Influence of Heating Rate on Morphologies and Magnetic Properties of α-Fe₂O₃

A variety of hematite microstructures are synthesized through oxalic acid-assisted thermal treatment of iron films sputtered onto glass substrates. Petal-like α-Fe₂O₃ nanoslices and honeycomb-like α-Fe₂O₃ particles of micrometer sizes are obtained after annealing at 500°C but with different rates of heating to the final annealing temperature. Structures and morphologies of the samples are studied by means of x-ray diffraction, scanning electron microscopy and atomic force microscopy. These structures are believed to be formed during the period of increasing temperature to the final annealing temperature. Superconducting-quantum-interference-device magnetometer measurements show room-temperature ferromagnetism in these samples.