Influence of carboxylic acid type on microstructure and magnetic properties of polymeric complex sol–gel driven NiFe2O4

• Citric, oxalic and tartaric acids were used for synthesis of NiFe2O4.
• Carboxylic acid type affects the produced powders.
• At low temperatures all carboxylic acids produce iron-deficient NiFe2O4 and α-Fe2O3.
• α-Fe2O3 is correlated with the decomposition of Fe(III) carboxylate precursors.

Citric, oxalic and tartaric acids were used for synthesis of NiFe2O4 using polymeric complex precursor route. The dry precursor gels were calcined at various temperatures (400–1100 °C) for 2 h. All carboxylic acids produce iron-deficient NiFe2O4 with considerable amount of α-Fe2O3 at 400 °C. Increase in the annealing temperature caused reaction of α-Fe2O3 with iron-deficient ferrite phase. The amount of initially formed α-Fe2O3 is directly correlated with stability constant and inversely correlated with the decomposition temperature of Fe(III) carboxylate precursors. In case of tartaric acid precursor, single phase of the ferrite was obtained at 450 °C. However, in case of oxalic acid and citric acid precursors, single phase ferrite was obtained at 550 °C and 700 °C, respectively. The lattice parameters were increased with increasing annealing temperature and with decreasing the amount of α-Fe2O3. Maximum saturation magnetization (55 emu/g) was achieved using tartaric acid precursor annealed at 1100 °C.

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