Influence of the microstructure on the magnetism of Co-doped ZnO thin films

TL;DR

This study investigates how the microstructure of Co-doped ZnO thin films influences their magnetic properties, revealing that defect-related ferromagnetism diminishes with increased cobalt content and depends on growth conditions.

Contribution

It demonstrates that Co substitutes into ZnO without forming clusters and links ferromagnetism to defects rather than Co clustering or secondary phases.

Findings

Ferromagnetism decreases as Co content increases

Co substitutes into ZnO without forming clusters

Defects near interfaces influence magnetic behavior

Abstract

The prediction of ferromagnetism at room temperature in Co-ZnO thin films has generated a large interest in the community due to the possible applications. However, the results are controversial, going from ferromagnetism to non-ferromagnetism, leading to a large debate about its origin (secondary phase, Co clusters or not). By carefully studying the micro-structure of various Co-ZnO films, we show that the Co2+ partly substitutes the ZnO wurtzite matrix without forming Co clusters. Surprisingly, the ferromagnetism nature of the films disappears as the Co content increases. In addition, our results suggest that the observed ferromagnetism is likely associated to a large amount of defects- close to the interface and strongly depending on the growth temperature- which may explained the spreading of the results.