Single Molecule Spin valves

Transport in the frame of the Landauer formalism for the single particle case is examined for carbon nanotubes decorated with magnetic molecules. Non-standard ab-initio calculations using constrained density functional theory to ensure the correct charge and magnetization densities are performed. Density functional calculations are performed on magnetic molecules in different spatial configurations: gas phase, crystal phase, and compound; the latter configuration type corresponds to a close-to-experiment system in which magnetic molecules are attached to a non-magnetic one. Based on the magnetization of the sitting molecules, two different magnetic states are examined. They are termed as antiparallel and parallel cases. They correspond to the experimental realizations shown elsewhere. The Kohn-Sham matrices, which are the result of the density functional simulations, are then used as an input for the transmission simulations which is performed using the Landauer formalism. Two transmission spectra are calculated corresponding to the alpha and beta spin channels per simulation. Differential conductance maps show a higher conductance for the parallel case compared to the antiparallel one for all the gate voltages where the conductance is different from zero. ... mehrAn empirical model is presented which mimics the real systems’ behaviour. It consists on a spin polarized tight-binding chain with two atoms per site where two defects are added to the central region simulating the real magnets. To model the CNT small bandgap, two orbitals per atom site were used. Similar results to those of the real system are calculated. It was found that the reason of the difference in conductance between one spin state and the other is that in the parallel case, the transmission for alpha and beta spin channels around the region of interest overlap giving a total transmission (which is the sum of both spins’ transmissions) larger to that of the antiparallel case where the alpha and beta transmissions are separated.