Structural and Magnetic Characterization, Biomedical Applications, and Hyperfine Interactions of Quaternary Nanospinel Ferrites

In this study, the following, Co_0.25Ni_0.25Mn_0.25Zn_0.25Fe₂O₄ (CoNiMnZn), Co_0.25Ni_0.25Mn_0.25Cu_0.25Fe₂O₄ (CoNiMnCu), Co_0.25Ni_0.25Zn_0.25Cu_0.25Fe₂O₄ (CoNiZnCu), Co_0.25Mn_0.25Zn_0.25Cu_0.25Fe₂O₄ (CoMnZnCu), and Ni_0.25Mn_0.25Zn_0.25Cu_0.25Fe₂O₄ (NiMnZnCu), nano spinel ferrites (NSFs) have been synthesized via a sol-gel auto combustion route. Their XRD analysis confirmed the formation of cubic crystalline nanoproducts without any impurity. The crystallite size of the products varied between 15 and 26 nm. EDX analysis confirmed the chemical composition of each product. According to Mössbauer results, Zn²⁺ ions occupy A sites. The s-electron density of Fe³⁺ ions at the A and B sites increased with the Zn²⁺ doping. The magnetic features of samples with various combinations of Co, Ni, Cu, Mn, and Zn were systematically investigated at room temperature (RT, 300 K) and 10 K. Key magnetic parameters <i>M</i> _s (saturation magnetization), <i>M</i> _r (remanent magnetization), <i>H</i> _c (coercivity), squareness ratio, magnetic moment, and magnetocrystalline anisotropy field) are extracted to elucidate the influence of cationic doping and temperature on their magnetic response. Among all samples, CoNiMnCu displayed the highest magnetic hardness and anisotropy, while NiMnZnCu NSFs exhibited soft magnetic behavior with high <i>M</i> _s and low <i>H</i> _c. The results demonstrate significant improvements in magnetic ordering and anisotropy at 10 K across all samples, revealing the temperature-driven enhancement of ferrimagnetic coupling. These findings highlight the tunability of magnetic performance through cation engineering and provide guidance for designing spinel ferrites tailored to specific technological applications, such as permanent magnets, sensors, and magnetic devices. The breast cancer cell (MCF-7) biomedical application of all samples showed a significant decrease in cancer cells as revealed by the MTT assay. Among all samples, CoNiZnCu NSFs showed the highest anticancer activities, as the cell viability was 57.95%. We have also examined the treatment of NSFs on HEK-293, and we detected a reduction in cancer cell viability. However, treatment of NSFs showed more cytotoxicity to breast cancer cells than normal cells. The cells were also stained with DAPI staining. The treatment of CoNiZnCu NSFs produced significant cytotoxicity in breast cancer cells. Moreover, CoNiZnCu NSFs induced chromatin abridgment and apoptotic bodies' formation in the cancer cells. The antimicrobial potential of synthesized metal-based compounds was investigated against <i>Enterococcus faecalis</i> and <i>Candida albicans</i>. Five NSFs were tested at a 16 mg/mL concentration using the broth dilution method. <i>E. faecalis</i> showed strong susceptibility to all compounds except CoNiMnZn NSFs. <i>C. albicans</i> exhibited mild resistance, with only CoMnZnCu NSFs showing notable antifungal activity. The findings highlighted selective and promising antimicrobial effects based on the microbial structure.