  Atomic contacts made of ferromagnetic metals present zero-bias anomalies in
the differential conductance due to the Kondo effect. These systems provide a
unique opportunity to perform a statistical analysis of the Kondo parameters in
nanostructures since a large number of contacts can be easily fabricated using
break-junction techniques. The details of the atomic structure differ from one
contact to another so a large number of different configurations can be
statistically analyzed. Here we present such a statistical analysis of the
Kondo effect in atomic contacts made from the ferromagnetic transition metals
Ni, Co and Fe. Our analysis shows clear differences between materials that can
be understood by fundamental theoretical considerations. This combination of
experiments and theory allow us to extract information about the origin and
nature of the Kondo effect in these systems and to explore the influence of
geometry and valence in the Kondo screening of atomic-sized nanostructures.
