Mössbauer Effect Study of FeCl₂·4H₂O in the Antiferromagnetic State

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Measurements of the Mössbauer effect of ⁵⁷Fe in powder and single-crystal absorbers of FeCl₂·4H₂O have been made in a temperature region 0.16–0.18 K, far below its Néel temperature (1.1 K). The unit cell of this salt comprises two inequivalent Fe sites whose environments are related by 180° rotation about the b axis. The Mössbauer effect parameters and the orientations of the EFG principal axes and of the internal magnetic field, relative to the crystalline axes, are determined by computer analysis of the observed spectra. A possibility is pointed out that the EFG major axis and the internal field vector at each site tip out of the a′b plane.