Raman spectroscopy and magnetic properties of bulk ZnO:Co single crystal

We report on the investigation of structural and magnetic properties of the cobalt-based diluted magnetic semiconductor with wurtzite structure: Zn1−xCoxO. Single crystals were grown by chemical vapour transport. From the Raman measurements in the temperature range 10–300 K on samples with Co concentration of 5%, we detect the presence of very small quantities of hcp-Co and also the presence of anti-ferromagnetic CoO impurities. This result is in agreement with the behaviour of magnetisation measurements under pulsed magnetic fields. High frequency–high field ESR reveals clearly the large crystal field splitting of the energy levels of isolated Co2+ ions.