Size and structural dependence of the magnetic properties of small 3<i>d</i>-transition-metal clusters

The size and structural dependence of magnetic properties of small ${\mathrm{Cr}}_{\mathrm{n}}$, ${\mathrm{Fe}}_{\mathrm{n}}$, and ${\mathrm{Ni}}_{\mathrm{n}}$ clusters are determined by using a tight-binding Hubbard Hamiltonian in the unrestricted Hartree-Fock approximation. Results are given for the average magnetic moment \ensuremath{\mu}${\ifmmode\bar\else\textasciimacron\fi{}}_{n}$, local magnetic moments, and magnetic ordering at T=0. We obtain for ${\mathrm{Fe}}_{\mathrm{n}}$ (n\ensuremath{\le}15) that \ensuremath{\mu}${\ifmmode\bar\else\textasciimacron\fi{}}_{n}$ varies as a function of n due to the interplay between the changes in coordination number and bond length as a function of cluster size, which may be related to recent experiments. The dependence of the structural cluster stability on magnetism is discussed. Results are also given for the cohesive energy, average bond length, and local densities of states.