Evolution of Cation-Site Defects, d⁰ Ferromagnetism and Electron Spin Resonance Signal in p-Type Luminescent In-Doped SnO₂ Thin Films: Influence of In Situ O₂ Pressure and Film Thickness

We report the impacts of in situ O2 pressure and film thickness on the inherent crystalline defects and correlated room temperature ferromagnetism (RTFM) in nonmagnetic indium (In)-doped SnO2 thin films fabricated using pulsed laser deposition (PLD). When deposition (O2) pressure is increased from 7.5 × 10–3 Torr to 7.5 Torr, the thickness of the film has reduced while the values of lattice microstrain, crystallite size and resistivity of p-type semiconducting In:SnO2 films have increased. Appearance of additional Raman vibrational modes A2g (574 cm–1) and Eu LO (354 cm–1) signifies the existence of serious surface or lattice disorder within the host. On increasing deposition pressure, a remarkable enhancement saturation magnetization (MS) and Curie temperature (TC) of the ferromagnetic films are observed compared to the undoped film. In lower pressure, evidence of two major paramagnetic defect centers such as singly ionized oxygen vacancy (VO+) and Sn monovacancy (VSn) or associated defect complexes like (VSn-VO) comprising Landé g-factors around 2.003 and 1.89, respectively, have been detected in electron spin resonance (ESR) spectroscopy. For the films deposited in higher O2 pressure, VSn defects become the dominant paramagnetic defect centers while the abundance of VO+ has greatly diminished. The substantial correlation between MS and corresponding ESR signal suggests VSn-driven hole-mediated ferromagnetism in p-type In-doped SnO2 films. Hence, the study illustrates an effective approach to trigger cation-site defect-engineered high-TC FM in low-dimensional oxide semiconductors for spintronic and opto-spintronic applications.