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

A series of epitaxial Fe_2−xTi_1+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 Fe_1.5Ti_1.5O₅ and the insulating Fe_1.3Ti_1.7O₅, as n-type oxides, showed promising thermoelectric properties with giant Seebeck coefficients up to the mV/K level. The electrical conduction in the Fe_1.5Ti_1.5O₅ 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 Fe_2−xTi_1+xO₅ films as tunable ferromagnetic semiconductors.