ANTIFERROMAGNETIC ORDER IN CA2CUO2CL2, SR2CUO2CL2 AND SR2CUO3+X

The magnetic order in the tetragonal M(2)CuO(2)Cl(2), M=Ca,Sr and in S r2CuO3+x compounds was studied by using Mossbauer spectroscopy of 0.5% Fe-57-doped samples. These compounds crystallize in a K2NiF4 - type t etragonal structure, isostructural to La2-xSrxCuO4 superconductors. In this structure, one crystallographic site exists for copper atoms, wh ich form CuO2 planes. Sr2CuO3 prepared under ambient pressure has an o rthorhombic structure, while the tetragonal Sr2CuO3+x is obtained when prepared under high oxygen pressure. Both copperoxychlorides are anti ferromagnetically ordered with T-N approximate to 260K, very similar t o T-N in La2CuO4 or Nd2CuO4. The strontium-cuprates are magnetically o rdered at 4.2K with T-N below 10K.