Influence of microstructure on room temperature ferromagnetism in Ni implanted nanodimensional ZnO films

Room temperature ferromagnetism (RT-FM) is observed in ZnO/Si thin films on implantation of 200 keV ${\text{Ni}}^{2+}$ ions at fluences of $6\times {10}^{15}$ , $8\times {10}^{15}$ , and $2\times {10}^{16}\text{ions}/{\text{cm}}^2$ . RT-FM observed without any preheat or postheat treatment is studied by alternating gradient magnetometry. The average grain size, oxygen vacancies, and charge carrier concentration are found to be maximum in the film implanted at fluence of $8\times {10}^{15}\text{ions}/{\text{cm}}^2$ , which also shows maximum saturation magnetization $\left(M_s\right)$ . In all implanted films no extra crystalline phase (apart from ZnO) is observed. Exchange interaction between the charge carriers generated due to thermal effects of ion implantation and the localized spins of Ni is considered as main reason behind RT-FM. The effect of microstructure of the films on exchange interaction and hence on RT-FM properties is also discussed.