Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nanoparticles.

We have studied the electronic structure of Fe-doped ZnO nanoparticles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy, resonant photoemission spectroscopy, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe³⁺ ionic state with mixture of a small amount of Fe²⁺ and that Fe³⁺ ions are dominant in the surface region of the nanoparticles. It is shown that the room temperature ferromagnetism in the Fe-doped ZnO nanoparticles primarily originated from the antiferromagnetic coupling between unequal amounts of Fe³⁺ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of ∼2–3 nm. [ABSTRACT FROM AUTHOR]