High temperature ferromagnetism in Mn-doped SnO2 nanocrystalline thin films

Abstract

It has been possible to induce room temperature ferromagnetism, exhibiting high transition temperature, in tin oxide thin films by introducing manganese in a SnO2 lattice. The observed temperature dependence of the magnetization predicts a Curie temperature exceeding 550 K. A maximum saturation magnetic moment of 0.18±0.04 μB per Mn ion has been estimated for spray pyrolized Sn1−xMnxO2−δ thin films, with x=0.10. For Mn concentration (x) higher than 0.10, the films show linear behavior. The magnetization-versus-field studies indicate that the origin of ferromagnetism lies neither in ferromagnetic metal clusters nor in the presence of metastable phases. The structure factor calculations reveal that Mn has been incorporated in the SnO2 lattice. Also, the electron transport investigation indicates that there is a change of Mn occupancy from substitutional to interstitial sites of the SnO2 lattice when the Mn concentration exceeds 7.5 at. %. These films do not exhibit anomalous Hall effects at room temperature. The optical absorption study indicates that the Sn1−xMnxO2−δ system behaves like a random alloy. The generation of additional free electrons by F doping in Sn0.90Mn0.10O2−δ thin films does not cause any increase in the magnetic moment per Mn ion, suggesting no significant role of electrons in bringing about the magnetic ordering.