Giant magnetoresistance of multiwall carbon nanotubes modeling the tubeferromagnetic-electr.pdf

a r X i v : c o n d - m a t / 0 4 0 2 3 5 9 v 1 [ c o n d - m a t .m e s - h a l l ] 1 3 F e b 2 0 0 4 Giant magnetoresistance of multiwall carbon nanotubes: modeling the tube/ferromagnetic-electrode burying contact S. Krompiewski,1 R. Gutie?rrez,2 and G. Cuniberti2 1Institute of Molecular Physics, Polish Academy of Sciences, PL-60179 Poznan?, Poland 2Institute for Theoretical Physics, University of Regensburg, D-93040 Regensburg, Germany (Dated: October 10, 2003) We report on the giant magnetoresistance (GMR) of multiwall carbon nanotubes with ultra small diameters. In particular, we consider the effect of the inter-wall interactions and the lead/nanotube coupling. Comparative studies have been performed to show that in the case when all walls are well coupled to the electrodes, the so-called inverse GMR can appear. The tendency towards a negative GMR depends on the inter-wall interaction and on the nanotube length. If, however, the inner nanotubes are out of contact with one of the electrodes, the GMR remains positive even for relatively strong inter-wall interactions regardless of the outer nanotube length. These results shed additional light on recently reported experimental data, where an inverse GMR was found in some multiwall carbon nanotube samples. PACS numbers: 73.63.-b,81.07.De,85.35.Kt,85.75.-d I. INTRODUCTION Carbon nanotubes belong to the most promising new materials for the future molecular electronics, they are believed to potentially replace in the near future the silicon-based conventional electronics. To illustrate the enormous scientific and technological progress that has been made since carbon nanotubes were discovered it is worth to mention new concepts such as: the room temperature single electron transistor,1 the ballistic car- bon nanotube field-effect transistor2 or the non-volatile random access memory for molecular computing.3 Re- cently several both experimental4,5,6 and theoretical7,8,9 papers have been published on spin-depend