Particle Size Dependence of Magnetic Properties in Zinc Ferrite Nanoparticles Jun Hee Cho1, Sang Gil Ko1, Yang kyu Ahn1, Eun Jung Choi2 * 1Department of Nanochemistry & Biochemistry, Konyang University, Nonsan, Chungnam, Korea 320-711 2Department of opthalmic Optics, Konyang University Daejeon 302-728, Korea

Experimental Procedure 1. Synthesis : Microemulsion method 2. X-ray diffraction pattern (XRD) 3. Superconducting quantum interference device (SQUID) 4. Mössbauer spectroscopy DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

Synthesis of nanosize ZnFe2O4 particles Metal Ion Aqueous Solution (ZnCl2/FeCl3 0.1M) Drying  & Aging (600K) Decantation & Washing with Solvent & Aalcohol Coprecipitation (Zinc-Iron Hydrixide Carbonate Particles with Surfactant) Mixing & Stirring  at R.T. Nanosize Zn-Ferrite Particles Alkali Aqueous Solution (Na2CO3 0.2M) Microemulsions 0.2M AOT in iso-Octane Water drops in oil MFe(OH)n Exchange of water content Precipitation & Particle growth Surfactant stabilized particle DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

X-ray diffraction pattern of ZnFe2O4 nanoprticles 1. Cubic spinel structure 2. Lattice parameter α0=8.43Å 3. Cation distribution    (Zn0.72Fe0.28)[Zn0.28Fe1.78]O4 DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

Magnetic hysteresis curve of ZnFe2O4 nanoparticles 5K 100K 200K 300K DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

Mössbauer spectrum at various temperatures DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

Mössbauer spectrum at various temperatures DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

Cation distribution DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY (Zn1-xFex)[ZnxFe2-x]O4 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 ER is the recoil energy of 57Fe for the 14.4 keV gamma ray. θ and kB represent the Debye temperature and the Boltzmann constant. (Zn0.72Fe0.28)[Zn0.28Fe1.72]O4 DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

Superparamagnetic Broadening from the distribution of quadrupole splittings Mössbauer line shift EQ 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 EQ taken over all directions vanishes, i.e. DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY

DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY The line broadening from this random distribution is not zero: that is,  Another source of broadening can be estimated from the linewidth, 0.42 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 0.17 mm/s of the doublet is the result of distributions of the isomer shift and magnitudes of q 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

Conclusions DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY ▶ Nanosize ZnFe2O4 particle have been synthesized using     microemulsion method. ▶ Cubic mixed spinel structure ▶ the lattice constant :  α0=8.43Å ▶ Combined broadening from distribution of quadrupole splitting and isomer shift is not negligible. ▶ Cation distribution (Zn0.72Fe0.29)[Co0.29Fe1.72]O4 ▶ Neel temperature : 120 K DEPARTMENT OF OPTHALMIC OPTICS KONYANG UNIVERSITY