Crystalline MnFe2O4 particles with particle sizes in submicrometers were produced by flame-combusting the freeze-dried citrate precursors. Aqueous solutions of nitrates, containing Fe3+ and Mn2+ chelated by citric acid and with controlled pH using NH4OH additions, were freeze-dried. The freeze-dried citrate precursors were then thermally treated by combustion using a butane-induced flame, to decompose organic constituents and to form ferrites. The resultant particles were characterized using XRD, TG, DSC, FT-IR, SEM, and SQUID. At pH ≥ 3, the flame-combusted specimens were composed of crystalline MnFe2O4 with average crystallite sizes of 28.5 ± 1.2 nm and exhibited magnetic characteristics of 48.7 ± 1.5 emu/g in magnetization measured at 1.5 kOe, 13.4 ± 0.2 emu/g in remanence magnetization, and 55.7 ± 3.9 Oe in coercive force.
Journal of Alloys and Compounds 394(1-2), pp.286-291