Chapter 5: Intrinsic Defect Induced Room Temperature
5.10. Conclusions
nvolved in the exchange interaction. However, more studies are required to pinpoint the exact mechanism of high temperature FM . N evertheless, besides the established applications of TiO 2 nanostructures, these results open up the possibility of defect engineered TiO 2
nanostructures as potential platform for future spintronic and magneto-optic devices.
F ig . 5.1 0 .Initial portion of the M – H curve fitted with B M P model (eqn (5.5)) for samples (a) D 9 0 0 and (b) G 50 0 . S ymbols are for experimental data and the solid line is a fit with the B M P model.
E xtracted parameters are listed in T a b le 5.1. (c) Integrated P L intensity versus calculated B M P density showing a nearly linear behavior.
intensity of oxygen vacancy related peak in the P L spectra, large concentration of and Ti3+ states revealed from X P S , shifting of infrared vibration modes at 47 6 cm-1 towards the lower frequency after vacuum annealing confirm the presence of large concentration of oxygen vacancies and these are shown to be responsible for the enhanced FM in as-grown and vacuum annealed sample. The observed R TFM is explained on the basis of a B M P model and extracted density of B M P is shown to directly scale with the integrated P L intensity that arises from oxygen vacancies. Thus, our results provide convincing evidence for oxygen vacancy induced strong ferromagnetism at and above room temperature in the undoped TiO 2 nanoporous N R bs. These findings not only help to gain better insight into the defect engineering of R TFM in undoped TiO 2, but also constitute an important step for the development of practical nanospintronic devices which can be operated at and above R T.
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To understand the enhanced properties of the TiO2 nanostructures (NS), successful fabrication of a wide range of materials is significant where the morphologies can be precisely controlled with designed functionalities. In particular, lattice parameters are very important structural characteristics and thus their variations directly affect the properties of nanomaterials and the relevant applications. The control of lattice parameters through the intrinsic defects may provide new routes to achieving novel functionalities in advanced materials that can be tailored for future technological applications. In this chapter, we have investigated the microscopic origin of lattice expansion and contraction in undoped rutile TiO2 nanostructures by employing several structural and optical spectroscopic tools.
Depending on the growth conditions and post growth annealing, lattice contraction and expansion are observed in the nanostructures and it is found to correlate with the nature and density of intrinsic defects in rutile TiO2.