This invention relates generally to a magnetic head for a perpendicular magnetic recording system, and more particularly to a thin film magnetic head which is especially adapted for recording on double-sided discs or media.
As is well known, magnetic recording methods are classified generally into two modes. The first is a recording mode using longitudinal residual magnetization on the surface of the recording media, while the other mode uses perpendicular residual magnetization. The longitudinal magnetic record method has long been employed. However, because of the potential increase in storage capacity for a given recording area, the next major breakthrough in magnetic recording of digital data is expected to be the transition from longitudinal recording (where the data is recorded horizontally along a circular data track on a disc surface) to vertical recording (where data is recorded perpendicular to the data surface).
In the development of perpendicular recording systems, known systems are based on the concepts shown in FIGS. 1 and 2. In the configuration shown in FIG. 1, the recording medium consists of a "hard" magnetic layer 1, with vertical orientation; a "soft" magnetic underlayer 3; and a non-magnetic substrate 5. The read/write head is composed of two portions: a very narrow main pole 8 to concentrate the magnetic flux in a small area, and a magnetic auxiliary pole 10 having a much greater surface area and carrying the read/write coil. FIG. 1 shows that the portion of the flux pattern that passes through the "hard" magnetic layer 1 is essentially vertical. The flux path is then dispersed in the "soft" magnetic underlayer to be collected by the large surface area of auxiliary pole 10. The primary disadvantage of this system is that since the main pole 8 and auxiliary pole 10 are face-to-face on opposite sides of the recording medium, this system cannot be used for magnetic recording systems using a rigid substrate recording medium such as a rigid magnetic disc unit, nor for a two-sided recording system. Moreover, the recording efficiency is rather low because of the separation of the main and auxiliary poles.
A second configuration suggested for vertical recording is using a conventional head as used for longitudinal recording see FIG. 2, called a Karlquist head. This can be used in conjunction with a single layer medium. Therefore, it does allow recording on both sides of the medium; but it has many disadvantages. Specifically, it can be seen by reference to FIG. 3, which is aligned below the head of FIG. 2, that the vertical component of the flux pattern is relatively small and longer when compared with the horizontal component. Therefore, a Karlquist head recording on a single layer vertically oriented medium does not promise a significant increase in recording density over longitudinal recording because of the excess length of each recorded bit.
U.S. Pat. No. 4,404,609 (Jones) and 4,438,471 (Oshiki, et al.) disclose prior art efforts at improving the deficiencies of the two basic approaches. These patents are incorporated herein by reference insofar as they are useful for their disclosures of the formation and materials incorporated in thin film heads. However, both of these patents disclose a vertical head recording system in which the heads are quite complex to fabricate.