Shell Thickness-Dependent Anisotropy in CoFe ₂ O ₄ @NiFe ₂ O ₄ Core/Shell Nanoparticles for Magnetic Heating

Using seed-mediated high temperature decomposition method, we synthesized CoFe2O4@NiFe2O4 core/shell nanoparticles with controlled shell thicknesses from ~1 to 6 nm and evaluated their performance in magnetic hyperthermia. A clear enhancement in heating efficiency was observed, with SAR values increasing from ~40 W·g−1 for bare CoFe2O4 to ~80 W·g−1 for the thickest-shell sample. This trend is attributed to optimized magnetic anisotropy and particle volume, enhancing thermal stability and energy dissipation under alternating magnetic fields below Hergt–Dutz limit. These findings support the strategic design of hard@soft ferrite architectures for biomedical heating applications. Although the particles are capped with oleate ligands from the synthesis, these results highlight the tunability of hard@soft ferrite systems and offer insight into the future design of biocompatible hyperthermia agents.