Electronic structure and magnetic properties of ${\text{Ni}}_{3n}{\text{Al}}_n$ clusters

The equilibrium structure, electronic, and magnetic properties of ${\text{Ni}}_{3n}{\text{Al}}_n$, $\left(n=1,8\right)$ clusters are investigated using ab initio total-energy calculations based on density functional theory. Asymmetric and amorphous structures are observed for $n>1$ clusters, in contrast with the earlier work reported based on Gupta potentials; where, clusters with ${\text{Ni}}_3\text{Al}$ compositions were found to be symmetric. Magnetic moment per atom in these clusters is significantly enhanced with respect to the bulk. The distribution of magnetic charge on Ni and Al atoms is highly inhomogeneous and depends on their number of Al and Ni neighbors. The Al atoms quench the magnetic moments of ${\text{Ni}}_{3n}{\text{Al}}_n$ clusters when compared with the magnetic moments of pure Ni clusters. The analysis of the charge density shows a net transfer of charge from $s$-type orbital of Ni to $p$-type orbital of Al. The density of states exhibits features like Heusler alloys. The implications of this on the conductance in such clusters are discussed.

Figure 1

(Color online) Ground-state structures of ${\text{Ni}}_{3n}{\text{Al}}_n$, $\left(n=1,5\right)$ clusters with their two low-lying isomers. (a) represents the ground state, (b) indicates the first isomer and (c) indicates the second isomer structure. Grey spheres represent Ni atoms and purple spheres represent Al atoms.

Figure 2

(Color online) Ground-state geometries of ${\text{Ni}}_{3n}{\text{Al}}_n$, $\left(n=6,8\right)$ clusters with their two isomers. (a) represents the ground state, (b) indicates the first isomer and (c) indicates the second isomer structure. Grey spheres represent Ni atoms and purple spheres represent Al atoms.

Figure 3

(Color online) Charge-isodensity surfaces of the ground-state structures of ${\text{Ni}}_{3n}{\text{Al}}_n$ clusters. The purple spheres are Al atoms.

Figure 4

(Color online) The spin-up and spin-down density of states of ${\text{Ni}}_{3n}{\text{Al}}_n$ clusters. The spin-up density of states is shown in the upper panel and the spin-down density of states is shown in the lower panel. The Fermi energy level of each cluster is shown by a vertical line. The energy gaps can be seen in Fig. 5.

Figure 5

(Color online) The energy level diagram of the ${\text{Ni}}_{3n}{\text{Al}}_n$ clusters. The distribution of the spin-up energy levels is shown on the left-hand side and the distribution of the spin-down energy levels is shown on the right-hand side for each cluster. The Fermi energy level of each cluster is marked by a blue horizontal line.

Figure 6

(Color online) Constant positive spin density surfaces of the ground-state structures of ${\text{Ni}}_{3n}{\text{Al}}_n$ clusters corresponding to $0.1e{\text{Å}}^{-3}$. Grey spheres represent Ni atoms and purple spheres represent Al atoms.