Open No. 08-30942).
In the prior art, the servo band is recorded by applying a recording signal to the servo head so as to magnetize given areas on a servo band, which has not yet been magnetized, in one direction. Specifically, as shown in FIG. 14A, in order to avoid saturation of a servo signal reading element (MR element) in the servo band SS″, a pulse current PC″ comprising a zero current and a plus pulse current (hereinafter referred to as pulse current) is formed on a servo band SB″, which has not yet been magnetized. As shown in FIG. 14B, upon using the pulse current PC″, areas except for a servo pattern SP″ of a magnetic tape MT″ is not magnetized at a time when the pulse current is zero current, while the servo pattern SP″ is magnetized in one direction due to a leakage magnetic flux from a servo writing gap at a time when the plus pulse current is run, which writes the servo signal SS″ thereon as a result. On the other hand, in the conventional device for recording and playing a magnetic tape, a point for changing magnetization is detected by change in an electric resistance by a servo signal-reading element, and output the point for changing magnetization as differential wave form (voltage) as the reading signal. Consequently, as the electric resistance becomes larger, a peak voltage of the reading signal of the servo signal SS″ becomes larger, enhancing an S/N ratio of the reading signal. Consequently, as shown in FIG. 14C, the reading signal RSL″ of the servo signal SS″ becomes large in the case where change in the magnetization of the servo signal SS″ itself is large, or in the case where a reading area is large due to long width of the servo signal reading element.
It is, however, expected that the density of the magnetic tape will become much higher, i.e., as high as several Terabits. This will increase a number of data trucks and make the magnetic tape thinner. Accordingly, the amount of the magnetism, which can be detected at the time of reading the servo signal SS″ is decreased, and the change in magnetization amount of the servo signal SS″, which can be detected by the servo signal reading element, is decreased. Consequently, as shown in FIG. 14D, the peak voltage of a reading signal RSS″ of the servo signal SS″ is decreased, and the SN ratio of the reading signal RSS″ is deteriorated. As a result, the servo signal SS″ cannot be read out in the conventional device for recording and playing a magnetic tape in a precise manner, making it impossible to highly precisely control the position of the magnetic head.
An object of the present invention is, therefore, to provide a composite magnetic head, which can enhance the SN ratio of the reading signal of the servo signal and which can avoid the deterioration in the quality of data signal recorded on the data band, and another object of the present invention is to provide a process for producing such a composite magnetic head.