Optimum Layer Structure of Antiferromagnetic-Coupled Multilayer for SPT Perpendicular Writer Heads

Abstract

Perpendicular magnetic recording using a single-poletype (SPT) writer head and a double-layer perpendicular medium with a soft underlayer (SUL) has several advantages for high-density magnetic recording. It is therefore a promising candidate for a next-generation magnetic recording system. However, the pole-erase phenomenon, which is a signal reduction caused by a remanent head field from the main pole, prevents high-density recording. We investigated an SPT writer head with antiferromagnetic-(AFM-) coupled main pole to avoid the pole-erase phenomenon by using recently developed combined micromagnetics and finite-element method simulations. We demonstrated that the recording head field decreases monotonically with increasing number of AFM-coupled layers. On the other hand, residual field (pole-erase field) strength dramatically decreases to around half while applying an AFM-coupled bi-layer for the main pole. The pole-erase field is almost constant in the case of two or more layers. The optimum layer number of an AFM-coupled multilayer for the main pole is from two to four layers from the recording and pole-erase field point of view. We confirmed the same tendency by experimental observation of the pole-erase.