Pre-reaction mixing temperature and time control shape and size anisotropy in solvothermal Fe3O4 nanostructures

Magnetic Fe 3 O 4 nanoparticles are widely used in magnetothermal applications, where heating efficiency depends on magnetic anisotropy. Here, we report a template-free solvothermal strategy that decouples shape and size control. Pre-reaction mixing temperature and duration determine the formation of Fe 3 O 4 nanospheres or nanorods, while hexadecylamine concentration and solvothermal time independently control rod length (~35–80 nm). Transmission electron microscopy (TEM) confirms uniform morphology, and X-ray diffraction (XRD) verifies single-phase inverse spinel Fe 3 O 4 . Pre-reaction Fourier-transform infrared (FTIR) spectroscopy provides insight into growth mechanism. Magnetization (M-H) measurements revealed that rod shape and size influence coercivity and saturation magnetization and AC magnetometry under clinically relevant conditions (200 kHz, 20 kA/m) showed that intermediate-sized rods (~45 nm) exhibit the highest heating efficiency (specific absorption rate ~ 145 W/g), relative to spheres and other rod length. This strategy enables anisotropy-optimized nanoparticles for magnetothermal biomedical applications. • Template-free solvothermal route enables independent control of Fe 3 O 4 nanoparticle shape and size. • Pre-reaction mixing temperature and time govern nanosphere versus nanorod formation. • Rod length is turned independently via hexadecylamine concentration and reaction time. • FTIR reveals temperature-dependent precursor coordination controlling morphology. • Intermediate length nanorods showed maximized magnetothermal heating efficiency.