  The influence on the I-V characteristics and tunnel magnetoresistance (TMR),
of impurities embedded into the insulating barrier I separating the two
ferromagnetic electrodes F of a magnetic tunnel junction, was theoretically
investigated. When the energy of the electron's bound state at the impurity
site is close to the Fermi energy, it is shown that the current and TMR are
strongly enhanced in the vicinity of the impurity. If the position of the
impurity inside the barrier is asymmetric, e.g. closer to one of the interfaces
F/I, the I-V characteristic exhibits a quasidiode behavior. The case of a
single impurity and of a random distribution of impurities within a plane were
both studied.
