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The origin of the stabilized simple-cubic (SC) structure in Po is explored by using the first principle band calculations. We have found that the prime origin is the inherent strong spin-orbit (SO) interaction in Po, which suppresses the Peierls-like structural instability as usually occurs in p-bonded systems. Based on the systematic analysis of electronic structures, charge densities, Fermi surfaces, and susceptibilities of Se, Te, and Po, we have proved that the stable crystal structure in VIA elements is determined by the competition between the SO splitting and the crystal field splitting induced by the low-symmetry structural transition. The trigonal structure is stabilized in Se and Te by the larger crystal field splitting than the SO splitting, whereas in Po the SC structure is stabilized by the large SO splitting., Comment: 4 pages, 4figures

We have investigated electronic structures and magnetic properties of potential ZnO based diluted magnetic semiconductors: (Fe, Co) and (Fe, Cu) codoped ZnO. The origins of ferromagnetism are shown to be different between two. (Fe, Co) codoped ZnO does not have a tendency of Fe-O-Co ferromagnetic cluster formation, and so the double exchange mechanism will not be effective. In contrast, (Fe, Cu) codoped ZnO has a tendency of the Fe-O-Cu ferromagnetic cluster formation with the charge transfer between Fe and Cu, which would lead to the ferromagnetism through the double-exchange mechanism. The ferromagnetic and nearly half-metallic ground state is obtained for (Fe, Cu) codoped ZnO., Comment: 6 pages, 6 figures

We have explored the effects of the Li intercalation on the electronic and magnetic properties of transition-metal (TM) doped anatase TiO$_2$. By Li intercalation, Mn-doped TiO$_2$ exhibits the insulator to metal transition. On the other hand, Li-intercalated Fe-doped TiO$_2$ has the insulating ground state for low concentration of Li/Ti=0.067, but the metallic ground state for high concentration of Li/Ti=0.133. We discuss the $n$-type carrier induced ferromagnetism in Li-intercalated TM-doped anatase TiO$_2$. Based on the Li-intercalated TM-doped anatase TiO$_2$, we propose a potential spintronic and electrochromic device controlled by the electric-field., Comment: 4 pages, 4 figures

The effects of $n$-type carrier doping by Li intercalation on magnetism in undoped and Co-doped anatase TiO$_2$ are investigated. We have found that doped $n$-type carriers in TiO$_2$ are localized mainly at Ti sites near the intercalated Li. With increasing the intercalation, local spins are realized at Ti. In the case of Co-doped TiO$_2$, most of the added $n$-type carriers fill the Co 3$d$ bands and the rest are localized at Ti. Therefore, Co magnetic moment vanishes by Li intercalation to have a nonmagnetic ground state., Comment: 6 pages, 2 figures, to appear in a special issue of Physica B, proceedings of the 2nd Hiroshima Workshop on Transport and Thermal Properties of Advanced Materials (Aug. 2002; Hiroshima, Japan)

We have investigated electronic structures of a room temperature diluted magnetic semiconductor : Co-doped anatase $\rm TiO_{2}$. We have obtained the half-metallic ground state in the local-spin-density approximation(LSDA) but the insulating ground state in the LSDA+$U$+SO incorporating the spin-orbit interaction. In the stoichiometric case, the low spin state of Co is realized with the substantially large orbital moment. However, in the presence of oxygen vacancies near Co, the spin state of Co becomes intermediate. The ferromagnetisms in the metallic and insulating phases are accounted for by the double-exchange-like and the superexchange mechanism, respectively. Further, the magnetic ground states are obtained for Mn and Fe doped $\rm TiO_{2}$, while the paramagnetic ground state for Ni-doped $\rm TiO_{2}$., Comment: 5 pages, 4 figures

We have theoretically designed the half-metallic (HM) antiferromagnets (AFMs) in thiospinel systems, $\rm Mn(CrV)S_{4}$ and $\rm Fe_{0.5}Cu_{0.5}(V_{0.5}Ti_{1.5})S_{4}$, based on the electronic structure studies in the local-spin-density approximation (LSDA). We have also explored electronic and magnetic properties of parent spinel compounds of the above systems; $\rm CuV_{2}S_{4}$ and $\rm CuTi_{2}S_{4}$ are found to be HM ferromagnets in their cubic spinel structures, while $\rm MnCr_{2}S_{4}$ is a ferrimagnetic insulator. We have discussed the feasibility of material synthesis of HM-AFM thiospinel systems., Comment: 4 pages, 5 figures