Theoretical prediction of antiferromagnetism in layered perovskite Sr2TcO4

We theoretically investigate the magnetic properties of Sr2TcO4, a 4d transition-metal layered perovskite of the K2NiF4 type with half-filled t(2g) states. The effect of local Coulomb repulsion between the t(2g) orbitals is included within the density-functional theory (DFT) + U and DFT + dynamical mean-field theory (DMFT) methods. The DFT+ DMFT predicts paramagnetic Sr2TcO4 to be close to the Mott insulator-to-metal transition, similarly to the cubic compound SrTcO3. The intersite exchange interactions computed within the DFT+ DMFT framework point to a strong antiferromagnetic coupling between the neighboring Tc sites within the layer. We then evaluate the Neel temperature T-N within a classical Monte Carlo approach including dipolar interactions, which stabilize the magnetic order in the frustrated K2NiF4 lattice structure. Our approach is validated by applying it to a set of layered and cubic perovskites, for which we obtain T-N in fair agreement with experiment. Within the same approach we obtain the T-N of Sr2TcO4 to be about 450 K. We explore also the effect of anisotropy in exchange interactions due to spin-orbit coupling. These lead to a somewhat higher transition temperature, 550 K.