Magnetization Reversal in Exchange-Coupled Composite Media-Experiment and Modeling

In this work, we report on a study of magnetization reversal in a number of different configurations of exchange-coupled composite (ECC) media. Experimental measurements and atomistic modeling of the ECC samples have provided information about the optimization of properties of this type of media that may be achieved through tuning of medium parameters such as the layer thicknesses, anisotropy and exchange coupling, both in-plane and between the layers. Focus has also been directed on the role of the intrinsic demagnetizing field H-D and how it affects reversal. We find that the introduction of oxygen to exchange decouple the grains in the plane also reduces the interlayer exchange coupling for a low M-s soft layer. The demagnetizing field from the hard layer causes the soft layer moment to lie in-plane reducing the squareness. Decreasing the level of oxygen results in in-plane exchange coupling and hence sheared hysteresis loops. The highest squareness values were found for samples with thin soft layers and where M-s (hard) approximate to M-s (soft). It is also a requirement for the anisotropy of the soft layer to be sufficient for the moment to remain perpendicular.