Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001)

Abstract

Magnetic anisotropies of Co-implanted ZnO (0001) films grown on single-crystalline Al2O3 (11 (2) over bar0) substrates have been studied by ferromagnetic resonance (FMR) technique for different cobalt implantation doses. The FMR data show that the easy and hard axes have a periodicity of 60 in the film plane, in agreement with the hexagonal structure of the ZnO films. This six-fold in-plane magnetic anisotropy, which is observed for the first time in ZnO-based diluted magnetic semiconductors, is attributed to the substitution of cobalt on Zn sites in the ZnO structure, and a clear indication for long range ferromagnetic ordering between substitutional cobalt ions in the single-crystalline ZnO films. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3223583]