Room temperature ferromagnetism and phonon properties of pure and doped TiO2 nanoparticles

We have considered the origin of RTFM in TiO2 nanoparticles (NPs). Further we have studied the properties of the Eg1 phonon mode. The phonon frequency of anatase TiO2 NPs increases whereas in the case of rutile TiO2 NPs it decreases as the particle size decreases. The phonon damping is always enhanced in the nanosized materials. The hardening of the Eg1 mode and the softening of the Eg3 mode in anatase TiO2 NPs could be explained with the different anharmonic spin-phonon interaction constants of these modes. The doping effects with different transition metal ions on the Eg1 phonon mode are also discussed.