W riter Flux Closure and Transition Degradation Mechanism in Perpendicular Recording

Perpendicular recording applications use a soft magnetic underlayer (SUL) in the media to enhance the writer field and control its angle. In this paper, a micromagnetic/FEM model (MagPar) was used to investigate the physics of the write process while a nonlinear magnetoelectrical model (Klaassen) helped identify the value of the damping constant under a particular MagPar mesh. The field strength and direction produces a domain under the writer pole in areas where the field opposes the SUL magnetization direction. These areas are located over the next tracks (right or left). This temporary domain changes the response of the SUL by affecting the flux path and increasing the return pole field near the domain. Since the return poles are very large and behave quite linearly, fields in some areas near the return pole edge are bigger due to large writer currents with overshoot and little or no damping from saturated regions. The return pole fields could be large enough to degrade transitions in adjacent tracks particularly when they are applied multiple times to those tracks. The erasure location changes with current polarity and SUL magnetization direction