Fe₃S₄/Fe₃O₄/MWCNT nanocomposites: an investigation on structural, magnetic, and AC induction heating properties

This study reports, for the first time, the seed-assisted sequential synthesis of dual magnetic phase Fe₃S₄/Fe₃O₄ nanocomposites integrated with multi-walled carbon nanotubes (MWCNTs) using a combined co-precipitation and solvothermal approach, providing an effective strategy for tailoring their structural, magnetic, and AC induction heating properties. The coexistence of Fe₃S₄ and Fe₃O₄ phases is confirmed by X-ray diffraction and X-ray photoelectron spectroscopy analyses. The red-shifted Raman bands and electron microscopy studies verify the successful incorporation and growth of magnetic nanoparticles on the MWCNT surfaces. Thermogravimetric analysis confirms the thermal stability of the nanocomposites within the temperature range relevant for therapeutic applications. The Fe₃O₄/Fe₃S₄-MWCNT (FO/FSMWC) and Fe₃S₄/Fe₃O₄-MWCNT (FS/FOMWC) nanocomposites exhibit room-temperature saturation magnetizations of ∼59 and ∼47 emu g^-1, respectively, with distinct coercive responses arising from their different phase arrangements. Magnetic hyperthermia studies reveal efficient AC magnetic field-induced heating, achieving temperatures above the therapeutic threshold (∼42 °C) within ∼120 s under biologically safe alternating magnetic field conditions. However, despite its ∼20% lower saturation magnetization, the FS/FOMWC nanocomposite exhibits a higher specific absorption rate (SAR) of ∼37.33 ± 2.54 W g^-1 at a field amplitude and frequency of ∼33.1 kA m^-1 and ∼126 kHz, respectively, which is ∼29% higher than that of the FO/FSMWC nanocomposite under similar exposure conditions. This enhanced heating efficiency is attributed to the higher coercivity of FS/FOMWC, whereas the comparatively lower SAR of FO/FSMWC can be associated with stronger interparticle interactions arising from the observed magnetic phase agglomeration, as suggested by the microscopy analysis. These findings demonstrate that dual magnetic phase Fe₃S₄-Fe₃O₄-MWCNT nanocomposites exhibit good thermal stability and tunable magnetic and magnetothermal properties through controlled phase formation, highlighting their potential as promising magnetic agents for magnetic hyperthermia and related biomedical applications.