Lattice expansion in nonoxidized FePt nanoparticles: X-ray absorption measurements

Wet-chemically synthesized FePt nanoparticles were structurally characterized not only in the as-prepared state but also after the removal of organic ligands and reduction in Fe oxides by a soft in situ hydrogen plasma treatment. By the analyses of the extended x-ray absorption fine structures at the Pt L₃ absorption edge, we found an enhanced lattice constant with respect to the bulk material for the oxide-free nanoparticles with clean surfaces. This shows that there exists a lattice expansion in FePt nanoparticles, which is an intrinsic property of the particles, and neither caused by Fe oxides at the surface nor by the organic ligands surrounding the nanoparticles in the as-prepared state. In addition, a first evidence of an inhomogeneous composition within the nanoparticles is given.