1. Exchange Interactions Dipolar Interactions Competition between exchange and dipolar interactions leads to domain formation Atom Magnetic Domains

2. Vary Spacing Vary Size Vary Ordering Magnetic Nanoparticle Arrays

3. Fe synthesized using air free solution chemistry methods Thermal decomposition of Fe(CO) 5 in octyl ether Particles coated with surfactant Washed with ethanol and dispersed in hexane D. F. Farrell, S. A. Majetich, and J. P. Wilcoxon, J. Phys. Chem. 107, 11022-11030 (2003). Nanoparticle Synthesis

4. 7.0 ± 0.8 nm 9.2 ±0.7 nm Seeded with Pt (Fe:Pt ~1000:1) Heterogeneously Nucleated Fe

5. 9.1 ± 0.9 nm 11.2 ± 1.0 nm 19 nm No Pt salt, larger amount of oleic acid surfactant Homogeneously Nucleated Fe

6. Heterogeneous Homogeneous Fe oxide rings dominate Electron Diffraction

7. Heterogeneously Nucleated Homogeneously Nucleated 2 Blocking T’s: Fe, Fe oxide H = 200 Oe Field-cooled, Zero field-cooled Magnetization 7.0 ± 0.8 nm 11.2 ± 1.0 nm 0.01vol. % Blocking Temperatures

8. Particle Concentration Nucleation Method Fe conc.Particle Diameter #Particles per mL Heterogen.0.051 M5.8 ± 0.5 nm 3.6      Heterogen.0.0957 M7.2 ± 0.5 nm 3.5      Heterogen.0.614 M8.6 ± 1.6 nm 1.3      Heterogen.0.81 M8.4 ± 1.0 nm 1.9      Homogen.0.0284 M11.2 ± 1.0 nm----- Found from calibrated x-ray fluorescence of solutions* Use to determine total mass of Fe  s * Dr. Jess P. Wilcoxon, Sandia National Laboratories

9. Oxide Shell Thickness Relate  s of particles to weighted average of  s of Fe core and M s of oxide shell  s,part m part =  s,core m core +  s,shell m shell Diameter ss Fe coreOxide shell 7.0 ± 0.7 nm heterogeneous 175 emu/g5.8 nm0.6 nm 9.2 ± 0.7 nm heterogeneous 175 emu/g8.4 nm0.4 nm 11.2 ± 1.0 nm homogeneous 110 emu/g7.0 nm2.1 nm

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