Magnetic excitations and electronic interactions in Sr$_2$CuTeO$_6$: a   spin-1/2 square lattice Heisenberg antiferromagnet
  Sr$_2$CuTeO$_6$ presents an opportunity for exploring low-dimensional magnetism on a square lattice of $S=1/2$ Cu$^{2+}$ ions. We employ ab initio multi-reference configuration interaction calculations to unravel the Cu$^{2+}$ electronic structure and to evaluate exchange interactions in Sr$_2$CuTeO$_6$. 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 Sr$_2$CuTeO$_6$ is an almost realization of a nearest-neighbor Heisenberg antiferromagnet but with relatively weak coupling of 7.18(5) meV. 
P. Babkevich, Vamshi M. Katukuri, B. F{\aa}k, S. Rols, T. Fennell, D.   Paji\'c, H. Tanaka, T. Pardini, R. R. P. Singh, A. M...
cond-mat.str-el