Coupled granular/continuous medium for thermally stable perpendicular magnetic recording

We studied coupled granular/continuous (CGC) perpendicular media consisting of a continuous multilayer structure and a granular layer. The addition of Co/Pt multilayers decreased the nucleation field from 200 to −1800 Oe and increased the squareness from 0.9 to 1.0. The moment decay at room temperature was significantly reduced from −4.8% to −0.05% per decade. At elevated temperatures, strong exchange coupling between a granular layer and a continuous layer is needed for thermal stability. The exchange-coupled continuous layer reduces thermal demagnetization as it effectively increases the grain size, tightens the grain distribution, and prevents the reversal of individual grains. Magnetic Force Microscope image showed a larger magnetic cluster size for the CGC structure. Compared to the CoCr 18Pt 12 medium, the CGC medium had 2.3 dB higher output. However, the noise for the CGC medium increased with the recording density, while the noise for the CoCr 18Pt 12 medium remained constant from 4 to 15 kfc/mm. Further optimization and noise reduction are still required for future high density recording.