Increasing the size of Fe_3-δO₄ Nanoparticles by Performing a Multistep Seed-Mediated Growth Approach

Abstract

Iron oxide nanoparticles were synthesized by an original multistep seed-mediated growth approach. The thermal decomposition of an iron stearate precursor was performed successively up to 5 times to produce nanoparticles with a narrow size distribution from 6.4 to 15.0 nm. The chemical composition and crystal structure of each set of nanoparticles was characterized by TEM, FT-IR, XRD, and Mössbauer spectrometry. Each layer was successively grown at the surface of a pristine Fe3‑δO4 nanoparticle by epitaxial relationship and resulted in a single crystal structure. An intermediate wash after each thermal decomposition step resulted in the surface oxidation of each layer. Therefore, the maghemite phase increased relative to the magnetite phase as the nanoparticle expanded. Finally, the study of the magnetic properties by SQUID magnetometry showed the trend of the magnetic anisotropy energy to increase as a function of the nanoparticle size. In contrast, the coercive field and the magnetization saturation display nonmonotonic variations that may result from the interplay of intrinsic and collective properties.

A detailed investigation of the core@shell structure of exchanged coupled magnetic nanoparticles after performing solvent annealing

“…The reverse FFTs show some defects for both CS and CSR although those calculated for Fe 3Àd O 4 pristine nanoparticles did not show any defects. 42 Furthermore, closer analysis on the edge of nanoparticles shows that there are more defects in the shell of both CS and CSR (see the ESI †). It shows that the CoO shell either before or after annealing at high temperatures contains more defects than the core.…”

A Detailed Investigation of the Onion Structure of Exchanged Coupled Magnetic Fe3−δO4@CoFe2O4@Fe3−δO4 Nanoparticles

“…Therefore, such a thicker cobalt ferrite shell may result from the partial solubilisation of the iron oxide core followed by the recrystallization 35 of Fe monomers with Co monomers in a similar way we reported earlier. 23,39,40 Considering that a stoichiometric ratio of Fe and Co stearate was used, we expect the cobalt ferrite shell to be under stoichiometric.…”

“…Both soft/hard and hard/soft interfaces resulted in blocked magnetization at room temperature, although these nanoparticles are mostly composed of iron oxide with a size below 16 nm. Such enhanced magnetic properties account from a more complex structure that resulted from the partial replacement of CoO by cobalt ferrite at both interfaces during the synthesis steps …”

“…Such enhanced magnetic properties account from a more complex structure that resulted from the partial replacement of CoO by cobalt ferrite at both interfaces during the synthesis steps. 40 In this context, we have designed new multicomponent nanoparticles to rationally investigate their structure by combining advanced characterization techniques. Hence, we report here on onion-like magnetic nanoparticles which consist of an iron oxide core combined with a first shell of cobalt ferrite and a second shell of iron oxide, i.e., a Fe 3−δ O 4 @ CoFe 2 O 4 @Fe 3−δ O 4 structure.…”

Robots Built Robots: Nanorobots Customized by Intelligent Robot

“…The synthesis of magnetite nanoparticles with controlled sizes has long been of scientific and technical interest. Especially in biological applications, the synthesis of nanoparticles of specific sizes has been a technical challenge. − In fact, in the previous works, − many scientific studies provide methods for synthesizing magnetic nanoparticles of specific sizes. For example, in one previous work, the author used a seed-mediated growth method to control the size of magnetic nanocrystals.…”