Perpendicular Magnetic Recording Integration and Robust Design

We have investigated the effects of stray magnetic field upon a perpendicular magnetic recording (PMR) system, which consists of a single pole type head and a double-layered perpendicular medium. We found that fields in the plane of the disk could cause serious erasure. External magnetic flux concentrates around the edges of a return pole and can cause very large fields to appear in the medium. In addition, the writing operation significantly enhances this erasure. We called this kind of erasure "corner erasure." Experimental 2.5-inch hard disk drives (HDDs) were used to study the combined effect of the external field and write field. We checked SER degradation after applying an in-plane field of 0.8 kA/m (10 Oe). With no write-current applied, there is no degradation. However, as little as 0.8 kA/m (10 Oe) applied during writing causes severe degradation equivalent to that produced by a 4.0 kA/m (50 Oe) field applied when the head is reading on-track. It is concluded that the realization of PMR in commercial HDD would require new transducer designs to solve these problems. We devised a new return pole design which has a stepped-back wing to improve the robustness against in-plane stray fields. The alternative design greatly reduces the concentration of magnetic flux at the edges of return pole. Consequently, the stepped wing structure achieves about twice the robustness of the conventional rectangular return pole. A method was developed to allow external field sensitivity to be carefully checked. The method allows the degraded areas of data to be associated with the exact feature on the head that caused the problem