FeTiO₃/Fe₂O₃ Multilayered Films for New Magnetic Semiconductors above Room Temperature

Abstract

Well-crystallized Fe1.18Ti0.82O3 and Fe1.18Ti0.82O3/Fe2O3 bilayered films were successfully prepared by using reactive helicon plasma sputtering technique. The solid solution films, Fe2−xTixO3, between hematite (α-Fe2O3) and ilmenite (FeTiO3) with various Ti concentrations, x, were epitaxially formed on the α-Al2O3(0001) single-crystalline substrates. The magnetic and electric properties of the solid solution films were systematically changed with increasing the Ti concentration. The film with the intermediate composition of Fe1.18Ti0.82O3 had the largest saturation magnetization at low temperature. However, the TC of solid solution films was linearly decreased with increasing the Ti concentration. The Fe1.18Ti0.82O3 film without Fe2O3 layers showed lower TC of about 200 K, while the TC of the Fe1.18Ti0.82O3/Fe2O3 bilayered film increased to about 220 K. The strong magnetic coupling between layers seemed to increase the TC of the attached Fe1.18Ti0.82O3 layer. The sharp interface between Fe1.18Ti0.82O3 and α-Fe2O3 layers was confirmed by the XPS depth profiling.

Preparation and characterization of epitaxial Fe2−xTixO3 films with various Ti concentrations (0.5<x<1.0)

“…The CEMS spectrum of a ͑001͒-oriented epitaxial FeTiO 3 film is known to have an asymmetric doublet with an intensity ratio of approximately 1:3 because the electric field gradient axis in FeTiO 3 coincides with the c axis. 13 The observed asymmetry in the doublet patterns for x = 0.94 suggested the high crystallinity of the prepared films. The paramagnetic spectra consisted of two asymmetric doublets ͑labeled A and B in Table I͒ With a decrease in the Ti concentration, the averaged IS value for Fe 2-x Ti x O 3 changed linearly from the one characteristic of Fe 2+ ions to that of Fe 3+ ions.…”

“…We previously reported the preparation of wellcrystallized epitaxial Fe 2-x Ti x O 3 films with various Ti concentrations in the range 0.6Ͻ x Ͻ 1.0. [12][13][14] The films were formed on sapphire single-crystalline substrates by the reactive sputtering technique using a Fe-Ti alloy target to accurately control the oxygen partial pressure and substrate temperature. The T C value of Fe 2-x Ti x O 3 films increased linearly with decreasing Ti concentration.…”