Electronic structure, spin state, and magnetism of the square-lattice Mott insulatorLa2Co2Se2O3from first principles

Abstract

Electronic and magnetic structures of the recently synthesized cobalt oxyselenide ${\text{La}}_{2}{\text{Co}}_{2}{\text{Se}}_{2}{\text{O}}_{3}$ (structurally similar to the superconducting iron pnictides) are studied through density-functional calculations. The obtained results show that this material is a Mott insulator and it has a very stable ${\text{Co}}^{2+}$ high-spin ground state with a ${t}_{2g}$-like orbital ordering, which is substantiated by the calculated crystal-field excitation energies. The square lattice of the ${\text{Co}}^{2+}$ spins is found to have a strong antiferromagnetic (a weak ferromagnetic) coupling for the second-nearest neighbors via O $({\text{Se}}_{2})$ and an intermediate antiferromagnetic one for the first-nearest neighbors with the strength ratio about 10:1:3. The present results account for the available experimental data and the prediction of a planar frustrated $(2\ifmmode\times\else\texttimes\fi{}2)$ antiferromagnetic structure would motivate a new experiment.