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Nanoparticle Mn-Zn-Ni ferrite powders, Mn<sub>1−2x</sub>Zn<sub>x</sub>Ni<sub>x</sub>Fe<sub>2</sub>O<sub>4</sub> (0.0 ≤ x ≤ 0.3), were fabricated using the sol-gel method, and their structural and magnetic properties were investigated. Using X-ray diffraction and Mössbauer spectroscopy, we confirmed the formation of crystallized particles annealed at 523 K. All the Mn-Zn-Ni ferrite powders showed a single phase with a spinel structure. The size of the ferrite powders grains increased as the rate of Zn and Ni substitution was increased. The Mössbauer spectra for x ≥ 0.1 in Mn<sub>1−2x</sub>Zn<sub>x</sub>Ni<sub>x</sub>Fe<sub>2</sub>O<sub>4</sub> could be fitted by superposition of two Zeeman sextets and one doublet due to the ferrimagnetic and the superparamagnetic phases. However, for x = 0.0, the Mössbauer spectrum could be fitted to one doublet due to the superparamagnetic phase. From the variation of the Mössbauer parameters and the absorption area ratio, the cation distributions were determined. In the Mn<sub>1−2x</sub>Zn<sub>x</sub>Ni<sub>x</sub>Fe<sub>2</sub>O<sub>4</sub> powder samples, the coercivity increased from 41.66 Oe for x = 0.0 to 49.87 Oe for x = 0.3 as the rate of substitution was increased, but the saturation magnetization showed a maximum value of 29.26 emu/g for x = 0.2.