X-ray Anomalous Scattering of Diluted Magnetic Oxide Semiconductors: Possible Evidence of Lattice Deformation for High Temperature Ferromagnetism

We have examined whether the Co ions crystallographically substitute on the Ti sites in rutile and anatase Ti_{1-x}$Co$_{x}$O$_{2-delta}$thin films that exhibit room-temperature ferromagnetism. Intensities of the x-ray Bragg reflection from the films were measured around the$K$-absorption-edge of Co. If the Co ions randomly substitute on the Ti sites, the intensity should exhibit an anomaly due to the anomalous dispersion of the atomic scattering factor of Co. However, none of the anatase and rutile samples did exhibit an anomaly, unambiguously showing that the Co ions in Ti$_{1-x}$Co$_{x}$O$_{2-delta}$are not exactly located at the Ti sites of TiO$_2$. The absence of the anomaly is probably caused by a significant deformation of the local structure around Co due to the oxygen vacancy. We have applied the same method to paramagnetic Zn$_{1-x}$Co$_{x}$O thin films and obtained direct evidence that the Co ions are indeed substituted on the Zn sites.Comment: 5 pages, 4 figures, accepted in PR

Effects of synthetic dopamine-melanins on oxygen radical formation induced by metal ions with dopamine.

To understand the possible physiological roles of the neuromelanins, we examined effects of synthetic dopamine-melanins on oxygen radical formation by metal ions with dopamine. Oxygen radical formation was detected by DNA cleavage analysis. Addition of metal-free synthetic dopamine-melanins inhibited DNA cleavage induced by Fe or Cu ions with dopamine. On the other hand, in the presence of dopamine, dopamine-melanins loaded with Cu and Fe induced DNA cleavage without addition of free metal ions. It was clarfied that dopamine-melanins loaded with Cu and Fe generated hydroxyl radicals in the presence of dopamine, on the basis of the findings thet catalase and mannitol inhibited the DNA cleavage. Our results suggest that metal-free neromalanins inhibit hydroxyl radical formation induced by ions with dopamine by sequestering metal ions