Self – organized FePt nanoparticles in MgO synthesized by ion-implantation and high-temperature annealing

The formation of FePt nanoparticles (NPs) in MgO crystals after sequential ion implantation and high temperature annealing has been observed and analyzed by means of structural and magnetic characterization. Self-organized FePt NPs were synthesized by an implantation of Fe and Pt ions to the depth of ~90 nm under the MgO surface and post-implantation annealing at 800°C. Structural and magnetic properties of produced NPs have been investigated using x-ray diffraction (XRD), magetometry measurements, and theoretical calculations of ion distributions and magnetization behavior. FePt NPs represent preferential orientation to MgO matrix with a relation of FePt[001]||MgO[001] and FePt[110]||MgO[100]. Using the Preisach formalism of magnetization, the spontaneous moment of FePt was estimated to be in a range ~600 – 3500 mu_B depending on the ion fluences, and corresponds to the NP’s size of 3.5 – 20 nm obtained from XRD study. Several structural phases of FePt NPs, such as, FePt3, disordered fcc and ordered L10 phase were observed in different samples. The evident tendency of L10 ordering after high fluence ion implantation and high-temperature annealing is demonstrated. Optimized regimes of implantation and annealing processes are reported in addition to physical properties of FePt NPs.