(A=Sr, Ba)*

Double perovskites are found to exhibit novel properties desirable in spintronic applications. Here, by means of density functional theory calculations, we investigate the electronic and magnetic properties of newly synthesized ALaNiOsO₆ (where A=Sr, Ba). We found the magnetic phase transition in these materials. The calculated total energy indicates antiferromagnetic ground state for SrLaNiOsO₆ and ferromagnetic ground state for BaLaNiOsO₆ with their easy axis along [010] directions, respectively. Both materials shows Mott insulating behavior with dominant contributions from Os-5d bands around the Fermi level. The sizable strength of spin-orbit coupling in Os plays significant role in opening the band gap in these compounds. Our results agrees with the experimental findings (0.3 eV) for both the materials. Furthermore, we predict a possible meta-magnetic transition in BaLaNiOsO₆ similar to the Dirac Mott insulator Ba₂NiOsO₆.