Electronic structure and magnetism of the diluted magnetic semiconductor Fe-doped ZnO nano-particles

TL;DR

This study investigates the electronic structure and origin of room-temperature ferromagnetism in Fe-doped ZnO nanoparticles using advanced spectroscopic techniques, revealing Fe ions mainly in the Fe$^{3+}$ state and antiferromagnetic coupling as the ferromagnetism source.

Contribution

It provides detailed spectroscopic analysis showing Fe ions are mostly Fe$^{3+}$ and identifies antiferromagnetic coupling as the origin of ferromagnetism in Fe-doped ZnO nanoparticles.

Findings

Fe ions are predominantly Fe$^{3+}$ with some Fe$^{2+}$.

Fe$^{3+}$ ions are mainly at the surface region.

Room temperature ferromagnetism arises from antiferromagnetic coupling.

Abstract

We have studied the electronic structure of Zn$_{0.9}$Fe$_{0.1}$O nano-particles, which have been reported to show ferromagnetism at room temperature, by x-ray photoemission spectroscopy (XPS), resonant photoemission spectroscopy (RPES), x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD). From the experimental and cluster-model calculation results, we find that Fe atoms are predominantly in the Fe$^{3+}$ ionic state with mixture of a small amount of Fe$^{2+}$ and that Fe$^{3+}$ ions are dominant in the surface region of the nano-particles. It is shown that the room temperature ferromagnetism in the Zn$_{0.9}$Fe$_{0.1}$O nano-particles is primarily originated from the antiferromagnetic coupling between unequal amounts of Fe$^{3+}$ ions occupying two sets of nonequivalent positions in the region of the XMCD probing depth of $\sim$ 2-3 nm.