Giant Resistance Change across the Phase Transition in Spin-Crossover Molecules

The electronic origin of a large resistance change in nanoscale junctions incorporating spin-crossover molecules is demonstrated theoretically by using a combination of density functional theory and the nonequilibrium Green's function method for quantum transport. At the spin-crossover phase transition, there is a drastic change in the electronic gap between the frontier molecular orbitals. As a consequence, when the molecule is incorporated in a two-terminal device, the current increases by up to 4 orders of magnitude in response to the spin change. This is equivalent to a magnetoresistance effect in excess of 3000%. Since the typical phase transition critical temperature for spin-crossover compounds can be extended to well above room temperature, spin-crossover molecules appear as the ideal candidate for implementing spin devices at the molecular level.