  We report on magnetotransport measurements on millimetric super-lattices of
Co-Fe nanoparticles surrounded by an organic layer. At low temperature, the
transition between the Coulomb blockade and the conductive regime becomes
abrupt and hysteretic. The transition between both regime can be induced by a
magnetic field, leading to a novel mechanism of magnetoresistance. Between 1.8
and 10 K, high-field magnetoresistance due to magnetic disorder at the surface
of the particles is also observed. Below 1.8 K, this magnetoresistance abruptly
collapses and a low-field magnetoresistance is observed.
