Magnetically Superior and Easy to Handle L10-FePt Nanocrystals

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.