Tunneling Conductance and Magnetoresistance in Ferromagnet/Ferromagnet/d-Wave Superconductor Double Tunnel Junctions

The tunneling conductance and tunneling magnetoresistance (TMR) areinvestigated in ferromagnet/insulator/ferromagnet/insulator/d-wavesuperconductor (FM/I/FM/I/d-wave SC) structures by applying an extendedBlonder-Tinkham-Klapwijk (BTK) approach. We study the effects of theexchange splitting in the FM, the magnetic impurity scattering in the thininsulator interface of FM/I/FM, and noncollinear magnetizations in adjacentmagnetic layers on the TMR. It is shown (1) that the tunneling conductanceand TMR exhibit amplitude-varying oscillating behavior with exchangesplitting, (2) that with the presence of spin-flip scattering in insulatorinterface of FM/I/FM, the TMR can be dramatically enhanced, and (3)that the TMR depends strongly on the angle between the magnetization of twoFMs.