Size effects on the magnetism of vanadium clusters

Abstract

The magnetism of free vanadium clusters (V$_{N}$, $2\leq N \leq 169 $) with a bcc-like structure is studied using a d electron tight binding Hamiltonian. The spin polarized density of states is calculated self-consistently in the unrestricted Hartree-Fock approximation. We have found that the free V clusters shown different magnetic behavior depending on their size. Results for the local magnetic moments, $\mu_i$, average magnetic moment, $\bar \mu$, and the magnetic order at $T=0$ are obtained as a function of $N$. For the V$_{N}$ clusters $\bar \mu$ varies as a function of $N$ due to the interplay between the changes in coordination number and local environment; for $N \leq 4$ the ground state is ferromagnetic whereas for $N \geq 9$ the ground state is mainly antiferromagnetic in agreement with ab initio and tight binding calculations, respectively. In the case of large size clusters the local magnetic moments of most of the internal atomic shells vanish to avoid local frustrations leading the system in this way to very small magnetic moment as the cluster size increases.