  We study the Kondo and transport properties of a quantum dot with a single
magnetic Mn ion connected to metallic leads. By employing a numerical
renormalization group technique we show that depending on the value of
ferromagnetic coupling strength between the local electronic spin and the
magnetic moment of the Mn, two distinct Kondo regimes exist. In the weak
coupling limit, the system can be found in a completely screened Kondo state
describing a local magnetic moment decoupled from the rest of the system. In
contrast, in the strong coupling regime the quantum dot spin and the local
magnetic moment form a single large-spin entity partially Kondo screened. A
crossover between these two regimes can be suitably tuned by varying the tunnel
coupling between the quantum dot electron and the leads. The model investigated
here is also suitable to study magnetic molecules adsorbed on a metallic
surface. The rich phenomenology of these systems is reflected in the
conductance across the system.
