Microscopic Description of Magnon-Optical-Phonon Interaction in FeCl2·2H2O

A simple physical mechanism is described for the magnon-optical-phonon interaction observed in Fe${\mathrm{Cl}}_2$·2${\mathrm{H}}_2$O: A vibration of the waters of hydration gives rise to a modulating Coulomb potential at the ${\mathrm{Fe}}^{2+}$ site; this potential acts on the orbital part of the ${\mathrm{Fe}}^{2+}$ wave function and is coupled to the spin via the spin-orbit coupling. The calculated magnitude (∼1.2 ${\mathrm{cm}}^{-1\mathrm{}}$) of the interaction is in remarkably good agreement with the experimental value of 1.3 ${\mathrm{cm}}^{-1\mathrm{}}$.