Large Magnetoresistance at Room Temperature in Organic Molecular Tunnel Junctions with Nonmagnetic Electrodes

Abstract

We report room-temperature resistance changes of up to 30% under weak magnetic fields (0.1 T) for molecular tunnel junctions composed of oligophenylene thiol molecules, 1-2 nm in length, sandwiched between gold contacts. The magnetoresistance (MR) is independent of field orientation and the length of the molecule; it appears to be an interface effect. Theoretical analysis suggests that the source of the MR is a two-carrier (two-hole) interaction at the interface, resulting in spin coupling between the tunneling hole and a localized hole at the Au/molecule contact. Such coupling leads to significantly different singlet and triplet transmission barriers at the interface. Even weak magnetic fields impede spin relaxation processes and thus modify the ratio of holes tunneling via the singlet state versus the triplet state, which leads to the large MR. Overall, the experiments and analysis suggest significant opportunities to explore large MR effects in molecular tunnel junctions based on widely available molecules.

Theory of magnetoresistance of organic molecular tunnel junctions with nonmagnetic electrodes

“…10, and we consider it to be the baseline result of our model. However, we also find that a small exchange splitting of the initial state energy levels and a difference in the gfactors of the electrons forming the initial state pairs can result in negative magnetoresistance over certain field ranges.…”

“…10 The transport was shown to be due to non-resonant tunneling by comparing the conductances of molecules of different lengths, and the relative was found to be essentially independent of the length of the molecule and also independent of the direction of the magnetic field.…”

“…However the model developed has electron-hole symmetry and in a simplified version was used to explain hole-tunneling phenomena in Ref. 10.…”

Large Negative Differential Resistance and Rectification from a Donor–σ–Acceptor Molecule in the Presence of Dissimilar Electrodes

“…Recently, Frisbie et al. showed that the Au−S tunnel junction played a significant role in determining the magnetoresistance effect of the Au−(oligophenylene thiol)−Au device . To investigate the role of the junction for the present device, we plotted the PDOS contributions of the junction elements; all other atoms of the device and relevant results are depicted in Figure S5 a and b, respectively, in the Supporting Information.…”

A New Photo-Control Method for Organic–Inorganic Interface Dipoles and Its Application to Photo-Controllable Molecular Devices

“…The built-in electric field induces an additional charge redistribution across the interface, which modifies the surface electronic properties of condensed matter used as the substrate. To date, the effects of SAM formation on the magnetism, 15,16,1922 conductiv-ity, 9,10,18,23,24 and superconductivity 2527 have been reported by several research groups.…”