Electronic and thermal spin transport in single-molecule junctions based on a spin-crossover Fe(II) complex

Abstract

Due to the switchable magnetic bistability between the low-spin (LS) and high-spin (HS) states, spin-crossover (SCO) complexes have become one of the most promising candidates for designing molecular spintronic devices. Here, based on density functional theory calculations combined with the non-equilibrium Green’s function technique, we explore the spin-dependent transport properties of a molecular junction constructed by an experimentally synthesized mononuclear SCO Fe(II) complex sandwiched between two gold electrodes with applied voltage or temperature bias. Under the small bias voltages, our results clearly reveal that the current through the molecular junction in the HS state is significantly larger than that in the LS state, with an IHS/ILS ratio reaching up to 30. Moreover, in the HS state, the current is dominated by the spin-down electrons, leading to a robust spin-filtering effect with a nearly 100% spin-polarized current, a behavior that proves insensitive to the contact structures between the molecule and electrodes. Furthermore, by applying temperature bias through the molecular junction in the HS state, two interesting spin caloritronic properties, including nearly perfect thermal spin filtration and negative differential thermal resistance, are observed. These theoretical findings suggest that the examined SCO Fe(II) complex holds potential applications in molecular spintronics and spin caloritronics.