Molecular spintronics: spin-dependent electron transport in molecular wires

We present a theoretical study of spin-dependent transport through molecular wires bridging ferromagnetic metal nanocontacts. We extend to magnetic systems a recently proposed model that provides a quantitative explanation of the conductance measurements of Reed et al. [Science 278 (1997) 252] on Au break-junctions bridged by self-assembled molecular monolayers (SAMs) of 1,4-benzene-dithiolate (BDT) molecules. Based on our calculations, we predict that spin-valve behavior should be observable in nickel break-junctions bridged by SAMs formed from BDT. We also consider spin transport in systems consisting of a clean ferromagnetic nickel STM tip and SAMs of benzene-thiol molecules on gold and nickel substrates. We find that spin-valve behavior should be possible for the Ni substrate. For the case where the substrate is gold, we show that it should be possible to inject a highly spin-polarized current into the substrate. (C) 2002 Elsevier Science B.V. All rights reserved.