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Formation of the hard-magnetic epsilon iron oxide phase from akaganéite nanoparticles
Navya Joseph1, Surya Gopi1, Aladin Ullrich2
1Department of Physics, Cochin University of Science and Technology, Cochin 682022 Kerala, India.
Abstract:
Elongated akaganéite (β-FeOOH) nanoparticles were prepared by a forced hydrolysis route using FeCl3·6H2O employing various urea concentrations.β-FeOOH nanoparticles stabilized within the SiO2matrix were annealed at different temperatures, ranging from 500 °C to 1300 °C. It was observed thatβ-FeOOH underwent a temperature-induced conversion toγ-Fe2O3and subsequently toϵ-Fe2O3. Due to theϵ-Fe2O3phase formation, the coercivity rapidly increased to 16 kOe for samples annealed at 900 °C and reached values up to 21.5 kOe when annealed at 1200 °C. At a higher temperature of 1300 °C, theϵ-Fe2O3phase transforms mainly into theα-Fe2O3phase, which causes the coercivity to rapidly drop to negligible values.
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