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

► Room temperature ferromagnetism (FM) observed in Nb doped titania (TNO) films.
► 10–30 nm Nb2O5 precipitates in TNO films enhance saturation magnetization (Ms).
► The largest Ms is the 800 °C annealed 40 nm-thick TNO films on glass nanospheres.
► The Ms reduces as films increased in thickness or deposited on flat Si substrates.
► Nano-precipitates and interfaces are important for enhanced FM in TNO 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 (Ms). The largest Ms is found in the 800 °C annealed 40 nm-thick TNO films on glass nanospheres (~ 6 × 104 A/m) and the Ms 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.