Metal-oxide buffer layer for maintaining topological bumpy surface underlayer of columnar CoPt-SiO₂ granular media deposited at high substrate temperature

Investigation of surface topography for underlayer with various metal-oxide buffer layer (BL) materials for magnetic recording media is reported. In the previous study, it was found out that the application of a high substrate temperature deposition process to a granular layer with a magnetic alloy and a non-magnetic oxide material, such as CoPtCr-SiO₂, will induce lamellar and spherical grains due to the flattening of the underlayer bumpy surface by recrystallization. By depositing a CoCr-SiO₂ BL onto the Ru underlayer at room temperature, CoCr grains grow epitaxially onto Ru grains and SiO₂ segregates to Ru boundaries. Consequently, bumpy surface morphology of the underlayer is maintained even though heated to around 400°C before depositing the granular layer. Therefore, CoPt magnetic grains of a Co_82.4Pt_17.6- 27.7 vol. % SiO₂ granular film deposited on the underlayer grow epitaxially on CoCr grains with columnar structure. As a result, high average K_u of around 6.7×10⁶erg/cm³ can be obtained. Among the studied BL materials, CoCr-SiO₂ shows the highest thermal resistance with root mean square surface roughness (R_q) of around 1.7nm after heating at around 400°C. To obtain columnar magnetic grains with critical thickness more than 13nm, underlayer with R_q more than 1.6nm is needed.