Magnetic Properties and Magnetization Reversal of Thin Films and Nanodots Consisting of Exchange-Coupled Composite Co/Pd Multi-Layer and Co Layer with Orthogonal Anisotropies

We report on the fabrication and measurement of the switching characteristics of Co/Pd multi-layer thin films and nanodots. We used the method of anomalous Hall effect to obtain the hysteresis curves of both in-plane and out-of-plane magnetization. While Co/Pd thin film is found to switch by nucleation followed by domain propagation, Co/Pd nanodots switch by quasi-coherent rotation. We found that the coercivity of Co/Pd increases by a power law with respect to decreasing dots size. The coercivity can be reduced by exchange coupling the Co/Pd multi-layer to a 2 nm thick Co layer. Adding a Cu spacer layer between the Co/Pd multi-layer and Co layer provides a reliable way to modulate the strength of exchange coupling and tailoring the coercivity. As the Cu spacer becomes thicker, the coercivity increases. The exchange energy density is estimated to be 14.6 Merg/cm³ and the exchange constant, 2.92 erg/cm². The dependence of saturation field and coercivity on the thickness of the Cu spacer layer is fitted to the same empirical model and the exchange interaction is found to decay exponentially with distance. The exchange-coupled samples switch by quasi-domain propagation for both thin films and nanodots.