Several MnxFe3-xO4 MNPs with different Mn 2+ content but similar sizes and shapes were synthesized by a one-step thermal decomposition method, modifying different parameters such as the metallic precursors ratio (Fe(acac)3/Mn(acac)2), the surfactant/precursors ratio (OA/metallic precursors) and/or the final volume of solvent (see Table in the S.I.). In all cases, the rest of the synthetic parameters, that is, the heating rate, time and temperature at nucleation and growth steps were maintained constant.