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

An ilmenite-hematite solid solution (Fe2–xTixO3) is one of the candidates for practical magnetic semiconductors with a high Curie temperature. We have prepared well-crystallized epitaxial Fe2–xTixO3 films with a wide range of Ti concentrations—x=0.50, 0.60, 0.65, 0.76, 0.87, and 0.94—on α-Al2O3(001) substrates. The films are prepared by a reactive helicon plasma sputtering technique to evaporate Fe and TiO targets simultaneously under optimized oxygen pressure conditions. The structural characterizations of the films reveal that all films have a single phase of the ordered structure with R3¯ symmetry, where Ti-rich and Fe-rich layers are stacked alternately along the c axis. All films have large ferrimagnetic moments at low temperature, and room temperature magnetization is clearly observed at x<0.7. The inverse temperature dependence of the resistivities of the films indicates their semiconducting behavior. The film resistivities decrease with decreasing Ti concentration.