Theoretical study of nonlinear transition shift in double-layer perpendicular media

Nonlinear transition shift (NLTS) in perpendicular media is studied theoretically. From an analytic expression for demagnetizing field in perpendicular media, the difference between transition shift and NLTS is shown. A finite-element model is used to study the influence of a high permeability write head on the demagnetizing field from the adjacent transition. The results show a negligible effect, unlike longitudinal recording. Using a write model, the relationship between NLTS and write field gradient of perpendicular media shows that NLTS approaches a constant as the gradient increases. We also demonstrate that the measurement of the undifferentiated signal (the direct readback signal from perpendicular media) using the harmonic elimination technique produces misleading results.