Writer flux closure, transition degradation mechanism, and frequency dependent side track erasure in perpendicular recording

Abstract

In this second part of the work, the MAGPAR micromagnetic/finite element model was reused to investigate the physics of the write and erase processes in perpendicular recording. The damping constant needed in the Landav–Lifshitz–Gilbert equation was found by applying the Klaassen nonlinear eddy current damped model and set to be 0.1. Previous work highlighted the fact that domains were formed in the soft magnetic underlayer (SUL) under the writer pole in regions where the field opposes the SUL magnetization direction. The domains participate in flux closure and help a more linear response out of the return pole that enhanced fields with an overshoot and opposite polarity relative to the main pole field. These return pole fields could cause adjacent track erasure and MAGPAR was used to study the physics behind it. Particular attention was given to the analysis of frequency or time dependent effects caused by flux delays from the slow moving SUL domains (between the main and return poles). In contrast, fast writing near the main pole was the result of nonlinear flux driven by efficient writers and large currents with overshoot. The writer and SUL used in this work caused a 550ps delay. The delay was analyzed over a range of frequencies between 50 and 1000MHz (i.e., linear densities). The numerical and experimental results showed that this delay played an important role in the erasure process. The strength and location of the return pole erasure fields were affected by the current frequency (i.e., the delay). In particular, the erasure level was substantially reduced at the middle frequencies due to the time match between the current pulses and the domain propagation that influenced flux closure. Return pole field strength increased again at higher frequencies.