Extrinsic nature of the room temperature ferromagnetism in (ZnO)1−x(MnO2)x for

Room temperature ferromagnetism (RTFM) has been thoroughly examined in a series of polycrystalline (ZnO)1−x(MnO2)x samples prepared by solid-state reaction method. All these samples, covering a wide range of MnO2 concentration, viz., 0.01 ≤ x ≤ 0.97 , calcined at 400 ∘C are found to possess some ferromagnetic contribution in their M – H behaviour. A typical ferromagnetic behaviour in the isothermal measurements of magnetization performed on a few samples at temperature as high as 200 ∘C, not reported hitherto, indisputably corroborates that the Curie temperature T C is greater than 200 ∘C. The saturation magnetization of the FM contribution in these samples appears to be governed by the initial amount of MnO2 (and not of ZnO) employed for their synthesis. With sintering at higher temperature, the FM fraction disappears in all these samples — a fact, which is indicative of the metastable or inhomogeneous nature of the observed RTFM. These detailed investigations substantiate the emerging consensus that the origin of ferromagnetic ordering in ZnO:Mn system is extrinsic in nature.