Optical properties and spin dynamics of FeCl2

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Abstract
The optical absorption spectrum of FeCl2 is reported in the energy range 0.6-3 eV and for temperatures between 1.2 and 300 °K. The observed absorption bands are weak and some have an anomalous temperature dependence below TN, Néel temperature (23.5 °K). A model is proposed to explain the anomalous temperature dependence involving spin-exciton coupling. According to the model information about the nearest-neighbor spin correlation function can be obtained simply from optical absorption data at all temperatures. Results are presented and compared with various models in the different temperature regions