Enhanced ferromagnetic response in ZnO:Mn thin films by tailoring composition and defect concentration

The presence of structural defects degrade the crystalline quality of ZnO:Mn thin films and affects the magneto-optical properties of ZnO:Mn thin films. The donor defects in ZnO, which are known to be the source of n-type conductivity in ZnO host matrix, play an important role in limiting the ferromagnetism to lower temperatures. A systematic study of structural, optical and magnetic properties was carried out with the primary focus on understanding the relationship between the defect concentration, material composition and ferromagnetic properties. Single phase ZnO:Mn thin films with wurtzite structure were grown under ambient argon-oxygen admixture to investigate the effect of stoichiometry and interstitial oxygen on magnetic properties. A consistent increase in crystallinity of ZnO:Mn thin films (without precipitation of Mn) with increasing argon-oxygen admixture gas pressure was observed. Extended near band edge (NBE) emission spectra with marked decrease in photoluminescence (PL) ratio in optical characterization revealed improved optical quality of ZnO:Mn thin films. Magnetic measurements revealed enhanced room temperature ferromagnetism (RTFM) in sample grown at optimum argon-oxygen ambient pressure. The enhancement was directly related to maximal core level X-ray photoelectron spectroscopic peak of stoichiometric ZnO which, in turn, favors strong hybridization of Mn in the ZnO host matrix.