The nonconventional technique known as citrate precursor method has been successfully used to modify the magnetic properties of substituted Mg–Mn ferrites. We have found that the magnetic properties of these mixed ferrites change considerably by this method. It is observed that citrate precursor method could be used to obtain close composition control, better homogeneity, lower processing temperature, higher purity, lower porosity and more uniform grain growth. This results in favorable magnetic properties. In the present study, we have investigated various magnetic properties like saturation magnetization, magneton number, thermal variation of AC susceptibility, Neel temperature and initial permeability. In all the three series, the saturation magnetization and initial permeability improved significantly with indium and cobalt substitution. Neel temperature of each sample was calculated from AC susceptibility data. Higher values of Neel temperature were obtained for samples with increased content of cobalt. Magnetic losses obtained are from 1–2 orders lower as compared to those for Mg–Mn ferrites prepared by conventional ceramic method, which suits high-frequency applications. The possible mechanisms contributing to these properties are discussed in this paper.