Structures and properties of transition-metal-doped TiO2 nanorods

• Transition-metal-doped rutile TiO2 nanorods were synthesized by molten salt method.
• Transition metal ions were successfully incorporated into TiO2 lattice.
• Room temperature ferromagnetism was observed in undoped TiO2.
• Ti vacancy is likely to be the origin of ferromagnetism.
• Transition metal doping enhances the paramagnetic signal.

Titanium dioxide (TiO2) doped with magnetic elements is a promising candidate for the applications of spintronic devices. In this work, we have successfully synthesized rutile TiO2 nanorods doped with a variety of transition metals (Co, Ni, Mn and Fe) through a molten salt method. XRD and Raman results indicate the effective incorporation of dopant ions into TiO2 lattice. SEM and TEM images demonstrate that most of the samples are grown along the c-axis with the shape of nanorods except 1%Fe-doped sample. The M-H loops indicate that all the samples exhibit weak room temperature ferromagnetism. Whereas, in undoped TiO2, diamagnetic and ferromagnetic signals are detected at room temperature and the coexistence of the paramagnetic phase is found at 5 K. It is evident that the incorporation of various dopants such as Co, Ni, Mn or Fe into TiO2 nanostructures gives rise to paramagnetism instead of enhancing the ferromagnetic ordering.