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Mossbauer spectra of ten members of the solid solution series (Fe1-xRhx)2O3, taken over a wide range of temperature, are analyzed in terms of the different magnetic environments possible for the 57Fe nuclei. Hyperfine interaction parameters are given as a function of x at 20 K and at 296 K. Molecular field theory gives J3=-11.0+or-1.0K and J4=-15.3+or-1.0K, and can also explain the temperature dependence of the hyperfine fields in a sample with x=0.36 for T/TN<or approximately=0.7. There is evidence for longer range interactions. A supertransferred hyperfine field of 7.8 kOe per superexchange neighbour is inferred from the spectra at 20K, and a covalency parameter Asigma 2=0.1 is deduced. The ionicity of the Fe-O bond is approximately 80% and the 3d spin of Fe3+ is 2.32. The quadrupole coupling and isomer shift, calculated by including overlap distortion of the iron orbitals by the ligands are in agreement with much of the data. It is estimated that the iron hyperfine field and nuclear electron density are changed by -100 kOe and 5.6 au-3 in alpha Fe2O3 compared with the free ion.
Coey et al. (Thu,) studied this question.
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