Magnon‐phonon coupling in metamagnetic systems: Evidence for one phonon‐two magnon interactions

Spin‐phonon interactions in the linear chain compounds FeCl2⋅2H20, CoCl2⋅2H20, and CoBr2⋅2H20 are considered. It is shown that the recent data of Torrance and Hay on CoBr2⋅2H20 provides strong evidence for the existence of coupling terms involving one phonon and two spin operators. A semi‐quantitative microscopic discussion is given of the spin‐phonon Hamiltonian, within which existing experimental data on all three systems is correlated. It is shown that a consistent picture of the spin‐phonon coupling in these materials can be generated, and additional experiments are suggested to further verify this picture and further probe the spin‐phonon interaction.