Magnetic Phase Separation in the Oxypnictide Sr2Cr1.85Mn1.15As2O2.

Layered Sr2M3As2O2-type oxypnictides are composed of tetrahedral M2Pn2 and square planar MO2 layers, the building blocks of iron-based and cuprate superconductors. To further expand our understanding of the chemical and magnetic properties of the Sr2Cr3-xMnxAs2O2 solid solution, Sr2Cr2MnAs2O2 has been synthesized. The compound crystallizes in the I4/mmm tetragonal space group with a refined stoichiometry of Sr2Cr1.85Mn1.15As2O2. The M(2) site within the M2Pn2 slab is occupied by 42.7% Cr and 57.3% Mn, and the magnetic moments order antiferromagnetically below TN(M2) = 540 K with a C-type antiferromagnetic structure. The M(1) site within the MO2 layers is fully occupied by Cr, and antiferromagnetic order is observed below TN(M1) = 200 K. Along c, there are two possible interplanar arrangements: ferromagnetic with the (1/2, 1/2, 0) propagation vector and antiferromagnetic with the (1/2, 1/2, 1/2) propagation vector. Magnetic phase separation arises so that both propagation vectors are observed below 200 K. Such magnetic phase separation has not been previously observed in Sr2M3As2O2 phases (M = Cr, Mn) and shows that there are several competing magnetic structures present in these compounds.