  We present low-temperature electron transport measurements on a single-wall
carbon nanotube quantum dot exhibiting Kondo resonances at low temperature.
Contrary to the usual behavior for the spin-1/2 Kondo effect we find that the
temperature dependence of the zero bias conductance is nonmonotonic. In
nonlinear transport measurements low-energy splittings of the Kondo resonances
are observed at zero magnetic field. We suggest that these anomalies reflect
interactions between the nanotube and a magnetic (catalyst) particle. The
nanotube device may effectively act as a ferromagnetically contacted Kondo dot.
