Long-Range Order Parameter of Oriented L1₀-FePt Nanoparticles Determined by Electron Diffraction

Two-dimensionally dispersed L₀-FePt nanoparticles as small as 12 nm with orientation was fabricated by electron-beam evaporation and post-annealing at 873 K. After a prolonged annealing at 873 K for 86.4 ks, the increase of coercivity was almost saturated and coercivity reached 434 kAm ^-1 at 300 K, which is very small compared to recent reports on FePt nanoparticles with sizes larger than 20 nm. Long-range order parameter of the fabricated nanoparticles was determined by electron diffraction at 200 kV taking the multiple scattering into consideration. Obtained order parameter remained 0.55 ± 0.02 for the nanoparticles with an axial ratio c/a of 0.961 ± 0.003. The low degree of order is thought to be responsible for the small coercivity. Effect of Debye-Waller factor on the order parameter was discussed.