Aggregation-based growth and magnetic properties of inhomogeneous Cu-doped ZnO nanocrystals

The authors report on the ferromagnetic ordering in 1.86 at. % Cu-doped ZnO nanocrystals synthesized by a solvothermal route. The distribution of Cu in ZnO lattice was inhomogeneous. In the Cu-poor cores, a spin-split acceptor impurity band model was proposed to explain the ferromagnetism. While in the Cu-rich surface layers, the shallow donorlike defects generated by imperfect oriented attachment could not only compensate a few holes but also readily occupy the Cu 3d states to destroy CuO4 tetrahedra, hence resulting in the short-range antiferromagnetic clusters. As a result, an interesting exchange biasing phenomenon took place at the ferromagnetic/antiferromagnetic interface. (c) 2007 American Institute of Physics.