An effective strategy for synthesizing spinel NixMn1-xFe2O4 by oxidation roasting technology: Synergetic reaction and phase evolution behavior

An oxidation roasting technology has been reported as an effective technology for successfully synthesizing nickel manganese ferrite Ni x Mn 1-x Fe 2 O 4 (0 < x < 1) with a spinel crystal structure. The experimental results demonstrated the successful synthesis of nickel manganese ferrite Ni 0.5 Mn 0.5 Fe 2 O 4 samples with relatively high purities at an oxidation roasting temperature of 1200 °C for 2 h with a Ni:Mn:Fe molar ratio of 1:1:4. The synthesized samples exhibited a magnetization saturation (Ms) value of 53.71 emu/g, a coercivity (Hc) value of 34.88 Oe, and a remanent magnetization (Mr) of 3.64 emu/g. Additionally, these samples had a total pore volume of 0.071 cm 3 /g, a Specific Surface Area (SSA) of 24.13 cm 2 /g, and an Average Particle Size (APS) of 12.32 nm. It was concluded that the synthesis route of Ni x Mn 1-x Fe 2 O 4 could be theoretically summarized into two routes. One route involves the simultaneous substitution of divalent iron (Fe 2+ ) and trivalent iron (Fe 3+ ) in the spinel structure of (Fe)[Fe] 2 O 4 by divalent manganese ions (Mn 2+ ) and trivalent nickel ions (Ni 3+ ), resulting in the formation of (Mn) x (Fe) 1-x [Ni] y [Fe] 2-y O 4 with a spinel crystal structure. In this structure, the Ni 3+ ions preferentially occupy the octahedral sites, whereas the Mn 2+ ions predominantly reside in the tetrahedral sites of the nickel manganese ferrites (Mn) x (Fe) 1-x [Ni] y [Fe] 2-y O 4 . Furthermore, the mixed spinel crystal structure of (Ni) y (Fe) 1-y [Mn] x [Fe] 2-x O 4 could be transformed into nickel manganese ferrite (Mn) x (Fe) 1-x [Ni] y [Fe] 2-y O 4 under the influence of a higher oxidization roasting temperature. Nickel manganese ferrite Ni x Mn 1-x Fe 2 O 4 (0 < x < 1) with normal and inverse spinel structures inevitably coexists and co-transformed in the synthesis process of Ni x Mn 1-x Fe 2 O 4 by oxidation roasting technology.