Intrinsic room temperature ferromagnetism in Co-implanted ZnO

TL;DR

This study demonstrates intrinsic room temperature ferromagnetism in Co-implanted ZnO films, attributed to Co substitution in Zn sites, supported by structural, magnetic, and spectroscopic evidence.

Contribution

It provides evidence of intrinsic ferromagnetism in Co-doped ZnO at room temperature, with detailed analysis of its origin and magnetic properties.

Findings

Presence of a homogeneous ferromagnetic phase with high Curie temperature

Magnetic moment per Co atom close to theoretical high-spin Co2+ value

Detection of magnetic dichroism confirming intrinsic ferromagnetism

Abstract

We report on the structural and magnetic properties of a cobalt-implanted ZnO film grown on a sapphire substrate. X-ray diffraction and transmission electron microscopy reveal the presence of a (10-10)-oriented hexagonal Co phase in the Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter of is about 5-6 nm, form a Co rich layer in the substrate close to the ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two different magnetic phases in the implanted region. One originates from the Co clusters in Al2O3, the other one belongs to a homogeneous ferromagnetic phase with a ferromagnetic Curie temperature far above room temperature and can be attributed to Co substitution on Zn sites in the ZnO layer. We have observed magnetic dichroism at the Co L2,3 and O K edges at room temperature as well as the multiplet structure in x-ray absorption spectra around the Co L3 edge, supporting the intrinsic nature of the observed ferromagnetism in Co-implanted ZnO film. The magnetic moment per substituted cobalt is found about 2.81 Bohr magneton which is very close to the theoretical expected value of 3 Bohr magneton per Co atom for Co 2+ in its high spin state.