Synthesis, Characterization and Hard Ferromagnetism in FePt/ZnO Nanocomposites with Ultra-Small Size

摘要

Multi-component hybrid nanostructures containing two nanoscaled components of FePt and ZnO were successfully fabricated through seed mediated growth. The preformed FePt nanoparticles, which were fabricated either by the reduction of ${hbox{Pt}}{({{rm acac}})_{2}}$ and the decomposition of ${rm Fe(CO)}_{5}$ or by simultaneous chemical reduction of ${hbox{Pt}}{({{rm acac}})_{2}}$ and ${hbox{Fe}}{({{rm acac}})_3}$ by 1,2-hexadecanediol at high temperature, work as the hetero-nucleation seeds for the preparation of hybrid nanostructures. The end products can be either FePt@ZnO core/shell nanoparticle assembly or FePt/ZnO nanocomposites, depending on the seeding particle size. If the seeding particle size is larger than 3.5 nm, core/shell nanoparticle assembly was formed, while if the seeding particle is smaller than 2 nm, FePt/ZnO nanocomposites were formed. For the FePt@ZnO core/shell, HRTEM showed a quasi-epitaxial growth between the FePt core and the ZnO shell. The ZnO shell was highly deformed. The core/shell nanoparticle assembly exhibits both semiconducting and magnetic properties which is superparamagnetic at room temperature. For the nanocomposites, the as-synthesized ultra-small 1.9 nm ${{hbox{FePt}}_3}$ nanoparticles are superparamagnetic. After embedding into the ZnO matrix, those superparamagnetic nanoparticles become magnetically hard with coercivity field of 650 Oe at room temperature. First-principles calculations indicate a giant interfacial anisotropic energy, induced by the strong spin-orbit interaction between Pt and O at interface, leading to room-temperature permanent ferromagnetism- The findings shed light on research for new material designs with giant interfacial anisotropy for various applications.