Protonation control of spin transport properties in magnetic single-molecule junctions

Abstract

The protonation-controlled conductance switching of 4,4′-vinylenedipyridine (44VDP) molecular junctions was experimentally reported by Brooke et al. (Nano Lett 18(2): 1317–1322, 2018), where a change induced by protonation in the bonding at the molecule–metal interface was proposed as the key ingredient. Here, we perform a first-principles study on the spin-dependent transport properties of 44VDP molecular junctions modulated by protonation. The switching mechanism in the experiment is clarified; namely, the weak coupling strength at the molecule–metal interface is triggered by protonation of pyridyl groups in the 44VDP molecule. In particular, the protonation process modifies the organic–ferromagnetic spinterface, which reduces the number of hybrid interface states and causes an inversion of tunneling magnetoresistance from positive to negative values. Furthermore, a protonation-induced excellent spin-filtering effect is realized. This work sheds light on the mechanism of protonation at the organic–ferromagnetic interface and provides a promising way to realize multifunctional devices in organic spintronics.