Nonstoichiometry of epitaxial FeTiO{sub}(3+δ) films

摘要

Epitaxial thin films of (001)-oriented FeTiO{sub}(3+δ) were prepared on α-Al{sub}2O{sub}3(001) single crystalline substrates by helicon plasma sputtering technique. The FeTiO{sub}(3+δ) films had large oxygen nonstoichiometry, which seriously depended on both substrate temperature and oxygen pressure during the sputtering deposition. The valence states of Fe ions in FeTiO{sub}(3+δ) changed monotonically from Fe{sup}(2+) to Fe{sup}3+ with decreasing the substrate temperature from 900 to 400°C or with increasing the oxygen pressure from 0.9 to 1.8013310{sup}(-6) Pa. The change of Fe valence states from Fe{sup}(2+) to Fe{sup}(3+) induced the magnetic phase transition only for the films prepared at 900°C. The films containing Fe{sup}(2+) were paramagnetic while those with Fe{sup}(3+) were antiferromagnetic at room temperature. The oxygen nonstoichiometry of the FeTiO{sub}(3+δ) films was probably produced by cation vacancies and disarrangement of Fe{sup}(3+) and Ti{sup}(4+) ions, which randomly occupied both interstitial and substitutional sites of the FeTiO{sub}3 related structure.