Epitaxial thin films of room-temperature ferromagnetic semiconductor based on Fe2TiO5–FeTi2O5 solid solution

Abstract

A series of epitaxial Fe2−xTi1+xO5 (0 ≤ x ≤ 0.7) solid solution thin films was fabricated on SrTiO3 (100) substrates by pulsed laser deposition. A (230)-oriented single phase with an orthorhombic structure was obtained within a narrow growth temperature window (850–900 °C). Both the semiconducting Fe1.5Ti1.5O5 and the insulating Fe1.3Ti1.7O5, as n-type oxides, showed promising thermoelectric properties with giant Seebeck coefficients up to the mV/K level. The electrical conduction in the Fe1.5Ti1.5O5 film obeyed the Arrhenius law at 200–300 K but transitioned to three-dimensional variable range hopping at 120–180 K. Furthermore, at and above room temperature (∼400 K), all the films (x = 0, 0.3, 0.5, and 0.7) exhibited significant ferromagnetic behavior, which was closely dependent on the different ratios of Fe2+, Fe3+, and Ti4+ ions. These results potentially lay a solid foundation for future cost-effective spintronics applications of Fe2−xTi1+xO5 films as tunable ferromagnetic semiconductors.