Acceptor-defect mediated room temperature ferromagnetism in (Mn2+, Nb5+) co-doped ZnO nanoparticles

In this study we report room temperature ferromagnetism in Manganese and Niobium co-doped ZnO nanoparticles synthesized by sol-gel method. The room temperature ferromagnetic ordering in the Zn0.99-2.5xNbxMn0.01O nanoparticles is found to vary as a function of Nb5+ concentration. Highest value of saturation magnetization, Ms was obtained for the composition co-doped with 2% niobium. Results obtained from Electron paramagnetic resonance and Photoluminescence studies have been combined to establish the acceptor-defect mediated ferromagnetic ordering in these nanoparticles. A quasi-indirect exchange mechanism mediated by singly ionized zinc vacancies, VZn, is proposed to explain the enhanced ferromagnetic ordering in (Mn, Nb) co-doped ZnO nanoparticles.