Synthesis, structure, and properties of tetragonal Sr2M3As2O2 (M-3=Mn-3, Mn2Cu, and MnZn2) compounds containing alternating CuO2-type and FeAs-type layers

Polycrystalline samples of Sr2Mn2CuAs2O2, Sr2Mn3As2O2, and Sr2Zn2MnAs2O2 were synthesized. Their temperature- and applied magnetic field-dependent structural, transport, thermal, and magnetic properties were characterized by means of x-ray and neutron diffraction, electrical resistivity rho, heat capacity, magnetization, and magnetic susceptibility measurements. These compounds have a body-centered-tetragonal crystal structure (space group I4/mmm) that consists of MO2 (M=Zn and/or Mn) oxide layers similar to the CuO2 layers in high superconducting transition temperature T-c cuprate superconductors, and intermetallic MAs (M=Cu and/or Mn) layers similar to the FeAs layers in high-T-c pnictides. These two types of layers alternate along the crystallographic c axis and are separated by Sr atoms. The site occupancies of Mn, Cu, and Zn were studied using Rietveld refinements of x-ray and neutron powder diffraction data. The temperature dependences of rho suggest metallic character for Sr2Mn2CuAs2O2 and semiconducting character for Sr2Mn3As2O2 and Sr2Zn2MnAs2O2. Sr2Mn2CuAs2O2 is inferred to be a ferrimagnet with a Curie temperature T-C=95(1) K. Remarkably, we find that the magnetic ground-state structure changes from a G-type antiferromagnetic structure in Sr2Mn3As2O2 to an A-type ferrimagnetic structure in Sr2Mn2CuAs2O2 in which the Mn ions in each layer are ferromagnetically aligned but are antiferromagnetically aligned between layers.