Fe-site substitution effect on the structural and magnetic properties in SrFeO₂

We investigated the Fe-site substitution effect on the structural and magnetic properties of the infinite layer iron oxide Sr(Fe_1-xM _x)O₂ (M = Co, Mn) using synchrotron X-ray diffraction, neutron diffraction, and ⁵⁷Fe Mössbauer spectroscopy. Both systems have a similar solubility limit of x ≈ 0.3, retaining the ideal infinite layer structure with a space group of P4/mmm. For the Fe-Co system, both in-plane and out-of-plane axes decrease linearly and only slightly with x, reflecting the ionic radius difference between Fe²⁺ and Co ²⁺. For the Fe-Mn system the lattice evolution also follows Vegard's law but is anisotropic: the in-plane axis increases, while the out-of-plane decreases prominently. The magnetic properties are little influenced by Co substitution. On the contrary, Mn substitution drastically destabilizes the G-type magnetic order, featured by a significant reduction and a large distribution of the hyperfine field in the Mössbauer spectra, which suggests the presence of magnetic frustration induced presumably by a ferromagnetic out-of-plane Mn-Fe interaction.