Intrinsic localized spin modes in ferromagnetic chains with on-site anisotropy

Intrinsic localized spin modes have been investigated in chains of classical spins coupled ferromagnetically by nearest-neighbor exchange interactions. For this case no localized modes are found. If on-site anisotropy of sufficient magnitude is included, however, localized spin modes appear. The degree of localization increases as the ratio of the anisotropy constant A to the exchange constant J increases. Modes of both even and odd parity occur. The degree of localization also increases if the maximum spin deviation increases with A/J held fixed. The results are applied to the specific case of ${\mathrm{CsFeCl}}_3$. Possibilities for the observation of intrinsic localized spin modes are discussed.