Mechanism of defect induced ferromagnetism in undoped and Cr doped TiO 2 nanorods/nanoribbons

Autor: Kenji Imakita, Minoru Fujii, P. K. Giri, Batakrushna Santara
Rok vydání: 2016
Předmět:
Zdroj: Journal of Alloys and Compounds. 661:331-344
ISSN: 0925-8388
Popis: We have studied the effect of doping concentrations, growth temperature and calcinations on the structural, optical and magnetic properties of the undoped and Cr doped TiO 2 nanorods/nanoribbons (NR/NRb), in order to develop an improved understanding on the mechanism of room temperature (RT) ferromagnetism (FM) in these nanostructures. Both undoped and doped TiO 2 NR/NRb exhibit RT FM and a ∼2.6 fold enhancement in magnetization is observed in 0.3% Cr doped TiO 2 NR/NRb as compared to the undoped NR/NRb, and the magnetization increases considerably after vacuum annealing. However, no measureable FM is observed for the precursor TiO 2 powder, despite the presence of high concentration of oxygen vacancies in it. On the other hand, the magnetization decreases at higher doping concentration (0.7% Cr) as compared to 0.3% Cr doped sample. Thus, our studies revealed that a simple oxygen vacancy and/or Cr ions alone cannot yield the RT FM in TiO 2 nanostructures. We argue that the oxygen vacancy with appropriate charge redistribution and their orbital overlapping, and exchange interaction with the nearby unpaired 3d electron of Ti 3+ in undoped TiO 2 and/or unpaired 3d electrons of Cr 3+ dopant with proper charge distribution and occupation inside the host lattice in Cr doped TiO 2 nanostructures play the pivotal role for the ferromagnetic ordering and observed RTFM. The presence of oxygen vacancy related F + -center and Cr 3+ are confirmed from the electron spin resonance and x-ray photoelectron spectroscopy measurements.
Databáze: OpenAIRE
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