Mössbauer studies of the antiferromagnetic Sr₂CuCl₂O₂ and Ca_0.85Sr_0.15CuO₂ materials

Mössbauer spectroscopy of 1% ⁵⁷Fe doped samples was used to study the magnetic order in the tetragonal Sr₂CuCl₂O₂ and Ca_0.85Sr_0.15CuO₂ materials. In both materials the CuO₂ planes are 3D antiferromagnetically ordered and T_N deduced from these measurements are 260(10) and 500(20) K, respectively, in good agreement with recent neutron diffraction data. The crystal structure of Sr₂CuCl₂O₂ is closely related to that of the R₂CuO₄ system which has approximately the same T_N. On the other hand, the tetragonal Sr₂CuCl₂O₂ structure can be derived from the orthorhombic Sr₂CuO₃ structure, in which endless Cu-O chains are formed. This chain configuration is similar to the Cu(1) sites in YBCO. Sr₂CuO₃ does not order magnetically down to 4.1 K.