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

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.