MR recording media: microstructure and magnetic properties

To achieve high recording areal density, it is required that future MR media have high coercivity (H_c), high coercive and remanent squareness (S^* and S), low media noise and narrow track recording performance. The microstructure, which strongly affects magnetic properties, should be fully controlled in media fabrication process. The microstructural characteristics like grain size, grain separation, orientation, lattice mismatch, second phases, and stacking faults can affect intergranular magnetic coupling and media noise. The composition of ternary and quaternary cobalt alloy systems, e.g. CoCrTa, CoCrPt, and CoCrPtTa, has significant effects on magnetic performances. The underlayer design, e.g. Cr, CrV_x, and CrTi_x, can affect lattice mismatch, stacking fault density, and other microstructural features. Stress, shadowing, preferred orientation, and c-axis alignment are four mechanisms which control orientation ratio (OR). Oriented medium has more stress-induced noise than isotropic medium has. Thin film medium with bicrystal structure has 5 dB better SNR than non-bicrystal medium. Ultra clean sputtering process (UC-process) can enhance coercivity and reduce noise. For GMR recording media, it requires Hc>3000 Oe and M_rt <0.5 memu/cm². Media with CoCrPtTa, and CoSm/Cr design will be compared for areal density upto 10 Gb/in². Mechanisms of high coercive force and low noise in MR media are reviewed in connection with microstructure and magnetic properties