Nd2Fe14B and FePt nanoparticles with a diameter below the diffraction limit of laser light were successfully prepared by an ultrashort pulse laser ablation in cyclohexane. The self-passivating amorphous carbon layer resulting from the fragmentation of the surrounding solvent prevents the nanoparticle from aggregation and oxidation. The coercivity of the Nd2Fe14B nanoparticles smaller than the critical single domain size was about 2.2 times as high as that of the initial Nd2Fe14B particles in spite of the decrease in crystallinity. Furthermore, the coercivity of the FePt nanoparticles after heat treatment dramatically increased, which was about 20 times higher than that of the initial FePt sample.