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
