Tunable magnetoresistance in an asymmetrically coupled single-molecule junction

ROM 2015-06
Author: Dr. Cyrus F. Hirjibehedin / c.hirjibehedin@ucl.ac.uk
Institute: London Centre for Nanotechnology / Department of Physics & Astronomy / Department of Chemistry / UCL, UK
Instrument: Cryogenic STM & SFM

Phenomena that are highly sensitive to magnetic fields can be exploited in sensors and non-volatile memories. For example, a change in the electrical conductivity of a substance with magnetic field (i.e. magnetoresistance) is exploited in the read head of hard drives to detect changes in the orientations of the magnetic domains that store binary data. The scaling of such phenomena down to the single molecule level may enable novel spintronic devices. In this work, we report magnetoresistance in a single molecule junction arising from a region of negative differential resistance (NDR) – a decrease in current with increasing applied voltage - that shifts in a magnetic field at a rate two orders of magnitude larger than expected Zeeman shifts.

This sensitivity to the magnetic field produces two voltage-tunable forms of magnetoresistance, which can be selected via the applied bias. The NDR is caused by transient charging of an iron phthalocyanine (FePc) molecule on a single layer of copper nitride (Cu2N) on a Cu(001) surface, and occurs at voltages corresponding to the alignment of sharp resonances in the filled and empty molecular states with the Cu(001) Fermi energy. An asymmetric voltage-divider effect enhances the apparent voltage shift of the negative differential resistance with magnetic field, which inherently is on the scale of the Zeeman energy. These results illustrate the impact that asymmetric coupling to metallic electrodes can have on transport through molecules, and highlight how this coupling can be used to develop molecular spintronic applications.


Ben Warner1,2, Fadi El Hallak1,†, Henning Prüser1, John Sharp3, Mats Persson3,4, Andrew J. Fisher1,2, and Cyrus F. Hirjibehedin1,2,5,*


1London Centre for Nanotechnology, University College London (UCL), London WC1H 0AH, UK

2Department of Physics & Astronomy, UCL, London WC1E 6BT, UK

3Surface Science Research Centre and Department of Chemistry, University of Liverpool, Liverpool, L69 3BX, UK

4Department of Applied Physics, Chalmers University of Technology, SE-412 96, Göteborg, Sweden

5Department of Chemistry, UCL, London WC1H 0AJ, UK

Present address: Seagate Technology, Londonderry BT48 0BF, U.K.


(1) http://www.ucl.ac.uk/
(2) http://www.london-nano.com/
(3) http://www.ucl.ac.uk/hirjibehedin