Abstract
We discover that large uniaxial magnetocrystalline anisotropy driven by the simultaneous presence of spin-orbit coupling and structural distortions is the origin of the giant coercivity observed experimentally in the double perovskite Lu2NiIrO6. The magnetic easy axis turns out to be the monoclinic b-axis with an anisotropy constant as high as 1.9 x 10(8) erg/cm(3). The predicted coercive field of 50 kOe and Curie temperature of 220 K agree with the experimentally observed values and point to potential of Lu2NiIrO6 in spintronics applications. We find that the spin-orbit coupling induces a rare Ir4+ J(eff) = 1/2 Mott insulating state, suggesting that Lu2NiIrO6 provides a playground to study the interplay between spin-orbit coupling and electronic correlations in a 5d transition metal oxide. The spin-orbit coupling also results in a direct band gap with the valence and conduction states localized on different transition metal sublattices, i.e., efficient electron-hole separation upon photoexcitation and low electron-hole recombination.