Magnetic Properties of Sr[sub 2]FeO[sub 3]F, a Highly Anisotropic Oxi-Fluoride

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Abstract
Strontium iron oxi‐fluoride has the “two‐dimensional” K 2 NiF 4 structure in which the Fe3+ ions are situated in an axially distorted octahedron of ligand ions. The fluorine ions, which prefer the axial sites and fill half of them, subject the Fe3+ ions to a large axial crystal field. To study the effect that this field has on the static magnetic properties, moment measurements were made between 5 and 700°K and in fields up to 19 kOe. Above 50°K, the susceptibility exhibits an apparent Curie‐Weiss paramagnetism with a Curie constant that is less than one‐half that expected for free Fe3+ ions. It is shown that this behavior is consistent with the dominance of the crystal field anisotropy energy in the paramagnetic state of this material. Below 50°K, although the temperature dependence of the susceptibility in this region is again unusual, the appearance of a small parasitic residual moment due to slight Fe2+ impurities indicates the presence of long range magnetic order.

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