Multiply Twinned Structures in Gas-Phase Sintered Stoichiometric FePt Nanoparticles

Abstract

Stoichiometric FePt nanoparticles with sizes in the range 3 - 6 nm were prepared in the gas-phase and thermally sintered prior to deposition. Whereas unsintered particles exhibit irregular shapes and a low degree of crystallinity, the majority of the sintered particles are multiply twinned and have predominantly icosahedral structure. There is no indication for the occurance of L1₀ ordering in the gas-phase sintered particles, although previous post-deposition annealing experiments of unsintered particles had shown the occurrence of partial formation of the L1₀ FePt intermetallic phase. On the other hand, analysis of the structural data obtained from (high resolution) electron microscopy shows that the relative amount of icosahedral particles increases with increasing sintering temperature. This result is discussed on the basis of a structure model of an irregular icosahedron, which is built up from distorted tetrahedral building blocks. The distortion in each tetrahedron is in accordance with the tetragonally compressed unit cell of the L1₀-phase.