Signature of Intrinsic High‐Temperature Ferromagnetism in Cobalt‐Doped Zinc Oxide Nanocrystals

Nanocrystalline Zn1–xCoxO (x = 0.020, 0.056, and 0.098) powders exhibit intrinsic high-temperature ferromagnetism, as suggested by the well-defined hysteresis loops shown in the figure. The origin of this ferromagnetism is thought to be electron transfer from host Zn 4s↑ states to unfilled dopant Co 3d↓ states (shown in the inset to the figure), which leads to the formation of a spin-split impurity band at the Fermi level in the gap.