An 57Fe Mössbauer effect study of magnetic ordering in the Fe2O3Cr2O3 system

⁵⁷Fe Mössbauer effect spectra have been obtained as a function of temperature for a series of Fe₂O₃Cr₂O₃ compositions in the range 0.2–75% Fe₂O₃. From 30% of Fe₂O₃ upwards, the dependence of the reduced internal magnetic field $\text{H}{}_{\mathrm{<mtext>eff</mtext>}}\text{(T)}\text{H}{}_{\mathrm{<mtext>eff</mtext>}}\text{(T = 0)}$ on reduced temperature, $\text{T}\text{T}{}_{\mathrm{N}}$, was found to be identical with that for α-Fe₂O₃, indicating the persistence of Fe₂O₃-type ordering over this composition range. For 0.2% of ⁵⁷Fe₂O₃ in Cr₂O₃, the reduced field values fall far below those for α-Fe₂O₃ or Cr₂O₃, and weak coupling of Fe₃⁺ with Cr³⁺ has been inferred.A Morin transition similar to that for α-Fe₂O₃ was not present for samples containing 75% of Fe₂O₃. Quadrupole shifts ? were found to be negative and diminishing between 75 and 30% Fe₂O₃, and positive between 20 and 0.2%. The limiting value at lowest dilution of 0.113 ± 0.010 mm/sec corresponds to a nuclear quadrupole coupling constant e²qQ of 0.45 ± 0.04, approximately half that for α-Fe₂O₃. Cone angles for Fe³⁺ spin vectors in the spin-spiral arrangements for intermediate compositions have been derived, and are similar to, but less extreme than those deduced from neutron diffraction data.