Effect of Diffusion Stopper Layer on Surface Morphology of MgO Underlayer of L 1₀-FePt Granular Layer for HAMR

Media for the heat assisted magnetic recording generally consist of four blocked layers with diffrent functions such as a soft magnetic underlayer (SUL), a heat sink layer (HSL: an orientation inductive layer, an orientation control layer (OCL), and Heat transition layer), a thermal insulating layer (TIL), and a recording layer. From the media flatness point of view, the problem is that network-shaped upheaval and nodule structures with a height of several nanometers appear on the TIL surface. By investigating the mechanism of formation of morphorogy for TIL and considering flattening methods, it was found that 1) both network-shaped upheaval and nodule structures were essencially caused by diffusion of elements constituting the amorphous SUL and underlying layers through the grain boundaries in the bcc-OCL and HSL during high temperature deposition, and 2) the thickness of a diffusion stopper layer needed to suppress the formation of nodules is estimated to be 8 nm.