Tailored design of CoxMn1-xFe2O4 nanoferrites: a new route for dual control of size and magnetic properties

This work reports the tailored design of novel mixed ferrite nanoparticles, CoxMn1-xFe2O4 (x = 0, 0.3, 0.7, and 1), through an optimized one-pot aqueous coprecipitation process. The influence of the substitution between Mn(II) and Co(II) and of the alkaline agent, isopropanolamine (MIPA) or NaOH, on the morphological, chemical and magnetic properties of the nanomaterials was investigated. The joint action between chemical substitution and type of alkaline agent allowed a precise tuning of the particle size, magnetic properties and inversion degree of the spinel structure. A wide range of particle dimensions (from 3 to 30 nm) and saturation magnetization (from 57 to 71 emu g(-1)) was achieved. The increase of Co(II) content from x = 0 to x = 1 led to a systematic decrease of the particle size, regardless of the base type, which could be modelled by an exponential decay function. For each Co : Mn composition, the use of MIPA instead of the traditional NaOH promoted a three times reduction of the particle size and simultaneously switched the magnetic state of the CoxMn1-xFe2O4 nanomaterials from ferromagnetic to superparamagnetic. These results constitute a step forward in the challenging quest for high-performance magnetic nanoprobes by an eco-friendly synthesis route.