Paramagnetism in Mn/Fe implanted ZnO

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line Fe-57 Mossbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive Mn-57 ions at room temperature. The Mossbauer spectra of the dilute Fe impurities are dominated by sextets whose angular dependence rules out an ordered magnetic state (which had been previously proposed) but are well accounted for on the basis of Fe3+ paramagnetic centers on substitutional Zn sites with unusually long relaxation times (> 20 ns).