  Spin and orbital magnetic moments of cationic iron, cobalt, and nickel
clusters have been determined from x-ray magnetic circular dichroism
spectroscopy. In the size regime of $n = 10 - 15$ atoms, these clusters show
strong ferromagnetism with maximized spin magnetic moments of 1~$\mu_B$ per
empty $3d$ state because of completely filled $3d$ majority spin bands. The
only exception is $\mathrm{Fe}_{13}^+$ where an unusually low average spin
magnetic moment of $0.73 \pm 0.12$~$\mu_B$ per unoccupied $3d$ state is
detected; an effect, which is neither observed for $\mathrm{Co}_{13}^+$ nor
$\mathrm{Ni}_{13}^+$.\@ This distinct behavior can be linked to the existence
and accessibility of antiferromagnetic, paramagnetic, or nonmagnetic phases in
the respective bulk phase diagrams of iron, cobalt, and nickel. Compared to the
experimental data, available density functional theory calculations generally
seem to underestimate the spin magnetic moments significantly. In all clusters
investigated, the orbital magnetic moment is quenched to $5 - 25$\,\% of the
atomic value by the reduced symmetry of the crystal field. The magnetic
anisotropy energy is well below 65 $\mu$eV per atom.
