  Manipulation of tunneling spin-polarized electrons via a ferroelectric
interlayer sandwiched between two ferromagnetic electrodes, dubbed Multiferroic
Tunnel Junctions (MFTJs), can be achieved not only by the magnetic alignments
of two ferromagnets but also by the electric polarization of the ferroelectric
interlayer, providing great opportunities for next-generation multi-state
memory devices. Here we show that a La0.67Sr0.33MnO3
(LSMO)/PbZr0.2Ti0.8O3(PZT)/Co structured MFTJ device can exhibit multilevel
resistance states in the presence of gradually reversed ferroelectric domains
via tunneling electro-resistance and tunneling magnetoresistance, respectively.
The nonvolatile ferroelectric control in the MFTJ can be attributed to separate
contributions arising from two independent ferroelectric channels in the PZT
interlayer with opposite polarization. Our study shows the dominant role of
"mixed" ferroelectric states on achieving accumulative electrical modulation of
multilevel resistance states in MFTJs, paving the way for multifunctional
device applications.
