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

H e a t S t i r

D. F. Farrell, S. A. Majetich, and J. P. Wilcoxon, J. Phys. Chem. 107, 11022-11030 (2003).

Nanoparticle Synthesis

7.0 ± 0.8 nm 9.2 ±0.7 nm

FeFeSeeded 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 Fe

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. 0.051 M 5.8 ± 0.5 nm 3.6

Heterogen. 0.0957 M 7.2 ± 0.5 nm 3.5

Heterogen. 0.614 M 8.6 ± 1.6 nm 1.3

Heterogen. 0.81 M 8.4 ± 1.0 nm 1.9

Homogen. 0.0284 M 11.2 ± 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 Ms of oxide shell

s,partmpart = s,coremcore + s,shellmshell

Diameter s Fe core Oxide shell

7.0 ± 0.7 nm heterogeneous

175 emu/g 5.8 nm 0.6 nm

9.2 ± 0.7 nm heterogeneous

175 emu/g 8.4 nm 0.4 nm

11.2 ± 1.0 nm homogeneous

110 emu/g 7.0 nm 2.1 nm

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