Theoretical prediction of antiferromagnetism in layered perovskite Sr2TcO4

We theoretically investigate the magnetic properties of ${\mathrm{Sr}}₂{\mathrm{TcO}}₄$, a $4d$ transition-metal layered perovskite of the ${\mathrm{K}}₂{\mathrm{NiF}}₄$ 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 ${\mathrm{Sr}}₂{\mathrm{TcO}}₄$ to be close to the Mott insulator-to-metal transition, similarly to the cubic compound ${\mathrm{SrTcO}}₃$. 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 N\'eel temperature ${T}_N$ within a classical Monte Carlo approach including dipolar interactions, which stabilize the magnetic order in the frustrated ${\mathrm{K}}₂{\mathrm{NiF}}₄$ 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 ${\mathrm{Sr}}₂{\mathrm{TcO}}₄$ 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.