Abstract

We propose a theoretical explanation for the puzzling size dependence of the magnetic properties of Mnn clusters. Our approach combines noncollinear ab initio calculations and effective spin Hamiltonians. We show that a remarkable interplay between different magnetic couplings, which is already present in the dimer, leads to a complex size-dependent magnetic behavior, dominated by noncollinear magnetism, frustration, and small cluster magnetic moments. Our results are in good agreement with experiment. © 2006 The American Physical Society.