Shell Thickness-Dependent Anisotropy in CoFe2O4@NiFe2O4 Core/Shell Nanoparticles for Magnetic Heating

Using the 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 specific absorption rate (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 (AMFs) below Hergt–Dutz limit. These findings support the strategic design of hard and 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 and soft ferrite systems and offer insight into the future design of biocompatible hyperthermia agents. © 1965-2012 IEEE.