Perpendicular magnetic recording is one method of achieving high recording densities. In perpendicular magnetic recording using a single-pole type (SPT) head, a main pole film with stable operation must be employed. In this respect, use of a single-layer main pole film has a serious limitation because of its domain structure. On the other hand, multilayer main pole films are thought to have no such limitations, because closure domains are eliminated by magnetic coupling. However, SPT heads using multilayer thin films often show instability in reproduce processes. We found that the instability could be removed by applying a dc magnetic field to the multilayer main pole. The stress in the multilayer film was related to instability in the head's behavior. We also showed that an underlayer between the magnetic layers and the substrate is necessary to eliminate the stress in multilayer films.
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