Transition position and amplitude fluctuation noise model for longitudinal thin film media

Integrated noise power in longitudinal thin film media increases with transition density. This phenomenon has been attributed to the medium noise being concentrated in the transition regions with the areas between transitions being relatively quiet. This paper presents a transition noise model for square wave recording on longitudinal thin film media considering two sources of noise: phase shift (or transition jitter) and amplitude. The transition jitter noise is due to random fluctuations in the transition positions, while the amplitude noise is due to random shape fluctuations in the transitions. It is assumed that random medium coercivity fluctuations cause transition position fluctuations. The random transition shape fluctuations are modeled by allowing the transition parameter to be a random variable. These transition parameter variations are assumed to be caused by random medium magnetization fluctuations. Each written transition produces a demagnetizing field that affects the positions and shapes of subsequent transitions. The properties of both types of noise are discussed.