Perovskite-related strontium orthoferrite,
SrFeO3−δ, 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 μB
per Fe3+
ion at 2 T and 300 K), indicating the absence of ferro- or ferrimagnetism. The
57Fe
Mössbauer 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.