In this work, systematic X-band electron magnetic resonance (EMR) studies for YMnO3/Si ferroelectric gate structures were performed to trace a variation of interface characteristics as different sputtering condition of O-2/(Ar + O-2) ratio. Our result showed that the EMR signal intensities were increased with increasing O-2/(Ar + O-2) ratio. In addition, it was suggested from detailed analyses that the observed EMR signals could be originated from Mn nanoclusters existing in both the polycrystalline Y2O3 layer and the amorphous Si-enriched Y-Si interface layer in YMnO3/Si thin film structure. And also, a correlation between the decrease of crystallinity in YMnO3/Si film and the content of Mn nanoclusters within the polycrystalline Y2O3 layer and/or the amorphous Y-Si layer was discussed. (c) 2005 Elsevier B.V. All rights reserved.