The Mössbauer Study of the Ferrous Ion in FeCl2

The Mössbauer spectra of Fe 57 in FeCl 2 have been measured over the temperature range of 1.5°K–530°K. The temperature dependence of the observed e 2 q Q /2 is fairly strong. Even below the Néel temperature of 24°K, the spectra showed only two absorption lines due to the electric field gradient at the iron nucleus and did not show any typical patern of six absorption lines due to the internal magnetic field. The quadrupole splitting changed abruptly by about 30% through the Néel temperature. The parameters obtained are as follows; e 2 q Q /2=0.80 mm/sec, δ=1.26 mm/sec at room temperature (above the Néel temperature) and e 2 q Q /2=1.36 mm/sec, δ=1.50 mm/sec and H int =0±8 koe at liquid helium temperature (below the Néel temperature). These characteristic features are completely explained with the following Hamiltonian for ferrous ion in the orbital triplet; \(H{=}λ' lS-({lz}²-2/3)-2Jx{}Sz{}Sz\) with the values of λ'=95 cm -1 , Δ =119 cm -1 and 2 J x =7.3 cm -1 .