Engineering Magnetic States in Size-Controlled CoFe2O4 Nanoparticles for Enhanced Magnetic Hyperthermia

Abstract Understanding how magnetic-state evolution governs heat-generation efficiency remains a central challenge in the rational design of magnetic hyperthermia nanomaterials. Herein, size-controlled cobalt ferrite (CoFe2O4) magnetic nanoparticles (MNPs) with systematically varied particle dimensions were synthesized by thermal decomposition and investigated using first-order reversal curve (FORC) analysis to elucidate the magnetic origins of hyperthermia performance. Structural characterization revealed spherical MNPs with systematically varying particle-size distributions, while magnetic measurements indicated a progressive evolution from single-domain-dominated behavior toward increased superparamagnetic contributions with decreasing particle size. FORC analysis resolved coercive field distributions and magnetostatic interactions, providing semi-quantitative magnetic-state fingerprints for comparative analysis across the nanoparticle series. Correlation of FORC descriptors with hyperthermia measurements indicated that a favorable magnetic state, characterized by a residual single-domain fraction coexisting with a substantial near-zero-field population, was associated with enhanced heat-generation efficiency. The optimized MNPs achieved high specific loss power (SLP) values of 1434.0 W g−1 in hexane and 1393.3 W g−1 in aqueous ferrofluids under an alternating magnetic field of 400 kHz and 400 Oe. The maximum-SLP condition was used as a materials-performance benchmark rather than a directly clinically deployable operating condition; the observed concentration-, field-, and frequency-dependent responses provide opportunities to tune the heating output toward application-relevant temperature ranges. Systematic investigations further demonstrated strong dependencies of SLP on nanoparticle concentration, field amplitude, and excitation frequency, all consistent with the FORC-derived magnetic-state framework. These findings support a structure−magnetism−hyperthermia relationship in cobalt ferrite MNPs and demonstrate the utility of FORC analysis for identifying magnetic states associated with enhanced hyperthermia performance, while providing design guidance for future magnetic nanomaterials.