Spintronics with single molecules

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(111) or antiferromagnetic Mn films on Fe(100) 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 defined 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.