Novel Metallic State Carrying Localized Spins in the Molecular Conductor(DMET)2FeBr4

Abstract
(DMET)2FeBr4 which undergoes a metal-insulator transition at Tc=200K has an alternating stacked structure of DMET donor conducting sheets and FeBr4 magnetic sheets. Above Tc it is in a quasi-1D quarter-filled metallic state, where the Curie-Weiss type magnetism is described in terms of DMET+ donor spins and Fe3+ spins. Below Tc the magnetism, governed only by Fe3+ spins, shows antiferromagnetic order at TN=3.5K. The localized spin feature of π carriers above Tc , which contradicts metallic conduction, is reasonably well understood in terms of the sliding motion of a Wigner lattice state.