Ferromagnetism in a Heavy Atom Heterocyclic Radical Conductor

摘要

Molecular materials displaying both conductive and magnetic properties are typically based on the use of charge transfer salts. Examples of single component molecular solids displaying multifunctional behavior are rare, as the design of the necessary molecular building blocks is a challenging task. The basic electronic requirement for such molecules is the availability of at least one unpaired electron that can serve as both charge carrier and magnetic coupler. In principle, this condition is met by molecular radicals. A number of organic nitroxyls have been shown to order ferro-magnetically, but their ordering temperatures (T_c) are less than 2 K. Spin-canted antiferromagnetism (weak ferromagnetism) has been found for an oxoverdazyl at 5.4 K and also in a heterocyclic dithiadiazolyl at 35.5 K. In none of these systems, however, do the unpaired electrons serve as charge carriers, as the high molecular disproportionation energies lead to a large on-site Coulomb barrier (U) to charge migration.