Fe3O4 is obtained after annealing the amorphous iron oxide, at 300 °C for 12 h under N2 atmosphere. The γ-Fe2O3 phase is obtained after annealing Fe3O4 at 200 °C for 4 h under ambient conditions. The α-Fe2O3 phase is obtained after annealing the maghemite at 600 °C for 6 h under ambient condition. In the Figure by Dar and Shivashankar, we can see the Raman spectrum of magnetite nanoparticles, with peaks at about 330, 537 and 663 cm -1 . The maghemite NPs have peaks around 340, 492 and 703 cm -1 .