201212th tEEE International Conference on Nanotechnology (IEEE- NANO) The International Conference Centre Birmingham 20-23 August 20112, Birmingham, United Kingdom Spintronics with single molecules w_ Wulfekel, T. Miyamachi, S. Schmaus, T.K. Yamada, A.F. Takcs, A. Bagrets, F. Evers, T. Balashov, M. Gruber, V. Davesne, M. Bowen, and E. Beaurepaire Abtact-We demonstrate that with the help of Scanning Tunneling Microscopy (STM), spintronic functions can be realized with single molecules. First, spin transport across single organic molecules was investigated and a molecular giant magnetoresistance (GMR) junction was realized. For this, single phthalocyanine molecules (Pc) were contacted by two ferromagnetic electrodes or by an antiferromagnetic and a ferromagnetic electrode. As substrates, ferromagnetic Co nano-islands grown Cu(ll1) or anti ferromagnetic Mn flms on Fe(IOO) were used, onto which the Pc molecules were deposited. The magnetic state of the substrate was determined by spin-polarized STM with Co or Fe tips. Then, the tip of the STM was approached in a controlled way to contact the molecule. Below 0.4 nm distance, an attractive interaction between the tip and the molecule leads to a jump to contact of one of the side groups of the molecule and to a well defned molecular junction. Through the contacted molecule, a GMR of 60% was observed in case of Co substrates and Co tips. In case of Mn surfaces and Fe tips, a negative GMR of -50% was seen. These results are explained on basis of ab initio calculations showing a selective hybridization of the molecular states with states of the electrodes. Second, we demonstrate that single spin-crossover molecules can be switched between a non-magnetic and a magnetic state reversibly and deterministically by the application of local tunneling currents and that the lifetimes of both states exceed practical measuring times of STM. Thus, we demonstrate a magnetic memory device containing a single magnetic molecule and which can be read and written entirely by electric currents. l Manuscript received June 20, 2012. This work was supported in part by the Deutsche Forschungsgemeinschaf (DFG WU 349/3-1), the Center for Functional Nanostructures (CFN), the Alexander-von-Humboldt Foundation, the French-German University, the Argence Nationale de la Recherche (ANR-06-NANO-033-01 and ANR-09-JCJC-0137) and the Baden-WOrtemberg Stifung (KFN). W Wulfekel is with the Karlsruhe Institute of Technology, 76131 Kalsruhe, Germany (phone: +49-721-60843440; e-mail: wulfwulfekel@ kit.edu). T Miyamachi is with the Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany. S. Schmaus was with the Kalsruhe Institute of Technology, 76131 Karlsruhe, Germany and is now at the Max-Planck Institute for Solid State Research, 70569 Stuttgart, Germany. TK. Yamada was with the Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany and is now at Chiba Universit, Chiba 263-8522, Japan. A.F. Takacs was with the Kalsruhe Institute of Technology, 76131 Karlsruhe, Germany and is now at the Babes-Boyai University, 400084 Cluj-Napoca, Romania. A. Bagrets, F. Evers and T Balashov are with the Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany. M. Gruber, Y Davesne, M. Bowen and E. Beaurepaire are with the IPCMS, 67034 Strasbourg, France. I. INTRODUCTION S pin electronics is used today mainly in read heads in hard disk drives and random access memory. To increase the information density, the devices need to be scaled down in size which has become challenging in the recent past. Although tunneling magnetoresistance (TMR) devices ofer large values of magnetoresistance, the large areal resistance puts a limit to downsizing the devices, as in these the current through the devices becomes too small and a fast read out is hampered [1]. In contrary to that, current perpendicular to the plane GMR junction show a very low areal resistance, such that devices using this principle sufer fom comparably large lead resistances reducing the overall magnetoresistance of the complete device [2]. A promising approach to exteme downsizing is to form a single molecular contact between the two magnetic electrodes of a GMR junction. An even more promising molecular class are spin crossover (SCQ) complexes containing a transition metal ion that can be switched between a low-spin (LS) and a high spin (HS) state by exteral stimulus as temperature, light, pressure, magnetic or electric felds or charge fow [3-5]. The two confgurations may lead to diferent conductances but, more importantly, their switchable spin of the metal ion has a high potential for magnetic storage within individual molecules [6]. In this work, we will address all these fnctions using low temperature scanning tunneling microscopy (STM) [7] to realize and characterize molecular fnctions down to the individual molecule. II. GIANT MAGNETORESISTANCE ACROSS SINGLE MOLECULES A. Contacting single phthalocyanine molecules with an STM Recently phthalocyanine molecules attracted interest with regard to their electronic properties on diferent metal substrates [8]. The behavior of this group of molecules on magnetic (Co) and non-magnetic (Cu) surfaces were investigated. Figure Ia displays the chemical structure of a phthalocyanine molecule. These molecules are used to bind metal cations in the center, and by incorporation of diferent metals their properties can be changed. In our experiments hydrogen (H2PC) and cobalt phthalocyanine (CoPc) were studied. As substrate we use the (llI) surface of a copper single crystal, which was cleaned by cycles of Ar-sputtering and annealing. The molecules were sublimed fom a