Double exchange model in cubic vanadates
  We investigate the role of the double exchange mechanism for stability of the metallic C-type antiferromagnetic (C-AF) phase, which was observed experimentally in hole doped La$_{1-x}$Sr$_x$VO$_3$. The double exchange model treats localized electrons in xy orbitals as classical S=1/2 spins, which interact by Hund's exchange $J_H$ with yz/zx electrons in partly filled $t_{2g}$ orbitals. Including strong on-site Coulomb repulsion $U$ between $t_{2g}$ electrons, and using slave boson method we demonstrate that C-AF and metallic phase can be stabilized due to the specific features of the hopping in degenerate and partly filled $t_{2g}$ orbitals. 
Krzysztof Wohlfeld and Andrzej M. Oles