Chapter 6 - Vertical Biasing Techniques

Abstract

In the design of both anisotropic magneto-resistive head (AMRHs) and giant magneto-resistive (GMR) spin valves it is usually necessary to provide both vertical and horizontal magnetic bias fields. This chapter discusses most of the techniques proposed for applying a vertical bias field on a magneto-resistive element in historical order. The permanent magnet bias structure is the simplest idea for providing vertical magnetic bias. The main advantage of this scheme is that the many years of experience in making thin-film recording media can be applied to the permanent magnet (PM) film. Disadvantages include the fact that a high magnetic field, of magnitude about equal to the coercivity of the PM material, is present at the top edge immediately adjacent to the tape or disk. Another disadvantage is that the errors in fabrication, which result in an incorrect vertical bias field, cannot be adjusted easily after the magneto-resistive heads (MRH) is made. Post fabrication adjustment of the vertical biasing is, on the other hand, easily accomplished in the current biasing schemes. In the current bias, the current flowing into the MRH is divided into two parts. One flows through the magneto-resistive element (MRE). The second part flows through a layer of electrically conductive, nonmagnetic material, which is electrically insulated from the MRE. The other biasing schemes described are: soft Adjacent Layer (SAL) vertical bias arrangement, the double-element MRE vertical biasing scheme, self-bias, exchange bias, the barber-pole biasing scheme, the split-element scheme, and the servo-bias scheme.