Mono-dispersed FeCo Alloy NPs Made in Solution

"Synthesis and Stabilization of FeCo Nanoparticles"
Chaubey, G. S.; Barcena, C.; Poudyal, N.; Rong, C.; Gao, J.; Sun, S.; Liu, J. P. J. Am. Chem. Soc. ASAP published on 05/12/2007.
doi: 10.1021/ja0708969

Synthesis:
"Reductive decomposition of Fe(III) acetylacetonate (Fe(acac)3) and Co(II) acetylacetonate(Co(acac)2) in a mixture of surfactants and 1,2-hexadecanediol (HDD) under a gas mixture of 93% Ar + 7% H2 at 300 °C." H2 is believed to be crucial because of the NPs' prone to oxidation.

Properties:
Marginal size control achieved by varying ligands:

• 20 nm using oleic acid/oleyl amine (the latter alone does not work well)
• 10 nm using oleic acid/TOP

Surfactants contribute to more than 20% of the particle weight

Size-dependent magnetic properties:

• Magnetization (Ms): 207 emu/g for 20 nm; 129 emu/g for 10 nm.
• Similar to bulk Fe/Co alloy, maximum magnetization occured at Fe:Co = 1.5.

Overcoming Instability:

• Oxidation in air: 48 h resulting in more than 20 % decrease (20 nm slightly more)
• Annealing (500C, 93%Ar+7%H2, 30min) to stablize particles by forming a carbon shell: Ms improve to 230 emu/g after annealing (compare to 245 emu/g for bulk metal).