High-Tc ferromagnetism in a Co-doped ZnO system dominated by the formation of a zinc-blende type Co-rich ZnCoO phase.

The modulation of the distribution of magnetic ions embedded in the host is crucial for the functionality of dilute magnetic semiconductors. Through an element-specific structural characterization, we observe the formation and enhancement of an unrevealed Co-doped ZnO phase and consequently magnetic properties from paramagnetism to ferromagnetism are controlled by surface-modification.