Ni Doped Fe₃O₄ Magnetic Nanoparticles

In this work, the effect of nickel doping on the structural and magnetic properties of Fe₃O₄ nanoparticles is analysed. Ni _x Fe_3–x O₄ nanoparticles (x = 0, 0.04, 0.06 and 0.11) were obtained by chemical co-precipitation method, starting from a mixture of FeCI₂·4H₂O and Ni(AcO)₂·4H₂O salts. The analysis of the structure and composition of the synthesized nanoparticles confirms their nanometer size (main sizes around 10 nm) and the inclusion of the Ni atoms in the characteristic spinel structure of the magnetite Fe₃O₄ phase. In order to characterize in detail the structure of the samples, X-ray absorption (XANES) measurements were performed on the Ni and Fe K-edges. The results indicate the oxidation of the Ni atoms to the 2+ state and the location of the Ni²⁺ cations in the Fe²⁺ octahedral sites. With respect to the magnetic properties, the samples display the characteristic superparamagnetic behaviour, with anhysteretic magnetic response at room temperature. The estimated magnetic moment confirms the partial substitution of the Fe²⁺ cations by Ni²⁺ atoms in the octahedral sites of the spinel structure.