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

Abstract

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 Co82.4Pt17.6− 27.7 vol. % SiO2 granular film deposited on the underlayer grow epitaxially on CoCr grains with columnar structure. As a result, high average Ku⊥ of around 6.7 × 106 erg/cm3 can be obtained. Among the studied BL materials, CoCr-SiO2 shows the highest thermal resistance with root mean square surface roughness (Rq) of around 1.7 nm after heating at around 400 °C. To obtain columnar magnetic grains with critical thickness more than 13 nm, underlayer with Rq more than 1.6 nm is needed.