  The parent compound of high-Tc superconducting cuprates is a unique Mott
state consisting of layers of spin-1/2 ions arranged on a square lattice and
with a record high antiferromagnetic coupling within the layers. Compounds with
similar characteristics have long been searched for. Nickelates and iridates
had been proposed as cuprate analogs but so far have not reached a satisfactory
similarity. Here we use a combination of experimental and theoretical tools to
show that the commercial compound AgF2 is an excellent cuprate analog with
remarkably similar electronic parameters to La2CuO4 but larger buckling of
planes. Two-magnon Raman scattering reveals a superexchange constant which
reaches 70% of that of a typical cuprate. We argue that structures that reduce
or eliminate the buckling of the AgF2 planes could have an antiferromagnetic
coupling that matches or surpasses the cuprates.
