Magnetic order in perovskite-related SrFeO2F

Perovskite-related strontium orthoferrite, SrFeO3-delta, has been fluorinated by a low temperature reaction with poly(vinylidene fluoride) to give the compound SrFeO2F. X-ray powder diffraction shows that fluorination leads to an expansion of the unit cell which is consistent with partial replacement of oxygen by fluorine and consequent reduction in the oxidation state of iron. Magnetometry experiments in the temperature range 10-400 K showed small aligned moments (0.003 +/- 0.000 05 mu(B) per Fe3+ ion at 2 T and 300 K), indicating the absence of ferro- or ferrimagnetism. The Fe-57 Mossbauer spectra recorded at temperatures below about 300 K show broadened, but unsplit, sextet patterns whilst spectra recorded above this temperature show clear splitting of the sextet structure and a magnetic ordering temperature of 685 +/- 5 K. A model related to the pattern of substitution by fluorine on the octahedral arrangement of oxygen sites around iron is proposed in which SrFeO2F undergoes a magnetic transition at about 300 K from a low temperature state with random spin directions to an antiferromagnetic state.