Study of diluted magnetic semiconductor: Co-doped ZnO

We report on the high-temperature ferromagnetism in Co-doped ZnO films fabricated by the sol–gel method above 350 K. The lattice constant of c axis of wurtzite Zn1−xCoxO follows Vergard’s law for 0<x<0.25. For Zn1−xCoxO with x⩾0.25, a secondary phase is detected. The Zn1−xCoxO exhibits ferromagnetic behavior with a Curie temperature higher than 350 K. By the results of x-ray photoelectron spectroscopy measurement, we assume that Co occupied the Zn site without changing the wurtzite structure. In the case of x=0.2, the coercive field measured by a magnetization–magnetic field hysteresis curve at 350 K was nearly 80 Oe. Additionally, we investigated the electric structure through first-principles pseudopotential plane-wave calculation.