(A) study on thermally stable ultra-high density granular type

Abstract

The perpendicular recording films of CoCrPt ternary grains isolated by various oxides are the most widely used recording layer. Small grain size is a very critical requirement for high density recording. Grain core size of $CoCrPt-SiO_2$ media could be reduced by grain refinement in the Ru(Cr) underlayer with oxygen reactive sputtering. As grain size decreases, thermal stability of the present $CoCrPt-SiO_2$ media becomes a more critical issue because the energy barrier to the spontaneous magnetization reversal depends on particle volume and anisotropy constant. It can be relieved by using higher $K_u$ materials than conventional $CoCrPt-SiO_2$. However, considering the write field of the present writing heads, there are not many choices in media material selection. In this study, stacked structure of different magnetic materials in $K_u$ was proposed in order to overcome this dilemma. In the first part, exchange decoupling of $CoCrPt-SiO_2$ film is discussed. $Al_2O_3$ and MgO were examined as grain boundary segregation materials besides $SiO_2$. $SiO_2$ incorporated CoCrPt layers had higher coercivity and squareness than those of MgO and $Al_2O_3$ cases. This would be attributed to the well-isolated CoCrPt grains by $SiO_2$. The different behaviors are thought to be associated with different kinetics of diffusion for the different oxide elements rather than thermodynamic energy. The effect of Ru layer morphology on the physical grain separation in recording layer is investigated in order to lessen the intergranular exchange coupling. A two-step Ru underlayer was employed for both good texture development and better grain isolation. Narrow c-axis dispersion is attributed to the bottom Ru layer deposited at low pressure, and physically isolated top Ru grains are induced by high pressure deposition. When CoCrPt layers are deposited on the top of the well isolated Ru grains, there is one to one grain relationship between Ru and CoCrPt grains, therefore CoC...