[en] The effect of gamma irradiation and the substitution by Er³⁺ ions on the microstructure, magnetic and electrical properties was studied for some ferrite samples of the general formula Ni_0.1Mn_0.5Zn_0.4Er_xFe_2−xO₄, (0 ≤ x ≤ 0.1, step 0.025). The samples are prepared using the standard ceramic technique. The structure of the prepared samples is confirmed using x-ray diffraction patterns. The samples are irradiated at a certain dose of 100 kGy using gamma rays of ⁶⁰Co source. The obtained results show high stability of the crystalline structure where no new phases were found as a result of the high dose of gamma irradiation. The lattice parameter of the prepared samples is found to increase with increasing Er³⁺ content. The surface morphology of the samples and the percentage of the ions are studied using scanning electron microscope and EDAX analysis respectively. The effect of temperature and substitution by Er³⁺ ions on the saturation magnetization and initial permeability are also studied. The experimental results indicate that, the substitution by Er³⁺ ions led to improve the magnetic properties of the studied samples. Also, the obtained results show a decrease in the saturation magnetization and improvement in the coercivity of the samples as a result of gamma irradiation. On the other hand, the present study shows an increase in the DC conductivity due to the substitution by Er³⁺ ions and gamma irradiation. The final results show that, the sample of x = 0.025 has high magnetic properties and low porosity which can be exploited in a certain technical applications. (author)