XPS study of thermal effects on FePt and FePtAg nanoparticles

In this work, the thermal effect on the carbonaceous coating of FePt and FePtAg annealed films is investigated by XPS measurements and a possible mechanism of the particle agglomeration is studied. XPS measurements show that the carbon content of the as-deposited films remains constant either on the surface or the under layers. The carbonaceous coating up-forward movement may subsequently result in a decrease of interparticle spacing of deep layers of the annealed films, and thereby facilitate the nanoparticles coalescing. In addition, the up-movement of carbonaceous coating is found to be a crucial reason of the particle agglomeration during high temperature annealing process. The higher the anneal temperature, the richer carbon content of the film surface. Also with increasing the annealing temperature, the Ag content of FePtAg film surface becomes higher than that of the under layers. The rich Ag content of the surface may be ascribed that the Ag atoms with a low surface energy segregate from the FePt particles and even partially move up to the surface at higher annealing temperatures. For both films, increasing the annealing temperature increases the coercivity.