Microstructure and thermal stability of advanced longitudinal media

Thermal stability will ultimately limit the maximum areal density achievable with conventional longitudinal recording. The key aspects of the media microstructure contributing to thermal stability are the grain size and grain size distribution, alloy composition, alloy segregation, lattice defects and strain. Grain size distributions are created by the random nucleation processes occurring during media deposition. For media on glass substrates, c-axis in-plane preferred orientation can be achieved with either Co (112~0) or (101~0) planes parallel to the substrate surface. Improved squareness, S, is observed with the (112~0) orientation due to stronger crystallographic texture, however, larger changes in coercivity with decreasing magnetic layer thickness are observed compared to (101~0). Continued increases in areal density will require tighter grain size distributions and improved microstructural control of very thin magnetic layers.