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

Vary Spacing Vary Size Vary Ordering Magnetic Nanoparticle Arrays

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, (2003). Nanoparticle Synthesis

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

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

Heterogeneous Homogeneous Fe oxide rings dominate Electron Diffraction

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

Particle Concentration Nucleation Method Fe conc.Particle Diameter #Particles per mL Heterogen M5.8 ± 0.5 nm 3.6      Heterogen M7.2 ± 0.5 nm 3.5      Heterogen M8.6 ± 1.6 nm 1.3      Heterogen.0.81 M8.4 ± 1.0 nm 1.9      Homogen 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

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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