Effect of annealing on phase formation, microstructure and magnetic properties of MgFe₂O₄ nanoparticles for hyperthermia

In this study the effect of annealing time is confirmed to alter the morphology (shape and size) of magnesium ferrite nanoparticles (MgFe₂O₄) synthesized by autoclave route, employing ferric and magnesium nitrate salts as precursors. Annealing was applied at 1000 ^°C for different durations (2, 30 and 60 h) and Rietveld refinements of X-ray diffraction patterns confirm the formation of pure spinel phase and show that the annealing time has a dominant effect on the crystallite size as it increases from 29 up to 89 nm for 2 to 60 h, respectively. Scanning electron microscopy observations confirm that longer annealing time enhances particle growth, in agreement with the crystallite size obtained by X-ray diffraction analysis. Room temperature magnetic measurements reveal a ferromagnetic behavior with a saturation magnetization (M_s) ranging from 25.84 emu/g for annealing at 2h and 29.49 emu/g at 60 h. Self-heating characteristics under an alternating current (AC) magnetic field of 17mT and frequency of 331 kHz were investigated for hyperthermia applications using Magnetherm from Nanotherics. Temperature-time curves indicate that the as-prepared MgFe₂O₄ nanoparticles show a considerable heating rate, with a maximum temperature of 48 ^°C in a very short period of time of 15 min and specific absorption rate (SAR) of 19.23 W/g, when annealed for 60 h.