1. Particle Size Dependence of Magnetic Properties in Cobalt Ferrite Nanoparticles Jun Hee Cho 1, Sang Gil Ko 1, Yang kyu Ahn 1, Eun Jung Choi 2 * 1 Department of Nanochemistry & Biochemistry, Konyang University, Nonsan, Chungnam, Korea 320-711 2 Department of opthalmic Optics, Konyang University Daejeon 302-728, Korea

2. Experimental Procedure 1. Synthesis : Microemulsion method 2. X-ray diffraction pattern (XRD) 3. Transmission electron microscope (TEM) 4. Mössbauer spectroscopy DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

3. Synthesis of nanosize CoFe 2 O 4 particles Metal Ion Aqueous Solution (CoCl 2 /FeCl 3 0.1M) Drying & Aging (600K) Decantation & Washing with Solvent & Aalcohol Coprecipitation (Cobalt-Iron Hydrixide Carbonate Particles with Surfactant) Mixing & Stirring at R.T. Nanosize Co-Ferrite Particles Alkali Aqueous Solution (Na 2 CO 3 0.2M) Microemulsions 0.2M AOT in iso-Octane Microemulsions 0.2M AOT in iso-Octane Water drops in oil Surfactant stabilized particle Exchange of water content Precipitation & Particle growth MFe(OH)n DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

4. X-ray diffraction pattern of CoFe 2 O 4 nanoprticles 1. Cubic spinel structure 2. Lattice parameter α 0 =8.39 Å 3. Average size : 88 Å DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

5. TEM image and Particle size distribution of CoFe 2 O 4 nanoparticles Cobalt ferrite paricles average size calculated : 88 Å ― calculated : log-normal distribution Log-normal distribution DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

6. Magnetic Hysteresis (SQUID) of cobalt ferrite DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

7. Mössbauer spectrum at various temperatures ▶ a typical paramagnetic doublet → paramagnetic behavior of the particles ▶ Isomer-shift value : 0.35 mm/s ▶ Quadrupole splitting value : 0.78 mm/s (R.T.) DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

8. Cation distribution Co 1-x Fe x )[Co x Fe 2-x ]O 4 Area ratio of the A and B subspectra for the above distribution Where ∱ A and ∱ B represent the recoil-free fraction of A and B site Fe ions, respectively. Recoil Free Fraction ∱ Where E R is the recoil energy of 57 Fe for the 14.4 keV gamma ray. θ and k B represent the Debye temperature and the Boltzmann constant. (Co 0.66 Fe 0.34 )[Co 0.34 Fe 1.66 ]O 4 DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

9. Line broadening from the distribution of quadrupole splittings Mössbauer line shift E Q from the pure magnetic lines due to the quadrupole interaction where θ and Ф are the polar and azimuth angles of the magnetic hyperfine field vector relative to the principal axes of the electric-field- gradient tensor. On assuming that the maximum electric field gradient q and the asymmetry parameter ŋ are independent of θ and Ф, the average value of E Q taken over all directions vanishes, i.e. DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

10. The line broadening from this random distribution is not zero: that is, Another source of broadening can be estimated from the linewidth, 0.47 mm/s, of the quadrupole dooublet above the Curie temperature. In view of the 0.25 mm/s linewidth of an iron foil, a line broadening of 0.22 mm/s of the doublet is the result of distributions of the isomer shift and magnitudes of α and ŋ in addition to the thickness effect of the absorber. Thus, the combined broadening from distribution of quadrupole splitting and isomer shift can not be negligible. DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

11. ▶ Nanosize CoFe2O4 particle have been synthesized using microemulsion method. ▶ Cubic spinel structure ▶ the lattice constant : α 0 =8.39 Å ▶ Average size : 88 Å ▶ Combined broadening from distribution of quadrupole splitting and isomer shift is not negligible. ▶ Cation distribution (Co 0.66 Fe 0.34 )[Co 0.34 Fe 1.66 ]O 4 ▶ Neel temperature : 330 K Conclusions DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY