Crystal structure and magnetism in κ -Al₂O₃-type Al_xFe_2-xO₃ films on SrTiO₃(111)

We prepared κ-Al₂O₃-type structured Al_xFe_2-xO₃ films in the range of x = 0 - 1.70 deposited on SrTiO₃(111) substrates and investigated their crystal structures and magnetic properties. All films could be stabilized in the κ-Al₂O₃-type orthorhombic phase, and the lattice parameters were found to be monotonically decreased with an increase in the Al content. Néel temperature of Al_xFe_2-xO₃ films was found to decrease with an increase in Al content, until the Al_1.70Fe_0.30O₃ film showed paramagnetic behavior. On the other hand, saturation magnetization showed a maximum 0.79 μ_B/Fe at 10 K in the Al_0.91Fe_1.09O₃ film, manifesting the preferential occupation of Al in the tetrahedral site. Cross sectional TEM observation has revealed the columnar growth of Al_xFe_2-xO₃ films with an average width of ∼10 nm on the bottom layer that may have a similar cation arrangement with a bixbyite-type structure.