Cation oxidation states and magnetic properties of MnxFe3−xO4 magnetic nanoparticles

10-nm MnxFe3−xO4 (x = 0, 0.3, 0.7) magnetic nanoparticles (MNPs) with single cubic structure were prepared by thermal decomposition method. The magnetic properties and cation oxidation state of MnxFe3−xO4 MNPs were investigated. Integrated analysis of X-ray diffraction indicates that Mn doping induces lattice expansion. Electron energy-loss spectroscopy results show that the fraction of Mn2+ and Mn3+ is 0.5:0.5 in Mn0.3Fe2.7O4 MNPs, and 2:1 in Mn0.7Fe2.3O4 MNPs. The saturation magnetization of Mn0.3Fe2.7O4 MNPs remain unchanged compared to magnetite MNPs, while the saturation magnetization of Mn0.7Fe2.3O4 MNPs decrease significantly. The reduction of magnetization is due to the lattice distortion, which weakens the superexchange interaction between B-site cations. Raising the ratio of Mn2+ and avoiding lattice distortion are beneficial to improve the magnetic properties of manganese ferrite. Further in vitro experiments show that Mn0.3Fe2.7O4 @SiO2 MNPs have good magnetic hyperthermia properties.