Magnetic Properties of Core-Shell FePt(CFx) Nanocluster Films*

A core-shell FePt nanocluster system, in which the magnetic core is coated with a layer of a non-magnetic shell, is of great interest for study and tailoring magnetic properties such as magnetization, anisotropy and interparticle interactions. In this study core-shell FePt clusters with fluorocarbon (CF$_{x})$ shell are synthesized by a cluster-deposition system with gas-aggregation technique. Monodispersed core-shell structure FePt(CF$_{x}) \quad _{ }$clusters are produced with average diameter of 4 nm and with a uniform size distribution. High magnetic anisotropy L1$_{0}$ phase FePt(CF$_{x})$ cluster-assembled films were realized via post-deposition annealing. Crystal structure and nanostructure of the films were studied by XRD and TEM. Magnetic properties of the films were measured at temperatures between 10 K and 300 K. Results show that the FePt L1$_{0}$ ordering temperature is decreased by addition of CF$_{x}$.$_{ }$Interparticle interactions were studied by measuring the $\Delta $M curves. Thermal stability of the films was also studied by fitting the temperature dependence of coercivity with the Sharrock formula. Our results indicate that the magnetic properties of the core-shell FePt(CF$_{x})$ nanoclusters are tunable for various nanomagnetic applications.