Grain Topography in Perpendicular Thin-Film Media and Impact of Possible Surface Anisotropy

In this paper, we present a combined transmission electron microscopy study and micromagnetic modeling investigation of current granular-continuous-composite (CGC) perpendicular thin-film media. Our transmission electron microscopy-EELS elemental analysis on CoCrPt-TiO_x layers found evident Cr segregation to the grain boundaries as well as in the middle of a grain where Co and Pt appears to be deficient. Similar localized Co and Pt deficiency is also found in CoCrPt-SiO_x media, however, Cr segregation is much less evident. STEM-HAADF analysis reveals that the apparent non-uniform composition is the result of a ldquocavity-likerdquo topography of the magnetic grains. It is argued that the ldquocavityrdquo grain topography significantly enhances the grain boundary surface area. Micromagnetic modeling investigation was conducted to study the impact of possible surface anisotropy to the corresponding grain switching field. A systematic numerical analysis is presented.