Role of carboxylate ion and metal oxidation state on the morphology and magnetic properties of nanostructured metal carboxylates and their decomposition products

Sub-micron rods and spheres of cobalt succinate sesquihydrate and iron succinate tri-hydrate/pentahydrate respectively have been synthesized by the reverse micellar route. These precursors are an excellent source for the synthesis of metal and metal oxide nanoparticles. Cubes of (edge length ∼ 150 nm) Fe₃O₄ and elongated particles of Fe ₂O₃ (∼diameter of 200 nm) were obtained. The role of oxidation state of the metal ion in controlling the morphology of the nanostructured dicarboxylates has been investigated. Rods with shorter length were obtained when longer chain dicarboxylate was used as ligand. Heating in nitrogen atmosphere also provided pure Co and α-Fe nanoparticles. The Fe nanoparticles show nearly 100% superparamagnetism. Temperature-dependent magnetic studies show a Morin-like transition for Fe₂O₃ nanoparticles at 223 K and the Verwey transition at 115 K for Fe ₃O₄ nanoparticles. Co₃O₄ nanoparticles showed antiferromagnetic ordering at 20 K.