Graded media: Optimization and energy barriers (invited) Available to Purchase

It is shown that columns of perpendicular recording media with a spatially varying anisotropy $K(x)$ offer improved characteristics in comparison to homogeneous $K=const$ media. With a quadratically varying $K(x)$ the ratio $ξ$ of the energy barrier to the coercive field can exceed the homogeneous value by a factor of about 3. An improved architecture is suggested, which brings $ξ$ even closer to its theoretical maximum of 4. This is achieved by adding a hard capping layer, which enhances the pinning properties of the hard end of the column. Next, the field dependence of the energy barrier $Eb(H)$ is determined and found to be linear. A simple explanation is provided for this linear dependence. Finally, the reversal pathway is analyzed in detail and found that in these graded media partially formed domain walls are stable. They move into the column gradually, leading to a linear decrease of the magnetization. An analytical theory is constructed to account for this unconventional reversal pathway.