Spin transport in carbon nanotubes bundles: An ab-initio study

First principles investigations are performed on understanding the spin-polarized transport in carbon nanotubes and carbon nanotube bundles consisting of (8,0) and (17,0) SWCNTs kept in vertical (out-of-plane) arrangement and contacted by two CrO2 Half-Metallic-Ferromagnetic (HMF) electrodes. On comparison of the results for all the structures, it is observed that carbon nanotube bundle consisting of (17,0) CNT offers high TMR ∼100% and the transport phenomenon is tunneling, since there are no transmission states near Fermi level. However, in individual (8,0) and (17,0) CNT the transport is not because of tunneling, since there are significant number of transmission states near Fermi level. High Magneto Resistance (MR) 96% and 99% is observed in individual (8,0) and (17,0) CNTs respectively. Both TMR and Spin Injection Efficiency η (Spin-Filtration) are higher in (17,0) carbon nanotube bundle structure, which is due to carbon nanotube bundle acting as a perfect barrier in vertical (out-of-plane) arrangement resulting in negligible spin-down current (I↓) in both Parallel Configuration (PC) and Antiparallel Configuration (APC).