Room temperature ferromagnetism of ZnO nanocrystals in amorphous ZnO- Al2 O3 matrix

Abstract

In this work, we demonstrate room temperature ferromagnetism of ZnO nanocrystals (NCs) embedded in alumina-based amorphous matrix. Our study has shown that solid solution occurred for lower Al concentration [≥x=0.09 for (Zn1-x, Alx) O]. No ferromagnetism appears in Al-doped ZnO with x≥0.09. With higher Al concentration, alumina-based amorphous structure appeared and fully amorphous was found in the composition of (Zn 0.30, Al0.70) O. Ferromagnetism was found in (Zn 1-x, Alx) O with a threshold of 16 mol % of Al. The room temperature ferromagnetism was found to be attributed to ZnO NCs in an alumina-based amorphous ZnO- Al2 O3 matrix. Ferromagnetism reached a maximum with a volume percentage of ZnO NCs to be ∼27 vol %. The detailed investigations (transmission electron microscopy, x-ray photoelectron spectroscopy, and superconducting quantum interference device) show that the optimized size of these NCs is in the range of 4-5 nm. No ferromagnetism appears if the sample contains a fully amorphous structure. © 2009 American Institute of Physics.