Specific heat of decamethylferrocenium tetracyanoethanide (DMeFc)(TCNE)

Abstract

We report the specific heat C(T) of (DMeFc)(TCNE) for temperatures 3 K<T<50 K. We observe an anomaly at $T_c$=4.82 K corresponding to a transition to a three-dimensional (3D) macroscopic ferromagnet. A broad maximum at ≊15 K corresponds to an exchange interaction of J≊35 K along the chain axis. We propose a generalized 1D Hubbard Hamiltonian to account for this feature. Below $T_c$ results are consistent with the opening up of a gap of approximately 2 meV in the spin-wave spectrum due to the anisotropy in the exchange interaction within the 1D chains.