Amorphous clusters in Co implanted ZnO induced by boron preimplantation

We demonstrate the formation of superparamagnetic/ferromagnetic regions within ZnO(0001) single crystals sequentially implanted with B and Co. While the preimplantation with B plays a minor role for the electrical transport properties, its presence leads to the formation of amorphous phases. Moreover, B acts strongly, reducing the implanted Co. Thus, the origin of the ferromagnetic ordering in local clusters with large Co concentration is itinerant d-electron as in the case of metallic Co. The amorphous Co-based phases are nondetectable by common x-ray diffraction.