Manganese zinc ferrous fumarato–hydrazinate precursor, Mn0.6Zn0.4Fe2(C4H2O4)3·6N2H4 was synthesized for the first time and characterized by chemical analysis, infrared spectral studies, and thermal analysis. Infrared studies show band at 977 cm−1 indicating bidentate bridging nature of the hydrazine in the complex. Thermogravimetric (TG) studies show two steps dehydrazination followed by two steps total decarboxylation. The precursor on touching with burning splinter undergoes self propagating autocatalytic decomposition yielding ultrafine Mn0.6Zn0.4Fe2O4. XRD studies confirms single phase formation as well as nanosize nature of “as prepared” Mn0.6Zn0.4Fe2O4. The saturation magnetization of the “as prepared” Mn0.6Zn0.4Fe2O4 was found to be 31.46 emu gm−1, which is lower than the reported, confirms the ultrafine nature of the oxide.