Possible High-TCLayered Ferromagnetic Insulator Sr2NiRuO4: An Ab Initio Study

Magnetic insulators are often antiferromagnetic and layered compounds usually show low ordering temperature. On the other hand, layered ferromagnetic (FM) insulators with high TCare very rare although they could be quite useful for spintronic applications. Here, using crystal field level analysis in combination with density functional theory calculations as well as Monte Carlo simulations, we predict that the layered insulator Sr2NiRuO4would have a strong FM coupling with TCas high as 240 K. The tetragonal crystal field in the Ni–O–Ru square plane stabilizes the S= 1/2 Ni+and S= 3/2 Ru3+states. The unique level ordering and occupation optimize the FM Ni–Ru superexchange interactions in the checkerboard arrangement, thus suggesting Sr2NiRuO4as an unusual high-TClayered FM insulator. This work highlights the potential of charge–spin–orbital degrees of freedom for stabilizing strong FM coupling in layered oxides.