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Synthesis and magnetic properties of nanostructured metallic Co, Mn and Ni oxide materials obtained from solid-state metal-macromolecular complex precursors

Díaz, C., Valenzuela, M. L., Laguna-Bercero, M. A., Orera, A., Bobadilla, D., Abarca, S., Peña, O.
RSC advances 2017 v.7 no.44 pp. 27729-27736
air, chitosan, cobalt, cobalt oxide, combustion, ferrimagnetic materials, graphene, heat treatment, magnetic properties, manganese, manganese chloride, manganese oxides, nanoparticles, nickel, nickel oxide, polymers, temperature, transmission electron microscopy
The simple reaction of chitosan with metallic salts yields (chitosan) (MLn)ₓ, MLn = MnCl₂, CoCl₂, NiCl₂, macromolecular complexes which, after a thermal treatment at 800 °C under air, give nanostructured Mn₂O₃, Co₃O₄ and NiO. The polymer acts as a template in the solid state, which is eliminated after the combustion process. At an intermediate stage, a layered graphitic carbon matrix was observed by HRTEM over the grown metal oxides. A mechanism for the growth of nanostructured oxides is discussed, including Raman studies. The nanostructured Mn₂O₃, Co₃O₄ and NiO particles grow over graphite layers and the solid-state role of chitosan is crucial for the formation of this graphite substrate. An antiferromagnetic transition was observed in Co₃O₄ nanoparticles, with TN = 38 K, whereas NiO nanoparticles behave as a superparamagnetic material with a blocking temperature above 300 K.