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 precipitationetoptactic reaction method using pod-like gamma-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 similar to 13, in which the pod-like gamma-FeOOH is coated by poor-crystalline Ni(OH)(2) clusters, formations of gamma-Fe2O3 and NiO through dehydroxylation of pod-like gamma-FeOOH and decomposition of Ni(OH)(2), and production of NiFe2O4 during the whole calcination. An endothermic decomposition of Ni(OH)(2) at 280 degrees C similar to 380 degrees C blocks the transition of gamma-F(e)2O(3) into alpha-Fe2O3 so that NiO reacts directly with gamma-Fe2O3 to produce NiFe2O4. The final product calcinated at 900 degrees C, uniformly in rod-like shape with a length-diameter ratio of 5 similar to 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. (C) 2011 Elsevier Masson SAS. All rights reserved.