Magnetic hardness of graded interface exchange spring L10-FePt films with Co nanoinclusions

Abstract

Hard-magnetic films with precisely tuned switching fields are of great interest for microsystems, when both the manipulation and the stability of the magnetization are brought into play. Here, we report on the exchange spring mechanism developed in compositionally-graded nanocomposite films of FePt integrating x per cent of Co nanoclusters (x varying from 0 to 50%), made from a combination of mass-selected cluster beam deposition (MS-LECBD) and e-beam evaporation. This technique offers a precise control over the nanoinclusion size (8 nm diameter) and its volume fraction in the host FePt matrix. The focus is put on the interplay between the local microstructure and the magnetic coercivity through a combinatorial approach that involves local determinations of composition, magnetization reversal from scanning magneto-optical Kerr effect and element-specific spin and orbital magnetic moments from X-ray magnetic circular dichroism. We show that Co-rich inclusions allow a fine tuning of the coercivity and that a consequent increase of effective magnetic spin moment at the Co edge is obtained in our system