Magnetic Interaction Between Recording Layer and Soft Underlayer in Granular-Type Perpendicular Magnetic Recording Media With Thin Intermediate Layer

CoPt-TiO₂ granular-type media with extremely thin Ru intermediate layer were prepared on a highly oriented high-B_s FeCo soft underlayer (SUL). The minimum Ru layer thickness for obtaining the squareness ratio (SQ) more than 0.99 was 1.6 nm. The H_c of the recording layer and the H_ch (H_c in the hard axis direction) of the SUL oscillated as a function of Ru intermediate layer thickness. The oscillation period was 0.5-0.8 nm. A medium with Ru intermediate layers of larger H_c (peak position) showed smaller H_ch of the SUL than that of valley position. Strong magnetic interlayer interaction deteriorates the magnetic properties of the recording layer and the SUL. The recording performance was measured for the media with different magnetic interlayer interaction by using a single-pole-type (SPT) head. The S/N for the medium with the strong interlayer interaction largely decreased compared with that for the medium with weak interlayer interaction. This indicates that magnetic interaction between the recording layer and the SUL can be controlled by choosing an appropriate film thickness of Ru intermediate layer.