  Tailoring the magnetic properties of iron oxide nanosystems is essential to
expand their biomedical applications. In this study, the 34 nm iron oxide
nanocubes with two phases consisting of Fe3O4 and alpha-Fe2O3 were annealed for
2 hours in the presence of O2, N2, He, and Ar to tune the respective phase
volume fractions and control the magnetic properties. X-ray diffraction and
magnetic measurements were carried out post-treatment to evaluate the changes
of the treated samples compared to the as-prepared, which showed an enhancement
of the alpha-Fe2O3 phase in the samples annealed with O2, while the others
indicated Fe3O4 enhancement. Furthermore, the latter samples indicated
enhancements in the crystallinity and saturation magnetization while coercivity
enhancement was most significant in the samples annealed with O2, resulting in
the highest specific absorption rates (up to 1000 W/g) in all the applied
fields of 800, 600, and 400 Oe in agar during magnetic hyperthermia
measurements. The general enhancement in the specific absorption rate
post-annealing underscores the importance of the annealing atmosphere in the
enhancement of the magnetic and structural properties of nanostructures.
