Structural, electronic, and magnetic study on hematite nanorods: Effect of carbon coating and annealing temperature

In this work, spindle shape α-Fe₂O₃ nanorods and carbon-coated α-Fe₂O₃@C nanorods were synthesized using a simple hydrothermal method followed by calcination at a temperature of 600 °C. Morphology, structural, surface, and magnetic properties of the synthesized samples were studied before and after calcination. XRD results prove the formation of a single corundum phase α-Fe₂O₃ after hydrothermal preparation at 180 °C. The crystallite size of α-Fe₂O₃ decreases by calcination in contrast with α-Fe₂O₃@C. Through calcination, meso-size pores were formed as investigated by TEM. These pores are more in α-Fe₂O₃ nanorods. Using XPS surface analysis, more O-H bonds were found in α-Fe₂O₃ nanorods. TEM, XPS, and FTIR techniques were used to prove the formation of the Carbon layer on α-Fe₂O₃@C nanorods. Intensive characterization and the magnetic properties of α-Fe₂O₃ and α-Fe₂O₃@C nanorods were also carried out and reported. VSM measurements show an increase in magnetic moment with smaller coercivity and remanence via C-coating and calcination. The Morin transition as investigated using VSM and Mossbauer measurements, appears for pure hematite nanorods after calcination under atmospheric pressure. This transition is suppressed as shown for nanosize particles with c/a of ≥ 2.74 which was also applicable for samples made by other workers.