Tunneling magnetoresistance of double-barrier magnetic tunnel junctions in sequential and coherent regimes

Taking into account the transport with coherent and sequential components, we study the conductance and tunneling magnetoresistance (TMR) in double F/I/F/I/F tunnel junctions with F the ferromagnet and I the thin insulating layer. It is found that the TMR ratio for the F/I/F/I/F junction in the sequential regime cannot go beyond the larger one between the TMR ratios of the two single F/I/F junctions forming the double junction. The coherent transport of electrons results in oscillations of the tunneling conductance and TMR with thickness L of the middle F layer, the sequential component leading to a decay of the oscillation amplitude with L.