Simulations of magnetic recording in coupled granular/continuous perpendicular media with random pinning sites

Magnetic recording in coupled granular/continuous (CGC) media is simulated using a three-dimensional (3-D) micromagnetic model. Pinning sites are introduced via a random anisotropy constant K_u, which follows a log-normal distribution with a mean value u> of 1 × 10⁶ (ergs/cc) and a standard deviation σ_Ku (ergs/cc). For a range σ_Ku, we vary the thickness of the continuous layer c and the thickness of the granular layer g, while maintaining a constant media thickness. We analyze simulated tracks to produce SNR data for a range of c and σ_Ku. We find that increasing σ_Ku reduces signal and increases bit transition irregularity and noise, which is then reduced via a mechanism driven by domain wall (DW) energy minimization by increasing c. Thus, we find that previous results hold in a more realistic CGC media model that contains random irregularity. In order to explain the observed effects, we identify three regimes of behavior that depend on the energy of domain wall relative to the pinning energy barriers provided by the granular layer.