Oxygen-pressure-tuned phase stability, microstructure, and magnetic properties of BiFeO₃ films on titanium-buffered silicon

Stabilizing functional magnetic behaviour in BiFeO₃ films on silicon is hindered by parasitic phase formation, unstable defect chemistry, and poor strain accommodation at oxide–semiconductor interfaces. Here, oxygen-pressure-controlled growth is demonstrated as an effective interface-engineering strategy to regulate phase stability, microstructure, and magnetic functionality in BiFeO₃ films deposited on titanium-buffered silicon by pulsed laser deposition. By varying the oxygen partial pressure at a fixed substrate temperature, a narrow and reproducible growth window is identified in which phase-pure rhombohedral BiFeO₃ is stabilized without epitaxial lattice matching or noble-metal buffer layers. X-ray diffraction shows suppression of Bi₂O₃ formation and balanced lattice distortion at low oxygen pressure, while X-ray photoelectron spectroscopy confirms near-stoichiometric surface chemistry with reduced perturbed oxygen coordination, indicating effective regulation of interfacial oxygen chemical potential by the TiOₓ/Ti buffer. Cross-sectional images reveal transformation of the Ti buffer into a vertically graded TiOₓ/Ti architecture that provides strain accommodation and chemical isolation from silicon. Magnetic force microscopy and temperature- and field-dependent magnetization measurements demonstrate a soft weak-ferromagnetic response persisting to room temperature only within this interface-optimized growth regime. These results establish oxygen-pressure-controlled interface engineering as a scalable, silicon-compatible route for integrating functional oxide magnetism beyond epitaxial constraints.