Hydrothermal synthesis of Co-doped ZnO flakes with room temperature ferromagnetism

A series of high quality Zn_1-xCo_xO (x≤0.10) flakes were synthesized by hydrothermal route. XRD and TEM characterizations indicate that the as-prepared samples were crystalline with wurtzite structure and no metallic Co or other secondary phases were found. Optical absorption and Raman results further confirm the incorporation of Co²⁺ ions in the ZnO lattice. Magnetic measurements indicate that the Zn_1-xCo_xO (x≤0.1) flakes show obvious ferromagnetic characteristics at room temperature. However, at higher doping content of Co²⁺, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The decrease of ferromagnetism with increasing doping concentration demonstrates that ferromagnetism observed at room temperature is an intrinsic property of Zn_1-xCo_xO flakes, and does not originate from any secondary phase.