Variability in the extent of ordering for individual FePt L1$_{0}$ nanoparticles

L1$_{0 }$ordered phase FePt nanoparticles are of interest as high-density magnetic recording media due to the large uniaxial magnetocrystalline anisotropy,$ K_{u}$ observed in bulk and thin film samples. Similarly high \textit{Ku} values have not yet been achieved for small ($<$10nm) FePt nanoparticles. Mixtures of ordered and disordered nanoparticles are often observed and have been attributed to nucleation barriers for the ordering transformation in individual small nanoparticles. For FePt, $K_{u}$ is known to depend strongly on the extent of long-range chemical order. In this work we report on the variability of the extent of order amongst ordered L1$_{0}$ FePt particles. Well-isolated, small FePt nanoparticles were prepared from discontinuous FePt films, using ultra high vacuum dc magnetron sputtering. A Tecnai F30 analytical transmission electron microscope was used to characterize the FePt nanoparticles. Convergent beam electron diffraction patterns from individual nanoparticles were compared to multislice simulations to determine the extent of order of single nanoparticles.