Electron paramagnetic resonance study of Zn1-xCoxO: A predicted high-temperature ferromagnetic semiconductor

The magnetic properties of Co2+ ions in epitaxial (Zn,Co)O layers with 10% Co concentration have been studied by electron paramagnetic resonance spectroscopy. The Co-related EPR spectrum is characterized by a 200-G broad anisotropic single line with g factors close to those of the isolated Co2+ ion. The temperature dependence of the EPR signal follows a Curie-Weiss law with a critical temperature of +12 K. We find no evidence for a high-temperature ferromagnetic state. Magnetocrystalline anisotropy is observed and a canted spin arrangement is suggested.