Room‐Temperature Spin‐Dependent Transport in Metalloporphyrin‐Based Supramolecular Wires

Abstract

Here we present room-temperature spin-dependent charge transport measurements in single-molecule junctions made of metalloporphyrin-based supramolecular assemblies. They displayl arge conductance switching for magnetoresistance in as ingle-molecule junction. The magnetoresistance depends acutely on the probed electron pathway through the supramolecular wire:those involving the metal center showed marked magnetoresistance effects as opposed to those exclusively involving the porphyrin ring which present nearly complete absence of spin-dependent charge transport. The molecular junction magnetoresistance is highly anisotropic, being observable when the magnetization of the ferromagnetic junction electrode is oriented along the main molecular junction axis,a nd almost suppressed when it is perpendicular. The key ingredients for the abovee ffect to manifest are the electronic structure of the paramagnetic metalloporphyrin, and the spinterface created at the molecule-electrode contact.

Magnetoresistive Single‐Molecule Junctions: the Role of the Spinterface and the CISS Effect

“…Magnetically active molecules typically allow spin polarization of the electrical current flowing through a SM junction. Magnetically active molecules are paramagnetic systems owing to their open-shell electronic structure inherent to the presence of metal atoms [2,4,9] or organic radicals. [10,11] Such molecular systems provide energetically available α-or βpolarised spin-orbital channels for charge transport in the SM junction, unlike diamagnetic ones.…”

“…This has been found experimentally by Aragonès et al comparing the conductance of paramagnetic metal ions such as Mn II , Co II , Fe II and Ni II in SM devices based on mononuclear metal complexes [7] and metalloporphyrins. [4] Only spin-split molecular orbitals close to the Fermi level [13] become relevant and, therefore, contribute significantly to charge transport, allowing efficient spin filtering of the current transmitted through the SM device. Fe II and Co II complexes showed large magnetoresistance due to the unfilled beta t 2g orbitals close to the Fermi level of electrodes.…”

“…This has been recently shown in paramagnetic supramolecular junctions [14,15] based on metalloporphyrins. [4] Metalloporphyrin-based SM junctions display different pathways for the transmitted electrons, which are tuned by the final supramolecular structures in the SM junction. [15] Different supramolecular interactions are promoted at different electrode-electrode gap separations of the nanoscale junction, resulting in specific electron pathways, some of them not involving the paramagnetic metal centre (Figure 2a).…”

“…Out of all the probed electron pathways, only those involving the paramagnetic metal centre, i. e. Co II , featured spin-dependent conductance (see Figure 2b). [4] In this vein, Yang et al [9] developed the opposite approach. By varying the direction of an external magnetic field, they were able to adjust the electron pathway through an iron phthalocyanine along with the MR response of the device.…”

“…This is achieved by using an electron spin-source [1] and/or -drain [2] electrode as part of the design of the MR SM junction. Spinpolarisable (ferromagnetic) electrodes, such as Fe or Ni, [3,4] have been typically used in MR SM junction experiments to act as both electron spin-drain and/or -source. [1,3] The ferromagnetic electrode in the SM junction experiment defines the population of electron spin orientation of the current that flows through the MR SM-device, which in turn modulates the device conductance (Figure 1a).…”