Non-homogeneous Ti <sub>, High Co 1-x </ Sub> The Co. <sub> X </ Sub> The O <sub> 2 </ Sub> Ferromagnetic Semiconductor Preparation, Structure And Physical Properties

Magnetic semiconductors have been extensively studied due to their great importance in spintronics devices. For the TiO₂-based magnetic semiconductors, some researchers believed that the ferromagnetism at room temperature originates from the Co metal clusters embedded in TiC>2. Now most researchers tend to believe that the ferromagnetism is an intrinsic property of Ti_1-xCo_xO₂ magnetic semiconductor. Therefore the origin of the weak ferromagnetism at room temperature is still an open question till now. In these investigations, the Co concentrations in TiO₂ were usually limited to a few percents, and the observed saturation magnetization was very small. The magnetoresistance (MR) of the magnetic semiconductors is another great important subject in the spintronics devices, but it usually appears at very low temperature. There are few reports about the magneto-optic Kerr effect (MOKE) in magnetic semiconductor materials. The intrinsic chemical inhomogeneity in the form of "clustered states" has been regarded as a common feature of the magnetic semiconductors, colossal MR manganites, and high temperature superconducting cuprates. Some researchers have done the theoretic work on this filed. For example, using the first-principles density-functional approaches, impurity distributions and magnetic properties of Co-doped anatase TiO₂ have been investigated. From the total energy calculations for various possible configurations, it was found that the Co atoms in magnetic semiconductors prefer the non-uniform doping mode with short Co-Co distances. Furthermore this non-uniform distribution is crucial for the ferromagnetic ordering observed in Ti_1-xCo_xO₂, whereas the antiferromagnetic state prevails in uniformly doped cases investigated (x = 0.0625). Recently, the special chemical inhomogeneity has been found in Mn-doped Ge magnetic semiconductors, which show Mn-rich and Mn-depleted phases rather than metallic Mn clusters. The intrinsic compositional inhomogeneity can greatly influence on the magnetization, Curie temperature, electronic transport, magnetoresistance and so on. Until now, the study on the intrinsic chemical inhomogeneity in the magnetic semiconductors is still...