Structural and magnetic studies of TiO2 rutile implanted with vanadium ions

Single crystal (100) and (001) TiO2 rutile plates were implanted with vanadium 40 keV ions to the fluence of 1.5 x 10(17) ion cm(-2). A set of samples was also annealed at high-temperature in air to restore oxygen stoichiometric content and recover the TiO2 lattice structure after the high-dose ion implantation. In addition, a control set of TiO2 rutile plates was implanted with 40 keV argon ions to the same fluence to explore the effect of radiation-induced defects on magnetic properties. Rutherford backscattering spectroscopy (RBS), x-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometry (VSM) measurements were carried out to characterize the structural and magnetic properties of the vanadium-implanted TiO2. Both as-implanted and subsequently annealed V-TiO2 samples reveal ferromagnetic response at room temperature. Strong ferromagnetism observed in the vanadium-implanted (001) TiO2 plates is related to the \substitutional V4+ ions coupled by the indirect exchange via electrons trapped at oxygen vacancies, while much weaker ferromagnetism in the (100)oriented plates and the Ar-implanted samples is attributed to lattice defects induced by the high-dose ion irradiation. Suppression of the ferromagnetic response in the vanadium-implanted (001) TiO2 after the thermal treatment is explained by filling in the oxygen vacancies due to oxygen diffusion during annealing in air atmosphere.