The variation of Mn-dopant distribution state with x and its effect on the magnetic coupling mechanism in Zn_1-xMn_xO nanocrystals

Zn_1-xMn_xO (x=0.0005, 0.001, 0.005, 0.01, 0.02) nanocrystals are synthesized by using a wet chemical process. The coordination environment of Mn is characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, and its X-ray absorption fine structure. It is found that the solubility of substitutional Mn in a ZnO lattice is very low, which is less than 0.4%. Mn ions first dissolve into the substitutional sites in the ZnO lattice, thereby forming Mn²⁺O₄ tetrahedral coordination when x ≤ 0.001, then entering into the interstitial sites and forming Mn³⁺O₆ octahedral coordination when x ≥ 0.005. All the samples exhibit paramagnetic behaviors at room temperature, and antiferromagnetic coupling can be observed below 100 K.