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The results on the synthesis, microstructure, structure and DC magnetization studies of nanocomposite Zn,Ni ferrite/NiO powder obtained by thermal decomposition of acetylacetonato complexes are reported in this paper. According to the results obtained by inductively coupled plasma optical emission spectroscopy (ICP-OES) element analysis and multiphase Rietveld refinement, the three samples made are composed of spinel-ferrite (86.7%-96.7%) and NiO (3.3%-13.3%) phases. The compositions of the spinel-ferrite (SP) phase in the investigated samples, S1-S3, are Zn _0.72 Ni _0.24 Fe _1.98 O ₄ , Zn _0.56 Ni _0.29 Fe _2.07 O ₄ and Zn _0.40 Ni _0.40 Fe _2.10 O ₄ , respectively. Due to the cation deficiency in spinels, created vacancies induce a partial change in the cation valence, . The vacancy distribution is found to be random at 8a and 16d cation sites, except in sample S3, where all vacancies are over octahedral sites. The x-ray line broadening due to crystallite size effect is found to be isotropic for all spinels, while the x-ray line broadening due to the strain effect is anisotropic. A correlation between the Zn ²⁺ occupancy of the tetrahedral site and the 650 cm ^-1 Raman peak intensities is shown. The observed coercivity decrease and shift in hysteresis loop in the samples are caused by the interaction between spinel and NiO phase. The results of M(H) measurements point to the properties of an ensemble of interacting nanoparticles. High saturation magnetization values and superparamagnetic behaviour at room temperature point to the technological significance of the title compounds. © IOP Publishing Ltd.