Healing Effect of Graphene Oxide in Achieving Robust Dilute Ferromagnetism in Oxygen-Deficient Titanium Dioxide

Titanium dioxide (TiO2) is an important wide band-gap semiconductor with promising application for next generation spintronics. Unfortunately, the lack of inherent spin ordering enormously hinders the widening scope of TiO2, and the origination of ferromagnetic properties still needs to be comprehensively explored due to the fact that manipulating the magnetic property in semiconductor through defect engineering remains a great challenge. Here we systematically investigate the room-temperature ferromagnetism (RTFM) behavior of defective anatase TiO2-x with the exposed (001) facet grown on reduced graphene oxide (rGO). First-principles simulations were performed to examine two types of intrinsic oxygen defects in TiO2-x: vacancy on surface (VO-sur) and at subsurface (VO-sub), among which only the VO-sub contributes a considerable magnetism. Interestingly, simulations revealed a so-called healing effect for the oxygen functional groups in rGO, by removing the VO-sur defect of TiO2-x, which helps establish good interface and thereby ensures good coupling between rGO and VO-sub defects. Calculations show that the interaction of rGO with Ti3+-oxygen vacancy associates alters spin asymmetric electron distribution around VO-sub and consequently introduces significant spin asymmetric defect states near the Fermi level. Hence rGO triggers a significant magnetic enhancement in TiO2-x. Importantly, our findings pave a new avenue for effective design and manipulation of spin states in an undoped dilute ferromagnetic semiconductor for spintronics application.