Berlin 2012 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 35: Poster Session II (Polymeric biomolecular films; Nanostructures; Electronic structure; Spin-orbit interaction; Phase transitions; Surface chemical reactions; Heterogeneous catalysis; Particles and clusters; Surface magnetism; Electron and spin dynamics; Surface dynamics; Methods; Electronic structure theory; Functional molecules)
O 35.68: Poster
Dienstag, 27. März 2012, 18:15–21:45, Poster B
d0 ferromagnetic interface between non-magnetic perovskites — •Riku Oja and Risto M. Nieminen — Aalto University, Helsinki, Finland
In perovskite oxides, oxygen p bands are narrow and have a high density of states just below the band gap. Also, oxygen p electrons have a strong exchange coupling. Hence, Stoner criterion for itinerant ferromagnetism is fulfilled in hole-doped d0 perovskites, if the hole density is high enough. Obtaining high hole densities, moving the Fermi level to the oxygen p band, is easily done by so-called intrinsic doping by a charge-imbalanced interface between two d0 perovskites. This introduces holes (for p type interface) or electrons (for n type interface) confined in the interface region.
We have performed DFT and DFT+U calculations with both LSDA and GGA for both types of KTaO3/SrTiO3 interfaces. The atomically sharp p type interface has been observed in experiments. The hole on oxygen 2p orbitals is localized on SrTiO3 side of the interface and is spin-polarized. Very small values of on-site Hubbard interaction U on oxygen p orbitals cause complete spin-polarization and half-metallic, ferromagnetic holes. The antiferromagnetic solution has higher energy. For the n type interface, on the other hand, electrons on Ti d orbitals do not magnetize completely.
As the density of states at the top of the O p band is higher than at the bottom of the Ti d band, we conclude that p type interfaces between d0 perovskites are good materials for interfacial ferromagnetism below ferroelectric thin films.