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Crystallographic and Magnetic Properties of Co, Zn, Ni-Zn Substituted Nano-size Manganese Ferrites Synthesized by Sol-gel Method
Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, MnFe2O4, Mn0.8Co 0.2Fe2O4, Mn0.8Zn0.2Fe2O4 and Mn0.8Ni0.1Zn0.1Fe2O4, were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently studied. The MnFe2O4 ferrite powder annealed at temperatures above 523 K exhibited a spinel structure, and the particle size increased as the annealing temperature increased. All ferrites annealed at 773 K showed a single spinel structure, and the lattice constants and particle size decreased with the substitution of Co, Zn, and Ni-Zn. The Mössbauer spectrum of the MnFe2O4 ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the Mössbauer spectra of the MnFe2O4, Mn0.8Co0.2Fe2O4, and Mn0.8Zn0.2Fe2O4 ferrite powders annealed at 773 K could be fitted as the superposition of two Zeeman sextets due to the tetrahedral and octahedral sites of the Fe3+ ions. However, the Mössbauer spectrum of the Mn0.8Ni0.1Zn0.1Fe2O4 ferrite powder annealed at 773 K consisted of two Zeeman sextets and one quadrupole doublet due to its ferrimagnetic and paramagnetic behavior. The area ratio of the Mössbauer spectra could be used to determine the cation distribution equation, and we also explained the variation in the Mössbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. Relative to pure MnFe2O4, the saturation magnetizations and coercivities were larger in Mn0.8Co 0.2Fe2O4 and smaller in Mn0.8Zn0.2Fe2O4, and Mn0.8Ni0.1Zn0.1Fe2O4. These
variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.