Spin and orbital magnetic moments in carbon-encapsulated Fe50 Pt50 nanoparticles

X-ray absorption and magnetic circular dichroism spectra of as-deposited and postannealed Fe50 Pt50 /C granular multilayers were measured at both the Fe and Pt L2,3 edges. We demonstrate that the partial L 10 ordering of the FePt nanoparticles induced by thermal annealing results in an increase of the effective spin magnetic moments by 200% at the Fe site and by 65% at the Pt site, while the orbital moments are enhanced, in comparison with the as-deposited particles, by 325% and 15% at the Fe and Pt sites. In addition, a change in the x-ray absorption near-edge structure at the C K edge gives evidence for a preferential graphitization of the carbon matrix, which provides a better protection of the nanoparticles against external degradation as required for the application of these particles in future magnetic devices.