<p>The Cd²⁺ and Eu³⁺ co-substituted nickel ferrites (Ni_1-xCd_xFe_2-yEu_yO₄; x = y = 0,0.2,0.4,0.6,0.8) are synthesized by the sol–gel auto-combustion method. The synthesized samples underwent characterization employing TGA-DTA, XRD, FESEM, FT-IR, Raman, UV, and magnetic properties analyses. Thermogravimetric analysis was performed on the ferrite samples to monitor their phase development. The XRD confirmed that all the samples possess a single-phase cubic structure with the <i>Fd-3&#xa0;m</i> space group. Incorporation of Cd²⁺ and Eu³⁺ led to an increase in the lattice constant with decreases in crystalline size from 38.37&#xa0;nm to 35.16&#xa0;nm. FESEM analysis indicated average grain sizes decreased from 53.68&#xa0;nm (for NCFE-0) to 46.99&#xa0;nm (for NCFE-8). Additionally, EDS analysis confirmed the presence of desired elements. The FTIR spectra also confirmed the existence of spinel ferrite through the presence of characteristic M–O (metal–oxygen) bonding in the samples and exhibited two distinct frequency bands associated with phonon vibrational stretching within the octahedral and tetrahedral lattice positions. Raman spectroscopy revealed changes in cation distribution along with crystal deformation as the amount of Cd²⁺ and Eu³⁺ ions increased. The Eg reduced from 1.39&#xa0;eV to 1.32&#xa0;eV as the Cd²⁺ and Eu³⁺ content rises. Furthermore, the magnetic characteristics of all NCFE samples confirmed their soft magnetic nature, and saturation magnetization, remanence were decreased for Cd²⁺ and Eu³⁺ co-substituted nickel ferrites. Hence, due to the soft magnetic nature, Cd²⁺ and Eu³⁺ co-substituted nickel ferrites could serve as promising candidates for high-frequency device applications.</p>