Ab-initio study of disorder effects on the electronic and magnetic structures of Sr2_2FeMoO6_6

We have investigated the electronic structure of ordered and disordered Sr$_2$FeMoO$_6$ using {\it ab-initio} band structure methods. The effect of disorder was simulated within super-cell calculations to realize several configurations with mis-site disorders. It is found that such disorder effects destroy the half-metallic ferro-magnetic state of the ordered compound. It also leads to a substantial reduction of the magnetic moments at the Fe sites in the disordered configurations. Most interestingly, it is found for the disordered configurations, that the magnetic coupling within the Fe sub-lattice as well as that within the Mo sub-lattice always remain ferro-magnetic, while the two sub-lattices couple anti-ferromagnetically, in close analogy to the magnetic structure of the ordered compound, but in contrast to recent suggestions.Comment: 7 pages, 3 figure

Theory of Transition Temperature of Magnetic Double Perovskites

We formulate a theory of double perovskite coumpounds such as Sr$_2$FeReO$_6$ and Sr$_2$FeMoO$_6$ which have attracted recent attention for their possible uses as spin valves and sources of spin polarized electrons. We solve the theory in the dynamical mean field approximation to find the magnetic transition temperature $T_c$. We find that $T_c$ is determined by a subtle interplay between carrier density and the Fe-Mo/Re site energy difference, and that the non-Fe same-sublattice hopping acts to reduce $T_c$. Our results suggest that presently existing materials do not optimize $T_c$

Phase diagram and influence of defects in the double perovskites

The phase diagram of the double perovskites of the type Sr_{2-x} La_x Fe Mo O_6 is analyzed, with and without disorder due to antisites. In addition to an homogeneous half metallic ferrimagnetic phase in the absence of doping and disorder, we find antiferromagnetic phases at large dopings, and other ferrimagnetic phases with lower saturation magnetization, in the presence of disorder.Comment: 4 pages, 3 postscript figures, some errata correcte

Intelligent video event analysis and understanding

In this paper, we present a motion segmentation approach based on the subspace segmentation technique, the generalized PCA. By incorporating the cues from the neighborhood of intensity edges of images, motion segmentation is solved under an algebra framework. Our main contribution is to propose a post-processing procedure, which can detect the boundaries of motion layers and further determine the layer ordering. Test results on real imagery have confirmed the validity of our method

Behind the depth uncertainty: Resolving ordinal depth in SFM

10.1007/978-3-540-88690-7-25Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)5304 LNCSPART 3330-34

Electronic structure of half-metallic double perovskites

We present the self-interaction corrected local spin density (SIC-LSD) electronic structure and total energy calculations, leading also to valencies of the ground state configurations, for the half-metallic double perovskites such as Sr$_{2}$FeMoO$_{6}$, Ba$_{2}$FeMoO$_{6}$, Ca$_{2}$FeMoO$_{6}$, and Ca$_{2}$FeReO$_{6}$. We conclude that the Fe and Mo (or Re) spin magnetic moments are anti-parallel aligned, and the magnitude of the hybridization induced moment on Mo does not vary much between the different compounds. The hybridization spin magnetic moment on Re is of the order of -1.1 $\mu_{B}$, while that on Mo is about -0.4 $\mu_{B}$, independently of the alkaline earth element. Also the electronic structure of all the compounds studied is very similar, with a well defined gap in the majority spin component and metallic density of states for the minority spin component, with highly hybridized Fe, Mo (or Re), and oxygen bands.Comment: 6 pages, 2 figure