The effect of chain length on the temperature dependence of a spin-cluster resonance signal in a one-dimensional Ising ferromagnet

The temperature dependence of the high-field spin cluster resonance observed in the one-dimensional ferromagnet FeTAC at low temperatures is shown to depend on the numbers of ferrous ions in the chains. The longer the chain, the lower is the temperature at which deviations from the previously obtained linear relationship between In(intensity) and 1/T occur. Calculations for the distribution of chain lengths obtained by the random substitution of a nonmagnetic impurity are made for several impurity concentrations and compared with the experimental data points for a pure FeTAC sample. The results indicate that, in this case, other types of crystal defect must limit the chain lengths.