Synthesis of rod-shaped NiFe2O4 spinel ferrites by the precipitation–toptactic reaction and investigation of magnetic properties

The rod-shaped NiFe2O4 spinel ferrites were synthesized by the precipitation–toptactic reaction method using pod-like γ-FeOOH as raw materials. The synthesis processes of rod-shaped NiFe2O4 spinel ferrites include preparation of the rod-shaped precursor with a length-diameter ratio of 12 ∼ 13, in which the pod-like γ-FeOOH is coated by poor-crystalline Ni(OH)2 clusters, formations of γ-Fe2O3 and NiO through dehydroxylation of pod-like γ-FeOOH and decomposition of Ni(OH)2, and production of NiFe2O4 during the whole calcination. An endothermic decomposition of Ni(OH)2 at 280 °C ∼ 380 °C blocks the transition of γ-Fe2O3 into α-Fe2O3 so that NiO reacts directly with γ-Fe2O3 to produce NiFe2O4. The final product calcinated at 900 °C, uniformly in rod-like shape with a length-diameter ratio of 5 ∼ 8, smaller than that of the as-received precursor, present a higher coercivity than that of spinel nickel ferrites in irregular shape, which may be attributed to its strong shape anisotropy.

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► Rod-shaped NiFe2O4 ferrites are prepared by precipitation–toptactic reaction method.
► The whole synthesis processes rod-shaped NiFe2O4 ferrites are investigated.
► The rod-shaped NiFe2O4 shows a higher coercivity due to its strong shape anisotropy.