Controlled co-deposition of FePt nanoparticles embedded in MgO: a detailed investigation of structure and electronic and magnetic properties

Films of FePt nanoparticles (NP) embedded in MgO were obtained by controlled co-deposition of FePt NP pre-formed by a gas aggregation source and of Mg evaporated in Oxygen atmosphere. Control over the deposition rate permitted to pass from FePt@MgO core-shell morphology to a film of MgO embedding FePt NP. Transmission Electron Microscopy (TEM) and High Resolution-TEM revealed the core-shell structure of the NP, with FePt core (of average diameter <d>= 4.75 nm) presenting a multi-twinned icosahedral structure, and MgO partially in crystalline form. The functional effect of MgO shell in shielding the FePt core from external oxidation was shown with XPS. Upon controlled annealing transition from A1 to L10 ordering could be obtained, with structural and morphological re-arrangement. The magnetic hysteresis loops obtained from Alternating Gradient Field Magnetometry at room temperatures show a “wasp-waist” shape, with small values of coercive field (Hc=300-1400 Oe), decreasing at increasing amount of co-deposited MgO.