EXCITATION OF MULTIPLE MAGNON BOUND STATES IN ANISOTROPIC LINEAR CHAINS.
Interim technical rept.,
HARVARD UNIV CAMBRIDGE MASS DIV OF ENGINEERING AND APPLIED PHYSICS
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The Co spins in metamagnetic CoCl2.2H2OCC2 form ferromagnetic Fo linear chains. Below 17.2K these Fo chains are ordered in either an antiferromagnetic AF, ferrimagnetic Fi, or ferromagnetic Fo phase, depending on the magnitude of the applied field. Far infrared measurements performed on CC2 reveal absorption which is identified as AF resonance, Fi resonance, and Fo resonance in the respective phases. Furthermore, these magnons appear to interact with an unexpected excitation which is believed to be an optical phonon. The observed frequencies of both the phonon and the magnetic resonances are well described by a conventional spin wave calculation with an anisotropic exchange interaction and a phenomenological magnon-phonon coupling. Perhaps the most striking feature of the data, however, is the appearance of absorption in each phase having Zeeman energies corresponding to g-values of about 14, 21, 28, and even 35, in addition to the normal spin waves which have a g-value of approx. 7. Furthermore, the energy of an n-fold multiple excitation is markedly less than n times the energy of a single one. These excitations are called spin clusters or magnon bound states, and this is the first direct observation of these excitations. In order to account for the deviations of the experimental data from the predictions of the Ising model, a general theoretical method is developed. The existence of magnon bound states in a two- and three-dimensional spin system is also discussed. Author
- Electricity and Magnetism
- Solid State Physics