Observation and manipulation of paramagnetic oxygen vacancies in Co-doped TiO2 nanocrystals

Abstract

Electron paramagnetic resonance measurements were presented to investigate paramagnetic oxygen vacancies (F+ centers) in Co-doped TiO2 nanocrystals. Surface and interior F+ centers were manipulated by washing or/and annealing. Anisotropic surface F+ centers are so instable as to be destroyed at high temperature, while isotropic interior F+ centers are rather stable even at 430°C. The correlation of ferromagnetism with F+ centers was observed, which provided direct experimental evidence for F+-center-mediated coupling in diluted magnetic oxides.

Synthesis and physical properties of the hollandite‐type titanium oxide KxTi8O16

“…A saturation magnetization for the ferromagnetic component was estimated by subtracting the paramagnetic component from M-H data to be 4 x 10 -3 emu/g. The obtained value is similar to the values in V-doped TiO 2 powders [9], Cr [10] and Co [11] -doped TiO 2 nanoparticles and reduced A and R-type TiO 2 powders [12]. The saturation magnetization corresponds to 4 x 10 -4 μ B per Ti 3+ ion.…”

Search for Origin of Room Temperature Ferromagnetism Properties in Ni-Doped ZnO Nanostructure

“…However oxygen vacancies, which are an important class of point defects in oxides and also known as colour centres (F centres) 53 shows three dissimilar charge states, as F 2+ (unoccupied), F + (singly occupied), and F 0 (doubly occupied), in the ZnO lattice. In case of F 2+ and F 0 vacancies have spin-zero ground states; hence they do not induce FM in ZnO 54,55 . However in case of F + vacancy which is singly occupied can contributes in activate bound magnetic polarons (BMPs) and magnetic moment in DMSs 54 .…”

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

“…(1) Isolated F + centers (oxygen vacancy with one electron) which were seen in EPR experiments 18 with spin 1 2 , can couple antiferromagnetically with vacancy clusters (superexchange) to give a ferrimagnet with a net moment.…”