Monatomic Au wire with a magnetic Ni impurity: Electronic structure and ballistic conductance

The influence of a magnetic impurity (Ni atom) on the electronic, magnetic, and Landauer conductance properties of a monatomic Au wire is studied by first-principles density-functional calculations. We compare two adsorption geometries: bridge and substitutional. We find that the Ni atom remains magnetic in both cases; however, in the bridge geometry, the total spin is close to 1/2 and the symmetry of the hole is $d_{3z^2-r^2}$ while in substitutional it is larger than 1/2 with two degenerate holes with symmetry $d_{yz}$ and $d_{zx}$. By using the Büttiker-Landauer theory, we find that in the first case the ideal, frozen spin conductance is somewhat diminished by the Ni impurity, although quite sensitive to calculation details such as the position of the empty Ni $d$ and $s$ states, while in the substitutional case conductance remains close to the ideal value $G_0$ $\left(=2e^2/h\right)$ of the pristine gold wire.

Figure 1

(Color online) Supercells of monoatomic linear ${\text{Au}}_{15}$ wires with a Ni impurity (a) for the bridge case and (b) the substitutional case.

Figure 2

Planar average of the magnetization density integrated on the $xy$ plane and plotted along $z$ for (a) the bridge and (b) the substitutional case. The tics on the $\widehat{x}$ axis indicate the positions of the atoms.

Figure 3

(Color online) The spin-resolved charge-density difference $\Delta \rho \left(r\right)={\rho }_{\text{Ni}/\text{Au}-\text{wire}}\left(r\right)-\left[{\rho }_{\text{Ni}}\left(r\right)+{\rho }_{\text{Au}-\text{wire}}\left(r\right)\right]$ for the bridge case and for the substitutional case. The charge flows from black (negative) region to white (positive) region.

Figure 4

Projected density of states onto $s$, $d_{3z^2-r^2}$, $d_{zx}$, and $d_{x^2-y^2}$ orbitals (even states with respect to mirror reflection about the $xz$ plane) of Ni and of the two Au atoms in contact with Ni, for the bridge case. The PDOS of the monatomic Au wire are also shown (dashed lines).

Figure 5

Projected density of states onto $d_{yz}$ and $d_{xy}$ orbitals (odd states with respect to mirror reflection about the $xz$ plane) of Ni and of the two Au atoms in contact with Ni, for the bridge case. The PDOS of the monatomic Au wire is also shown (dashed lines).

Figure 6

Projected density of states onto $s$, $d_{3z^2-r^2}$, $\left(d_{yz},d_{zx}\right)$, and $\left(d_{xy},d_{x^2-y^2}\right)$ orbitals of Ni and the two Au atoms in contact with Ni for the substitutional case. The PDOS of the monatomic Au wire are also shown (dashed lines).

Figure 7

Majority-spin (left) and minority-spin (right) conductance as a function of energy relative to the Fermi energy for the bridge and substitutional cases. The conductance of a perfect Au wire is also shown (dashed line) for comparison.

Figure 8

PDOS onto the Ni $d$ orbitals calculated with $U=3\text{eV}$ (dashed lines) compared to the case of $U=0$ (solid lines), corresponding to GGA calculations. The results for bridge and substitutional geometries are shown in the left and right panels, respectively. The arrows indicate the shifts in the positions of some PDOS resonances around the Fermi level due to the inclusion of $U$. For these calculations, a supercell containing 16 Au atoms was used.