  We investigate the magnetic properties of small transition metal clusters
using a simple statistical model, which requires some input data from ab initio
spin-density functional calculations. In our study we consider a
thermodynamically equilibrated ensemble of clusters with different structures,
spin multiplicities, and ground state energies. We calculate the physical
properties of this system by weighting the individual configurations according
to the Boltzmann statistics. We find that presence of isomers with very similar
ground state energies, yet very different magnetic properties, gives rise to a
rich magnetic behaviour of the system which differs significantly from what
would be expected for single configurations. We apply the present model to to
determine the magnetic susceptibility of a cluster ensemble of Langevin
paramagnets. Our results show that some of the anomalies in the magnetic
behaviour of transition metal clusters might be understood in the framework of
our model which is, of course, limited by the extremely high computational
effort needed to obtain the input data.

Condensed Matter