Switching Field Control by Utilizing Ferromagnetic Grain Boundary in Cap Layer for CoPt-Based Full Granular Media

摘要

Investigation of magnetic properties and nanostructure for full granular media with CoPt−Gd ₂ O ₃ granular cap layers (CLs) of various Gd ₂ O ₃ content were conducted. Media with low surface roughness of 0.19 nm is maintained even though Gd ₂ O ₃ content is reduced from 30 to 5 vol%, which is lower than that of media with CoPtCrB continuous CL. The result is supported by surface morphology observed by transmission electron microscopy. According to cross section element analysis, homogeneous nanostructure in the thickness direction with one- text on-one columnar growth of magnetic grain is observed. Reduction of Gd ₂ O ₃ content increases indirect intergranular exchange coupling through CL which results in media with higher nucleation field and lower saturation field than that of media with CoPtCrB continuous CL. Furthermore, at a CL thickness of 6 nm, when Gd ₂ O ₃ content is reduced from 30 to 15 vol%, switching field distribution is reduced from 0.11 to 0.05. These results suggest that the reduction of Gd ₂ O ₃ content of the CoPt−Gd ₂ O ₃ granular CL is effective to reduce the switching field distribution of the full granular media to be lower than that of media with CoPtCrB continuous CL while retaining the extremely smooth media surface.