Goethite (α-FeOOH) nanopowders synthesized via a surfactant-assisted hydrothermal method: morphology, magnetic properties and conversion to rice-like α-Fe2O3 after annealing

Abstract

Acicular goethite (α-FeOOH) nanopowders were synthesized at a high temperature via a CTAB-assisted hydrothermal method. Their morphologies, mechanism of saturation magnetization and coercivity, and conversion to rice-like α-Fe₂O₃ after annealing are studied. It is found that the α-FeOOH should be synthesized at a temperature lower than 240 °C, and the acicular α-FeOOH structure actually consists of slender α-FeOOH nanorods. With the increase of CTAB content from 0.2 g to 0.4 g, the synthesized α-FeOOH nanorods become more and more slender, accompanying with the enhancement of the saturation magnetization from about 0.05 emu g⁻¹ to about 0.25 emu g⁻¹, which can be ascribed to the increase of the surface area of the α-FeOOH nanorods. The as-synthesized acicular α-FeOOH powders exhibit a large coercivity with a maximum value of about 120 kA m⁻¹ (∼1500 Oe) due to the shape anisotropy. It is also found that the acicular α-FeOOH powders gradually convert to rice-like α-Fe₂O₃ particles after annealing at high temperatures.