Synthesis and magnetic properties of the size-controlled Mn–Zn ferrite nanoparticles by oxidation method

Size-controlled Mn0.67Zn0.33Fe2O4 nanoparticles in the wide range from 80 to 20 nm have been synthesized, for the first time, using the oxidation method. It has been demonstrated that the particle size can be tailor-made by varying the concentration of the oxidant. The magnetization of the 80 nm particles was 49 A m2 kg−1 compared to 34 A m2 kg−1 for the 20 nm particles. The Curie temperatures for all the samples are found to be within 630±5 K suggesting that there is no size-dependent cation distribution. The critical particle size for the superparamagnetic limit is found to be about 25 nm. The effective magnetic anisotropy constant is experimentally determined to be 7.78 kJ m−3 for the 25 nm particles, which is about an order of magnitude higher than that of the bulk ferrite.