Preparation of monodisperse and highly coercive L1₀-FePt nanoparticles dispersible in nonpolar organic solvents

A method to prepare monodisperse and highly coercive L1₀-FePt nanoparticles that are dispersible in nonpolar organic solvents such as toluene, chloroform, and hexane was developed. By vigorously stirring the SiO ₂-coated L1₀-FePt nanoparticles synthesized by the "SiO₂-nanoreactor" method (Appl. Phys. Lett. 2005, 87, 032503) in a mixture of an aqueous NaOH solution, chloroform, and hexadecyltrimethlyammonium bromide, the SiO₂ coating was dissolved off, and bare FePt nanoparticles could be extracted to the chloroform phase without degrading their magnetic properties. These particles showed a tendency to form a close-packed lattice on slow drying of the chloroform-based solution. The present success may promote the practical application to ultra-high-density magnetic recording and also may open the door to providing these particles with new physical and/or chemical functions.