  We have studied the Junction Magnetoresistance (JMR) and the Differential
junction magnetoresistance (DJMR) for double tunnel junctions with magnetic
metals in the Coulomb Blockade regime. Spikes are seen in both the JMR and the
DJMR vs. voltage curves. They occur at those places where the current increases
by a step. In all cases the large bias limit can be obtained by adding the
resistances of each of the junctions in series. The JMR is positive in all the
cases we studied, whereas the DJMR can be positive or negative as a function of
the voltage. Moreover, the relative variation of the DJMR as a function of the
voltage is larger than the variation of the JMR with the voltage.
