Magnetism of a Nitrogen-Implanted TiO₂ Single Crystal

Single rutile crystal TiO₂ was implanted using nitrogen ions with energy of 60 keV. The microstructure, ultraviolet−visible light absorption spectra, conductivity and magnetism are investigated. Except for the nitrogen dopant, no impurity can be detected by x-ray diffraction and x-ray photoelectron spectra. The absorption in the visible light region is enhanced with nitrogen implantation dose increasing. By measuring the temperature dependence of resistance, it is found that the sample implanted with 1×10¹⁸ ions/cm² is changes from insulating to semiconducting, and the variable range hopping is the main conducting mechanism. Room-temperature ferromagnetism is also obtained in this sample. The magnetism as a function of temperature can be well fitted using the three-dimensional spin wave model plus the Curie–Weiss model, indicating that there is a mixed phase of ferromagnetism and paramagnetism.