Carbonization driven magnetic domain evolution in Ni@C Nanocomposites: Impact on magnetic anisotropy and heating efficiency

• Hybrid Ni@C based multifunctional magnetic nanocomposites with a MOF-type microstructure. • Carbonization temperature determines the phase composition and crystallinity. • High specific absorption rate and intrinsic loss power from magnetic calorimetric measurements. • Controlled carbonization optimizes Ni@C nanoparticles for heating applications. Hybrid nanocomposites of nickel nanoparticles (Ni NPs) embedded in a carbon matrix hold significant promise for environmental remediation by integrating the adsorption capacity of carbon with the antimicrobial effects induced by localized heating of Ni NPs under magnetic hyperthermia. In this work, we investigate the evolution of the structural, magnetic and thermal properties of Ni@C nanocomposites as a function of the carbonization temperature. Samples within the magnetic single domain and multidomain regimes have been used to explore their potential for magnetic hyperthermia-assisted water remediation. To assess the influence of these different regimes on the tranverse suscepbility (TS) and magnetic heating performance, two representative samples, S600 and S1000, were selected to span the single-domain to multi-domain particle regimes. TS measurements show that S1000 exhibits a higher effective anisotropy field ( H Keff ) , attributed to its larger particle size and enhanced magnetic anisotropy. However, calorimetric magnetic heating studies reveal that S600 demonstrates significantly higher specific absorption rate (SAR) and intrinsic loss power (ILP) values, especially at lower concentrations. This enhanced heating efficiency is linked to its smaller particle size, reduced dipolar interactions, and magnetically soft behavior at room temperature. Consequently, more effective magnetic relaxation under moderate fields is enabled, highlighting the importance of optimizing nanoparticle size, anisotropy, and matrix dispersion to improve magnetic heating performance, offering design strategies for non-biomedical applications such as water purification and microbial inactivation.