Interface effect on the magnetic anisotropy of CoPt clusters

We study the magnetic anisotropy of CoPt clusters produced by condensation of a stoichiometric vapor with an inert gas (helium) and co-deposited with various matrices. From electron transmission microscopy we show that the clusters have a mean diameter of about 2 nm with a narrow size distribution and present the FCC A1 disordered phase. At high temperature, the clusters display a superparamagnetic behavior. The transition to the blocked state enables us to determine the clusters magnetic anisotropy energy (MAE). From a careful analysis, we show in the one hand that CoPt clusters present a higher volume and intrinsic surface MAE than pure Co ones. In the other hand, the presence of platinum at the interface in CoPt clusters decreases the strong interfacial exchange anisotropy observed for Co clusters embedded in MgO