Structural and Magnetic Characteristics of Hematite and Magnetite Films Prepared by Electrodeposition and Heating

Abstract

Hematite (α-Fe2O3) films were prepared by cathodic polarization in an aqueous solution containing iron (Ⅱ) sulfate hydrate, potassium hydroxide, dimethylamine-borane (DMAB), and L-ascorbic acid and their structural and magnetic characteristics were investigated with X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscope observation, optical absorption measurement, and vibrating sample magnetometer (VSM), in addition to electrochemical characterizations for the electrodeposition before and after heating in ambient atmosphere and vacuum. The hematite films prepared at −1.0 and −1.1 V possessed characteristic hexagonal lattice and bandgap energy around 2.2 eV, and some amount of Fe2+ was contained in the hematite film, with increased Fe2+ content at −1.0 V. The films prepared at −0.8 and −0.9 V showed characteristic hematite bandgap energies with a decreased absorption but did not show any structural characteristics from the XRD and Raman spectra. The hematite films prepared at −1.0 V, and −1.1 V showed ferromagnetic features with 11 A·m2·kg−1 and 2.3 A·m2·kg−1 in saturation mass magnetization and 29.5, and 25 mT in coercivity, respectively. The hematite film was thermally transformed to magnetite (Fe3O4) possessing characteristic cubic lattice by heating at 673 K in vacuum, and the saturation mass magnetization increased to 89.2 A·m2·kg−1.