Preparation of Epitaxial Fe_3−xTi_xO₄ Solid Solution Films by Sputtering Method

Abstract

Titanomagnetite solid solution Fe_3−xTi_xO₄ films have been prepared on α-Al₂O₃(0001) substrates by a reactive sputtering method. Nearly single phase of Fe_3−xTi_xO₄ with (111)-orientation was epitaxially formed on the substrate. The epitaxial relationship of Fe_3−xTi_xO₄ [11̄0] (111) || α-Al₂O₃ [11̄00] (0001) was confirmed. All films with x < 0.6 exhibited ferrimagnetic property at room temperature. The saturation magnetization of the films showed systematic changes depending on the Ti concentration x. The Ti⁴⁺ ions in Fe_3−xTi_xO₄ can be expected to substitute for the octahedral Fe³⁺ ions by following the Néel-Chevallier model. The films had thermally activated semiconductor behavior and the electrical resistivity with exponentially increasing of the Ti concentration. In-direct optical band gap observed from an absorption spectroscopy also shows monotonical increase with the increasing of Ti concentration.