Ferromagnetic Cu–O–Cu coupling in CaCu3Sn4O12 probed by neutron diffraction

The A-site ordered perovskite oxide with the formula CaCu3Sn4O12 has been synthesized in polycrystalline form under moderate pressure conditions (3.5 GPa) in combination with high temperature (1000 °C). This oxide crystallizes in the cubic space group (no. 204) with the unit-cell parameter a = 7.64535(6) Å at 300 K. The SnO6 network is extremely tilted, giving rise to a square planar coordination for Cu2+ cations. The non-magnetic character of Sn4+ offers an excellent opportunity to probe the magnetism of Cu2+ at the A sublattice in CaCu3Sn4O12. Magnetic susceptibility shows that this compound is ferromagnetic below TC = 10 K, which is an unusual magnetic behaviour in cuprates. This peculiar aspect has been examined by neutron powder diffraction. The refinement of the magnetic structure at 4 K indeed indicates a parallel coupling between Cu2+ spins with a magnetic moment of 0.5 μB/Cu atom.