Nickel Substitution Effects on Nano-sized Co, Mn and MnZn Ferrites Synthesized by Sol-gel Method

Nickel substituted nano-sized ferrite powders, Co 1-x Ni x Fe₂O₄, Mn 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ (0.0 ≤ x ≤ 0.2), were fabricated using a sol-gel method, and their crystallographic and magnetic properties were subsequently compared. The lattice constants decreased as quantity of nickel substitution increased, while the particle size decreased in Co 1-x Ni x Fe₂O₄ ferrite but increased for the Mn 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ ferrites. For the Co 1-x Ni x Fe₂O₄ and Mn 1-x Ni x Fe₂O₄ (0.0 ≤ x ≤ 0.2) ferrite powders, the Mossbauer spectra 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 Mn 0.8 Zn 0.1 Ni 0.1 Fe₂O₄ consisted of two Zeeman sextets and one single quadrupole doublet due to the ferrimagnetic and paramagnetic behavior. The area ratio of the Mossbauer spectra could be used to determine the cation distribution equation, and we also explain the variation in the Mossbauer parameters by using this cation distribution equation, the superexchange interaction and the particle size. The saturation magnetization decreased in the Co 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ ferrites but increased in the Mn 1-x Ni x Fe₂O₄ ferrite with nickel substitution. The coercivity decreased in the Co 1-x Ni x Fe₂O₄ and Mn 1-2x Zn x Ni x Fe₂O₄ ferrites but increased in the Mn 1-x Ni x Fe₂O₄ ferrite with nickel substitution. These variations could thus be explained by using the site distribution equations, particle sizes and spin magnetic moments of the substituted ions.