Spin-Polarized Transport Phenomena in Double Magnetic Tunnel Junctions Caused by Ferromagnetic CoFe Nanoparticles

We present some unusual spin-polarized transport phenomena in asymmetric double barrier magnetic tunneling junctions (ADBMTJs) with CoFe/AlO
_x
/ferromagnetic nanoparticle (FM-NPs)/AlO
_x
/Ta structures. The conductance curves and the magnetoresistance ratio clearly oscillate with applied bias voltage, indicating the presence of Coulomb blockade effects due to isolated ferromagnetic nanoparticles in the parallel configuration in the ADBMTJ. The oscillation period is about 1.5 mV at 2 K.