Dynamics of transition writing in antiferromagnetically coupled magnetic recording media

Abstract

Antiferromagnetically coupled (AFC) media are an important extension of longitudinal magnetic recording to high bit densities while maintaining thermal stability. In this paper micromagnetic calculations examine the writing of isolated transitions in the top and bottom layers of a double layer AFC medium as a function of bottom layer thickness and interfacial exchange coupling at pico second time resolution. It is demonstrated that there can be a significant difference between the switching time of the top layer and the time required for completing the bottom layer magnetization processes during writing. The AFC media are modeled as two granular epitaxial films with grain diameters of 8 nm and grain boundary thickness of 1 nm. The thickness of the top layer is kept fixed at 15 nm while the bottom layer thickness is varied from 1 nm to 9 nm. The interfacial AF coupling between top and bottom layer is studied in the range of 0.1 to 0.5 erg/cm2. The dynamic Langevin equations are solved for these films at a temperature of 350 K. A magnetic write head flying at 14 nm is used to write isolated transitions with a record current rise time of 100 ps (zero-to-peak).