  We have studied the electronic and magnetic properties of double perovskites
Gd2MgIrO6 by first-principles density functional theory (DFT). Based on the DFT
calculations, Gd2MgIrO6 is found to have a ferromagnetic (FM) ground state. The
material undergo half-metallic ferromagnets to Mott-Hubbard insulator
transition which happens due to strong correlation in Gd-4f and Ir-5d states.
Our results shows that the 5d electrons of Ir hybridize strongly with O-2p
states near the Fermi level giving rise to the insulating state of Gd2MgIrO6.
Our study suggests that the enhanced magnetic moment is a result of itinerant
exchange rather than the exchange interaction involving individual ions of Gd
and Ir atoms. The total magnetic moment calculated in the present studies is 15
{\mu}B per formula unit for Gd2MgIrO6.
