Dresden 2009 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 31: Magnetic Particles and Clusters I

MA 31.5: Vortrag

Donnerstag, 26. März 2009, 11:15–11:30, HSZ 401

Near-surface strain in FePt nanoparticles — •Ulrich Wiesenhütter, Darius Pohl, Elias Mohn, Ludwig Schultz, and Bernd Rellinghaus — IFW Dresden, P.O. Box 270116, D-01171 Dresden, Germany

The structure of single crystalline, decahedral, and icosahedral FePt nanoparticles is systematically investigated by aberration-corrected HRTEM. Particular attention is paid to near-surface lattice strains which are indicative of a possible Pt segregation towards the surface. Statistical HRTEM investigations reveal that in icosahedral FePt nanoparticles, an average expansion of the crystal lattice of 9.5% is observed within the outermost atomic layers. In order to check if this reproducibly observed near-surface strain is merely a property of the bare particle surface or if it is rather due to a segregation of Pt towards the surface, the effect of electron beam-induced sintering of adjacent particles on the lattice expansion is studied. It is found that the near-surface strain survives the inter-particle coalescence and remains located at the former surface position which in deed corroborates the picture of a local enrichment of Pt at the particle surface. Similar lattice expansions are observed in decahedral and truncated octahedral FePt nanoparticles. In single crystalline particles however, the magnitude of the lattice dilation is found to be smaller as compared to the icosahedra. This indicates that in the latter, the observed near-surface lattice dilation may be enhanced due to strains inherent to the particle structure. The effect of the particle size on the magnitude of the strain will be discussed.