Reconsidering the possibility of room temperature ferromagnetism in Mn-doped zirconium oxide

¹ Institut für Theoretische Festkörperphysik, Karlsruhe Institute of Technology - D-76128 Karlsruhe, Germany
² School of Engineering and Science, Jacobs University Bremen, Campus Ring 1 - D-28759 Bremen, Germany
³ Institut Lumière Matière, Université Lyon 1-CNRS - F-69622 Villeurbanne Cedex, France

^(a) akash.chakraborty@physik.uni-regensburg.de
^(b) georges.bouzerar@univ-lyon1.fr

Received: 5 July 2013
Accepted: 3 December 2013

Abstract

The possibility to induce long-range ferromagnetic order by doping oxides with transition metal ions has become a very exciting challenge in the last decade. Theoretically, it has been claimed that Mn-doped ZrO₂ could be a very promising spintronic candidate and that high critical temperatures could be already achieved even for a low Mn concentration. Some experiments have reported room temperature ferromagnetism (RT-FM) whilst some others only paramagnetism. When observed, the nature of RT-FM appears to be controversial and not clearly understood. In this study, we propose to clarify and shed light on some of theses existing issues. A detailed study of the critical temperatures and low-energy magnetic excitations in Mn-doped ZrO₂ is performed. We show that the Curie temperatures were largely overestimated previously, due to the inadequate treatment of both thermal and transverse fluctuations, and disorder. It appears that the Mn-Mn couplings cannot explain the observed RT-FM. We argue, that this can be attributed to the interaction between large moments induced in the vicinity of the manganese. This is similar to the non-magnetic defect-induced ferromagnetism reported in oxides, semiconductors and graphene/graphite.