Magnetic Phase Separation in the Oxypnictide Sr(2)Cr(1.85)Mn(1.15)As(2)O(2)

[Image: see text] Layered Sr(2)M(3)As(2)O(2)-type oxypnictides are composed of tetrahedral M(2)Pn(2) and square planar MO(2) layers, the building blocks of iron-based and cuprate superconductors. To further expand our understanding of the chemical and magnetic properties of the Sr(2)Cr(3–x)Mn(x)As(2)O(2) solid solution, Sr(2)Cr(2)MnAs(2)O(2) has been synthesized. The compound crystallizes in the I4/mmm tetragonal space group with a refined stoichiometry of Sr(2)Cr(1.85)Mn(1.15)As(2)O(2). The M(2) site within the M(2)Pn(2) slab is occupied by 42.7% Cr and 57.3% Mn, and the magnetic moments order antiferromagnetically below T(N)(M2) = 540 K with a C-type antiferromagnetic structure. The M(1) site within the MO(2) layers is fully occupied by Cr, and antiferromagnetic order is observed below T(N)(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 Sr(2)M(3)As(2)O(2) phases (M = Cr, Mn) and shows that there are several competing magnetic structures present in these compounds.