Investigation of Electronic Energy Levels in a Weak Ferromagnetic Oxygen‐Deficient BiFeO _2.85 Thick Film Using Absorption and X‐Ray Photoelectron Spectroscopic Studies

ABSTRACT We grew a 2‐μm‐thick film of single‐phase BiFeO 3 on a Si (100) substrate by pulsed laser deposition with a substrate temperature of 575°C and an oxygen partial pressure of 0.06 mbar. X‐ray diffraction analysis indicated that the film exhibits textured growth along the (110) plane and possesses a rhombohedral R3c structure. Investigations using scanning electron microscopy and atomic force microscopy revealed an average grain size of about 300 nm and a surface roughness of 18 nm for the film. Energy‐dispersive X‐ray analysis estimated the composition of the film to be BiFeO 2.85 . Temperature‐ and magnetic field‐dependent magnetization measurements demonstrated weak ferromagnetic properties in the BiFeO 2.85 film, with a nonzero spontaneous magnetization at H = 0 Oe across the temperature range of 2–300 K. Furthermore, the exchange bias field ( H EB ) of the film changed from the positive exchange bias field (+ H EB = +6.45 Oe) at 200 K to a negative field (‐ H EB = −8.12 Oe) at 100 K, indicating a shift in macroscopic magnetism from antiferromagnetic to weak ferromagnetic order below 200 K. Elemental analysis via X‐ray photoelectron spectroscopy revealed that the Fe ions in the BiFeO 2.85 film are in a 3+ valence state, and a peak feature at 532.1 eV confirmed the presence of induced oxygen vacancies. UV–visible‐NIR and valence band spectroscopic studies showed that the direct band‐gap energy and the separation between the valence band maximum and Fermi energy were approximately 2.27 and 0.9 eV, respectively, which are red‐shifted when compared to its bulk form.