Influence of Co2+ ions doping in Ni0.7-xCoxZn0.3Fe2O4 nanoferrites: A study of structural, morphological, optical, and magnetic properties

In the last few years, there has been a notable focus on the synthesis of soft magnetic nanoferrites with different properties for different applications. Highly efficient Cobalt (Co) assisted Ni_0.7-xCo_xZn_0.3Fe₂O₄ (x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) nanoferrites were prepared via citrate gel combustion technique. XRD analysis revealed the single-phase cubic lattice growth, with a typical crystal size spanning between 33.81 and 42.45 nm. The unit cell volume and lattice parameter of Ni_0.7-xCo_xZn_0.3Fe₂O₄ exhibited a significant increment with varying Co concentration (x = 0.1. 0.3, and 0.5), primarily because of expanded ionic radius of Co. Analysis with HRTEM revealed crystal sizes varying between 39.3 and 69.8 nm, confirming the nanocrystalline nature of the synthesized samples. Additionally, FESEM images indicated a spherical-like morphology for the nanoferrites. EDX analysis further validated the existence of all required elements such as Ni, Zn, Co, Fe, and O whitin the samples. SAED patterns and HRTEM images describe the pure and homogeneous crystalline cubic spinel lattice of nanoferrite including Moire fringes and d-spacing values consistent with XRD data and standard references. The FT-IR patterns exhibited absorption peaks within 533.1–545.6 cm⁻¹ range, associated with metal–oxygen bond stretching vibration. The optical characteristics of the nanoferrites indicated activity in both the ultraviolet and visible ranges. The enhancement of visible light absorption in Ni_0.7Zn_0.3Fe₂O₄ nanoferrite through Co doping has been achieved. The band gap energy was noted to be reduced from 1.66 eV to 1.37 eV as the Co content increases from x  = 0.0 to 0.5 in Ni_0.7-xCo_xZn_0.3Fe₂O₄ nanoferrites. Magnetic characterization of the Co-doped samples reveals significant enhancements in magnetic behaviour. Saturation magnetization (Ms) improved from 69.93 to 80.36 emu/g with Co-doping, indicating an improved magnetic response. Similarly, the coercivity (Hc) and remanent magnetization (Mr) showed substantial increases, from 86.18 Oe to 160.97 Oe and from 13.65 emu/g to 25.61 emu/g, respectively. Among the samples, the nanoferrite with x  = 0.4 exhibited the maximum value of Ms, while x  = 0.5 demonstrated the highest values of Mr and Hc, suggesting the impact of Co concentration on optimizing magnetic properties across different compositions. Hence, x  = 0.4 and 0.5 compositions of Ni_0.7-xCo_xZn_0.3Fe₂O₄ nanoferrites would be strong candidates for electronic devices like sensors and memory strage.