a b s t r a c tBio-compatible composite particles composed of hydroxyapatite (Ca 10 (PO 4 ) 6 (OH) 2 , HAp) and ferrite (maghemite (␥-Fe 2 O 3 ) or magnetite (Fe 3 O 4 )) were synthesized by two-step synthesis. In this work, coprecipitation method using aqueous solution of FeSO 4 and FeCl 3 was employed to synthesize ␥-Fe 2 O 3 and Fe 3 O 4 particles. It was found that the resultant phase was changed by the molar ratio of FeSO 4 and FeCl 3 , and optimal molar ratio to suppress the coexistence of ␣-FeOOH was FeSO 4 /FeCl 3 = 2. The suspension composed of crushed ferrite particles, Ca(NO 3 ) 2 and H 3 PO 4 aqueous solution with surfactant ultrasonically nebulized into mist and the mist was pyrolyzed at 500 • C to synthesize HAp-ferrite composite particles. The shape of the synthesized composite particle was round with dimple, and the particle size was around 0.5-3 m in diameter. The composite particle showed saturation magnetization of 0.833 emu/g. Net saturation magnetization of the ferrite component was calculated to be 46.4 or 48.0 emu/g under the assumption that the ferrite was composed of ␥-Fe 2 O 3 or Fe 3 O 4 , respectively.

Fe 3 O 4 -BaTiO 3 composite particles were successfully prepared by ultrasonic spray pyrolysis. A mixture of iron(III) nitrate, barium acetate and titanium tetrachloride aqueous solution were atomized into the mist, and the mist was dried and pyrolyzed in N 2 (90%) and H 2 (10%) atmosphere. Fe 3 O 4 -BaTiO 3 composite particle was obtained between 9001 and 9501C while the coexistence of FeO was detected at 10001C. Transmission electron microscope observation revealed that the composite particle is consisted of nanocrystalline having primary particle size of 35 nm. Lattice parameter of the Fe 3 O 4 -BaTiO 3 nanocomposite particle was 0.8404 nm that is larger than that of pure Fe 3 O 4 . Coercivity of the nanocomposite particle (390 Oe) was much larger than that of pure Fe 3 O 4 (140 Oe). These results suggest that slight diffusion of Ba into Fe 3 O 4 occurred.