Cobalt-doped ZnO – a room temperature dilute magnetic semiconductor

Room temperature ferromagnetism is observed in thin films of ZnO doped with 1–25 at.% cobalt. Bulk samples were synthesized by a solid-state reaction technique and (1 1 0) textured thin films were prepared by pulsed laser deposition on R-cut sapphire substrates. Films are semiconducting and transparent. Resisitivity increases with increasing cobalt content. Room temperature magnetic moments of 0.5-5 mB per Co atom were measured in the thin films. Optical spectrometry indicates that cobalt enters the tetrahedral sites of the wurtzite structure as Co2+.