Non-DMS related ferromagnetism in transition metal doped zinc oxide

TL;DR

This paper reviews the challenges and pitfalls in inducing ferromagnetism in ZnO through transition metal doping, emphasizing the importance of distinguishing true DMS behavior from secondary phases and defects.

Contribution

It highlights the various sources of ferromagnetism in transition metal doped ZnO and discusses the difficulties in correctly identifying the origin of magnetic effects.

Findings

Multiple sources of ferromagnetism in doped ZnO identified

Secondary phases and defects can mimic DMS behavior

Ion implantation can induce unintended magnetic effects

Abstract

We review pitfalls in recent efforts to make a conventional semiconductor, namely ZnO, ferromagnetic by means of doping with transition metal ions. Since the solubility of those elements is rather low, formation of secondary phases and the creation of defects upon low temperature processing can lead to unwanted magnetic effects. Among others, ion implantation is a method of doping, which is highly suited for the investigation of those effects. By focussing mainly on Fe, Co or Ni implanted ZnO single crystals we show that there are manifold sources for ferromagnetism in this material which can easily be confused with the formation of a ferromagnetic diluted magnetic semiconductor (DMS). We will focus on metallic as well as oxide precipitates and the difficulties of their identification.