Reconsidering the possibility of room temperature ferromagnetism in Mn doped Zirconium oxide

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 ZrO$_2$ 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 ZrO$_2$ 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 can not 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.