Manganese ferrofluid MNPs were prepared by using coprecipitation method. The metal salt precursors, ferric (III) chloride hexahydrate (FeCl3.6H2O, 99%, Merck, Germany), manganese (II) nitrate tetrahydrate (Mn(NO3)2.4H2O, 99%, Merck, Germany) were dissolved in distilled water at 0.1 M and 0.05 M concentrations, respectively. The molar ratio of metal salts solution [Fe3+]/[Mn2+] was 4:1 (10 ml and 5 ml) to maintain the stoichiometry of the spinel ferrite. The solutions were blended at 65–70 °C and then added into a boiling sodium hydroxide (NaOH 0.69 M) solution. The reaction was carried out at 85 °C for 2 hr at pH of 12, under the nitrogen atmosphere (Eq. (1)).