Synergistic influence of anisotropy and dipolar interactions on the self-heating efficiency of magnetic nanocomposites

Abstract

This work presents a comprehensive investigation into the interplay between magnetocrystalline anisotropy and dipolar interactions in governing the magnetic hyperthermia performance of Cu_1−xCo_xFe₂O₄@SiO₂ (x = 0, 0.1, 0.3, 0.5) nanocomposites (NCs). Through precise tuning of the magnetic nanoparticle (MNP) to SiO₂ matrix ratio, we systematically modulate interparticle dipolar interactions and probe their impact on thermal performance under alternating magnetic fields (11.98–14.98 kA m⁻¹). Structural characterization via XRD confirms a cubic spinel phase, while SEM, TEM, and EDX analyses reveal spherical MNPs uniformly dispersed within an amorphous SiO₂ matrix. Magnetic measurements at 300 K demonstrate a monotonic increase in saturation magnetization and effective anisotropy constant with cobalt substitution (x). Strikingly, specific absorption rate (SAR) measurements expose a compelling dependence on SiO₂ content: NCs with high and moderate SiO₂ fractions exhibit a direct correlation between SAR and the anisotropy energy barrier. However, in highly agglomerated systems with minimal SiO₂, this relationship deviates from monotonicity, defying the predictions of linear response theory and challenging prevailing assumptions in the literature. This deviation underscores the critical role of strong dipolar interactions in disrupting the expected anisotropy-driven heating efficiency. This study provides pivotal comprehension of the self-heating mechanisms of MNPs, paving the way for their optimized deployment in biomedical applications such as magnetic hyperthermia and targeted thermal therapies.