Light-scattering study of phonon-magnon coupling in antiferromagnetic FeCl2. 2H2O

Raman spectroscopy has been used to study the phonon-magnon coupling in the antiferromagnetic phase of ferrous chloride dihydrate. The interaction has been studied as a function of temperature, from 2 K to $T_N=23\mathrm{}$ K, and applied field, from 0 to 28 kG. The phonon is assigned as a $B_g$ symmetry libration mode, in accord with the predictions of Torrance and Slonczewski; it is found to be "soft," decreasing in energy as $T\to 0$. The phonon-magnon coupling constant is nearly field independent but decreases to zero at $T_N$. It is found that no zero-field splitting of the magnon occurs, within 0.2-${\mathrm{cm}}^{-1\mathrm{}}$ instrumental resolution, in contrast to the 0.8-${\mathrm{cm}}^{-1\mathrm{}}$ splitting inferred from the infrared spectrum. The magnon $g$ value is determined to be 1.7 ± 0.1, in contrast to Torrance's value of 2.23 ± 0.02.