Magnetic in-plane components of FePt nanogranular film on polycrystalline MgO underlayer for heat-assisted magnetic recording media

A systematic study is conducted on the effect of MgO substrate/underlayer in terms of the surface roughness, grain boundary, and crystallographic texture on the magnetic in-plane components (medium noise) of the FePt-based heat-assisted magnetic recording (HAMR) media. Cross-sectional transmission electron microscope observations revealed that good (001) texture can be developed in FePt nanogranular films even when they are grow on a rough surface of a single crystal-MgO (001) substrate or across the grain boundaries of a (001)-textured polycrystalline-MgO underlayer. The misoriented FePt grains with magnetic easy axes (c-axes) tilted away from the film normal direction mainly originate from their epitaxial growth on the initially misoriented MgO underlayer grains. Micromagnetic simulation results revealed that the FePt grains with misorientation angle larger than ∼20° are attributed to the detected magnetic in-plane components. Based on these experimental results, we discuss how to improve the (001) texture of the polycrystalline underlayer as well as to develop FePt-based HAMR media with enhanced signal-to-noise ratio.