Crystallographic and Magnetic Properties of Co, Zn, Ni-Zn Substituted Nano-size Manganese Ferrites Synthesized by Sol-gel Method

Abstract

Cobalt-, zinc-, and nickel-zinc-substituted nano-size manganese ferrite powders, MnFe₂O₄, Mn 0.8 Co 0.2 Fe₂O₄, Mn 0.8 Zn 0.2 Fe₂O₄ and Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄, 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 Mossbauer spectrum of the MnFe₂O₄ ferrite powder annealed at 523 K only showed a doublet due to its superparamagnetic phase, and the Mossbauer spectra of the MnFe₂O₄, Mn 0.8 Co 0.2 Fe₂O₄, and Mn 0.8 Zn 0.2 Fe₂O₄ 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 Fe 3+ ions. However, the Mossbauer spectrum of the Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄ 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 Mossbauer spectra could be used to determine the cation distribution equation, and we also explained the variation in the Mossbauer 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 Mn 0.8 Co 0.2 Fe₂O₄ and smaller in Mn 0.8 Zn 0.2 Fe₂O₄, and Mn 0.8 Ni 0.1 Zn 0.1 Fe₂O₄. These variations could be explained using the site distribution equations, particle sizes and magnetic moments of the substituted ions.