SPIN-CLUSTER-RESONANCE SPECTRA IN AN S=2 ONE-DIMENSIONAL ISING FERROMAGNET

The electron-paramagnetic-resonance technique has been used to obtain an unambiguous identification of resonances between spin-cluster state s from the distinctive satellite spectra observed in the ranges 10-36 GHz and 2.6-4.2 K from a large single crystal of the one-dimensional I sing ferromagnet [(CH3)3NH]FeCl3.2H2O, known as FeTAC. The frequency a nd temperature dependencies of the spectra are explained by the additi on of the term DELTAS(x) to the Zeeman term in the effective S = 1/2 s pin Hamiltonian describing the first set of excited cluster states. Th e spin-cluster levels are the eigenvalues of the resulting tridiagonal matrix, and lead to a satellite structure in FeTAC which is independe nt of the chain length for chains of more than about 30 Fe2+ ions.