Nonlinearities in thin-film media and their impact on data recovery

Nonlinear distortion in thin-film media is studied based on dibit magnetization patterns created from a micromagnetic computer simulation. It is observed that the demagnetization field from previously written transitions causes large nonlinear distortions by inducing position shifts of later transitions. Even after the nonlinearities due to such position shifts are removed, significant residual nonlinearities were observed in all media considered. While total nonlinear distortion is larger with films with sharper transitions, the residual nonlinear distortion after the removal of position shifts is larger in the exchange coupled film than the uncoupled film. An attempt was also made to quantify the nonlinear effects on the performance of two competing modulation codes, namely, the rate 8/9 (0,k) code and the rate 2/3 (1,7) code. The results suggest that, despite the higher rate loss, the (1,7) code remains highly competitive against the more recently introduced (0,k) code, as the increased minimum transition spacing provides considerable immunity against nonlinear distortion