Mysterious magnetism of ZnO
Detailed investigations have been performed at the diluted magnetic semiconductor system ZnO:5%Co. This system shows no ferromagnetism at the Co ions, which was completely unexpected. The ferromagnetism (FM) observed in this system is therefore not understood at all. Even the microscopic source of the FM is not clear a all. Recent results suggest oxygen vacancies as a source for FM (summary).
In the last decade ZnO nanomaterials have shown unexpected ferromagnetism like behavior, with about no temperature dependence, indication extraordinary high Curie temperatures. This is totally unexpected, because of the filled (empty) shell configurations of ZnO, which should provide only diamagnetic behavior. Usually thin films have been investigated with nanocrystalline grain structure and only very small and therefore ambiguous results have been published. We could produce bulk like ferromagnetic samples, just by pressing pure ZnO powder to compacted pellets. We also found proof for the true magnetism using muon spin rotation (µSR) ( for details see Scientific Reports 5, Article number: 8871 (2015)).