Stoichiometry-engineered cobalt ferrite-based nanomaterials with tunable magnetism, magnetostriction, and in vitro cytotoxicity

Composition-dependent Co-Fe oxide samples with nominal Co x Fe 3-x O 4 stoichiometry (x = 0.5–1.1) were prepared by sol-gel auto-combustion to examine their phase constitution, microstructure, magnetic behavior, pellet-scale magnetostriction, and in vitro response toward MCF-7 breast-cancer cells. Rietveld analysis showed coexistence of cubic spinel ferrite and α-Fe 2 O 3 for x = 0.5–0.8, whereas x = 0.9–1.1 were predominantly single-phase spinel; crystallite sizes were approximately 20–30 nm. At 300 K, coercivity reached 1.86 kOe for x = 0.7. Sintered-pellet measurements also gave the largest longitudinal magnetostriction at x = 0.7 (λ∥,max = -425 ppm), while x = 0.9 and 1.0 showed lower measured strain magnitudes. In MTT assays conducted without an applied magnetic field, growth inhibition increased with concentration and was highest for x = 1.1 and x = 1.0, reaching 46.2% and 44.7%, respectively, at 1000 µg mL - 1 after 48 h. Phase-contrast microscopy and DAPI nuclear staining showed concentration-dependent loss of confluence, cell rounding, and nuclear condensation or fragmentation. These observations indicate cytotoxic damage but do not by themselves establish apoptosis or its molecular mechanism. Because magnetostriction was measured on sintered pellets, whereas the biological assays used nanoparticle suspensions under zero-field conditions, the two data sets are treated as independent outcomes. The present results establish composition-dependent structure–magnetic–magnetostrictive relationships in Co–Fe oxide nanomaterials together with their baseline in-vitro response, while the measured magnetostrictive properties provide a materials-level basis for future magnetic-field-assisted biomedical investigations.