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drastically differs from syntheses in homogeneous solu-tion.[85-93] The major differences are:

1. The reactant concentration is two orders of magnitude lower than that in homogeneous solution.

2. A spinel structure can be obtained in the absence of Fe(III) at the starting point of the reaction, whereas the ratio Fe(II)/Fe(III) must be higher than 0.4 in homogeneous solution. In the latter case, with a high Fe(II) salt concentration and without Fe(III) derivatives,[94-96] the formation of Fe3O4 micrometer particles is observed. Their morphology depends critically on parameters similar to those described above (reactant concentrations, pH, ionic strength, etc.). Furthermore, it has been impossible to produce particles in the nanosize range when Fe(II) salt is used for the synthesis.

3. Changing the micellar concentration controls the particle size. In homogeneous solution, it is controlled by changing the type of salt (chlorides, nitrates, perchlorates, etc.), Fe(II)/Fe(III) ratio, pH, and ionic strength of the media. Such drastic changes in experimental conditions induce a large modification in the particle interface (hydroxide formations, etc.) and magnetic properties[92,93] of the nanocrystals. Conversely, using colloidal solutions makes it possible to produce nanocrystals with magnetic properties that do not depend on their coating.[81]

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