Effect of Cobalt Doping
Concentration on the Crystalline
Structure and Magnetic Properties of Monodisperse Co<sub><i>x</i></sub>Fe<sub>3–<i>x</i></sub>O<sub>4</sub> Nanoparticles
within Nonpolar and Aqueous Solvents
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Abstract
In this work, we investigate the effect of cobalt substitution
on the size evolution, crystal structure, and magnetic properties
of Fe<sub>3</sub>O<sub>4</sub> nanoparticles. Monodisperse Co<sub><i>x</i></sub>Fe<sub>3–<i>x</i></sub>O<sub>4</sub> nanoparticles were prepared, using a one-step method, by
direct heating process of iron(III) and cobalt(II) acetylacetonates
in high-boiling-point inert organic solvent. The quantities of precursors
added were based on stoichiometric Fe/Co ratio of desired ferrite.
Elemental analyses ICP-AES evidenced successful cobalt doping. The
doped particles showed a cobalt-deficient composition. Transmission
electron microscopy demonstrated the large changes of particle size
as a function of cobalt doping. The magnetization measurements showed
an unchanged saturation magnetization only up to <i>x</i> = 0.24, beyond which it significantly decreased. To make the as-synthesized
nanoparticles suitable for biomedical applications, oleic acid ligands
are exchanged with caffeic acid molecules leading to stable nanoparticles
in physiological conditions