Magnetic property modification of L10 FePt thin films by interfacial diffusion of Cu and Au overlayers

Both Cu-FePt and Au-FePt bilayer thin films were prepared by depositing a Cu or An cap layer on a fully ordered FePt film at room temperature. A heat treatment at 300degreesC-600degreesC was then applied to the bilayer samples to facilitate interfacial diffusion. For the Cu-FePt system, extensive volume diffusion between L1(0) FePt and Cu layers occurred as the samples were annealed at 500degreesC and higher temperatures, forming a ternary Fe-Pt-Cu phase with face centered cubic (fcc) structure. As the annealing temperature was lowered to 400degreesC, the diffusion was dominated by grain-boundary mechanism. The best coercivity thus obtained was 14.0 kOe, being 22% larger than that of FePt film without cap layer. For the Au-FePt system, grain-boundary diffusion remains dominant even the annealing temperature is as high as 600degreesC. In both Cu-FePt and Au-FePt bilayer systems, grain-boundary diffusion was found to successfully enhance the coercivity. The AM plot data indicate that incoherent rotation among magnetic grains can be responsible for the high coercivity.