Micromagnetic modelling of composite perpendicular media

A combination of standard micromagnetic simulations, numerical calculation of energy barriers, and global optimization methods is used to predict the optimum parameters for composite perpendicular media. An exchange spring media consisting of a soft layer grown columnar on top of a hard magnetic layer is used. Micromagnetic simulations show that a soft layer thickness of 10 nm decreases the coercive field already by a factor of 3.2. The energy barrier of a grain is calculated taking into account the demagnetizing fields in the hard layer and in the soft layer as well as the exchange field between neighboring grains. A global optimization method was used to determine the media parameters that maximize the energy barrier under the constraint of a fixed saturation field (given maximum write field).