  We report a successful synthesis of monodisperse L10-FePt nanocrystals which
are not only superior in magnetism but also easy to handle through being
dispersible in solvents. Thanks to a thick SiO2-coating, the thermal treatment
needed to form the L10 structure can be done even at 900 oC without inducing
coalescence and coarsening. The protecting shell was thereafter removed in a
specific way that enabled us to recover the L10-FePt nanocrystals in a
water-dispersion. The SiO2-coated nanocrystals show a high coercivity of 18.5
kOe at room temperature in spite of their core size of only 6.5 nm in diameter,
and the hysteresis loop of the water-dispersed nanocrystals, which were frozen
under an external field, was almost rectangular indicating that their magnetic
and structural orientation could be attained.
