Characterization of Magnetic Components in the Diluted Magnetic Semiconductor Zn$_{1-x}$Co$_x$O by X-ray Magnetic Circular Dichroism

TL;DR

This study uses X-ray techniques to analyze the magnetic properties of Co-doped ZnO thin films, revealing that ferromagnetism originates from Co ions substituting Zn sites, with antiferromagnetic interactions among non-ferromagnetic Co ions.

Contribution

It provides detailed spectroscopic evidence linking Co ion states to ferromagnetism in Zn$_{1-x}$Co$_x$O, highlighting the role of Co substitution and magnetic interactions.

Findings

Co$^{2+}$ ions are tetrahedrally coordinated by oxygen.

Ferromagnetism is associated with Co ions substituting Zn sites.

Non-ferromagnetic Co ions are strongly antiferromagnetically coupled.

Abstract

We report on the results of x-ray absorption (XAS), x-ray magnetic circular dichroism (XMCD), and photoemission experiments on {\it n}-type Zn$_{1-x}$Co$_x$O ($x=0.05$) thin film, which shows ferromagnetism at room temperature. The XMCD spectra show a multiplet structure, characteristic of the Co$^{2+}$ ion tetrahedrally coordinated by oxygen, suggesting that the ferromagnetism comes from Co ions substituting the Zn site in ZnO. The magnetic field and temperature dependences of the XMCD spectra imply that the non-ferromagnetic Co ions are strongly coupled antiferromagnetically with each other.