Room-temperature ferromagnetism induced by Na co-doping and K co-doping in the rare earth Er doped ZnO nanocrystallites

We report the ferromagnetic behavior induced by co-doping Er-doped ZnO nanocrystallites with Na and K ions. All the samples, viz., ZnO:Er, Er + Na co-doped ZnO, and Er + K co-doped ZnO nanocrystallites have been synthesized by using the solution combustion technique. The XRD studies confirm the hexagonal wurtzite structure for all the samples. Average size of nano-crystallites has been observed to increase due to doping with Er, and then co-doping with alkali metals Na and K. Studies of SEM, TEM and EDAX were used to determine the morphology, size and presence of elements in the ZnO nanocrystallites. The FT-Raman studies show that there is no peak shift due to the co-doping of these elements; the peak at 437 cm−1 corresponds to the standard Raman active E2 (high) mode. The VSM studies have shown that the co-doped samples exhibit ferromagnetism at room temperature itself, which is very unusual since the co-dopants are non-magnetic alkali metals. The ferromagnetic ordering of Na or K co-doped ZnO:Er is mainly attributed to oxygen vacancies and also to the minor impurity phase in ZnO lattice.