Reduction of Crystalline High-B_s Soft Underlayer Thickness for Obtaining Low Medium Noise in Epitaxial Perpendicular Recording Media

Abstract

  CoPt-TiO₂ granular-type media with extremely thin Ru intermediate layer of 1.9 nm were prepared on a highly oriented high-B_s FeCo soft underlayer (SUL) pinned by an IrMn antiferromagnetic layer. The FeCo SUL thickness was changed to reduce the medium noise. CoPt clusters surrounded by relatively wide boundaries were formed for the medium with the FeCo SUL of 40 nm. As the FeCo SUL thickness was decreased, the cluster size and the number of the CoPt grains was decreased. The CoPt grains were mostly isolated for the medium with the FeCo SUL of 20 nm. The average cluster size was 7.4 nm in diameter. The recording performance was evaluated by using a single-pole-type head. This new-designed medium has high writability and large reproduced output compared to an old-designed medium with an amorphous SUL of 80 nm and an intermediate layer of 30 nm. As the FeCo SUL thickness was decreased down to 10 nm, the medium noise was greatly decreased at the recording densities of more than 200 kfci. As a result, the S/N was increased as the FeCo SUL thickness was decreased down to 10 nm at the recording densities of more than 200 kfci. The film thickness of the FeCo SUL could be reduced down to 10-20 nm.