Magnetically superior and easy to handle L 1 0 -FePt nanocrystals

We report synthesis of monodisperse L 1 0 -FePt nanocrystals that are not only superior in magnetism but also easy to handle through being dispersible in solvents. Thanks to a thick Si O 2 coating, the thermal treatment needed to form the L 1 0 structure can be done even at 900 ° C without inducing coalescence and coarsening. The protecting shell was thereafter removed in a specific way that enabled us to recover the L 1 0 -FePt nanocrystals in a water dispersion. The Si O 2 -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.