Nano-precipitates induced room temperature ferromagnetism in heavily Nb-doped titania thin films

Room temperature ferromagnetism (FM) is observed for annealed heavily niobium doped titania (TNO) thin films on silicon substrates and on glass nanospheres. Precipitation of ∼ 10–30 nm-diameter Nb₂O₅ nanoparticles occurs in the TNO films air-annealed at 600 °C or above and enhances their saturation magnetization (M_s). The largest M_s is found in the 800 °C annealed 40 nm-thick TNO films on glass nanospheres (∼ 6 × 10⁴ A/m) and the M_s reduces as films increased in thickness or deposited on flat Si substrates or annealed at lower temperature or in hydrogen. This work demonstrates that nano-precipitates and interfaces are both significant factors in achieving enhanced FM in the titania based thin films. - Highlights: ► Room temperature ferromagnetism (FM) observed in Nb doped titania (TNO) films. ► 10–30 nm Nb₂O₅ precipitates in TNO films enhance saturation magnetization (M_s). ► The largest M_s is the 800 °C annealed 40 nm-thick TNO films on glass nanospheres. ► The M_s reduces as films increased in thickness or deposited on flat Si substrates. ► Nano-precipitates and interfaces are important for enhanced FM in TNO films