Magnetic Excitations and Electronic Interactions in Sr₂CuTeO₆: A Spin-1/2 Square Lattice Heisenberg Antiferromagnet

Sr₂CuTeO₆ presents an opportunity for exploring low-dimensional magnetism on a square lattice of S=1/2  Cu²⁺ ions. We employ ab initio multireference configuration interaction calculations to unravel the Cu²⁺ electronic structure and to evaluate exchange interactions in Sr₂CuTeO₆. The latter results are validated by inelastic neutron scattering using linear spin-wave theory and series-expansion corrections for quantum effects to extract true coupling parameters. Using this methodology, which is quite general, we demonstrate that Sr₂CuTeO₆ is an almost ideal realization of a nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling of 7.18(5) meV.