Electronic structures and magnetic properties of La$_{2-x}$Sr$_x$MnNiO$_6$

We have investigated hole carrier doping effects in La$_{2}$MnNiO$_{6}$, which is getting attraction for being a high $T_C$ ferromagnetic insulator. Employing the {\it ab-initio} band structure method, we have examined the changes in the electronic structures and the valence states of Sr-doped La$_{2-x}$Sr$_x$MnNiO$_6$ with varying Sr doping ratio. Upon Sr doping, which corresponds to the effective hole doping, we have found a transition from a ferromagnetic insulating phase to a robust half-metallic phase. We have verified that the substantially weak x-ray magnetic circular dichroism (XMCD) signal observed for La$_{2-x}$Sr$_x$MnNiO$_6$, as compared to the undoped system, is caused by anti-site disorder at $B$-sites in a Sr-doped system.