Synthesis, morphology and microstructure of pomegranate-like hematite (α-Fe2O3) superstructure with high coercivity

We found novel and superior magnetic properties of the hematite (alpha-Fe2O3) that originate from an internal microstructure of particles and strong inter-particle interactions between nanocrystal sub-units. The hematite particles were synthesized by thermal decomposition of iron (III) nitrate without any template or surfactant. The purity, size, crystallinity, morphology, microstructure and magnetic features of the as-prepared particles were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy (RS) and SQUID magnetometry. An XRD study reveals a pure phase of alpha-Fe2O3 whereas TEM shows alpha-Fe2O3 spheres with a diameter of about 150 nm. RS also shows high quality and purity of the sample. Moreover, TEM and HRTEM images show a pomegranate-like superstructure and evidence that the spherical particles are composed of individual well-crystallized nanoparticle sub-units (self-assembled nanoparticles) with a size of about 20 nm. Magnetic measurements display hysteretic behavior at the room temperature with remanent magnetization M-r = 0.731 emu/g, saturation magnetization M-S = 6.83 emu/g and coercivity H-C = 4350 Oe, as well as the Morin transition at T-M = 261 K. These results and comparison with those in the literature reveal that the sample has extremely high coercivity. The magnetic properties of the sample are discussed in relation to morphology, internal microstructure, surface effects and exchange and dipole-dipole interactions. (C) 2012 Elsevier B.V. All rights reserved.