Size and doping dependence of the phonon properties of SnO2 nanoparticles

Using a microscopic model, taking into account the spin-phonon interactions and the Green's function technique, we have studied the phonon properties of pure and ion-doped SnO2 nanoparticles (NPs). The phonon energy of SnO2 NPs decreases whereas the damping increases with decreasing particle size. Near the Curie temperature in the NPs, there appears an anomaly in the phonon energy omega(T) and damping gamma(T). The phonon properties are very sensitive to the anharmonic spin-phonon interaction R. They can increase or decrease for R > 0 or R < 0 with increasing of temperature, respectively. In dependence of the radius of the doping ions, the phonon energies omega could be reduced (Co, Fe, Sm, Nd) or enhanced (Cu). The phonon damping is always enhanced in the doped NPs. In summary, due to the size and temperature effects, we obtain changes in the phonon energy and damping in pure SnO2 NPs, whereas in ion-doped ones, the doping effects strengthen these properties.