A series of Cu0.2Zn0.2Ni0.6-xMgxFe2O4 (x = 0.00, 0.15, 0.30, 0.45 and 0.60) nanoferrites was synthesised by co-precipitation process. Cubic spinel structure and replacement of Ni2+ with Mg2+ ions of prepared ferrites were confirmed by XRD pattern. Average crystallite size was decreased (23.62–17.22 nm) whereas lattice constant (8.4029–8.4428 Å) increased with the addition of Mg2+ concentration. The value of specific surface area ranges from 52.51 to 67.83 m2/g for the prepared nanomaterials suggesting that soft ferrites might be used for supercapacitors. The distribution of ions on tetrahedral site along with force constant was revealed by FTIR. The DC resistivity observed from 6.83 × 109 to 1.40 × 108 ohm.cm confirms the semiconducting nature of soft ferrites. The value of direct and indirect energy B.G ranged from 3.40 to 3.68 eV & 0.84–1.03 eV, respectively. The prepared nanomaterial shows metallization criterion from 0.41 to 0.44 eV1/2 (i.e. 0.34 <MMC<0.45) along with high values of non-linear refractive index and therefore could be used in non-linear optics according to Dimitrov and Komatsu theory. The value of Urbach energy (0.4862–1.8235 eV) and static refractive index (0.74–0.98) showed a mixed behaviour with the increase of Mg2+ concentration. The varying trends of coercivity and saturation magnetization revealed that composed ferrites are appropriate for density recording media.