Room temperature superparamagnetism in rutile TiO₂ quantum dots produced via ECR sputtering

Nanostructures (NS) have been fabricated on rutile TiO₂(1 1 0) single crystal surfaces using Ar ion beam sputtering technique. Pronounced quantum confinement effects in TiO₂ nanodots lead to reduction in optical reflectance and bandgap widening. Moreover, a direct correlation between the size of NS and magnetic behavior is observed. This suggests that the size of NS plays crucial role in the evolution of magnetic nature. Though the smallest (∼5 nm) NS display superparamagnetic (SPM) behavior, ferromagnetism is observed for larger nanostructures. Single domain nature of TiO₂ quantum dots is responsible for the observed SPM behavior.