BETS as a source of molecular magnetic superconductors (BETS = bis(ethylenedithio)tetraselenafulvalene)

Abstract

BETS-based salts (BETS = bis(ethylenedithio)tetraselenafulvalene) incorporating Fe³⁺ ions are most interesting candidate systems for the observation of interplay of conductivity and magnetism. Indeed, in λ-(BETS)₂FeCl₄, conduction electrons in the BETS layers do interact with spins localised on the (FeCl₄)⁻ anions. Systematic studies on (BETS)₂Fe_xGa_1−xCl _4−yBr_y mixed-composition compounds, in which the electronic properties can be finely tuned by the chemical composition, have provided a number of interesting results, including the characterisation of a molecular antiferromagnetic metal, a conductor with an antiferromagnetic metal state at ambient pressure, and an antiferromagnetic superconductor. Unprecedented superconductor–insulator transitions and superconductor–metal transitions have been also observed.