The Dilute Magnetic Properties Of Transition Metal And Non-metal Co-doped Titanium Dioxide

Diluted magnetic semiconductors?DMSs?refer to the fact that some fractions of the atoms in nonmagnetic semiconducting materials are replaced by transition metal?TM?ions?such as Mo,Ag,Au,Mn,Ru?that are possess semiconductor characteristics and the occurrence of room temperature ferromagnetic response,which has drawn a considerable attention due to their application prospects in large scale integrated circuit,high frequency device and optoelectronic device.DMSs have been extensively studied both experimentally and theoretically for room temperature ferromagnetic.However,there are a number of conflicting reports on origin of the magnetism at room temperature in the samples grown under similar conditions.For this reason,the origin of room temperature ferromagnetism?RTFM?in DMSs materials remain a very controversial topic,whether it is due to an intrinsic or an extrinsic effect.The main purpose of the present work is to bring further insight into the origin of the room temperature ferromagnetic,we investigated the physical properties especially the magnetic properties of TM and non-metal co-doped TiO₂ films combined experiments with first-principles calculations.The details are shown below:1.The TiO₂ films and Au cluster doped Ti O2 films fabricated by sol-gel and sputtering methods.X-ray diffraction?XRD?analysis reveals that the samples have the pure anatase TiO₂ structure.Ultraviolet visible spectrophotometer?UV-vis?analysis reveals that the Au introduced by sputter coating exist as Au cluster form in these Au ?-doped TiO₂ samples.X-ray photoelectron spectra?XPS?analyses confirm that the value of Au valence is zero in Au cluster doped TiO₂ film?annealed in air?.The Ti³⁺ ions are usually introduced by oxygen vacancy?VO?due to the reduced oxygen partial pressure.However the information of Ti³⁺ was not given by the XPS spectra.In order to investigate the existence of VO,the photoluminescence?PL?spectra are given.The PL spectra observation shows that the formation of VO in these samples.The vibrating sample magnetometer?VSM?measurement shows that all the TiO₂ sample exhibit room temperature ferromagnetism.The values of the saturation magnetizations?Ms?are in the order of Au ?-doped TiO₂?annealed in N₂?> un-doped TiO₂?annealed in air?> Au ?-doped TiO₂?annealed in air?.The first principles calculation results show that the formation energy of Au cluster doped TiO₂ films is lower than that of the VO and Au cluster co-doped TiO₂ films.The effects of the Au cluster dopant are the retard of the formation of surface VO and the electrons transfer from 3d states of Ti atoms to Au 5d states in Au cluster doped TiO₂ films.The co-doping of surface Vos,bulk Vos and Au clusters led to the spin-split of Ti 3d and O 2p in Au cluster doped TiO₂ films?annealed in N₂?which yield the highest saturation magnetization.Therefore,the results indicate that the VO plays a crucial role in room temperature ferromagnetic properties for TiO₂ films.2.The C doped and C-Fe co-doped TiO₂ films fabricated by sol-gel methods.XRD analysis reveals that the samples have the pure anatase TiO₂ structure.UV-vis analyses confirm that the Fe-C co-doped sample yields the largest red shift which indicates the doping of Fe or C element may narrow the band gap.The PL spectra observation shows that the formation of VO in these samples.VSM measurement shows that all the TiO₂ sample exhibit room temperature ferromagnetism?RTFM?.The values of the Ms are in the order of Fe-C co-doped TiO₂ > Fe-C co-doped TiO₂?annealed in O2?> C doped TiO₂ > C doped TiO₂?annealed in O2?.The calculated net moment values are in the order of Fe-C co-doped TiO₂ > C doped TiO₂ with VO existing,in accord with the experimental results.3.Un-doped,Mo doped,N doped and Mo-N co-doped TiO₂ nanotubes?TNTs?films were prepared by a two-step anodic oxidation method.XRD studies showed that the impurities of magnetic Mo atoms or N atoms were doped into anatase TiO₂ lattices.It is revealed by the results of PL measurement that VO exists.VSM measurement shows that all the samples the values of the Ms are in the order of Mo-N co-doped TiO₂ > Mo-doped TiO₂ > N-doped TiO₂ > un-doped TiO₂.Thus,the Mo-N co-doped film achieved the highest RTMs.The enhancement of the Ms are origin from the cooperating of the doping VO,Mo and N.XPS analyses confirm that all the sample appearance of Ti³⁺ indicates the existence of Vos.