1. Field of the Invention
The present invention relates to a magnetic head and, more particularly, an induction type magnetic head for use in a magnetic disk drive, a magnetic tape drive, and so forth.
2. Description of the Prior Art
An induction type magnetic head has been employed to record magnetic information on a magnetic disk or a magnetic tape or to reproduce the magnetic information recorded on the magnetic disk or the magnetic tape. However, in recent years, with the practical implementation of magnetoresistive devices, the induction type magnetic heads have often been exclusively used for magnetic recording.
The induction type magnetic head (inductive head) has in general a cross sectional structure as shown in FIGS. 16A and 16B. A spiral coil 1 is interposed between a lower magnetic pole 2 and an upper magnetic pole 3 via an insulating layer 4. The upper magnetic pole 3 denotes a magnetic pole which is positioned on the side far from a recording track of a magnetic recording medium, i.e., which is made of a film being finally formed.
If the induction type magnetic head is employed in combination with a reproduction only MR magnetic head to which the magnetoresistive device is installed, such a configuration is commonly adopted that the lower magnetic pole of the induction type magnetic head can also serve as an upper shielding layer of the MR magnetic head. Thus, miniaturization of the magnetic head can be attained and also displacement between write position and read position can be prevented from being generated.
In the induction type magnetic head, an infinitesimal gap is formed between top ends of the upper magnetic pole 3 and the lower magnetic pole 2 via the insulating layer 4. The upper magnetic pole 3 is formed to have a narrowly tapered top end, as shown in FIG. 16B. Such tapered slant .theta. relative to a surface line of the top end is called a squeezing angle or a taper angle.
Normally a permalloy thin film is employed as a soft magnetic thin film serving as the upper magnetic pole 3. A film thickness .delta. of the thin film is about 3.5 to 4.0 .mu.m and the taper angle .theta. is 45 to 55 degrees. Recently, in order to prevent reduction in the recording magnetic field due to a narrower write gap, material with high saturation magnetic flux density (high Bs) such as Ni.sub.50 Fe.sub.50 has been employed as the upper magnetic pole 3, or a composite magnetic pole which is made by laminating a high Bs thin film and the permalloy thin film has been employed. However, even in such configuration, the film thickness .delta. of the overall upper magnetic pole is 3.0 .mu.m or more and the taper angle .theta. is 30 degrees or more.
By the way, there has been a necessity of driving the recording head at the high frequency of about 100 MHz or more as the recording density is increased in recent years.
In the high frequency induction type magnetic head, dibit resolution has been utilized as an important index to estimate the high recording density characteristic. The dibit resolution can be given by a value (V.sub.dibit /V.sub.iso) which is derived by dividing a recording/reproducing output V.sub.dibit composed of only two bits at the high frequency (e.g., 100 MHz) by a recording/reproducing output V.sub.iso composed of only two bits at the low frequency (e.g., 10 MHz). In general, a value of 40% or more has been needed as the dibit resolution.
However, in the case that the induction type magnetic head is employed at the high frequency range of more than 100 MHz, sufficient consideration as to the influence of eddy current caused in the writing head (especially, upper magnetic pole) has not been taken in the prior art. As a consequence, the upper magnetic pole is improperly designed for high frequency applications. For purposes of example, the film thickness .delta. and the taper angle .theta. of the upper magnetic pole are formed excessively large compared to the properties of material used as the upper magnetic pole, such as saturation magnetic flux density Bs, electric resistivity .rho., etc. Therefore, it has been believed that it is difficult to improve the recording resolution, etc. by increasing the dibit resolution up to 40% or more in the high frequency band beyond 100 MHz.