  We have investigated the core issue of atomic lattices in monodispersed Ni
nanoparticles (NPs) of sizes 3.8 nm to 10.1 nm using detailed analysis of X-ray
diffraction, synchrotron radiation X-ray absorption spectroscopy (XAS) and
magnetization data. This has revealed the very remarkable coexistence of atomic
face-centered cubic (fcc) and hexagonal closed-packed (hcp) lattices in samples
with particle size less than or equal to 6.0 nm with the prevalence of only fcc
phase beyond this. They are also associated with reduced coordination number,
modified electronic structure, and surface atom coordination with ligands.
Magnetization data furthermore reveal coexistence of ferromagnetism and
superparamagnetism at 300 K. Considered to be due to dominant roles of ligands,
they are likely to open up far-reaching implications to their future
applications.

Mesoscale and Nanoscale Physics