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

Abstract

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 $J=\ensuremath{-}217\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. At low temperatures, slow magnetic relaxations (below $13\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) and irreversible magnetic behavior (below $4.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) 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 $\ensuremath{\Delta}E=117\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These relaxations are interpreted as a thermally activated reversal of magnetization through the energy barrier $\ensuremath{\Delta}E$, associated with creation and propagation of domain walls in one-dimensional anisotropic Heisenberg systems.