Tuning the Electrical Conductivity of Nanotube-Encapsulated Metallocene Wires

We analyze a new family of carbon nanotube-based molecular wires, formed by encapsulating metallocene molecules inside the nanotubes. Our simulations, which are based on a combination of nonequilibrium Green function techniques and density functional theory, indicate that these wires can be engineered to exhibit desirable magnetotransport effects for use in spintronics devices. The proposed structures should also be resilient to room-temperature fluctuations, and are expected to have a high yield.

Figure 1

Two schematic views of a ${\mathrm{TMCp}}_2@3(7,7)$ nanotube with two encapsulated metallocenes, whose axes are aligned either parallel or perpendicular to the nanotube axis. Each metallocene has a TM atom in the middle, sandwiched by two rings of five carbon and five hydrogen atoms. Hydrogen atoms are not displayed in the figure.

Figure 2

Densities of states $g_i$ of ${\mathrm{CoCp}}_2$, projected onto the $d$-shell orbitals of the cobalt atom for spin-up (solid line) and down (dashed line). The index $i$ denotes the orbital flavor, $i=x^2-y^2,xz,3z^2-r^2,yz,xy$.

Figure 3

(a) Binding energy $E_B$, (b) charge transferred to the nanotube $\Delta Q$, and (c) magnetic moment $m$, of ${\mathrm{CoCp}}_2@N(n,n)$ wires, where $n$ varies from 6 to 10. Circles in solid (dashed) lines correspond to parallel (perpendicular) ${\mathrm{CoCp}}_2@N(n,n)$. Squares in solid (dashed) lines correspond to parallel (perpendicular) ${\mathrm{CoCp}}_2@4(n,n)$.

Figure 4

Band structure of parallel ${\mathrm{TMCp}}_2@3(7,7)$, for spin-up and -down electrons, where $\mathrm{TM}=\mathrm{Fe}$, Co, and V. The perpendicular case is similar but now also the cobaltocene bands are flat. Top (bottom) panels are for spin-up (-down) electrons.

Figure 5

Conductance of the ${\mathrm{CoCp}}_2@3(7,7)$ magnetoresistive devices for (a) spin-up and (b) spin-down electrons. $u$, $d$, $dd$, and $ddd$ conductances are plotted with solid lines, dashed lines, dash-dotted lines, and dash-double-dotted lines, respectively.

Figure 6

Band structure of parallel ${\mathrm{CoCp}}_2@2(11,0)$, ${\mathrm{VCp}}_2@2(11,0)$, and $2{\mathrm{CoCp}}_2@1(12,4)$ for spin-up (top panels) and -down electrons (bottom panels).