Nonlinearities and noise in perpendicular dibit recording

Nonlinearities and medium noise in perpendicular recording are studied by simulating the dibit recording process. Strong nonlinear bit shift is observed: the second transition shifts away from the first transition. Transition noise on the second transition decreases with a reduction of the bit separation due to a shortening of the second transition. To a very good approximation, even when the bit separation is very small, medium fluctuations are determined only by the cross track average magnetization. The cross track correlation of nonexchange coupled granular media with sufficiently low magnetization is roughly one grain diameter