Coherent transport in high performance double magnetic junctions

Spin-dependent transport is considered in double magnetic tunnel junctions of two types F-I-F-I-F and F-I-N-I-F with thin insulating (I) barriers between the ferromagnetic (F) or non-magnetic (N) electrodes. Using the Landauer formalism within single-band tight-binding dynamics for atomically perfect epitaxial multilayers, the dependencies of tunnel magnetoresistance (TMR) on the on-site atomic energies epsilonI or epsilonN and number nI of atomic planes in the respective layers are obtained. It is found that the maximum TMR corresponds to the "shallow band" regime with respect to epsilonN and a series of peaks appears with respect to nI, essentially enhancing the performance of a simple F-I-F junction. These results suggest the material and structural choices for optimum TMR devices of advanced compositions.