Synthesis, structure, and properties of tetragonal Sr 2 M 3 As 2 O 2 ( M 3 =Mn 3 , Mn 2 Cu , and MnZn 2 ) compounds containing alternating CuO 2 -type and FeAs-type layers

Polycrystalline samples of ${\text{Sr}}_{2}{\text{Mn}}_{2}{\text{CuAs}}_{2}{\text{O}}_{2}$, ${\text{Sr}}_{2}{\text{Mn}}_{3}{\text{As}}_{2}{\text{O}}_{2}$, and ${\text{Sr}}_{2}{\text{Zn}}_{2}{\text{MnAs}}_{2}{\text{O}}_{2}$ 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 $\ensuremath{\rho}$, heat capacity, magnetization, and magnetic susceptibility measurements. These compounds have a body-centered-tetragonal crystal structure (space group $I4/mmm$) that consists of $M{\text{O}}_{2}$ ($M=\text{Zn}$ and/or Mn) oxide layers similar to the ${\text{CuO}}_{2}$ layers in high superconducting transition temperature ${T}_{c}$ cuprate superconductors, and intermetallic $M\text{As}$ ($M=\text{Cu}$ 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 $\ensuremath{\rho}$ suggest metallic character for ${\text{Sr}}_{2}{\text{Mn}}_{2}{\text{CuAs}}_{2}{\text{O}}_{2}$ and semiconducting character for ${\text{Sr}}_{2}{\text{Mn}}_{3}{\text{As}}_{2}{\text{O}}_{2}$ and ${\text{Sr}}_{2}{\text{Zn}}_{2}{\text{MnAs}}_{2}{\text{O}}_{2}$. ${\text{Sr}}_{2}{\text{Mn}}_{2}{\text{CuAs}}_{2}{\text{O}}_{2}$ is inferred to be a ferrimagnet with a Curie temperature ${T}_{\text{C}}=95(1)\text{ }\text{K}$. Remarkably, we find that the magnetic ground-state structure changes from a $\text{G}$-type antiferromagnetic structure in ${\text{Sr}}_{2}{\text{Mn}}_{3}{\text{As}}_{2}{\text{O}}_{2}$ to an $\text{A}$-type ferrimagnetic structure in ${\text{Sr}}_{2}{\text{Mn}}_{2}{\text{CuAs}}_{2}{\text{O}}_{2}$ in which the Mn ions in each layer are ferromagnetically aligned but are antiferromagnetically aligned between layers.