Room-Temperature Magnetoresistance in Single-Molecule Devices

The goal of this communication is to present a well-defined experimental/theoretical route map to reach single-molecule devices based on porphyrin systems showing magnetoresistance at room temperature. We have already reported that STM measurements of deposited metal tiocyanate (and selenocyanate) complexes on heavy metal surfaces that have large spin-orbit contributions allows to detect magnetoresistance. Such magnetoresistance effect is similar to that reported by Fert and Grünberg in magnetic metal layers used in hard disk heads, just the inversion of the magnetization of the magnetic tip results in an important change in the transport properties of the device and more recently, in magnetic RAM memories as STT-MRAM devices. In this study, we also provide results for empty porphyrin and metalloporphyrins based devices attached to the electrodes through thiol-pyridine axial ligands. Our study shows a theoretical analysis and the practical implementation through two-terminal devices using STM equipment to achieve the room temperature molecular-based spintronic nanodevices. It is worth noting that such metalloporphyrin devices show larger complexity than the previously studied systems: (i) three peaks in the STM conductance histograms (only one in the metal tiocyanate complexes); (ii) magnetoresistance effect was also found if the electrons are injected from the magnetic nickel tip (for the tiocyanate systems only the effect was detected injecting from the gold substrate); (iii) magnetoresistance effect is smaller than in the tiocyanate systems. Non-equilibrium Green functions combined with DFT calculations have been employed in order to rationalize such results.