Impact of Embedded Co Nanoparticles on Local Magnetic Properties of L1₀-FePt Films

Hard magnetic films with precisely tuned switching fields are of great interest for advanced magnetic microsystems. Here, we report on the specific evolution of semi-hard magnetic properties of L1(0)-FePt films integrating a graded concentration of soft cobalt nanomagnets. These nanocomposites are prepared by the combination of mass selected cluster beam deposition (MS-LECBD) and e-beam evaporation techniques where 8 nm Co nanoparticles (Co-NPs) are embedded with various x atomic concentration up to 50%, into Fe/Pt multilayers. Subsequent annealing allows us to reach the alloy chemical order for the FePt matrix by conserving Co-rich nanometer-sized inclusions. The focus is put on the interplay between the local microstructure and the coercive magnetic field through a combinatorial approach that involves local determinations of composition, magnetization reversal from scanning magneto-optical Kerr effect (MOKE), and element-specific spin and orbital magnetic moments from X-ray magnetic circular dichroism (XMCD) performed at the Co and Fe L-edges of absorption. We show how the nanostructuration changes the magnetic coercivity, and how both Co and Fe effective magnetic spin moments evolve with the composition of the nanocomposite film.