Magnetization processes in exchange-coupled double-layer films with in-plane and perpendicular anisotropy

Magnetic curves in exchange-coupled double layers (ECDL) with planar and perpendicular anisotropies are experimentally determined by Faraday measurements. In order to interpret unusual hysteresis loops, we have extended the model of Kobayashi applied to our systems. We show that all possible ECDL films can be grouped in two bilayer types. In the first one, the sublattice magnetization of transition metal (TM) and rare earth (RE) of each layer rotates coherently with external magnetic field and we call this Type P (parallel). In the second type, the TM (resp. RE) magnetization of the first-layer rotates in the opposite direction to the corresponding magnetization of the second layer and we call this Type A (antiparallel). By changing the film composition or its temperature, we can obtain a transition from one type to the other with also a change of the magnitude of the interface energy which can be measured experimentally.