The paper presents the results of a study of ceramic samples Mn1-xNixFe2O4, obtained by solid state sintering at 1200 °C with subsequent quenching. The temperature dependence of the real and imaginary parts of magnetic permeability was measured. It has been shown that nickel substitution result in an increase of a Curie temperature. The temperature dependence of the magnetic permeability and heat capacity was compared. Two exothermic peaks were found on the temperature dependence of heat capacity. It is shown that one of the peaks corresponds to a magnetic phase transition. Based on high-temperature X-ray diffraction data, it has been suggested that the second peak correspond to the rearrangement of the ferrite crystal lattice. © 2025 Elsevier B.V., All rights reserved.