Simultaneous excitation of a magnon plus a phonon in CoBr22H2 O: A new type of bound state?

The first observation of the excitation of a magnon plus a phonon is reported. The agreement between far-infrared measurements on CoBr22H2O and a simple theory is excellent. In addition, the transition probability is shown to be a consequence of a simple magnon-phonon interaction. We also discuss the possibility and evidence that this excitation corresponds to a bound state of a magnon plus a phonon. © 1973 The American Physical Society.