Slow magnetic relaxations in the anisotropic Heisenberg chain compound Mn(III) tetra(ortho-fluorophenyl)porphyrin-tetracyanoethylene

Magnetic properties of manganese(III) tetra(ortho-fluorophenyl)porphyrin-tetracyanoethylene were studied by ac and dc measurements on polycrystalline samples. This compound consists of ferrimagnetic chains, in which magnetic moments of Mn ion (S=2) in the center of a porphyrin disc and of a tetracyanoethylene radical (s=1/2) are antiferromagnetically coupled with the exchange integral of J=-217 K. At low temperatures, slow magnetic relaxations (below 13 K) and irreversible magnetic behavior (below 4.5 K) were observed, which strongly resemble behavior of a single chain magnet, reported for Ising systems. Temperature dependence of the relaxation time is well described by the Arrhenius equation with the activation energy Delta E=117 K. These relaxations are interpreted as a thermally activated reversal of magnetization through the energy barrier Delta E, associated with creation and propagation of domain walls in one-dimensional anisotropic Heisenberg systems.