A systematic study on the room temperature ferromagnetism (RTFM) in undoped and Mn-doped ZnO nanoparticles (NPs) prepared by the coprecipitation method has been reported. The neutral and singly ionized zinc vacancy defects exhibited in the results of photoluminescence (PL), micro-Raman spectroscopy, and electron paramagnetic resonance (EPR) studies are found to be of ferromagnetic origin in bare ZnO, and it has been confirmed that Mn2+ ions substitutionally enter at Zn2+ sites in wurtzite ZnO. The results of positron annihilation and coincidence Doppler broadening measurements corroborate the Zn vacancies and their clusters. It is observed that in Mn:ZnO, the magnetic ordering is changed from ferro- to paramagnetic because of interacting adjacent Mn-Mn ions. The higher saturation magnetization of 565 × 10-3 emu/g is explained by a quasi indirect exchange mechanism based on the interaction of bound magnetic polarons formed by the Zn vacancies (VZn) and nearby Mn ions. Further, first principle calculations reveal the magnetic centers in nonmagnetic ZnO with VZn and the stable ferromagnetic ordering in Mn:ZnO at the optimum distance of Mn-Mn ≈ 3.26 Å.
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R. Ponnusamy, Selvaraj, S. C., Ramachandran, Mc, Murugan, P., Nambissan, P. M. G., and Sivasubramanian, D., “Diverse Spectroscopic Studies and First-Principles Investigations of the Zinc Vacancy Mediated Ferromagnetism in Mn-Doped ZnO Nanoparticles”, Crystal Growth and Design, vol. 16, pp. 3656-3668, 2016.