Abstract:
Chemically ordered FePt nanoparticles were obtained by high temperature annealing a mixture of
FePt particles with NaCl. After the NaCl was removed with de-ionized water, the transformed FePt
nanoparticles were redispersed in cyclohexanone. X-ray diffraction patterns clearly show the L10
phase. Scherrer analysis indicates that the average particle size is about 8 nm, which is close to the
transmission electron microscopy TEM statistical results. The coercivity ranges from 16 kOe to
more than 34 kOe from room temperature down to 10 K. High resolution TEM images reveal that
most of the FePt particles were fully transformed into the L10 phase, except for a small fraction of
particles which were partially chemically ordered. Nano-energy dispersive spectroscopy
measurements on the individual particles show that the composition of the fully transformed
particles is close to 50/ 50, while the composition of the partially transformed particles is far from
equiatomic. TEM images and electron diffraction patterns indicate c-axis alignment for a monolayer
of L10 FePt particles formed by drying a dilute dispersion on copper grids under a magnetic field.
For thick samples dried under a magnetic field, the degree of easy axis alignment is not as high as
predicted due to strong interactions between particles.
