  Planar macroscopic magnetic tunnel junctions exhibit well defined zero bias
anomalies when a thin layer of ferromagnetic CoFe(B) nanodots is inserted
within a MgO based tunnel barrier. The conductance curves exhibit a single and
a double peak, respectively, for anti-parallel and parallel alignment of the
magnetizations of the electrodes which sandwich the tunnel barrier. This leads
to a suppression of the tunneling magnetoresistance near zero bias. We show
that the double peak structure indicates that the zero-bias anomaly is
spin-split due to a magnetic exchange interaction between the magnetic nanodots
and the ferromagnetic electrodes. Using a model based on an Anderson quantum
dot coupled to ferromagnetic leads, we show that these results imply the
coexistence of a Kondo effect and ferromagnetism.
