Magnetooptical determination of the parameters of exchange interactions in antiferromagnetic iron carbonate

The dispersion and temperature dependence of the Faraday effect in siderite—iron carbonate of natural origin—was studied. It is shown that the Faraday rotation in siderite in the visible region of the spectrum is of an electric dipole nature and is of the paramagnetic type. It is concluded from an analysis of the temperature dependence of the inverse specific rotation (Φ/ ±H)−1 that the concept of the paramagnetic Curie temperature for iron carbonate becomes meaningless in the temperature range from TN = 38 K up to 300 K. The temperature dependence of the magnetic susceptibility χ(T) is reconstructed from the experimental temperature dependence of the specific Faraday rotation. Analysis of the high- and low-temperature parts of this dependence in the molecular-field approximation shows that the exchange interaction between ions in the same sublattice (second magnetic neighbors) is antiferromagnetic. The parameters characterizing the intersublattice 2J1q1/k = −(11.0±1.5) K and intrasublattice 2J2q2/k = −(2.5±1.5) K exchange interactions are determined.

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