MAGNETOELECTRONIC EFFECTS IN PYROCHLORE TL2MN2O7 - ROLE OF TL-O COVALENCY

First principles calculations are used to elucidate the magnetic and e lectronic structure of pyrochlore Tl2Mn2O7. It is found that the bondi ng has an important covalent contribution from Tl-O interactions. The high spin ferromagnetic ground state has a very large differentiation between minority and majority spin electronic properties. In particula r, the minority spin channel contains a single, nearly spherical high velocity Fermi surface derived from strongly mixed combinations of Tl, Mn, and O orbitals, while the majority spin channel contains three sm aller Fermi surfaces with much lower Fermi velocities. The proximity t o a band edge in the majority channel may lead to localization of thes e states if sufficient disorder is present. In any case, highly spin d ifferentiated transport results, with the conduction dominated by the minority channel.