Recording Performance Analysis of Perpendicular Magnetic Recording Media With Anisotropy Graded Oxide and Cap Layers

We have experimentally and analytically studied the writeability and recording characteristics of perpendicular magnetic recording media in which the anisotropy (K_u) of the granular oxides and the magnetization (M_s) and lateral exchange coupling (A_ex) of the cap layer were varied. The analytical results are obtained with a 9-spin model, which consists of 3 grains with 3 layers each, representing dual oxide media with a capping layer. The 9-spin model estimates bit error rate (BER) using an error-pattern-correcting code (EPCC) based iterative channel model. The experimental results qualitatively agree well with the analytical results of the 9-spin model. High K_u gradient oxides and high M_s cap layer improve writeability and BER, whereas high A_ex in the cap layer degrades switching field distribution and off-track capability. Media switching field and switching field distribution strongly depend on spatial distribution of the external field. Both experimental and analytical results indicate that an appropriate design of K_u graded media with an optimum cap layer can effectively reduce jitter and switching field distribution for given head fields, resulting in higher recording density.